Effects of global change on bird and beetle populations in boreal forest landscape: an assemblage dissimilarity analysis

Aim  Despite an increasing number of studies highlighting the
impacts of climate change on boreal species,  the main factors
that will drive changes in species assemblages remain ambiguous. 
We study how species community composition would change following
anthropogenic and natural disturbances. We determine the main drivers of
assemblage dissimilarity for bird and beetle communities. Location
Côte-Nord, Québec, Canada. Methods We quantify two climate-induced
pathways based on direct and indirect effects on species occurrence under
different harvest management scenarios. The direct climate effects
illustrate the impact of climate variables while the indirect effects are
reflected through habitat-based climate change. We develop empirical
models to predict the distribution of more than 100 species over the next
century. We analyze the regional and the latitudinal species assemblage
dissimilarity by decomposing it into 'balanced variation in species
occupancy and occurrence' and 'occupancy and occurrence
gradient'.   Results Both pathways increased
dissimilarity in species assemblage.   At the regional
scale, both effects have an impact on decreasing the number of winning
species. Yet, responses are much larger in magnitude under mixed climate
effects (a mixture of direct and indirect effects). Regional assemblage
dissimilarity reached 0.77 and 0.69 under mixed effects versus 
0.09 and 0.10 under indirect effects for beetles and birds, respectively,
between RCP8.5 and baseline climate scenarios when considering harvesting.
Latitudinally, assemblage dissimilarity increased following the climate
conditions pattern.  Main conclusions The two pathways are
complementary and alter biodiversity, mainly caused by species turnover.
Yet, responses are much larger in magnitude under mixed climate effects.
Therefore, the inclusion of climatic variables considers aspects other
than just those related to forest landscapes, such as life cycles of
animal species. Moreover, we expect differences in occupancy between the
two studied taxa. This could indicate the potential range of change in
boreal species concerning novel environmental conditions.