Understanding long‐term changes in ecological communities during global change is a priority for 21st‐century ecology. Deserts, already at climatic extremes, are of unique interest because they are projected to be ecosystems most responsive to global change. Within a 500‐km² landscape in the Mojave Desert, USA, we measured perennial plant communities at 100 sites three times (1979, 2008, and 2016) during 37 yr to evaluate six hypotheses of community change. These hypotheses encompassed shifts in community measures (e.g., diversity, cover) and species elevational distributions, biotic homogenization, disproportionately large change at the highest elevations, relationships between turnover and species’ responses to disturbance and drought, and that environmental refugia (e.g., moist topographic positions) would receive species during climatic warming and drying. Most community measures changed temporally, such as species density (species/600 m²) increasing 23% and plant cover doubling between 1979 and 2016. There was no increase in nonnative species and minimal evidence for biotic homogenization. High‐elevation communities did not display greater change than low‐elevation communities. Moreover, environmental refugia factored little in species shifts. While species distributional changes were unrelated to affinity for disturbance, the six most persistent species (persisting on >80% of sites) were long‐lived shrubs not associated with disturbance. Overall, seemingly paradoxically, climatic warming and drying was associated with increasing plant abundance. Comparing the 1970s to 2007–2016, precipitation in the study area declined 16% from 17 to 14 cm/yr and average daily minimum temperature rose 13% (1.2°C). The current climate with fewer freezes, together with reduced grazing, could be among the most optimal for desert perennials in the past century, although potential response lags to continuing warming and drying are uncertain. This study of long‐term elevational shifts in communities during global change is among few in deserts, and the average upward elevational shift of 6 m/decade for species in our study is within the range reported for temperate biomes. However, the 41% of species moving downslope is unusually high. We propose that dynamics within desert perennial communities follow a core‐transient species model where a site's species are either highly persistent or transient in approximately equal proportions.

中文翻译：

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37年土地利用和气候变化期间荒漠植物群落的持久性和周转率

了解全球变化过程中生态群落的长期变化是21世纪生态学的优先事项。已经处于极端气候的沙漠引起了人们的独特兴趣，因为预计它们将成为对全球变化最敏感的生态系统。500公里以内²在美国莫哈韦沙漠的自然景观中，我们在37年中三次（1979年，2008年和2016年）对100个站点的多年生植物群落进行了测量，以评估群落变化的六个假设。这些假设包括社区措施（例如多样性，覆盖率）和物种海拔分布的变化，生物同质化，最高海拔处的变化不成比例，营业额与物种对干扰和干旱的反应之间的关系以及环境避难所（例如潮湿）地形位置）将在气候变暖和干燥期间接收物种。大多数社区措施随时间发生变化，例如物种密度（物种/ 600 m ²），在1979年至2016年之间增长了23％，植物覆盖率翻了一番。非本地物种没有增加，生物同质化的证据也很少。高海拔社区没有比低海拔社区显示更大的变化。此外，环境避难所几乎没有影响物种转移。尽管物种分布的变化与干扰的亲和力无关，但六个最持久的物种（在> 80％的位点上生存）是与干扰无关的长寿命灌木。总体上看似矛盾的是，气候变暖和干燥与植物丰度增加有关。与1970年代与2007–2016年相比，研究区域的降水量从17厘米/年降低到16厘米/年，降幅为16％，日平均最低气温升高了13％（1.2摄氏度）。当前气候下的冰冻较少，放牧减少，尽管不确定对持续变暖和干燥的潜在反应滞后，但在过去一个世纪中，对多年生荒漠来说，这可能是最理想的选择。这项关于全球变化期间社区长期海拔变化的研究在沙漠中为数不多，而且我们研究中物种的平均向上海拔变化6 m / decade在所报告的温带生物群落范围内。但是，有41％的物种向下坡移动异常高。我们建议，沙漠多年生群落内部的动态遵循核心瞬态物种模型，在该模型中，某个地点的物种要么是高度持久的，要么是以近似相等的比例过渡的。这项关于全球变化期间社区长期海拔变化的研究在沙漠中为数不多，而且我们研究中物种的平均向上海拔变化6 m / decade在所报告的温带生物群落范围内。但是，有41％的物种向下坡移动异常高。我们建议，沙漠多年生群落内部的动态遵循核心瞬态物种模型，在该模型中，某个地点的物种要么是高度持久的，要么是以近似相等的比例过渡的。这项关于全球变化期间社区长期海拔变化的研究在沙漠中为数不多，我们研究中物种的平均向上海拔变化6 m / decade在所报告的温带生物群落范围内。但是，有41％的物种向下坡移动异常高。我们建议，沙漠多年生群落内部的动态遵循核心瞬态物种模型，在该模型中，某个地点的物种要么是高度持久的，要么是以近似相等的比例过渡的。