Open Source GIS Tools Helping Save Mangrove Forests

July 12, 2017
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At the end of the Baja Peninsula between the states of Sinaloa and Nayarit lies the Marismas Nacionales,or National Marshes, the largest intact mangrove forest on the Pacific Coast of Mexico. The ecosystem services provided by these hundreds of square miles of mangrove forests are important to the local economy, especially the families who rely on fishing and shrimping. The mangrove ecosystems in the Marismas Nacionales also provide other benefits sustaining and fulfilling human life, such as local coastal erosion protection and carbon sequestration. Mangrove forests can remove greenhouse gases like carbon dioxide from the atmosphere and they store enormous amounts of carbon in their sediments, leaves, and other biomass. Yet over the last 45 years, mangrove forests in the Marismas Nacionales have been in decline. The construction of dams is a likely cause. Dams create imbalances in salinity and sediment that can affect large areas of mangrove forest.

map of Marismas Nacionales

 Map showing the location of Marismas Nacionales on the Pacific Coast of Mexico near the Baja Peninsula. 

Ecologists Without Borders and Pronatura México are two nongovernmental organizations that have been trying to quantify and, ultimately, help reverse the decline of mangrove forests in the Marismas Nacionales. In the summer of 2015, EcoWB approached the University of Washington looking for students with GIS experience to recommend a solution. EcoWB needed a cost-effective option that was documented in enough detail for their partner organizations in Mexico to implement it themselves. The UW graduate student team recommended that EcoWB use a free and open source GIS toolkit from the Natural Capital Project’s Integrated Valuation of Ecosystem Services and Tradeoffs. The lessons learned from the team’s work, described below, suggest that, in some situations, a free and open source GIS solution is a better option than a proprietary one.

 Inside of a damaged mangrove forest surrounded by healthier mangrove due to water flow restrictions in Francisco Villa, Nayarit, Mexico (Photo by Eric Knudsen).

The InVEST toolkit is a collection of free and open source geospatial models, developed by the Natural Capital Project, for assessing how changes to an ecosystem inevitably lead to changes in the flows of benefits to people. One of these models, the Coastal Blue Carbon model, can assess how much carbon is being stored and sequestered as land cover changes over time. The Coastal Blue Carbon model can also be used to estimate the economic value and the possible market price of sequestered carbon, including predicting the economic value of future restoration scenarios to improve ecosystem services.

Initially, the graduate student team used both proprietary and free and open source desktop GIS applications to prepare the input data for the InVEST Coastal Blue Carbon model. For its design and testing work, the graduate student team combined general purpose mangrove forest data with mangrove forest data collected in the field in the Marismas Nacionales. The team also had access to land use and land cover data from 1970 to 2010 covering over 770 square miles of mangrove in the Marismas Nacionales. A good understanding of mangrove forests in the field proved to be critical. The Coastal Blue Carbon model lets users input values collected locally in the field, rather than general purpose estimates, which can improve the accuracy of the model’s estimates of above- and below-ground carbon stocks and sequestration. The model also requires users to assign values of high, medium, or low disturbance to land use and land cover changes.

Map of carbon sequestration from 1973 to 1990 and from 1990 to 2015, illustrating use of the InVEST tool to identify where declines in carbon sequestration due to the degradation of mangroves has been occurring.

The figure above illustrates some of the results. The graduate student team was able to produce maps showing carbon stocks, carbon sequestration, and the net present value of carbon sequestration for the northern and southern extents of the Marismas Nacionales mangrove forests for the period 1973 to 2010. Mapping changes over time from 1970 and 2010 illustrated exactly where the highest declines in carbon sequestration were occurring in the Marismas Nacionales. In addition, the graduate student team modeled a mangrove restoration scenario for 2015 that demonstrated how the ecosystem services provided by the mangrove forests could recover.   

EcoWB and Pronatura México believe that the maps will make local communities and governmental agencies in Mexico more aware of the value of the mangrove forest ecosystem services in the Marismas Nacionales and help them focus their restoration activities. Eric Knudsen from EcoWB said, “The GIS analysis was used to help local communities determine the importance of restoring a deteriorating mangrove forest. Mangroves are important because they fringe shallow coastal wetlands where their leaf litter contributes to highly productive nursery areas for young fish and shrimp, which are the basis of commercial and artisanal subsistence fisheries.”

However, involving more of the community in reversing the decline of the mangrove forests in the Marismas Nacionales requires moreincentives. Using a free and open source geospatial model like the InVEST Coastal Blue Carbon model to estimate carbon credits, and then selling those carbon credits on the international carbon market, represents one potential way of providing local incentives for mangrove restoration in Mexico, but several challenges have to be overcome. Mangroves are currently not listed as part of the international carbon credit market. In addition, while there are specific guidelines when it comes to measuring carbon storage and sequestration on dry land, similar standards do not exist for coastal mangrove forests.

Nonetheless, the results did help Pronatura México get governmental agencies and community leaders more interested in supporting the restoration of the mangrove forests. In fact, one member of the graduate student team was sent to Mexico in order to provide hands-on training in the use of the models. Miguel Vargas, director of Pronatura México said, “The principal benefit is the information gathering in a short time lapse, showing the areas with the most damage as well as the areas that have been recovered. Also, it is of great importance to know what areas are emitting carbon to prioritize restoration efforts.” Future work is needed to improve the accuracy of estimates of the value of the ecosystem services that the Marismas Nacionales mangrove forests supply to people, but by providing step-by-step documentation using a free and open source desktop GIS and the InVEST toolkit, the graduate student team lessened many of the technical burdens on EcoWB and Pronatura México when it comes to including more geospatial analysis in their future work.

References

Lopez, Anssel, and Kimberly Nepsa. (2015). Carbon storage: Utilizing carbon-based modeling for mangrove restoration efforts, Marismas Nacionales, Mexico. Master of GIS for Sustainability Management Program. Seattle: University of Washington.

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