Evaluating the robustness of nature-based solutions: future resilience of sedum-based soft capping as a conservation approach for heritage sites in Britain and Ireland

Figures & data

Figure 1. Map showing the location and nature of 84 documented soft capping projects and trials, with inset map of sites in Britain and Ireland. Two notable natural soft cap growth sites are also included.

Figure 2. Sedum-based soft capping on masonry at (a) Godstow Abbey, Wolvercote, Oxford, England (Listed Grade II) installed in 2009 using sedum matting and (b) test walls in Wytham Woods, Oxfordshire, England, where sedum plugs were installed in 2008 around the cap edge (Wood et al., 2018). Areas primarily populated with sedums are highlighted with white dashed lines.

Figure 3. Schematic of (a) model inputs, (b) model runs, (c) model outputs and (d) data analysis used in this study to generate modelled presence likelihoods for four soft capping species (Sedum album, S. acre, S. anglicum and Saxifraga granulata).

Table 1. Rationale of record inclusion criteria.

Criteria of record	Rationale
Observation of in-situ plants	All records were of live plants. Given that these species have a long history and wide distribution in the study area, we assumed that they have occupied areas representative of their environmental niche.
Taken between 1970 and 2022	The baseline period for the environmental variables was 1970–2000 (Section Environmental Parameters) and, ideally, the distribution records would be from the same time period. However, prior to 2000, there was limited/very patchy recording of these species across Europe. Therefore, to ensure our observed records reflected the true European distribution, we extended the period to 2022. Thus, any changes in species distributions in the period 2001–2022 are associated with the baseline period, meaning the modelled cooler/wetter limits of a species’ distribution may be wider than in reality. Nevertheless, as the ability of these species to survive in the United Kingdom is more likely to be impacted by hotter and drier weather, the inclusion of more modern observational data was assumed to have little impact on the results.
Located between 30° to 70° N and −15° to 30° E	These spatial bounds were chosen to include southern, central and eastern Europe so that regions with current climates similar to future climates in Britain and Ireland were captured.
Reference coordinate precision of at least 3 km	The reference coordinate precision of each plant record is approximately equal to, or higher than, the resolution of the environmental data. This meant observations recorded at a hectad scale (10 km × 10 km square) were not included in this study.
Geographically unique	This removed duplicate records from the same locations, limiting sample bias in the dataset.

Figure 4. Comparative cumulative distributions of presence probabilities for terrestrial grid cells across Britain and Ireland with records for: (a) Sedum album, (b) S. acre, (c) S. anglicum and (d) Saxifraga granulata. The presence probabilities associated with 2% and 20% of the locations with a record of species presence are indicated with dot-dashed and dashed lines, respectively. Values below the 2% threshold, between 2 and 20% thresholds and above the 20% threshold are associated with a weak, moderate and strong likelihood of survival, respectively.

Figure 5. Habitat suitability for Sedum album, S. acre, S. anglicum and Saxifraga granulata in the recent past (1970–2000) and under low and high emission scenarios for mid- and end-century. Areas are coloured according to whether they have a strong (green), moderate (blue) or weak (red/brown) likelihood of presence.

Figure 6. Percentage of land area in England (a, e, i, m), Wales (b, f, j, n), Scotland (c, g, k, o) and Ireland (d, h, l, p) with a weak (red), moderate (blue) or strong (green) likelihood for Sedum album (a-d), S. acre (e-h), S. anglicum (i-l) and Saxifraga granulata (m-p) presence in the recent past (1970–2000), by mid-century and by end-century under low and high emission scenarios. Histograms showing the distributions of presence probabilities are provided in Figures S5–S8.

Figure 7. The latitudinal and longitudinal distribution of weak (red), moderate (blue) and strong (green) likelihoods under historic and future scenarios. Future distributions with notable change (as defined in section Thresholds) are shown in bold/opaque colours, while distributions with no notable change are shown with transparent colours.

Wood, C., Cathersides, A., & Viles, H. A. (2018). Soft capping on ruined masonry walls. https://research.historicengland.org.uk/Report.aspx?i=16216

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