Threats to Deciduous Woodlands: Climate Change and Deforestation

Different threats affect woodland in different ways

Deciduous woodland is an ecosystem dominated by trees that shed their leaves seasonally. Its trees, other plants and animals depend on one another and on conditions such as temperature and water availability. Climate change can alter those conditions, while deforestation removes woodland to make space for other land uses.

To understand climate threats, distinguish three aspects of the ecosystem. Structure means its physical arrangement, including vegetation layers and habitats. Function means the processes taking place, such as growth and reproduction. Biodiversity means the variety of living organisms. A single threat can affect all three.

Climate change can damage woodland structure

Temperate deciduous woodlands have some capacity to cope with changing conditions: many of their species can tolerate a range of conditions. This does not make them immune to future climate change.

Rising temperatures combined with drier conditions can increase the risk of forest fires. Fire can destroy trees and other vegetation, removing habitats and changing the woodland's structure. Increased extreme weather, such as severe storms, can also destroy trees. Losing trees therefore changes the physical woodland as well as threatening the organisms that depend on it.

Changes in water supply and seasons affect woodland function

Drought is a prolonged period with unusually little rainfall. Periods of drought can threaten tree survival and leave trees more vulnerable to disease. This affects the woodland's ability to maintain healthy vegetation.

Milder winters can also cause flowering and fruiting to happen earlier. The woodland may still contain trees, but the timing of its biological processes has changed. Climate change is therefore not only a threat to how much woodland remains; it can change how that woodland functions.

Biodiversity is threatened by changing conditions

Milder winters may allow more pests and disease-causing organisms to survive rather than being killed by winter cold. These can threaten woodland species. Higher temperatures may also allow invasive species to enter the ecosystem, changing the range of organisms living there.

Animals and birds may alter the timing of breeding, migration and hibernation as the climate changes. These changes affect the seasonal activities of woodland wildlife. Together with habitat damage and disease, they can threaten biodiversity.

Population growth and urbanisation create pressure for land

The social causes of deforestation involve people's needs, including places to live and transport connections. Population growth increases demand for housing. As urban areas expand, deciduous woodland may be cleared to provide building land.

Population growth also increases pressure on transport infrastructure. More vehicles and demand for journeys can lead to more roads, with woodland cleared along their routes. Wood is also used in construction, connecting the demand for housing to demand for timber.

These causes overlap: an expanding settlement can require land for houses, land for roads and wood for building. Social demand therefore creates economic incentives to clear woodland or extract timber.

Timber extraction and agricultural change create economic pressure

Timber extraction provides wood for sale and use. Deciduous trees can grow slowly, so felling them faster than they can be replaced reduces woodland resources. There may also be an incentive to replace slow-growing deciduous trees with faster-growing, more profitable trees. Tree cover may remain, but the variety of habitats and species can decline. This is a change in woodland composition, not necessarily permanent clearance of all woodland.

Agricultural change creates pressure when demand for agricultural products encourages land to be brought into farming. Much of the UK land suitable for farming was cleared of deciduous woodland centuries ago, but remaining ancient woodland can still face pressure from agricultural demand.

Agriculture can also affect woodland without clearing it. Pesticides and herbicides sprayed onto nearby crops can affect woodland organisms. Distinguish this damage to an existing ecosystem from deforestation, which converts woodland land to another use.

Using GIS to identify a pattern of forest loss

A geographical information system, or GIS, displays information linked to locations as map layers. A forest-loss layer can be examined alongside layers showing roads, settlements or land use. Switching layers on and off helps reveal relationships that would be harder to identify from separate maps.

Begin with the key, which explains the colours or symbols. Establish whether a colour represents woodland present at a starting date, loss during a particular period, or another category. Check the dates, scale and geographical area. A time filter lets you compare loss in different periods; keep the area and data definition the same, and use equally long periods when comparing amounts of loss.

Look for concentrations, scattered patches, linear patterns and areas with little loss. Describe their location using directions and mapped features. Then compare relevant layers: for example, does loss occur close to settlement edges or transport routes?

A worked illustration of the GIS method

The following fictional illustration represents a woodland divided into sixteen equal squares, each 100 metres wide. All squares represent woodland at the start of 2018. The key distinguishes loss during 2018–2020 from loss during 2021–2023. A separate settlement layer shows built-up land immediately east of the woodland.

Read the two loss categories separately first. The earlier period has three loss squares: two on the eastern edge and one in the south-west. The later period has four loss squares, all in the eastern half. Combining the periods shows that six of the seven loss squares are in the eastern half, close to the settlement.

A useful description is: ‘Tree-cover loss is concentrated in the eastern half beside the settlement, with an isolated patch in the south-west. Later loss remains concentrated in the east and extends into squares farther inside the woodland.’ This identifies the overall pattern, an exception and change over time.

The settlement layer suggests that urban expansion could be involved. However, proximity does not prove a cause: evidence of new buildings or a change in land use would be needed to support that explanation.

Transfer this method to an actual GIS map by reading its own key, dates, scale and place names, selecting comparable time periods and examining relevant layers. The simplified squares here demonstrate the reasoning, not the detail or accuracy of a real forest-monitoring dataset.

Tree-cover loss is not always deforestation

Global Forest Watch's University of Maryland dataset uses satellite imagery to detect tree-cover loss at a resolution of 30 metres. It covers woody vegetation at least five metres tall, including natural forests, planted forests and tree plantations. To study deciduous woodland specifically, the loss information needs to be considered alongside information identifying that woodland type.

Mapped tree-cover loss can result from human activity or natural events, and can be temporary or permanent. Clearing woodland permanently for housing or farmland is deforestation. Harvesting a plantation that will regrow, or trees dying during a storm, can appear as tree-cover loss without being deforestation.

GIS therefore helps establish where and when tree cover has been lost. Additional land-use information, imagery or investigation helps establish why it happened and whether the woodland has been permanently converted to another use.