• Changing temperature and precipitation will force many forest ecosystems to shift 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

Forest regimes of several forest types for past (1960-1990) and projected (2070-2100) changes. Figure provided by the United States Global Change Research Program (USGCRP, 2009).

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 plant life, was updated in 2012. 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.

The 2012 Plant Hardiness Zone map which is the standard used by growers to know the type of plants that can thrive in a location. Figure provided by the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS).

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 It’s improbable that many, if not most, tree species in the Eastern U.S. will be able to move to habitats beyond their existing ranges over the next 100 years. 4 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. 5 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.

Effects of a Changing Climate

The many effects of climate change will have a pervasive effect on forests in the Great Lakes region over the next few decades. 6 While forest productivity has benefited from higher atmospheric carbon dioxide concentrations and longer growing seasons, increased frequency of drought stress due to changing precipitation patterns will lead to increased tree mortality, mitigating this effect. 7 Increased mortality of younger trees is projected as they are more sensitive to heat and drought related stress. 8 Warming winters will reduce snowpack that insulates soil from freezing temperatures, increasing frost damage to shallow tree roots and reducing tree regeneration. 9 10

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%. 11 As forest ecosystems of the Midwest have been severely altered or removed entirely, natural habitats have become lost and fragmented. 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. 12 13 Changing climate conditions will likely lead to the expansion of invasive plant species and insect pests. Detrimental effects of insect pests and tree pathogens are expected to intensify as increasing winter survival of pests due to warming winters will allow them to expand into new regions. 14 15 Additionally, human-caused impacts, such as the preferential selection of species, have reduced forest ecosystem diversity, making them inherently more susceptible to disease, rapid ecosystem change, and stress. 16 

The regime and severity of many forest vulnerabilities have been changing and 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. 

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. 17 18 19

As with natural forests, climate change is expected to amplify existing stressors to urban forests. 20 Exposure to pests and diseases, more frequent heatwaves 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 distribution and abundance of these species. For example, white cedar and paper birch have particular significance for defining culture and way of life for Native American tribes throughout the region. 21

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 generate $23 million per year in northern Minnesota and $50 million in from those collected on federal and state land in Wisconsin. 22 23 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. 24 The collection of these forest products may be influenced by future changes in climate if focal species experience declines or life-cycle alterations.

Projected shifts in forest composition in the central hardwood region (southern Missouri, Illinois, Indiana, and Ohio) are expected to reduce the economic value of timber in the region by up to $788 billion by the year 2100 (based on a high emissions scenario). 25

Adaptation and Management Practices

As forestry professionals take note of the risks of climate change, climate adaptation methods are increasingly being incorporated into land and resource management practices. For example, over 150 organizations participating in the Climate Change Response Framework have worked toward implementing climate adaptation methods in the region’s forests. 26 Management actions can include activities that enhance species diversity in existing forests or increase the prevalence of species that are best suited for future climatic conditions. 27


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