Josh Dorrough

The relative effects of tree clearing, increased livestock densities and nutrient enrichment have rarely been compared across markedly different organism types, but negative effects are generally predicted. In contrast, adoption of rotational grazing is thought to benefit biodiversity in pastures but there are few supporting data. We examined the response of native plants, birds and reptiles to livestock management in south‐eastern Australia. We selected 12 pairs of rotationally and continuously grazed farms. Two 1‐ha plots were established in native pastures on each farm, one cleared and the second still retaining woodland tree cover. Stocking rates, fertilizer histories and landscape tree cover varied among farms. The abundance and richness of all taxa was lower in cleared pastures. The less mobile organisms (reptiles and plants) were positively correlated with tree cover at landscape scales, but only when trees were present at the plot scale. This pattern was driven by a few observations in landscapes with approximately 50% tree canopy cover. Neither bird abundance nor richness was correlated with stocking rates or nutrient enrichment, but plant richness responded negatively to both. The response of reptiles varied, declining with nutrient enrichment but positively correlated with livestock densities. These responses may be partly interpreted within the context of prior filtering of species pools through long‐term grazing pressure. No taxa responded positively to rotational grazing management. We predict that reductions in livestock density and soil nutrients will directly benefit plants and less so reptiles, but not birds. Indirect benefits are predicted for birds and reptiles if management increases persistence of trees within paddocks. Although some forms of rotational grazing can increase woodland tree recruitment, rotational grazing in itself is unlikely to enhance diversity.

Livestock grazing and fertilisation are primary management activities that determine variation in plant species composition within grazed temperate grassy ecosystems of Australia. The present paper provides an extensive catalogue of the responses of individual species to grazing and fertilisation that can be used to guide management and restoration in differing situations. A hierarchical model that links plant species identities, simple plant traits and two continuous predictive variables (livestock density and available phosphorus) was used to estimate probability of occurrence of plant species across grazing and phosphorus gradients. Certain species and groups of species, particularly native perennial geophytes, ferns and shrubs, were especially sensitive to increases in each of these management gradients, whereas a small group of exotic plants were most tolerant. In the moderately intensive livestock production landscapes sampled, most native plant species preferred ungrazed areas with low available phosphorus. Many non-native plant species also tolerated or preferred such habitats. Less than 1% of all observed species are predicted to occur at high levels of available phosphorus (75 mg kg–1) and heavy stocking (9 dry sheep equivalents ha–1). There is, however, a suite of native species that persist at moderate livestock densities, but only if soils are not phosphorus-enriched. These data can be used to guide options for restoration including ranking of potential sites or selection of species for reintroduction. In most cases, livestock grazing intensity is thought to be the primary factor influencing plant species composition in grazed woodlands. These data, however, highlight the great importance of fertilisation history in limiting ground-layer plant diversity and determining options for management.

Summary: Many ecological management problems involve assessing competing options based on the trade‐off between economic costs and short‐ and long‐term probabilities of success. In many cases the time to success is crucial, and opportunity costs may be greater than direct costs of implementation. We analyse the problem of how to choose between options when risks of failure vary systematically. Ecological uncertainty propagates through to uncertainty about economic outcomes. We used an ecological model of tree recruitment that accounted for uncertainty surrounding the effects of climate and seed fall, coupled with a farm economics model, to examine how a land manager should act when deciding between active and passive revegetation (planting seed/seedlings or relying on natural recruitment, respectively) for restoration purposes on a farm managed for livestock production. The outcome of the analysis was driven by the relative sizes of up‐front costs and opportunity costs, which were a function of potential productivity and the time until successful revegetation was achieved. Active revegetation was less costly than passive revegetation in high‐productivity situations, because there was less risk of long periods without production and the associated opportunity costs. At low productivity, passive revegetation was less costly than active revegetation. However, because the probability of a successful outcome increased over time, passive revegetation is only likely to be preferred over medium time‐frames (> 5 years) and the strategy may not be chosen by risk‐averse farmers. Synthesis and applications. This analysis has implications for (i) decision‐making by individual land managers and regional planners and (ii) the design of policies for delivery of incentive schemes targeted at revegetation. Risk‐averse individual land managers are likely to select active regeneration scenarios, particularly when costs of capital works are shared with the community. For a regional planner, the analysis aids thinking about the probable balance of financial assistance schemes for attaining regional objectives: over high‐productivity areas, capital works programmes and short‐term opportunity cost incentives (< 5 years) are cheaper; at low productivity, incentive schemes for medium‐ to long‐term land retirement will be cheaper. This analysis provides a starting point for devising the mix of approaches required to achieve broad‐scale revegetation targets, which would include greater investment in uncertain, long‐term strategies.