The effects of topographic variation and the fire regime on coarse woody debris: Insights from a large wildfire

Fire shapes the composition of ecosystems through its effects on vegetation structure. Fire is integral to the dynamics of coarse woody debris - logs and dead trees - as it both consumes existing debris and generates new material through its influence on tree death and collapse. Image credit: Edgar Vonk via Flickr

Fire shapes the composition of ecosystems through its effects on vegetation structure. Fire is integral to the dynamics of coarse woody debris — logs and dead trees — as it both consumes existing debris and generates new material through its influence on tree death and collapse. Image credit: Edgar Vonk via Flickr

Authors: Michelle Bassett, Evelyn K Chia, Steve W J Leonard, Dale G Nimmo Greg J Holland, Euan G Ritchie, Michael F Clarke and Andrew F Bennett

Published in: Forest Ecology and Management, volume 340 (March 2015)

Abstract

Coarse woody debris (CWD) is a common structural component of terrestrial ecosystems, and provides important habitat for biota.

Fires modify the distribution of CWD, both spatially and temporally. Changes in fire regimes, such as those arising from prescribed burning and changing climatic conditions, make it critical to understand the response of this resource to fire.

We created a conceptual model of the effects of fire on logs and dead trees in topographically diverse forests in which trees often survive severe fire. We then surveyed paired sites, in a damp gully and adjacent drier slope, ~3.5 years after a large wildfire in south-eastern Australia.

Sites were stratified by fire severity (unburnt, understorey burnt and severely burnt), and fire history (burnt ≤3 years or ≥20 years prior to the wildfire).

Both components of the fire regime influenced CWD availability in gullies. Severe wildfire and fire history ≤3 years reduced the volume of small logs (10–30 cm diameter) in gullies, while severe wildfire increased the number of large dead trees in gullies. CWD on slopes was not affected by fire severity or history at ~3.5 years post-fire.

Log volumes on slopes may recover more quickly after wildfire through rapid collapse of branches and trees. Gullies generally supported more logs than slopes, but longer inter-fire intervals in gullies may allow fuel loads to accumulate and lead to comparatively larger fire impacts.

Given that fire severity and fire interval are predicted to change in many fire-prone ecosystems in coming decades, this study highlights the importance of understanding the interacting effects of multiple components of the fire regime with landscape structure. In particular, variation in fire interval and fire severity in relation to topographic position will influence the pattern of accumulation of coarse woody debris across the landscape, and therefore the structure and quality of habitats for biota.

Bassett M, Chia EK, Leonard SWJ, Nimmo DG, Holland GJ, Ritchie EG, Clarke MF, Bennett AF (2015) The effects of topographic variation and the fire regime on coarse woody debris: Insights from a large wildfire, Forest Ecology and Management, 340, 126–134 PDF DOI