A quantitative state and transition model for the Mitchell grasslands of central western Queensland

Abstract

Concerns of reduced productivity and land degradation in the Mitchell grasslands of central western Queensland were addressed through a range monitoring program to interpret condition and trend. Botanical and edaphic parameters were recorded along piosphere and grazing gradients, and across fenceline impact areas, to maximise changes resulting from grazing. The Degradation Gradient Method was used in conjunction with State and Transition Models to develop models of rangeland dynamics and condition. States were found to be ordered along a degradation gradient, indicator species developed according to rainfall trends and transitions determined from field data and available literature. Astrebla spp. abundance declined with declining range condition and increasing grazing pressure, while annual grasses and forbs increased in dominance under poor range condition. Soil erosion increased and litter decreased with decreasing range condition. An approach to quantitatively define states within a variable rainfall environment based upon a time-series ordination analysis is described. The derived model could provide the interpretive framework necessary to integrate on-ground monitoring, remote sensing and geographic information systems to trace states and transitions at the paddock scale. However, further work is needed to determine the full catalogue of states and transitions and to refine the model for application at the paddock scale.

Rangelands at equilibrium and non-equilibrium: recent developments in the debate

“…Management of such systems should be opportunistic and take advantage of, or create, conditions which allow switches to a more desirable state. Although state-and-transition models are considered to characterize rangelands not at equilibrium (Westoby et al, 1989;Briske et al, 2003), they have been applied to rangelands in conjunction with succession-based models (Phelps and Bosch, 2002).…”

Managed livestock grazing is compatible with the maintenance of plant diversity in semidesert grasslands

“…sericuem, and Panicum decompositum) are widespread and abundant in Mitchell grasslands (Table 3), but have probably diminished with livestock grazing. Aristida latifolia has previously been recognized to indicate the early stages of degradation (Phelps and Bosch 2002), but this perspective may reflect its perception as a pest with seeds that irritate sheep and taint wool . Substantial increases in the relative abundance of Dichanthium sericeum occur in the Mitchell grassland during periods of above average rainfall (Orr 1981, Orr Notes: Life-form abbreviations are: AG, annual grass; AH, annual herb; PG, perennial grass; and PH, perennial herb.…”

“…Substantial increases in the relative abundance of Dichanthium sericeum occur in the Mitchell grassland during periods of above average rainfall (Orr 1981, Orr Notes: Life-form abbreviations are: AG, annual grass; AH, annual herb; PG, perennial grass; and PH, perennial herb. Evidence of grazing response was taken from the following studies: 1, Orr (1980); 2, Foran and Bastin (1984); 3, Orr and Evenson (1984); 4, Dorrough et al (2011);5, Fensham et al (1999); 6, Fensham and Skull (1999); 7, Phelps and Bosch (2002);8, McIntyre et al (2003); and 9, Lewis et al (2008). Palatability was taken from the following studies: 1, Cunningham et al (1981); and 2, Milson (2000).…”

State and Transition Models: Theory, Applications, and Challenges

“…Following the initial interest in the STM approach and continued, sporadic development of models for different plant communities (e.g., Phelps and Bosch 2002), there is little evidence that STMs have been formally incorporated into pastoral management in Australia, by either individual producers or by land management agencies (Watson and Novelly 2012). There is, however, anecdotal evidence that STMs have influenced how rangeland professionals communicate with land managers.…”