Findings and Recommendations

The research began in 2021/22. A review of existing evidence was completed in 2021 and indicated that:

• Where existing mature woodland and hedgerows or isolated trees provide suitable seed sources and the site conditions are favourable, then natural colonisation provides the potential to expand tree cover relatively quickly (within five years). In other circumstances, there is a risk of little apparent colonisation progress in the short to medium term and the result can be a scrubland rather than woodland habitat. Therefore, natural colonisation depends primarily on choice of site, ground conditions and suitable seed source.
• Natural colonisation by trees and scrub is progressive and, as well as contributing towards increased woodland cover, it can potentially provide complex habitat mosaics of high biodiversity value. The projected biodiversity gains from natural colonisation processes (after first excluding grazers) include highly diverse transitional habitat that could be expected to last for 20 years or more.
• There may also be benefits to long-term carbon sequestration or storage. However, these are yet to be quantified. The unpredictability of natural colonisation may result in it being judged as less reliable in achieving rapid carbon storage when compared to tree planting or direct seeding systems.

Other results from the project are described for each of the science work streams.