Cover and floristics of microphytic soil crusts in relation to indices of landscape health

An extensive field survey of 282 sites over 500 000 km(2) of rangeland in eastern Australia was carried out to investigate the relationships between cover and floristics of microphytic soil crusts and indices of landscape health. Empirical quadrat-based data were used to calculate three indices of landscape health (soil stability, infiltration capacity and nutrient status) according to the method of Tongway (1994). Analyses were based on a subset of 104 sites from landscapes dominated by red earths and calcareous earths, where the loss of microphytic crust cover is indicative of a loss in soil productive potential. Crust cover and floristics were further compared with an objective but widely used method of assessing rangeland condition based on the use of photostandards. Crust cover was a significant though weak predictor of stability of calcareous earth soils only (P < 0.001, R-2 = 0.106). On red earths, cover was a significant descriptor of rangeland condition (P < 0.001, R-2 = 0.171). However, overall, the percentage of the soil occupied by soil crusts was regarded a poor predictor of landscape health. Generally, increases in the number of lichen and bryophyte taxa at a site were associated with increasing rangeland condition (P < 0.001, R-2 = 0.178), landscape stability (P = 0.047, R-2 = 0.027) and nutrient status (P < 0.001, R-2 = 0.115), though these relationships varied according to soil type. Canonical Correspondence Analyses indicated that some Lichens and bryophytes were consistently associated with either stable, good condition sites (Xanthoparmelia spp., Catapyrenium lacinulatum, Buellia subcoronata, Aloina bifrons, Riccia lamellosa, Fossombronia spp.) or unstable, poor condition sites (Heterodea benugleholei, Cladonia spp., Barbula calycina, Bryum spp., Desmatodon convolutus, Eccremidium arcuatum). The majority of taxa however had no strong affinity with the four indices of landscape health. When easily recognisable morphological groups of lichens were related to landscape health indices, the group comprising yellow-green foliose lichen was the most strongly associated with stable, healthy sites. The results suggest that disturbances influencing soil stability and soil surface condition such as trampling and fire are likely to lead to changes in the composition of soil crust communities.