| dc.description.abstract |
Factors contributing to changes in the condition of saltbush communities (Airiplcs ~wicaria) in the Riverine Plain andBarrier Range regions of New South Wales were measured under a variety of seasonal situations. Groups of eight plots, rcpresentinga range of past grazing intensity, were established at each location and measurements were made of species biomass,canopy cover and frequency, forage availability and soil fertility.In both regions, high graz,ing intensity was characterized by the elimination of the saltbush (A. ~~esicaria) and an increasein other species, such as Astwbla (mitchell grass), Sclc3rokarrza spp. (copperburrs), annual Airiplrx spp. and a wide range ofephenleral species. These changes were best characterized by canopy cover measurements which gave a quantitative assessruentof the vegetation changes (in contrast to frequency) and gave values that were less seasonally variable than biomass. Up to 83species were recorded, but these were aggrcpated into approximately 9 groups to simplify the collection and analysis of data,without loss of information.On the Barrier Range site, the A. ~csic'aria was replaced by palatable specics, so that thcre was little loss of overall forageproduction. Similarly, there was little cvidence of loss of soil fertility, as rneasured by various measures of soil nitrogen, availablephosphorus and oraanic carbon. There was no erosion on these sites, although this may occur on other saltbush communitiesthat grow on texture contrast soils.On the basis of these results? four separate indices of condition are proposed for saltbush cotnniunities. These arc basedon the n~easurement in the growing season of the canopy cover of major perennial and biennial species or specics groups. Theyare (i) the relative cover of A. 11rsicariu (the major observable change in thcse communities), (ii) the relative total cover ofdesirable forage species (an index of forase productivity), (iii) pcrccntage similarity (an index of conmunity change for conservationpurposes), and (iv) the relative area of eroded soil surface. |
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