Influence of climate, soil and land cover on plant species distribution in the European Alps

Although the importance of edaphic factors and habitat structure for plant
growth and survival is known, both are often neglected in favor of
climatic drivers when investigating the spatial patterns of plant species
and diversity. Yet, especially in mountain ecosystems with complex
topography, missing edaphic and habitat components may be detrimental for
a sound understanding of biodiversity distribution. Here, we compare the
relative importance of climate, soil and land cover variables when
predicting the distributions of 2’616 vascular plant species in the
European Alps, representing approximately two thirds of all European
Flora. Using presence-only data, we built point-process models (PPMs) to
relate species observations to different combinations of covariates. We
evaluated the PPMs through block cross-validations, and assessed the
independent contributions of climate, soil and land cover covariates to
predict plant species distributions using an innovative predictive
partitioning approach. We found climate to be the most influential driver
of spatial patterns in plant species with a relative influence of ~58.5%
across all species, with decreasing importance from low to high
elevations. Soil (~20.1%) and land cover (~21.4%), overall, were less
influential than climate, but increased in importance along the elevation
gradient. Furthermore, land cover showed strong local effects in lowlands,
while the contribution of soil stabilized at mid-elevations. The
decreasing influence of climate with elevation is explained by increasing
endemism, and the fact that climate becomes more homogeneous as habitat
diversity declines at higher altitudes. In contrast, soil predictors were
found to follow the opposite trend. Additionally, at low elevations,
human-mediated land cover effects appear to reduce the importance of
climate predictors. We conclude that soil and land cover are, like
climate, principal drivers of plant species distribution in the European
Alps. While disentangling their effects remains a challenge, future
studies can benefit markedly by including soil and land cover effects when
predicting species distributions.