Ecological and Agricultural Impacts of Introduced Deer across the Australian Alps


Dr Andrew W. Claridge, RNSW National Parks and Wildlife Service, Queanbeyan, NSW 2620

Background Context

Deer are among the most introduced of all large mammals around the world (Lever 1985). This is certainly the case in the southern hemisphere, including Australia and New Zealand (Moriarty 2004a). In both countries, a number of species of deer have increased massively in abundance, as well as distribution, since being introduced. Côte et al. (2004) reviewed the ecological impacts of deer overabundance globally, finding that through their foraging activities they affect the growth and survival of many herb, shrub and tree plant species, changing patterns of relative abundance and vegetation dynamics. Since they are highly adapted large herbivores with multi-chambered stomachs capable of microbial digestion of cellulose and utilisation of relatively low quality forage, most plant species are at potential risk. In turn, these negative impacts on plants can flow on to other organisms including insects, birds and other mammals. Long-term effects of browsing can include a reduction in vegetation cover as well as a loss in diversity of plant species (Rose and Platt 1987; Stewart et al. 1987; Husheer et al. 2003; Husheer and Frampton 2005; Husheer 2007).

In New Zealand, the threat of deer to native ecosystems has been recognised and many studies have described negative impacts, particularly on plants (see Forsyth et al. 2003). However, a combination of control, commercial harvesting and hunting has reduced most deer populations by 75-95% of peak levels of the mid 1900’s (Nugent et al. 2001). In Australia by way of contrast, deer populations are increasing rapidly, with prevailing attitudes influenced by economic value for hunting together with a paucity of documented evidence of impacts on vegetation, let alone other wildlife (Dolman and Wäber 2008). For example, in Tasmania the range and abundance of fallow deer (Dama dama) has massively increased, from around 7000-8000 animals in the 1970’s occupying an area of around 400000 ha, to between 20000-30000 animals occupying an area of around 2.1 million ha in the early 2000’s (Potts et al. 2014). Modelling of this trend further predicts ongoing expansion of this population under a range of different scenarios, including existing game management. Of note, the current regime in Tasmania is based on managing the fallow deer as a hunting resource while giving farmers permission to kill animals to protect their crops. Such an approach is unlikely to prevent further population growth.

In south-eastern mainland Australia the situation is little better. Estimates of harvest from game licence holders in Victoria indicate that around 50000 deer were taken in 2013 alone, including around 42000 sambar deer and 6000 fallow deer (Moloney and Turnbull 2013). Since these estimates are increasing from one year to the next, it is reasonable to assume that the base population of these species is also increasing and must be significant. Even major perturbations such as major wildfires do not appear to keep deer populations in check. Forsyth et al. (2011, 2012) documented changes in sambar deer abundance in Victoria following the Black Saturday fires. They used faecal pellet counts on defined transects in Kinglake National Park, which was intensely burnt, and at Mount Buffalo National Park, which remained unburnt. At Mount Buffalo Park counts of scats increased over the four years of counting, whereas at Kinglake the scat counts increased in the two years prior to the fire, before being non-existent immediately after the fire then sparse a year later. However, across a number of other sites across the Victorian Alps, it was found that occupancy of sites by sambar deer was only weakly reduced 16-24 months after the fires. In summary, the species appeared to be bouncing back immediately after the fires.

Studies reporting on the ecological and other impacts of deer in Australia are sparse. For the most part, they are based on anecdotal observations of damage by deer to plants (Keith and Pellow 2004; Peel et al. 2005; Bailey et al. 2015). In a few cases, the level of this damage has also been quantified (Moriarty 2004b; Bilney 2013). However, the economic costs of deer to human enterprises on agricultural land have hardly been studied (Finch and Baxter 2007). This report redresses this situation in part by providing a synthesis of several different research projects that variously aimed to document the ecological and agricultural impacts of deer across the Australian Alps. These projects are presented as seven case studies. For the ecological impacts component of the overall work, the following issues were addressed: (i) the occurrence and types of impacts of deer in Alpine bog systems; (ii) the occurrence and types of impacts of deer at sites occupied by the rare and endangered northern corroboree frog; (iii) the impacts of deer on an endangered shrub, the leafy anchor plant; (iv) the various impacts of deer on woody trees and shrubs in an endangered ecological woodland community; (v) browsing and other impacts of deer on different plant species identified during the process of carrying out (i)-(iv), and; (vi) patterns of utilisation of wallows by deer in sensitive landscapes. Collectively, these were chosen as example studies from an extensive list of endangered species and other entities identified from various Commonwealth, State and Territory legislations.

For the agricultural impacts work a simple case study was designed to evaluate the extent to which deer occupying forested areas in Alpine National Parks utilised adjacent private properties. The specific aims were twofold. Firstly, to provide estimates on the number of deer using access points into and out of pasture adjacent to public lands. Secondly, to determine the frequency with which deer utilised cleared pastures from one month to another and also between successive deployments. Although there were plenty of other sorts of studies that might have been carried out to look at agricultural impacts, this one was more readily handled within the confines of the overall study.

Irrespective of whether the case studies below describe ecological or agricultural impacts of deer, they are written up in the same format, with background context to the work given first, then methods and results, then data interpretation and discussion and finally recommendations for further studies. As these case studies essentially stand-alone, there is no overall concluding statement about the broader research effort since it is unnecessary. Similarly, there is no final synthesis of future research as it has already been articulated on a case-by-case basis. In these respects the format of the overall report is a little different from the norm.

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