Assessing the effects of fragmentation and climate change on woodland animal populations

A hot topic in the conservation of British wildlife is the role of volunteers. The benefits of volunteer involvement are potentially great, through the contribution that citizen scientists can make in collecting the data, the impact on volunteer's personal growth,  and the potential to engage the wider public with nature. A partnership between Oxford University's WildCRU and Environmental Change Institute (ECI), together with CEH and Earthwatch, has designed a four year research programme into the effects of climate change on the UK's fragmented woodlands. Unusually, this programme has been customised specifically to maximise opportunities for benefitting, and benefiting from, citizen scientists, in this case volunteers from the HSBC. The project is centred in Wytham Woods, near Oxford, and sits within the WildCRU's Upper Thames Project that seeks to integrate research on biodiversity and its conservation with the agro-ecosystem of the Thames catchment. The volunteers assist with studies of a diverse range of animal species, from small mammals to woodlice and moths, to understand the linkages between animals and the ECI's complementary research on fundamental carbon dynamics in the woodland.

The combined effects of habitat fragmentation and climate change are thought likely to significantly affect many species across the UK. Hotter, drier summers, wetter winters and an increase in unpredictable and extreme weather conditions mean that changes in species distributions and behaviour are already apparent. The woods around Oxford provide a model typical of lowland temperate woodland, fragmented by forestry, agricultural practices and urbanisation. Fragmentation, and concomitant reduction in population sizes and dispersal opportunities, are of course acknowledged threats to conservation, the effects of which are likely to be worsened by climate change. The programme aims to answer such questions as how much connectivity is needed between woodland patches to enable movement between populations? And, do changes in species abundance and composition affect key ecosystem processes such as decomposition and nutrient recycling?

Woodlice and millipedes

In British woodlands woodlice and millipedes are the most abundant macro-decomposers. While not directly responsible for the decomposition process they make important indirect effects through the breakdown of leaf litter into smaller particles, mixing of the leaf litter into a homogenous state, and moving it to more favourable microclimate conditions, and many studies have shown that in the absence of soil macrofauna litter disappearance is greatly reduced. Changes in climate may affect the abundance and composition of these invertebrates, the majority of which favour damp conditions.  Volunteers have proved to be very reliable at identifying the common species of woodlice and millipedes and the first surveys have already shown differences in the species composition and abundances between the drier edge habitats and the wetter core woodland areas.  A series of experimental studies are underway to look at how these changes affect the decomposition of leaf litter in the edge and core woodland plots.

Moths

Moths are an excellent group on which to study the combined effects of climate change and woodland fragmentation.  They are a large and diverse group, with a large subset of species which depend on woodland during some stage of their life-cycle. They are already known to be good indicators of habitat quality and respond rapidly to climate change effects, making them good surrogates for other insect groups.  Previous studies by WildCRU researchers have shown the importance of field margins and hedgerow trees for farmland species (Merckx et al., 2009).  This summer we have initiated a landscape-scale mark-release-recapture (MRR) study to document the use of core and edges of woodland fragments of a range of sizes from 360 ha down to single isolated trees. By marking and releasing every individual of a set of 92 focal woodland associated species we are able to monitor their movements within the landscape.  For example, how important are the hedgerows and isolated trees connecting fragments? Are larger fragments more important than small fragments?  This study is providing the first results showing how these species are affected by woodland fragmentation, and creating a framework for predictions of how their populations will be affected by climate change.  Preliminary results so far show that both woodland size and connectivity are important, and that even small woodland fragments have a large abundance and richness of moths.  Moreover, many moths appear to be moving large distances across the landscape, and recaptures along hedgerows and at isolated oak tress indicate that they are using these landscape features.

Wood mice and bank voles

Small mammals are being monitored in the core and edges of the woodlands as part of the on-going mammal monitoring programme begun in the 1940's by Charles Elton to monitor the long-term changes in the distribution and abundance of small mammals within the woodland.  Results from the first field season of mammal trapping suggest that populations of bank voles and wood mice, which suffered large declines in their populations over the last decades due to increasing deer numbers and a corresponding loss of ground vegetation (Flowerdew & Ellwood, 2001), are not recovering despite an intensive deer management programme within the woods.  This raises the possibility that the effects of several wet summers and cold winters/springs may be operating as countermanding pressures on rodent survival and reproduction, despite the recovery of the vegetation.