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Did early logging or changes in disturbance regimes promote high tree densities in river red gum forests?


McGregor, HW and Colloff, MJ and Lunt, ID, Did early logging or changes in disturbance regimes promote high tree densities in river red gum forests?, Australian Journal of Botany, 64, (6) pp. 530-538. ISSN 0067-1924 (2016) [Refereed Article]

Copyright Statement

Copyright CSIRO 2016

DOI: doi:10.1071/BT16025


Density of woody plants is thought to have increased in many ecosystems in Australia since European colonisation. Globally, there has been much debate as to whether this phenomenon is driven by the process of post-disturbance recovery - whereby historical logging resulted in the replacement of large, mature trees with smaller, younger trees - or by the process of encroachment - whereby cessation of disturbance events reduced the mortality of seedlings and saplings. We examined the extent to which historical changes in forest structure are compatible with each of these models. The study was conducted in river red gum Eucalyptus camaldulensis Dehnh. floodplain forest on the River Murray at Millewa Forest, southern New South Wales. We compared 'historical' (1860s) stand structure to 'current' structure in 45 one-hectare quadrants randomly stratified between three forest productivity classes. Historical trees were determined by stumps or stags likely to have been cut during the late 1800s. Size and position of each historical and current tree was recorded, and used to calculate stem density, basal area, canopy cover and the area of the 'zone of influence' (the peripheral extent of the root zone). Current stand structure was vastly different from historical structure. Stem density has increased 9-fold, from a mean of 17 (historical) to 147 (current) trees ha-1. However, basal area increased only slightly, from 13.0 to 15.3m2ha-1. Canopy cover increased substantially from 22.1 to 33.5% cover, as did zone of influence, from 55 to 81% cover. Evidence for both the post-disturbance recovery and encroachment hypotheses was found. The 9-fold increase in stem density between historical and current stands was attributable largely to the replacement of large trees with small trees, because basal area had increased only slightly (by 18%). However, the increase in basal area was associated with a substantial increase in canopy cover and area of the zone of influence, supporting the encroachment hypothesis. Regardless, the post-disturbance recovery hypothesis accounts for the bulk of changes in this river red gum forest.

Item Details

Item Type:Refereed Article
Keywords:encroachment hypothesis, floodplain ecosystem, historical ecology, post-disturbance recovery hypothesis, resource gradient, tree growth, woody thickening
Research Division:Biological Sciences
Research Group:Ecology
Research Field:Terrestrial ecology
Objective Division:Environmental Management
Objective Group:Terrestrial systems and management
Objective Field:Terrestrial biodiversity
UTAS Author:McGregor, HW (Dr Hugh McGregor)
ID Code:117836
Year Published:2016
Web of Science® Times Cited:7
Deposited By:Biological Sciences
Deposited On:2017-06-28
Last Modified:2017-11-01

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