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Resistance of tropical seedlings to drought is mediated by neighbourhood diversity
Michael J. O’Brien, Glen Reynolds, Robert Ong and Andy Hector
Occasional periods of drought are typical of most tropical forests, but climate change is increasing drought frequency and intensity in many areas across the globe, threatening the structure and function of these ecosystems. The effects of intermittent drought on tropical tree communities remain poorly understood and the potential impacts of intensified drought under future climatic conditions are even less well known. The response of forests to altered precipitation will be determined by the tolerances of different species to reduced water availability and the interactions among plants that alleviate or exacerbate the effects of drought. Here, we report the response of experimental monocultures and mixtures of tropical trees to simulated drought, which reveals a fundamental shift in the nature of interactions among species. Weaker competition for water in diverse communities allowed seedlings to maintain growth under drought while more intense competition among conspecifics inhibited growth under the same conditions. These results show that reduced competition for water among species in mixtures mediates community resistance to drought. The delayed onset of competition for water among species in more diverse neighbourhoods during drought has potential implications for the coexistence of species in tropical forests and the resilience of these systems to climate change.
Seedling water stress under rainfall and neighbourhood treatments. Physiological response of seedlings to drought (red) and ever-wet (blue) conditions in mixture, non-sibling and sibling neighbourhoods. Leaf water potentials (95% CI) were significantly lower under drought for non-sibling and sibling neighbourhoods (n = 24 for each neighbourhood × rainfall treatment), but the leaf water potential was statistically indistinguishable between the drought and ever-wet conditions for species mixtures.
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