- Changing temperature and precipitation will force many forest ecosystems northward, but many tree species will be unable to migrate fast enough to keep up with the pace of climate change.
- Climate change will amplify existing stressors to natural and urban forests.
- Climate change impacts on forests will impair the ability of many forested watersheds to produce reliable supplies of clean water and other forest products.
- Climate change will alter cultural and recreational connections to forest ecosystems.
Northward Migration of Forest Regimes
As temperatures rise and precipitation patterns change, regions once suitable for traditional forest types will shift northward. Boreal forest types will likely lose their advantage in areas where they currently dominate the landscape. Instead, woodlands, savannahs, grasslands, and deciduous forests will likely occupy a greater area. The currently dominant and culturally-significant maple-beech-birch forest type of the Great Lakes region is projected to be almost entirely displaced, outcompeted by forest types typically found farther south.1 2
Plant Hardiness Zones
In one visible example, USDA Plant Hardiness Zones, which provide an accessible estimation of planting and growing recommendations for trees and other plantlife, were updated in 2006. As extreme cold temperatures have become less of a risk in many areas, the optimal regime for many plant species has moved north, and growing recommendations have moved with them. Much of the Great Lakes region is now in a different Plant Hardiness Zone than prior to 2006.
Forest Migration Rates and Climate Change
Many forest species will be unable to migrate fast enough to keep up with the pace of warming, as has already been seen during periods of past, natural climate change.3 4 It's improbable that many, if not most, tree species in the Eastern U.S. will be able to colonize habitat beyond their existing ranges over the next 100 years.5 While many northern tree species may be able to migrate northward at a rate of up to 100 km per century, suitable habitat for tree species in the Midwest will shift as much as 400-600 km by 2100, suggesting that natural migration rates will be too slow to keep up with climate change.6 7 Loss of habitat and the fragmenting of forests due to agricultural use and development inhibit tree migration, making the actual movement of tree species substantially slower than the projected shifts in optimum latitudes based on temperature and precipitation.
Amplification of Existing Stressors
Forest ecosystems throughout the Great Lakes region are already exposed to a wide range of natural and human-associated stresses aside from a changing climate. Invasive species, pests, diseases, land-use change, forest fragmentation, and atmospheric pollution are some examples.
Land use conversion is the most pervasive human-caused change to forests in the region. Agricultural expansion has drastically reduced forest cover from pre-European settlement to the present. Forest cover in Ohio has been reduced from 95% to 30.2% and Illinois has gone from 40% forest cover to 13%.8 9 As forest ecosystems of the Midwest have been severely altered or removed entirely, natural habitats have become lost and fragemented. These existing stressors from land use pose major obstacles that will make it extremely difficult or impossible for tree species to now migrate to new, suitable habitats quickly enough to keep up with the rapid pace of climate change.10 11 Additionally, human-caused impacts, such as the preferential selection of species, have reduced forest ecosytem diversity, making them inherently more susceptible to disease, rapid ecosystem change, and stress.12
The regime and severity of many forest vulnerabilities has been changing an may change more rapidly in the future. Impacts once confined to southern parts of the region or constrained by limited extreme heat, for example, will begin to encroach on areas where these vulnerabilities are currently limited or nonexistent. The increasing risk of damage due to severe weather during wet periods, increased risk of drought during dry periods, and the spread of pests northward into the region are primary concerns.
Impacts to Urban Forests
Urban forests provide many benefits to their nearby areas. They decrease heating and cooling demands for neighboring buildings, are stormwater mitigation assets, improve recreational opportunities, and support overall public well-being.13 14 15
As with natural forests, climate change is expected to amplify existing stressors to urban forests.16 Exposure to pests and diseases, more frequent heat waves and drought, increased atmospheric pollution, heat island effects, salt damage, and variable water supplies are all existing vulnerabilities that may be affected.
Impacts to Cultural, Recreational, and Commercial Connections with Forests
Particular tree species hold unique cultural importance, and in many cases, climate change will affect the distribtution and abundance of these species. For example, white cedar and paper birch have particular significance for defining a culture and way of life for Native American tribes throughout the region.17 The suitable habitat for both species is expected to experience large declines over the next century.5
Culturally significant forest products are critical to regional industries that rely on the harvest and sale of these goods. Balsam fir bough collection and their use in Christmas wreaths generates $23 million per year in northern Minnesota and $50 million in from those collected on federal and state land in Wisconsin. 18 19 From 1992 to 2010, the maple syrup industry produced an average of $2.4 million in Ohio, $2.6 million in Michigan, and $2.9 million in Wisconsin. 20 Collection of these forest products may be influenced by future changes in climate if focal species experience declines or life-cycle alterations.
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- 8. Illinios Department of Natural Resources, 2010: Illinois Statewide Forest Resource Assessments and Strategies, 47 pp.
- 9. Ohio Department of Natural Resources, 2010: Ohio Statewide Forest Resource Assessment, 188 pp.
- 10. Swaty, R., K. Blankenship, S. Hagen, J. Fargione, J. Smith, and J. Patton, 2011: Accounting for Ecosystem Alteration Doubles Estimates of Conservation Risk in the Conterminous United States. PLoS ONE, 6, 10.
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- 12. Nowacki, G. J., and M. D. Abrams, 2008: The demise of fire and "Mesophication" of forests in the eastern United States. Bioscience, 58, 123-138.
- 13. McPherson, E. G., D. Nowak, G. Heisler, S. Grimmond, C. Souch, R. Grant, and R. Rowntree, 1997: Quantifying urban forest structure, function, and value: the Chicago Urban Forest Climate Project. Urban ecosystems, 1, 49-61.
- 14. Nowak, D. J., and D. E. Crane, 2002: Carbon storage and sequestration by urban trees in the USA. Environmental Pollution, 116, 381-389.
- 15. Younger, M., H. R. Morrow-Almeida, S. M. Vindigni, and A. L. Dannenberg, 2008: The Built Environment, Climate Change, and Health: Opportunities for Co-Benefits. American Journal of Preventive Medicine, 35, 517-526.
- 16. Roloff, A., S. Korn, and S. Gillner, 2009: The Climate-Species-Matrix to select tree species for urban habitats considering climate change. Urban Forestry & Urban Greening, 8, 295-308.
- 17. Dickmann, D. I., and L. A. Leefers, 2003: The forests of Michigan. University of Michigan Press, 297 pp.
- 18. Minnesota Department of Natural Resources, 2010: Minnesota Forest Resource Assessment, 153 pp.
- 19. Wisconsin Department of Natural Resources, 2010: Wisconsin’s Statewide Forest Assessment 2010. Accessed online at:
- 20. USDA Economic Research Service, Sugar and Sweeteners: Recommended Data. Available at http://www.ers.usda.gov/Briefing/Sugar/Data.htm. Accessed January 24, 2012.