Northwest Conifer Connections: Forests and Climate

How do forests affect the climate?

Douglas fir forest

We all experience how a forest can affect the local climate, moderating both hot and cold temperatures. On a larger scale, can forests affect the global climate?

The climate of our planet is warming. It is common knowledge that climate scientists have attributed this warming to increasing amounts of greenhouse gasses in the atmosphere, mainly carbon dioxide (CO₂), and that the primary source of the increase in CO₂ is the burning of fossil fuels. It’s also well-known that plants, and especially trees, remove CO₂ from the atmosphere, storing the carbon and releasing the oxygen back into the air. It stands to reason that preserving existing forests and planting new forests would tend to reverse the increasing levels of CO₂.

However, the relationship between forests and climate warming is a complex one, and the effect that forests have on climate is a mixed one. Some forest types are more effective at storing carbon than others. Tropical forests generally store the most carbon per acre, but old-growth temperate forests can actually store more carbon than a tropical rain forest. Preserving and restoring forests in these areas can help mitigate the effects of rising CO₂ levels.

Fragmented forest near Mt. Hood

On the other hand, the northern arboreal forests do not store great amounts of carbon. Furthermore, they can contribute to global warming, because they absorb more heat from the sun than unforested land in the polar regions. More sunlight is reflected from areas covered by grasses or snow. So restoring or planting new forests in the northern regions is not an effective way to reduce global warming.

Unfortunately, continued deforestation is adding significant amounts of CO₂to the atmosphere. In the last 40 years almost 20% of the rainforest in the Amazon has been lost. Almost 20% of global greenhouse gas emissions are from deforestation, more than the total emissions from cars, busses, and airplanes.*

Deforestation in the Amazon

Recent efforts to mitigate rising CO₂in the atmosphere have focused on planting new forests. However, efforts to plant new forests often prove to be ineffective, and the result can be more detrimental than the benefit of storing the CO₂. Instead of restoring natural forests, many of these efforts are plantings of monoculture supported by the use of herbicides and commercial fertilizers. Also, these plantings often replace natural forests, displace local people, and disrupt their livelihood.

To make matters worse, these plantings, rather then decreasing the rise of greenhouse gasses, often are done as trades that allow big industry to release those very gasses that contribute to global warming. The net benefit of these efforts is zero.

In spite of these problems, preserving natural forests is necessary to prevent the release of their stored carbon. If done correctly, restoring forests can remove significant amounts of CO₂ from the atmosphere. However, we should not fool ourselves into thinking that these efforts can solve the problem of rising CO₂. To solve that problem, we must stop burning fossil fuels and move to renewable sources of energy.

How does climate change affect forests?

First we must realize that natural forests have adapted to the climate that exists where they grow. In the Pacific Northwest, it has taken thousands of years for our forests to adapt to the current climate. If the climate changes suddenly, trees cannot just fly to a more suitable location like migrating birds. Trees can migrate over long distances, but it may take thousands or millions of years. They can adapt to a changing climate in place, but this would also take thousands or millions of years. They cannot readily adapt to rapid climate change.

As the climate warms and rain patterns change, our forests may be more likely to suffer damage, leaving them more vulnerable to disease, insect infestation, and catastrophic fire. Thus, our efforts to preserve forests to prevent climate change can be undermined by the climate change we have already caused. If we want to protect our forests, we must significantly reduce the use of fossil fuels and move to renewable sources of energy.