Notes · Environmental ScienceUK · A-Levels

Forest resources

This chapter examines forests as a resource and as ecosystems that provide services far beyond timber. It covers the goods and ecosystem services forests provide, the link between forest productivity and biodiversity, the causes and consequences of deforestation, and the management and restoration that can make forest use sustainable, connecting forests to the carbon cycle, climate, soils and water throughout.

4 sections~14 min reading time3 competenciesLevel Foundation 1 · Standard 2 · Advanced 1

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Exam profile

AO1 · Describe the resources and services forests provide, the causes of deforestation and the methods of sustainable managementAO2 · Apply productivity and carbon concepts to forest data and calculate rates of changeAO3 · Analyse the causes of deforestation and evaluate the effectiveness of sustainable forest management

Operators:describeexplainanalyseevaluatecalculateassess

basic level

AS-Level expects you to describe the goods and services forests provide, the causes and consequences of deforestation and the main sustainable-management methods.

higher level

The full A-Level requires you to relate productivity to biodiversity, work with forest data, and evaluate the effectiveness of management and restoration.

Depth

Text

Contents · 4 sections

Forest resources

The resources and services forests provide#

FoundationAQA 7447 3.5.3

The goods and services provided by a forest

Fig. 1Forests provide goods (timber, products) and services (carbon, water, soil, biodiversity, recreation).

Forests are valued first for their goods: timber for construction and fuel, pulp for paper, and a wide range of non-timber products such as fruits, nuts, resins, rubber and medicines. These goods are the reason forests are exploited, and they can in principle be harvested sustainably if the rate of removal does not exceed the rate of regrowth. But focusing only on the goods undervalues forests, because their greatest value often lies in the services they provide, which are not bought and sold and so are easily overlooked.

Forests provide a rich set of regulating and supporting ecosystem services. They are major stores of carbon and, as they grow, absorb carbon dioxide from the atmosphere, so they help regulate climate; they intercept rainfall and release it slowly, regulating the water cycle and reducing floods and droughts; their roots bind the soil and their canopy shelters it, preventing the erosion met in the soils chapter; and they support enormous biodiversity, providing habitat for a large fraction of the world's terrestrial species. They also offer cultural services of recreation, education and spiritual value.

These services connect forests to almost every other topic in the course. Their role as a carbon store and sink links them to the carbon cycle and climate change; their regulation of water links them to the hydrosphere; their protection of soil links them to the soils chapter; and their habitat value links them to biodiversity and conservation. This web of connections explains why the loss of forest has such wide-ranging consequences, felt far beyond the cleared land itself.

Recognising the full value of forests, goods plus services, is the key to arguing for their conservation, because the short-term profit from clearing a forest for timber or farmland is often much less than the long-term value of the services lost. Placing a value on services such as carbon storage and flood protection, though difficult, has strengthened the case for keeping forests standing, and underlies schemes that pay for the protection of forests. This framing sets up the evaluation of deforestation and management in the rest of the chapter.

Worked example

Valuing standing forest

A company can profit by clearing a forest for timber and cattle. Outline the services that would be lost and use them to argue against clearance.

Carbon and climate
Clearing releases the forest's stored carbon and removes a future sink, worsening climate change, a cost borne globally.
Water and soil
Without the forest, rainfall runs off faster, increasing floods and droughts, and the unprotected soil erodes, silting rivers and losing fertility.
Biodiversity and conclusion
The habitat and its species are lost. Because these services are large and hard to replace, their value can exceed the short-term profit from timber and cattle, arguing against clearance.

Result: The lost carbon, water, soil and biodiversity services can outweigh the short-term profit, so keeping the forest is often the better choice.

Typical mistakes

Valuing forests only for timber and ignoring the larger, hidden value of their ecosystem services.
Forgetting that a growing forest is a carbon sink (absorbing carbon dioxide) as well as a carbon store.

Active revision

Explain why clearing a forest for farmland may cost more in lost ecosystem services than it gains in farm output.

Active recall

Recall the key points — then reveal.

Sources: AQA AS and A-level Environmental Science (7447) specification (AQA) · GCE AS and A level subject content (Department for Education)

Forest productivity and biodiversity#

StandardAQA 7447 3.5.3

Net primary productivity of forest biomes

Fig. 2Net primary productivity of the forest biomes (illustrative values): productivity, and with it biodiversity, is highest in the tropics.

Forests differ greatly in their productivity, and the pattern follows climate, as established in the living-environment chapter. Tropical rainforests, with year-round warmth, light and rainfall, have among the highest net primary productivity of any ecosystem; temperate forests, with a distinct cold season, are less productive; and boreal forests (taiga), limited by cold and a short growing season, less productive still. Because productivity sets the energy available to the ecosystem, it strongly influences how much life a forest can support.

High productivity is linked to high biodiversity. The tropical rainforest, the most productive forest biome, is also the most biodiverse ecosystem on land, supporting an extraordinary variety of species; the abundant energy and the complex, layered, year-round habitat allow many species to find niches, as the niche concept from the first chapter predicts. This link between productivity and biodiversity means that the most productive forests are also the richest in species, so their loss is doubly serious, taking both a great store of carbon and a great store of biodiversity.

The different forest biomes therefore have different conservation significance and vulnerabilities. Rainforests hold vast biodiversity and carbon but grow on soils whose fertility depends on rapid nutrient cycling, so once cleared they recover slowly and the exposed soil is quickly degraded; boreal forests hold huge amounts of carbon in their cold soils and are increasingly affected by warming. Understanding these differences is important for setting conservation priorities and for predicting the consequences of clearing a particular forest.

Interpreting forest data, such as comparing the productivity or biodiversity of different biomes, or relating them to climate, is a standard analytical task. The key relationships to hold in mind are that productivity follows climate, that biodiversity tends to follow productivity, and that both are highest in the tropics, so that the forests most worth conserving on grounds of biodiversity and carbon are often those under the greatest pressure from clearance for agriculture.

Worked example

Relating productivity to biodiversity

Data show a tropical rainforest has both a higher net primary productivity and a far greater number of species than a boreal forest. Explain the connection.

Productivity and climate
The rainforest's warm, wet, sunlit climate allows high, year-round photosynthesis, giving a high net primary productivity; the cold, short season of the boreal forest limits productivity.
Productivity and niches
The abundant energy and complex, layered habitat of the rainforest provide many niches, so many species can coexist.
Conclusion
Higher productivity supports higher biodiversity, so the rainforest holds far more species; its loss removes both great carbon and great biodiversity.

Result: The rainforest's high productivity, set by its climate, supports many niches and so far greater biodiversity than the boreal forest.

Typical mistakes

Assuming rainforest soils are fertile; their fertility depends on rapid recycling, so cleared land degrades quickly.
Treating productivity and biodiversity as unrelated; the most productive forests tend also to be the most biodiverse.

Active revision

Explain why tropical rainforests support far more species than boreal forests, referring to climate and productivity.

Active recall

Recall the key points — then reveal.

Sources: AQA AS and A-level Environmental Science (7447) specification (AQA) · GCE AS and A level subject content (Department for Education)

Deforestation: causes and consequences#

StandardAQA 7447 3.5.3

The consequences of deforestation

Fig. 3Deforestation releases carbon, destroys habitat, erodes soil and disrupts the water cycle.

Deforestation, the permanent clearance of forest, is driven mainly by the demand for land and resources. The largest cause is clearance for agriculture, both for large commercial crops and cattle ranching and for subsistence farming; logging for timber and pulp, mining and oil extraction, road and dam building, and the gathering of fuelwood also contribute. These pressures are greatest in the tropics, where population growth and the demand for commodities meet the most biodiverse and carbon-rich forests, which is why tropical deforestation is of such global concern.

The consequences of deforestation are severe and reach far beyond the cleared land. Biodiversity is lost as habitat is destroyed, often before the species are even known; carbon stored in the trees and soil is released to the atmosphere, both by burning and by decomposition, so deforestation is a significant source of greenhouse-gas emissions and removes a future carbon sink; and the loss of the protective canopy and roots exposes the soil to the erosion and loss of fertility met in the soils chapter, while the loss of the forest's regulation of water increases flooding and can reduce local rainfall.

These consequences are connected and can reinforce one another. Losing forest releases carbon and worsens climate change, which can further stress the remaining forest; eroded, degraded soil makes the cleared land less productive, sometimes driving the clearance of yet more forest; and the disruption of the water cycle can dry the region. In the worst cases, clearing a large area of rainforest can pass a threshold beyond which the forest can no longer sustain its own rainfall, a tipping point of the kind met in the climate chapter.

The scale and rate of deforestation are commonly presented as data to interpret, and calculating a rate or a percentage change is a standard quantitative task. In evaluating deforestation, the point to grasp is that the local, short-term benefit, usually farmland or timber, is set against large, often global and long-term costs in carbon, biodiversity, soil and water, which is why deforestation is treated as one of the central environmental problems and why sustainable management is needed.

\text{percentage forest loss} = \frac{\text{area lost}}{\text{original area}} \times 100

Percentage forest loss

Used to express the scale of deforestation over a period; a rate is found by dividing by the number of years.

Worked example

Calculating a rate of deforestation

A forest covering 40 000 square kilometres loses 1200 square kilometres over four years. Calculate the percentage lost and the average annual rate of loss.

Percentage lost
$\dfrac{1200}{40\,000} \times 100 = 3\%$ lost over the four years.
Annual rate
$\dfrac{1200}{4} = 300$ square kilometres per year, or $\dfrac{3\%}{4} = 0.75\%$ per year.
Consequences
The clearance releases stored carbon and removes a sink, and exposes the soil to erosion, among other effects.

Result: 3% of the forest is lost over four years, an average of 300 square kilometres (0.75%) per year.

Typical mistakes

Giving only biodiversity loss and ignoring the carbon, soil and water consequences of deforestation.
Forgetting that deforestation removes a future carbon sink as well as releasing the stored carbon.

Active revision

A rainforest region loses 1200 square kilometres of an original 40 000 square kilometres over four years. Calculate the percentage lost and the annual rate, and outline two consequences.

Active recall

Recall the key points — then reveal.

Sources: AQA AS and A-level Environmental Science (7447) specification (AQA) · GCE AS and A level subject content (Department for Education)

Sustainable forest management and restoration#

AdvancedAQA 7447 3.5.3

Sustainable forest-management strategies

Fig. 4Sustainable forestry combines careful harvesting, protection, restoration and reduced demand.

Sustainable forest management aims to obtain timber and other products while maintaining the forest's structure, biodiversity and services, so that use can continue indefinitely. Its methods contrast with clear-felling. Selective logging removes only some trees, leaving the forest largely intact to recover; replanting and natural regeneration replace what is taken; long rotations and reduced-impact logging limit damage; and agroforestry combines trees with crops or livestock so that land produces both food and timber and keeps tree cover. The principle is to harvest no faster than the forest regrows and to protect the services alongside the goods.

Wider measures protect forests at the landscape and market scale. Protected areas set aside forest from exploitation; certification schemes label timber and products from sustainably managed forests so that consumers can choose them, creating a market incentive for good management; and reducing demand, for example by using timber efficiently, recycling paper and cutting waste, lessens the pressure on forests. Because much deforestation is driven by demand for commodities, tackling that demand and its supply chains is as important as managing the forests themselves.

Afforestation (planting new forest) and reforestation and restoration (re-establishing lost forest) are used both to provide timber and as tools for conservation and climate mitigation, since growing forests absorb carbon dioxide. Their benefits are real but limited: a young plantation stores far less carbon and biodiversity than the mature natural forest it may replace, monocultures of a single species have little of the biodiversity of a natural forest, and restoration takes decades and cannot instantly replace what was lost. Planting trees is therefore valuable but is not a substitute for protecting existing forest.

Evaluating forest strategies means weighing the production of goods against the protection of services, and judging effectiveness against cost and practicality. Selective logging protects the forest but yields less timber per hectare than clear-felling; certification helps only if consumers pay attention and the labelling is honest; protected areas conserve forest but must be enforced and can conflict with local livelihoods, so success often depends on involving and benefiting local people. The strongest management combines sustainable harvesting, protected areas, restoration and demand reduction, and recognises that protecting standing natural forest is usually more valuable than replacing it later.

Worked example

Evaluating reforestation

A government proposes to allow rainforest clearance for farmland while planting an equal area of fast-growing plantation elsewhere, claiming this is carbon-neutral. Evaluate the claim.

Carbon
The mature rainforest holds a very large store of carbon released on clearance, whereas the young plantation stores far less for decades, so the swap releases carbon now and recovers it only slowly.
Biodiversity
A single-species plantation has a tiny fraction of the biodiversity of the natural rainforest, so the biodiversity loss is not compensated at all.
Judgement
The claim is misleading: the exchange is not carbon-neutral for a long time and does not replace the biodiversity or other services, so protecting the standing forest is far better.

Result: Planting a plantation does not compensate for clearing rainforest, because the carbon and biodiversity losses are large, immediate and slow to recover.

Typical mistakes

Treating tree-planting as a full substitute for protecting existing forest; young plantations hold far less carbon and biodiversity.
Listing methods without evaluating their effectiveness, cost and dependence on enforcement or consumer choice.

Active revision

Evaluate whether planting new plantation forests can compensate for the clearance of natural rainforest, considering carbon, biodiversity and time.

Active recall

Recall the key points — then reveal.

Sources: AQA AS and A-level Environmental Science (7447) specification (AQA) · GCE AS and A level subject content (Department for Education)

References & sources

Sources

AQA

AQA AS and A-level Environmental Science (7447) specification

Department for Education

GCE AS and A level subject content

Forest resources

4 sections~14 min reading time3 competenciesLevel Foundation 1 · Standard 2 · Advanced 1

Forest resources

Key points

Valuing standing forest

Key points

Relating productivity to biodiversity

Key points

Calculating a rate of deforestation

Key points

Evaluating reforestation

Sources

Forest resources

Key points

Valuing standing forest

Key points

Relating productivity to biodiversity

Key points

Calculating a rate of deforestation

Key points

Evaluating reforestation

Sources