Rewilding should aim to restore ecosystems whilst promoting biodiversity. It should inspire us to think of wild, diverse landscapes, rich with wildlife. Yet, in the United Kingdom, rewilding initiatives are becoming increasingly associated with plans to plant more trees. In 2018, government announced a £50 million scheme with the aim of planting 11 million trees by 2022. Since then, similar, smaller-scale plans have been adopted by landowners, private companies and conservation charities, who use terms like rewilding, reforestation and restoration interchangeably. In the midst of this, a debate has begun between those who advocate for natural regeneration and those who favour tree planting. What is clear from both sides, however, is the need for more trees. This growing trend, too frequently disguised as rewilding, is becoming increasingly problematic.  

Reforestation has become a central aim of rewilding discourse and projects. Tree-planting often takes place in huge exclosures where large herbivores, usually deer, are permanently removed by fences. This isn’t surprising, particularly in places like Scotland. A visit to the Scottish Highlands should be enough to persuade anyone of the devastating impact of deer and sheep there: the Caledonian forest has been reduced to a homogenous wasteland in many parts. We are aware of the loss of biodiversity that this has caused: the WWF Living Planet report found that land degradation contributed considerably to the dramatic decrease in UK wildlife populations. Yet, when tree-planting is implemented as a quick fix solution, ecosystem processes are ignored and biodiversity continues to be overlooked.  

The increasing popularity of reforestation has reached far beyond rewilding initiatives. There is an abundance of tree-focused charities in the UK, from Trees for Life to Trees for Cities and The Woodland Trust. There is also an increasing presence of trees on social media and a rise in planting campaigns for schools, organisations and individuals. The trend is even reflected in the scientific literature. A study published earlier this year made headlines when it found that an additional 0.9 billion hectares of land around the world are ‘suitable’ for converting to forest for the purpose of carbon capture. In the UK, this would mean a shift from one largely homogenous habitat to another, with the potential for native grasslands and moorlands to disappear altogether.

From social media to science, NGOs to the news, we are inspired by old tales and folklore surrounding trees, encouraged by stories of tree planting across the globe and angered by the decision of councils to fell and net. We are right to be, but we must also be aware of an increasing movement in social and political spheres towards trees becoming a panacea for the climate crisis and the biodiversity crisis.

Such a simplified approach is problematic for a number of reasons. Firstly, carbon sequestering is not an adequate way to address the climate crisis. It does not tackle our reliance on fossil fuels, nor our model of economics which dictates that we consume resources far beyond our means. Moreover, reaching climate targets should not be limited to carbon: maintaining permafrost and reducing the albedo effect are also important. Both are sensitive to land use and inhibited by tree planting.  Secondly, and more crucially, this present focus on afforestation ignores the biodiversity crisis altogether.

Even when the biodiversity crisis is addressed in tree-planting, discussion tends to focus on the need to avoid a monoculture, the dangers of introduced tree species and conifer plantations. However, even if we were to plant native, mixed broadleaf forests, this would be inadequate for promoting biodiversity. The failure in this thinking is a result of the outdated assumption that a forest is the end goal for nature. In this assumption, we dismiss the role of large herbivores as agents of disturbance and increased habitat heterogeneity in an ecosystem.

Perhaps we are unable to imagine a positive role for herbivores when we look at the barren hills of Wales, Scotland, The Lakes and Peak. The detrimental effect of herbivores on woodlands and vegetation has prevented us from seeing the value of their role in an ecosystem. Populations of large herbivores have risen far beyond their historical baseline across the UK; their predators have been missing for several centuries. Uncontrolled populations of deer, for example, have soared, aided further by the popularity of sporting estates in Scotland, where high numbers of deer are purposefully maintained. Since the agricultural revolution, domestic herbivores like sheep and cattle have also contributed to the depletion of the countryside in the UK. The resulting overpopulation of both wild and domesticated herbivores has led to overgrazing on a dramatic scale. We are left with a depleted landscape where saplings, scrub and other vegetation are unable to establish.

Large herbivores, at a more natural, lower population density, are fundamental for maintaining important ecosystem processes. For example, disturbance from herbivores through grazing, browsing and trampling is an important process for altering the structure of vegetation. Browsing and grazing have a pollarding or coppicing effect on vegetation, causing a greater number of branches, flowers and/or fruit to be produced. This in turn could support a greater number of birds, pollinators and invertebrates.

Disturbance from large herbivores is also important for creating a diverse range of habitats: from woody scrub and thicket to open pastures; from moorland and meadows to denser forest. In doing so, herbivores prevent succession to a single homogenous state – the closed canopy woodland. This forms a mosaic of different habitats for different forms of wildlife, allowing corn buntings to flourish on open moors and providing nightingales the shelter of scrub. Oaks and other light-demanding species also have room to grow in open groves, whilst bramble can develop to protect saplings. Herbivores also play an important role in seed dispersal and biogeochemical cycles: they transport nutrients and seeds through a landscape, helping vegetation to naturally regenerate.  Rewilding is increasingly envisioned as a way to return the United Kingdom to a forested landscape. Tree planting for the purposes of mitigating climate breakdown has strengthened this vision. Yet to see forest as the end goal ignores the evolutionary role of large herbivores in shaping vegetation structure, in keeping it shifting and in promoting biodiversity. We must recognise their value in our rewilding efforts and, in doing so, understand the resilience and diversity of heterogeneous landscapes.