Gavin Melville

A ground cover-based incentive approach to enhancing resilience in rangelands viewed as complex adaptive systems

Inconsistencies can commonly be expected between the financial goals of rangeland grazing enterprises and public conservation goals such as maintenance of ground cover to reduce erosion. Where the State wishes to promote conservation outcomes, incentive schemes which reward these outcomes on privately managed grazing lands are an option. We describe one such scheme intended to achieve conservation outcomes and support the development of resilience in the complex adaptive (human–environmental) rangeland system through payments related to measured ground cover. A pilot program in western New South Wales has shown that the practical operation of such a program is uncomplicated and that while several theoretical issues could be further refined there is a rationale for extension of the program based on parameters and processes that are agreed by the participants. We suggest that development of such a scheme should be considered as part of the policy mix related to natural resource management and drought assistance.

Application of LiDAR data to maximise the efficiency of inventory plots in softwood plantations

BackgroundPrecision in describing plantation attributes is a key requirement for forestry managers and inventory surveys aim to extract the most precise information possible using the smallest number of plots. This paper quantifies the potential efficiencies to be gained by using Light Detection and Ranging (LiDAR) data as an aid to estimation of standing timber volume in softwood plantations. A range of inventory design and estimation methods were investigated in terms of their overall predictive efficiency.MethodsField measurements representing four different populations from two Pinus radiata D. Don plantations in New South Wales, Australia, were used to inform statistical models which were then employed to simulate populations of inventory plots. These plots were then “surveyed” using a variety of simulated sampling strategies to quantify the benefits from using LiDAR data as auxiliary information. Model-based and design-based methods were both investigated. Survey design options included stratification and plot selection strategies; estimation options included ratio estimation and regression modelling. Results were compared in terms of the relative bias and root mean squared error of the estimates.ResultsThe study suggests that relative efficiencies of two-fold or better, are possible with either model-based or model-assisted estimators compared to traditional inventory surveys which use grid samples and simple design-based estimators. This would enable a halving in the required sample size for the same precision for field inventories in these plantations.ConclusionThe use of LiDAR data as an aid to survey design produces marked efficiency gains compared to traditional inventory methods.

Temporary cropping in semi-arid shrublands increases native perennial grasses

Thickening of native shrubs is a major problem in many ‘semi-arid woodlands’ as significant increase in shrub density is often negatively correlated with herbaceous vegetation and leads to reduced pasture production and soil erosion. This project aimed to test the hypothesis that temporary cropping (up to three crops in 15 years) consistently increases the density of native perennial grasses following the removal of shrubs. A total of 30 paddocks that had been cropped during the last 20 years were randomly selected using a satellite-based database that documented annual clearing and cropping history from 1987 to 2003. Paddocks were classified into four types based on clearing and cropping history and grazing management – not cleared (shrubs), regrowth (re-invaded by shrubs), set stocked (cropped and grazed), light/rotationally grazed (cropped and grazed). The responses of vegetation and soil (chemical and physical) properties to clearing and cropping were evaluated. Results indicated that ground cover, native perennial grass cover and standing dry matter were highest under light/rotationally grazed conditions. The shrub state represents a stable state within the Cobar pediplain brought about due to land-use change in the form of overgrazing and/or the removal of fire from the system. An alternative stable state was achieved as a result of disturbance in the form of clearing, cropping and grazing management thereby directly altering the shrub population. The resilience of this state is largely dependent on the grazing management system used and on the prevention of shrub from re-establishing while failure to control shrubs could lead to the re-emergence of the Shrub State. We conclude that native grasslands do regenerate following cropping after removal of shrubs. The importance of grazing management for restoring perennial ground cover following removal of shrubs and temporary cropping has been clearly demonstrated by the study.

Sub-Compartment Variation in Tree Height, Stem Diameter and Stocking in a Pinus radiata D. Don Plantation Examined Using Airborne LiDAR Data

Better information regarding the spatial variability of height, Diameter at Breast Height (DBH) and stocking could improve inventory estimates at the operational Planning Unit since these parameters are used extensively in allometric equations, including stem volume, biomass and carbon calculations. In this study, the influence of stand stocking on height and DBH of two even aged radiata pine (Pinus radiata D. Don) stands were investigated using airborne Light Detection and Ranging (LiDAR) data at a study site in New South Wales, Australia. Both stands were characterized by irregular stocking due to patchy establishment and self-thinning in the absence of any silvicultural thinning events. For the purpose of this study, a total of 34 plots from a 34 year old site and 43 plots from a nine year old site were established, from which a total of 447 trees were sampled. Within these plots, DBH and height measurements were measured and their relationships with stocking were evaluated. LiDAR was used for height estimation as well as stem counts in fixed plots (stocking). The results showed a significant relationship between stem DBH and stocking. At both locations, trees with larger diameters were found on lower stocking sites. Height values were also significantly correlated with stocking, with taller trees associated with high stocking. These results were further verified of additional tree samples, with independent field surveys for DBH and LiDAR-derived metrics for height analysis. This study confirmed the relationship between P. radiata tree heights and stem diameter with stocking and demonstrated the capacity of LiDAR to capture sub-compartment variation in these tree-level attributes.

The relationship between soil organic carbon and soil surface characteristics in the semi-arid rangelands of southern Australia

The potential carbon sequestration in rangelands is largely due to the extensive areas they occupy, even though levels of soil organic carbon (SOC) are low. There is considerable uncertainty in achieving this potential due to the inherent patchy spatial and temporal distribution of rangeland vegetation and resources. At a paddock scale, determining appropriate sampling scales is a critical first step in the accurate estimation of size and spatial distribution of stocks of SOC. This issue was addressed by examining the spatial distribution of SOC and determining the association of SOC with other site characteristics such as ground cover and vegetation. This was done in a pilot study conducted in a 136-ha paddock located on the Cobar Pediplain Bioregion in western New South Wales, Australia. Each of 104 sites was sampled using a 0.25-m2 quadrat to assess biomass and ground cover category (percentage of perennial plants, bare ground, cryptogams, annual plants and litter) of a soil core taken from the centre of each quadrat, and proximity to trees and shrubs. The soil core was used to determine total organic C (TOC), total N (TN) and the C : N ratio at four depths (0–5; 5–10; 10–20; 20–30 cm). From the quadrat and ground cover categories of the soil cores, six microsite categories were identified using cluster analysis: cryptogams; litter (≥25% litter); bare (≥60% bare ground); annual (≥40% annual plants); litter-P (≥15% litter and ≥10% perennial plants) and perennial (≥30% perennial plants). Microsite, depth in soil profile and the presence of trees and shrubs all had a significant (P < 0.001) effect on TOC concentration. The predicted means (s.e. of mean) of TOC at the soil surface (0–5 cm) were perennial 1.26 (0.04) %; litter-P 1.20 (0.05) %; annual 1.18 (0.06) %; litter 1.12 (0.05) %; bare 1.03 (0.05) % and cryptogams 0.88 (0.06) %. Higher concentrations of TOC were associated with the presence of trees and were almost 30% higher in close proximity (<1 m) to a tree. There was a consistent finding that higher concentrations of TOC, TN and the high values of C : N ratio were each associated with higher ground cover of perennial plants. The autocorrelation range for soil C stocks was ~30 m and for categories of ground cover which varied from 10 m to over 200 m. The spatial predictions for ground cover of perennial plants closely mirrored those for C stocks, which were 22.9 Mg C ha–1 in the top 30 cm of soil in this environment. As both tree proximity and ground cover had a significant effect on TOC, quantifying the levels of soil organic C at a paddock scale will require an understanding of the spatial patterns of vegetation (woody and ground cover), which provides a basis for within-paddock stratification before soil sampling.

Aerial mapping canopy damage by the aphid Essigella californica in a Pinus radiata plantation in southern New South Wales: what are the challenges?

Summary Surveying the location and level of damage by insect pests and diseases, such as canopy damage by the Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), a common defoliating pest of Pinus radiata, is now formally embedded in the management practices of most Australian softwood-growing companies. Aerial surveys, also known as aerial sketch-mapping, are a cost-effective means of mapping broad-scale canopy damage, but their accuracy is dependent on a range of factors including the spatial and temporal expression of symptoms associated with different damaging agents. For E. californica, the most distinctive symptom is yellowing (needle chlorosis) of the crown followed by defoliation of affected needles. The aim of this study was to compare canopy damage categories obtained by aerial sketch-mapping with mean crown damage estimates derived from a systematic, plot-based sampling scheme of a Pinus radiata plantation in Green Hills State Forest in southern New South Wales with a known history of E. californica infestations. We identified significant challenges to rating accurately the level of canopy damage from E. californica by aerial sketch-mapping. While the location of chlorotic crowns may be mapped reliably, our results suggest that it is much more difficult to visually resolve different levels of canopy damage within affected stands. Using an ‘incidence × severity’ damage rating score, only two classes of canopy damage were confidently separated (i.e. Low (not detected or trace levels) and High (having a damage score of greater than 25%)). Accurate location of these classes of damage allows targeted, ground-based surveys for follow-up diagnostics and more detailed estimates of damage at the crown scale.

Increasing the perennial grass component of native pastures through grazing management in the 400–600 mm rainfall zone of central western NSW

Native grass-based pastures in the 400–600 mm rainfall zone of central NSW are an important basis for extensive grazing industries. However, over time they have been invaded by exotic weeds. This study aimed to evaluate several grazing strategies for the maintenance or improvement of native grasslands based on pasture productivity and species diversity. Seven grazing strategies, ranging from set stocking to permanently removing stock, were employed to evaluate the strategy that would best maintain a high proportion of desirable perennial grass species. Grazing treatments were evaluated based on their effects on pasture composition and on the density of selected key grass species such as Enteropogon acicularis (Lindl.) Lazar. (curly windmill grass). Managing the utilisation of the key desirable species E. acicularis combined with weed control was the most successful strategy in terms of increasing the density of the key species, although no treatment increased the proportion of desirable perennial grasses and desirable broadleaf species. This was followed by a ‘farmer’s choice’ strategy, which involved combining phosphorus fertiliser application, weed control and rest from grazing. In contrast, strategies that involved either a ‘summer lockup’ or ‘weed control’ alone performed poorly. It is concluded that native pastures in this region could be rehabilitated, and their productivity restored, by following strategies that provide rest from grazing, based on the utilisation levels of key, species combined with control of annual weeds.

DBH and height show significant correlation with incoming solar radiation: a case study of a radiata pine (Pinus radiata D. Don) plantation in New South Wales, Australia

The aim of this study was to determine whether diameter at breast height (DBH, at 1.3 m) and total height of radiata pine (Pinus radiata D. Don) trees showed any significant relationships with microsite estimates of solar radiation. A total of 77 plots were established in two even-aged stands of radiata in Nundle State Forest, New South Wales, Australia. Within these plots, tree DBH and height measurements were recorded and their relationships with solar radiation evaluated. Airborne light detection and ranging (LiDAR) data were processed to generate a high resolution digital elevation model (DEM), and the DEM was used for calculating the incoming solar radiation. Overall, at both study sites, taller and larger trees were found on areas with lower solar radiation, possibly due to a lower loss in soil moisture. The findings of this study suggest that LiDAR-derived DEM estimates of solar radiation are significantly correlated with DBH and height variation, and therefore suitable for use as a sub-compartment stratification variable as well as for possible inclusion in fine-scale estimates of P. radiata growth and productivity.

Impact of local slope and aspect assessed from LiDAR records on tree diameter in radiata pine (Pinus radiata D. Don) plantations

ContextReliable information on tree stem diameter variation at local spatial scales and on the factors controlling it could potentially lead to improved biomass estimation over pine plantations.AimsThis study addressed the relationship between local topography and tree diameter at breast height (DBH) within two even-aged radiata pine plantation sites in New South Wales, Australia.MethodsA total of 85 plots were established, and 1,302 trees were sampled from the two sites. Airborne light detection and ranging (LiDAR) was used to derive slope and aspect and to link them to each individual tree.ResultsThe results showed a significant relationship between DBH and local topography factors. At both sites, trees on slopes below 20° and on southerly aspects displayed significantly larger DBHs than trees on steeper slopes and northerly aspects. Older trees with similar heights also exhibited a significant relationship between DBH and aspect factor, where greater DBHs were found on southerly aspects.ConclusionsThe observed correlation between tree DBH and LiDAR-derived slope and aspect could contribute to the development of improved biomass estimation approaches in pine plantations. These topographical variables are easily attained with airborne LiDAR, and they could potentially improve DBH predictions in resource inventories (e.g. stand volume or biomass) and support field sampling design.

Effects of nitrogen and phosphorus on vegetation dynamics of a degraded native grassland in semi-arid south-eastern Australia

The roles of nitrogen (N) and phosphorus (P) in controlling vegetation transitions in a degraded semi-arid grassland were investigated in a factorial experiment that combined two initial levels of perennial plant density (low and high), three levels of N (N+, N0 and N–) and two levels of P (P+ and P0). Increased levels of both N and P were achieved by fertiliser addition while sucrose was used to reduce the level of N. Vegetation dynamics were driven primarily by soil N rather than P. Addition of sucrose, which was inferred to result in the immobilisation of mineral N, reduced the growth of annual species and facilitated the establishment and growth of native perennial grasses. Addition of P generally had no significant effect on dry matter production, either in total or for species grouped as forbs, annual grasses and perennial grasses, or on recruitment and mortality of perennial grasses. However, at some times of observation addition of P increased ground cover and/or the basal circumference of some perennial grass species. Basal circumference for Enteropogon acicularis was also increased by addition of N. Soil biological activity, measured by decomposition of cotton strips, was increased by addition of N, which maintained vegetation in an annual-dominated condition, and was not affected by addition of P. Carbon addition has the potential to assist restoration of this grassland. However, the capacity of some native grass species to respond to increased fertility suggests that once restoration is achieved some increase in fertility may be beneficial for pastoral production.