Woodland expansion is being touted as one of the most effective ways of soaking up excess atmospheric carbon dioxide, and native hardwoods are regarded as the best choice of tree for biodiversity – but left to themselves, native woodlands will not achieve the level of growth that the climate crisis demands.

Environmental scientists and ecologists at the University of Plymouth have released research indicating that browsing behaviour by livestock is a major determinant of the expansion and connection of the UK's fragmented upland oak woodlands, the so-called ‘temperate rainforests’ beloved by ecologists.

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 was not always a negative factor, particularly when bracken was present.

Researchers found that, if carefully managed, trampling by browsing livestock such as cattle and ponies could 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 20metres of the nearest adult tree. This level of natural expansion, the researchers said, was insufficient to adequately aid carbon storage, flood mitigation and biodiversity provision at the pace or scale required in these upland landscapes.

So instead, they suggest strategically targeted interventions and selective planting into certain vegetation types to test the need for tree guards and other protection such as fences.

Read more: Woodland cover increases 41% at Beinn Eighe

Dr Thomas Murphy, currently an Industrial Research Fellow on the University’s Low Carbon Devon project, said: “Our findings 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 newly published research makes a series of recommendations for landowners and policy makers:

• Livestock grazing (particularly cattle) should be encouraged close to adult native oak trees at the edge of woodlands as they reduce dense and competitive vegetation;

• On sites where oak seedlings and saplings (One to three years old) have colonised, livestock should be excluded for a minimum period of 12 years to increase sapling survival, growth and establishment;

• On upland valley slopes where current ecosystem services provision is low and woodland establishment is required for connecting woodland habitat and rapid soil hydrological recovery, strategic planting and grazing management schemes should be encouraged;

• Older and larger oak saplings (four to seven years) could be planted directly into areas where dense vegetation protects saplings from animal livestock.