MapWAPS Project

MapWAPS Project - Mapping Woody invasive Alien Plant Species

The Water Research Commission has funded a project which aims to map woody invasive alien plants and their impacts in four key strategic water source areas. Strategic water source areas are those which supply a disproportionately large amount of water relative to their area. Called “MapWAPS” for short, this project was launched on 1 April 2022 and will run for three years until March 2025.

Aim: To use freely available satellite imagery and cloud computing to map alien trees in some of the strategic water source areas that do not have recent information on biological invasions and their impact

Why is this important?

These maps are a crucial tool for water resource managers, conservationists, and policymakers to make informed decisions in protecting South Africa's precious water sources. Invasive alien trees have the potential to outcompete native vegetation, alter natural habitats, and disrupt ecosystems. By mapping their distribution, extent, and impact, we gain valuable insights into the areas under threat, enabling proactive conservation measures.

These maps serve as indispensable tools for environmental management, allowing stakeholders to identify high-risk zones, prioritize intervention efforts, and implement targeted control strategies. Additionally, mapping invasive alien trees is essential for safeguarding water sources, as these species often consume excessive water, posing a significant threat to the delicate balance of water ecosystems.

The data generated through mapping empowers decision-makers, conservationists, and community members to collaboratively address the challenges posed by invasive alien trees and work towards preserving the integrity of our natural landscapes. For example, mapping different wattle taxa in the uMzimvubu Catchment can inform local communities as to the feasibility of biochar programmes. Black Wattle (Acacia mearnsii) is a higher value wood product compared to Silver Wattle (Acacia dealbata).

Study Sites

The invasive alien tree maps cover four strategic water source areas in four different provinces in South Africa: the Luvuvhu Catchment (Limpopo), the Sabie-Crocodile Catchments (Mpumalanga), the Tugela Catchment (KwaZulu-Natal) and the uMzimvubu Catchment (Eastern Cape). Typically the mapping focusses on woody invasive alien taxa, such as pines, wattle, gums, poplars, as well as a few other more shrubby taxa such as Bugweed (Solanum mauritianum). The taxa mapped in each catchment depend on what the key issues in those catchments are, as advised by key stakeholders.

The four proposed project study catchments. The surface water strategic water source areas are indicated by blue filled polygons, tertiary catchments by orange lines, provinces in black, and the major rivers in dark blue

Methods

During the fieldwork campaigns, the MapWAPS team engaged in extensive data collection and collaboration with stakeholders and local community partnerships, such as the uMzimvubu Catchment Partnership, and the newly formed Tugela Catchment Partnership. To promote open science and data sharing, each part of the data collected will be archived and made publicly available. This includes the training data on iNaturalist.org, as well as the maps which are available on the SUNScholar Repository, and the code, which will be made available via GitHub at the end of the project.

This study uses satellite imagery from the Sentinel-2 mission developed by the European Space Agency (ESA) as part of the Copernicus program. It consists of a constellation of two identical satellites, Sentinel-2A and Sentinel-2B, launched in 2015 and 2017, respectively. The primary objective of the Sentinel-2 mission is to provide high-resolution optical imagery of Earth's surface for various applications, including land monitoring, agriculture, forestry, and environmental management.

The satellites carry a multispectral imaging instrument that captures data in 13 spectral bands, ranging from visible to infrared wavelengths. With a revisit time of 5 days, Sentinel-2 enables regular and systematic monitoring of changes on the Earth's surface, contributing valuable information for sustainable resource management and disaster response. The data are also free, which is critical for resource-constrained regions. In addition, we make use of free cloud computing platforms, such as Google Earth Engine, which allows us to minimize processing costs.

Outputs: Explore the maps

To access the quicklooks of the alien tree maps for each of the study catchments, please use the following links:

Luvuvhu Catchment: https://mapwaps-luvuvhu.projects.earthengine.app/view/mapwaps-luvuvhu

Sabie-Crocodile Catchments: https://mapwaps-sabiecroc.projects.earthengine.app/view/mapwaps-sabiecroc

Tugela Catchment: https://mapwaps-tugela.projects.earthengine.app/view/mapwaps-tugela

uMzimvubu Catchment: https://mapwaps-umzimvubu.projects.earthengine.app/view/mapwaps-umzimvubu

Outputs: Download the data

To access the data for each of the study catchments, please use the following links:

MapWAPS Invasive Alien Plant map for the Tugela Catchment: https://doi.org/10.25413/sun.25066151

MapWAPS Invasive Alien Plant Map for the uMzimvubu Catchment: https://doi.org/10.25413/sun.25050401

MapWAPS Invasive Alien Plant Map for the Luvuvhu Catchment: https://doi.org/10.25413/sun.25050314

MapWAPS Invasive Alien Plant map for the Sabie-Crocodile Catchments: https://doi.org/10.25413/sun.25050368

Check out an example of one of our alien tree classifications here: This specific app is for the uMzimvubu Catchment, Eastern Cape, South Africa

Publications

Mapping project sheds new light on alien invasion of SA catchments; Waterwheel: https://www.wrc.org.za/mdocs-posts/the-water-wheel-may-june-2024/

New project aims to map alien invasive trees; Waterwheel: https://www.wrc.org.za/wp-content/uploads/mdocs/WW%20Jan-Feb%202023%20web.pdf

Project Team

The project team is led by Dr Alanna Rebelo of the Water Science Unit at the Agricultural Research Council – Natural Resources and Engineering, and includes PhD student Liam Cogill, MSc student Thandeka Skosana, and Prof Karen Esler of the Conservation Ecology and Entomology Department, Stellenbosch University. Prof David le Maitre was also involved in the proposal writing.

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