Biocomplexity, Spatial Scale, and Fragmentation: Implications for Arid and Semi-arid Ecosystems (SCALE)

Dalrymple Shire, Northern Queensland, Australia

Dalrymple Shire covers 66,709 km2 of the Burdekin River catchment in northern Queensland (roughly the size of the Republic of Ireland). The shire is framed by the Great Dividing Range to the West and coastal ranges to the east. There is a strong rainfall gradient, with an average of 1200 mm of precipitation in the northeast to 500 mm in the southwest. Precipitation is highly seasonal with 80% of rain falling in the summer months between December and April. Interannual variation in rainfall is high (CV% 30-48), and El Niño events are associated with drier than average conditions. Open eucalypt woodlands are the dominant vegetation type in the region. The most extensive grassland community is associated with Black Speargrass (Heteropogon contortus) but these areas were probably dominated by kangaroo grass (Themeda triandra var australis) prior to European settlement. Over the past 30 years, many of these areas have been invaded by Indian couch (Bothriochloa pertusa), an exotic, annual, stoloniferous grass. The Shire contains a variety of soil types, from relatively nutrient-rich, self-mulching clays of volcanic origin to nutrient-poor sandy duplexes. These soil types support vegetation communities that differ in species composition, seasonality, and forage production. Heterogeneity at the landscape scale results from the complex of soil and vegetation types and other topographic features, such as the border ranges, and the ephemeral and permanent watercourses. Extensive grazing has been the dominant land use since European settlement, with leasehold of public lands predominating land tenure.