IntroductionMounting evidence suggests that geographic ranges of tree species worldwide are shifting under global environmental changes. Little is known, however, about if and how these species’ range shifts may trigger the range shifts of various types of forests. Markowitz’s portfolio theory of investment and its broad application in ecology suggest that the range shift of a forest type could differ substantially from the range shifts of its constituent tree species.MethodsHere, we tested this hypothesis by comparing the range shifts of forest types and the mean of their constituent species between 1970–1999 and 2000–2019 across Alaska, Canada, and the contiguous United States using continent-wide forest inventory data. We first identified forest types in each period using autoencoder neural networks and K-means cluster analysis. For each of the 43 forest types that were identified in both periods, we systematically compared historical range shifts of the forest type and the mean of its constituent tree species based on the geographic centroids of interpolated distribution maps.ResultsWe found that forest types shifted at 86.5 km·decade-1 on average, more than three times as fast as the average of constituent tree species (28.8 km·decade-1). We showed that a predominantly positive covariance of the species range and the change of species relative abundance triggers this marked difference.DiscussionOur findings provide an important scientific basis for adaptive forest management and conservation, which primarily depend on individual species assessment, in mitigating the impacts of rapid forest transformation under climate change.

中文翻译：

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全球变化下基于质心的范围变化中，森林类型超过了树种

简介越来越多的证据表明，全球树种的地理范围正在随着全球环境变化而发生变化。然而，人们对这些物种的分布范围变化是否以及如何引发各种类型森林的分布范围变化知之甚少。马科维茨的投资组合理论及其在生态学中的广泛应用表明，森林类型的范围变化可能与其组成树种的范围变化有很大不同。方法在这里，我们通过比较森林类型的范围变化和平均值来检验这一假设。使用全大陆森林清查数据，对 1970 年至 1999 年和 2000 年至 2019 年阿拉斯加、加拿大和美国本土的组成物种进行了调查。我们首先使用自动编码器神经网络和 K 均值聚类分析来识别每个时期的森林类型。对于这两个时期确定的 43 种森林类型中的每一种，我们根据插值分布图的地理质心系统地比较了森林类型的历史范围变化及其组成树种的平均值。结果我们发现森林类型变化了 86.5公里·十年-1平均而言，是组成树种平均速度（28.8公里·十年）的三倍多-1）。我们表明，物种范围的显着正协方差和物种相对丰度的变化引发了这种显着差异。讨论我们的研究结果为适应性森林管理和保护提供了重要的科学依据，这主要取决于个体物种评估，以减轻气候变化下森林的快速转变。