Invasive insects impact carbon and hydrologic cycles in an Eastern Pine/Oak forest.

Invasive forest insects can impact ecosystem functioning by altering carbon, nutrient and hydrologic cycles.  Although invasive species are now ubiquitous, their effects are difficult to quantify, and recovery times are often unknown.  We used eddy covariance and forest census data to quantify the effects of gypsy moth (Lymantria dispar) defoliation on carbon (C) and hydrologic cycles in the New Jersey Pine Barrens.  Two years of data were used to contrast C and hydrologic fluxes; 2005 with little herbivory and 2006 with nearly complete consumption of canopy and understory oaks and understory shrubs.  Frass and leaf fragments in litterfall during the summer of 2006 totaled 19.6 ± 9.2 g C m^-2, and represented ca. 30 % of deciduous-species litterfall in 2005. Net ecosystem exchange (NEE) of CO₂ was +140 g C m^-2 yr^-1 and -103 g C m^-2 yr^-1, in 2005 and 2006, respectively.  Hydrologic fluxes in evapotranspiration (ET) were less affected; ET was 409 vs. 279 mm during the summer of 2005 and 2006, respectively.  June 2006 showed the greatest reduction in ET rates, with June 2006 totaling only 57% of ET measured in June 2005 (63 vs.110 mm).  Although severe, these were apparently only transient perturbations.  Leaf area of oaks and shrubs had recovered to ca. 70% of values during the previous year by early August, and total litterfall in 2006 was 84% of litterfall amounts in previous years.  NEE and ET fluxes had recovered to those in 2005 by Sept and October 2006.