Will Conifers Weather Global Warming?

Recent posts on this blog looked at how conifers survive the snow and cold. As increasing carbon dioxide in the atmosphere causes climate warming, cold may become the least concern for our forests. But how will conifers deal with the fact that the climate is getting warmer? As with everything related to the life of living things, it's complicated. But we can see some of the effects of climate change because they are happening now. And we can see some future potential outcomes just by understanding something about the lives of trees and how they react to their environment.

At the outset, it is important to remember that, like all living things, conifers growing in the natural environment are adapted to the climate conditions where they are. Each species is adapted to survive where it grows. In the Pacific Northwest, it has taken thousands of years for our forests to adapt to the current climate.

Going up north. One response to warming climate is to move to where it is cooler. Birds can fly to cooler temperatures in the north. Even mammals can move up slope to cooler locations in the mountains. But these options can be a problem for trees. Roots do not make good legs. Even so, successive generations of trees can move as each generation distributes its seeds a few hundred feet. Yes, trees can migrate over long distances, but it may take thousands of generations and millions of years. When climate change is rapid, migrating trees cannot keep up.

Trees marching up Mt. Hood?

Migrating up slope also can present significant problems. The space gets smaller as you near the top of the mountain. And if it becomes too hot for you at the top, you just have nowhere to go. Migrating north can present barriers as well. Mountains can be a barrier, as can rivers, lakes, and even oceans.

Adapting. Natural selection enables trees to adapt. When conditions change, the genetic variability in a population will enable some trees to survive and pass their genes to the next generation. In this way, a species can adapt to a changing climate in place, but like migration, this process could also require thousands or millions of years. Trees cannot readily adapt to rapid climate change.

Are we then putting our forests in danger by causing global warming? Well, the answer to that is complicated, and varied. The temperate forests of the Pacific Northwest will likely be less affected by climate change than those in the southwest U.S. Also, the consequences of climate change for forests is not just about rising temperatures. There are related factors that may more seriously impact our forests.

Vista Ridge fire on Mt. Hood

Drought.  As the climate warms, weather patterns change. Most seriously, rainfall patterns change. Some areas will get more rainfall. Some will get less. Entire forests may be plagued by drought. In these forests, tree species that are drought intolerant will not survive. Mild winters also contribute to summer drought. Winter snowpack stores water that melts in the spring and provides water for growing trees. However, warmer temperatures bring rain in winter instead of snow. The runoff comes early, and trees are left high and dry in the summer.

Wild fires. Drought-stressed forests are subject to an ever increasing risk of wild fires. With increasing drought, fires burn hotter and are more destructive. We have already seen recent devastating wild fires all over the western U.S.

White pine blister rust is killing 
pines on Mt. Hood

Insect invasions and disease. Trees weakened by drought are also vulnerable to insect invasions and disease. Winter cold can help keep insect invasions in check. But with warmer temperatures, the insects can survive the winter and attack forest trees in force the following summer. Recent mild winters have enabled the mountain pine beetle to destroy millions of acres of lodgepole pine and ponderosa pine forests in western North America.

More carbon dioxide. One mitigating factor for forests and other plants would seem to be the increasing levels of carbon dioxide in the atmosphere. The very thing that is causing global warming could be a boon for our forests. They use carbon dioxide and store the carbon in root, limb, and their massive trunks. Perhaps we can look to forests to store carbon and help prevent more global warming. However, this scenario may not pan out as well as you might think. Just as trees are acclimated to their climate, they are also acclimated to the amount of carbon dioxide in the atmosphere. They won't necessarily grow faster if carbon dioxide concentrations are higher. Other factors often limit growth. Some experiments have shown that increasing carbon dioxide levels does increase production in some conifer species. Others, not so much. Furthermore, forests decimated by drought, wild fires, and disease won't benefit at all from increased carbon dioxide. Thus, our efforts to preserve forests to prevent climate change can be undermined by the climate change we have already caused.

Forest conservation. One thing is clear: Preserving our forests is important. They can be a significant repository of carbon. Forest destruction only adds to the rising carbon dioxide in the atmosphere. How we protect forests from the effects of climate change is not as clear, but much research has been done. Some work is being done to develop trees that are resistant to disease and can tolerate changes in climate. Foresters are planting trees in new locations where they can thrive. Yet, more research is needed to determine the effects of the changing climate on forests and develop ways to help forests adapt to change.

How can we help? We can support restoration and reforestation efforts. Planting trees is good exercise, too. We can also reduce our consumption of fossil fuels by avoiding travel in fuel-burning cars and airplanes, and instead opting to travel by electric cars, bicycles, and our feet. We can make other lifestyle choices that leave a smaller carbon footprint. We can live more simply and install solar panels on our houses. We will have a smaller impact on our planet, and the the trees in our forests will be happy.

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See Also

Climate change’s effects on temperate rain forests surprisingly complex

CNN:Global warming threatens forests, study says

U. S. Forest Service Climate Change Resource Center

Wikipedia: Mountain pine beetle

Effects of Elevated Atmospheric Carbon Dioxide Concentration and

Temperature on Forests 

The Influence of Carbon Dioxide or Ozone Concentration on Growth and Assimilate Partitioning in Seedlings of Nine Conifers