From facilitation to competition: temperature‐driven shift in dominant plant interactions affects population dynamics in seminatural grasslands

Abstract

Biotic interactions are often ignored in assessments of climate change impacts. However, climate-related changes in species interactions, often mediated through increased dominance of certain species or functional groups, may have important implications for how species respond to climate warming and altered precipitation patterns. We examined how a dominant plant functional group affected the population dynamics of four co-occurring forb species by experimentally removing graminoids in seminatural grasslands. Specifically, we explored how the interaction between dominants and subordinates varied with climate by replicating the removal experiment across a climate grid consisting of 12 field sites spanning broad-scale temperature and precipitation gradients in southern Norway. Biotic interactions affected population growth rates of all study species, and the net outcome of interactions between dominants and subordinates switched from facilitation to competition with increasing temperature along the temperature gradient. The impacts of competitive interactions on subordinates in the warmer sites could primarily be attributed to reduced plant survival. Whereas the response to dominant removal varied with temperature, there was no overall effect of precipitation on the balance between competition and facilitation. Our findings suggest that global warming may increase the relative importance of competitive interactions in seminatural grasslands across a wide range of precipitation levels, thereby favouring highly competitive dominant species over subordinate species. As a result, seminatural grasslands may become increasingly dependent on disturbance (i.e. traditional management such as grazing and mowing) to maintain viable populations of subordinate species and thereby biodiversity under future climates. Our study highlights the importance of population-level studies replicated under different climatic conditions for understanding the underlying mechanisms of climate change impacts on plants.

Key challenges and priorities for modelling European grasslands under climate change

“…In permanent swards with multiple species a range of factors including epigenetic and plastic change and genetic change through natural selection and species sorting, shape grassland responses to the environment. Inter-specific interactions may affect responses to climate change, including changes in biomass production, sward composition and species diversity (Miranda-Apodaca et al, 2015;Olsen et al, 2016). Improved modelling of these types of grassland depends on the advancement of ecological knowledge, and progress in related topics including multi-species, nutritive value and soil and water modelling (challenges 1, 2, 10).…”

Biotic interaction effects on seedling recruitment along bioclimatic gradients: testing the stress‐gradient hypothesis

“…; Olsen et al. ). To understand effects of climate change on ecosystem processes and diversity we therefore need to understand the complex interplay between biotic interactions and different aspects of climate.…”

“…; Olsen et al. ). The novel aspect of our study is that we examine how biotic interactions affect the seedling recruitment stage of plants inhabiting upland grasslands and how the nature of these interactions shifts along two different and interacting climatic stress gradients: temperature and precipitation.…”

“…Higher temperatures and precipitation may increase productivity and thereby increase the role of competitive relative to facilitative biotic interactions (Olsen et al. ). In this study, we use a grid of sites spanning regional‐scale temperature and precipitation gradients in boreal and alpine grasslands in the fjord landscape of southern Norway (Klanderud et al.…”

Reintroducing Environmental Change Drivers in Biodiversity–Ecosystem Functioning Research

“…In our model, the effects of species interactions on a focal species are only altered through changes in the density of species with which it interacts. This assumption has been shown to prevail in some systems [66], but not in others [67, 68]. Arguably the best-known example of environmental effects on per-capita interactions is the ‘stress gradient hypothesis’, where there is a shift from competitive (i.e.…”