This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
Cite this article
Fennell M, Wade M, Bacon KL.2018. Japanese knotweed (Fallopia japonica): An analysis of capacity to cause structural damage (compared to other plants) and typical rhizome extension. PeerJ Preprints6:e27023v1https://doi.org/10.7287/peerj.preprints.27023v1
Fallopia japonica (Japanese knotweed) is a well-known invasive alien species in the United Kingdom and elsewhere in Europe and North America. The plant is known to have a negative impact on local biodiversity, flood risk, and ecosystem services; but in the UK it is also considered to pose a significant risk to the structural integrity of buildings that are within 7 m of the above ground portions of the plant. This has led to the presence of the plant regularly being used to refuse mortgage applications. Despite the significant socioeconomic impacts of such automatic mortgage option restriction, little research has been conducted to investigate this issue. The ‘7 m rule’ is derived from widely adopted government guidance in the UK. This study considered if there is evidence to support this phenomenon in the literature, reports the findings of a survey of invasive species control contractors and property surveyors to determine if field observations support these assertions, and reports a case study of 68 properties, located on three streets in northern England where F. japonicawas recorded. Additionally, given the importance of proximity, the 7 m rule is also tested based on data collected during the excavation based removal of F. japonicafrom 81 sites. No support was found to suggest that F. japonicacauses significant damage to built structures, even when it is growing in close proximity to them and certainly no more damage than other plant species that are not subject to such stringent lending policies. It was found that the 7 m rule is not a statistically robust tool for estimating likely rhizome extension. F. japonica rhizome rarely extends more than 4 m from above ground plants and is typically found within 2 m for small stands and 2.5 m for large stands. Based on these findings, the practice of automatically restricting mortgage options for home buyers when F. japonicais present, is not commensurate with the risk.
This is a submission to PeerJ for review.
Survey results, collected from PCA and RICS contractors and surveyor, respectively
Tab 1: PCA member rhizome extent survey responses. Tab 2: PCA member structural damage survey responses. Tab 3: RICS member structural damage survey responses.