Savanna Responses to Feral Buffalo in Kakadu National Park, Australia

Abstract

Abstract. Savannas are the major biome of tropical regions, spanning 30% of the Earth's land surface. Tree : grass ratios of savannas are inherently unstable and can be shifted easily by changes in fire, grazing, or climate. We synthesize the history and ecological impacts of the rapid expansion and eradication of an exotic large herbivore, the Asian water buffalo (Bubalus bubalus), on the mesic savannas of Kakadu National Park (KNP), a World Heritage Park located within the Alligator Rivers Region (ARR) of monsoonal north Australia. The study inverts the experience of the Serengeti savannas where grazing herds rapidly declined due to a rinderpest epidemic and then recovered upon disease control.Buffalo entered the ARR by the 1880s, but densities were low until the late 1950s when populations rapidly grew to carrying capacity within a decade. In the 1980s, numbers declined precipitously due to an eradication program. We show evidence that the rapid population expansion and sudden removal of this exotic herbivore created two ecological cascades by altering ground cover abundance and composition, which in turn affected competitive regimes and fuel loads with possible further, long-term effects due to changes in fire regimes. Overall, ecological impacts varied across a north-south gradient in KNP that corresponded to the interacting factors of precipitation, landform, and vegetation type but was also contingent upon the history of buffalo harvest. Floodplains showed the greatest degree of impact during the period of rapid buffalo expansion, but after buffalo removal, they largely reverted to their prior state. Conversely, the woodlands experienced less visible impact during the first cascade. However, in areas of low buffalo harvest and severe impact, there was little recruitment of juvenile trees into the canopy due to the indirect effects of grazing and high frequency of prescribed fires once buffalo were removed. Rain forests were clearly heavily impacted during the first cascade, but the long term consequences of buffalo increase and removal remain unclear. Due to hysteresis effects, the simple removal of an exotic herbivore was not sufficient to return savanna systems to their previous state.

Managing the matrix: decadal responses of eucalypt‐dominated savanna to ambient fire regimes

“…Time since moderate or severe fire was included also as a fire term in four ''best'' or ''alternative'' models for shrub density and shrub species richness classes, including as a significant term in the best model for tall shrub density, explaining 24% of null deviance. In the absence of other major disturbance, we suggest that, as an artifact of the variable ''time since moderate or severe fire,'' ground layer competition is likely to have contributed to observed declines in density in smaller woody classes given potential for increased ground layer competition associated with (1) reduced (albeit slight) mean basal area van Wilgen 1996, Scholes andArcher 1997), (2) above-average rainfall (Scanlon et al 2005), (3) limited herbivory , Petty et al 2007, and (4) increased fire severity associated with increased fuel load accumulation with time since fire .…”

“…By contrast, burning of sandstone uplands varied markedly between parks; 70% of sandstone savanna was burned on average in Litchfield, 51% in Nitmiluk, and 29% in Kakadu. The assessment period also coincided with low densities of feral Asian water buffalo and cattle (hence higher grassy fuel loads) following very substantial population reductions through the late 1980s and early 1990s associated with a national bovine disease eradication program (Skeat et al 1996, Petty et al 2007). …”

“…Ambient fire regimes over the study period were generally EDS-dominated, mostly of mild fire intensity, and contrasted substantially with more intense treatments at Kapalga, and mostly at lesser frequencies than at both Munmarlary and Kapalga (Cook and Goyens 2008), and grazing and browsing by feral ungulates was slight (Petty et al 2007). In response, structural and species changes were variable but often substantial, notably resulting in recruitment of relatively fire-sensitive tall-tree juveniles and small trees, but declines in smaller-sized juveniles.…”

Estimating Economic Carrying Capacity for an Ungulate Guild in Western Canada

“…Translocation receives the greatest level of public support, but disease concerns have reduced the safety of translocating wildlife [111][112][113][114]. Along with the high costs of handling and management, resource managers have explored alternatives for vegetation management including prescribed burning [59] and intra-guild competition [43,58,[115][116][117].…”

Defining Environmental Risk Assessment Criteria for Genetically Modified (GM) Mammals and Birds to be placed on the EU market

“…EFSA reserves its rights, view and position as regards the issues addressed and the conclusions reached in the present document, without prejudice to the rights of the authors. Water buffalo, mainly a problem in Australia (Petty et al 2007) Cattle are a better surrogate…”