The browsing index: new tool uses browsing pressure to monitor deer populations

Usual counts of deer populations generally show low reliability, especially at the high-density levels deer have recently reached in most parts of Europe. Since 1990, researchers and managers have looked for index methods to replace counts. Monitoring vegetation changes over time in response to deer browsing could be useful for managers to index deer abundance. We assessed the feasibility of using Aldous-derived vegetation surveys to monitor the population-habitat interaction over time. We first developed an original statistical procedure to define a reliable measure of deer browsing. Then we applied our browsing index to a case study involving a roe deer (Capreolus capreolus) population that was monitored intensively over 18 years and increased 5-fold in size. Our browsing index closely tracked the roe deer population size, the species-specific browsing rates differed widely, and bramble (Rubus sp.) could be reliably used to assess total browsing pressure of roe deer. Because it is an easy tool to use and involves much lower costs than traditional counts, our browsing index can be viewed as an efficient and reliable indicator of ecological change according to deer population status