Invasive Species Spread: Mapping the Impacts of Climate Change from Space
Nepal is considered to be one of the most vulnerable nations to climate change. The country’s unique geographic and topographic variations contribute to its rich biodiversity, which is at great risk from the spread of invasive species. As invasive species are more adaptable to change, they are wiping out critical native species that help communities and ecosystems thrive.
Using satellite imaging, the Innovation Lab for Integrated Pest Management and Tribhuvan University in Nepal monitor the spread of invasive weeds, tracking species specifically between the period of 1990 to 2018. The programs account for climatic changes that have occurred over the last 30 years – such as fluctuations in rainfall and temperature – to measure how climate change impacts the spread of the invasive weeds over time.
Chromolaena odorata is one such weed, and is considered one of the world’s worst invasive alien species. Native species are greatly impacted by Chromolaena’s spread. The weed alters soil health, and due to the high level of nitrate content in its leaves, it’s poisonous to cattle.
Tribhuvan University graduate student Sita Gyawali utilized multispectral and medium spatial resolution satellite data – using programs such as Landsat, World View 2, and ArcGIS – to show that Chromolaena has significantly increased in spread over the last 30 years. The weed’s expansion in the Chitwan Annapurna Landscape (CHAL) area was 0.62% in 1992, and 0.87%, 1.11%, 1.29% in the years of 2000, 2010, and 2018, respectively. In total, its coverage increased from 201 sq. km to 412 sq. km, indicating that the weed is still invading new areas. The invasion of Chromolaena is expanding mostly in the mid-hill region of Nepal, considered to encompass the country’s most fertile lands.
“Images from such programs as Landsat and World View have become an invaluable source of data for detecting the spatial distribution of Chromolaena in Nepal,” said Gyawali. “Historical time series of remotely sensed data presents opportunities for characterizing habitat preferences of new species. This information provides us the insight we need in order to find management technologies that can combat the weed.”
In addition to Chromolaena, the project is also assessing the distribution expansion of the invasive weed Lantana camara. Lantana can be extremely destructive, as it smothers native vegetation, reducing species diversity and leading to species extinction. Tribhuvan University graduate student Sandeep Dhakal used Landsat images to show that the weed has increased in spread over the last 30 years, progressing from 0.24%, 0.9%, 1.45%, and 2.74 % in area in CHAL in the years 1992, 2000, 2009, and 2018, respectively. The largest area of distribution was found in Middle Mountain, followed by Siwalik and high mountains.
“Effective mapping of invasive species extent and determining the risk they pose for future invasions is incredibly important to Nepal,” said Dhakal. “The food we eat, the land our animals graze on, and more is at risk if we do not continue to utilize these types of programs to understand invasive species impact.”
Tribhuvan University students knew little about remote sensing before the start of the Virginia Tech-managed project. They gained satellite monitoring and modeling expert assistance from collaborators at the University of Virginia’s Biocomplexity Institute, who also operate the IPM Innovation Lab's monitoring program of the invasive insect pest Tuta absoluta. Through this project alone, the IPM Innovation Lab has supported 27 students for their graduate degrees in Nepal.
“For students to come into this program and learn a completely new skill – one that they will be able to apply to future careers – is a major contribution to building Nepal’s local research capacity,” said Pramod K. Jha, head of the program. “We know that invasive species respond quickly to change. As climate change persists and globalization continues, we cannot afford to wait to see how our lands are changing over time. Monitoring systems using satellite imaging help give us a bird’s eye view of not only how quickly this change is happening, but how quickly we need to react to ensure no further damage is done.”
Graduate students involved in the invasive weed modeling program in Nepal have already published 42 research publications in international and national journals in the areas of climate change, satellite imaging, biodiversity, and beyond.