Global change re-structures alpine plant communities under 15 years of
warming, nitrogen, and snow addition: disentangling density independent
and dependent effects
Global change is altering patterns of community assembly, with net
outcomes dependent on species’ responses to the environment, both
directly and mediated through biotic interactions. Here, we assess
alpine plant community responses in a 15-year factorial nitrogen
addition, warming and snow manipulation experiment. We used a dynamic
competition model to estimate the density-dependent and independent
processes underlying changes in species-group abundances over time.
Density-dependent shifts in competitive interactions drove long-term
changes in abundance of species-groups under global change.
Density-independent processes were important when counteracting
environmental drivers limited the growth response of the dominant
species. Furthermore, competitive interactions shifted with
environmental change, primarily with nitrogen, and drove non-linear
abundance responses across environmental gradients. Our results
highlight that global change can either reshuffle species hierarchies or
further favor already dominant species; predicting which outcome will
occur requires incorporating both density-dependent and independent
mechanisms and how they interact across multiple global change factors.