Simulated impacts of insect defoliation on forest carbon dynamics

Abstract

Many temperate and boreal forests are subject to insect epidemics. In the eastern US, over 41 million meters squared of tree basal area are thought to be at risk of gypsy moth defoliation. However, the decadal-to-century scale implications of defoliation events for ecosystem carbon dynamics are not well understood. In this study, the effects of defoliation intensity, periodicity and spatial pattern on the carbon cycle are investigated in a set of idealized model simulations.A mechanistic terrestrial biosphere model, ecosystem demography model 2, is driven with observations from a xeric oak-pine forest located in the New Jersey Pine Barrens. Simulations indicate that net ecosystem productivity (equal to photosynthesis minus respiration) decreases linearly with increasing defoliation intensity. However, because of interactions between defoliation and drought effects, aboveground biomass exhibits a nonlinear decrease with increasing defoliation intensity. The ecosystem responds strongly with both reduced productivity and biomass loss when defoliation periodicity varies from 5 to 15 yr, but exhibits a relatively weak response when defoliation periodicity varies from 15 to 60 yr. Simulations of spatially heterogeneous defoliation resulted in markedly smaller carbon stocks than simulations with spatially homogeneous defoliation. These results show that gypsy moth defoliation has a large effect on oak-pine forest biomass dynamics, functioning and its capacity to act as a carbon sink.

Decadal-Scale Reduction in Forest Net Ecosystem Production Following Insect Defoliation Contrasts with Short-Term Impacts of Prescribed Fires

“…GEP returned to pre-disturbance values soon after each disturbance, corresponding to the rapid recovery of leaf area at each stand [11,17,21,54,56]. Following the cessation of herbivory or other disturbances that damage foliage early in the growing season (including experimental defoliation), canopy and understory oak species typically produce a second flush of leaves driven by the reallocation of nonstructural stored carbon (NSC) [36,37,54,55].…”

“…Similarly, predicting the impact of invasive insects on long-term forest C dynamics using process-based simulation models has been only partially successful. Although process-based models have accurately captured the effects of gypsy moth defoliation on tree biomass, stand species composition, and the dynamics of GEP and ANPP, they have generally underestimated the long-term reduction in NEP in forests of the PNR following disturbance [9][10][11]. For example, the Ecosystem Demography 2 Model parameterized for xeric hardwoods and conifers and to represent defoliation events and tree mortality at oak-dominated stands in the PNR over 200-year simulations indicated that defoliation intensity was linearly related to decreases in annual NEP, but also predicted that post-disturbance NEP exceeded 80 to 90 g C m −2 year −1 at all levels of defoliation [11].…”

“…In the mid-Atlantic region, estimates of net primary production (NPP) and net ecosystem production (NEP) for intermediate-age forests are highest for oak-hickory forests and lowest for pine-dominated forests [8][9][10]. Overall NEP has been projected to decline slowly as forests age across the region [1, 9,11,12], with productivity declining more slowly for hardwood-dominated forests than conifer-dominated forests [5,9,10]. These intermediate-age forests now experience disturbance regimes dominated by wind and ice storms, insect damage, and managed wildland fire that differ in temporal and spatial scales and intensity compared to past stand-replacing disturbance such as intensive timber management or large wildfires [6,[13][14][15][16].…”

Implementation of a Marauding Insect Module (MIM, version 1.0) in the Integrated BIosphere Simulator (IBIS, version 2.6b4) dynamic vegetation–land surface model

“…Many previous studies have represented insect damage in DVLSMs or less comprehensive climate-driven terrestrial models (Randerson et al, 1996;Krinner et al, 2005;Seidl et al, 2008;Wolf et al, 2008;Albani et al, 2010;Schäfer et al, 2010;Edburg et al, 2011;Medvigy et al, 2012;Mikkelson et al, 2013b;Chen et al, 2015). To our knowledge, however, our study is the first to assess, over daily to centennial timescales, the impacts from insect damage on vegetation dynamics and the carbon, energy, and water cycles in an integrated way (see Sect.…”

“…The effects of prescribed mortality due to mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) outbreaks in western US on coupled carbon-nitrogen dynamics (Edburg et al, 2011) and water and energy exchanges (Mikkelson et al, 2013b) have been studied in the Community Land Model (CLM) DVLSM. Medvigy et al (2012) used the Ecosystem Demography version 2 (ED2) DVLSM to simulate the impacts of defoliation by the gypsy moth (Lymantria dispar Linnaeus) on vegetation coexistence and carbon dynamics in the eastern US. Background herbivory or insect outbreaks have also been simulated in DGVMs and other climate-driven terrestrial models (Randerson et al, 1996;Seidl et al, 2008;Wolf et al, 2008;Albani et al, 2010;Schäfer et al, 2010;Chen et al, 2015) less comprehensive than DVLSMs.…”