Effects of plant functional group removal on caterpillars (Gynaephora alpherakii) performance and plant production in an alpine meadow

Loss of plant functional group diversity has significant repercussions for ecosystem productivity globally. However, our understanding of how this loss of specific functional groups, particularly those providing non-food resources, influences herbivores and, consequently, ecosystem productivity remains limited. To elucidate these, we conducted a series of experiments consisting of (1) a two-factor field experiment, where we manipulated the forb abundance and caterpillar presence to assess their interactive effects on plant productivity and caterpillar performance, (2) a field complementary shelter addition experiment, designed to isolate and evaluate the effects of microclimatic changes resulting from forb removal, and (3) a confirmatory microcosm experiment to validate the field findings under controlled by monitoring the herbivory patterns. Our results show that forb removal significantly decreased the aboveground plant biomass (APB) by 41.3%, but did not affect the APB of sedges. The presence of caterpillars significantly decreased total APB by 16.7% and APB of sedges by 34.8%, but these effects disappeared with forbs removed. Specifically, forb removal significantly increased caterpillar mortality rates by 319% and decreased caterpillar body size by 27.2%, which in turn diminished the herbivory pressure on sedges. Changes in caterpillar performance were correlated with maximum and average soil surface temperatures influenced by forb removal and the addition of shelters. Further investigation by the confirmatory microcosm experiment indicated that the absence of forbs decreased the feeding time of caterpillars and deprived caterpillars of refuge from the midday heat and intense sunlight, ultimately resulting in lower body size and higher larval mortality. Our findings suggest that forb removal disrupts trophic interactions, with potential cascading effects on herbivore populations, plant community structure, and ecosystem productivity. These results underscore the importance of plant functional diversity in maintaining ecosystem stability, especially under changing environmental conditions.