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Evidence indicates that an increase in temperature and greater moisture stress will lead to increases in these kinds of stressors, but research to date has examined only a few species. Invasive species are already a persistent and growing challenge across much of the United States. Changes may exacerbate this problem, as warmer temperatures may allow some invasive plant species, insect pests, and pathogens to expand their ranges farther north. Northern Minnesota may lose some of the protection offered by a traditionally cold climate and short growing season.

Large variation exists for projected changes in precipitation for the Upper Midwest. Although individual model projections may differ, there is general agreement that annual precipitation is expected to increase slightly (2 to 4 inches) during the 21st century. Models also tend to agree that precipitation patterns between seasons may shift substantially. Averages across multiple climate models indicate that winter and spring may experience 20-30% more precipitation by the end of the century, while summer precipitation is projected to decrease by less than 10%.

Evidence at both global and local scales indicates that growing seasons have been getting longer, and this trend is projected to become even more pronounced over the next century. As seasons shift so that spring arrives earlier and fall extends later into the year, phenology may shift for plant species that rely on temperature as a cue for the timing of leaf-out, reproductive maturation, and other developmental processes. Longer growing seasons could also result in greater growth and productivity of trees and other vegetation, but only if balanced by available water and nutrients.

Cold-season soil temperatures are projected to increase between 1.8 and 5.4 °F by the end of the century, and total frost depth is projected to deline by 40 to 80 percent across northern Wisconsin and western Upper Michigan by the end of the century. These conditions could increase water infiltration into the soil and reduce runoff, but they may also lead to greater soil water losses through increased evapotranspiration.

A variety of models project that across the Upper Midwest, more winter precipitation will be delivered as rain, more snow will melt between snowfall events, and the snowpack will not be as deep or consistent. Lake-effect snowfall may increase in the short-term, but these events may convert to rain as temperatures increase.

Soil moisture is expected to change in response to warmer temperatures and seasonal changes in precipitation. Changes are likely to vary seasonally as well as geographically. More intense and prolonged precipitation events would be expected to create wetter soil conditions, while increased temperatures and less frequent rainfall events would lead to drier soils .

Model results project that species currently near their northern range limits in the region may become more abundant and more widespread under a range of climate futures.Results from forest impact models suggest that species such as black cherry, chestnut oak, and yellow-poplar may have increases in both suitable habitat and biomass, and some deciduous forest types have the potential for productivity increases across the assessment area.

Across northern latitudes, warmer temperatures are expected to be more favorable to individuals near the northern extent of their species’ range and less favorable to those near the southern extent.Results from climate impact models project a decline in suitable habitat and landscape-level biomass for northern species such as black spruce, red spruce, tamarack, and paper birch, as well as spruce-fir forest communities. These northern species may persist in the region throughout the 21st century, although with declining vigor.

Many invasive species that currently threaten regional forests may benefit directly from projected climate change or benefit from the relatively slower adaptation response of native species. Increases in carbon dioxide increase growth for many plant species, andcChanges in climate may have allowed some invasive plant species to expand their ranges northward, including bush honeysuckle, privet, and kudzu. Some invasive species are tolerant of drought, fire, flooding, and other disturbances and may be at an even greater advantage under future climate conditions.

A variety of models project that winters will become more mild across New England and northern New York as temperatures increase. Warmer temperatures will cause more winter precipitation to be delivered as rain. Snowfall, snow depth, and snow pack duration are all expected to be reduced.