Abundance of deer in Victoria: Regional and statewide estimates of deer density and their impact on vegetation

Authors

J.G. Cally and D.S.L. Ramsey

Arthur Rylah Institute for Environmental Research
Technical Report Series No. 368

Summary

Deer populations are anticipated to be increasing and widespread across Victoria. Given the range of impacts deer have on biodiversity, public safety, water quality, agriculture, and Aboriginal cultural heritage,  The statewide deer monitoring project was developed as a multi-year project to fill these knowledge gaps, with monitoring commencing in 2021. This report summarises the monitoring data collected to estimate statewide and regional deer distribution and abundance, as well as impacts on ecosystem health.

Deer were detected at 148 of the 317 camera traps across Victoria, and some form of deer sign (camera or transect) was recorded at 186 of the 317 sites. Total deer abundance on Victorian public-tenured land was 191,153 (90% CI: 146,732, 255,490). Sambar deer were the most abundant species across Victoria (123,061 [90% CI: 96,200, 157,638]), followed by Fallow (48,932 [90% CI: 29,888, 85,063]), Red (12,672 [90% CI: 4,719, 35,465]), and Hog (4,243 [90% CI: 2,121, 8,464]) deer.

Results from the modelling suggested that five variables influenced the spatial variation in deer abundance including bioregion, the percentage of bare soil, distance to pastural land, precipitation seasonality, and amount of forest edge surrounding a site. All deer species tended to have higher densities in closer proximity to pastoral land, but this effect was stronger for Fallow and Red deer.

The amount of forest edge in the landscape positively impacted the abundance for Fallow deer. It was also weakly positively associated with the abundance of Sambar and Hog deer, but negatively associated with the abundance of Red deer. We also found evidence for relationships between deer density and several components of vegetation structure and composition. An increased density of deer was related to decreased native woody understorey cover, decreased percentage of bare soil (and conversely, increased native herbaceous understorey cover).

Higher densities of deer were also related to increased probabilities of exotic plant species (weeds) being present at a site, with the presence of weeds being 1.17 [90% CI: 1.04, 1.33] times more likely for every 1 deer/km2 increase in deer density.

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