A study of spatial pattern and its determinants amongst the species of a saxicolous lichen community at Jonas Rockslide, Jasper National Park, Alberta

The spatial patterning of saxicolous lichens is studied at Jonas Rockslide in the Rocky Mountains at Jasper National Park, Alberta, Canada. The rockslide is composed of quartzite sandstone blocks, ranges in altitude from 1500m to 2200m and is 3km in length and 1km wide. The sizes of the largest Rhizocarpon (sub-genus Rhizocarpon) thalli lead to the hypothesis that it is over 500 years old. Single rockfaces are sampled on altitudinal transects. Each rockface is sampled with a grid of points, retaining positional information, and the species of lichen present at each point is recorded. Environmental information such as aspect, altitude and slope of the rockface is also recorded at each rockface.;A canonical correspondence analysis, CANOCO, is used to investigate the correlation of environmental factors such as slope of the rockface and altitude of the rockface with lichen distributions over whole rockfaces divided into sections. The variables slope, altitude and insolation received are important correlates of lichen distributions overall, however, the lichens cannot be readily delimited into discrete groups.;Biotic interactions are investigated in a series of association analyses and thallus size data is used to investigate dynamic processes amongst the species present. The large number of small thalli indicates that this is a dynamic community with recruitment occurring into lichen populations. Associations between species reflect shared microhabitat requirements.;The genus Rhizocarpon is represented by twelve species at this site and raises the question of how so many apparently similar species can co-exist. Each Rhizocarpon species is found to occupy a different position in the complex of environmental gradients and thus competition between the members of this genus is likely to be small.;One hundred and six species of saxicolous lichens are recorded at this site, of which 21 have a cover value greater than 1%. An analysis using the within rockface positional information shows that a number of species are not randomly distributed over the rock surface. Some species are more often found on the upper and outer parts of the rockface, whereas others are more often on the lower and inner portions. These non-random distributions are hypothesised to reflect microenvironmental differences across a rockface and this is supported by the available microclimatic evidence.;The study reveals a complex and dynamic community of saxicolous lichens.