Herbivore and pathogen effects on tree growth are additive, but mediated by tree diversity and plant traits

Abstract

Herbivores and fungal pathogens are key drivers of plant community composition and functioning. The effects of herbivores and pathogens are mediated by the diversity and functional characteristics of their host plants. However, the combined effects of herbivory and pathogen damage, and their consequences for plant performance, have not yet been addressed in the context of biodiversity–ecosystem functioning research. We analyzed the relationships between herbivory, fungal pathogen damage and their effects on tree growth in a large‐scale forest‐biodiversity experiment. Moreover, we tested whether variation in leaf trait and climatic niche characteristics among tree species influenced these relationships. We found significant positive effects of herbivory on pathogen damage, and vice versa. These effects were attenuated by tree species richness—because herbivory increased and pathogen damage decreased with increasing richness—and were most pronounced for species with soft leaves and narrow climatic niches. However, herbivory and pathogens had contrasting, independent effects on tree growth, with pathogens decreasing and herbivory increasing growth. The positive herbivory effects indicate that trees might be able to (over‐)compensate for local damage at the level of the whole tree. Nevertheless, we found a dependence of these effects on richness, leaf traits and climatic niche characteristics of the tree species. This could mean that the ability for compensation is influenced by both biodiversity loss and tree species identity—including effects of larger‐scale climatic adaptations that have been rarely considered in this context. Our results suggest that herbivory and pathogens have additive but contrasting effects on tree growth. Considering effects of both herbivory and pathogens may thus help to better understand the net effects of damage on tree performance in communities differing in diversity. Moreover, our study shows how species richness and species characteristics (leaf traits and climatic niches) can modify tree growth responses to leaf damage under real‐world conditions.

Neighbour species richness and local structural variability modulate aboveground allocation patterns and crown morphology of individual trees

“…We are aware that we could not account for physiological responses, diversity‐mediated effects of herbivory and pathogens, or belowground interactions which have been shown to be additional important factors for tree growth (Ishii & Asano ; Bu et al ; Schuldt et al ). Variation in topography and soil conditions may also effect tree growth but those factors were found to be of weak explanatory power in the BEF‐China experiment (Kröber et al ; Fichtner et al ).…”

Plant neighbour identity and invasive pathogen infection affect associational resistance to an invasive gall wasp

“…Infection of a host tree by fungal pathogens is thus an important but often neglected factor that can drive associational resistance. For instance, Schuldt et al (2017) reported a positive relationship between damage of foliar herbivores and pathogens, which resulted in additive negative effects on tree growth. However tree species richness lead to AS to insects but AR to pathogens, with an overall reduced impact of both damaging agents combined on tree growth.…”

Individual tree traits shape insect and disease damage on oak in a climate‐matching tree diversity experiment

“…Moreover, tree diversity effects on pathogens have been less frequently investigated than for insect pests (Hantsch et al, 2014;Jactel & Brockerhoff, 2007;Pearse & Hipp, 2009). Even fewer studies have considered diversity effects on both pests and pathogens together, despite the potential for multitrophic interactions which could impact upon associational effects (Schuldt et al, 2017). For instance, initial damage to a plant by insect herbivores or pathogens can have both a reciprocal and antagonistic effect on subsequent plant attackers, via cross-talk between plant defense signaling pathways that are induced following attack (Moreira, Abdala-Roberts, & Castagneyrol, 2018).…”