Understanding Why Grey Squirrels (Sciurus carolinensis) Bark Strip in British Woodlands: A Systematic Map

Abstract

Background: The damage to trees caused by grey squirrels in Britain undermines the UK Government's ambitious afforestation targets for expanding woodland area to sequester carbon. The motivations of grey squirrel bark stripping are poorly understood, hindering the development of non-lethal management options that target bark stripping. Aim: We provide a broad synthesis of the literature on the bark-stripping behaviour of squirrel species with the specific goal of identifying methods to understand and mitigate the bark-stripping behaviour of grey squirrels in Britain. Methods: We searched for articles that described or investigated the bark-stripping behaviour of squirrel species. Literature searches were conducted in English, Spanish, Simplified Chinese and Traditional Chinese using relevant platforms for literature-search databases. Information extracted from the articles included coding variables defined by study meta-data, study design and contextual variables for bark-stripping behaviour. Results: We identified 188 relevant articles on sciurid bark-stripping behaviour in North America, South America, Europe, Asia and Africa. Most studies were observational (65%), identifying important tree and stand characteristics associated with tree susceptibility to damage. Experimental studies (15%) largely aimed to identify methods to prevent damage caused by squirrels, with none finding an effective, practical and humane solution for preventing or reducing damage. Evidence for the causes of bark-stripping behaviours remains sparse, particularly for species that cause significant economic damage. Conclusion: Future research should prioritise experimental designs and interdisciplinary collaborations aiming to establish causal understanding. For the grey squirrel, we propose multiple hypotheses that warrant further investigation, including nutritional deficiencies, self-medication, scent-marking and agonistic behaviours.