Plant Life-History Attributes: Their Relationship to Disturbance Response in Herbaceous Vegetation

Abstract

I Species composition and disturbance state (level of soil disturbance, grazing and water addition) were recorded for 120 (30-m2) plots in temperate grassland of the New England Tablelands (Australia). Three different classificatory schemes were used, based on (a) life-form (sensu Raunkiaer); (b) dispersal unit morphology and (c) vegetative reproduction. We analysed the effects of the different disturbance types and intensities on number and proportion of species belonging to these groups. The results were used to describe the spectrum of life-histories likely to be present at sites in different states of exogenous disturbance. 2 Soil disturbed sites had proportionately more therophytes, versatile/flat rosettes and wind dispersed species. Two features are likely to lead to success in soil disturbed sites: ability to colonize open space (e.g. therophytes, wind dispersal) and capacity to capture resources effectively (e.g. flat architecture of rosettes). Non-disturbed sites had more geophytes, chamaephytes, phanerophytes, proto-hemicryptophytes and erect rosettes, with greater numbers of vegetatively reproducing species. 3 Heavily grazed sites had higher proportions of therophytes and versatile/flat rosettes and species with mobile seeds than sites with light grazing. Moderately grazed sites had increased proportions of versatile and erect rosettes and more species with adhesive seeds (mainly grasses). Lightly grazed sites had a greater diversity in terms of evenness of all life-forms, dispersal morphologies and reproductive modes. 4 Water enriched sites had fewer geophytes and phanerophytes and some chamaephytes, erect rosettes and proto-hemicryptophytes. This loss was only partially compensated by a gain in versatile and partial rosettes but richness decreased overall. Water enrichment was unrelated to dispersal unit morphology or the potential for vegetative reproduction. 5 Of the three attributes examined, life-form was most useful in characterizing community response to different disturbance types. Traits related to regeneration (seed morphology and capacity of vegetative reproduction) were relevant to soil disturbance only. Our results support the use of such classifications for monitoring the effects of disturbance.