Seeking the trees: a rewilding diary by Emily Warner

In this fifth extract from Emily Warner’s rewilding diary for The Clearing, she reflects on her work comparing and documenting regenerating plant communities in the ungrazed heathland and forest, in Glen Affric in the Scottish Highlands. In this latest edition Emily considers deer and trees, and their complex relationship.

Seeking the trees

Absent from this story so far, but their impact ever present in the forest and character of the landscape, are the deer. The fences exclude them from the regenerating forest, but more widely it is clear that they are abundant. The deer took on an almost mythical aura during the summer, we saw little of them, but their marks and impact provided a clue to their number. Then one evening, emerging from the bothy, we were confronted by a herd. Their heads turned towards us and we attempted to count the pairs of ears, pricked above wary and curious faces. We stopped when we got to fifty, struggling to pick apart each shadowy individual, until suddenly our threat became too much, and with a gathering trot they moved up the glen.

Of course, the deer and the trees are inextricably linked, the deer are the engineers of the forest, they hold the key to its destiny, yet themselves rely upon it: a delicate balance. Much as we humans have played a role in the landscape, erecting fences and planting trees in the present, clearing forest and farming land as we go deeper into the past, the deer also influence the trajectory of their habitat. Unconscious of their future, the deer rip and tear at the young saplings, gorging on the protein rich food source in the understorey of the forest. The forest is a key resource for a species that is a woodland animal, providing shelter during the harsh Scottish winters and a nutritious food source in the understorey shrubs and regenerating trees. The grazed hillsides that are almost ubiquitous throughout the Scottish Highlands emphasise the deer’s effectiveness at preventing natural forest regeneration.

To document the extent of the deer’s impacts we conducted seedling surveys across the survey plots, comparing the grazed treeless heathland to the regenerating ungrazed forest, and comparing that to grazed and ungrazed areas of mature forest. Counting the seedlings within the boundaries of each plot was an absorbing task. Our search was meticulous, and hopefully exhaustive, but challenged by boulders, leggy heather, dense bracken and sprawling willows. Two things were marked: seedlings occur much less frequently in the grazed treeless areas and when they do occur outside the fence, they are maintained in a bonsai state by constant grazing. Hidden below the shrub layer are tiny stunted seedlings that have been grazed back repeatedly by deer, the evidence of repeated false starts described in their contorted form. In the grazed treeless plots not a single seedling taller than the protective ground layer of shrubs was found.

It became clear that the combination of the presence of trees and absence of grazing has a complex effect on the development of the next generation of trees, influencing both the species present and their potential to grow. In the mature forest plots, rowan seedlings were more prevalent than in any of the other plots we sampled. Hinting at the birds that must perch amongst the branches of the mature trees, releasing the rowan seeds in their droppings. As a result, even in the grazed plots, rowan seedlings were surprisingly abundant. Despite this, the effects of grazing were striking: of the 360 rowan seedlings that were found across the grazed mature forest plots only two had reached a height of more than 0.5 m. Rowan is one of the most palatable Caledonian forest species, and where the deer have access to it they selectively remove it from the forest. In contrast, the ungrazed mature forest plots also harboured abundant rowan seedlings, but covering a healthy spectrum of heights from less than 0.5 m to taller than 1.5 m.

The relationship between the future of the forest in this landscape and the future of the deer is complicated further by a third dimension: people. For many, the bare and treeless hillsides of the Scottish Highlands represent an important cultural landscape, one maintained and managed for the sport of deer stalking. To a certain extent, the numbers of deer present in the landscape reflect the will of large sporting estates, which generate an income based around stalking deer. However, in a landscape with no natural predators and with the human desire to maintain the recreational opportunities that large deer populations provide, the deer population is booming. Growing numbers of deer act in direct opposition to the regeneration of the forest, and overall this scenario also compromises the health of the deer populations. The increasing population of deer has occurred in parallel with a decline in the condition of the animals, living in a landscape without the forest habitat that should support them.

The fences provide an impermanent solution to the deer problem. The smaller roe deer can often squeeze under or around the gates, plundering the young trees inside the enclosure. Whilst the fences themselves are subject to the unrelenting Scottish winters, and require constant checking and maintenance to ensure they continue to act as a defence against deer. In one enclosure, a 10 m strip of fencing had been crushed by a small landslide. Inside, the marks of the deer were everywhere. Paths had been worn through the undergrowth, and areas of trees that had been used for shelter were stripped of their bark. The tastes of the deer were also clear: the palatable rowan trees had suffered particularly, and we encountered many torn and snapped saplings.

The deer are a direct barrier to forest restoration: they clearly prevent the regeneration of the forest and alter the composition of the tree community that does manage to regenerate. However, they do have a role to play in the ecosystem, and in lower numbers the level of disturbance that they would create could actually be positive. Add to this the conflicting human investment in different deer levels and you have a seemingly intractable problem. The fences are a way of allowing trees to regenerate and a diverse seedling community to grow up, but in the longer term we must aim for a more sustainable solution and a naturally regulated ecosystem where clumsy human interventions are no longer needed.

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Emily Warner is a PhD student based at the Departments of Plant Sciences and Zoology at the University of Oxford. Her research aims to understand the benefits of replanting native forest, with a particular focus on the uplands of the United Kingdom.

Photography by the author.