Understanding how forest communities respond and recover following disturbance is key to determining drivers of local biodiversity as well as predicting future shifts in forest community composition under climate change. Decades of advancements in disturbance ecology literature have emphasized the broad importance of disturbances in driving patterns of plant biodiversity. However, quantifying species-specific responses to climate-driven increases in disturbance frequency and intensity remains challenging, particularly among diverse old-growth plant communities with disparate life strategies. Many modern predictions of post-disturbance forest regeneration quantify physical abiotic changes such as light availability, competitive density, and nutrient supply as drivers of seedling demography. This paradigm has driven the ‘winners and losers’ approach to understanding post-disturbance regeneration, where early-successional, shade-intolerant species are better adapted to survive and thrive in disturbed abiotic conditions compared to late-successional, shade-tolerant species. In the Pacific Northwest, however, germination trends among shade-intolerant trees such as Douglas fir (Pseudotsuga menziesii) and shade-tolerant trees such as Western hemlock (Tsuga heterophylla) may reveal novel relationships between wildfires, seedling production, and forest regeneration. Here, we present findings from observing understory community dynamics in the Pacific Northwest following a large-scale, mixed-severity wildfire and discuss implications for forest regeneration and biodiversity.
Results/Conclusions
Our results demonstrate high post-fire germination among shade-tolerant tree species such as Western hemlock. Of our observations across 80 understory plots along a fire severity gradient, Western hemlock was the most abundant, but also experienced disproportionately high mortality rates following an extreme heat event in June of 2021. We also find high levels of regeneration of species important to nutrient cycling, such as N-fixing Deerbrush (Ceanothus integerrimus)across fire severity. Our findings highlight the importance of future tests to determine whether functional trait differences among plant species might alter traditional paradigms of succession and regeneration in post-fire landscapes. We discuss ongoing research aims along with understory plant demographic rates across a variety of functional roles.
