Todd P. Robinson

Mapping Mesquite (Prosopis) Distribution and Density Using Visual Aerial Surveys

Abstract Mapping the distribution and abundance of invasive plants is a high priority, but establishing cost-effective and practical techniques at appropriate scales remains elusive. Mesquite is a highly invasive shrub that cannot currently be reliably distinguished from other plant species using remote sensing technologies, at least not at accuracies necessary for mapping mesquite at very low densities. This paper describes and tests an alternative method. A visual, aerial technique was used to map a large mesquite (Leguminoseae: Prosopis spp.) population in Australia; 216 654 ha was surveyed in 18.5-ha grid cells to include the entire population. The objective was to test the ability of this technique to detect and map mesquite at very low densities for surveillance and to assist in prioritizing management effort and, where mesquite was well established, to categorize mesquite into broad canopy cover classes for change detection and to identify habitat associations. The survey technique was very effective at detecting isolated mesquite plants (< 0.6% canopy cover across a grid cell), which is considerably better than existing remote sensing technologies. Detection of low-density mesquite was particularly important, as most occupied grid cells (55%) had isolated mesquite, and their management may offer the best return on investment. The technique was also competitive cost wise (

A low-altitude mountain range as an important refugium for two narrow endemics in the Southwest Australian Floristic Region biodiversity hotspot

0.39 USD per hectare) and required relatively little expertise. Grid cells with moderate (20%–50%) to dense (> 50%) canopy covers were almost all restricted to a 32 500-ha area on the floodplain delta of the Fortescue River, where the original introductions occurred. Cover class estimates appeared to be well calibrated between observers within a survey; however, they were poorly calibrated between independently conducted surveys, suggesting that further methodological refinement is necessary if this technique is to be reliable for change detection.

Seasonal differences assist in mapping granite outcrops using Landsat TM imagery across the Southwest Australian Floristic Region

Background and Aims Low-altitude mountains constitute important centres of diversity in landscapes with little topographic variation, such as the Southwest Australian Floristic Region (SWAFR). They also provide unique climatic and edaphic conditions that may allow them to function as refugia. We investigate whether the Porongurups (altitude 655 m) in the SWAFR will provide a refugium for the endemic Ornduffia calthifolia and O. marchantii under forecast climate change. Methods We used species distribution modelling based on WorldClim climatic data, 30-m elevation data and a 2-m-resolution LiDAR-derived digital elevation model (DEM) to predict current and future distributions of the Ornduffia species at local and regional scales based on 605 field-based abundance estimates. Future distributions were forecast using RCP2.6 and RCP4.5 projections. To determine whether local edaphic and biotic factors impact these forecasts, we tested whether soil depth and vegetation height were significant predictors of abundance using generalized additive models (GAMs). Key Results Species distribution modelling revealed the importance of elevation and topographic variables at the local scale for determining distributions of both species, which also preferred shadier locations and higher slopes. However, O. calthifolia occurred at higher (cooler) elevations with rugged, concave topography, while O. marchantii occurred in disturbed sites at lower locations with less rugged, convex topography. Under future climates both species are likely to severely contract under the milder RCP2.6 projection (approx. 2 °C of global warming), but are unlikely to persist if warming is more severe (RCP4.5). GAMs showed that soil depth and vegetation height are important predictors of O. calthifolia and O. marchantii distributions, respectively. Conclusions The Porongurups constitute an important refugium for O. calthifolia and O. marchantii, but limits to this capacity may be reached if global warming exceeds 2 °C. This capacity is moderated at local scales by biotic and edaphic factors.

A Comparison of Inverse Distance Weighting and Ordinary Kriging for Characterising within- paddock Spatial Variability of Soil Properties in Western Australia

Knowledge of the location and extent of granite outcrops (GOs) in the Southwest Australian Floristic Region is important to understand their role as refugia. We present a methodology to map GOs using biannual Landsat TM imagery. An adaptive vegetation cover mask capitalising on seasonal differences, combined with a supervised classification, allowed differentiation of granite from other land covers on five GOs across the rainfall gradient. This methodology provided high classification accuracy (Overall Kappa ranged from 0.83 to 0.91) irrespective of location. Therefore, there is potential to use these methods to compile a more complete GO inventory over the region.

Exploring passenger rail markets using new station catchment size and shape metrics

Site-specific crop management requires matching resource application and agronomic practices with soil and crop requirements, as they vary in space and time within a field. As such, information on the composition of soils at either farm or paddock scale is essential. Soil composition over an entire paddock might not be uniform. For instance, it may not be efficient to fertilise an entire paddock if only the northeast corner show deficiencies. Furthermore, it is not possible to sample every centimetre of the paddock, as this would be a very time consuming and costly procedure. Ideally, we should be able to collect enough sample points so that continuos maps of soil properties can be accurately produced using spatial interpolation techniques, and good judgements can be made about the soil composition of an entire paddock. Two spatial interpolators, namely kriging and inverse distance weighting (IDW) are compared in this paper, evaluating their accuracy in the prediction of seasonally stable soil properties at paddock level. Organic matter content and soil reaction (pH) are the soil properties selected for this investigation, as previous research by Yule et al. (1996) and Brady and Weil (1999) has found these properties to be correlated to cropping potential. The selected spatial interpolators are tested on an existing data set (e.g. 100 soil samples) collected using a stratified random approach over a 60 ha paddock, located in the southwest of Western Australia. The research approach consists of three main steps. Firstly, basic descriptive statistical techniques are applied to identify the presence of outliers. Secondly, selected interpolators are applied to generate continuous maps of the soil properties, and finally the mean root mean square error (RMSE) is used as the validation index, and to select the best spatial interpolator for the soil properties selected. Therefore, for each soil property, every fourth sample is removed from the main data set and put aside to validate the result of the interpolation method. Likewise, the map of uncertainty generated by using the kriging interpolation method is used as an additional source for evaluating the quality of the prediction maps. The RMSE results show IDW to perform slightly better than kriging for pH (e.g. 0.38 vs 0.39) and organic matter (1.25 vs 1.34)

Testing the performance of spatial interpolation techniques for mapping soil properties

ABSTRACT This paper presents a novel spatial market segmentation method to determine key user groups of a train station (such as gender, age and access mode), based on the size and shape of the station catchment area of each group. Two new indices – area ratio and composite ratio – are developed to quantify the importance of user groups for a train station. This method is applied to identify key user groups at seven train stations in Perth, Western Australia. The study offers a new way to explore the travel behaviour of train users and provides insights for rail transport planning and marketing.