USDA Forest Service, Northern Research Station, Silas Little Experimental Forest, New Lisbon, New Jersey, United States of America.
Environmental Studies, Bates College, Lewiston, Maine, United States of America.
PLoS One. 2022 May 4;17(5):e0265955. doi: 10.1371/journal.pone.0265955. eCollection 2022.
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.
在过去的二十年中，舞毒蛾对栎属林分和南部松甲虫（Dendroctonus frontalis Zimmermann）对松属林分的侵害造成的破坏远远超过了其他干扰因素对大西洋中部沿海平原森林的影响。我们使用未受干扰和受昆虫影响的林分的森林普查数据，结合栎属、混合和松属林分中干扰前后的涡度协方差测量，来量化这些侵害如何改变了新泽西州南部皮恩兰兹国家保留地的森林组成、结构和碳动态。在栎属林分中，舞毒蛾多年的取食导致栎属树木死亡率超过 40%，并释放了松树苗和林下植被，而在混合和松属林分中，树木死亡率最小。在松属林分中，南部松甲虫的侵害导致松树死亡率超过 85%，但对丘陵地带的硬木或低地的其他硬木有最小的影响，而在硬木林分中，只有很少的松树受到侵害。由于昆虫驱动的干扰既延迟又加速了以单一属为主的林分的演替，但对混合林分的影响较小，因此，长期的干扰动态有利于形成和维持不均匀年龄的栎-松混交林。森林组成的变化可能对森林生产力和蒸散作用影响不大；尽管季节模式不同，栎属林分的净生态系统生产力（NEP）日最高值出现在生长季，而松属林分的最低值出现在生长季，但栎属、混合和松属林分的综合年 NEP 率相似。我们的研究记录了昆虫侵害在大西洋中部地区形成混交林的情况，并表明管理混交林可以减少对森林产品的破坏，并为生态系统功能提供更大的连续性。
