Abstract
The spread of an alien invasive grass (gamba grass—Andropogon gayanus) in the tropical savannas of Northern Australia is a major threat to habitat quality and biodiversity in the region, primarily through its influence on fire intensity. Effective control and eradication of this invader requires better insight into its spatial distribution and rate of spread to inform management actions. We used full-waveform airborne LiDAR to map areas of known A. gayanus invasion in the Batchelor region of the Northern Territory, Australia. Our stratified sampling campaign included wooded savanna areas with differing degrees of A. gayanus invasion and adjacent areas of native grass and woody tree mixtures. We used height and spatial contiguity based metrics to classify returns from A. gayanus and developed spatial representations of A. gayanus occurrence (1 m resolution) and canopy cover (10 m resolution). The cover classification proved robust against two independent field-based investigations at 500 m2 (R2 = 0.87, RMSE = 12.53) and 100 m2 (R2 = 0.79, RMSE = 14.13) scale. Our mapping results provide a solid benchmark for evaluating the rate and pattern of A. gayanus spread from future LiDAR campaigns. In addition, this high-resolution mapping can be used to inform satellite image analysis for the evaluation of A. gayanus invasion over broader regional scales. Our research highlights the huge potential that airborne LiDAR holds for facilitating the monitoring and management of savanna habitat condition.
Highlights
Savannas cover 20% of the global terrestrial land surface and account for 30% of terrestrial net primary production (NPP)[1]
In this study we explore the potential for very high-resolution airborne LiDAR to map the presence and distribution of A. gayanus in the tropical savannas of northern Australia
Andropogon gayanus is a perennial C4 grass that is structurally distinct from native grasses of northern Australia
Summary
Savannas cover 20% of the global terrestrial land surface and account for 30% of terrestrial net primary production (NPP)[1]. Global changes in land-use and climate threaten many of the ecosystem services that savannas provide, and the spread of alien invasive plants that alter fire regimes presents major additional ecological challenges [3]. Over the past two decades, there has been increased research focus on invasive alien grasses— mapping their distribution, determining patterns of spread, quantifying their ecological impacts and developing more effective management strategies. The focus on this group of invaders is the consequence of the substantial threat that they pose to the structure and function of many of the world’s ecosystems [4]. Ecological impacts include the displacement of native species and consequent reduction in native flora and fauna, significant changes to nutrient and water cycling, and substantial changes to fire behaviour and altered fire regimes [5,6]
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