Integration of FIA data and pest surveys to assess regional tree and forest health

Background/Question/Methods

The impacts of damaging forest pests on growth and mortality of host species have been studied at specific sites, but there have been few attempts to evaluate landscape scale impacts on growth and mortality rates. In this study we integrate two types of pest activity data with regional forest inventory data collected by the US Forest Service's Forest Inventory and Analysis (FIA) program to quantify density of standing dead host trees, growth volume of host species, and mortality volume of host species. For beech bark disease (BBD) and hemlock woolly adelgid (HWA), years of infestation were assigned to FIA plots based on county-level maps of historical spread. For gypsy moth (GM), years of defoliation were assigned to FIA plots by intersecting the plots with 30 years of spatially explicit defoliation records. A secondary objective was to evaluate the utility of a regionally sampled annual forest inventory for quantifying impacts of forest pasts at the landscape scale.

Results/Conclusions

The impacts of the three forest pests on regional levels of standing dead host trees, growth volume of host species, and mortality volume of host species were clear in many cases. A few examples of the quantified results of this study are provided here. Annual net growth rates of American beech decrease as duration of beech scale infestation increases; uninfested counties have a growth rate that is nearly four times higher than counties infested for more than 40 years. Annual eastern hemlock mortality rates increase with duration of HWA infestation; plots in areas infested by HWA for greater than 25 years have a mortality rate that is nearly six times greater than plots in uninfested areas. The number of standing dead oak trees per acre is two to three times higher in areas defoliated by gypsy moth. When combined with pest activity information, the annualized FIA inventory system provides a dataset that can be used to quantify the impact of forest pests across landscapes.