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Do feral buffalo (Bubalus bubalis) explain the increase of woody cover in savannas of Kakadu National Park, Australia?

Bowman, David, Riley, J., Boggs, Guy S., Lehmann, Caroline and Prior, Lynda (2008). Do feral buffalo (Bubalus bubalis) explain the increase of woody cover in savannas of Kakadu National Park, Australia?. Journal of Biogeography,35(11):1976-1988.

Document type: Journal Article

IRMA ID A00004xPUB90
Title Do feral buffalo (Bubalus bubalis) explain the increase of woody cover in savannas of Kakadu National Park, Australia?
Author Bowman, David
Riley, J.
Boggs, Guy S.
Lehmann, Caroline
Prior, Lynda
Journal Name Journal of Biogeography
Publication Date 2008
Volume Number 35
Issue Number 11
ISSN 0305-0270   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-53849141508
Start Page 1976
End Page 1988
Total Pages 13
Place of Publication Oxford
Publisher Blackwell Publishing
Field of Research 0403 - Geology
0406 - Physical Geography and Environmental Geoscience
HERDC Category C1 - Journal Article (DEST)
Abstract Aim: To study changes in woody vegetation in both floodplains and eucalypt savanna over a 40-year period using multi-temporal spatial analysis of variation in density of a large introduced herbivore, the Asian water buffalo (Bubalus bubalis). Feral buffalo built up to high densities in the study area until c. 1985, after which a control programme almost eliminated the animals. From 1990, low densities of managed buffalo were maintained inside an enclosure. We compared trends in woody vegetation when buffalo were high-density feral, low-density managed or absent.

Location: The study area was located in and around a 116-km2 buffalo enclosure inside Kakadu National Park, in monsoonal northern Australia.

Methods: We analysed sequences of digitized and geo-rectified aerial photographs, acquired in 1964, 1975, 1984, 1991 and 2004, to chart changes in woody cover on the floodplain and in the savanna. On the floodplain we assessed whether trees were present at these times at 14,568 points, and buffalo density was estimated from the density of animal tracks. In the savanna we estimated woody cover at pre-selected sites. Generalized linear modelling was used to analyse changes in woody vegetation, using elevation and presence of woody vegetation in neighbouring points on the floodplain, and buffalo regime and initial woody cover in the savanna.

Results: Changes in animal track density reflected park-wide historical estimates of buffalo numbers. Tree cover increased in both floodplain and savanna, but this was only weakly related to buffalo density. The best predictor of whether a floodplain cell converted from treeless to woody, or the converse, was the woodiness of neighbouring vegetation. There was slightly less thickening with high buffalo densities. In savanna, low densities of managed buffalo were weakly associated with increases in tree cover relative to either high densities of feral buffalo or no buffalo.

Main conclusions: Our study indicates that buffalo are not a major driver of floodplain and eucalypt savanna dynamics. Rather, the observed increase in woody cover in both savanna and flood plains concords with regional trends and may be related to increased atmospheric CO2, increasing rainfall and changing fire regimes during the study period.
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Created: Mon, 27 Apr 2009, 11:14:56 CST by Sarena Wegener