Giving Lower Plants the Upper Hand

The mild, wet conditions in the south-west of England, brought about by the Gulf Stream and our proximity to the sea, have created perfect conditions for the establishment of Atlantic Woodlands. These moist, humid woods—also known as Celtic Rainforests—are brimming with lush green ferns, carpets of mosses and lichens covering tree trunks and hanging from the canopies. Building Resilience in South West Woodlands is a new Heritage Lottery-funded project—led by Plantlife—that addresses the challenges faced by the Atlantic woodlands of Devon, Somerset and Cornwall.

The project received development funding to test out techniques and develop plans so that an application for a full 3-year project could be made later in 2018. The project explores ways Atlantic Woodlands could be made more resilient to climate change, tree disease, invasive species and changes in woodland management. At the same time the project will raise awareness of the importance of lichens and mosses through involving schools, local communities, volunteers and land managers in monitoring and studying the woodlands and their unique flora.

The project at East Dartmoor NNR focusses on the reserve’s ancient boundaries as this is often where the oldest, lichen-rich trees are found. These linear features spread across much of the reserve forming corridors between different areas. Twelve boundaries were selected in total to link together areas with known lichen interest, and to bring them into favourable management so that these lichens can flourish and colonise new areas.

If the full project gets the go-ahead, its objectives will be to conduct management on-and-around these boundaries to increase the abundance and diversity of mosses and lichens. There will also be a significant monitoring component to the project, so that lessons learnt from this management may be captured and shared with other woodland owners. To achieve this, survey work will be conducted by volunteers at different points in time— using a citizen-science approach: 1) prior to management to capture the current status of the boundaries, 2) after management to show changes in light levels and 3) several years after management to show changes in the moss and lichen abundance as well as changes to the ground flora and shrub composition.

Vinnimore boundary, running along parts of the Old Manaton Road, was selected as a trial site for this surveying and management work. The boundary consists of an earth bank and a row of beautiful, ancient oak trees with a thick holly understorey. In October and November last year, 12 volunteers received training from Plantlife and surveyed 660m of the boundary, encompassing 25 trees. All of the oaks had mosses and lichens growing on them, but whilst the coverage of mosses was higher on the trees than lichens, more lichen species were found. Crustose lichens, which form a thin layer on the trunks of trees, were found on all of the surveyed tree trunks. Fruticose lichens, which consist of a branched shrub-like thallus, were only found on three trunks. They are currently more likely to be found in the canopies of these trees where there is more light.

Holly was clearly very abundant on the banks, and it is highly likely this is suppressing other tree seedlings, as well as lichens and mosses. After the boundary survey was complete contractors were instructed to thin-out the holly, leaving or pollarding a small proportion as it provides an important habitat to a host of invertebrates and lichens. Another survey by our volunteers immediately after the management work showed that there was an 80% reduction in the number of holly trees. This is expected to lead to a substantial increase in the levels of light reaching the boundary. Future summer surveys will attempt to quantify the changes in light levels reaching the boundaries by estimating the percentage canopy openness using visual estimates, and using sophisticated fisheye photography to calculate light levels reaching the tree-trunks. Unfortunately these surveys were not able to show this as they were conducted in the winter when the trees were leafless. As demonstrated below though, the survey photographs clearly show a difference in the abundance of holly surrounding the oaks.

Management will significantly increase the levels of light reaching the trunks of ancient trees, benefiting the lichens found there

It will be interesting to see how the removal of holly and other shade-casting vegetation changes the composition of the ancient boundaries. We hope to see more oak, hazel and rowan seedlings, and more ferns, in the next few years of monitoring. We should also start to see changes in the lichens on the trunks, though some of this change will happen more gradually. As more light is being let in, it will be important to monitor whether bracken and bramble cover increase, as these could also suppress lichens and bryophytes on the lower trunks, and ferns on the ground.

The next steps for this project will be to gain a better understanding of the other 11 ancient boundaries across the reserve. We’ve already started mapping the species of trees and their densities along the boundaries to inform future management for mosses and lichens. One of the key results from this exercise was to highlight the individuality of each boundary; as a result each boundary is likely to harbour a different mixture of mosses and lichens and will have its own set of challenges in terms of management.

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Example of a map showing the survey results from one of the ancient boundaries

We’d like to say a big thank you to all the volunteers that helped us to survey Vinnimore boundary – we couldn’t have done it without you!

If you’d like to get involved in our next round of summer surveying please do get in touch by contacting – Natural England, Yarner Wood Office on 01626 832 330 or by contacting Plantlife 

Written By Daniel Brown, Conservation Assistant 

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