Climate Change

Climate change is affecting human systems and ecosystems around the world. The issue of global change is multi-faceted, and includes complex feedback loops that may perpetuate warming and affect ecosystem stability. In general, intact forests play a unique role in mitigating the effects of climate change because trees store a large amount of carbon in their biomass, and through photosynthesis trees can remove CO2 from the atmosphere. However, when forested land is deforested and permanently converted to another land use, this carbon is released into the atmosphere instead of removed. According to the IPCC, deforestation from land use change is responsible for 17% of annual global CO2 emissions. Preservation of forestland is critical for sequestering this carbon dioxide, while also providing protection of biodiversity and ecosystem services.

In addition to carbon sequestration, forest coverage affects temperature through evaporative cooling and albedo. For example, tropical forests that assimilate large amounts of CO2 into biomass have strong evapotranspiration, which leads to local evaporative cooling. On the other hand, surface albedo is low in boreal forests, which tend to contribute to positive temperature forcing. Climate models give insight into how these climate-forcing relationships play out in different forest environments; however, it is difficult to apply generalizations from models to specific ecosystems to determine the effects of climate change. Additionally, ecosystems are so complex that it is difficult for models to include every unforeseen process that is occurring. A great deal of research is needed to improve the quality of climate models and understand the many relationships between forests and climate change.

Just as forests can affect climate through CO2 uptake, climate change could have both positive and negative impacts on forests. In some areas, an increase in CO2 in the atmosphere may have a fertilization effect for certain plant species, causing them to perform and grow better. Additionally, increased temperatures can result in a longer growing season. However, increased temperatures due to climate change can also exacerbate drought, water stress, and pests and pathogens, leading to major forest dieback events. Review articles by Anderegg et al. and Allen et al. have documented these large mortality events around the world, and cite the combined abiotic stresses (high temperature, low water availability), and biotic stresses (pests and pathogens) as the driving forces for dieback.

The relationships between climate change and forests are not straightforward, and there is still a large amount of research that must be conducted to fully understand forests in a changing climate. Navigate through the links below to read about climate change and forests in the boreal, tropical, and temperate regions.


Sources:

Allen, C. D., Macalady, A. K., Chenchouni, H., Bachelet, D., McDowell, N., Vennetier, M., … Cobb, N. (2010). A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. Forest Ecology and Management, 259(4), 660–684.

Anderegg, W. R. L., Kane, J. M., & Anderegg, L. D. L. (2012). Consequences of widespread tree mortality triggered by drought and temperature stress. Nature Climate Change, 3(1), 30–36.

Ashton, M. S., Tyrrell, M. L., Spalding, D., & Gentry, B. (2012). Managing Forest Carbon in a Changing Climate. New York: Springer.

Bonan, G. B. (2008). Forests and Climate Change: Forcings, Feedbacks, and the Climate Benefits of Forests. Science, 320(5882), 1444–1449.

IPCC. (2007). IPCC Climate Change 2007: An Assessment of the Intergovernmental Panel on Climate Change.