Peter D. Erskine

Restoration of Degraded Tropical Forest Landscapes

The current scale of deforestation in tropical regions and the large areas of degraded lands now present underscore the urgent need for interventions to restore biodiversity, ecological functioning, and the supply of goods and ecological services previously used by poor rural communities. Traditional timber plantations have supplied some goods but have made only minor contributions to fulfilling most of these other objectives. New approaches to reforestation are now emerging, with potential for both overcoming forest degradation and addressing rural poverty.

Nitrogen relations of natural and disturbed plant communities in tropical Australia

Abstract Nitrogen relations of natural and disturbed tropical plant communities in northern Australia (Kakadu National Park) were studied. Plant and soil N characteristics suggested that differences in N source utilisation occur at community and species level. Leaf and xylem sap N concentrations of plants in different communities were correlated with the availability of inorganic soil N (NH+4 and NO−3). In general, rates of leaf NO−3 assimilation were low. Even in communities with a higher N status, including deciduous monsoon forest, disturbed wetland, and a revegetated mine waste rock dump, levels of leaf nitrate reductase, xylem and leaf NO−3 levels were considerably lower than those that have been reported for eutrophic communities. Although NO−3 assimilation in escarpment and eucalypt woodlands, and wetland, was generally low, within these communities there was a suite of species that exhibited a greater capacity for NO−3 assimilation. These “high- NO−3 species” were mainly annuals, resprouting herbs or deciduous trees that had leaves with high N contents. Ficus, a high-NO−3 species, was associated with soil exhibiting higher rates of net mineralisation and net nitrification. “Low-NO−3 species” were evergreen perennials with low leaf N concentrations. A third group of plants, which assimilated NO−3 (albeit at lower rates than the high-NO−3 species), and had high-N leaves, were leguminous species. Acacia species, common in woodlands, had the highest leaf N contents of all woody species. Acacia species appeared to have the greatest potential to utilise the entire spectrum of available N sources. This versatility in N source utilisation may be important in relation to their high tissue N status and comparatively short life cycle. Differences in N utilisation are discussed in the context of species life strategies and mycorrhizal associations.

Restoring degraded tropical forests for carbon and biodiversity

The extensive deforestation and degradation of tropical forests is a significant contributor to the loss of biodiversity and to global warming. Restoration could potentially mitigate the impacts of deforestation, yet knowledge on how to efficiently allocate funding for restoration is still in its infancy. We systematically prioritize investments in restoration in the tropical landscape of East Kalimantan, Indonesia, and through this application demonstrate the capacity to account for a diverse suite of restoration techniques and forests of varying condition. To achieve this we develop a map of forest degradation for the region, characterized on the basis of aboveground biomass and differentiated by broad forest types. We estimate the costs of restoration as well as the benefits in terms of carbon sequestration and improving the suitability of habitat for threatened mammals through time. When the objective is solely to enhance carbon stocks, then restoration of highly degraded lowland forest is the most cost-effective activity. However, if the objective is to improve the habitat of threatened species, multiple forest types should be restored and this reduces the accumulated carbon by up to 24. Our analysis framework provides a transparent method for prioritizing where and how restoration should occur in heterogeneous landscapes in order to maximize the benefits for carbon and biodiversity.

Sustaining metal-loving plants in mining regions

The recent United Nations RIO+20 Conference on Sustainable Development highlighted the rapid increase in industrial mineral exploration and extraction over the past two decades ([ 1 ][1]). Endemic metallophyte plants, which have evolved where metal accumulations extend to the Earths surface, have

A Methodology to Monitor Airborne PM10 Dust Particles Using a Small Unmanned Aerial Vehicle

Throughout the process of coal extraction from surface mines, gases and particles are emitted in the form of fugitive emissions by activities such as hauling, blasting and transportation. As these emissions are diffuse in nature, estimations based upon emission factors and dispersion/advection equations need to be measured directly from the atmosphere. This paper expands upon previous research undertaken to develop a relative methodology to monitor PM10 dust particles produced by mining activities making use of small unmanned aerial vehicles (UAVs). A module sensor using a laser particle counter (OPC-N2 from Alphasense, Great Notley, Essex, UK) was tested. An aerodynamic flow experiment was undertaken to determine the position and length of a sampling probe of the sensing module. Flight tests were conducted in order to demonstrate that the sensor provided data which could be used to calculate the emission rate of a source. Emission rates are a critical variable for further predictive dispersion estimates. First, data collected by the airborne module was verified using a 5.0 m tower in which a TSI DRX 8533 (reference dust monitoring device, TSI, Shoreview, MN, USA) and a duplicate of the module sensor were installed. Second, concentration values collected by the monitoring module attached to the UAV (airborne module) obtaining a percentage error of 1.1%. Finally, emission rates from the source were calculated, with airborne data, obtaining errors as low as 1.2%. These errors are low and indicate that the readings collected with the airborne module are comparable to the TSI DRX and could be used to obtain specific emission factors from fugitive emissions for industrial activities.

Measuring fire severity using UAV imagery in semi-arid central Queensland, Australia

ABSTRACT Remote-sensing methods for fire severity mapping have traditionally relied on multispectral imagery captured by satellite platforms carrying passive sensors such as Landsat Thematic Mapper /Enhanced Thematic Mapper Plus or Moderate Resolution Imaging Spectroradiometer. This article describes the analysis of high spatial resolution Unmanned Aerial Vehicle (UAV) imagery to assess fire severity on a 117 ha experimental fire conducted on coal mine rehabilitation in an open woodland environment in semi-arid Central Queensland, Australia. Three band indices, Excess Green Index, Excess Green Index Ratio, and Modified Excess Green Index, were used to derive differenced (d) fire severity maps from UAV data. Fire severity data sets derived from aerial photograph interpretation were used to assess the utility of employing UAV technology to determine fire severity impacts. The dEGI was able to separate high severity, low severity, and unburnt areas with an overall classification accuracy of 58% and Kappa statistic of 0.37; outperforming the dEGIR (overall accuracy 55%, Kappa 0.31) and the dMEGI (overall accuracy 38%, Kappa 0.06). Classification accuracy increased for all indices when canopy shadows were masked, with dEGI improving to an overall accuracy of 68% and 0.48 Kappa. The McNemar’s test indicated that there was no significant difference between the classification accuracies for dEGI and dEGIR (p < 0.05). The test also demonstrated that dMEGI was significantly lower in accuracy compared to dEGI and dEGIR (p < 0.05). We quantified the proportion of burnt area within each severity class and calculated that 32% of the site was burnt at high severity, 34% was burnt at low severity, and 34% of the block was unburnt due to the patchy nature of the fire. We discuss the UAV-specific errors associated with fire severity mapping, and the potential for UAVs to assist land managers to assess the extent and severity of fire and subsequent recovery of burnt ecosystems at local scales (104m2–1 km2).

SPOTing long-term changes in vegetation over short-term variability

This study investigates change detection in the vegetation cover of a closed gold mine to assess whether the rehabilitated vegetation responds in a similar manner to the surrounding environment. Rehabilitation took place in seven rehabilitation areas within the mine site. SPOT scenes covering the site were acquired at six time periods from September 2004 to September 2005, and annually in the dry season from 2004 to 2010, except for 2008. Normalized difference vegetation index, soil-adjusted vegetation index and transformed soil-adjusted vegetation index were tested to estimate the percentage vegetation cover (PVC) using a linear regression model. The results showed higher PVC during wet season and lower PVC during the dry season in the native vegetation surrounding the mine site. However, temporal and spatial patterns of PVC in rehabilitated and native areas were similar only in the TD40ha rehabilitation area, one of the seven rehabilitation areas. This area was the first to be rehabilitated and had the most intensive rehabilitation effort using tube stock planting in March 1998. The seasonal variability showed a high correlation with an r2 value of 0.77 in TD40ha rehabilitation area in tailings dam, which was similar to the native area with an r2 value of 0.82. The findings of this study suggest that it is important for monitoring programs to take into account seasonal variation and environmental covariates, such as rainfall in order to successfully assess patterns in vegetation condition over time.

Tools for the Discovery of Hyperaccumulator Plant Species and Understanding Their Ecophysiology

Globally the discovery of hyperaccumulator plants has been hindered by systematic screening of plant species, and is highly biased towards Ni hyperaccumulators. This is mainly due to the existence of a reagent paper test that is only specific to nickel (based on dimethylglyoxime) such that more than 400 of the approximately 500 known hyperaccumulators species are for Ni. New technical advances now permit massive screening of herbarium specimens using non-destructive, portable X-Ray Fluorescence Spectroscopy (XRF), an approach that has already led to the discovery of numerous hyperaccumulator species new to science. The elemental distribution in selected hyperaccumulator plant tissues can then be further studied using techniques such as desktop or synchrotron micro-XRF, nuclear microprobe (PIXE), scanning/transmission electron microscopy with energy-dispersive spectroscopy (SEM/TEM-EDS), secondary ion mass spectrometry (SIMS) or laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). The use of histochemical dyes combined with light microscopy further aids in the identification of anatomical and structural features of the studied plant tissues.

The role of topography and plant functional traits in determining tropical reforestation success

1. Early establishment and sapling growth is a key phase in ensuring cost-effective reforestation success in relation to biodiversity outcomes. Therefore species selection must consider the interaction between plant functional traits and the often-challenging and heterogeneous biophysical environment of degraded landscapes. 2. In this study, we examine how microtopography (slope) results in spatial heterogeneity of soil nutrients, especially phosphorus (P) in a degraded tropical pasture landscape in Queensland, Australia. We then explore how this small-scale heterogeneity influences the growth of two native tree species, Cardwellia (C.) sublimis (Proteaceae) and Flindersia (F.) brayleyana (Rutaceae), which differ in key nutrient-acquisition strategies. 3. The proteaceous C. sublimis was found to be buffered from possible P limitation in degraded soils due to its effective P acquisition by cluster roots. In contrast to C. sublimis, which showed no difference in growth after 5 years across a range of soil conditions, F. brayleyana was found to be highly responsive to soil conditions with increased growth in low-slope, higher P availability areas. The ability of F. brayleyana to take advantage of high soil P levels, including the development of leaves with higher P concentrations, resulted in an apparent switch in competitive fitness between these two species across a landscape gradient. 4. Synthesis and applications. In a detailed study of a landscape reforestation experiment in North Queensland, Australia, we demonstrate that site edaphic factors can vary within tens of meters due to topographic relief, and that species respond differently to these conditions. We therefore show the need to consider both the spatial heterogeneity of edaphic factors and the below ground functional traits of potential reforestation species when planning reforestation programs.

Metallophytes on Zn-Pb mineralised soils and mining wastes in Broken Hill, NSW, Australia

The wastes of metalliferous mining activities produce a substrate that is generally unfavourable for normal plant establishment and growth. However, metallophytes have evolved to grow in hostile environments that are rich in metals. They possess key properties that commend them for revegetation of mines and metal-contaminated sites. This field survey aimed to identify native metallophytes occurring on minerals wastes and mineralised outcrops in Broken Hill (New South Wales, Australia). Foliar concentrations of minerals were very high compared with non-mineralised soils but within the range expected for plants in such environments. Neither hyperaccumulators nor obligate metallophytes have been found, but they may be present on isolated mineralised outcrops in the wider Broken Hill area; however, a range of facultative metallophytes was identified in this study. These species could be introduced onto mining leases if establishment protocols for such species were developed.