Fig. 2: Conceptual diagram illustrating how mean annual temperature may affect the interplay between species pools and different environmental filters during the establishment of plant communities after fire.

Previous observation in the current study’s plots found microbial communities to rapidly reassemble within the first year after fire, shifting fungal proportions to nutrient-mobilizing bacterial decomposers over increasing mean annual temperature (MAT)¹⁷. In order for primary production to outpace enhancement of decomposition in a warming climate, boreal forests need to either increase regrowth rates of previously occupant vegetation or transition to more warmth-adapted plant species. In the case of plant community turnover, novel species must pass through multiple environmental filters in order to contribute to forest biomass accumulation. It was hypothesized that shifts away from ericoid and ectomycorrhizal inhibition of plant diversity and nutrient cycling, under burning and increasing MAT, would allow for stronger postfire establishment of more temperate vegetation structure, such as greater proportions of broadleaf trees in regrowth on the forest floor. Despite the relaxing of these bio-nutrient-associated filters at higher MAT, a combination of poor soil substrate quality (thick organic layers) and dispersal limitation (here unmeasured) was expected to continue to inhibit overall species richness of plant community assembly. These complex interactions were anticipated to emerge more simply as a biodiversity constraint on the ability of plant communities to utilize increasing MAT to acquire biomass across the 49 sampled plots. A potential consequence of these limitations is a mobilization of carbon and nutrient (N, downward arrows: leaching, upwards: biotic immobilization) away from the ecosystem at rates faster than their reaccumulation, potentially establishing plant priority effects that determine longer term trajectories of forest recovery and associated carbon storage capacity.