Niche separation of bryophytes in grikes of the limestone pavements of northern England

The limestone pavements of northern England vary greatly from the wooded pavements of Morecambe Bay to the large areas of open pavement in Yorkshire. The diverse morphology of limestone pavements underpins biodiversity allowing vegetation to occupy different ecological niches. The grikes of limestone pavements create a protected, humid and shaded space suitable for woodland plants with a bryophyte flora that is unique and species rich due to the high proportion of heterogenous microhabitats. The niche separation of bryophytes has been observed in multiple studies, typically focusing on moisture. Based on a 70-year-old study from the British Ecological Society, the niche separation of bryophytes in a matrix of depth and light is observed in the grikes of open limestone pavements. Ten plots of open pavement (less than 10% scrub cover) and seven plots of wooded pavement (mature trees, greater than 10% scrub cover) of 250 m2 across eight sites were selected. 30 grikes at each plot were chosen using strategic random sampling and species, light levels, and grike characteristics were recorded. Data was analysed using R version 4.4.2 and generalised additive models to assess relationships between light, depth and species organisation. 3464 observations were made across all sites comprising a total of 27 species. In open pavements it was found that in the first 50 cm of the grike the light levels were variable allowing for generalist species to grow with niche overlap. Deeper down in the grike where there was a constant percentage reduction in light, there was greater niche separation. In contrast wooded pavements showed a greater overlap of species all growing at the top of the grike with a much lower diversity compared to the open pavements. These findings show that limestone pavements should be managed to allow for a mosaic of vegetation without complete tree cover.