Forest [FAR1]

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.

Under a high emissions scenario, researchers forecast more insect pest damage in northern forests due to increased metabolic activity in active periods and increased winter survival. Drought-stressed trees are also typically more vulnerable to insect pests and diseases.

White pine can tolerate a wide range of soil and moisture conditions. This species may do well with a moderate amount of future warming, but models indicate that white pine will fare worse under hotter, drier climate scenarios. Under the most extreme temperature increases, warming in the assessment area may exceed the physiological limits of white pine. Although white pine is not projected to have increased habitat suitability or productivity, its wide ecological amplitude may enhance its ability to persist across a range of sites.

White pine can thrive with periodic surface wildfires. Conditions that promote wildfires are generally projected to become more common in northern Wisconsin and Michigan by the end of the century. Increases in periodic fire may be beneficial by reducing ladder fuels and competition, although substantially more frequent or severe fire may favor red or jack pine forests.

White pine forests are relatively drought tolerant and may tolerate some degree of greater precipitation variability under climate change. This forest system is present across a wide range of soils and landforms, and some sites may be more affected by altered soil moisture regimes than others. Moisture stress could favor red pine, jack pine, or northern pin oak on already marginal sites.

These are boreal species near their southern range limits in Wisconsin and Michigan. Multiple forest impact models tend to agree that these species are more likely to decline in suitable habitat and biomass across a range of climate scenarios by the end of the century. Several species in this system are limited by high growing-season temperatures, so projected warming in the assessment area may exceed the physiological limits of this forest system.

Low species diversity gives these forests few alternatives if conditions shift beyond tolerable limits, and low genetic diversity is a concern for red pine in particular.

Under a high emissions scenario, researchers forecast more insect pest damage in northern forests due to increased metabolic activity in active periods and increased winter survival. Drought-stressed or overstocked stands are also typically more vulnerable to insect pests and diseases. The possibility exists for new pests such as western bark beetles to arrive in northern Wisconsin or western Upper Michigan.