Urban Forest Health

Potentially lower groundwater levels from increasing evaporation combined with groundwater withdrawals could reduce groundwater upwelling. However, some models suggest that hydrologic changes may be minimal with similar to slightly increased precipitation and higher groundwater recharge projected. In addition, sites fed by deep aquifers are expected to experience less hydrologic change. Nutrient enrichment through changing land use or groundwater pollution may be one of the greatest threats and could increase non-native invasive species.

Potential changes in precipitation patterns and groundwater infiltration could alter hydrologic regimes, though both floating mats and sites with abundant Sphagnum may buffer some of these potential future changes. Glossy buckthorn and non-native cat-tail are also major concerns and will benefit from projected increases in nutrient loading of groundwater and surface water as well as longer growing seasons. Tamarack, the major tree species of Bog Relict, is projected to decline, although as a pioneer species, it has the ability to regenerate rapidly when conditions are favorable.

More frequent large rain events could increase sedimentation and soil disturbance, leading to increases in non-native invasive species. Nutrient loading of both groundwater and surface water could also fuel invasives. Potential changes in precipitation patterns and groundwater infiltration could alter hydrologic regimes. Although Alder Thicket is generally adapted to short-term water level fluctuations, higher water levels over the long-term could convert some sites to marsh.

With a few exceptions, many dominant non-forested wetland plants also occur well in southerly locations, indicating they may be less sensitive to changes in temperature than to changes in the delicate balance in hydrologic regimes and nutrients. Those species that may be most vulnerable tend to be associated with communities that occur at the southern edge of their range, such as Boreal Rich Fen, Shore Fen, and, in the southern part of the state, Bog Relict and Alder Thicket.

Non-native invasive species are already a problem in many wetland communities. Longer growing seasons disproportionally benefit invasives like reed canary grass, which can continue growing longer in the fall than native grasses and sedges. In addition, sedimentation and excess nutrients favor species like non-native cattail and Phragmites. Elevated levels of atmospheric CO2 may favor woody species, including invasive shrubs like glossy buckthorn.

Altered hydrology is the greatest anticipated impact on non-forested wetlands due to climate change. The likelihood of more extreme precipitation events increases the risk of erosion and sedimentation as well as nutrient runoff, which can fuel the transportation and growth of non-native invasive plants and weedy native species. The impact of these events is likely to be greatest lower in the watershed, where floodwaters collect for a longer period of time.

Multiple factors may contribute to increasing drought risk across the Midwest. Trends of higher temperatures, longer growing seasons, and more multi-day periods without rainfall may have compounding effects. Additionally, vapor pressure deficit (the difference between how much moisture is in the air and the amount of moisture the air can hold at saturation) is projected to increase by 20-80% by the end of the century across a range of climate scenarios. This will lead to a net drying effect as the air draws more moisture out of plants and soil.