My research covers the broad areas of rangeland ecology, specifically the effects of animals (ecosystem engineers) on soil processes, ecology of desert soil crusts, and monitoring of soil and rangeland health. The focus of my research is on the semi-arid woodlands of eastern Australia, and I have long-term research interests in west-central Idaho and the south-western Chihuahuan desert in the western United States.

 

Animals can influence plants and other animals in a variety of different ways, either directly through predation, competition or facilitation, or indirectly through their activities. These indirect, non-trophic effects include activities such as consuming material or moving sediment around in the landscape. This latter type of effect has recently been termed ecosystem engineering;. Ecosystem engineering occurs when animals disturb the soil while foraging or creating bedding sites.

 

Foraging pits influence a range of soil and ecological processes such as nutrient cycling, infiltration of water, and capture and decomposition of organic material. These effects in turn influence plant germination, productivity and diversity, often with positive feedback effects on the animal creating the pit. The engineering effects of animals is being investigated in a number of studies in Australia and the western United States.

 

 

European rabbits (Oryctolagus cuniculus) are Australia's number one vertebrate pest, and have negative impacts on plant structure and composition, and soil and landscape health. Over much of their range rabbits live in large underground colonies (warrens), and while excavating their burrow they create extensive and sustained soil disturbance. But how damaging are rabbits to the environment?

 

Research results from the semi-arid woodland indicate that warrens have more bare ground, and less litter, plant and cryptogam cover. Their surfaces are more erodible and unstable than control surfaces. Reduced cryptogam cover reduces the germination of perennial grasses, and increases germination of weedy species.

 

Rabbit digging has a detrimental effect on soil physical and chemical properties. Warren soils tend to be nutrient-deprived, with lower levels of biologically-derived C and N, greater EC, pH and concentrations of exchangeable Ca and Mg compared with non-warrens.

 

Altered soil chemistry may be an impediment to the restoration of native plant communities. When warrens are ripped they support a greater plant cover, but this is generally weedy species. Restoration of the original woodland vegetation, even after the destruction of warren by mechanical ripping, is likely to be a slow and protracted process.

 

 

In shrub-steppe landscapes in the western United States, American badgers (Taxidea taxus) excavate about 26 t/ha of soil while foraging for ground squirrels. This soil is deposited as a fan-shaped mound over 5-8% of the surface. Densities of 800 mounds/ha are not uncommon, creating a patchwork of diggings of various ages within the sagebrush steppe.

 

Ongoing research indicates that plant, cryptogam and litter cover increases, and bare soil decreases, as badger mounds age. Excavation pits trap litter, which results in higher concentrations of labile C. However mound soils contain low concentrations of C, N, S, and soluble Ca, Mg and K. Mounds are more erodible, have lower rates of infiltration, seal up when wet, and shed any water as runoff.

 

 

 

 

Bilbies and bettongs were once widespread across arid Australia but suffered major range declines with the introduction of feral predators (fox, cat), overgrazing, altered fire regimes and the introduction of the rabbit. Digging by these animals, a form of ecosystem engineering, is thought to have been an essential for creating small-scale patchiness that allows arid landscapes to function. We found that most pits were dug in the dunes and the ecotones (area between the dunes and the gibbers). More litter was trapped by the pits in the dunes and ecotones than in the gibber, and the composition of the trapped litter differed between different landscapes.

 

Termites and ants are critical to the functioning of arid Australia. Our research has shown that ants move considerable quantities of soil and lead to the development of fertile soils, and termites affect both nutrient pools and the flow of water into the soil. We are currently looking at the interactions between ant species and geomorphology in driving differences in water flow in a desert watershed in New Mexico, and the long-term effect of fallen timber and down logs in ant activity in a semi-arid woodland.

 

Long-term monitoring of vegetation and soil is an essential part of managing landscapes sustainably. My research focuses on monitoring of rangelands and assessing the health of vegetation remnants. The Rangelands Assessment Program, which commenced in 1988, aims to assess the health of rangelands within selected vegetation communities (range types) in western NSW. More than 350 sites have been established across western NSW. Each site is visited annually and measurements made of plant composition and productivity, soil stability and erosion. These measurements are matched by management information such as stocking records and yield information provided by cooperating landholders. We have been exploring ways of assessing rangelands health, and our research has shown that most monitoring sites have changed very little in the past 15 years. We attribute this to the fact that the rangelands have been grazed for more almost 200 years and have reached a relatively stable, though less productive and diverse state.

 

Data from the rangelands assessment program is currently being used to test models of the relationships between diversity and resilience of rangeland ecosystems and whether diverse landscapes recover more quickly after droughts. In the Murrumbidgee Irrigation Area near Griffith in southern NSW, we have used a hierarchical approach based on structure, composition and function of the landscape, to derive indices of the current status of remnants in terms of their biodiversity value. Similar approaches are being used in agricultural areas in collaboration with the Murrumbidgee Catchment Management Authority.

 

 

Biological soil crusts are made up of non-vascular plants (sometimes called cryptogams) and surface soils. The group includes lichens, bryophytes (mosses and liverworts), algae, cyanobacteria, fungi and bacteria. Crusts play important roles in terrestrial and aquatic ecosystems. They protect the soil against erosion, fix nitrogen, phosphorus and carbon and sequestering it in the soil, moderate soil moisture, influence the germination and establishment of vascular plants, and provide habitat for soil animals.

 

Our research has centred on the distribution of crusts, their roles in ecological and soil processes in arid Australia. NSW, and their usefulness as monitoring tools. In some ecosystems they are important indicators of landscape health. Current work is examining soil crusts in the higher rainfall box woodlands. Our results indicate that the grassy box woodlands support a rich suite of crust species, particularly in dense white cypress pine (Callitris glaucophylla) woodlands.

 

Research from western Queensland by one of my students Wendy Williams has indicated that cyanobacterial crusts found beneath thin layers of sand or dust are able to fix nitrogen after small rainfalls or dew events even during droughts. This process appears to be a crucial part of the arid soil nutrient cycle, aiding post-drought recovery of the vascular plant community.

 

Soil health is an important component of landscape and vegetation health, and has been identified as a key indicator of condition in many catchments in southern NSW. Research from two woodland communities in the Murrumbidgee Irrigation Area indicates that there were no differences in nutrient status between sites in poor condition and those in good condition. While sites may appear degraded in terms of their plant cover, plant composition or general vigour of the tree canopy, soil condition appears to be remarkably resilient, and is not likely to limit the restoration of poor condition sites.

 

Research in the MIA has also demonstrated that simple field measures based on the cover of plants, litter and cryptogams, as well as soil roughness, soil hardness and surface texture were highly related to soil chemistry (carbon, nitrogen, phosphorus) providing land managers with relatively simple, rapid and cost-effective methods of monitoring soil health in woodland remnants.

 

 

Vegetation has major impacts on the way water moves through the soil and the production and retention of nutrients. In the semi-arid woodlands, trees are focal points of soil activity and major drivers of ecosystem processes. As landscapes become degraded, the importance of trees in controlling excess surface water becomes critical, and our work in southern Australia has shown that trees behave as 'ecosystem wicks', providing entry points to overland flow and preventing the disposal of water into drainage lines.

 

Our research near Wagga Wagga in southern NSW has shown that trees are critical for nutrient production, and isolated trees (alive or dead) produce resource-rich patches extending our from their crowns. Nutrient retention in woodlands is currently being examined in Callitris glaucophylla woodlands with a range of disturbance histories near Forbes.