Key Concepts

After completing this chapter, you will be able to:

1. Explain why forests are considered as renewable resources.
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.

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.

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 23.2). 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 23.2. 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 23.8 depicts the decreasing amounts 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.

Figure 23.8. 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 23.9 depicts the distribution of timberland, forest that can grow commercial-grade timber, across the U.S.

Figure 23.9. 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. 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 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

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

Conclusions

Renewable resources are the only fundamental basis of a sustainable economy. 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. 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). 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 timber.
2. Indicate, giving reasons, whether you think forest resources are being used in a sustainable manner in the United States.
3. 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?

References Cited And Further Reading

Alvarez, M. 2018. Tree growth, mortality, harvesting and planting. U.S. Endowment for Forestry and Communities. https://usforests.maps.arcgis.com/apps/MapJournal/index.html?appid=ec04704969514f20b1eb63280275c34c#. Accessed June 18, 2021.

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

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

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.

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.

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