Multi‐trophic bottom‐up effects of plant functional diversity on arthropod communities in a tropical forest restoration experiment

Plant diversity affects both ecosystem functioning and the functional and taxonomic diversity of multiple trophic levels. However, in the literature, it is unclear if this pattern is driven by species richness per se or by the functional diversity or composition (e.g. resource‐use strategy) of the community.

Here, we use a novel Hawaiian lowland restoration experiment where plots were planted with the same number of plant species ( n  = 10), but different functional diversities and different resource‐use strategies. The different plant combinations created a range of trait values with species placed in trait space according to their life history traits under the fast–slow plant economics spectrum. Because resource quality varied for detritivores, we were able to test how litter mixtures influenced litter decomposition rates and ground‐dwelling arthropod taxonomic and functional diversity and abundance at high (predators) and low (detritivores, fungivores) trophic levels.

Using Structural Equation Models, we found that plant functional diversity (measured using functional dispersion and Rao's Q indices) but not resource‐use strategy increased both litter decomposition rates and low trophic level arthropod richness and functional diversity. Arthropod abundance increased arthropod taxonomic richness at the two trophic levels but decreased functional diversity at the low level. Finally, we also found indirect bottom‐up effects of plant functional diversity on arthropod functional diversity at the high trophic level.

Our findings demonstrate that interactions between food webs and plant functional diversity jointly shape biodiversity–productivity relationships, emphasizing the need to adopt a multi‐trophic perspective when studying biodiversity and ecosystem function relationships and designing restoration strategies.