Early positive effects of tree species richness on herbivory in a large‐scale forest biodiversity experiment influence tree growth

Abstract

Despite the importance of herbivory for the structure and functioning of species-rich forests, little is known about how herbivory is affected by tree species richness, and more specifically by random vs. non-random species loss. We assessed herbivore damage and its effects on tree growth in the early stage of a large-scale forest biodiversity experiment in subtropical China that features random and non-random extinction scenarios of tree mixtures numbering between one and 24 species. In contrast to random species loss, the non-random extinction scenarios were based on the tree species’ local rarity and specific leaf area – traits that may strongly influence the way herbivory is affected by plant species richness. Herbivory increased with tree species richness across all scenarios and was unaffected by the different species compositions in the random and non-random extinction scenarios. Whereas tree growth rates were positively related to herbivory on plots with smaller trees, growth rates significantly declined with increasing herbivory on plots with larger trees. Our results suggest that the effects of herbivory on growth rates increase from monocultures to the most species-rich plant communities and that negative effects with increasing tree species richness become more pronounced with time as trees grow larger. Synthesis. Our results indicate that key trophic interactions can be quick to become established in forest plantations (i.e. already 2.5 years after tree planting). Stronger herbivory effects on tree growth with increasing tree species richness suggest a potentially important role of herbivory in regulating ecosystem functions and the structural development of species-rich forests from the very start of secondary forest succession. The lack of significant differences between the extinction scenarios, however, contrasts with findings from natural forests of higher successional age, where rarity had negative effects on herbivory. This indicates that the effects of non-random species loss could change with forest succession.

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

“…However, the positive relationship between herbivore and pathogen damage in our study became weaker with increasing tree species richness (at least the potential effects of pathogens on herbivore damage). This can be explained by the opposite effects of tree richness on herbivory and pathogen damage (see also Hantsch et al., 2014; Schuldt et al., 2010, 2015). Herbivore assemblages in our study system are dominated by generalists (Zhang et al., 2017), which can benefit from the diversity of resources available in more diverse tree communities (Lefcheck, Whalen, Davenport, Stone, & Duffy, 2013; Zhang et al., 2017).…”

“…Our data are based on leaf damage and tree growth surveys on more than 10,000 individual trees in a subtropical tree diversity experiment (Bruelheide et al., 2014), which covers gradients in tree species richness from monocultures to mixtures containing as many as 24 different species. A previous analysis provided insight into the initial effects of tree species richness on herbivory and tree growth relationships shortly after tree planting (Schuldt et al., 2015) but did not consider pathogen damage and its interaction with herbivory. Our study provides new and comprehensive data from a later developmental stage, where the planted trees have grown much larger and started to interact and form a closed canopy.…”

The Impact of Tree Diversity on Different Aspects of Insect Herbivory along a Global Temperature Gradient - A Meta-Analysis

“…In search for factors that underlie the documented biogeographic gradient, we ask for more research on how associational effects depend on and follow global gradients in i) regional species diversity of herbivores and host plants, ii) herbivore density and pressure, especially during times of outbreaks [25, 28–30, 52–56], iii) herbivore specialization [4, 5, 8, 9, 20, 57], iv) tree defences [25, 27, 29, 31, 52, 58] and v) abiotic factors affecting tree or herbivore development (e.g. precipitation, climate stability, CO 2 -concentration, UVB-radiation).…”

“…Insect herbivory is controlled by top-down mechanisms involving natural enemies of herbivores [2], bottom-up mechanisms including tree defences [3] and associational effects provided by tree diversity [4, 5]. So-called associational effects occur if herbivory on individual trees is influenced by the identity and density of neighbouring trees [6] and are assumed to be key regulators of herbivory [6, 7].…”

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

“…AR describes the lower risk of a given plant being infested when surrounded by heterospecific neighbours (Jactel and Brockerhoff 2007;Barbosa et al 2009). Although the opposite pattern-associational susceptibility (AS)-can also be observed (White and Whitham 2000;Schuldt et al 2015), AR seems a more common phenomenon in forest ecosystems (Jactel and Brockerhoff 2007;Castagneyrol et al 2014a; but see Kambach et al 2016). AR has been described mainly for native pest species but it can be hypothesized that similar mechanisms are involved for invasive pests (Jactel et al 2006;Guyot et al 2015).…”