The long-term effects of climate change on the world’s forests

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How is climate change affecting rainforests – and is it affecting their ability to mitigate climate change? A new and global study has attempted to provide a quantitative answer to these questions.

The Earth’s ecosystem has a very central actor that we know well from our daily lives, but whose importance we often do not appreciate: plants. Plants are the group of living beings with the largest mass on Earth.

Plants are responsible for one of the fundamental processes of life – photosynthesis.

Living beings use sunlight to absorb carbon dioxide from the air and convert it into organic matter. The sugars formed during photosynthesis are the basis of almost all food chains on Earth.

Because plants absorb carbon dioxide from the air and fix it in organic molecules, they greatly influence the concentration of carbon dioxide in the atmosphere and climate change. Today, plants absorb about 30% of greenhouse gases emitted by human activities, thus slowing down global warming.

However, it is not certain that plants will absorb as many greenhouse gases in the future as they do today, as warming itself can damage vegetation. A warmer and drier climate in the tropics can cause trees’ death, reducing the amount of carbon dioxide they absorb from the air.

This can lead to a positive feedback loop, where warming causes an increase in carbon dioxide and thus further warming.

To find out whether global warming can damage vegetation and, if so, how this damage can affect the warming process. Researchers are now trying to find a connection between the climate and the survival of plants.

One way is to study the effects of exceptional climatic conditions such as the El Nino years. Studies of this kind examine the short-term effects of climate on vegetation.

However, the climate can also have long-term effects that are different from the short-term effects.

How forests are managed has an impact on climate change

The climate determines the type of forest – in our latitudes there are predominantly deciduous mixed forests, in the north boreal coniferous forests and in the tropics evergreen rainforests. 

But the forest also influences the climate, it has a cooling effect on its surroundings, it changes the reflection of sunlight into space and it plays an important role in the water balance of the landscape. 

Trees remove the greenhouse gas CO2 from the atmosphere by storing the carbon in their wood. When a tree dies, the carbon is released again as CO2 when the wood is broken down, and a small part is stored in the soil.

Intact natural forests therefore act as a CO2 sink, i.e. they absorb more CO2 than they give off. The way we deal with the forest can have positive or negative effects on climate change:

What are the impacts of forestry on climate change

If wood is used in houses, bridges or furniture, the “built-in” CO2 is removed from the cycle for years or decades, and ideally even for centuries. 

Overall, trees and forests have a slowing effect on global warming and building with wood can protect the climate. Even unused ones accumulate large amounts of carbon in their biomass over decades and centuries and thus act as a brake on climate change. However, if more wood is harvested or burned than grows back, the CO2 balance is negative. 

Extensive slash and burn operations and the ruthless cutting down of forests (e.g. for growing animal feed or for bioethanol and palm oil) cause more greenhouse gas emissions than all cars and airplanes in the world combined.

This makes it clear how important it is to protect forests. If we do not succeed in stopping the destruction of forests, the vast tropical rainforests could collapse as the drought increases. The carbon released as a result would further heat up the climate – a nightmare for humans.

Effects of climate change on the forest and its inhabitants

Climate change inevitably affects the forest: For Central Europe, the general forecast is that there will be longer, hotter summers and shorter, milder winters.

Effects on forest growth and productivity

Many aspects related to climate change are likely to affect forest growth and productivity. Few examples are described below: Rising temperatures, changes in precipitation and increased carbon dioxide (CO2).

Warming generally extends the length of the growing season. It also shifts the geographical range of some tree species. Habitats of some tree species are likely to move northwards or to higher altitudes. Other species will be threatened locally or regionally if conditions in their current geographical areas are no longer suitable.

For example, species currently found only on mountain tops in some regions may become extinct when the climate heats up, as they cannot move to higher altitudes.

Climate change is likely to increase the risk of drought in some areas and extreme rain and flooding in others. High temperatures change snow melting times and affect seasonal water availability. Although many trees are partially drought-resistant, future droughts may be even more damaging than in the past due to rising temperatures.

In addition, drought increases the risk of forest fires, as dry trees and shrubs serve as fuel for fires. Drought also reduces the trees’ ability to produce sap, which protects them from destructive insects such as pine beetles.

Carbon dioxide is necessary for photosynthesis, the process by which green plants use sunlight to grow. If sufficient water and nutrients are available, an increase in CO2 levels in the atmosphere can make trees more productive, which can change the distribution of tree species.

Growth will be higher in nutrient-rich soils without water restrictions and will decrease as fertility and water supply decreases.

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