The abundant‐center hypothesis posits species are most abundant in the center of their climatic range and forms a key assumption in many species distribution models. However, this hypothesis has not been rigorously evaluated in plant communities, in part because abundance as a fraction of dominance is rarely incorporated. Here, we ask whether tree species frequency and abundance peak in the center of their distributions on continental‐scale climate gradients across the Rocky Mountains and Interior West, USA. We used forest inventory data to model frequency (percentage of plots in a given climate a species occurred in) and relative abundance (percentage of basal area in plots) as a flexible function of climate for the 20 most common tree species on temperature and precipitation gradients. Frequency patterns were predominately “bell‐shaped” and centered for species in the middle of both gradients and monotonic toward the extremes. Relative abundance patterns were primarily monotonic, especially with precipitation. In the middle of the temperature gradient, however, it is notable that six dominant and widespread species had peaks in both frequency and abundance that were centered and symmetric. Only one species had this pattern with precipitation. When frequency is considered, evidence for the abundant‐center hypothesis is robust, especially in the middle portion of each gradient, and indicates patch occupancy probability generally declines away from a species' climatic optimum. For relative abundance, the hypothesis is largely refuted, particularly on the precipitation gradient. Together, these results suggest that climate's influence on patch colonization and occupancy dynamics is a fundamental filter on distribution patterns in Rocky Mountain forests, but that climate gradients are only weakly related to relative abundance and hence provide limited insight into the ecological processes that determine local dominance once a species is present in a site.

中文翻译：

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气候梯度上树木物种分布的中心出现频率峰值，而不是相对丰度

丰富中心假说假设物种在其气候范围的中心位置最丰富，并构成许多物种分布模型中的关键假设。但是，尚未在植物群落中对这一假设进行严格的评估，部分原因是很少将丰度作为优势的一部分。在这里，我们询问在落基山脉和美国内陆西部的大陆尺度气候梯度上，树种的频率和丰度是否在其分布的中心达到峰值。我们使用森林资源清册数据对频率（降水发生梯度）的频率（相对于物种发生在给定气候条件下的耕地百分比）和相对丰度（耕地基础面积的百分比）进行建模，以作为气候的弹性函数。 。频率模式主要是“钟形”的，并且以物种居中为中心，处于两个梯度的中间，并且向极端单调。相对丰度模式主要是单调的，尤其是在降水情况下。然而，在温度梯度的中间，值得注意的是，六个优势和广泛分布的物种在频率和丰度上都具有集中且对称的峰值。只有一种物种具有这种降水模式。当考虑频率时，丰富中心假说的证据是有力的，尤其是在每个梯度的中部，并且表明斑块占用概率通常会从物种的气候最优值开始下降。对于相对丰度，该假设在很大程度上被驳斥，特别是在降水梯度上。总之，这些结果表明气候“