Eucalypt forests dominated by epicormic resprouters are resilient to repeated canopy fires

Abstract

1. Wildfire occurrence and severity are projected to increase in response to anthropogenic climate change, leading to fire regimes that may exceed the limits of tolerance for some species. Plants capable of regenerating from aerial shoots following high intensity fires, termed 'epicormic resprouters', are assumed to be resilient to changes in fire regimes. However, empirical tests of the response of epicormic resprouters to extreme fire regimes, such as repeated canopy fires at short intervals, are currently lacking.2. This study examined the effect of combinations of understorey fire and canopy fire across two successive wildfires (2007, 2013) on the resilience of eucalypts that resprout epicormically. The study took place in a temperate eucalypt forest in south eastern Australia. Measures used to infer community resilience included stem topkill and damage, and seedling recruitment. It was predicted that: (a) stems will exhibit lower resistance (i.e. increased topkill and damage) to canopy fire than understorey fire; (b) recruitment will be higher following canopy fire than understorey fire; (c) prior exposure to canopy fire will reduce stem resistance and recruitment in response to subsequent wildfires; and (d) stem resistance will vary depending on bark traits.3. Topkill of saplings and small stems (<30 cm diameter at breast height) was higher in sites that recently (i.e. 2013) experienced canopy fire as opposed to understorey fire. Recent fire severity had no effect on topkill of large trees. Tree species with dense bark on the main stem and larger branches were less prone to topkill or partial stem and branch mortality than species with fibrous bark or exposed branches. Seedling recruitment was greater following canopy fire than understorey fire. Exposure to past canopy fire (i.e. in 2007) did not decrease stem resistance or recruitment. Synthesis.The results of this study suggest that communities of eucalypts that can resprout epicormically following fire will experience demographic shifts following repeated canopy fires. However, given the high resistance of large trees and rapid post-fire recovery of the seedbank, ecosystem conversion appears unlikely. The findings support the presumption that forest communities of epicormic resprouters are highly resilient to shifts in fire regimes.

Time since fire and prior fire interval shape woody debris dynamics in obligate‐seeder woodlands

“…Consequently, we propose that the concepts of our model of woody debris dynamics will have relevance for a diversity of obligate-seeder forests and woodlands with stand-replacement fires, with relevant calibration of temporal patterns of change according to productivity, plant species traits, and decomposition rates of individual communities. In contrast to the strong effects of time since fire and fire interval on woody debris attributes found here, in forests and woodlands dominated by epicormically resprouting trees, woody debris changes with time since fire can be more modest or undetectable (Graham and McCarthy 2006, Loucks et al 2008, Bassett et al 2015, buffered by the resilience to fire of biomass stocks in epicormicresprouter trees (Pausas and Keeley 2017, Nolan et al 2018, Collins 2019.…”

“…), buffered by the resilience to fire of biomass stocks in epicormic‐resprouter trees (Pausas and Keeley , Nolan et al. , Collins ).…”

“…In these plants, protected buds under bark typically mediate trunk survival through fire, with the consequence that these components of biomass potentially remain as live vegetation (c.f. woody debris) through multiple fire events (Pausas and Keeley , Collins ). Many biomes contain a mix of obligate‐seeder and epicormic‐resprouter dominated forests and woodlands (Clarke et al.…”

Hydraulic and photosynthetic limitations prevail over root non‐structural carbohydrate reserves as drivers of resprouting in two Mediterranean oaks

“…The capacity for resprouting, particularly widespread across angiosperm trees, is a major mechanism providing post-fire and post-drought resilience in Mediterranean ecosystems and other parts of the world (Sánchez-Pinillos et al, 2016). However, the capacity for resprouting appears to have limits and is diminishing (Karavani et al, 2018, Resco de Dios 2020, notably with increased drought severity or fire recurrence (Batllori et al, 2018, Collins, 2019, Fairman et al, 2019, Pratt et al, 2014.…”

Quantifying the impact of severe bushfires on biodiversity to inform conservation

“…Empirical evidence from the US also demonstrates that, with climate change, post-re weather conditions show reduced capacity for forest recovery 71 . The recent large bush res affected Eucalypt forest communities that are resilient to high severity wild re 72 , but less is known about their response to high frequency, high severity res. Increased re frequency is expected to promote shrub recruitment and shift ecosystems away from tree-dominated landscapes in Australian alpine environments 17 and enable encroachment of wild re into re refugia 73 .…”