There is global recognition that woodland expansion could be one of the most effective solutions in the fight against climate change.
However, new research has shown that the level of growth needed to produce the amount of trees required by UK targets is unlikely to be achieved through natural means alone.
Environmental scientists and ecologists at the University of Plymouth showed that browsing behaviour by livestock is a major determinant of the expansion and connection of fragmented UK upland oak woodlands – so-called ‘temperate rainforests’.
The study, focused on Dartmoor in South West England, found the presence of livestock led to far fewer oak saplings surviving. When saplings did survive, they were smaller and in poorer condition, and seldom lived beyond eight years old without protection.
Interestingly, however, disturbance by grazing livestock may not be all bad and its precise impact may depend on surrounding plant species.
For example, although toxic bracken may help protect the youngest tree seedlings from grazing animals, too much bracken may reduce suitable conditions for oak sapling establishment due to increased competition for light.
If carefully managed, trampling by browsing livestock such as cattle and ponies can open up areas of bracken and so help support the conditions for temperate rainforests to expand.
The study assessed the natural regeneration of oak saplings away from oak woodlands at multiple sites on Dartmoor and showed that native oak establishment was largely confined to within 20m of the nearest adult tree.
This level of natural expansion, the researchers say, is insufficient to adequately aid carbon storage, flood mitigation and biodiversity provision at the pace or scale required in these upland landscapes.
They suggest instead strategically targeted interventions and selective planting into certain vegetation types to test the need for tree guards and other protection such as fences.
This, they say, could be used to improve the environmental sensitivity of planting schemes in protected landscapes such as Dartmoor and other National Parks, while reducing their visual impact.
“The planting of trees and an end to deforestation are increasingly being highlighted as low cost and environmentally sensitive mechanisms to combat climate change. These measures have been factored into the net-zero agendas of UK and other governments, with world leaders also pledging to address the issue during COP26 in Glasgow last year.