The potential for biodiversity offsetting to fund effective invasive species control.

Compensating for biodiversity losses in 1 location by conserving or restoring biodiversity elsewhere (i.e., biodiversity offsetting) is being used increasingly to compensate for biodiversity losses resulting from development. We considered whether a form of biodiversity offsetting, enhancement offsetting (i.e., enhancing the quality of degraded natural habitats through intensive ecological management), can realistically secure additional funding to control biological invaders at a scale and duration that results in enhanced biodiversity outcomes. We suggest that biodiversity offsetting has the potential to enhance biodiversity values through funding of invasive species control, but it needs to meet 7 key conditions: be technically possible to reduce invasive species to levels that enhance native biodiversity; be affordable; be sufficiently large to compensate for the impact; be adaptable to accommodate new strategic and tactical developments while not compromising biodiversity outcomes; acknowledge uncertainties associated with managing pests; be based on an explicit risk assessment that identifies the cost of not achieving target outcomes; and include financial mechanisms to provide for in-perpetuity funding. The challenge then for conservation practitioners, advocates, and policy makers is to develop frameworks that allow for durable and effective partnerships with developers to realize the full potential of enhancement offsets, which will require a shift away from traditional preservation-focused approaches to biodiversity management.

Ultimate drivers of native biodiversity change in agricultural systems.

The ability to address land degradation and biodiversity loss while maintaining the production of plant and animal products is a key global challenge. Biodiversity decline as a result of vegetation clearance, cultivation, grazing, pesticide and herbicide application, and plantation establishment, amongst other factors, has been widely documented in agricultural ecosystems. In this paper we identify six ultimate drivers that underlie these proximate factors and hence determine what native biodiversity occurs in modern agricultural landscapes; (1) historical legacies; (2) environmental change; (3) economy; (4) social values and awareness; (5) technology and knowledge; and (6) policy and regulation. While historical legacies and environmental change affect native biodiversity directly, all six indirectly affect biodiversity by influencing the decisions that land managers make about the way they use their land and water resources. Understanding these drivers is essential in developing strategies for sustaining native biodiversity in agricultural landscapes into the future.

A long-term experimental test of the dynamic equilibrium model of species diversity.

The dynamic equilibrium model of species diversity predicts that ecosystem productivity interacts with disturbance to determine how many species coexist. However, a robust test of this model requires manipulations of productivity and disturbance over a sufficient timescale to allow competitive exclusion, and such long-term experimental tests of this hypothesis are rare. Here we use long-term (27 years), large-scale (8 × 50-m plots), factorial manipulations of soil resource availability and sheep grazing intensity (disturbance) in grasslands to test the dynamic equilibrium model. As predicted by the model, increased productivity not only reduced plant species richness, but also moderated the effects of grazing intensity, shifting them from negative to neutral with increasing productivity. Reductions in species richness with productivity were associated with dominance by faster growing (i.e. high specific leaf area) and taller plants. Conversely, grazing favoured shorter plants and this effect became stronger with greater productivity, consistent with the view that grazing can lead to weaker asymmetric competition for light. Our study shows that the dynamic equilibrium model can help to explain changes in plant species richness following long-term increases in soil resource availability and grazing pressure, two fundamental drivers of change in grasslands worldwide.

Species invasions and the limits to restoration: learning from the New Zealand experience.

Species invasions impose key biotic thresholds limiting the success of ecological restoration projects. These thresholds may be difficult to reverse and will have long-term consequences for restoration because of invasion legacies such as extinctions; because most invasive species cannot be eliminated given current technology and resources; and because even when controlled to low levels, invasive species continue to exert substantial pressure on native biodiversity. Restoration outcomes in the face of biological invasions are likely to be novel and will require long-term resource commitment, as any letup in invasive species management will result in the loss of the conservation gains achieved.

Biodiversity offsets: two New Zealand case studies and an assessment framework.

Biodiversity offsets are increasingly being used for securing biodiversity conservation outcomes as part of sustainable economic development to compensate for the residual unavoidable impacts of projects. Two recent New Zealand examples of biodiversity offsets are reviewed-while both are positive for biodiversity conservation, the process by which they were developed and approved was based more on the precautionary principal than on any formal framework. Based on this review and the broader offset literature, an environmental framework for developing and approving biodiversity offsets, comprising six principles, is outlined: (1) biodiversity offsets should only be used as part of an hierarchy of actions that first seeks to avoid impacts and then minimizes the impacts that do occur; (2) a guarantee is provided that the offset proposed will occur; (3) biodiversity offsets are inappropriate for certain ecosystem (or habitat) types because of their rarity or the presence of threatened species within them; (4) offsets most often involve the creation of new habitat, but can include protection of existing habitat where there is currently no protection; (5) a clear currency is required that allows transparent quantification of values to be lost and gained in order to ensure ecological equivalency between cleared and offset areas; (6) offsets must take into account both the uncertainty involved in obtaining the desired outcome for the offset area and the time-lag that is involved in reaching that point.

Estimation of Tree Size Diversity Using Object Oriented Texture Analysis and Aster Imagery.

This study investigates the potential of object-based texture parameters extracted from 15m spatial resolution ASTER imagery for estimating tree size diversity in a Mediterranean forested landscape in Turkey. Tree size diversity based on tree basal area was determined using the Shannon index and Gini Coefficient at the sampling plot level. Image texture parameters were calculated based on the grey level co-occurrence matrix (GLCM) for various image segmentation levels. Analyses of relationships between tree size diversity and texture parameters found that relationships between the Gini Coefficient and the GLCM values were the most statistically significant, with the highest correlation (r=0.69) being with GLCM Homogeneity values. In contrast, Shannon Index values were weakly correlated with image derived texture parameters. The results suggest that 15m resolution Aster imagery has considerable potential in estimating tree size diversity based on the Gini Coefficient for heterogeneous Mediterranean forests.

Comment on "Why are there so many species of herbivorous insects in tropical rainforests?".

Novotny et al. (Reports, 25 August 2006, p. 1115) argued that higher herbivore diversity in tropical forests results from greater phylogenetic diversity of host plants, not from higher host specificity. However, if host specificity is related to host abundance, differences in relative host abundance between tropical and temperate regions may limit any general conclusion that herbivore diversity scales directly with host-plant diversity.

Analysis of the growth of rimu (Dacrydium cupressinum) in South Westland, New Zealand, using process-based simulation models.

Two process-based models were used to identify the environmental variables limiting productivity in a pristine, mature forest dominated by rimu (Dacrydium cupressinum Sol. ex Lamb.) trees in South Westland, New Zealand. A model of canopy net carbon uptake, incorporating routines for radiation interception, photosynthesis and water balance was used to determine a value for quantum efficiency when climate variables were not limiting. The annual net carbon uptake by the canopy was estimated to be 1.1 kg C m(-2) and the quantum efficiency 22.6 mmol mol quanta(-1). This value of quantum efficiency, combined with other parameters obtainable from the literature, was then used in a model of forest productivity (3-PG), to simulate changes in net productivity and the allocation of carbon to tree components. The model was adjusted to match a measured stem increment of 10.6 Mg ha(-1) over a period of 13 years. To achieve this while maintaining a low, but stable value for leaf area index, it was necessary to set the site fertility rating very low and select high values for the parameters describing the proportional allocation of total carbon to roots. This approach highlighted nutrient availability as the principal constraint on productivity for the ecosystem and identified critical measurements that will be necessary for using the model to predict the effects of climate change on carbon sequestration. The low rates of carbon uptake and productivity are consistent with the low nutrient supply available from the highly leached, acid soils, most likely attributable to frequent saturation and a very shallow aerobic zone.