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<p>Expansion of treeline ecotones and krummholz in alpine ecosystems negatively affects alpine plant diversity at small (quadrat) scales. However, tree encroachment also increases microhabitat variability, which supports diversity at regional scales. Here, we compared variability in surface microclimates across open and krummholz alpine habitats at Cardinal Divide, Alberta, Canada. We used generalized linear mixed effects models to assess the effects of krummholz tree cover, non-vegetated ground cover, and surface temperatures on alpine plant alpha (Shannon’s) diversity and partial Mantel tests to examine the influence of spatial variability in diel surface temperatures and cover on within- and between-plot species turnover (beta diversity). Sites were spaced across the divide to represent terrain features and were at a similar elevation (2000–2150&#xa0;m) with eight pairs of 8 × 8&#xa0;m plots established in adjacent open alpine and krummholz habitats, with each plot having 24 within-plot sample locations. We found a 2.1&#xa0;°C increase (<i>p</i> = 0.003) in within-plot maximum diel surface temperature variation (standard deviation) in krummholz plots (8.7&#xa0;°C) compared with open alpine plots (6.6&#xa0;°C). Interactions between diel surface temperature range and tree cover (non-linear) were associated with decreased alpha diversity in krummholz plots. On average, surface temperature variability was positively correlated to within- and between-plot beta diversity in open and krummholz habitats, with krummholz showing stronger correlations. Similarly, tree cover differences corresponded with increased beta diversity within- and between-plots, indicating that at larger (plot-level) scales, treeline expansion may increase diversity. As krummholz will likely expand, it is important to understand how they alter their environment and microclimates across different scales to better predict changes in biodiversity.</p>

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Diversity in a shrinking alpine world: how does the expansion of krummholz ecotones alter microclimates and alpine plant diversity?

  • 期刊论文

  • 发表日期：

    2026年6月19日

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  • Alexa A. C. MacDonald,
  • Scott E. Nielsen

摘要

Expansion of treeline ecotones and krummholz in alpine ecosystems negatively affects alpine plant diversity at small (quadrat) scales. However, tree encroachment also increases microhabitat variability, which supports diversity at regional scales. Here, we compared variability in surface microclimates across open and krummholz alpine habitats at Cardinal Divide, Alberta, Canada. We used generalized linear mixed effects models to assess the effects of krummholz tree cover, non-vegetated ground cover, and surface temperatures on alpine plant alpha (Shannon’s) diversity and partial Mantel tests to examine the influence of spatial variability in diel surface temperatures and cover on within- and between-plot species turnover (beta diversity). Sites were spaced across the divide to represent terrain features and were at a similar elevation (2000–2150 m) with eight pairs of 8 × 8 m plots established in adjacent open alpine and krummholz habitats, with each plot having 24 within-plot sample locations. We found a 2.1 °C increase (p = 0.003) in within-plot maximum diel surface temperature variation (standard deviation) in krummholz plots (8.7 °C) compared with open alpine plots (6.6 °C). Interactions between diel surface temperature range and tree cover (non-linear) were associated with decreased alpha diversity in krummholz plots. On average, surface temperature variability was positively correlated to within- and between-plot beta diversity in open and krummholz habitats, with krummholz showing stronger correlations. Similarly, tree cover differences corresponded with increased beta diversity within- and between-plots, indicating that at larger (plot-level) scales, treeline expansion may increase diversity. As krummholz will likely expand, it is important to understand how they alter their environment and microclimates across different scales to better predict changes in biodiversity.