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Deer poo analysis uncovers surprising role in woodland conservation efforts

A study of deer poo in North Wales could shed light on the conservation of woodlands in the UK.

A team from Bangor University and the University of Reading conducted the study amid a growing concern that increasing deer populations are negatively impacting the health and regeneration of UK woodlands.

However, according to findings published in the scientific journal , the researchers discovered that the deer are eating large quantities of bramble, which could serve to reduce that plant's growth and prevent it from outcompeting the saplings of vulnerable tree and shrub species.

Dr. Amy Gresham, who is now based at the University of Reading after leading the at Bangor University, said, "The results of this study were surprising. We expected that fallow deer would primarily graze on the abundant grasses in the area's livestock pasture, diversifying their diet over winter to browse on trees as they would need to compensate for lower food availability outside of the plant growing season.

"In fact, we observed that the diversity of the diet narrowed over winter, with bramble being the most prominent food resource.

"Bramble can protect saplings from deer by providing a spiny barrier to browsing, however bramble can also swamp saplings of tree and shrub species, and rare woodland flowers, that do not tolerate deep shade. Deer herbivory may in fact regulate bramble growth and prevent it from outcompeting saplings and other woodland plants.

"If we can understand more about what deer are eating, we can design targeted management strategies to protect vulnerable tree and shrub species."

Perusing poo samples

The researchers spent two years studying the diet of a fallow deer (Dama dama) population in the Elwy Valley in Denbighshire. The deer are causing concerns for biodiversity conservation, woodland regeneration and timber production.

The research team, based in the Molecular Ecology & Evolution at Bangor laboratory, used a new technology—DNA metabarcoding—to sequence the plant DNA present in around 350 fallow deer poo samples. These were collected in three woodlands in the Elwy Valley area in spring, summer, autumn and winter between 2019 and 2021.

The research team identified the plants present in the poo and built a profile of the diet across seasons. They found that bramble (Rubus fruticosus agg.) was the deer's main food throughout the year, making up 80% of the diet in the winter months. Broadleaf trees and shrubs became more prominent in the diet in the spring and summer, while conifer trees were found in very few samples.