Different temporal trends in vascular plant and bryophyte communities
along elevational gradients over four decades of warming
Abstract
Despite many studies showing biodiversity responses to warming, the
generality of such responses across taxonomic groups remains unclear.
Very few studies have tested for evidence of bryophyte community
responses to warming, even though bryophytes are major contributors to
diversity and functioning in many ecosystems. Here we report an
empirical study comparing long-term change of bryophyte and vascular
plant communities in two sites with contrasting long-term warming
trends, using “legacy” botanical records as a baseline for comparison
with contemporary resurveys. We hypothesized that ecological changes
would be greater in sites with a stronger warming trend, and that
vascular plant communities, with narrower climatic niches, would be more
sensitive than bryophyte communities to climate warming. For each
taxonomic group in each site, we quantified the magnitude of changes in
species’ distributions along the elevation gradient, species richness,
and community composition. We found contrasted temporal changes in
bryophyte vs. vascular plant communities, which only partially supported
the warming hypothesis. In the area with a stronger warming trend, we
found a significant increase of local diversity and beta-diversity for
vascular plants, but not for bryophytes. Presence absence data did not
provide sufficient power to detect elevational shifts in species
distributions. The patterns observed for bryophytes are in accordance
with recent literature showing that local diversity can remain unchanged
despite strong changes in composition. Regardless of whether one taxon
is systematically more or less sensitive to environmental change than
another, our results suggest that vascular plants cannot be used as a
surrogate for bryophytes in terms of predicting the nature and magnitude
of responses to warming. Thus, to assess overall biodiversity responses
to global change, abundance data from different taxonomic groups and
different community properties need to be synthesized.