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05 - Spatio-temporal characterization of tree and stand level canopy structure of fire-tolerant eucalypt forests after wildfires of different severity using Lidar data

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XXV IUFRO WORLD CONGRESS

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Abstract

Fire-tolerant eucalypt forests of south-eastern Australia are assumed to fully recover from even the most intense fires but surprisingly very few studies have quantitatively assessed that recovery. Accurate assessment of horizontal and vertical attributes of tree crowns after the fire is essential to understand the fire’s legacy effects on tree growth and on forest structure. In this study, we quantitatively assessed individual tree crowns nearly a decade after a 2009 wildfire that burnt extensive areas of eucalypt forest in temperate Australia. We used airborne lidar data validated with field measurements to estimate multiple individual tree crown metrics in 12 to 13 plots (0.05 ha) per each of four wildfire severities (unburnt, low, moderate, high). Significant differences in mean height of fire scarring as a proportion of tree height, and proportions of trees with epicormic (stem) resprouts were consistent with a gradation in fire severity in the order unburnt <low <medium <high. Linear mixed-effects models indicated persistent effects of both moderate- and high-severity wildfire on tree crown architecture. Trees at high-severity sties in two size classes (20 – 50 cm, >50 cm diameter) had significantly less crown projection area and live crown width as a proportion of total crown width than those at unburnt and low-severity sites. Significant differences in lidar-based metrics (crown cover, evenness, leaf area density profiles) also indicated that tree crowns at moderate- and high-severity sites were comparatively narrow and more evenly distributed down the tree stem. These conical-shaped crowns contrasted sharply with the rounded crowns of trees at unburnt and low-severity sites. Our data provide clear evidence that moderate- and high-severity wildfire can modify the structure of tree crowns in fire-tolerant resprouter forests for nearly a decade after the wildfire. The implications of these legacy effects on, for example, tree productivity and the accuracy of biomass allometric equations warrants further study.

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© Copyright 2020 Morressier GmbH.
All rights reserved.