Adapting Forests to Climate Change
How is Climate Changing?
Over the last century the earth’s surface has warmed by about one degree F. This warming was caused by a combination of factors: natural climate variability, increasing emissions of greenhouse gases from use of fossil fuels, and deforestation. In the Northeast and Midwest, temperature records show that the length of the growing season is increasing, and that rapid freezing events are more common in the early spring. As a consequence, forest ecosystems are changing. Observable changes are apparent in the timing of biological events (phenology) of both plant and animal species. For example, many spring events, such as flowering and leaf-out, now occur several days earlier than in the 1960’s. According to the most recent report of the Intergovernmental Panel on Climate Change, there is very high confidence that North America has experienced locally severe economic damage, plus substantial ecosystem, social and cultural disruption from recent weather-related extremes, including hurricanes, other severe storms, floods, droughts, heatwaves and wildfires. Continuing increases in the global temperature are beginning to force shifts in range as species move to higher latitudes or elevations as well as overall changes in community assemblages.
Climate models have projected significant increases in temperature over the next century for the Northeast and Midwest. Climate change will also affect rainfall patterns, but scientists cannot yet predict how regional rainfall patterns will change. Growing seasons will lengthen further in both spring and fall. According to the Intergovernmental Panel on Climate Change, there is very high confidence that the vulnerability of North America depends on the effectiveness and timing of adaptation and the distribution of coping capacity, which vary spatially and among sectors. Climate change will constrain North America’s over-allocated water resources, increasing competition among agricultural, municipal, industrial and ecological uses (very high confidence).
How Will Climate Change Affect Forests?
It is difficult to predict how climate change will affect forests. This is because there is uncertainty about the exact nature of future climate change, and because other factors that affect forests are changing at the same time. For example, the chemical composition of the atmosphere is changing: carbon dioxide is increasing; ground-level ozone is increasing, and acid deposition continues to be a problem. These factors interact in complex ways that are only partly understood. However, there is a general consensus among scientists that (1) productivity will increase with increasing atmospheric carbon dioxide and warming temperatures, (2) productivity will decrease with increasing tropospheric ozone, possibly resulting in the loss of some sensitive species, (3) tree species will “migrate” northward with warming, (4) seasonal changes such as freeze/thaw events will be altered, and (5) extreme weather events will become more likely. The anticipated rate of climate change is expected to be too rapid for existing trees to adapt, creating a high risk of widespread tree mortality, and increased threat from other forest stresses such as insects, diseases, and air pollution. These interacting threats will very likely affect industries that depend on healthy, productive forests.
What Can Be Done About Climate Change?
There are two approaches to combat climate change. One is to tackle the causes of climate change directly by reducing the amount of carbon dioxide and other greenhouse gases in the atmosphere. Two ways to do this are to reduce emissions of greenhouse gases from burning of fossil fuels, and to increase the amount of carbon stored in forests (carbon sequestration). Forests of the U.S. sequester about 250 millions tons (metric) of carbon annually, enough to offset about 15 percent of emissions from burning of fossil fuels. Analyses have shown that this rate of carbon sequestration by forests can be increased by 100 million metric tons per year for a period of 50 years or more, buying valuable time for new energy technology to be developed and applied to achieve permanent reduction in atmospheric carbon dioxide.
A second approach is to anticipate changes and prepare to adapt. This is a difficult approach to implement because of uncertainty about the exact nature of the changes. However, researchers are making progress in predicting how climate will change and how forests are likely to respond to climate change and the other factors affecting forests. New technology has made it possible to conduct experiments on intact forest communities under the effects of elevated greenhouse gases, and to simulate the behavior of forests as intact ecosystems under current climatic conditions. As scientific knowledge increases, forest managers can acquire knowledge about how to adapt their management practices. Some of the actions that can be taken now, without risk of future regrets, are to carefully monitor forests for evidence of the effects of climate change, and to be prepared to adapt ongoing management plans as climate changes.
NRS has a long history of research on the impacts of climate change and other factors on forest health and productivity, and on silvilcultural practices for sustainable forest management. NRS working with National Forest System Region 9 will prepare the Region’s foresters to understand and cope with potential climate change effects including consideration of interactions with other factors, and develop adaptation strategies. Future forest planning will require analyses of future scenarios of climate change effects on forest productivity, health, and species composition, and increased ability to consider uncertainty and risk. This will involve personnel with new skills to perform such analyses, and development analytical technology -- i.e., models of various kinds. For example, forest management models such as SILVAH are not sensitive to climate variability and will require additional features or linkage to other models that can simulate responses to changing atmospheric chemistry or changing disturbance patterns.
The NRS will (1) develop a plan to increase employee awareness of climate change and expected future impacts, and (2) identify several options for achieving the goal of adapting future forests to climate change, with specific attention to including the best available science about climate change into the forest planning process.
- Land managers increase awareness of the potential impacts of climate change on forest resources, and opportunities to enhance the resilience of forests to expected changes.
- Managers and policy makers develop forest plans that consider the uncertainty of future climate change effects.
- Land managers take actions to increase carbon sequestration while sustaining production of other forest benefits.
This is a new area of emphasis that will result in a variety of scientific products and decision-support tools. We are particularly interested in working with the models and processes that are currently used in the forest planning process, and adding features to them for addressing the potential future impacts of climate change.
- Yude Pan, Research Forester, US Forest Service – Northern Research Station
- John Hom, Biological Scientist, US Forest Service – Northern Research Station
- Rich Birdsey, Program Manager, US Forest Service- Northern Research Station
- Louis Iverson, Landscape Ecologist, US Forest Service- Northern Research Station
Last Modified: 07/24/2009