Background Insect Herbivory in Riparian Poplar Forests: the Role of Local, Landscape, and Regional Factors

Abstract

BackgroundForest management and landscape structure have long been considered as the main drivers of insect herbivory in forest landscapes, but relatively little is known about how ecological factors acting at local, landscape and regional scales shape background insect herbivory under natural conditions. Here, 90 primeval and managed poplar stands were sampled in riparian forests along the rivers in the Eastern part and the Western part of North China. We measured defoliation intensity of insect herbivores within forest stands in transects at near, intermediate and far distance from the rivers. We assessed the effects of region, landscape isolation, forest management, stand position, vegetation cover, and tree size on defoliation intensity. We also explored indirect effects of region and forest management on insect herbivory via changes in stand-level tree size and vegetation cover. ResultsDefoliation intensity increased with landscape-scale forest isolation and decreased with distance from forest stand to the river regardless of stand type. Defoliation intensity was higher in primeval stands than in managed poplar stands, but this difference only significant in the Eastern part of North China. Tree height varied among two regions and between primeval and managed stands. Defoliation intensity was strongly correlated with tree height and vegetation cover. But the effects of region and forest management on defoliation intensity were only partly explained by tree size and vegetation cover. ConclusionsThese results indicate that background insect herbivory can be driven by ecological factors at different scales and offer an insight into the impact of man-made changes along a gradient of landscape isolation in forest ecosystems. Our findings provide a multi-scale perspective to improve potential control strategies and risk assessment of insect damage on riparian forests in real-world situations.