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National forestry bodies have a statutory duty to take steps to conserve biodiversity. To help evidence the impact of management and policies, we have co-developed an evidence based, transparent and repeatable approach for assessing the biodiversity potential of the National Forest Estate with Forestry & Land Scotland and Forestry England. A number of metrics, including extent, condition, connectivity and diversity are measured as indicators of the potential of the estate to support biodiversity. Using survey data on forest and habitat structure, these metrics are assigned to individual forest stands to enable reporting at regional and national scales. The resulting index can then be used to inform locally targeted action, national long-term monitoring and objective reporting. An online, interactive tool allows users to visualise and explore the mapped scores.
National Forest Estate Biodiversity Index development
There are seven stages in the development of the Biodiversity Index (Fig. 1). The first 6 stages were undertaken between March 2020-April 2021 whilst refinements and the 7th stage is being delivered in March 2021 – April 2022.
Fig.1 Development stage of the National Forest Biodiversity Index
1. Co-development of a framework (March 2020-April 2021)
The PFE Biodiversity Index approach was co-developed with the aim of meeting the goals set out in Fig 2. Results were provided for all Scottish Regions and the Yorkshire Region using data for 2019. We held a consultation and surveyed a group of representatives from Forestry & Land Scotland, Forestry England and Natural Resources Wales in early 2021 to gather feedback on the methods, outputs and associated interactive webtool for exploring the results online.
Fig. 2 Attributes of a Biodiversity Index for the National Forest Estate
2. Select indicator metrics
Thirty-eight candidate biodiversity ‘metrics’ – woodland or environmental features that are associated with woodland biodiversity according to the scientific literature and expert judgement were considered for inclusion in the Index. Sixteen metrics were taken forward based on the availability of reliable data at the required spatial and temporal resolution. Each selected metric was assigned to one of four groups of indicators in accordance with Defra's Tree Health Resilience Strategy Goals (2018) – diversity, extent, condition and connectivity (Fig.3).
3. Compile data and develop methods
Environmental spatial data including annually updated forest management information for each subcompartment of the National Forest Estate, were combined and analysed to produce values for each metric for each subcompartment. Metrics are either local level metrics or landscape level metrics (Fig 3). Local level metrics are measured at different local management scales: the subcompartment, the block woodland (containing a number of subcompartments) and/or a 1 km ecological neighbourhood around the block woodland. Landscape level metrics are measured at the scale of the Region/District - all subcompartments falling within a Region are therefore assigned the same landscape score.
Fig. 3 Schematic of the groups of biodiversity metrics, the scale at which they report and how they are combined into Biodiversity Indices
4. The online interactive visualisation webtool
A webtool was produced that allows FLS and FE to explore the PFE Biodiversity Index using R Shiny.
Fig 4. Screen shot of visualisation tool
5. Assess metric outputs
Outputs for individual metrics were inspected for ability to discriminate attribute represented, for their match to expectations and for redundancy of information provided. Where necessary, metrics were removed to avoid the risk of double counting (i.e. where they were highly correlated with other, more useful metrics).
6. Index compilation
The metrics were combined to provide single scores (Fig. 3). This ‘aggregation process’ is carried out over several steps:
Each subcompartment received a single score for each of these outputs. Values can range from 0 to 1 (low extent – high extent) for the baseline year (2019). We used the Wroclaw or dendric method when combining metric scores because this approach is not sensitive to zero values and it is not fully compensatory (this describes the degree to which the high score of one metric/indicator can compensate the low score of another). Equal weights were applied (each metric/indicator counted equally to a combined score) due to a lack of scientific evidence or agreed expert judgement upon which to base weights.
Phase 2 (March 2021 – April 2022)
We continue to collaborate on the development and application of the tool. Work will focus on:
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