DiversiTree: diversifying our woodlands to increase resilience

The UK government plans to increase woodland cover as part of its plans to store more carbon, to mitigate climate change. However, many of the UK's trees are threatened by climate change and a range of pests and diseases, which might limit their ability to contribute to carbon storage and the wide range of other benefits delivered by woodlands. We therefore need to make our woodlands resilient to these future threats. Resilience is the ability of a system, such as a woodland, to recover from a disturbance. One commonly proposed approach to increase the resilience of woods is to increase their tree diversity. Thus, spreading the risk amongst many different trees, as we don't know exactly how each tree species will respond to climate change, nor what threats from pests and diseases they may face decades into the future. However, woodland managers have different perceptions of diversity, and how management may best deliver it, and we know that different tree species will support the woodland ecosystem in different ways. Therefore, it is important to combine stakeholders' knowledge with ecological knowledge to identify which tree species and management approaches best deliver diversification that increases resilience.

DiversiTree focuses on woods dominated by two conifer species, Scots Pine and Sitka Spruce, as in the year to March 2021 54% of all new woodland was coniferous. Scots Pine is the UK's only native conifer of economic significance. It is planted for timber production but is also the dominant species in the culturally iconic native Caledonian pinewoods. Scots Pine is at risk from the tree disease Dothistroma. Sitka Spruce is not native to Britain but is our most economically valuable tree species and is at risk from invasive bark beetles and climate change.

This project addresses four knowledge gaps related to the diversification of woodlands: 1) How do stakeholders understand forest diversity, their diversification strategies, and their visions and ambitions for diverse future forests? 2) Are the microbes found on the leaves of trees more diverse in woodlands with mixed tree species and does this help trees to better defend themselves against diseases? 3) How may diversification of tree species within a wood allow the continued support of woodland biodiversity? 4) How do we implement and communicate management strategies to increase woodland resilience?

To address these knowledge gaps, we work across disciplines bringing together ecologists, microbiologists, social scientists, and woodland managers. The Woodland Trust is embedded at the heart of our project to enable us to co-develop and check the feasibility of our results with practitioners. Results from interviews with woodland managers, focus groups and analyses of policy documents, will be used to improve knowledge of the options for woodland diversification, and both the enthusiasm for, and capacity to, implement diversification strategies.

The microbes on leaves are important for plant health. Utilizing existing long-term experiments, we will examine the microbes on the leaves of Scots Pine grown in monocultures and in mixed woods. We will assess if the diversity of microbes on a leaf increases as the diversity of tree species increases, and whether this enables the trees to resist existing diseases.
Surprising we don't have lists of which species use which trees. This information is required if we are to plant trees that will continue to support woodland biodiversity. We will collate data on the biodiversity hosted by Scots Pine and Sitka Spruce and assess which other tree species could also support the same biodiversity.

Finally, we bring the results together to co-develop with practitioners, management strategies for diversification and case studies illustrating how the results can be implemented. The results will be shared via videos, podcasts, social media, and practitioner notes in addition to publications in the scientific literature.