Environmental variation in an increasing incidence of dead trees in lowland to subalpine eucalypt forests and woodlands 2011–2021
Zimeng Liu A and Jamie B. Kirkpatrick![https://orcid.org/0000-0003-2763-2692](/media/client/orcid_16x16.png)
A School of Geography, Planning, and Spatial Sciences, University of Tasmania, Hobart, Tas. 7005, Australia.
Australian Journal of Botany 71(6) 296-305 https://doi.org/10.1071/BT22119
Submitted: 17 October 2022 Accepted: 31 July 2023 Published: 18 August 2023
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
Abstract
Context: There are not many analyses of variation in patterns and potential causes of tree death in eucalypt forests covering wide environmental gradients.
Aims: To determine the environmental patterns of standing and fallen dead trees in forests over 1200 m of elevation and whether tree death has increased as the climate has become warmer, drier and windier.
Methods: We measured tree death in 2011 and 2021 in the lowland to subalpine forests near Hobart, Tasmania, Australia and determined the best predictors of its incidence and change. High-resolution satellite images obtained from Nearmap were perused to count dead standing trees, fallen dead trees and live trees in a stratified random selection of 250, 4 ha sites, 10 of which were ground-truthed. Elevation, climatic variables, aspect, slope, fire history, soil type and vegetation type were used as potential predictors of tree death. General linear models were developed to explain response variables.
Key results: Standing dead trees increased 133% from 1.7 to 2.3 per ha between 2011 and 2021. Fallen dead trees increased 160%. Variables that were significant in at least one of the models for 2011 standing dead trees, 2011 fallen trees, change in standing dead trees 2011–2021 and changes in fallen dead trees 2011–2021 were elevation, fire history, aspect class, several vegetation types and several soil types.
Conclusions: Deficits in soil moisture as a major cause of death is consistent with several components of these models, with fire history possibly having a legacy effect and wind exposure possibly influencing the balance between standing and fallen dead trees.
Implications: Tree mortality is likely to move upslope with warming and drying. Managing the understorey of dry forests using fire might help in reducing competition for moisture, and, thus, reduce tree death in susceptible forest communities, but severe fires are likely to cause considerable mortality.
Keywords: conservation biology, drought, ecogeography, ecosystem dynamics, eucalypts, fire ecology.
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