Scaling the benefits of agri-environment schemes for biodiversity conservation in agricultural landscapes

Abstract

Agricultural expansion and intensification are major causes of biodiversity loss. To mitigate this, billions of dollars are committed by governments annually to agri-environment conservation schemes aiming to engage landholders, often at large (continental) scales, in sustainable farming practices. While some schemes have been successful in addressing the social and policy elements of farmland conservation, assessments of their effectiveness for conserving biodiversity in farming systems is lacking. Recent studies have demonstrated that the effectiveness of programs is influenced by a number of scale-dependent factors that may influence biodiversity response but remain poorly understood. Specifically, local- and landscape-scale management actions can influence biodiversity response, and hence the effectiveness of programs, but this aspect has been little explored. My research aimed to identify ways to enhance the effectiveness of agri-environmental schemes through a better understanding of scale-related management effects on herpetofauna (reptiles and amphibians); a critical and declining vertebrate group severely threatened by agricultural development. First, I summarise current knowledge of local- and landscape-scale factors influencing agri-environment scheme effectiveness for biodiversity, highlighting novel research priorities relevant to practitioners (Paper #1). I then conducted baseline herpetofaunal surveys at 325 treatment/control sites within a critically endangered remnant woodland targeted under a large-scale (>1000 km; 172,000 km2) agri-environment scheme; the Australian Government Environmental Stewardship Programme (Paper #2). This is the most extensive xii herpetofaunal survey conducted to date throughout this woodland ecosystem. I found high levels of spatial variation in species detected across the study area; with large differences in species richness between biogeographic regions but not between treatment and control sites. Second, I conducted multi-season vegetation, habitat structural and herpetofaunal surveys at each of the 325 sites to identify key habitat variables (Paper #3) and management activities (livestock grazing; Paper #4) at local levels. I found that habitat use varied over biogeographically distinct regions, suggesting schemes that consider regional differences in local habitat preferences may be more effective than schemes that ignore such variation. Furthermore, past and present livestock grazing influenced herpetofaunal populations, but in complex and varied ways that have previously been overlooked. Finally, I collected data on land-use surrounding the remnant woodland sites and its influence on reptile movement to quantify the impact of landscape modification on community structure (Paper #5) and habitat connectivity (Paper #6). Landscape modification resulted in a change in community composition and a loss of species co-occurrence, but not a loss of species. Importantly, changes in co-occurrence pattern were complex and allowed for a novel classification of species susceptibility to the threat of land modification. Additionally, I found that pasture height and crop-sowing direction influenced reptile movements within the agricultural matrix, and hence must be considered where connectivity is a goal of agri-environment investment (Paper #6). xiii Collectively, my research identifies several outcomes that strengthen the theoretical and applied opportunities for enhancing effectiveness of agri-environment schemes. These include: (1) An improved knowledge of the environmental and anthropogenic drivers of the distributions of herpetofauna (2) Incorporating ecological effects operating at different scales can help agri-environment schemes to become more effective (3) A range of management actions is required to meet the conservation requirements for herpetofauna (4) Large occupancy datasets should be collected to extend observations of ecological patterns to identify underlying ecological processes (5) Management recommendations can be adaptively integrated into existing agri-environment schemes; as well as in new schemes. Such considerations are of broad relevance for the design of large-scale conservation strategies targeting the conservation of biodiversity across agricultural landscapes.