Urban Forest Health

"Many invasive species that currently threaten forests in the Central Appalachians region may benefit directly from projected climate change or benefit from the slow response of native species. Increases in carbon dioxide have been shown to have positive effects on growth for many plant species, including some of the most invasive weeds in the U.S. Experiments with CO2 fertilization on kudzu seedlings have indicated increased growth, increased competition with native species, and range expansion.

An analysis of fire probability across the globe found the majority of models projected an increase in wildfire probability by the end of the century. This agreement is particularly high for temperate coniferous forests and temperate broadleaf and mixed forests, where fire probability models were most sensitive to mean temperature of the warmest month.

Given that warmer temperatures and seasonal changes in precipitation are expected across the region, it is reasonable to expect that soil moisture regimes will also shift. Longer growing seasons and warmer temperatures would generally be expected to result in greater evapotranspiration losses and lower soil-water availability later in the growing season, thereby increasing moisture stress on forests. Further, increases in extreme rain events suggest that greater amounts of precipitation may occur during fewer precipitation events, resulting in longer periods between rainfall.

In general, warming temperatures may lead to a decrease in the overall frequency of ice storms and snowstorms due to a reduction in the number of days that are cold enough for those events to occur. However, there is research to suggest that snowfall in lake-effect areas may increase over the short term if the necessary conditions are present: reduced ice cover on the Great Lakes must result in increased evaporation from the open water, and winter temperatures must remain cold enough for the movement of increased moisture over the land surface to generate snow.

Under the higher scenario (RCP8.5) the number of extreme events is projected to increase by two to three times the historical average in every region by the end of the 21st century, with the largest increases in the Northeast. Under the lower scenario (RCP4.5), these events are projected to increase by 50%–100%. Research shows that there is strong evidence, both from the observed record and modeling studies, that increased water vapor resulting from higher temperatures is the primary cause of the increases.

All global climate models agree that there will be changes in precipitation patterns across the Central Appalachians, but there is large variability among projections of future precipitation. Most climate models project increases in annual preciptation. Seasonally, winter and spring are also generally projected to have increases in precipitation during the next century. Projections of summer and fall precipitation vary more widely, with many models projecting decreased precipitation or only very slight increases (<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.

A variety of models project that an increasing amount of winter precipitation will be delivered as rain, more snow will melt between snowfall events, and the snowpack will not be as deep or consistent. In areas near Lake Erie, projected increases in air temperatures are expected to drive decreases in ice cover duration and extent on the Great Lakes, potentially allowing increased winter evaporation and the potential for increased lake-effect snow.

Temperatures in the Central Appalachians region (and across the broader Northeast) are projected to increase on average by 5.27 to 9.11 °F by the end of the century (2070 to 2099), with the greatest warming expected to occur during summer and fall. More warming (9.11 °F) is projected under a high climate scenario (RCP 8.5) and more moderate warming (5.27 °F) is projected under a moderate climate scenario (RCP 4.5). Studies from across the Midwest and Northeast consistently project 20 to 30 more hot days per year by the end of the century.

Model results suggest an increase in suitable habitat for many species at or near the northern extent of their current range, including shortleaf pine, post oak, and blackjack oak. In addition, habitat may become favorable to species not currently found in the assessment area, such as loblolly pine. However, habitat fragmentation and the limited dispersal ability of seeds are expected to hinder the northward movement of the more southerly species despite the increase in habitat suitability. Most species can be expected to migrate more slowly than their habitats will shift.