Using camera traps to quantify the effect of deer on woodland restoration

Woodland is one of the most biologically diverse ecosystems on Earth and an important habitat for many wildlife species. However, long-term deforestation worldwide has adversely impacted biodiversity and ecosystem functioning. Over recent decades deforestation rates have slowed, particularly in temperate regions where large-scale woodland planting schemes have greatly contributed to woodland expansion. However, the long-term effectiveness of woodland creation programmes in restoring species and ecosystem processes is still largely unknown, and we know surprisingly little about the factors likely to enhance/limit biodiversity in newly planted woodlands.

The occurrence, abundance and diversity of woodland-associated taxa are likely to be strongly influenced by local habitat characteristics (e.g. patch size and quality) and, to a lesser extent, by their surrounding landscape (e.g. proportion and spatial configuration of various land cover types). Deer can drastically alter woodland vegetation structure (e.g. density of foliage and stems), for instance by creating browse lines where edible foliage has been removed from the understorey, and by damaging seedlings and limiting tree recruitment. This can have profound effects on natural regeneration and play a crucial role in determining the future direction of secondary woodlands. In addition, changes in vegetation structure as a result of deer overabundance can cascade to other taxa including invertebrates, birds and small mammals. Although the impacts of high deer densities on woodland structure and biodiversity have been relatively well studied, it remains unclear how important these are relative to other factors. This information is crucial to underpin effective conservation strategies, prioritise alternative management actions and maximise the biodiversity benefits of woodland creation and restoration.

The Woodland creation & Ecological Networks project (WrEN) is a large-scale natural experiment designed to study the effects of 150 years of woodland creation on biodiversity and inform landscape-scale conservation (www.wren-project.com). As part of WrEN, since 2013 we have surveyed 106 secondary woodland sites which have been created on former agricultural land over the last 160 years in two regions of mainland Britain. We have collected data on the diversity and abundance of a wide range of taxa (1100+ species recorded to date, including vascular plants, lichens, bryophytes, invertebrates, small mammals, bats and birds); we have also characterised the vegetation structure of each site (e.g. tree density, amount of understorey and structural heterogeneity), and quantitatively described the surrounding landscapes up to 3 km from each site (e.g. % of land cover types and degree of connectivity to other woodland).

In this project, we will use the WrEN network of sites (a chrono-sequence of 106 secondary woodland patches planted 10-150 years ago on former agricultural land) to estimate deer densities using camera traps. We will then link this information with existing WrEN data to: 1) quantify the associations between deer density and local- (e.g. woodland vegetation structure) and landscape-level (e.g. amount of surrounding woodland) characteristics of secondary woodlands; and 2): assess cascading impacts on woodland biodiversity.