Vegetation changes with climate change in the Grandes Rousses mountain range

Questions: We assessed interactions between climate change, bedrock types and snow cover duration on the trajectories of taxonomic and functional composition of subalpine plant communities. We predict (i) an increase in species richness on siliceous bedrock due to a reduced competition and a decrease in richness on calcareous bedrock due to increasing drought stress, (ii) decreasing snow cover duration should induce a higher shrub encroachment in hollows as compared to ridges (iii) increasing growing season temperature should induce taller sizes and more conservative growth traits, in particular in hollows.

Location: Subalpine belt of the Grandes Rousses mountain range, south western Alps (France).

Methods: 189 vegetation plots were sampled in 1997 and 2017-2018. The duration of snow cover was assessed during two years in 1995-1997 and five functional traits were measured on 108 species in 2021. We performed multivariate analyses, quantified community weighted-means (CWM) of traits and used ANOVAs to detect responses to local-scale factors and changes in snow cover, temperature and precipitation since 1997 according to a nearby meteorological station.

Results: Overall, taxonomic composition weakly changed and changes were more dependent on the position of communities along the snow cover duration gradient than on their bedrock type. The abundance of drought-tolerant species increased at the border of hollows and there was, over all communities, a slight increase in the abundance of dwarf shrubs and tall herbaceous species, a strong decrease in short herbaceous species and, thus, an overall decrease in species richness. There were important overall changes in CWM of size traits, in particular leaf area which increased the most in hollows irrespective of bedrock types.

Conclusion: In this subalpine site the effects of decreasing snow cover duration overwhelmed the effects of bedrocks, which may explain the overall increase in competitive species and decrease in species richness.

Methods
189 vegetation quadrats were done in 1997 and 2018.

We measured plant traits and calculated CWM of traits at the two years of sampling.

### 问题
本研究旨在探究气候变化、基岩（bedrock）类型与积雪持续时长对亚高山植物群落（subalpine plant communities）分类组成与功能组成动态的调控作用。我们提出三项预测：(i) 硅质基岩（siliceous bedrock）生境因竞争缓解将使物种丰富度提升，而钙质基岩（calcareous bedrock）生境因干旱胁迫加剧将导致物种丰富度下降；(ii) 积雪持续时长缩短将促使洼地相较于山脊发生更显著的灌木入侵（shrub encroachment）；(iii) 生长季气温升高将促使植物株高增加及保守型生长性状表达更为突出，尤以洼地生境为甚。

### 研究区域
法国阿尔卑斯山西南部格朗德鲁斯山脉（Grandes Rousses mountain range）亚高山带。

### 研究方法
1997年与2017—2018年共布设189个植被样方进行调查；1995—1997年连续两年开展积雪持续时长监测；2021年针对108种植物测定了5项功能性状。本研究采用多元分析方法量化群落加权平均性状（community weighted-means, CWM），并通过方差分析（ANOVA）探究植物群落对局地尺度环境因子的响应，同时依托附近气象站数据解析1997年以来积雪持续时长、气温与降水的变化趋势。

### 研究结果
整体而言，植物群落的分类组成变化较弱，其变化更多取决于群落沿积雪持续时长梯度的分布位置，而非基岩类型。洼地边缘的耐旱物种相对丰度有所提升；所有群落中，矮灌木与高大草本植物的丰度均小幅上升，而矮小草本植物丰度显著下降，最终导致整体物种丰富度降低。群落大小相关性状的加权平均值发生了显著整体变化，其中叶面积增幅最为明显，且无论基岩类型如何，洼地生境的叶面积提升幅度均为最高。

### 研究结论
在该亚高山研究区域内，积雪持续时长缩短的影响远超基岩类型的作用，这或可解释竞争性物种丰度整体上升与物种丰富度下降的现象。

### 补充研究方法
1997年与2018年共设置189个植被样方；于两次采样年份分别测定植物性状并计算群落加权平均性状（CWM）。