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

摘要

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 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 mid-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 using 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) using 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 around 2000 m. Therefore altitude does affect species richness overall in this alpine region, but only has a weak effect on species density within the most common plant community.