Woodlands and woody debris: Understanding structure and composition to inform restoration.

Adrian D. Manning,David Tongway,David B. Lindenmayer,Ross B. Cunningham,RunGuo Zang

doi:10.1371/journal.pone.0224258

Abstract

Simplification of stand structure of forests and woodlands through human-induced modification is a serious threat to biodiversity. Restoring lost habitat complexity and heterogeneity, such as woody debris, requires an understanding of the relationships between different elements that contribute to stand structure. In this study, we examine the structure and composition of a critically endangered box-gum grassy woodland in south-eastern Australia and relationships with woody debris loads. We found that: (1) despite modification by humans and differing susceptibility to dieback, the two dominant tree species, Blakeley’s red gum, Eucalyptus blakelyi and yellow box, E. melliodora, occurred in similar proportions irrespective of vegetation density; (2) E. blakelyi had the largest number of stems and basal area, but while E. melliodora had fewer stems, it had a similar basal area to E. blakelyi. E. melliodora also showed fewer signs of dieback than E. blakelyi with between 40–50% trees in good condition compared to 2% for the latter species; (3) woody debris loads were low compared to other studies in woodland, but there were levels of heterogeneity indicating ‘natural’ accumulation was occurring; (4) tree basal area and woody debris loads had a 1:1 relationship across all sites and vegetation densities. Overall, our study indicated that ecosystem recovery was taking place (i.e. with many young trees), but there were fewer large trees that are known to supply most woody debris. Our findings highlight the slow accumulation of this critical resource because the volumes were lower than expected. Based on our results, we recommend: (1) aiming for approximately a 50:50 ratio of yellow box to Blakely's red gum basal area in woodland restoration projects; (2) to accelerate the recovery of woodland structure, addition of woody debris should be added at a minimum ratio of 1:1 to standing basal area (i.e. a basal area of 5.99 m2 requires a minimum volume of 3.11 m3) (3) managing for both volume and heterogeneity of woody debris loads; (4) preserving large diameter trees to harness proportionally higher woody debris and litter inputs.

Highlights

The structure and composition of vegetation is critically important for maintaining biodiversity, ecological processes and ecosystem services [1, 2]
We examined relationships between measured vegetation structure and woody debris loads in box-gum grassy woodlands in the northern part of the Australian Capital Territory (ACT) in two adjacent reserves with different management histories
The two dominant species across both reserves were yellow box and Blakely’s red gum; Eucalyptus macrorhyncha was abundant in Mulligans Flat, but not Goorooyarroo

Summary

Introduction

The structure and composition of vegetation is critically important for maintaining biodiversity, ecological processes and ecosystem services [1, 2]. Manipulation of that structure and composition through management is a way of influencing the future of a forest or woodland, and its value for biodiversity, ecological processes, and ecosystem services. A good example is the box-gum grassy woodlands in south eastern Australia, which occur in an internationally recognised endangered ecoregion [18]. Together with white box (E. albens), these woodlands once covered a vast area of south-eastern Australia prior to European settlement [19, 20]. They have been profoundly affected by clearing and modification, because they occurred on soils favoured for agriculture [19,20,21,22]. Box-gum grassy woodlands are listed nationally as a critically endangered ecological community [20, 25, 26]

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