Impact of high-severity fire in a Tasmanian dry eucalypt forest

Abstract

Dry eucalypt forests are believed to be highly fire tolerant, but their response to fire is not well quantified. We measured the effect of high-severity fires in dry eucalypt forest in the Tasmanian Midlands, the driest region on the island. We compared stand structures and fuel loads in long-unburnt (>15 years since fire) and recently burnt (<5 years since fire) sites that had been completely defoliated. Even in unburnt plots, 37% of eucalypt stems and 56% of acacia stems ≥5 cm in diameter were dead, possibly because of antecedent drought. The density of live eucalypt stems was 37% lower overall in burnt than in unburnt plots, compared with 78% lower for acacias. Whole-plant mortality caused by fire was estimated at 25% for eucalypt trees and 33% for acacias. Fire stimulated establishment of both eucalypt and acacia seedlings, although some seedlings and saplings were present in long-unburnt plots. The present study confirmed that eucalypts in dry forests are more tolerant of fire than the obligate seeder eucalypts in wet forests. However, there were few live mature stems remaining in some burnt plots, suggesting that dry eucalypt forests could be vulnerable to increasingly frequent, severe fires.

Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

“…Other disturbances, such as drought (in particular, a ‘very long’ rainfall deficit from 1996 to 2010 in south‐east Australia; BOM 2010) could have contributed to seemingly high percentage clump mortalities and top‐killed stems (37%) at Unburned sites, as has been recently recorded for other resprouter forests in southern Australia (Prior et al. ). In contrast to Unburned sites, high overall percentage clump mortalities at Triple burned sites (50%) reflected elevated mortalities of ‘large’ clumps (56%).…”

“…The rates of death are substantially higher than mortality rates after high‐severity fire in resprouter dry eucalypt forests (25%; Prior et al. ), in forest (8%) and savanna ecosystems (7%; Hoffmann et al. ) or following extreme drought in other eucalypt forests in southern Australia (26%; Matusick et al.…”

“…; Prior et al. ) suggests that even comparatively hardy forests dominated by strong resprouters cannot safely be assumed to be invulnerable to emerging fire regimes.…”

“…All sites were assessed between Feb and May 2015, ~2 yr after the last wildfire – an adequate interval for recovery and establishment of eucalypts and associated understorey in comparable forest types elsewhere (Prior et al. ). At each site, a fixed area plot (10 m × 50 m, 0.05 ha) was randomly positioned to be entirely within the E. pauciflora patch, at least 50 m from the patch edges, and with the length of the plot running along the contour.…”

“…; Prior et al. ; Nicholson et al. ); however, interactive effects of multiple fires, particularly under high‐severity conditions, remain largely unquantified (Haslem et al.…”