Climate Change Impacts on Forests in the Southeast United States Ellen Hawes Model Forest Policy Program Intern January 30, 2007

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1 Climate Change Impacts on Forests in the Southeast United States Ellen Hawes Model Forest Policy Program Intern January 30, 2007 The first question to answer in determining how forests in the Southeast will be impacted by climate change, is what form climate change will take. Most of the studies compare climate change scenarios from two to five of the major general circulation models (GCM). These include the Canadian Climate Center model, the Geophysical Fluid Dynamics Laboratory model, the Goddard Institute for Space Studies model, the Oregon State University model, and the UK Meteorological Office Hadley Center model. While changes depend on what model is used, some trends can be detected. In general, temperatures will increase in the region, precipitation will decrease, and fire severity will increase. The Canadian model predicts a warmer and drier Southeast than the Hadley model does. Climate change impacts individual trees through changes in atmospheric CO 2, changes in temperature and changes in precipitation. Increases in CO 2 generally lead to increased productivity by trees. Studies have shown increases in growth by loblolly pine (Westfall and Amateis 2003) and longleaf pine (Boyer 2001) that are most likely due to increased levels of atmospheric CO 2. However, some studies have shown that trees will adjust to increases in CO 2 and productivity will fall again. Furthermore, other nutrients may eventually limit increases in productivity. A model created by Woobury et al (1998), that took in to account changes in precipitation and temperature as well, predicted a 50% of decreased loblolly pine growth throughout its range. Many models look at the current relationship between climate and species range, but species may be limited more by competition than by climate, and could be successful outside their current range (USGS 1997, Winnett 1998). Studies done for the National Climate Assessment (Joyce et al 2001) found that the southern pine forest will decline in importance. The oak-pine forest type expands by 290% on the east coast. The loblolly-shortleaf pine type may be reduced by 32% overall, and shift north and west. The longleaf-slash type is projected to be reduced by 31%. Under the warmest scenarios, mixed forests in the South would be converted to grasslands and savannas (Bachelet et al 2001). However, the individual pine species do not show a decrease in occurrence, but oak increases in importance, shifting the forest 1

2 type to oak-pine or oak-hickory (Iverson and Prasad 2001). If hurricanes increase, bottomland hardwood forests may be replaced by shrubs and small trees (USGS 1997). Forest types will not shift as a whole and new community types will likely arise. Tree species richness is not predicted to change much (Currie 2001), although climate predictions for the Southeast are more variable than other parts of the country. The rate of change is hard to predict. Healthy, adult trees are much more resilient to changes in climate than seedlings. Therefore, changes in species ranges may lag by decades or centuries behind changes in climate. However, if disturbances such as fire or hurricanes increase in severity, the changes may occur more rapidly. Because the predicted rate of climate change is much more rapid than historical climate changes, species may not be able to migrate rapidly enough to new latitudes (Winnett 1998) and may decrease in importance. Furthermore, habitat fragmentation has placed many more obstacles to a smooth migration. Warmer temperatures will likely increases the severity of southern pine beetle outbreaks. Using four different climate models, climate change would increase the risk of southern pine beetle infestation by times. When including possible changes to the area and productivity of southern pine forests from climate change, the risk increases times (Gan 2004). Disturbances tend to favor the spread of non-native species, and climate change may increase their importance. References Alig, R.J., Adams, D.M. and B.A. McCarl Projecting impacts of global climate change on the US forest and agriculture sectors and carbon budgets. Forest Ecology and Management 169: This analysis was part of the National Climate Change Assessment. It uses a mathematical, multi-regional model to project economic impacts to the forest sector. The analysis shows that, overall, the forest sector is able to adapt through management, such as interregional migration of production and altered stand management, as well as substitution in consumption to different species or non-wood products. Timber production will likely increase, benefiting consumers but cutting into producer s profits. Timber production may decline in the South in the short-term, but it should rise in the long-term when compared to the North. Sawtimber and hardwood production will increase more than softwood and pulpwood production. Forest rotations are little changed in the South. Bachelet, D., Neilson, R.P., Lenihan, J.M. and R.J. Drapek Climate change effects on vegetation distribution and carbon budget in the United States. Ecosystems 4: In this analysis, both an equilibrium model (MAPPS) and a dynamic model (MC1) were used to simulate changes in equilibrium vegetation distribution and dynamic changes. The simulations find that the forests in the Southeast expand under more moderate warming scenarios over the next 100 years, but would decline under more severe warming, with catastrophic fires causing rapid conversion of many forested areas to savanna. In most scenarios, the temperate deciduous 2

3 forests are shifted north and replaced by the southern mixed forest type. The southern mixed forest type declines in density, and is replaced by savannas, and even by grasslands in the warmest scenarios. Boyer, W A generational change in site index for naturally established longleaf pine on a south Alabama coastal plain site. Southern Journal of Applied Forestry 25(2): years of research on the Escambia Experimental Forest in southern Alabama has shown an increase in site index for longleaf pine. The site index of the original second-growth stands averages 66ft. at 50 years, while the site index for naturally-established third-growth stands averages 83 ft. Soil conditions were similar and periodic fires were common in the development phase of both stands. The results were unexpected and may be due to climate change, either increases in temperature and precipitation, or increases in atmospheric CO 2. Currie, D.J Projected effects of climate change on patterns of vertebrate and tree species richness in the conterminous United States. Ecosystems 4: This analysis used regression models to relate contemporary species richness to climate, and then coupled this with climate projections from five general circulation models to predict future species richness. Currently, for most groups of terrestrial organisms, richness increases with increased temperature, and plateaus or decreases with the highest temperatures. It also generally increases with increased precipitation, declining with the highest levels. The analysis predicts little change in tree species richness in the Southeast, although predictions for Florida are variable. Mammal and bird richness is predicted to decrease throughout much of the region. Reptile and amphibian richness is expected to increase, although less in the southern US than northern US. It is possible that species richness will decline in the short-term as species not adapted to the rapid changes die out, while in the long-term, richness will increase again as species migrate in from other areas. The climate models vary more widely in predictions for the Southeast than other areas of the United States, so projections are difficult. DeWalle, D.R., Buda, A.R. and A. Fisher Extreme weather and forest management in the Mid-Atlantic region of the United States. Northern Journal of Applied Forestry 20(2): The article discusses the impacts of changes in severe weather on forest management in the Mid- Atlantic region. Climate change may change the frequency, severity and geographic extent of ice storms, hurricanes and tropical storms. The authors surveyed loggers and forest managers about past impacts of extreme weather on cost of operations, and what coping strategies they use. The economic impacts of oversupply from salvage operations and shortage conditions caused by loss of access to forest land are expected to balance each other out in the long term. Felzer, B., Reilly, J., Melillo, J., Kicklighter, D., Sarofim, M., Wang, C., Prinn, R. and Q. Zhuang Future effects of ozone on carbon sequestration and climate change policy using a global biogeochemical model. Climatic Change 73:

4 Exposure of plants to ozone reduces photosynthesis and thus reduces their ability to store carbon. Simulations from showed that some of the largest damages from ozone occurred in the Southeast United States. In the future, carbon sequestration in the region may be less than expected if ozone levels continue to be high. Gan, J Risk and damage of southern pine beetle outbreaks under global climate change. Forest Ecology and Management 191: Principal component analysis was used to establish regression relationships between climate and southern pine beetle infestations. Using four different climate models, climate change would increase the risk of southern pine beetle infestation by times. When including possible changes to the area and productivity of southern pine forests from climate change, the risk increases times. Temperature has a much greater effect on SPB infestations than precipitation. Warmer spring temperatures are the greatest contributor to increasing outbreaks. Warmer winters also lead to more outbreaks, while summer temperatures have a mixed impact and increased fall temperatures actually decrease outbreaks. Most models predict higher changes in winter and spring temperatures, so these effects dominate. Increased winter, spring and fall precipitation decreases the risk of outbreak in the following year. Iverson, L.R. and A.M. Prasad Potential changes in tree species richness and forest community types following climate change. Ecosystems 4: This study evaluates changes in tree species richness and forest community types under five different scenarios of climate change resulting from a doubling of atmospheric CO2. The analysis is done with an empirical modeling effort called regression tree analysis. The study shows that tree species richness across all counties of the eastern US increases slightly. Increases tend to be more with higher project temperatures. The oak-hickory community type is predicted to increase by 34%, primarily to the north and east, and the oak-pine type is predicted to increase by 290%, and dominates in the Southeast. The loblolly-shortleaf pine type and the longleaf-slash pine type show a significant reduction in 4 out of the 5 scenarios. However, in both cases, the individual pine species do not show a decrease in occurrence, but oak increases in importance, shifting the forest type to oak-pine or oak-hickory. The projections are heavily influenced by the projected increase in post oak (quercus stellata). The oak-gum-cypress has mixed results, depending on which model was used. Overall, most species are projected to move to the north. Past warming was slower and occurred in an unfragmented landscape. Today s warming is much more rapid and species will face numerous obstacles to migration. The study projects changes in potential habitat ranges, rather than actual ranges. It also does not account for species competition. A doubling of atmospheric CO2 could occur by the end of the century, but given the long lifespan of trees, there may be a lag time is species shifts. Iverson, L.R. and A.M. Prasad Potential redistribution of tree species habitat under five climate change scenarios in the eastern US. Forest Ecology and Management 155:

5 As in their 2001 paper, Iverson and Prasad use the statistical DISTRIB model to project changes in habitat for tree species in this eastern United States, this time focusing on 76 common tree species, and not evaluating forest community types. The weighted percentage shift in area of each species, based on the five climate models, is given. The potential shift in optimal latitude is also shown for each species. Joyce, L., Aber, J., McNulty, S., Dale, V., Hansen, A., Irland, L., Neilson, R. and K. Skog Potential consequences of climate variability and change for the forests of the United States. In Climate change impacts on the United States: the potential consequences of climate variability and change. National Assessment Synthesis Team. US Global Research Program. Available online 1/1/ The U.S. Global Change Research Program produced a national assessment on the potential consequences of climate change for various sectors. This chapter analyzes potential impacts on forests. The assessment relies primarily on two climate models: the Hadley model and the Canadian model. The Canadian model projects a scenario that is generally warmer and drier. Climate change impacts individual trees, forest processes and disturbance regimes. How these changes will interact and ultimately play out is uncertain. Increased atmospheric carbon will increase tree productivity and biomass. However, this increased productivity may flatten out if the availability of other nutrients does not keep pace. Nitrogen deposition may aid increased productivity, but higher ozone levels may cancel out this effect. New disturbance regimes will likely change the distribution of forest ecosystems. Hurricanes are an important disturbance in the Southeast, but research has not yet resolved whether hurricane frequency will increase or decrease. Fire and drought severity will both likely increase in the Southeast. Based on increased temperature and drought stress, the Hadley model predicts about 10% fire severity increase in the region, and the Canadian model predicts about 30% increase. Lightning strikes are also predicted to increase. The Canadian scenario projects that in the Southeast, drought and fire will cause a 75% reduction in carbon storage. The species composition of forests will shift due to climate change. The assessment found that the importance of white oak will decrease in the region, while the oak-pine forest type expands by 290%. The loblolly-shortleaf pine type may be reduced by 32% overall, and shift north and west. The longleaf-slash type is projected to be reduced by 31%. Under the warmest scenarios, mixed forests in the South would be converted to grasslands and savannas. Warming tends to increase species diversity in cold areas and decrease in already warm areas. Bird and mammal species richness is projected to decrease by 25% in low elevation areas of the Southeast. Many invasive species are restricted in range and reproduction by temperature. Warming could facilitate the spread of cold-sensitive species. Climate change will also likely increase disturbed areas, further facilitating the spread of invasive species. Changes in climate will also alter patterns of pest and pathogen outbreaks. The northern outbreaks of southern pine beetle will likely increase, but southerly outbreaks will decrease. Insects reproduce much more rapidly that trees, and will react to changes in climate more quickly. Economic modeling used in the assessment showed that increased timber production leads to decreased profits for producers, but benefits for consumers. Timber output increases more in the South than in the North, sawtimber production increases more than pulpwood, and hardwood 5

6 more than softwood. However, actual prices depend on complex market interactions unrelated to climate change. Lindner, M., Sohngen, B., Joyce, L.A., Price, D.T., Bernier, P.Y. and T. Karjalainen Integrated forestry assessments for climate change impacts. Forest Ecology and Management 162: This paper reviews different experiences with integrated forest sector impact assessments. Westfall, J.A. and R.L. Amateis. A model to account for potential correlations between growth of loblolly pine and changing ambient carbon dioxide concentrations. Southern Journal of Applied Forestry 27(4): Increasing amounts of atmospheric CO2 is likely leading to enhanced growth rates for loblolly pine. Data from unthinned loblolly pine stands across the Southeast were used to develop an equation that relates changes in ambient CO 2 concentrations to future site index. While the increase in CO 2 was not directly proven to be a cause of increased height growth, increases in CO 2 and increases in site index occurred simultaneously. For a given change in CO 2 concentration, a greater increase in site index occurred on lower quality sites. Although temperature and precipitation could also lead to increased growth, no trend in temperature and precipitation was detected over the study time period. If climate change increases temperatures and decreases precipitation, this could offset some of the increased growth caused by higher levels of CO 2. Winnett, S.M Potential effects of climate change on U.S forests: a review. Climate Research 11: This article reviews the major studies and models that have been used to project changes to U.S. forests from climate change. It mentions studies that find dramatic decline in southern pine forests in response to changes. The article describes how the rapid predicted rates of climate change may require unrealistic migration rates (350 miles/century) for species to stay in their current climatic ranges. However, many species may be limited in range due to competition with other species, and could exist outside their current range. Also, discussions of changes in forest types may mask large increases or decreases of specific species. Increases in CO2 have been found increase rates of growth, but trees may acclimate to higher levels. Increases in CO2 can also cause increases in water use efficiency, which would compensate somewhat from possibly drier conditions in the future. On the other hand, it will lead to higher levels of C in leaves and needles, and insects may have to consume more foliage to get an equal amount of N. Woodbury, P.B., Smith, J.E., Weinsten, D.A. and J.A. Laurence Assessing potential climate change effects on loblolly pine growth: a probabilistic regional modeling approach. Forest Ecology and Management 107: GIS was used to integrate current and predicted climate data with regional data including forest distribution, growth rate and stand characteristics. Four different general circulation models were 6

7 used to create a probabilistic climate change scenario. The model estimated a greater than 50% chance of a decrease in loblolly pine growth throughout most of its range. The model estimated a 10% chance than total basal area growth will decrease, and a 10% chance that it will increase. Change in carbon assimilation was the most influential factor. USGS Effects of climate change on southeastern forests. United States Geological Survey National Wetlands Research Council, Department of the Interior. Scientists from Rice University are analyzing long-term research data in eastern Texas to determine the effects of climate change. Data comes from coastal plain forests, including bottomland hardwoods. Analysis of tree ring growth showed that growth of individual trees is not slower near range boundary, so current species distribution may not be determined by climate. Also, white oaks, black oaks and pines all responded differently to climate changes, which mean their relative importance in the forest will likely change. Many trends in sapling recruitment were related to disturbances, such as flooding and drought. Flooding and hurricane damage both favored non-native species. Increased hurricane damage in the future may favor shrubs and small trees over canopy trees, decreasing carbon storage. Climate variability did produce small changes in tree growth, but did not affect reproduction or mortality. However, larger changes over a longer time period may have a much greater impact. 7