Long-term effect of forest harvesting on boreal species assemblages under climate change

Logging is the main human disturbance impacting biodiversity in forest
ecosystems. However, the impact of forest harvesting on biodiversity is
modulated by abiotic conditions through complex relationships that remain
poorly documented. Therefore, the interplay between forest management and
climate change can no longer be ignored. Our aim was to study the expected
long-term variations in the assemblage of bird and beetle communities
following modifications in forest management under different climate
change scenarios. We developed species distribution models to predict the
occurrence of 88 species of birds and beetles in eastern Canadian boreal
forests over the next century. We simulated three climate scenarios
(baseline, RCP4.5 and RCP8.5) under which we varied the level of
harvesting.   We also analyzed the regional assemblage
dissimilarity by decomposing it into balanced variations in species
occupancy and occupancy gradient. We predict that forest harvesting will
alter the diversity by increasing assemblage dissimilarity under all the
studied climate scenarios, mainly due to species turnover. Species
turnover intensity was greater for ground-dwelling beetles, probably
because they have lower dispersal capacity than flying beetles or birds. A
good dispersal capacity allows species to travel more easily between
ecosystems across the landscape when they search for suitable habitats
after a disturbance. Regionally, an overall increase in the probability of
occupancy is projected for bird species, whereas a decrease is predicted
for beetles, a variation that could reflect differences in ecological
traits between taxa. Our results further predict a decrease in the number
of species that increase their occupancy after harvest under the most
severe climatic scenario for both taxa.  We anticipate that under
severe climate change, increasing forest disturbance will be detrimental
to beetles associated with old forests but also with young forests after
disturbances.