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Positive interactions among alpine plants increase with stress


Plants can have positive effects on each other1. For example, the accumulation of nutrients, provision of shade, amelioration of disturbance, or protection from herbivores by some species can enhance the performance of neighbouring species. Thus the notion that the distributions and abundances of plant species are independent of other species may be inadequate as a theoretical underpinning for understanding species coexistence and diversity2. But there have been no large-scale experiments designed to examine the generality of positive interactions in plant communities and their importance relative to competition. Here we show that the biomass, growth and reproduction of alpine plant species are higher when other plants are nearby. In an experiment conducted in subalpine and alpine plant communities with 115 species in 11 different mountain ranges, we find that competition generally, but not exclusively, dominates interactions at lower elevations where conditions are less physically stressful. In contrast, at high elevations where abiotic stress is high the interactions among plants are predominantly positive. Furthermore, across all high and low sites positive interactions are more important at sites with low temperatures in the early summer, but competition prevails at warmer sites.

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Figure 1: Relative neighbour effect (RNE) at the 11 experimental sites.
Figure 2: Proportion of surviving target species in controls and neighbour removal treatments at high and low elevation experimental sites for all 11 locations combined.
Figure 3: Proportion of flowering or fruiting target species in controls and neighbour removal treatments at high and low elevation experimental sites for all 11 locations combined.
Figure 4: The relationship between relative neighbour effect (RNE) and the estimated maximum temperature in early summer (June in the Northern Hemisphere and December in the Southern Hemisphere) at each of the 22 experimental sites.


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We thank the National Center for Ecological Synthesis and Analysis, The National Geographic Society, the Civilian Research and Development Foundation, and the Andrew W. Mellon Foundation for financial support.

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Correspondence to Ragan M. Callaway.

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Callaway, R., Brooker, R., Choler, P. et al. Positive interactions among alpine plants increase with stress. Nature 417, 844–848 (2002).

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