Abstract
BackgroundInsect herbivory has profound impacts on ecosystem processes and services. Although many efforts have been made to recognize the main drivers of insect herbivory at different scales, the results are inconsistent. One likely reason is that studies have insufficiently captured the spatially heterogeneous factors such as soil type and forest stratum within the stand that may significantly affect insect herbivory. In particular, there is a lack of studies that address the detailed spatial patterns of insect herbivory which are influenced by these factors.MethodsWe measured the detailed spatial patterns of insect herbivory on cork oak (Quercus variabilis Bl.) in response to soil type (gravel soil and loam) and forest stratum (the upper, lower, and sapling stratum), and correlated these patterns with a set of influencing factors (litter coverage, coverage of shrubs and herbs, soil nutrients, soil moisture, and leaf traits) in a forest landscape.ResultsGenerally, insect herbivory was spatially heterogeneous within stands. Herbivory was significantly lower in gravel soil areas than in loam soil areas and the highest herbivory occurred in the lower stratum. However, there were also 41 individual plots in which the highest herbivory occurred in the upper stratum and 29 plots in which the highest herbivory occurred in the sapling stratum. There were significant differences in soil nutrient and water status between soil types, but no significant differences in leaf traits. The effects of forest stratum on leaf traits were also inconsistent with those on insect herbivory.ConclusionsLeaf traits may not be the main factors influencing insect herbivory in the field. Soil type may have major effects on herbivory patterns by influencing litter coverage while higher coverage of shrubs and herbs may reduce herbivory in the sapling stratum. These findings may advance our understanding of tree-herbivore interactions in real-world situations and have important implications for the sustainable management of forest ecosystems.
Highlights
To further investigate whether the spatial patterns of insect herbivory correlate with soil conditions and leaf traits, we examined soil moisture content and available N, P, and K across 186 plots and randomly selected 6 plots in loam and gravel soil areas respectively to examine the leaf traits including specific leaf area (SLA), tannin content, soluble sugar content, C content, N content in three strata
In contrast to the general spatial patterns across 186 plots, herbivory in some individual plots in gravel soil areas was higher than that in loam areas and there were 41 individual plots that the highest herbivory existed in the upper stratum and 29 individual plots that the highest herbivory existed in the sapling stratum
Soil type and litter coverage were significantly correlated with insect herbivory in three strata
Summary
There has been a growing interest in recognizing the key drivers of insect herbivory (e.g. Rossetti et al 2017; Castagneyrol et al 2019; Valdés-Correcher et al 2019). The results of these studies are inconsistent and a recent meta-analysis based on 89 individual studies demonstrated that habitat fragmentation had no significant effects on insect herbivory (Rossetti et al 2017). Tree diversity has been recognized as an important driver of insect herbivory in forest ecosystems. Many efforts have been made to recognize the main drivers of insect herbivory at different scales, the results are inconsistent. One likely reason is that studies have insufficiently captured the spatially heterogeneous factors such as soil type and forest stratum within the stand that may significantly affect insect herbivory.
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