Tree planting is often seen as a universal fix for climate change, biodiversity loss and even economies via carbon credits. But ask any conservation scientist at the GWCT and they’ll tell you that it is just not that simple.
When done well, woodland creation can restore landscapes, lock away carbon, and shelter declining wildlife. Done badly, it can fragment critical open habitats, increase predation risk, raise wildfire occurrence and displace already struggling species.
So how do we decide where a tree should be planted? GWCT research can help inform land managers on best practice concepts for planting trees based on different habitats, landscapes and species needs and assessing which factors apply to them.
Upland moorland and heath – Not all ‘empty’ land is spare
Across most of the UK’s uplands, moorlands and heaths may look like open, underused land. However, these are some of the most ecologically and culturally significant landscapes we have and they are home to highly specialised wildlife including grouse, mountain hares, curlew and even woodcock.
These species depend on large, unbroken stretches of heather, grassland and other vegetation unique to open moorland. GWCT research shows that curlew tend to avoid nesting close to woodland. This relationship is likely due to the increased predators such as foxes and crows associated with pockets of woodland. Meanwhile, data shows mountain hare populations thrive on well-managed grouse moors. However, recent modelling has shown hare occurrence is expected to decline by 7% due to habitat loss in the Cairngorms if the 350km² planned for woodland expansion goes ahead.
A crucial element linked to woodland expansion in this habitat is the expected loss of moorland management associated with the change in land use, particularly resulting in changes to vegetation and levels of predation management. More research is needed, as well as funding, to continue predation and habitat management to see if continued keepering of the land could help mitigate some of the negative effects of woodland plantations.
It is crucial that wetter moorland habitats such as wet heath, blanket bog, deep peat areas, and species-rich acid grasslands are preserved as open moorlands, and tree planting is avoided in these areas. Trees can dry up these habitats as well as fundamentally altering the characteristics of this landscape. Breaking up large moorland blocks fragments the habitat, providing cover for predators, and disrupting sightlines and access for species that rely on visibility and movement across open terrain, such as black grouse lekking sites.
Upland margins and transitional zones – Opportunities for smart planting
There is room for carefully designed woodland, especially along the margins of moorland, where small-scale, low-density planting can deliver climate benefits and wildlife gains.
Black grouse, for example, need both open moor and scattered native trees. In hard winters, GWCT data shows that birds near patches of birch, willow and rowan survived better thanks to the shelter and forage provided. Meanwhile, a study in 2020 found that active black grouse leks were only present in larger moorland areas. On average moorland patches with lekking birds were 26 times larger than the uninhabited moorland areas, highlighting that fragmentation is a real threat to this awe-inspiring behaviour.
Research on key species in this habitat suggest that using native broadleaf trees in small clusters or strips adjacent to rather than within moorland is essential. Evidence points towards maintaining open ground within planting areas including glades, rides and shrub-rich edges, and ensuring planting does not disrupt traditional management practices such as muirburn. Muirburn is a crucial tool for ensuring moorlands are maintained with a mosaic of heather ages and has been shown to support both habitat diversity as species like hares and grouse.
Wetlands, mire and heaths – Curlew Country
In lowland or valley-bottom landscapes, wet heaths and mires often sit alongside existing woodlands, making them tempting targets for planting. However, these areas are prime breeding areas for ground-nesting waders such as curlew and they can’t afford to lose them.
GWCT studies in the New Forest show curlews do best in wet heath and mire, where nest survival reaches 21% compared to just 5% in drier heath or grassland. Other GWCT research has found that predator activity is greater near woodland edges, with wader breeding success generally lower where woodland or scrub encroaches into open moorland. This pattern supports evidence from wider UK studies showing that predator impacts can extend hundreds of metres into open habitats from nearby tree cover.
Based on this it is best to avoid tree planting on lowland wet heath, fen, mire or bog – similar to that in the uplands. To protect open views and wetland integrity that curlew rely on for survival and population success, maintain buffer zones of at least 500m from known nesting sites. Helpfully, curlew are relatively site loyal, meaning it is possible to map and protect areas of known curlew nesting activity.
Wooded landscapes and forest interiors – Structure, not just area
In places already dominated by woodland, such as lowland plantation or ancient woodland remnants, there is scope for tree planting but this still needs proper planning and care.
Woodcock are one of our few woodland waders, they breed in open, young woodland and feed in surrounding fields. Recent GWCT research suggests that the age of woodland is crucial to their presence, with woodcock needing young, open woodland with glades. This habitat requires mixed staged planting to foster different aged trees, rather than dense, single-age conifer plantations, which offer little habitat value. When left to age, the canopy of single species woodland closes over time, causing a loss of understory diversity and valuable woodland floor habitat. This includes cover from predators as well as floral and insect diversity. In this context this understory diversity, linked to woodland age and structure, matters more than total tree count.
Many invertebrates such as butterflies as well as many plant species also benefit from mixed aged woodland with clearings. GWCT research has shown that woodland managed for pheasants have up to 32% more wild birds and twice as many butterflies. Broadly speaking, managing for game provides private funding and incentive for good woodland management, with knock-on benefits for wider wildlife. In contrast, there is less incentive to manage developing commercial plantations with wildlife in mind.
In a landscape devoid of all large herbivores that would have historically created woodland clearings, man-made rotational clearing can help support varied woodland ages and maintain openings as shrubby edges. Resurveying and thinning existing plantations could help bring them back into suitable condition for declining species, but support and further research is required.
Wildfire risk and tree choice – When trees make things worse
GWCT’s analysis of wildfire risk shows that poorly planned afforestation, especially with dense conifers, can raise fuel loads and lead to more intense, less manageable wildfires.
Gorse and heather can also grow tall and woody if left unmanaged and many areas of uplands and similar habitats across the globe are now seeing the devastating effect this can have when, inevitably, these go up in wildfires.
Wildfires not only release carbon, burn deep into the soil and threaten homes, they also destroy rare habitats and nesting wildlife. Avoiding monoculture and retaining grazing, other vegetation management or mix-use landscapes can help keep fuel loads down.
Conclusions
The wildlife that thrives in Britain’s open uplands and semi-natural grasslands does so not despite the landscape looking ‘empty’ but because of it. These places support life in subtle, often unseen ways.
Tree planting can enhance these landscapes but only if we respect the ecological roles that open spaces already play. As GWCT’s ever growing body of evidence shows, we can plant trees and restore biodiversity, we just need to do it in the right way.
Fostering natural regeneration of trees by protecting young shoots around existing woodland edges in the right areas, can be a positive step in the right direction for increasing tree abundance in some landscapes. This careful support for native species growing in desirable places is likely a more time and cost-efficient process via fostering young trees already set up for success.
Humans play a huge part of establishing and maintain habitats of all kinds, and it is the people with their boots on the ground, learning through experience what works that must be listened to.
Right tree, right place is not just a slogan but a survival strategy for species, habitats and conservation itself.