Insect infestations and the persistence and functioning of oak-pine mixedwood forests in the mid-Atlantic region, USA

Abstract

Damage from infestations of Lymantria dispar L. in oak-dominated stands and southern pine beetle (Dendroctonus frontalis Zimmermann) in pine-dominated stands have far exceeded impacts of other disturbances in forests of the mid-Atlantic Coastal Plain over the last two decades. We used forest census data collected in undisturbed and insect-impacted stands combined with eddy covariance measurements made pre- and post-disturbance in oak-, mixed and pine-dominated stands to quantify how these infestations altered forest composition, structure and carbon dynamics in the Pinelands National Reserve of southern New Jersey. In oak-dominated stands, multi-year defoliation during L. dispar infestations resulted in > 40% mortality of oak trees and the release of pine saplings and understory vegetation, while tree mortality was minimal in mixed and pine-dominated stands. In pine-dominated stands, southern pine beetle infestations resulted in > 85% mortality of pine trees but had minimal effect on oaks in upland stands or other hardwoods in lowland stands, and only rarely infested pines in hardwood-dominated stands. Because insect-driven disturbances are both delaying and accelerating succession in stands dominated by a single genus but having less effect in mixed-composition stands, long-term disturbance dynamics are favoring the formation and persistence of uneven age oak-pine mixedwood stands. Changes in forest composition may have little impact on forest productivity and evapotranspiration; although seasonal patterns differ, with highest daily rates of net ecosystem production (NEP) during the growing season occurring in an oak-dominated stand and lowest in a pine-dominated stand, integrated annual rates of NEP are similar among oak-, mixed and pine-dominated stands. Our research documents the formation of mixedwood stands as a consequence of insect infestations in the mid-Atlantic region and suggests that managing for mixedwood stands could reduce damage to forest products and provide greater continuity in ecosystem functioning.

Assessment of spongy moth infestation impacts on forest productivity and carbon loss using the Sentinel-2 satellite remote sensing and eddy covariance flux data

“…Our analysis showed the intense and widespread nature of the 2021 spongy moth infestation in the region where deciduous and mixed stands experienced large-scale defoliation resulting in 35% and 22% decrease in mean daily GPP values as compared to 2020 and 2022, respectively. Our study not only supported the earlier inferences that 2021 infestation was as record disturbance event in North America (Embrey et al 2012 ; CFIA 2021 ; Chung et al 2021 ; Gooderham et al 2021 ; Government of Canada 2021 ; MNRF 2021 ; MNDMNRF 2022 ; TRCA 2022 ; Clark et al 2022 ; Foster et al 2022 ; Coleman and Liebhold 2023 ; Latifovic and Arain 2024 ), but it also provides quantitative assessment of the photosynthetic C uptake reduction across the region due to defoliation (Dymond et al 2010 ; Medvigy et al 2012 ; Kretchun et al 2014 ). These C uptake reduction estimates have significance because in recent years most of the terrestrial C cycle studies in the literature have been reporting an increase in vegetation C uptake due to warmer temperatures, longer growing seasons and CO 2 fertilization effects (Goodale et al 2002 ; Harris et al 2016 ; Birdsey et al 2019 ; Fei et al 2019 ; Ameray et al 2021 ; Quirion et al 2021 ).…”