Adrian D. Manning

Should agricultural policies encourage land sparing or wildlife‐friendly farming?

As the demands on agricultural lands to produce food, fuel, and fiber continue to expand, effective strategies are urgently needed to balance biodiversity conservation and agricultural production. “Land sparing” and “wildlife-friendly farming” have been proposed as seemingly opposing strategies to achieve this balance. In land sparing, homogeneous areas of farmland are managed to maximize yields, while separate reserves target biodiversity conservation. Wildlife-friendly farming, in contrast, integrates conservation and production within more heterogeneous landscapes. Different scientific traditions underpin the two approaches. Land sparing is associated with an island model of modified landscapes, where islands of nature are seen as separate from human activities. This simple dichotomy makes land sparing easily compatible with optimization methods that attempt to allocate land uses in the most efficient way. In contrast, wildlife-friendly farming emphasizes heterogeneity, resilience, and ecological inter...

Biodiversity, ecosystem function, and resilience: ten guiding principles for commodity production landscapes

Biodiversity conservation in forestry and agricultural landscapes is important because (1) reserves alone will not protect biodiversity; (2) commodity production relies on vital services provided by biodiversity; and (3) biodiversity enhances resilience, or a systems capacity to recover from external pressures such as droughts or management mistakes. We suggest ten guiding principles to help maintain biodiversity, ecosystem function, and resilience in production landscapes. Landscapes should include structurally characteristic patches of native vegetation, corridors and stepping stones between them, a structurally complex matrix, and buffers around sensitive areas. Management should maintain a diversity of species within and across functional groups. Highly focused management actions may be required to maintain keystone species and threatened species, and to control invasive species. These guiding principles provide a scientifically defensible starting point for the integration of conservation and production, which is urgently required from both an ecological and a long-term economic perspective.

The Future of Scattered Trees in Agricultural Landscapes

Mature trees scattered throughout agricultural landscapes are critical habitat for some biota and provide a range of ecosystem services. These trees are declining in intensively managed agricultural landscapes globally. We developed a simulation model to predict the rates at which these trees are declining, identified the key variables that can be manipulated to mitigate this decline, and compared alternative management proposals. We used the initial numbers of trees in the stand, the predicted ages of these trees, their rate of growth, the number of recruits established, the frequency of recruitment, and the rate of tree mortality to simulate the dynamics of scattered trees in agricultural landscapes. We applied this simulation model to case studies from Spain, United States, Australia, and Costa Rica. We predicted that mature trees would be lost from these landscapes in 90-180 years under current management. Existing management recommendations for these landscapes--which focus on increasing recruitment--would not reverse this trend. The loss of scattered mature trees was most sensitive to tree mortality, stand age, number of recruits, and frequency of recruitment. We predicted that perpetuating mature trees in agricultural landscapes at or above existing densities requires a strategy that keeps mortality among established trees below around 0.5% per year, recruits new trees at a rate that is higher than the number of existing trees, and recruits new trees at a frequency in years equivalent to around 15% of the maximum life expectancy of trees. Numbers of mature trees in landscapes represented by the case studies will decline before they increase, even if strategies of this type are implemented immediately. This decline will be greater if a management response is delayed.

The role of carrion in maintaining biodiversity and ecological processes in terrestrial ecosystems

Carrion provides a resource for a subset of animal species that deliver a critical ecosystem service by consuming dead animal matter and recycling its nutrients. A growing number of studies have also shown various effects of carrion on different plant and microbial communities. However, there has been no review of these studies to bring this information together and identify priority areas for future research. We review carrion ecology studies from the last two decades and summarise the range of spatial and temporal effects of carrion on soil nutrients, microbes, plants, arthropods, and vertebrates. We identify key knowledge gaps in carrion ecology, and discuss how closing these gaps can be achieved by focusing future research on the (1) different kinds of carrion resources, (2) interactions between different components of the carrion community, (3) the ways that ecosystem context can moderate carrion effects, and (4) considerations for carrion management. To guide this research, we outline a framework that builds on the ‘ephemeral resource patch’ concept, and helps to structure research questions that link localised effects of carrion with their consequences at landscape scales. This will enable improved characterisation of carrion as a unique resource pool, provide answers for land managers in a position to influence carrion availability, and establish the ways that carrion affects the dynamics of species diversity and ecological processes within landscapes.

TEMPORAL CHANGES IN VERTEBRATES DURING LANDSCAPE TRANSFORMATION : A LARGE-SCALE NATURAL EXPERIMENT

Plantation development is a significant form of landscape change worldwide. We report findings from a large-scale longitudinal natural experiment that quantified changes in Australian vertebrates as a former grazing landscape was transformed to one dominated by a radiata pine (Pinus radiata) plantation. The study included four main “treatments”: woodland remnants surrounded by emerging radiata pine (52 sites, termed “woodland treatments”), stands of radiata pine (10 sites, “pine controls”), woodland remnants where the surrounding landscape remained unchanged (56 sites, “woodland controls”), and paddocks with scattered woodland trees that surrounded the 56 woodland remnants (10 sites, “paddock controls”). In our study region, woodland is distinguished from forest by differences in tree height, tree spacing, bole length, and canopy development. Between 1998 and 2006, occupancy rates of “woodland treatments” by most mammals and reptiles increased linearly. Similar trends occurred in the “woodland controls,” suggesting that species had increased landscape-wide, rather than displaying year × treatment interaction effects. We cross-classified birds according to the statistical significance and nature of time trajectories. Groups included those that: (1) declined in woodland treatments in comparison with woodland controls, (2) decreased within woodland treatments but increased in woodland controls, (3) declined across the entire study area, (4) increased within woodland treatments in comparison with woodland controls, (5) increased within woodland treatments but declined in woodland controls, and (6) increased across the entire study area. Attributes of woodland treatments significantly associated with temporal changes in bird occupancy included: (1) age of surrounding pine stands; (2) number of boundaries with surrounding pines; (3) size of the woodland patches; (4) dominant vegetation type of woodland patches; and (5) temporal changes in vegetation structure in the woodland treatments. Bird species associated with open country and woodland environments were disadvantaged by landscape transformation, whereas those that benefited were forest taxa and/or habitat generalists capable of inhabiting pine stands and adjacent woodland patches. Beyond this generalization, an unanticipated finding was a lack of association between life history attributes and landscape transformation. We suggest that several key processes are likely drivers of change at multiple spatial scales. Recognition of such processes is important for conservation in landscapes transformed by plantation expansion.

Eaten Out of House and Home: Impacts of Grazing on Ground-Dwelling Reptiles in Australian Grasslands and Grassy Woodlands

Large mammalian grazers can alter the biotic and abiotic features of their environment through their impacts on vegetation. Grazing at moderate intensity has been recommended for biodiversity conservation. Few studies, however, have empirically tested the benefits of moderate grazing intensity in systems dominated by native grazers. Here we investigated the relationship between (1) density of native eastern grey kangaroos, Macropus giganteus, and grass structure, and (2) grass structure and reptiles (i.e. abundance, richness, diversity and occurrence) across 18 grassland and grassy Eucalyptus woodland properties in south-eastern Australia. There was a strong negative relationship between kangaroo density and grass structure after controlling for tree canopy cover. We therefore used grass structure as a surrogate for grazing intensity. Changes in grazing intensity (i.e. grass structure) significantly affected reptile abundance, reptile species richness, reptile species diversity, and the occurrence of several ground-dwelling reptiles. Reptile abundance, species richness and diversity were highest where grazing intensity was low. Importantly, no species of reptile was more likely to occur at high grazing intensities. Legless lizards (Delma impar, D. inornata) were more likely to be detected in areas subject to moderate grazing intensity, whereas one species (Hemiergis talbingoensis) was less likely to be detected in areas subject to intense grazing and three species (Menetia greyii, Morethia boulengeri, and Lampropholis delicata) did not appear to be affected by grazing intensity. Our data indicate that to maximize reptile abundance, species richness, species diversity, and occurrence of several individual species of reptile, managers will need to subject different areas of the landscape to moderate and low grazing intensities and limit the occurrence and extent of high grazing.

The Future of Large Old Trees in Urban Landscapes

Large old trees are disproportionate providers of structural elements (e.g. hollows, coarse woody debris), which are crucial habitat resources for many species. The decline of large old trees in modified landscapes is of global conservation concern. Once large old trees are removed, they are difficult to replace in the short term due to typically prolonged time periods needed for trees to mature (i.e. centuries). Few studies have investigated the decline of large old trees in urban landscapes. Using a simulation model, we predicted the future availability of native hollow-bearing trees (a surrogate for large old trees) in an expanding city in southeastern Australia. In urban greenspace, we predicted that the number of hollow-bearing trees is likely to decline by 87% over 300 years under existing management practices. Under a worst case scenario, hollow-bearing trees may be completely lost within 115 years. Conversely, we predicted that the number of hollow-bearing trees will likely remain stable in semi-natural nature reserves. Sensitivity analysis revealed that the number of hollow-bearing trees perpetuated in urban greenspace over the long term is most sensitive to the: (1) maximum standing life of trees; (2) number of regenerating seedlings ha−1; and (3) rate of hollow formation. We tested the efficacy of alternative urban management strategies and found that the only way to arrest the decline of large old trees requires a collective management strategy that ensures: (1) trees remain standing for at least 40% longer than currently tolerated lifespans; (2) the number of seedlings established is increased by at least 60%; and (3) the formation of habitat structures provided by large old trees is accelerated by at least 30% (e.g. artificial structures) to compensate for short term deficits in habitat resources. Immediate implementation of these recommendations is needed to avert long term risk to urban biodiversity.

Pocket parks in a compact city: how do birds respond to increasing residential density?

Abstract The desire to improve urban sustainability is motivating many city planners to adopt growth strategies that increase residential density, leading to substantial changes to urban landscapes. What effect this change will have on biodiversity remains unclear, but it is expected that the role of public greenspace in providing wildlife habitat will become critical. We explored the role of urban “pocket parks” as habitat for birds, and how this role changed with increasing residential density in the surrounding neighbourhood. We found that parks in neighbourhoods with high levels of public greenspace (corresponding to less residential land) supported more bird species and individuals overall, and more woodland-dependent species, insectivores and hollow-nesters. Total greenspace area was more important (included in the best ranked models for all bird responses) than the configuration (number, average size and connectivity) of greenspace patches. The majority of species were common suburban birds, indicating that species we assume are tolerant to urban areas will be negatively affected by increasing residential density. Parks form part of an interconnected network of urban open space. For parks to continue to support a diverse native bird community, the network must be viewed, managed, and maintained in its entirety. We suggest three key management actions to improve the bird diversity values of urban greenspaces in compact cities: (1) Increase urban greenspace cover in residential neighbourhoods. (2) Increase vegetation structure in greenspace. (3) Encourage homeowners to plant trees and shrubs.

Species traits predict assemblage dynamics at ephemeral resource patches created by carrion.

Carrion is an ephemeral and spatially patchy resource that supports a diverse subset of species linked to nutrient cycling and the decomposition process. A number of studies have separately documented changes in the diversity of plants, arthropods and vertebrates at individual carcasses, but there are few studies that have examined how functional traits of different groups of organisms underpin their responses to carrion patches. We used a carrion addition experiment to compare changes in composition and functional traits of insect and plant assemblages at carcasses compared with control sites. We found that significant changes in insect assemblage evenness and heterogeneity was associated with species’ dispersal traits, and that plant assemblage responses to subsequent soil nitrogen changes was most apparent among graminoids and exotic species. Beetles at carcasses were twice as large as their counterparts at control sites during the first week of carrion decomposition, and also had higher wing loadings. Plants with high specific leaf area responded faster to the carcass addition, and twice as many species recolonised the centre of carcasses in exotic-dominated grassland compared with carcasses in native-dominated grassland. These results provide an example of how traits of opportunist species enable them to exploit patchy and dynamic resources. This increases our understanding of how carcasses can drive biodiversity dynamics, and has implications for the way carrion might be managed in ecosystems, such as appropriate consideration of spatial and temporal continuity in carrion resources to promote heterogeneity in nutrient cycling and species diversity within landscapes.

Linking bird species traits to vegetation characteristics in a future urban development zone: implications for urban planning

Identifying the relationships between species traits and patch-scale vegetation characteristics in areas designated for urban development can improve our understanding of how animal communities may change with urbanization. We explored the implications of this premise to the urban planning process in a mixed-use landscape in Canberra (Australia), prior to its development into new suburbs. We used RLQ analysis to relate bird foraging, nesting and body size traits to patch-scale vegetation characteristics. Relationships between species traits and vegetation characteristics within the development zone suggest that species that forage and nest on the ground and in the understory strata, and smaller-bodied species will be most negatively affected by urbanization. Identifying the relationships between species traits and vegetation characteristics may be used by urban planners to (i) identify potentially critical habitat and species at risk from development, (ii) inform the choice of impact mitigation measures, and/or (iii) distinguish between high and low mitigation measures. Analyses conducted early in the planning process can then be used to allocate proposed land uses in an ecologically sensitive way, and to plan appropriate mitigation measures.