Lack of reliable post-fire recovery mechanisms makes the iconic Tasmanian conifer Athrotaxis cupressoides susceptible to population decline

Abstract

Athrotaxis cupressoides is an iconic Tasmanian palaeoendemic conifer that is vulnerable to fire. A survey of three populations burnt by severe fire in 2016, conducted 1year post-fire, found 33% of stems were still alive, with many surviving stems suffering some canopy scorch. We re-surveyed these populations to quantify delayed mortality, resprouting, and presence of juveniles, and to determine whether fire impacts can be reliably assessed after 1year. We applied three measures of fire severity: canopy scorched, canopy consumed, and the minimum burnt twig diameter of neighbouring shrubs. We found overall stem survival in 2020 was 31%, and that 97% of stems that were dead 4years post-fire had died within the first year. Our best predictor of stem mortality was percentage canopy scorched. Overall, 1.8% of burnt stems resprouted, but severely burnt stems did not resprout. Juveniles were present ~9.9% of burnt trees in 2017, and only 1.8% in 2020. We conclude that A. cupressoides stems are not unusually fire sensitive, but rather, that the species’ vulnerability to severe fire results from its lack of reliable recovery mechanisms. This study shows that fire-caused mortality can be reliably assessed 1year post-fire, and possibly earlier. Interventions such as sowing seed or transplanting seedlings could be necessary to re-establish fire-killed populations.