Spatial Patterns Of Insect Herbivory In The Quercus Variabilis Bl.forest And The Major Driving Factors

It’s still an open problem to realize long-term effective control of the defoliator in forest pest management.Understanding the mechanism of insect herbivory is the premise to solve this problem,which is of great significance to the sustainable development of forestry in China.Although a large number of studies have explored the main drivers of insect herbivory,the results are inconsistent and cannot provide good guidance for forest pest management.Quercus spp.forests are widely distributed in China,which has great economic value and important ecological service function.However,in recent years,large areas of oak forests have been seriously damaged by defoliators,which not only caused tremendous economic losses,but also threatened the functions and services of forest ecosystem.We measured the detailed spatial patterns of insect herbivory on cork oak(Quercus variabilis Bl.)within a forest landscape 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 shrub and herb,physical and chemical characteristics of soil and leaves,stand factors and plant diversity).The main conclusions are as follows:(1)Soil texture and forest stratum had significant effects on insect herbivory.Generally,insect herbivory was spatially heterogeneous within stands.Herbivory was significantly lower in the gravel soil area than that in the loam area and the highest herbivory occurred in the lower stratum.However,there were also 41 individual plots that the highest herbivory occurred in the upper stratum and 29 individual plots that the highest herbivory occurred in the sapling stratum.There was a significant positive correlation between insect herbivory and litter coverage.The holding effect of loam on withered leaves was significantly higher than that of gravel soil may be one of the main reasons that the litter coverage was significantly higher in the loam area than that in the gravel soil area.Since leaf litter is necessary for the overwintering of defoliators,higher litter coverage in the loam area may provide a more suitable microhabitat for overwintering pupae and thus caused higher pupal density in the loam area.Soil textures may have major effects on the spatial patterns of insect herbivory by influencing litter coverage,and higher coverage of shrub and herb can reduce insect herbivory in each forest stratum,especially in the sapling stratum.(2)Insect herbivory was positively correlated with soil moisture content,negatively correlated with soil bulk density and soil sand content,but had non-significant correlations with soil total carbon,total nitrogen,organic carbon,available nitrogen,available phosphorus,and available potassium contents.The horizontal distribution of insect herbivory was relatively consistent with the distribution of physical indexes such as soil bulk density,soil moisture content,and soil sand content.Leaf traits could not explain the horizontal distribution pattern of insect herbivory.The variation of leaf traits among different strata was not consistent with the vertical pattern of insect herbivory.The results do not support that the nutrient status of different soil textures within stands can affect insect herbivory by influencing leaf traits.(3)Insect herbivory was positively correlated with tree height and DBH.The distribution of plant diversity in the shrub layer was mainly affected by soil texture,plant diversity in the loam area was significantly higher than that in the gravel soil area.There was a negative correlation between insect herbivory and shrub layer plant diversity in loam and gravel soil areas respectively.Especially,insect herbivory in the sapling stratum was significantly correlated with plant diversity in the shrub layer.Plant diversity in the shrub layer was significantly affected by canopy structure and light environment,and was negatively correlated with the canopy openness,the direct,diffuse,and total solar radiation under the canopy,and positively correlated with leaf area index(LAI).Under specific circumstances in the study area,plant diversity in the shrub layer could be reduced by increasing canopy openness and increasing understory light.In the process of forest management,the conservation and improvement of shrub layer plant diversity may help to reduce insect herbivory.This study explored detailed spatial patterns of insect herbivory in the Q.variabilis forest,analyzed and discussed the main drivers.This may promote understanding of the interaction between trees and insect herbivores in the natural environment,and also provide some references for further research and forest pest management.