Patterns in vascular plant species density in tall alpine herbfield along an increasing altitudinal gradient in an Australian alpine region

Abstract

Patterns in species density and richness per altitudinal interval have been found when sampling across plant-community boundaries, including in the largest contiguous alpine area in Australia. To see if similar patterns occur within a single community, vascular-plant composition was systematically sampled with replicate nested quadrats of increasing size (0.01, 0.06, 0.25, 1.00, 4.00, 25.00, 49.00 and 100-m2 size) sampled from ~1850-m to 2100-m altitude in tall alpine herbfield, Australia. The only significant relationships with altitude were quadratic relationships for the density of herb and graminoid species, with peak density at middle altitudes and a linear decline in total species richness with altitude for 0.06-m2 quadrats. The composition of 100-m2 quadrats was unrelated to altitude when tested with analysis of similarity for total composition, whereas the relationship was significant for growth-forms and the origin (local endemics, Australia endemics and weeds) of species. Location data from this, and 11 other studies were used to compare the species richness of more of the flora (183 species) in 50-m altitudinal bands. There were significant quadratic relationships for total species richness and the number of herb and shrub species, with a peak in richness at ~2000 m. Therefore, altitude does affect species richness overall in this alpine region, although it has only a weak effect on species density within the most common plant community.