The potential of applying soft capping approach on earthen and masonry built heritage

Cultural heritage sites worldwide are increasingly threatened by deterioration due to natural erosion and the intensified effects of climate change. Soft capping, an environmentally friendly approach for protecting built heritage using plants, has been underexplored from a biological perspective. This article aims to review studies on soft capping applied to earthen and masonry heritage from the 1980s to the present. The findings categorise soft capping into four types: Phototropic biofilms- and Lichen-capping, Bryophyte-capping, Spermatophyte-capping and Mixed plants-capping. The selection of soft capping type depends on the site's microclimates, building materials and the structure's geometry. Soft capping helps to regulate the microclimates of affected structures, slowing deterioration and enhancing their long-term sustainability. Additionally, it offers flexible adaptation to individual cases for optimal protection. Despite the considerable benefits of soft capping, further research and expanded databases are necessary to better understand factors such as type selection, composition, protective efficacy and limitations. This knowledge will enable more informed conservation strategies for applying soft capping to heritage sites in the future.