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Open AccessArticle

Spatial Dynamics of Invasive Para Grass on a Monsoonal Floodplain, Kakadu National Park, Northern Australia

1
Research Institute for Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory 0909, Australia
2
James Cook University, College of Science and Engineering, Cairns, Queensland 4879, Australia
3
The Western Australian Biodiversity Science Institute, 133 St. Georges Tce., Perth, WE 6000, Australia
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(18), 2090; https://doi.org/10.3390/rs11182090
Received: 11 July 2019 / Revised: 23 August 2019 / Accepted: 29 August 2019 / Published: 6 September 2019
African para grass (Urochloa mutica) is an invasive weed that has become prevalent across many important freshwater wetlands of the world. In northern Australia, including the World Heritage landscape of Kakadu National Park (KNP), its dense cover can displace ecologically, genetically and culturally significant species, such as the Australian native rice (Oryza spp.). In regions under management for biodiversity conservation para grass is often beyond eradication. However, its targeted control is also necessary to manage and preserve site-specific wetland values. This requires an understanding of para grass spread-patterns and its potential impacts on valuable native vegetation. We apply a multi-scale approach to examine the spatial dynamics and impact of para grass cover across a 181 km2 floodplain of KNP. First, we measure the overall displacement of different native vegetation communities across the floodplain from 1986 to 2006. Using high spatial resolution satellite imagery in conjunction with historical aerial-photo mapping, we then measure finer-scale, inter-annual, changes between successive dry seasons from 1990 to 2010 (for a 48 km2 focus area); Para grass presence-absence maps from satellite imagery (2002 to 2010) were produced with an object-based machine-learning approach (stochastic gradient boosting). Changes, over time, in mapped para grass areas were then related to maps of depth-habitat and inter-annual fire histories. Para grass invasion and establishment patterns varied greatly in time and space. Wild rice communities were the most frequently invaded, but the establishment and persistence of para grass fluctuated greatly between years, even within previously invaded communities. However, these different patterns were also shown to vary with different depth-habitat and recent fire history. These dynamics have not been previously documented and this understanding presents opportunities for intensive para grass management in areas of high conservation value, such as those occupied by wild rice. View Full-Text
Keywords: Vegetation mapping; landscape ecology; Invasive weeds; freshwater wetlands; adaptive land management; biodiversity conservation; fire; remote sensing Vegetation mapping; landscape ecology; Invasive weeds; freshwater wetlands; adaptive land management; biodiversity conservation; fire; remote sensing
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MDPI and ACS Style

Boyden, J.; Wurm, P.; Joyce, K.E.; Boggs, G. Spatial Dynamics of Invasive Para Grass on a Monsoonal Floodplain, Kakadu National Park, Northern Australia. Remote Sens. 2019, 11, 2090.

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