Pyrodiversity of boreal lake islands begets biodiversity of beetles, plants, and birds

Global fire regimes are changing, raising concerns about the ability of
fire-prone ecosystems to maintain biodiversity. We tested whether the
pyrodiversity-biodiversity hypothesis (i.e., variation in post-fire
characteristics promotes biodiversity) or alternative hypotheses better
explain patterns of biodiversity in a true island system. Using fixed-area
sampling plots in a chronosequence of 42 boreal lake islands spanning
gradients in island area (1-350.4 ha), isolation (0.1-7.9 km from
mainland), and fire history (1-231+ year since fire), we tested whether
alpha and beta diversity of beetles, plants, and birds increased with
spatial (within-island variation in burn severity) and temporal (variation
in time since fire among islands) pyrodiversity, respectively. Species
richness of plants and birds increased with spatial pyrodiversity,
indicating that habitat heterogeneity from localized variation in burn
severity supported more species in some groups. Beta diversity of all taxa
increased with temporal pyrodiversity, highlighting the importance of
conserving age-class variation within the boreal patch mosaic. In
contrast, the habitat amount hypothesis and island biogeography theory
were weak predictors of species richness across all taxa, and island area
and isolation did not consistently affect beta diversity among the
islands. Our findings emphasize the importance of maintaining
pyrodiversity in boreal landscapes to combat biodiversity loss in the age
of “megafires” and suggest leveraging the fire refugia effects of large
lakes within the region to conserve vital components of temporal
pyrodiversity such as old-growth forests.