Urban Forest Health

Potential changes in precipitation patterns and groundwater infiltration could alter hydrologic regimes. Tamarack and many of the dominant tree species are projected to decline, although red maple may be more adaptable. However, tamarack is a pioneer species and has the ability to regenerate rapidly when conditions are favorable, and the community may persist in more northern sites or in climate refugia. It will likely fare less well in southern locations and in isolated stands in fragmented landscapes with limited connectivity to other natural communities.

Changes in surface water hydrology are likely, with a projected increase in both droughts as well as the frequency and intensity of floods, along with associated sedimentation and nutrient enrichment. Changes to groundwater regimes are possible as well, although both an increase in groundwater recharge as well as decreases in ground water levels are possible. For both surface and groundwater-driven sites, increased nutrient enrichment is likely and could fuel an expansion of invasive species.

All global climate models agree that there will be changes in precipitation patterns across the assessment area, but there is large variability among projections of future precipitation. Most climate models project increases in total annual preciptation, with most of the precipitation occurring in winter and spring. Projections of summer and fall precipitation vary more widely, with many models projecting decreased precipitation or only very slight increases (<15%).

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 shrub-carr is generally adapted to short-term water level fluctuations, high water over the long-term could convert some sites to the marsh.

Increasing temperatures may lead to more water loss through evaporation, altering delicate hydrologic balances. However, with similar to slightly increased precipitation and higher groundwater recharge projected, hydrologic changes may be minimal. If water levels do rise or drop over time, sites with floating "bog" mats may be able to fluctuate naturally. Nutrient enrichment through changing land use and groundwater pollution may be one of the greatest threats and could increase non-native invasive species. However, several factors may reduce vulnerability.