The importance of plant density, plant basal area and plant mass per unit basal area as factors influencing the herbage mass of some native perennial grasses.

Abstract

Four native perennial grasses, Aristida ramosa R.Br. (wire grass), Bothrioc.llloa macra (Steud) S.T. Blake (red grass), Spovo- bolus elongatus R.Br. (slender rats tail grass) and Stipa variabilis Hughes (corkscrew grass) were collected from 60 randomly allocated quadrats (0.16 m2) in a grazed unfertilized native pasture in November 1979. In each quadrat all plants of each species were counted, harvested individually and their basal areas were estimated. The mass of green leaf, green stem, dead herbage and total herbage of each species was estimated using the mean mass of the individual plants harvested in each of the quadrats. A method for determining the relative importance of the components of this herbage mass viz. plant density, basal area and mass per unit basal area is presented and these values are compared for each species. Plant density contributed significantly fP <0.05) to green leaf, green stem, dead and total herbage mass estimates of A. ramosa and S. elongatus; basal area to all herbage mass estimates of A. ramosa, S. elongatus and S. variabilis; and mass per unit basal area to all herbage mass estimates of A. ramosa and B. macra. The plant basal area of individual plants contributed signifi- cantly more (P <0.05) to the herbage mass estimate of S. vaviabilis and S, elongatus plants than did mass per unit basal area, whereas for B. rnacra mass per unit basal area was the significant (P < 0.05) component. Field procedures for estimating herbage mass and assessing the relative significance of its components are discussed and the extra time taken to collect plant density, plant basal area, and plant mass per unit basal area datais outlined.