Globally, woodland expansion is seen as one of the most effective solutions in the fight against climate change.
However, a new study has revealed that the level of growth required to cultivate the number of trees needed by UK targets is unlikely to be accomplished by natural methods alone.
Ecologists and environmental scientists at the University of Plymouth demonstrated that browsing behavior by livestock is a huge determinant of the growth and connection of scrappy UK upland oak woodlands — so-called ‘temperate rainforests’.
The study, concentrated on Dartmoor in South West England, discovered that the presence of livestock resulted in far fewer oak saplings surviving. When saplings did endure, they were smaller and in weaker condition, and rarely lived over 8 years old without protection.
Remarkably, however, disturbances by grazing livestock may not be all negative and its precise effect may depend on neighboring plant species.
For example, although poisonous bracken may help safeguard the youngest tree seedlings from grazing animals, excess bracken may diminish suitable conditions for oak sapling establishment because of increased competition for light.
If prudently managed, trampling by grazing livestock such as ponies and cattle can open up areas of bracken and thus help support the conditions that temperate rainforests need to grow.
The study evaluated the natural regeneration of oak saplings away from oak woodlands at several sites on Dartmoor and exposed that native oak cultivation was mostly confined to within 20 m of the closest adult tree.
This degree of natural expansion, the scientists say, is unsatisfactory to effectively aid carbon storage, biodiversity provision, and flood mitigation at the scale or speed required in these upland landscapes.
They propose instead tactically targeted interventions and selective planting into specific vegetation types to test the requirement for tree guards and other fortifications such as fences.
This, they say, could be used to enhance the environmental sensitivity of planting arrangements in guarded landscapes such as Dartmoor and other national parks, while decreasing their visual impact.
Dr. Thomas Murphy, presently an Industrial Research Fellow on the University’s Low Carbon Devon project, headed the research as part of his Ph.D. He said:
“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.
“Our findings however suggest the expansion of oak woodland into UK upland pasture systems is not a simple process. They may have a critical role to play, but these important temperate rainforests have been historically degraded and are now highly fragmented. Reversing that trend is likely to require strategic planting and informed livestock management.
"Getting this right, however, will warrant a delicate balancing act and close cooperation with a range of stakeholders, including particularly landowners and graziers, at a time when upland farms are facing severe financial pressures and there are ongoing changes in incentives.”
The study is published in Ecological Solutions and Evidence, a journal of the British Ecological Society, and lists a series of proposals for policymakers and landowners:
- Livestock grazing (mainly cattle) should be allowed close to adult native oak trees at the border of woodlands as they decrease thick and competitive vegetation;
- On areas where oak seedlings and saplings (1-3 years) have colonized, livestock should be barred for a minimum period of 12 years to boost sapling survival, growth, and establishment;
- On upland valley slopes where existing provision for ecosystem services is low, and woodland establishment is necessary for linking woodland habitat and fast soil hydrological recovery, strategic planting, and grazing management schemes should be supported;
- Older and larger oak saplings (4-7 years) could be grown immediately into areas where thick vegetation safeguards saplings from animal livestock.
This is the most recent study by the university to scrutinize the health and advantages of native trees on the upland slopes of Dartmoor.
The same research group has earlier had shown that the planting of native woodlands in upland areas could play a major role in blocking flash flooding which has progressively impacted communities throughout the UK in recent years.
They have also teamed up with the creative agency Just Enough Brave on the Trees for Climate project, which developed a set of resources engineered to boost the accessibility of research for better native woodland expansion.
Murphy, T, R., et al. (2022) Optimising opportunities for oak woodland expansion into upland pastures. Ecological Solutions and Evidence. doi.org/10.1002/2688-8319.12126.