Insect herbivory is one of the most important ecological processes to affect plant-soil feedbacks and overall forest ecosystem health. Forest based free-air CO2 enrichment (FACE) experiments were established to help understand forest ecosystem responses to a future atmosphere with CO2 enrichment. One potentially critical process which remains understudied in FACE experiments is the impacts of eCO2 on herbivory and the consequences for herbivore-mediated ecosystem processes. In this study we assess how elevated carbon dioxide (eCO2) impacts (i) leaf level insect herbivory and (ii) the stand-level herbivore-mediated transfer of carbon (C) and nitrogen (N) from the canopy to the ground in a natural mature oak temperate forest community in central England (BIFoR FACE). Recently abscised leaves were collected every two weeks in through the growing season August to December from 2017-2019, with identification of four dominant species Quercus robur (Pedunculate Oak), Acer pseudoplatanus (Sycamore), Cratae-gus monogyna (Common Hawthorn) and Corylus avellana (Hazel). Selected leaves were scanned and visually analyzed to quantify leaf area loss from folivory monthly. Additionally, the herbivore-mediated transfer of C and N fluxes from the dominant tree species Q. robur was calculated from these leaf-level folivory estimates and other tree properties.
Results/Conclusions
This study finds that leaf-level herbivory at BIFoR FACE has not changed significantly across the first 3 years of eCO2 treatment when assessed across all dominant tree species, although we detected significant changes under the eCO2 treatment for individual tree species and years. Despite the lack of any strong leaf-level herbivory response, stand-level foliar C and N transferred to the ground via herbivory was substantially higher under eCO2 mainly because there was a ~50% increase in foliar production of Q. robur. This result cautions against concluding much from either the presence or absence of leaf-level herbivory responses to any environmental effect because their actual ecosystem effects are filtered through so many (usually unmeasured) factors.
