Update 2016-07-24: The organization has recently published a special website on the topic of forest and climate. Go there to learn more.
The atmospheric levels of carbon dioxide are rising continuously. Global temperatures also have a rising tendency. According to the UN’s Intergovernmental Panel on Climate Change (IPCC), the amount of carbon dioxide in the atmosphere carries the main responsibility for climate change, the so called “greenhouse effect”. Along with increasing temperatures, changes in precipitation patterns and storm frequency are expected. Anthropogenic activities such as deforestation and the burning of fossil fuels also play a role in climate change. The organization Protect the Forest is following the scientific developments regarding the climate’s effect on forest ecosystems and vice versa, the forests’ effect on the climate.
The element carbon, is needed for all life. Plants take up carbon through photosynthesis directly from the atmosphere as carbon dioxide. This uptake is a prerequisite for growth. The process is light-dependent and it ceases in the dark. In parallel with photosynthesis, another process, respiration, goes on, which means that carbon dioxide, is released. This process also continues during winter. During the bright hours of the growing season, these processes are simultaneous. This means that the plants have an uptake and a loss of carbon dioxide at the same time. If the uptake outweighs the release of carbon dioxide, there is a opportunity for growth.
But what does the balance between these two processes (photosynthesis and respiration) look like? The carbon dioxide “budget” can be counted on an annual basis. Both processes are temperature dependent. Photosynthesis has an optimal effect at around +15 to 20oC and declines at both lower and higher temperatures. Respiration increases with increasing temperature. This means that the release of carbon dioxide can dominate during hot summer days. Similarly, if the amount of light falls below a certain level, the release of carbon dioxide can outweigh the uptake.
An individual tree grows if the sum of absorbed carbon dioxide minus the sum of released carbon dioxide is positive. However, the soil is also a part of the forest ecosystem. An intact (unmanaged) forest ecosystem has over the centuries built-up and stored large quantities of carbon in biomass and in the soil. Forest ecosystems can therefore be seen like huge stocks of carbon. Most of this carbon is found in the ground, mainly in the top 0-30 cm layer, and then it decreases with the depth from the surface. The circulation of the organic matter in the soil is continuous through respiration, i.e. the process is ongoing day and night, all year round. Together with the respiration of the vegetation (plants, trees, etc.), the amount of produced carbon dioxide determines whether the forest’s ecosystem as a whole will serve as a carbon source (emitting carbon dioxide) or a carbon sink (taking up carbon dioxide).
The existing notion that old-growth forests cease to act as carbon sinks has begun to be questioned in scientific literature. Due to the large emissions of greenhouse gases from forest operations and because of the long time needed for the re-absorption of carbon dioxide, current international scientific literature has recommended that older forests should not be included in the global biofuel potential. Alongside all the other reasons to conserve natural forests, climate arguments should also be considered.
Forestry methods are of importance
Each manipulation of forest ecosystems (logging, etc.) leads to a release of large amounts of carbon dioxide. The harvested forest (biomass) is soon transformed into carbon dioxide again. In addition to this, soil degradation (soil scarification, vehicle-damaged soils, etc) drives the carbon dioxide production.
In Sweden, the prevailing clear-cutting practices are very devastating from a carbon dioxide point of view. After logging, the soil respiration increases and large quantities of carbon dioxide is released to the atmosphere. This increase is due to the soil being exposed to solar radiation, which is associated with an increase in temperature. The forest also ceases to function as a carbon sink when the trees that sequester carbon are removed. The sparse vegetation in a clear-cut area cannot compensate for the carbon dioxide that has been released. Nor can the young growing forest take up all the carbon dioxide that the soil emits. Studies at Lund University have shown that it takes up to 30 years before the carbon dioxide releases are compensated by the uptake of the new trees. Depending on the climate situation, it may take even longer.
Swamps and other wetlands store large amounts of carbon. When wetlands are drained, the net effect, in the form of emitted greenhouse gases (carbon dioxide, methane, nitrous oxide, converted into carbon dioxide equivalents), can be substantial.
The so called “regeneration felling”, i.e. clear-cutting forestry, in forests that are still managed, should be avoided in order to minimize the release of carbon dioxide. Thinning and selective cutting can be better forest management options since less carbon dioxide is released. Clear-cut areas should mainly be regenerated naturally, with a greater proportion of deciduous trees or coniferous/deciduous forests. The deciduous trees’ initial growth and thus the rate at which carbon is reabsorbed from the atmosphere is often faster compared to coniferous trees. At present, the net uptake of carbon from the atmosphere is bigger in protected Swedish forests than in managed forests. The few natural forests and intact forest areas that remain must be protected. In addition to maintaining the storage of carbon, these areas also increase the biodiversity’s ability to survive in a changing climate.
In production forests, the rotation period is continuously being shortened. This can be seen as a sign that the current forestry practices are not sustainable. The trees are harvested when they effectively continue to take up carbon dioxide. A lengthening of the rotation periods would increase the forestry’s opportunities to help the climate.
How does a warmer climate affect the forest?
It is often emphasized that tree growth is expected to benefit from a warmer climate, but the opposite might be the case. Growth is likely to increase as temperatures increase moderately, but the growth will be inhibited when it reaches a certain threshold. Respiration will then increase, while the uptake of carbon dioxide is expected to decrease. Decomposers in the soil grow faster and consume more substrate in a warmer climate, leading to a reduction of the soil’s carbon storage. These reactions accelerate the greenhouse effect.
A warmer climate increases evaporation. This can lead to water shortages and lower growth if rainfall does not increase. In cases where precipitation increases, a reduced light climate would probably increase in parallel with increasing cloudiness, which would result in less growth.
The debate sometimes emphasizes that increasing atmospheric levels of carbon dioxide would have a fertilizing effect. It is a theoretical argument that seems logical. However, it appears that increased growth does not take place. The most likely reason is that the uptake of carbon dioxide is not a limiting factor for trees or other plants. Some of the seemingly limiting factors are rather availability of nutrients, water and light.
Climate change will also pose greater stress and vulnerability to the forests and the species that live there. The few natural forests and intact forest areas that still exist must be protected. These areas resist and recover better from fires, storms, insect outbreaks and other damage, compared to fragmented and managed areas. These areas also give the trees, plants and animals the possibilities to mitigate, adapt and survive in a climate that is changing.
About 20 percent of the world’s carbon emissions come from deforestation, of which a significant share comes from the tropics. In the Amazon, rainforest is cut down to make room for cattle pastures and soybean cultivations. Sugar cane plantations push pastures and soybean cultivations deeper into the rainforest. In Indonesia and other countries, which are major producers of palm oil, the destruction of rainforest has been extensive as palm plantations are established. Palm oil is used for both biofuels and food. It is unjustifiable to sacrifice rainforest biodiversity for this crop. Deforestation and loggings must be perceived as probably the greatest threats to rainforests, and are also driving factors of carbon dioxide emissions.
Slash and burn agriculture is a common method used to make room for pastures and crops such as oil palms. Slash and burn means that the forest is felled and then burnt, making the soil more nutrient-rich and easier to cultivate. The method usually leads to extensive forest fires, which over the last decade have strongly affected Indonesia and Brazil, among other countries. A significant great proportion of the total global human-caused carbon emissions come from vegetation fires.
At the International Scientific Congress on Climate Change in Copenhagen in March 2009, new reports on climate impacts were presented. The models point to the risk of a global temperature increase of 5-6oC during the 21st century and that a 2oC increase is inevitable. The Amazon rainforest is considered to decrease by one third, even at relatively moderate temperature increases of 1-2oC. Reduced tropical winds and ocean currents can lead to delayed monsoons which will make dry periods last longer. The consequence of this would be changes in plant cover, replacing tropical rainforest with drier vegetation types. Since the tropics drive the global weather systems, such a scenario would be particularly alarming. Climate change might turn the Amazon, from being a major carbon sink, to a significant carbon source.
If the models are correct, the shift towards energy efficient and more climate-friendly systems must be accelerated. Man’s over-consumption and exploitation of natural resources is the major contributor to climate change and biodiversity loss. This trend must be reversed, because the survival of the world and its species is at stake.
- Felling of old natural forests must be stopped globally.
- All remaining old-growth forests and peatland forests should be excluded from logging.
- More nature reserves urgently need to be established.
- New, less damaging, forestry methods must replace the current clear-cutting and plantation practices.
- Rotation periods for production forests need to be considerably extended.
- All drainage must cease.
- Reduced energy consumption and reduced consumption of natural resources.
Skydda Skogen (2009): Climate and boreal forests
Canadian Boreal Initiative & Boreal Songbird Initiative (2009): The Carbon the World Forgot – Conserving the Capacity of Canada’s Boreal Forest Region to Mitigate and Adapt to Climate Change
Air Pollution & Climate Secretariat (2009): Boreal Forest and Climate Change
Greenpeace (2008): Turning Up the Heat – Global Warming and the Degradation of Canada’s Boreal Forest
International Boreal Conservation Campaign: Boreal Forest Protection Critical in world’s fight against global warming
International Boreal Conservation Campaign (May 14, 2007): Dear Canadian Government Leaders