Data and code from: Loss of resource-conservative species affects plant phylogenetic and functional structure under long-term snow addition

Climate change and human activities are increasingly influencing
ecological communities. Within this context, increasing extreme snow
events and persistent livestock grazing are known to pose significant
challenges to alpine ecosystems on the Tibetan Plateau. However, the
mechanisms driving long-term community assembly and structural changes
under these concurrent pressures remain unclear. Here, we used a 16-year
field experiment in a Tibetan alpine grassland to investigate the effects
of spring snow addition and yak grazing on taxonomic, phylogenetic, and
functional community diversity and structure. We found that snow addition
was the primary driver of community structure, while the effects of
grazing were less pronounced. Specifically, snow addition shifted the
phylogenetic structure from being random to overdispersed. This shift was
driven by the selective loss of species with conservative resource-use
strategies (i.e., those with high leaf dry matter content and low specific
leaf area), which were phylogenetically more closely related to the
residents than were the gained species. In contrast, communities remained
functionally clustered under all treatments. This resulted from opposing
structural shifts in individual traits, where leaf dry matter content
became more overdispersed, while plant height and leaf nitrogen content
(LNC) became more clustered, driven by the loss of taller species and the
gain of species with low LNC. This decoupling between phylogenetic and
functional responses suggests that environmental filtering selects for
convergent functional adaptations among phylogenetically distant species.
Our findings highlight the importance of considering multi-faceted
diversity metrics when exploring community assembly, and provide the first
experimental evidence that long-term snow addition reshapes plant
phylogenetic community structure on the Tibetan Plateau. Importantly, the
loss of conservative species suggests that altered snow regimes may
potentially shift key ecosystem functions in alpine grasslands. Our
findings also demonstrate that integrating species gain and loss is
essential for a predictive understanding of long-term community dynamics
under global change.