The lichens of chalk grassland

Abstract

Abstract: Following a nationwide survey, the lichen vegetation associated with chalk grassland in England is described. The flora can be divided into species associated with flints (78 spp.), those found on chalk pebbles (65) and those occurring on the ground (72). Factors governing the distribution of the species were investigated. An important determinant of the flint assemblage is the degree of surface leaching, which is linked to stability; large flints embedded in turf are particularly rich. Chalk-pebble lichens reach their maximum development at sites where faulting or other influences have hardened the substratum. Terricolous species have rather specialized requirements, being favoured by stresses associated with nutrient depletion, past disturbance, soil compaction, drought, rabbits, trampling by shoes (rather than hooves), and the presence of a small loess fraction in the soil. On both a national and a local scale, climate has been demonstrated to affect the distribution of certain species. Guidelines on the assessment of localities for conservation are provided and used to identify elite sites. A recent decline in the extent and species diversity of terricolous communities is giving cause for concern. Management requirements for conservation are discussed. They include recognizing the importance of intermittent disturbance; most of the richest sites are less than a hundred years old. The lichen flora has affinities with that present in urban areas. The survey provides an example of the importance of historical factors in determining the ecology of lichen communities in the cultural landscape.