Understand the mechanisms underlying diversity-productivity relationships (DPRs) is crucial to mitigating the effects of forest biodiversity loss. Tree-tree interactions in diverse communities are fundamental in driving growth rates, potentially shaping the emergent DPRs, yet remains poorly explored. Here, using data from a large-scale forest biodiversity experiment in subtropical China, we demonstrated that changes in individual tree productivity were driven by species-specific pairwise interactions, with higher positive net pairwise interaction effects on trees in more diverse neighbourhoods. The aggregated interaction effects subsequently determined the community DPRs. We further revealed that the positive differences between inter- and intra-specific interactions were the critical determinant for the emergence of positive DPRs. Surprisingly, the condition for positive DPRs corresponded to the condition for coexistence. Our results thus provide a novel insight into how pairwise tree interactions regulate DPRs, with implications for identifying the tree mixtures with maximised productivity to guide forest restoration and reforestation efforts.

Biological invasions have major impacts on a variety of ecosystems and threaten native biodiversity. Earthworms have been absent from northern parts of North America since the last ice age, but non-native earthworms were recently introduced there and are now being spread by human activities. While past work has shown that plant communities in earthworm-invaded areas change towards a lower diversity mainly dominated by grasses, the underlying mechanisms related to changes in the biotic interactions of the plants are not well understood. Here, we used a trait-based approach to study the effect of earthworms on interspecific plant competition and aboveground herbivory. We conducted a microcosm experiment in a growth chamber with a full-factorial design using three plant species native to northern North American deciduous forests, Poa palustris (grass), Symphyotrichum laeve (herb), and Vicia americana (legume), either growing in monoculture or in a mixture of three. These plant community treatments were crossed with earthworm (presence or absence) and herbivore (presence or absence) treatments. Eight out of the eleven above- and belowground plant functional traits studied were significantly affected by earthworms, either by a general effect or in interaction with plant species identity, plant diversity level, and/or herbivore. Earthworms increased the aboveground productivity and the number of inflorescences of the grass P. palustris. Further, earthworms countervailed the increasing effect of herbivores on root tissue density of all species, and earthworms and herbivores individually increased the average root diameter of S. laeve in monoculture, but decreased it in mixture. In this study, earthworm presence gave a competitive advantage to the grass species P. palustris by inducing changes in plant functional traits. Our results suggest that invasive earthworms can alter competitive and multitrophic interactions of plants, shedding light on some of the mechanisms behind invasive earthworm-induced plant community changes in northern North America forests.

The movement of animals affects the biodiversity, ecological processes, and resilience of an ecosystem. For the animals, moving has costs as well as benefits and the use of a given landscape provides insights into animal decisions and behavioral ecology. Understanding how animals use the landscape can thus clarify their effects on ecosystems and inform conservation measures aiming at preserving and restoring the ecological functions of animal dispersal. Here, we investigated the habitat preferences of African savanna elephants (Loxodonta africana) using GPS data from 155 individuals collected between 1998 and 2020 in Northern Kenya. In particular, we assessed how “energy landscapes”, i.e. the cost of locomotion due to the slope of the terrain and the animal body mass, together with elevation, vegetation productivity, water availability, and proximity to human settlements influence the habitat preferences of elephants. We found that the energy landscape is the most consistent predictor of elephants’ preferences, with individuals generally avoiding energetically costly areas and preferring highly productive habitats. We also found that other predictors such as elevation, water availability and human presence, are important in determining habitat usage, but varied greatly among elephants, with some individuals preferring habitats avoided by others. Our analysis highlights the importance of the energy landscape as a key driver of habitat preferences of elephants. Importantly, the enerscape modeling environment allowed us to develop testable hypotheses from rather coarse-grained data covering elephant movements and a few environmental parameters. Energy landscapes rely on fundamental biomechanical and physical principles and provide a mechanistic understanding of the observed preference patterns, allowing to disentangle key causal drivers of an animal’s preferences from correlational effects. This, in turn, has important implications for assessing and planning conservation and restoration measures, such as dispersal corridors, by explicitly accounting for the energy costs of moving.