Biomass allocation near an alpine treeline: Causes and consequences for diversity

Patterns of biomass allocation and species richness were examined along an altitude gradient (1 600 - 2 100 m) near the upper limit of trees and shrubs in the Snowy Mountains of southeastern Australia. Stem mass decreased significantly with increasing altitude, flower mass increased with altitude, but root and leaf mass did not vary. Root: shoot ratios and leaf and flower allocation increased significantly with altitude whilst stem allocation decreased significantly. Because stems comprised up to 80% of community biomass, most of the variation in allocation of other biomass components and root: shoot ratios were simply reflections of variation in absolute stem mass. Variation in stem mass was produced by phenotypic plasticity as well as a lack of stemmed species at high altitudes. Tree seedlings grown without neighbours for two years showed significantly higher stem allocation at low altitudes than at high altitudes. Two common stemless species were found only at high altitudes whilst a third occurred at all altitudes. Species richness was greatest at intermediate altitudes where maximum overlap occurred between stemmed and stemless species.