Spatial patterns of species and plant traits in response to 20 years of grazing exclusion in subalpine grassland communities
Spatial patterns of species and plant traits in response to 20 years of grazing exclusion in subalpine grassland communities
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DOI：
10.1111/j.1654-1103.2011.01277.x
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发表时间：
2011-06-01
影响因子：
2.8
通讯作者：
Alard, Didier
中科院分区：
文献类型：
--
作者：
Deleglise, Claire;Loucougaray, Gregory;Alard, Didier
问题长期放牧是否影响亚高山草原群落的冠层高度、植物种类和性状的空间格局？放牧排斥对物种和性状的空间格局是否也有类似的影响？物种空间格局的变化是否与物种丰富度的变化有关？位置法国阿尔卑斯山的亚巴拉松草原、维克斯山和欧桑山。方法在3个不同生产力的物种丰富的群落中，对9对放牧和非放牧的10m×10m样地进行植被空间采样和植物性状测量。我们通过Moran‘s I测量空间依赖的程度(或斑块大小)和强度来估计样地内冠层高度、物种和聚集特征值的空间格局。物种斑块大小和空间依赖强度的丰度加权平均值是在每个样地的所有物种和每个生活型的物种之间计算的。结果空间格局对放牧排斥的响应仅在斑块大小中被检测到，而空间依赖的强度不受影响。空间格局的变化依赖于群落，因为基于冠层高度和物种斑块大小的空间特征只有在生产力较低的群落中才会在放牧限制后增加。出乎意料的是，物种空间格局的变化并不支持特征值空间格局的变化。放牧排斥对几种生活型的丰度和斑块大小有显著影响。结论在物种丰富的群落中，放牧改变物种的空间分布(即斑块大小)，而不是改变种内聚集(即空间依赖的强度)。结果揭示了物种空间重组的可能机制，这些机制独立于丰度变化。因此，在评估放牧管理的影响时，除了考虑植被特征平均值的变化外，还应考虑空间格局的变化。
QuestionDoes long-term grazing exclusion affect spatial patterns of canopy height, plant species and traits in subalpine grassland communities? Are spatial patterns of species and traits similarly affected by grazing exclusion? Are changes in spatial patterns of species associated with changes in species abundances?LocationSubalpine grasslands, Vercors and Oisans Mountains, Alps (France).MethodsSpatial sampling of vegetation and measurements of plant traits were carried out within nine pairs of grazed and ungrazed 10 m x 10-m plots in three species-rich communities with different productivities. We estimated within-plot spatial patterns of canopy height, species and aggregated trait values by measuring the extent (or patch size) and intensity of spatial dependence with Moran's I. Abundance-weighted averages for species patch size and intensity of spatial dependence were calculated across all species per plot and across species per life form. Such measures derived from analysis of spatial dependence were considered spatial traits.ResultsResponse of spatial patterns to grazing exclusion was only detected in patch size, whereas intensity of spatial dependence was not affected. Changes in spatial patterns were community-dependent because spatial traits based on patch size of canopy height and species increased following grazing exclusion only in the less productive community. Unexpectedly, changes in spatial patterns of species did not support changes in spatial patterns of trait values. Abundances and patch sizes of several life forms were significantly affected by grazing exclusion. However, at the scale investigated, changes in abundance of life forms did not correspond to changes in their spatial patterns and vice versa.ConclusionIn species-rich communities, grazing alters spatial spread of species (i.e. patch size) rather than intra-specific aggregation (i.e. intensity of spatial dependence). Results revealed possible mechanisms of species spatial reorganisation that are independent of abundance variation. Therefore, it is important to consider changes in spatial patterns in addition to changes in mean values of vegetation features when assessing impacts of grazing management.