THE CONTRIBUTION OF CLIMBING PLANTS TO SURFACE ACIDITY AND BIOPITTING EVIDENT AT THE UNIVERSITY OF OXFORD BOTANIC GARDEN, UK
Fieldwork was executed at the University of Oxford Botanic Garden located in central Oxford, UK in order to examine enlarged holes on the surface of a c. 380-year-old border wall comprised of Headington stone. There are bee hotels located in the walled section within the Garden, where it is thought that red mason bees are responsible for the holes. Manual counts of the holes, however, revealed no clear spatial trend of an increasing frequency closer to the bee hotels. Supplementary research was conducted in order to ascertain the cause of these noticeable masonry holes. A digital pH meter was employed on-site with runoff collection of distilled water to measure surface acidity, which could be responsible for initial pitting on these limestone walls that could then be exploited (and enlarged) by bees. However, these large holes, measuring up to 23.41 mm across, could not be the product of environmental acidity alone, as due to organic acids released by (climbing) plants also found in this area. This multivariate problem is considered from all biological angles, including consideration of the influence of acidity due to vegetation (climbing plants) and the influence of bees. Both may be required for the establishment of these weathering features and their enlargement to holes. Even though it is known that bees are capable of removing sand grains to enlarge concavities in walls, they are not known to bore through limestone, which is considered to be a relatively hard stone.
Limestone; bioweathering; pitting; pH; English ivy; solitary (red mason) bees.
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