Tewksbury Joshua J, Lloyd John D
USDA Forest Service, Savannah River Institute, PO Box 700, 29809, New Ellenton, SC, USA.
Montana Cooperative Wildlife Research Unit, University of Montana, 59812, Missoula, MT, USA.
Oecologia. 2001 May;127(3):425-434. doi: 10.1007/s004420000614. Epub 2001 May 1.
Positive interactions often play an important role in structuring plant communities and increasing biological diversity. Using three scales of resolution, we examine the importance of a long-lived desert tree, ironwood (Olneya tesota), in structuring plant communities and promoting biological diversity in the Sonoran Desert. We examined the positive effects of Olneya canopies of different sizes on plant communities in mesic and xeric habitats throughout the central Gulf Coast subregion of Sonora, Mexico. In xeric sites, Olneya canopies had strong positive effects on plant richness and abundance, and small positive effects on the size of plants, underscoring the role of facilitation in extreme environments. In mesic sites, Olneya canopies had very little effect on perennials and a negative effect on ephemeral richness, suggesting predominantly competitive effects in this less stressful environment. Overall, Olneya canopies increased biological diversity where abiotic stress was high, but did not increase diversity in more mesic areas. Thus Olneya canopies caused consistent shifts in plant-community structure among xeric and mesic sites, but not when these landscapes were combined. Benefactor size also mediated positive interactions, with larger Olneya canopies supporting larger perennials in both xeric and mesic sites. Thus stress gradients and benefactor size both influenced the balance of facilitative and competitive effects under nurse-plant canopies, and the spatial scale at which facilitative effects shape community structure.
积极的相互作用通常在构建植物群落和增加生物多样性方面发挥重要作用。我们使用三种分辨率尺度，研究了一种长寿沙漠树木铁木（Olneya tesota）在构建索诺兰沙漠植物群落和促进生物多样性方面的重要性。我们研究了墨西哥索诺拉州中部海湾沿岸次区域不同大小的铁木树冠对中生和旱生生境中植物群落的积极影响。在干旱地区，铁木树冠对植物丰富度和丰度有强烈的积极影响，对植物大小有较小的积极影响，突出了促进作用在极端环境中的作用。在中生地区，铁木树冠对多年生植物影响很小，对一年生植物丰富度有负面影响，表明在这种压力较小的环境中主要是竞争作用。总体而言，在非生物胁迫较高的地方，铁木树冠增加了生物多样性，但在更多的中生地区并没有增加多样性。因此，铁木树冠导致了干旱地区和中生地区植物群落结构的一致变化，但当这些景观合并时则没有。受益者大小也介导了积极的相互作用，在干旱和中生地区，较大的铁木树冠支持更大的多年生植物。因此，胁迫梯度和受益者大小都影响了护荫植物树冠下促进作用和竞争作用的平衡，以及促进作用塑造群落结构的空间尺度。
