Landscape distribution and habitat use of sika deer using indirect signs of deer activity: a simple tool for forest managers

The populations of many deer species across Europe are widely reported to be increasing, leading to potentially greater impacts on forest ecosystems. Our understanding of factors driving the regional distribution (e.g. 1 km ² resolution) of deer populations is, however, often limited by a lack of knowledge of where deer are within the landscape. Deer distributions can be modelled at a national and regional scale based on presence/absence data or hunter returns, but a more granular assessment, using empirical observations at multiple sites, will allow identification of local density hotspots and coldspots, and more precise information on landscape factors driving habitat use. In this study, we assessed the distribution of alien invasive sika deer Cervus nippon across its putative range in the south west of Ireland – an area of approximately 10 000 km ² – using a semi‐quantitative activity index, based on indirect signs of deer activity (browse, trackways, faecal pellet and slot indices), at 249 individual forest sites. We then related levels of sika deer activity to landscape geomorphological and land use factors.

Sika deer activity was positively associated with landscapes characterised by unenclosed heathland, acidic peaty soils and low agricultural intensity, and negatively associated with landscapes characterised by improved grassland within enclosed fields, on more fertile, better‐drained mineral soils, with higher agricultural intensity. The areal extent and nature of conifer plantations and broadleaf woodlands was similar in both landscape types. The realised future range expansion of sika deer within the region may be less than previously reported, if deer remain largely restricted to these heathland landscapes. A wider use of the activity index method, by allowing more accurate assessment of deer distributions at landscape scales, will also facilitate the risk assessment and management of deer impacts to trees, crops and vehicular traffic.