Fire severity and the post‐fire soil environment affect seedling regeneration success of the threatened Persoonia hirsuta (Proteaceae)

Abstract

Climate change and land management decisions have considerably altered fire regimes globally resulting in increased risks of extreme fire seasons. Fire intensity is one characteristic of fire regime which is projected to increase. However, the magnitude and impact of intense fires on plant habitat and life history characteristics (such as the soil environment or seedling recruitment) remain unclear for many species. The widespread 2019–2020 Black Summer fires across Eastern Australia provided the opportunity to examine the impact of these fires on the short‐term regeneration of the Endangered Persoonia hirsuta (Proteaceae), an obligate seeding (reliant on regeneration from seed following fire) shrub presently threatened by population decline and dieback (plant death from branch and root tips backwards) of an unknown cause. In this study, we used a combination of metrics to estimate fire severity in the field at 22 plots across three fire‐affected populations which we used as a proxy to understand the relative impacts of fire intensity on P. hirsuta regeneration post‐fire. We also recorded the recruitment, growth, dieback and mortality of P. hirsuta seedlings at these plots over 21 months following the fires and examined whether the post‐fire soil environment (carbon, nitrogen and phosphorus) was related to fire severity and seedling responses. Seedling recruitment and growth were variable across sites and showed no relationship to fire severity. However, seedling dieback and mortality were significantly higher among plots exposed to high severity fires. Additionally, characteristics of the post‐fire soil environment varied by fire severity and explained variation in seedling recruitment, growth and dieback. Our work provides important evidence that already vulnerable populations of P. hirsuta may be further threatened by increasing fire severity, highlighting the importance of understanding the effects of fire on habitat and life history characteristics for threatened plants.