Forest composition drives bryophyte biomass, carbon and nitrogen storage in the boreal-temperate ecotone

Aims: Climate change and forest management have profoundly altered forest
ecosystem dynamics, with impacts on canopy composition and understory
vegetation. Forest type affects bryophyte ecosystem processes,
particularly related to carbon (C) and nitrogen (N) cycling. Within the
boreal-temperate ecotone, the Wabanaki-Acadian Forest harbors a diverse
canopy composition with many species at their distributional limit, making
it sensitive to climate change and human alterations, with unknown impacts
on bryophytes and their functions. We aimed to quantify how canopy
composition and moisture affect forest-floor bryophyte biomass, and C and
N stocks. Location: We sampled in 49 stands representing six forest types
of the Wabanaki-Acadian Forest of New Brunswick (Canada): mesic and wet
coniferous, mesic and wet deciduous, mixed, and cedar forests. Methods:
First, we developed an allometric model to predict bryophyte bulk density.
We then estimated bryophyte biomass and C and N contents for five
functional groups at each site using the ground-layer indicator method and
measured forest and soil characteristics at each site (e.g., forest
composition, soil pH, moisture class). Linear models, multivariate,
similarity percentages, and indicator species analyses were used for data
analysis. Results: The highest bryophyte biomass and C and N stocks was
found in conifer-dominated forests, especially where Sphagnum was
abundant, whereas it was low in mixed and deciduous forests which also had
a different functional composition. There was a strong negative non-linear
relationship between bryophyte biomass and broadleaf litter. Conclusions:
We provide the first reports of bryophyte biomass and C and N stocks in
the Wabanaki-Acadian Forest, which were consistent with its latitudinal
location at the southern edge of the boreal forest. Our findings highlight
the connections between forest composition and bryophytes in the Acadian
Forest and reveal the participation of forest-floor bryophytes in C and
nutrient cycling.