Key Concepts

After completing this chapter, you will be able to:

1. List the major classes of renewable resources and describe the character of each.
2. Identify ways by which renewable resources can be degraded by excessive harvesting or inappropriate management.
3. Describe the renewable resource base of the United States and discuss whether those resources are being used in a sustainable fashion.
4. Show how the commercial hunts of cod and whales have represented the “mining” of potentially renewable resources.

Introduction

Renewable resources are capable of regenerating after harvesting, so their use can potentially be sustained forever. For this to happen, however, the rate of use must be less than that of regeneration – otherwise, a renewable resource is being mined, or being used, as if it was a non-renewable resource.

The most important classes of renewable resources are water, agricultural soil quality, forests, and hunted animals such as fish, deer, and waterfowl. In the following sections we examine the use and abuse of these potentially renewable resources. (We previously looked at renewable sources of energy, such as hydroelectricity, solar power, wind, and biomass, in Chapter 11.)

Fresh Water

Although water is extremely abundant on Earth, about 97% of it occurs in the oceans and is too salty for many uses by organisms or the human economy. Of the remaining 3% that is fresh water, almost all occurs in glacial ice and is not easily available for use by people or other species. The “available” forms of fresh water mostly occur in the surface waters of lakes and rivers, or as groundwater in soil or rocks. These limited stocks of fresh water are a vital resource for ecosystem processes and for many of the economic activities of people.

Surface Water

Surface water is a collective term for lakes, ponds, streams, and rivers. Fresh water from these bodies can be used for drinking, cleaning, agricultural irrigation, generation of hydroelectricity, industrial cooling, and recreation. Surface waters are abundant in regions where the climate is characterized by more precipitation than evapotranspiration, which allows the aqueous resource to be recharged (see Chapter 4). However, in drier regions surface waters are uncommon or rare, and this presents a natural constraint on ecological and economic development.

In regions where there is a low rate of recharge of surface water, excessive use for irrigation or industrial or municipal purposes (such as drinking, washing, and flushing toilets) can rapidly deplete the resource. A deficiency of surface water in an arid region can lead to conflicts between local areas, and even between countries. Each region wants to have access to as much water as possible to support its agricultural and industrial activities and to service its urban areas. This is the reason why severe competition for surface water is a chronic problem in drier parts of the world, particularly in the Middle East, much of Africa, and southwestern North America.

In the Middle East, for example, the watershed of the Jordan River is shared by Israel, Jordan, Lebanon, and Syria. All of these countries have a dry climate, and all demand a share of the critical water resource. Also, in the Middle East, the watersheds of the Tigris and Euphrates Rivers originate in Turkey, while Iraq and (to a lesser degree) Syria are highly dependent down-river users that are threatened by hydroelectric and agricultural diversion schemes in Turkey. In northern Africa, the watershed of the Nile River encompasses territory in nine countries: Egypt, Ethiopia, Sudan, Rwanda, Burundi, Democratic Republic of Congo, Tanzania, Kenya, and Uganda. The collective needs of those countries for water exceed the limited capacity of even that great river.

In North America, the most contentious water-use conflicts involve the Colorado River and the Rio Grande, which are shared by the United States and Mexico. The use of water from these rivers is extremely intensive, particularly for irrigated agriculture. In fact, virtually all the flow of the Colorado River could potentially be used in the U.S. before it even reaches northern Mexico, where there is also a substantial demand. In addition, the chemical quality of the water is degraded by inputs of dissolved salts mobilized by agricultural practices in the U.S., a factor that severely compromises the potential use of any remaining river-water flow in Mexico. Because this binational problem is important, the two federal governments have negotiated a treaty that guarantees a minimum quantity of flow and water quality where the Colorado River crosses the international boundary. The Rio Grande has a similar problem, which is also being dealt with by a treaty between the two countries.

Even where surface waters are relatively abundant, their quality can be degraded by pollution by nutrients, hydrocarbons, pesticides, metals, or oxygen-consuming organic matter. Excessive nutrients can increase the productivity of surface waters, causing a problem known as eutrophication (see Chapter 24). Biological contamination by bacteria, viruses, and parasites from fecal matter of humans, pets, or livestock can render the water unfit for drinking or even for recreation. Thermal pollution, due to the release of heat from power plants or factories, can also cause ecological damage in receiving water bodies. The effects of acidification, metals, pesticides, and eroded materials can also be an important issue for surface waters, as is examined in detail in various following chapters.

Groundwater

Groundwater occurs in underground reservoirs of water known as aquifers, in which the fluid is present in the interstitial spaces and cracks of overburden and porous bedrock (Chapter 4). Groundwater can be an extremely valuable natural resource, especially in regions where lakes and rivers are not abundant. It is typically accessed by drilling and pumping to the surface.

Groundwater stores are recharged through the hydrologic cycle. This happens as water from precipitation slowly percolates downward through surface overburden and bedrock in a sometimes extensive area known as a recharge zone. In humid regions, where the amount of precipitation is greater than the quantity of water that is dissipated by evapotranspiration and surface flows, the excess serves to recharge groundwater. An aquifer that quickly recharges can sustain a high rate of groundwater pumping and can be managed as a renewable resource.

In drier environments, however, the amount of precipitation available to recharge groundwater is much smaller. An aquifer that recharges extremely slowly is essentially stocked with fossil water (or paleowater) that has accumulated over thousands of years or more. Such aquifers have little capability to recharge if their groundwater is used rapidly, so their stores are easily depleted. Slowly recharging aquifers are essentially a non-renewable resource, whose reserves are “mined” by excessive use.

The largest aquifer in the world, known as the Ogalalla, occurs beneath about 450-thousand km² of arid land in the western U.S. (Figure 12.1). The Ogalalla aquifer is recharged very slowly by underground seepage that mostly originates with precipitation falling on distant mountains. Most of the groundwater in the Ogalalla is fossil water that has accumulated during tens of thousands of years of sluggish infiltration. Although the aquifer is enormous (containing about 2.5 billion liters), it is being rapidly depleted by pumping at more than 170-thousand drilled wells. Most of the wells draw water for use in irrigated agriculture, and others for drinking and other household purposes. The level of the Ogalalla aquifer is decreasing by as much as 1 m/year in zones of intensive use, while the annual recharge rate is only about 1 mm/y. Clearly, the Ogalalla aquifer is being rapidly mined. Once it is effectively drained – which is likely to occur within several decades – irrigated agriculture in much of the southwestern United States may fail.

Figure 12.1 Ogallala Aquifer. This map depicts changes in the Ogallala Aquifer from before it was tapped to 2015. Although some areas have seen increases in water levels (mainly in Nebraska), most areas are seeing water levels decline, namely in Kansas and southward. Source: National Climate Assessment.

Groundwater resources are also threatened by pollution when chemicals are deliberately or accidentally discarded into the ground. For instance, groundwater may be polluted by gasoline leaking from underground storage tanks at service stations, degraded by the infiltration of agricultural fertilizer and pesticides, or contaminated by bacteria and nutrients seeping from manured fields or septic systems. Badly contaminated groundwater may not be usable as a source of drinking water, and even for the irrigation of crops.

It is important to understand that groundwater may be rendered persistently unusable as a source of drinking water if it has been contaminated by hazardous or toxic substances, such as hydrocarbons (gasoline, engine oil, or home-heating fuel), pesticides, nitrate originating with agricultural fertilizer, or Escherichia coli and other pathogens originating with the dumping of livestock manure or untreated urban sewage sludge. Because many aquifers recharge and turn over slowly, it may take decades or even centuries for these kinds of contaminants to be purged from the system. In general, the “dilution solution to pollution” does not work well when groundwater is the receiving medium. It is always precautionary to avoid activities that carry a risk of damaging the quality of water in an aquifer.

Water Supply and Use

The regions of the world with the smallest per-capita water resources are Asia, Africa, and Europe, a pattern that partly reflects the high population densities of those continents. In general, the U.S. has abundant supplies of both surface water and groundwater. Nevertheless, water is scarce in relatively arid regions of our country, such as the southwest. There, the shortage of water for irrigation is a constraint on agricultural development, a problem that may intensify in the future, according to most climate-warming scenarios.

Groundwater is an important resource in some regions of the U.S., particularly where surface water is not abundant or its chemical quality is poor. A local example is Suffolk and Nassau Counties in Long Island, New York. This highly developed and densely settled island has very little surface water and is solely dependent on groundwater for freshwater. Groundwater can also be degraded by the intrusion of saltwater, which can render the resource unfit for drinking or irrigation. In areas close to an ocean, deeper saline groundwater is typically overlain by a surface layer of fresh water (which is less dense than salt water and therefore “floats” above it). If fresh groundwater is withdrawn at a rate faster than the recharge capability of an aquifer, the deeper salt water will rise. Once this happens, it is extremely difficult to displace the salt water, and the ability of the aquifer to supply fresh water may have been destroyed. Not surprisingly, saltwater intrusion is currently a problem in many Long Island wells.

In general, national patterns of water use are influenced by the degree and kind of economic development, the population size, and amounts of rainfall. Among the less-developed nations, those that depend heavily on irrigated agriculture have a relatively high water use, with agriculture accounting for more than 85% of the total (Table 12.1). However, many less-developed countries with an arid climate, such as Ethiopia, Kenya, Somalia, and others, would also benefit greatly from having more irrigated agriculture. However, these countries do not have access to sufficient water for this kind of management, so per-capita water use, even while largely agricultural, remains small.

Table 12.1. Water Use in Selected Countries, 2014. Source: Data from FAO (2017).

Country	Total Withdrawal per capita (m3/year per inhabitant)	Agricultural Withdrawal (as % of total)	Industrial Withdrawal  (as % of total)	Municipal Withdrawal (as % of total)
Less Developed	–	–	–	–
Brazil	316.0	60.03	14.48	25.49
Ethiopia	99.14	91.84	0.4844	7.679
India	568.5	90.41	2.234	7.359
Indonesia	841.2	85.21	4.103	10.69
Saudi Arabia	705.4	82.23	4.283	13.49
More Developed	–	–	–	–
Australia	673.3	63.43	16.08	20.49
Canada	969.1	7.414	78.85	13.73
United States	1,367	39.66	47.20	13.14

Some developed countries have rather high per-capita water use. Canada and the United States, for example, use much of their surface water for generating hydroelectricity. In addition, the western United States has invested heavily in irrigated agriculture. Americans use about 322 billion gallons of water per day from total water withdrawals, 87% of which is freshwater and the remaining 13% of coastal saline and brackish water used for thermoelectric purposes. About 26% of that total water usage is groundwater. However, about 12% of Americans rely on groundwater for self-supplied domestic use (Dieter et al., 2015). Figure 12.2 shows domestic use of water by state in the U.S. for 2015.

Figure 12.2. Use of Water for Domestic Use in the United States, 2015. 283 million people received their domestic water from public supply. About 42.5 million people self-supplied their domestic water, almost entirely from groundwater sources. Source: USGS.

Water is used for myriad purposes in the U.S., by all individuals as well as municipal, institutional, and industrial users. Averaged across the country, about 45% of the total water use is to cool thermal electric plants (fueled by either fossil fuels or nuclear power), 4% for industrial purposes, 13% for public supply in municipalities (including residential, commercial, and industrial use), about 33%, for total irrigation, 3% for aquaculture, 1% for livestock, and 1%, for the mining and fossil-fuel industries (USGS, 2010).

Within the home, about 20% of the total use of water is typically for showers and baths, 24% to flush toilets, 17% to do laundry, 19% for faucet use, 12% lost to leakage, and 8% for other uses (Water Research Foundation, 2016). The water returned to the environment after these various uses is typically degraded in quality because of the presence of various kinds of dissolved and suspended substances.

In addition, about 12% of the water used for various purposes is consumed during the process. This occurs because some of the water evaporates into the atmosphere so that the discharge of used water is smaller than the quantity initially withdrawn. This is particularly true of most agricultural uses, in which much of the applied water evaporates from land surfaces.

In addition, the U.S. manages the flow of tremendous quantities of surface water using dams and reservoirs (see Chapter 24). This is done to generate hydroelectricity, control flooding, accumulate water for irrigation, and manage municipal reservoirs. The U.S. has about 8,100 major dams (taller than 15m), but only about 2,500 dams produce hydroelectricity. The vast majority are utilized for irrigation, flood control, municipal water supply, among other purposes. There are thousands of additional smaller dams as well.

Agricultural Resources

The production of an agricultural crop is measured in gross units, such as tonnes of wheat harvested on a farm, in a region, or in a country as a whole. The production is related to several factors, including the amount of land under cultivation and the productivity of the crop. By comparison, the productivity is a rate function and is standardized per unit area and unit time, such as the tonnes of wheat harvested per hectare in a particular year. The productivity is related to the management system being used, plus a vital quality of the land that is referred to as site capability.

Ultimately, the amount of agricultural land in any region (and on Earth) is a limited resource (Figure 12.3 and 12.4). To some degree, the area of land suitable for cultivating crops can be increased by clearing the pre-existing natural forest and grassland that may be growing on fertile sites, and by draining certain kinds of wetlands. There are, however, finite areas of those kinds of natural ecosystems that are suitable for conversion into arable land. Only about 30% of Earth’s surface is terrestrial, and most of that land is too cold, hot, dry, wet, rocky, or infertile to be converted into an agricultural land-use.

Figure 12.3. Agricultural Lands in the U.S. in 2007. Agricultural production relies on rainfall and site capability, which supply moisture, nutrients, and other factors crucial to plant growth. This map shows the percentage of land in each county that is used for agriculture. Source: USDA National Agricultural Statistics Service.

Some countries still have substantial areas of natural ecosystems that are suitable for conversion. Most of those countries are less-developed and have a rapidly growing population, and they are actively pursuing this tactic of economic development by clearing tropical rainforest, savannah, and wetlands. Other less-developed countries have few remaining areas of natural land that are suitable for agricultural development. In spite of their rapidly growing populations, these countries have not managed to create much additional cropland in the past several decades. For instance, this is the situation of Bangladesh, China, and India.

Figure 12.4. Share of Land Area Used for Arable Agriculture, 2015. The share of land area is measured as a percentage of total land area. Arable land area is land includes land under temporary crops, temporary meadows for mowing or for pasture, land under market or kitchen gardens and land temporarily fallow as defined by the Food and Agriculture Organization (FAO). Source: visualization provided by OurWorldInData.org is licensed under CC BY. Data source: World Bank.

Most wealthier countries are not developing much additional agricultural land, largely because their areas with good potential are already being used. In fact, many developed countries have taken a great deal of land out of agricultural use since about 1980. The land withdrawals have occurred for two major reasons: (1) to reduce the production of certain crops, which keeps their prices relatively high, and (2) to conserve environmental quality through less intensive use of marginal land that is prone to erosion and other kinds of degradation. In addition, some high-quality agricultural land has been lost to urbanization in most developed countries, including the U.S.

Site Capability

Agricultural site capability (or site quality) can be defined as the potential of an area of land to sustain the productivity of agricultural crops. Site capability is a complex ecological quality that depends on nutrients, organic matter, and moisture in the soil, plus additional factors that affect the productivity of crops. These factors are influenced by climate and drainage, by the vigor of ecological processes such as decomposition and nutrient cycling, and by the kinds of microbial and plant communities that are present.

Site capability is extremely important to the productivity of agricultural systems, and therefore to the production and availability of food. Because the beneficial qualities of cultivated land can be maintained and even improved by the use of appropriate management practices, site capability represents a potentially renewable resource. However, it can also be degraded by certain agricultural practices (see Chapter 13).

Ultimately, site capability for agriculture depends on seven interrelated factors: soil fertility, organic matter, bulk density (including compaction), resistance to erosion, moisture status, salinization, and the abundance of weeds. These factors are examined below:

Soil fertility is related to the ability of an ecosystem to supply the nutrients that are needed to sustain the productivity of a crop. Especially important are the sources of nitrogen, particularly inorganic forms such as ammonium and nitrate, as well as phosphate, potassium, calcium, magnesium, and sulfur. Soil fertility is influenced not only by the amounts of these nutrients, but also by factors that affect their availability to plants, such as:

• The cation exchange capacity, or the degree to which positively charged ions (these are cations) of such nutrients as ammonium (NH⁴⁺), potassium (K⁺), and calcium (Ca²⁺) are bound by soil.
• The anion exchange capacity, which is related to the binding of negatively charged ions (anions) such as nitrate (NO₃^–), phosphate (PO₄^3–), and sulphate (SO₄^2–).
• Soil acidity or alkalinity, which are usually measured as pH, and affect the solubility of many nutrients as well as key aspects of microbial activity
• The rate of oxidation of organically bound nutrients into inorganic compounds that plants can take up and use more effectively in their nutrition
• The enhancement of nutrient availability through the addition of agricultural fertilizer or other practices

For example, consider the process of nitrification (see Chapter 5), an important function that is performed by certain bacteria and that transforms ammonium into nitrate. The rate of nitrification is greatly decreased in soil that is acidic or waterlogged, which results in much less availability of nitrate to crops. Soil fertility is also degraded if excessive amounts of nutrients are removed when crops are harvested, and also by the compaction of soil, depletion of soil organic matter, waterlogging, and acidification.

Soil organic matter consists of plant debris and humified organic material. Organic matter contributes to the ability of soil to form a loose, crumbly structure called tilth. Soil with good tilth is well aerated, allows plant roots to grow freely, and retains moisture, all of which are important factors that affect crop growth.

In addition, some nutrients are components of soil organic matter. These organically bound nutrients are slowly released for plant uptake through the process of decomposition, which in this respect can be viewed as a natural, slow-release, organic fertilization. Organic matter in the soil also helps to retain ionic forms of nutrients through cation and anion exchange capacity. Intensive cropping with insufficient return of crop residues typically results in a loss of soil organic matter and degradation of the valuable ecological services it provides.

Bulk density of soil (its weight per unit volume) has a large effect on tilth and drainage. It is generally preferable to have a low bulk density, but this can be degraded by the loss of soil organic matter and by compaction caused by the repeated passage of heavy machinery, especially when fields are wet. Soil that has been degraded by compaction may become wetter, lack oxygen, and have impaired nutrient cycling and poor root growth. These changes can result in a substantial decrease of productivity.

Resistance to erosion is degraded when soil is left without a cover of vegetation or crop residues during the winter, when contour ploughing is not practiced (such as when cultivation runs down a slope rather than along it), and when steep terrain is tilled. In contrast, sites are resistant to erosion if they are well vegetated, have good tilth, are flat, and the climate is not excessively wet or windy. In effect, erosion represents an important problem because it is a loss of soil mass, which occurs as particles are carried away by the forces of wind or running water. Any agricultural practices that increase the rate of erosion should be viewed as a mining of soil capital. In severe cases, erosion can strip away the relatively fertile, surface horizons of the soil. In the worst cases, bedrock may be exposed and the land is forever ruined for agricultural use.

Moisture status is another important aspect of site capability. In general, an intermediate moisture status (referred to as mesic) is preferred for the growth of most crops. Excessively dry (xeric) sites will produce a small yield, and crops may perish from drought. In contrast, excessively wet (hydric) sites tend to have cool soil with little or no oxygen present, which are conditions that are stressful to most crops.

The moisture status of sites is largely affected by climatic factors, especially the rates of precipitation and evapotranspiration. Soil moisture is also affected by the drainage characteristics – coarse-grained soils may drain too rapidly and have little ability to hold moisture, while heavy clay soils may not drain well enough, retaining water close to the surface. Soils with good tilth tend to have a degree of drainage midway between these extremes.

Salinization refers to the accumulation of various kinds of salts in the soil, particularly excessive amounts of sodium, magnesium, potassium, chloride, or sulphate. These and other salts are present in irrigation water and in certain kinds of fertilizer and they remain behind when water evaporates to the atmosphere. Salinization is a common problem in agricultural fields that are irrigated but do not have enough drainage to carry the salts downward into the soil and away, causing them to accumulate at the surface.

The abundance of weeds is important because when abundant, they provide too much competition for crop plants. The term “weed” can be defined as plants that are judged to be interfering with some human purpose (see Chapter 26). An increased abundance of weeds may be caused when a particular species of crop is cultivated in a continuous fashion, without rotation with other crops. An excessive abundance of weeds is commonly managed by tilling the soil and/or by using herbicide. In addition, a buildup of weed populations can be avoided by rotating crops and by using other management practices that provide less favorable conditions for the unwanted plants.

Degradation of Site Capability

Over the longer term, intensive agricultural management can result in a degradation of site capability. When this happens, the productivity of crops decreases, and in severe cases the land may no longer be suitable for agricultural use. Fortunately, such damage can often be avoided or repaired by changing the management system. For example, inorganic fertilizer may be applied to the soil in an attempt to compensate for declining fertility. Organic soil conditioners, such as compost and manure, can also be added to mitigate losses of organic matter, thereby helping to maintain the fertility and tilth of soil. In other cases, pesticides may be used to try to manage weeds and other pests. These management options are, however, intensive in their use of material and energy resources, and they may cause additional damage to the site and nearby ecosystems. Ultimately, truly sustainable agricultural systems involve the use of management strategies that conserve site capability while minimizing the use of nutrients, pesticides, and non-renewable sources of energy (see the section on Organic Agriculture in Chapter 13).

Production and Management

In 2020, more than 7.8 billion people were alive, and almost all were reliant on agricultural crops as their prime source of food. There are also relatively minor amounts of food that are harvested from the wild, such as by fisheries, but agricultural production is responsible for the great bulk of the modern human diet.

In addition, our associated domestic animals largely depend on the production of agricultural crops. The numbers of livestock are actually greater than those of people, including about 1.5-billion cows, 1.5-billion sheep, 1.2-billion goats, 1.0-billion pigs, and 22 billion chickens (Chapter 10). Although some of these domestic livestock forage on wild plants in unbroken pastures (which have not been seeded to agricultural forage plants), many are fed grain and hay that has specifically been grown for them. In fact, about 40% of the global production of grain is fed to livestock. Eventually, food products derived from the livestock are eaten by people, who are secondary consumers (and top predators) in this part of the agricultural food chain.

If a country has an excess of agricultural production over domestic consumption, then it has a surplus available for export, while those with a deficit must import some of their food (Table 12.2). In general, the greatest food-exporting nations have a relatively developed economy. Although many poorer countries export certain foods such as coffee, palm oil, sugar, tea, and other cash crops, most less-developed countries have food deficits or are only marginally self-sufficient. The food deficits must be made up by expensive purchases of food that was grown elsewhere or by donations from wealthier countries (the latter is known as food aid).

Table 12.2. International Trade of Agricultural Produce. Cereals include maize, rice, sorghum, and wheat. Pulses are legumes, such as peas, beans, and soybeans. Tuber includes cassava, potatoes, sweet potatoes and turnips. Data are for 2019 and are in tons per year. Source: Data from FAO (2019).

Country	Cereal export quantity (tonnes)	Cereal import quantity (tonnes)	Tuber export quantity (tonnes)	Tuber import quantity (tonnes)	Pulse export quantity (tonnes)	Pulse import quantity (tonnes)
Argentina	50,738,533	25,069	289,075	14,726	603,886	8,723
France	31,631,631	2,228,349	2,716,452	1,116,201	350,862	143,670
U.S.	75,258,660	6,298,744	2,028,204	1,885,010	1,171,763	542,334
China	3,457,854	24,948,734	778,342	5,870,805	387,499	2,318,001
Japan	282,703	23,728,456	10,809	673,237	74	114,052
Mexico	1,449,747	22,305,806	60,153	6,298,744	182,520	197,183

 

In terms of the gross food value provided to people, the world’s most important crops are cereals, such as barley, maize, rice, sorghum, and wheat. Also, important, but secondary, are tuber crops, such as cassava, potato, sweet potato, and turnip. In any country, the total production of cereals plus other crops is a function of the amount of land devoted to the cultivation of those species, multiplied by the average productivity.

Productivity (or yield, typically measured in tonnes of crop harvested per hectare per year) reflects the combined influences of site capability and the kind of management system that is being used. In agriculture, management practices are intended to mitigate some of the constraints that are limiting crop productivity, including those associated with site quality, inclement weather, insect infestations, weeds, and diseases. The productivity of cereals and other crops varies greatly among countries, but it is not necessarily lower in less-developed countries than in more-developed ones (Figure 12.3). Although wealthier countries use highly mechanized management systems with inputs of fertilizer, pesticides, and sometimes irrigation water, less-wealthier countries may also use intensive management systems, albeit ones that depend more strongly on human and animal labor and with smaller material inputs.

Figure 12.5. Cereal Production in Selected Countries. Data is for 1974 to 2018. Source: visualization provided by OurWorldInData.org is licensed under CC BY. Data from FAO.

Note also that Figure 12.5 also has data that shows how the yield of crops has increased over the past five decades. The increases in productivity are rather impressive, and are due to crop varieties that have been selectively bred to respond well to intensive management systems, as well as to increased use of management practices such as the use of fertilizer, pesticides, and irrigation. The improved rates of yield have been key to increased rates of agricultural production during the same period. Of course, many of the benefits of increased agricultural production have been absorbed by large increases in population, especially in less-developed countries.

These trends are also shown by indicators of food production that are compiled by the Food and Agriculture Organization of the United Nations. The index is a composite indicator that takes into account the production of all important crop species, with the data being expressed relative to the base period 2014-2016 (for which the value is set to 100). The index covers all edible agricultural products and is a price-weighted summation measured in constant dollars, so that inflation is not an issue. Therefore, the index shows whether agricultural production has increased (> 100) or decreased (< 100) during the time period, both on a total and per-capita basis.

The global data show a strong and steady increase of overall agricultural production from 1968 to 2018, although the increase is much more moderate in the per-capita data (Table 12.3). In other words, most of the increase in global agricultural production during the past half-century has been eroded (on a per-capita basis) by population growth. Not surprisingly, this pattern is even more striking in the data for the least-developed countries, which show little improvement in per-capita food production over the period.

These observations suggest that there is a food “treadmill,” in which increases in food production, obtained by converting natural habitats and adopting more intensive management practices, are being mostly offset by population growth. The metaphor of a treadmill is apt in this case, because on that sort of running machine a great deal of effort is expended, but the runner stays in about the same place.

Table 12.3. Changes in two indicators of global agricultural production. The production index data (a), as well as the per-capita index (b), are relative to the period 2014-2016, which are set to a scale of 100. Source: Data from FAO (2018).

Year	Production Index	Production Per-Capita Index
1968	36.32	75.48
1978	45.65	78.26
1988	54.97	78.84
1998	67.65	83.41
2008	86.54	94.07
2018	104.67	101.22

It is important to understand that high yields that are obtained by the use of intensive agricultural systems are heavily subsidized by large inputs of non-renewable resources. For example, the most important agricultural fertilizers are inorganic compounds of nitrogen, such as urea or ammonium nitrate, both of which are manufactured using natural gas. The second- and third-most important fertilizer nutrients are compounds of phosphate and potassium, which are produced from mined minerals. In addition, most pesticides are manufactured from petrochemicals, using energy-intensive technologies (Figure 12.6). Moreover, the mechanization of agricultural systems involves the use of tractors pulling heavy equipment for tilling, harvesting, and other purposes. The manufacturing of these machines requires large amounts of non-renewable energy and materials, such as metals and plastics. Furthermore, the machines run on non-renewable fuels, such as gasoline or diesel.

There is great variation among countries in their use of pesticides. In general, the intensity of management is greater in wealthier countries, with greater use of fertilizer and pesticide, more mechanization, and larger more industrial farms.

Figure 12.6. Intensity of Pesticide Use.  This map shows a comparison of how much pesticide is used per hectare of cropland for each country, measured in kilograms per hectare. It can be seen that the intensity of pesticide use is greater in wealthier and more developed countries. Source: visualization provided by OurWorldInData.org is licensed under CC BY. Data from FAO.

Some agricultural systems used in less-developed countries are quite intensive and result in high yields. For example, in many humid tropical countries, rice is cultivated using a system known as paddy. Although some paddy-rice agriculture has been mechanized, it is often carried out on smaller-scale family farms. Typically, water buffalo are used to plough and till the dyked, flooded fields (each of which is a paddy). People then hand-transplant young rice plants, weed the crop with hoes, and eventually harvest by scything and gathering sheaves of the plant stalks. In places with evenly spaced precipitation through the year and naturally fertile soil, such as parts of Java, Sumatra, and the Philippines, as many as three rice crops can be grown each year. This non-mechanized paddy system can achieve high yields with relatively small inputs of inorganic fertilizer or pesticide.

Other agricultural systems used in less-developed countries are much less productive than paddy rice, generally because of suboptimal rainfall and less fertile soil. The least productive systems are used in semi-arid regions. Under such conditions, it is not possible to cultivate many plant crops. However, livestock such as camels, cows, goats, and sheep can roam extensively over the landscape, harvesting the sparse production of native forage. The dispersed plant biomass of semi-arid ecosystems is too small in quantity and too poor in nutritional quality for direct harvesting and use by people. However, grazing livestock are able to convert the poor-quality forage into a form (such as meat or milk) that people can utilize as food.

Increasingly, the agricultural systems used in less-developed countries are becoming more intensive in their management. In this sense, they are rapidly proceeding toward the kinds of systems used in developed countries. Indicators of this change include increasing use of fertilizer, pesticides, and mechanization. Another indicator is the increasing size of farm holdings, which occurs as the agricultural activities become commercialized and owned by large companies. These changes have resulted in increasing yields in many less-developed countries over recent decades. These increases of productivity are largely due to the cultivation of “improved” varieties of crop plants as well as the adoption of intensive agricultural practices.

The industrialization of agricultural production in these countries also results in important social changes. Of particular importance is the rapid amalgamation of small family farms into larger commercial units. This results in the displacement of many poor people from agricultural livelihoods. These economic refugees then migrate to towns and cities, which causes the rate of urbanization to be much faster than what would be expected from population growth alone.

Agriculture in the United States

The U.S. is one of the world’s great agricultural nations and a major contributor to international trade in food. The U.S.’s production of cereals was 465 million tonnes in 2018, which ranked 2nd in the world and comprised 17% of global production (FAO, 2018). In that same year U.S. exported 75 x 106 t of grain, which ranked 1st in the world (FAO, 2019). The gross domestic product (GDP) associated with agricultural production is about $602 billion, of which 23% is crops and 76% livestock (FAO, 2018). U.S. exports of agricultural products in 2019 had a value of $140 billion, and imports $31 billion (FAO, 2019).

At the beginning of the twentieth century, more than 40% of the U.S. labor force was employed in agriculture. At the time, farming mostly relied on animal and human labor as sources of energy for cultivation and harvesting. Most farms were relatively small, family-operated enterprises, run mainly as subsistence operations to produce food and other crops for use by the family. Any surplus production was traded in local markets for cash or manufactured goods. The agricultural surplus was eventually sold in U.S. cities or exchanged internationally by traders. Much of today’s agricultural activity in less-developed countries still has this sort of socio-economic character.

Today, however, most U.S. agriculture involves highly mechanized, industrial operations. Only about 1.6% of the national workforce is employed in farming (World Bank, 2021). Agriculture in the U.S. is now largely consolidated by large agricultural corporations that maximize their yields and profits through environmentally unsustainable practices. Virtually all cultivation, harvesting, and processing is accomplished by large fossil-fuelled machines. Tractors haul cultivating, seeding, and spraying machines, and self-contained harvesters harvest and process crops. As of 2007, in the U.S., tractors were used at a density of 271 units per 100 sq. km of arable land (World Bank, 2021).

The U.S. has an immense land base, some 9.15 million km², making it the third-largest country in the world. The area suitable for agriculture is widespread across the country, especially with improvements in technology. Farming occurs on a large scale in the Midwest, the Rockies, and the Pacific. Initially the region of the Great Plains provided extremely fertile soil and remnants of the vast migratory herds that were previoulsy hunted to near extinction. Over the course of the Westward Expansion, the increasing number of settlements and agricultural intensity resulted in the loss of much of the original fertility. Due to intensive land use and the loss of topsoil, the land’s historical fertility ultimately culminated in the devastating event known as the Dust Bowl in the 1930s (see U.S. Focus 12.1).

The ability of land to support agricultural uses is categorized by a system known as the Land Capability Classification. The land capability classes are defined on a scale of 1-8, indicating the level of limitations of the soil in their use for agricultural production:

• Class 1 soils have slight limitations that restrict their use.
• Class 2 soils have moderate limitations that reduce the choice of plants or require moderate conservation practices.
• Class 3 soils have severe limitations that reduce the choice of plants or require special conservation practices, or both.
• Class 4 soils have very severe limitations that restrict the choice of plants or require very careful management, or both.
• Class 5 soils have little or no hazard of erosion but have other limitations, impractical to remove, that limit their use mainly to pasture, range, forestland, or wildlife food and cover.
• Class 6 soils have severe limitations that make them generally unsuited to cultivation and that limit their use mainly to pasture, range, forestland, or wildlife food and cover.
• Class 7 soils have very severe limitations that make them unsuited to cultivation and that restrict their use mainly to grazing, forestland, or wildlife.
• Class 8 soils and miscellaneous areas have limitations that preclude their use for commercial plant production and limit their use to recreation, wildlife, or water supply or for esthetic purposes (USDA, 1961, 6-10).

Additionally, subclasses are assigned depending on the characteristic that serves as the limitation (i.e. erosion, saturation, low water retention or shallowness, climate, etc.).

Most of the highest-capability land is located in the Midwest, where the sites have relatively flat terrain and fertile soil. As of the last major survey done by the U.S. government in 1997, Indiana, Illinois, and Iowa were the only states to have a majority of land that fell within classes 1 and 2 (Figure 12.7).

Figure 12.7. Land Capability Class, by State, 1997. Source: Natural Resources Conservation Service, USDA.

As was previously examined, the quality of land for agriculture is influenced by such factors as soil fertility, organic matter concentration, drainage, and the abundance of weeds. All of these qualities can be degraded by inappropriate land management. It is important to monitor changes in these site factors over time, in order to track changes in the sustainability of agriculture. Unfortunately, suitable monitoring data do not yet exist in most areas, although programs are being designed.

There are, however, some general indications that soil fertility and other site factors are declining in quality over much of the agricultural land base. For example, in order to maintain the productivity of many agroecosystems, large amounts of fertilizer and soil conditioners must be added to the system. Similarly, herbicide, insecticide, fungicide, and other pesticides must be used to manage pests (see Chapter 26). The need to use intensive management practices to maintain productivity could, in itself, be considered a symptom of unsustainable stress on the agroecosystem. In addition, most fertilizers, pesticides, and their mechanized application systems are based on the mining and use of non-renewable resources, which represents another element of non-sustainability (see also Chapter 13).

Huge amounts of fertilizer and pesticides are used to increase crop productivity in the U.S. In 2015, 137 kg of fertilizer was applied to every hectare of cropland (World Bank, 2021). In 2018, agricultural land was fertilized with almost 12 million tonnes of nitrogen and 4 million tonnes of phosphate (FAO, 2018). American agricultural systems also utilize crop varieties that have been selectively bred to increase their potential productivity and resistance to pests and pathogens, to respond vigorously to fertilizer addition and other intensive management practices, and to grow well under regional climatic regimes. In conventional intensive agriculture, these crop varieties are often grown in a monoculture, where a whole field or plot of land will grow the same crop variety en masse, to maximize yield production of that crop. This is not to say that these varieties are optimally adapted to intensively managed agroecosystems. Due to the lack of biodiversity in these plots, the plot as a whole is more susceptible.  New pests and diseases often develop, so the crop-breeding industry must continuously respond to changes in ecological conditions. This perpetuates the “arms race” between humans and biological pests as they attempt to manage the constantly evolving blights and weeds that adapt to the new human-imposed conditions.

Overall, the intensification of industrial agriculture has greatly increased the production of crops in the U.S. Similarly large increases in production have been accomplished in other countries that have adopted intensive and mechanized agricultural systems. This includes Canada, most countries of Western Europe, and, increasingly, Brazil, China, India, Russia, Ukraine, and other rapidly developing countries. Increases in agricultural production have been accomplished mainly through intensified management and the cultivation of improved crop varieties, rather than by increasing the areas of cultivated land.

Just over 40% of U.S. land is cultivated agricultural land totaling over 2.1 million farms. While the size of farms have increased, the number of farms has decreased over time (USDA, 2014). Farming has also greatly intensified in the U.S., in terms of mechanization and the use of fertilizer and pesticides. In recent years, the largest production of crops have been for wheat (52 Mt), corn (maize; 364 Mt), barley (4 Mt), and soybean ( 97 Mt) (FAO, 2019). In addition, new crops have been introduced to the U.S. and are grown over large areas, including canola (oil rapeseed), lentils, soybeans.

Animal husbandry has also become intensive in the United States. Most production of chickens, cows, and pigs now occurs on so-called factory farms (i.e., concentrated animal feeding operations; CAFOs). This is an industrial system that involves raising livestock indoors under densely crowded conditions. The livestock are fed to satiation with nutritionally optimized diets, while diseases are managed with antibiotics and other medicines. Productivity may be enhanced with growth hormones (see Chapter 13).

Almost 10 billion chickens are raised annually for meat and eggs on U.S. farms, with most of them operating at industrial scale and intensity (FAO, 2019). In addition, more than 227 million turkeys are raised, mostly on factory farms. Larger livestock include about 34 million cows (and 9 million milk cows), 130 million pigs, 2.4 million sheep, and 77, 000 horses. Dairy cows and pigs are raised mostly on factory farms. Most beef cows spend part of their lives grazing outdoors in pastures or on semi-natural prairie. However, prior to slaughter, most of the animals are rounded up and then kept in crowded feedlots, where they are well fed so that they can gain weight rapidly. Sheep, goats, and horses are raised under less intensive conditions.

In overview, it is clear that since the beginning of the 20th century there has been an enormous increase in agricultural production. This has fed similarly rapid increases in the global populations of people and domestic animals. The rapid intensification of agriculture is, however, substantially dependent on the use of non-renewable sources of energy and materials, a fact that challenges the sustainability of the production systems. Moreover, intensive agricultural systems cause important damages to the environment, many of which are examined in later chapters, especially in Chapter 13.

Forest Resources

Forests of various kinds are extremely important terrestrial ecosystems. They cover extensive areas of the surface of Earth, and fix and store huge amounts of carbon. The total global forest area is 4.06 billion hectares, of which 16% is in temperate regions, 27% in boreal regions, and 45% in tropical regions (FAO, 2020). The present forest area is about half of what it was before humans began to cause deforestation about 10-thousand years ago, mostly to develop agricultural land. Although temperate and boreal forests now cover an area comparable to the tropical forest, their production is only about half as large, and they store only 60% as much carbon. There are also another 3 billion hectares of open woodlands and savannah. The most heavily forested regions are in North and South America, Europe, and Russia, all of which have more than 30% forest cover.

Worldwide, an immense area of about 25 million hectares of forest is cleared or harvested each year (Image 12.2). Tree biomass is harvested for three major reasons:

1. As a fuel for subsistence, that is, to burn as a source of energy for cooking and warmth
2. As an industrial fuel, used to generate electricity or to produce steam or heat for a manufacturing process
3. As a raw material to manufacture lumber, paper, composite materials such as plywood and waferboards, and other products, such as synthetic rayon and celluloid

In addition, forests may be cleared not so much for their biomass, but to create new agricultural or urbanized land. These longer-term ecological conversions result in deforestation, which is a permanent loss of forest cover.

The net primary production of global forests has been estimated to be about 49 billion tonnes per year, of which an extraordinary 40% is used by humans (Krausmann et al., 2012). Human use can be divided into the following categories:

• Short-term clearing of forests for shifting cultivation in less-developed countries (45%)
• More permanent conversion of forests to agricultural land-uses (18%)
• Harvesting of tree biomass (16%)
• Productivity of trees in plantations (12%)
• Loss during harvest (9%)

Image 12.2. Clear-cut. Clear-cutting is the most common method of harvesting forests in the United States. Depicted is a picture of a clear-cut in Eugene, Oregon. Source: “Clearcutting-Oregon” by Calibas is licensed under CC BY-SA 3.0.

Changes in Forest Cover

Forest resources in many countries are being rapidly depleted by high rates of clearing. This is particularly true in many tropical countries, where deforestation is largely driven by increasing populations and the resulting need for more agricultural land and wood fuels. Also important are the economic and industrial demands for tree biomass to manufacture into charcoal and products for international trade.

The global rate of deforestation was 10 million hectares per year between 2015 and 2020 (FAO, 2020). These are high rates of forest loss, and they appear to have increased since the late 1990s. Satellite data for Amazonia, for example, suggest that the rate of clearing increased by about 50% in 1996-1997, which was a relatively dry year that was favorable for removing tropical forest by burning for conversion into pasture or fields for growing soybeans. Between 2015 and 2020, Nigeria had an annual average deforestation rate of 163,310 hectares per year. Another African country, Ethiopia lost 92,000 ha per year during that period, while Honduras lost 23,190 ha (FAO, 2020). Figure 12.8 depicts the decreasing amonts of forested area from 1990-2020 for developing countries. The rapid deforestation that is occurring in most developing countries represents the mining of potentially renewable lumber, fuelwood, and other uses of tree biomass. In addition, deforestation in tropical and subtropical regions causes terrible ecological damages, such as endangerment and extinctions of biodiversity. These topics are examined in Chapter 27.

Figure 12.8. Forest Area of Net Food Importing Countries, Low Income Food Deficit Countries, Least Developed Countries, Landlocked Developing Countries (LLDCs), and Small Island Developing Countries (SIDCs), expressed over the period of 1990-2020. Source: visualization provided by OurWorldInData.org is licensed under CC BY. Data from FAO.

The forest areas in many developed countries have recently been stable or increasing, in contrast to the rapid deforestation that is occurring in most less developed countries. This is happening in spite of industrial harvesting of timber resources in many of those countries, largely to manufacture lumber and paper. Even with these harvesting practices, industrial forestry that is typically pursued in the U.S., Canada, and Western Europe allows, and even works to encourage the regeneration of another forest on harvested sites. Consequently, there is no net loss of forest cover, although the character of the ecosystem may change because of the management system being used, especially if tree plantations replace the natural forest

Although most developed countries now have a stable or increasing forest cover, this has not always been the case. Many of these countries were being actively deforested as recently as the beginning of the 20th century. Most of the early deforestation occurred in order to develop land for agriculture. For instance, most of Western Europe was still forested as recently as the Middle Ages (up until about 1500), as was eastern North America up until one to three centuries ago. Extensive deforestation also occurred during the First World War, when European countries were engaged in “total war” economies and were harvesting wood as quickly as possible, often for use as pit props in underground coal mining. Large parts of these regions are now largely devoid of forest cover, which has been replaced by agroecosystems and urbanized land.

This process of deforestation largely stopped around 1920 to 1930. At that time, forested areas began to increase in many developed countries. This happened because many small farms of marginal agricultural capability were abandoned and their inhabitants migrated to urban areas to seek work. Over time, the land reverted to forest. In much of Europe, this involved the establishment of plantations (tree-farms), usually of conifer species. In other regions there was natural afforestation as tree-seeds established new populations on disused rural land. For example, because of these socio-economic and ecological dynamics, the area of forest in much of the Maritime Provinces has approximately doubled since the beginning of the twentieth century. Similar changes have occurred in other developed regions of the world.

Harvesting and Managing Forests

Globally, the net trend is one of rapid deforestation. Between 2015 and 2020, about 10 million hectares of forest per year were lost to deforestation (FAO, 2020). Almost all of this aggressive deforestation is associated with the conversion of tropical forest into agricultural land, but the harvesting of forest products is also important in some regions. Globally, only about half of the original forest area remains.

In the U.S. there has been a focus on forest conservation and replanting of forests. In 2015, planted forests occupied 68 million acres in the U.S. which increased by about 8% since 2007. These planted forests encompass plantations for commericial harvesting as well as areas where desired tree species were planted along existing species to restore forest cover (Alvarez, 2018). Harvesting of biomass in the U.S. is largely for manufacturing into lumber, composite materials such as plywood and waferboard, and pulp and paper. This harvesting of biomass supports the U.S. forest products industry, which accounts for approximately 4% of the total U.S. manufacturing gross domestic product (GDP) (American Forest and Paper Association, 2019). Figure 12.9 depicts the distribution of timberland, forest that can grow commercial-grade timber, across the U.S.

Figure 12.9. Proportion of U.S. Land that is Timberland, 2007. Source: USDA Forest Service.

The regeneration of trees on harvested area (this is known as reforestation) is encouraged by the planting of seedlings and other aspects of silvicultural management. Many of the planted areas can be managed quite intensively to develop tree plantations, a system that represents the application of an agricultural model to the growing of trees, also known as agroforestry. Tree farms are generally more productive of biomass than natural forest, but they lack many elements of native biodiversity and other ecological and aesthetic values (Chapter 27). Other aspects of intensive forestry management may include the thinning of overly dense tree regeneration, the use of herbicide to reduce the abundance of non-crop plants (or “weeds”), and the use of insecticide if there is an irruption of insects that threaten the tree cop, such as spruce budworm.

Non-planted tracts of the harvested can also be regenerated back to forest. This occurs through a “natural regeneration” of tree species. Natural regeneration may involve seedlings that existed on the site prior to harvesting and survived the disturbance (known as advanced regeneration), seedlings that established from seeds dispersed onto the site from nearby forest, or seeds dispersed by mature seed-trees left on the site.

Additional environmental considerations should be when assessing the ecological sustainability of forestry. These issues, to be examined in Chapter 27, include the following:

• Long-term effects of harvesting and management on site capability, which may become degraded by nutrient losses and erosion
• Effects on populations of fish, deer, and other hunted species, which are also an economic “resource”
• Effects on indigenous biodiversity, including native species and naturally occurring ecosystems (such as old-growth forest)
• Effects on hydrology and aquatic ecosystems
• Implications of forestry for carbon storage (this is important with respect to anthropogenic influences on the greenhouse effect; Chapter 21)

These ecological values can be severely degraded by forestry, and this detracts from the ecological sustainability of this industrial activity.

Fish Resources

Wild populations of fish have long been exploited as food. In recent decades, there have been enormous increases in the rate of harvesting of wild fish, and also in the cultivation of certain species in semi-domestication, a practice known as aquaculture (Table 12.4). Like crop plants, livestock, and forests, populations of fish can be harvested in a sustainable manner, which would allow the yields to be maintained. However, fish stocks can also be over-harvested to the degree that their regeneration is impaired. When this happens, productivity declines and the bio-resource can disastrously collapse. Regrettably, the recent history of many of the world’s major fisheries provides abundant examples of over-exploitation causing rapid declines in resources (Image 12.3). The global harvest of fish, crustaceans, and shellfish in 2018 was about 178.5  million tonnes. This included 84.4 million tonnes of marine fish, 12.0 x 106 t of freshwater fish, and 82.1 x 106 t of fish grown in aquaculture.

Table 12.4. Fish Catches and Aquaculture in Selected Countries. Data are in 106 t/y in 2018. Countries are listed in order of decreasing catches of wild fishery. Source: Data from FAO (2018).

Country	Wild Fishery	Aquaculture
Global	96.4	82.1
China	14.6	47.6
Indonesia	7.2	5.4
Peru	7.2	0.10
Japan	3.1	0.64
Chile	2.1	1.3
Canada	0.83	0.19
U.S.	0.47	4.7

Image 12.3. Fishing Boat. Bottom-trawling is a technology used to harvest fish or scallops by drawing an open net along the seafloor, which in some respects is the marine equivalent of clear-cutting a forest. Source: NOAA.

U.S. fisheries constitute only a small fraction of economic activity, but in many coastal areas, fisheries constitute a major, or even the principal economic base (Table 12.5). Dutch Harbor in Alaska is one of the top fishing ports in the U.S., followed by Empire-Venice, Lousiana. The U.S. is one of the lead importers of fish and fishery products with imports valued at $40.3 billion and exports worth $28.8 billion for 2018 (NOAA, 2020).

Table 12.5. U.S. Domestic Landings of Selected Fishes in 2018. Data from NOAA (2020).

Species	Metric Tons	Thousand Dollars
Salmon
Chum	62,944	109,391
Sockeye	120,339	351,505
Tuna
Albacore	7,110	25,668
Bigeye	8,279	74,902
Shellfish
Crab	131,099	644,912
Shrimp	131,170	496,114

Other Hunted Animals

Marine Mammals

Marine mammals have been subjected to intensive commercial hunting in many oceanic regions. Initially, they were hunted mostly as a source of oil, which in pre-petroleum times was a valuable commodity as a fuel in lamps and for cooking. A few marine mammals, including Steller’s sea cow, the Caribbean monk seal, and the Atlantic grey whale, became extinct because of over-hunting, and many other species or populations became endangered. Among the best-known commercial hunts of marine mammals are those of the great whales of all oceans of the world.

Whaling

People have been hunting whales for centuries. The first species to be commercially hunted was the northern right whale (Balaena glacialis), which was considered the “right” whale to kill because it swims slowly and close to shore and floats when dead. Early records tell of hunts in the Bay of Biscay (coastal Europe) in the eleventh century. Men would row or sail near a right whale, harpoon it, allow it to tow their boat until exhausted, and then repeatedly lance the animal until it bled to death. The carcass would then be towed to shore and butchered, and the blubber rendered by boiling into a valuable oil. Even this crude hunt was enough to exterminate the right whale from European waters.

The development of steam ships made it possible to hunt swifter whales, such as the roquals (blue, fin, sei, and minke). The invention of the harpoon gun in 1873, and later the exploding-head harpoon, made it easy to kill even the biggest whales. By 1925, huge factory ships would spend months or years in remote waters, processing whales killed by a small fleet of boats, sometimes guided to their prey by spotter aircraft. Whales of all species and sizes could be efficiently located, killed, and processed. This onslaught resulted in a rapid, and profitable, depletion of whale stocks (Figure 12.8). With only a few exceptions, whale populations were not over-harvested to extirpation, but rather to commercial extinction – to a small population that was no longer profitable to find and kill.

Figure 12.8. Whales Killed per Decade. Number of whales killed globally per decade. Whaling peaked in the 1960s, then dropping off significantly. Only 9,229 whales were killed in the 2010s, compared to the 703,235 killed in the 1960s. Source: visualization provided by Our World in Data is licensed under CC BY. Data from Rocha et al. (2014) & the International Whaling Commission (IWC).

In response to concerns about declining populations of whales, the International Whaling Commission (IWC) was established in 1949. The IWC was given a mandate to develop and implement conservation-related controls over the multinational, highly capitalized, competitive, and profitable whaling industry. Unfortunately, the initial efforts of the IWC were not very successful, partly because it is so difficult to estimate whale stock sizes and recruitment and to determine accurate sustainable yields. More importantly, the major whaling nations were not particularly co-operative, and the IWC was not aggressive in setting and enforcing quotas small enough to ensure that whale populations would not be depleted. These problems are to be expected whenever a for-profit enterprise is allowed to regulate and police itself. According to J.L. McHugh, a former commissioner and chairperson of the IWC, “From the time of the first meeting of the Commission … almost all major actions or failures to act were governed by short-range economic considerations rather than by the requirements of conservation” (cited in Ellis, 1991).

Because of its enormous size, with the largest males reaching 32 m and 136 tonnes, the blue whale (Balaenoptera musculus) was initially the most profitable species in the Antarctic seas. The original population in those waters was about 180-thousand, and as many as 29-thousand were killed in a single year. Between 1955 and 1962, declining stocks meant an annual harvest of only 1-2-thousand. After 1965, killing this species was prohibited by the IWC. In total, about 331,000 blue whales were killed in Antarctic waters between 1920 and 1965. The present Antarctic population of blue whales is fewer than 2,000, only about 1% of their initial abundance. The global population is now about 3,000 individuals, compared with an initial 250-thousand.

As blue whales became depleted, the fin whale (B. physalus) became the favored species of the Antarctic hunt. This is the second-largest species, up to 21 m long. As many as 29-thousand animals were harvested in a year, causing this species to decline, though not to commercial extinction. More than 704-thousand fin whales were killed in this region. The present population is less than 85-thousand animals, about 21% of the original abundance. The global abundance is about 163-thousand, compared with an initial 700-thousand.

As the largest species became difficult to harvest because of their increasing rarity, initially “less desirable” species were hunted. These were the sei whale (B. borealis), humpback whale (Megaptera novaeangliae), sperm whale (Physeter macrocephalus), and minke whale (B. acutorostrata). These smaller species were also over-harvested, and their populations also declined.

Toward the end of the hunt in the Antarctic Ocean, the population of blue whales had been reduced by about 99%, humpback whales by 97%, sei whales by 82%, and fin whales by 79%. By the early 1980s, whalers were killing mostly the relatively small (up to 9.1 m long) and abundant minke whale. Finally, in 1982, the IWC announced a moratorium on Antarctic whaling, to begin in 1985-1986. Japan and the former USSR continued a commercial hunt until 1986-1987. Since then, only Japan has whaled in the Southern Ocean, killing hundreds of minke whales in most years for the purposes of “research,” as well as fin whales.

Industrial whaling also depleted whale stocks in the Northern Hemisphere. Early European explorers found large populations of northern right whales in waters off Atlantic Canada, and these valuable animals were soon hunted. The Basque hunt of 1530-1610 killed about 25-40-thousand right whales (but few afterward because of the severely depleted stocks). The right whale survives today in the western Atlantic as an endangered population of about 350 animals, only 3-4% of the original abundance. Although this species has been protected from hunting for more than 50 years, its abundance is not increasing much. This is probably because of mortality caused by accidental collisions with ships and entanglement in fishing gear.

Soon after the right whales were depleted off eastern North America, populations of bowhead whales (Balaena mysticetus) were discovered in Arctic Canada, Alaska, and eastern Siberia. Like right whales, the slow-swimming bowhead could be easily overtaken by whaling boats and killed. The population of about 55-thousand bowheads in the western Arctic was soon depleted. Bowhead whales are now rare, although their populations are increasing. These animals are no longer hunted commercially, although a hunt by Inuit in northern Alaska kills 20-40 animals per year. Since 1996, Alaskan Inuit have been allowed to again hunt a few bowhead whales, a practice that is permitted because of the importance of this species in their culture.

A final example of depletion of a whale stock involves the grey whale (Eschrichtius robustus) of western North America. This species winters and breeds in warm waters off Mexico and migrates up the Pacific coast to summer in the western Beringean Ocean. Commercial hunting began in 1845 and largely ended by 1900 because the stock had been reduced to an endangered several thousand animals. These were protected from further hunting, and the grey whale has since increased to about its pre-exploitation abundance of about 24-thousand animals. However, the species remains extirpated off Western Europe and is critically endangered in eastern Asia.

In total, more than 2.5 million whales of all species were killed during the commercial hunts of the past four centuries. Although there is now a ban on commercial whaling, Norway and Japan are still hunting minke whales, each killing several hundred per year. These and several other countries are lobbying aggressively for a return to a limited commercial hunt. In recent years, Japanese whaling interests have announced intentions to harvest larger numbers of minke whales, as well as fin whales and humpback whales in Antarctic waters. This was obviously a commercial harvest, but because biological and ecological data were collected, it was undertaken under the umbrella of “scientific” whaling.

Seal Hunting

Seals breed on land or sea ice, often in dense populations, and during the past several centuries, huge numbers have been commercially slaughtered for their skin, blubber, meat, and other products. Until the mid-twentieth century, seal hunting was an unregulated enterprise that severely depleted the resource, with several species made extinct and many regional and local extirpations. Since then, conservation measures have protected most seal populations. Some severely depleted species have managed to increase in abundance, such as the California sea lion (Zalophus californianus), northern fur seal (Callorhinus ursinus), and northern elephant seal (Mirounga angustirostris) in Pacific waters near North America.

One of the largest commercial hunts has involved the harp seal (Pagophilus groenlandicus), an abundant species of the northern Atlantic Ocean. These seals breed prolifically on pack ice in the Gulf of St. Lawrence and around Newfoundland and Labrador in Canada, and then in summer in the eastern Arctic. Harp seals are especially vulnerable to hunters in April, when large numbers of newborn pups, called whitecoats because of the color of their birth fur, lie about on the pack ice. Because they are not yet aquatic, the pups are easily approached and killed. Adults are also concentrated at that time and can be caught in nets, shot on the ice, or clubbed if they try to defend their young. The skins of harp seals are a valuable commodity, and many people enjoy eating their meat.

Historically in Canada, the largest hunts were by Newfoundlanders, but hunters from Labrador, Nova Scotia, Prince Edward Island, and Quebec have also been active. The numbers harvested in any year mostly depended on the ice conditions, which affect how close sealers can get to the whelping aggregations of seals. During the heyday of this enterprise, more than 600-thousand animals were harvested annually, as occurred in 1831, 1840, 1843, and 1844 (Busch, 1985). Overall, about 21-million harp seals were taken between 1800 and 1914. This vast slaughter of a large wild animal has only a few parallels, including the massacre of bison in the nineteenth century, the modern hunt of kangaroos in Australia, and that of deer in the Americas.

Another 12-million harp seals were taken between 1915 and 1982, with up to 380-thousand in one year (1956). Since then, the harvests have been smaller, mostly because of intense controversy about a commercial harvest of wild animal babies and the consequently diminished market for seal products. For instance, in 1984 the European Union (EU) banned the import of whitecoat pelts, which resulted in reduced harvests in Canada, from 190-thousand per year in 1981-1982 to 19-80-thousand per year during 1983-1990. (Note that young harp seals are not called whitecoats after they are 9-10 days old, when they begin to shed their white fur. At the time, older young could still be imported to the EU, but the most lucrative market had been for whitecoats. In 2010, the EU banned the importing of all sea products.)

In recent decades, animal-rights and conservation advocates, as well as elements of the popular media, have engaged in sensationalized reporting of the hunting of harp seals in Atlantic Canada. This has resulted in the hunt being widely regarded as a cruel and barbaric enterprise, mostly because baby seals, which are extremely attractive animals, were the object of the hunt. The young seals were killed by clubbing or shooting, which are humane methods of slaughter. However, some sealers were not competent in these killing methods, and videos have shown that during the rush to harvest young seals, animals might be inadequately clubbed and then skinned while apparently “alive” (or at least still twitching – the seals were likely brain-dead). Video images like this are extremely upsetting to most people, and they have been widely publicized by well-organized opponents of the Canadian hunt of harp seals.

Many people, however, do not agree with the portrayal of the seal hunt as being unusually “cruel and brutal.” They contend that the commercial harvesting of wild seals is no more ruthless than the slaughter of domestic livestock. For example, each year tens of millions of large mammals and hundreds of millions of chickens are raised and slaughtered annually in Canada and the U.S., often under cruel conditions, to provide meat and other products (see also Chapter 13). Clearly, there are elements of cruelty in the commercial slaughter of both wild animals and livestock. An analysis of the ethics of killing animals should also, however, recognize that seals are wild creatures while livestock are specifically bred, raised, and killed for consumption by humans. It is up to philosophers, and to individual consumers of animal products, to determine which of these commercial slaughters, if either, represents the greater moral outrage.

Although the intense hunting caused harp seals to decrease in abundance, the species was never depleted to the degree of biological or commercial endangerment. This was not a result of a conservation ethic by the sealers or their industry. In fact, sealers typically killed as many harp seals as they could, particularly before 1970 when the Canadian government began to regulate the hunt through a quota system. In general, only the physical difficulty of hunting in treacherous pack ice limited the numbers of seals that could be found and killed, and so prevented a severe depletion of their stocks.

When the commercial hunt was reduced in the late 1980s, the global abundance of harp seals was about 3 million animals, including 2 million in Canadian waters. Even then, the harp seal was among the world’s most populous large wild animals. In 2014, its abundance in Canadian waters was more than 7.4-million (there are also up to 0.6-million hooded seals and 0.5-million grey seals; Fisheries and Oceans Canada, 2014b). In fact, the rapidly increasing harp seal population is alarming some people, who are concerned that the seals are “eating too many fish” (although there is little evidence to support this idea).

In any event, harp seals are again being harvested. The harvest is intended to cull the seal population somewhat, while providing economic benefits through the sale of meat, hides, and other products (including penises, for which there is a market in eastern Asia). The most recent quota allowed the harvest of 400-thousand harp seals in 2013-2014, including adults and recently molted young (but not whitecoats). The quota for hooded seals was 8,200, and grey seals 60-thousand. However, the actual harvests are much smaller, largely because of collapsed markets in the European Union and elsewhere. The actual harvest of harp seals in 2013 was 94-thousand, with a market value of the raw pelts being about $3-million. A nominal goal of the management plan is to reduce the abundance of harp seals to about 3.85 million.

Terrestrial Hunting

Many terrestrial animals are also hunted in large numbers, including big mammals such as bears, deer, gazelles, kangaroos, and pigs. Many birds are also hunted, particularly grouse, pheasants, shorebirds, and waterfowl. Much hunting of wild animals is undertaken for subsistence purposes, but sport hunting is also important in some regions.

Many Americans hunt on a regular basis, whether for subsistence, as a sport, or for both reasons. In 2016, 11.5 million individuals 16 years and older hunted spending a total of $26 billion (USFWS, 2018). The most commonly hunted large mammals were deer (Table 12.6; Image 12.5). Big game hunting was the most popular type of hunting in 2016. There were 9.2 million hunters who pursued big game such as deer and elk on 133 million days (USFWS, 2018).

Table 12.6. Selected Game by Type of Hunting. Data are for 2016. Source: USFWS (2018).

Image 12.5. White-tailed Deer. Many white-tailed deer are harvested by hunters each year in the U.S. This white-tailed deer was photographed in Glacier National Park, Montana. Source: “White-Tailed deer doe” by GlacierNPS is licensed under Public Domain.

Waterfowl are also harvested in large numbers. About 1 million waterfowl hunters harvested 9,720,800 ducks and 2,691,900 geese in the 2019 season (USFWS, 2020). The most commonly hunted game birds in the U.S. (harvested in 2019) are the following:

• Mallard (Anas platyrhynchos), 2.9 million
• Green winged teal (Aix sponsa), 1.17 million
• Gadwall (Anas strepera), 1.05 million
• Wood duck (Aix sponsa), 946,838
• Blue-winged/cinnamon teal (Anas discors and A. cyanoptera), 802,057

It is important to monitor populations of species that are hunted or trapped to ensure that over-hunting does not cause them to decline to an unacceptable degree.

Conclusions

Renewable resources are the only fundamental basis of a sustainable economy. In this chapter, we learned that the most important kinds of renewable resources in the U.S. and the rest of the world are freshwater, agricultural products, forest biomass, fish, and hunted birds and mammals (renewable sources of energy were examined in Chapter 18). Some of these are wild resources that are harvested from natural ecosystems, while others are managed in agricultural systems to achieve higher yields (including in agroforestry and aquaculture). In general, the U.S. is rich in renewable natural resources. However it is important that the use of these resources are monitored and managed to not over-exploit them by excessive harvesting or inadequate management of their regeneration.

Questions for Review

1. What is meant by a renewable natural resource? Explain the principle by referring to one of the following: surface water and groundwater, agricultural site capability, timber, or a hunted animal.
2. What are the most important renewable resources in the United States? Indicate, giving reasons, whether you think those resources are being used in a sustainable manner.
3. Use data on natural resources in Chapters 12 and 18 to develop a “resource profile” for the region where you live. Consider the relative importance of non-renewable and renewable resources in the economy and the implications for longer-term sustainability.
4. What are the criteria for ecological sustainability?

Questions for Discussion

1. Identify a potentially renewable natural resource that has been over-harvested and depleted in your region. What are the reasons for the unsustainable use of the resource?
2. Should relatively abundant species of whales (such as the minke) or harp seals be hunted? Your answer should consider whether the species can be harvested in a sustainable manner, and should also address the ethics of hunting wild animals.
3. What are the political and economic problems of sharing water resources between countries or regions?
4. Although food can be purchased in a store, it does not really come from there – it is actually harvested from wild ecosystems or is cultivated in agriculture. Consider the food that you eat and the ethical and environmental issues associated with its production. You may find this question to be particularly interesting if you focus on meat, which is lethally harvested from millions of animals each year in the United States.

Exploring Issues

1. The International Whaling Commission has been asked to allow the resumption of whale hunting in American waters. They ask for your advice on the matter, and you decide to develop lists of benefits and damages that would occur if the hunting were allowed. Prepare these lists and explain how each item relates to the ecological sustainability of a potential whale harvest.

References Cited and Further Reading

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American Forest & Paper Association. 2019. Fun Facts. https://afandpa.org/our-industry/fun-facts. Accessed June 18, 2021.

Bolen, E.G. and W.L. Robinson. 2002. Wildlife Ecology and Management. 5th ed. Prentice Hall, Upper Saddle River, NJ.

Busch, B.C. 1985. The War Against the Seals: A History of the North American Seal Fishery. McGill-Queen’s University Press, Kingston, ON.

Chiras, D.D. and J.P. Reganold. 2004. Natural Resource Conservation: Management for a Sustainable Future. 10th ed. Prentice Hall, Upper Saddle River, NJ.

Craig, J.R. and D.J. Vaughan. 2010. Earth Resources and the Environment. 4th ed. Prentice Hall, Upper Saddle River, NJ.

Cushing, D.H. 1988. The Provident Sea. Cambridge University Press, Cambridge, UK. Ellis, R. 1991. Men and Whales. Knopf, New York, NY.

Dieter, C.A., Maupin, M.A., Caldwell, R.R., Harris, M.A., Ivahnenko, T.I., Lovelace, J.K., Barber, N.L., and Linsey, K.S., 2018, Estimated use of water in the United States in 2015: U.S. Geological Survey Circular 1441, 65 p., https://doi.org/10.3133/cir1441.

Ellis, A. and K. Ruble. 2019. Flint’s Deadly Water. PBS Frontline: WBGH/Boston. https://www.pbs.org/wgbh/frontline/film/flints-deadly-water/.

Fisheries and Oceans Canada. 2014b. Seals and Sealing in Canada. http://www.dfo-mpo.gc.ca/fm-gp/seal-phoque/index-eng.htm

Food and Agricultural Organization of the United Nations (FAO). 2017 AQUASTAT. FAO, Rome. http://www.fao.org/nr/water/aquastat/data/query/index.html

Food and Agricultural Organization of the United Nations (FAO). 2018. FAOSTAT. http://faostat3.fao.org/download/T/TP/E

Food and Agricultural Organization of the United Nations (FAO). 2019. FAOSTAT. http://faostat3.fao.org/download/T/TP/E

Food and Agricultural Organization of the United Nations (FAO). 2020. The State of the World’s Forests. http://www.fao.org/state-of-forests/en/. Accessed June 18, 2021.

Freedman, B. 1995. Environmental Ecology. 2nd ed. Academic Press, San Diego, CA.

Fryxell, J.M. and A.R.E. Sinclair. 2014. Wildlife Ecology, Conservation, and Management. Wiley-Blackwell, New York, NY.

Harris, J.M. and B. Roach. 2014. Environmental and Natural Resource Economics: A Contemporary Approach. 3rd ed. Routledge, New York, NY.

Hayden, A.,  J. Acheson, M. Kersula,  J. Wilson. 2015. Spatial and Temporal Patterns in the Cod Fisheries of the North Atlantic in Conservation & Society, Vol. 13, No. 4, pp. 414-425. https://www.jstor.org/stable/26393221.

Holechek, J.L., R.A. Cole, J.T. Fisher, and R. Valdez. 2002. Natural Resources: Ecology, Economics, and Policy. 2nd ed. Prentice Hall, East Rutherford, NJ.

Hutchings, J.A. and R.A. Myers. 1995. The biological collapse of Atlantic cod off Newfoundland and Labrador: An exploration of historical changes in exploitation, harvesting technology, and management. Pp. 39–93 in: The North Atlantic Fisheries: Successes, Failures, and Challenges. Institute of Island Studies, Charlottetown, PE.

Krausmann, Fridolin, et al., 2012. Long-Term Trajectories of the Human Appropriation of Net Primary Production: Lessons from Six National Case Studies. Ecological Economics, vol. 77. pp. 129–138., doi:10.1016/j.ecolecon.2012.02.019.

National Oceanic and Atmospheric Administration (NOAA). N.d. Atlantic Cod. https://www.fisheries.noaa.gov/species/atlantic-cod. Accessed June 18, 2021.

National Oceanic and Atmospheric Administration (NOAA). 2020. Fisheries of the United States, 2018. https://www.fisheries.noaa.gov/feature-story/fisheries-united-states-2018. Accessed June 18, 2021.

National Research Council. 1998. Review of Northeast Fishery Stock Assessments. https://doi.org/10.17226/6067.

Tietenberg, T. and L. Lewis. 2011. Environmental and Natural Resource Economics. 9th ed. Addison Wesley, Boston, MA.

United States Department of Agriculture (USDA). 1961. Land-capability classification. Agriculture Handbook No. 210. https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052290.pdf. Accessed June 18, 2021.

United States Department of Agriculture (USDA). 2014. Farms and Farmland. https://www.nass.usda.gov/Publications/Highlights/2014/Highlights_Farms_and_Farmland.pdf. Accessed June 18, 2021.

United States Geological Survey (USGS). 2010.  Estimated use of water in the United States in 2010. https://pubs.er.usgs.gov/publication/cir1405.

U.S. Fish and Wildlife Service (USFWS) 2018. 2016 National Survey of Fishing, Hunting, and Wildlife-Associated Recreation. https://www.census.gov/content/dam/Census/library/publications/2018/demo/fhw16-nat.pdf. Accessed June 18, 2021.

U.S. Fish and Wildlife Service (USFWS). 2020. Migratory bird hunting activity and harvest during the 2018–19 and 2019–20 hunting seasons. Laurel, MD. https://www.fws.gov/migratorybirds/pdf/surveys-and-data/HarvestSurveys/MBHActivityHarvest2018-19and2019-20.pdf. Accessed June 18, 2021.

World Bank. 2021. https://datacatalog.worldbank.org/dataset/world-development-indicators. Accessed June 18, 2021.