Preparing to search
Natural colonisation occurs when tree seed reaches a site and establishes where woodland has not recently existed. This differs from natural regeneration where new trees establish within existing woodland or where woodland has recently been located.
Supporting woodland expansion through such natural processes, is another method with potential to contribute to current tree cover establishment targets. Natural colonisation has several potential benefits including reduced costs, increased biodiversity value and natural matching of trees/genetic stock to sites (Hutchings and Quine, 2021). However, evidence of the full range of outcomes associated with natural colonisation across different sites, and over different timescales is limited. Interdisciplinary studies investigating and quantifying the benefits and dis-benefits of natural colonisation, alongside the attitudes of landowners and managers towards this expansion strategy are lacking.
Interdisciplinary fieldwork aims to establish a robust methodology to assess the efficacy of ‘natural colonisation’ as an approach to establish new woodland and its impacts on biodiversity and above and below ground carbon.
Key questions being evidenced are:
Methodology
Areas of natural colonisation established within agriculturally dominated landscapes and initiated with the previous 10-20 years were selected. Each of the sites contained three distinct areas of woodland:
At least three rectangular transects were used to capture spatial variation across the sites. All sampling took place within these transects: the whole transect was divided into sub-transects for terrestrial laser scanning and photogrammetry flights (results to be presented in the next phase of the project) and plots positioned along the transect were used to manually sample tree size and species, as well as other vegetation cover. Soil samples were taken across the same transects.
Preliminary findings year 1 (2021/22)
Trees appear to be colonising the studied sites in three main ways, related to tree dispersal mechanisms, potentially ground preparation and browsing pressure:
However, this first year pilot study has demonstrated the high degree of variability within and between the sites which need to be investigated further to be able to provide generalisable evidence.
Work in year 2 (2022/23) will expand the sample of sites to include a wider range of ages and starting land use.
This research aims to understand why different kinds of land managers may or may not be likely to utilise natural colonisation as a tree expansion strategy.
Work conducted in 2021/22 characterised different land managers, their understandings of and attitudes towards natural colonisation, barriers to uptake, and support and information needs.
The research found variation in how natural colonisation is understood by different land managers, as well as in the language used to refer to it as an expansion strategy. Further, it highlighted land managers’ need for knowledge and support in the form of successful examples, guides on best practice, and information about grants.
Following on from these findings, work is being conducted in 2023/24 to explore the language and messaging surrounding natural colonisation, to support more effective engagement and uptake of natural colonisation with different kinds of land managers. Work is also underway to identify which incentive schemes supporting natural colonisation have or have not been taken up by which kinds of land managers and the reasons behind this, to inform future scheme design and delivery.
This is being achieved by addressing the following questions:
Methodology
Year 1 Research
Objectives
In 2021/22 the research aimed to understand and characterise different kinds of land managers and why they may or may not be likely to utilise natural colonisation as an expansion strategy. It achieved this by answering the questions:
Findings and Recommendations from year 1
The majority of land manager across all types understand natural colonisation as an effective strategy for the provision of biodiversity/natural habitat and nature restoration, rather than to achieve other benefits of woodland creation (e.g. carbon sequestration, timber production).
Land managers were found to either select sites for natural colonisation close to existing areas of woodland, or undertake ‘enrichment’ planting of trees into areas of natural colonisation, as a strategy to spread risk and ensure their objectives for their land were achieved.
Land managers and their advisors require tools and guidance, particularly to support site selection and assess the likely outcomes of natural colonisation processes, relevant to their land holding type and landscape context.
Research in 2023/24 will expand on initial work further understanding those factors affecting different land managers decisions to use natural colonisation as a viable woodland expansion strategy.
A review of the literature found very little information on how carbon in woodland natural colonisation areas compares to planted areas of similar age. This part of the wider study set out to provide estimates of both tree biomass and soil carbon on natural colonised sites compared to adjacent tree planting of similar age.
Methodology
Areas of natural colonisation established within agriculturally dominated landscapes and initiated with the previous 10-20 years were selected. Each of the sites contained three distinct areas of woodland:
At least three rectangular transects were used to capture spatial variation across the different areas. All sampling took place within these transects: the whole transect was divided into sub-transects for terrestrial laser scanning and photogrammetry flights (results to be presented in the next phase of the project) and plots positioned along the transect were used to manually sample tree size and species, as well as other vegetation cover. Soil samples were taken across the same transects.
Preliminary findings and Latest updates to June 2022
Soil samples have been collected and are currently being analysed. Vegetation biomass has been quantified along each transect using traditional methods and terrestrial laser scanning and photogrammetry flights have been undertaken
Our research addresses these evidence gaps through three strands working on shared range of sites of across land in predominately agricultural contexts:
The research began in 2021/22. A review of existing evidence was completed in 2021 and indicated that:
Other results from the project are described for each of the science workstreams.