The seminar talked through the vital resource that mangroves are to humans and the future of our planet. Building on this, the talk showed why they are important and why they need to be safeguarded, as they have many beneficial ecosystem services. The talk focused on the creation of a global mangrove restoration map which will aid future mangrove conservation. No rocks as usual (yay!) and the continued theme relates to climate change.
Blog Theme: Conservation and restoration of mangroves, showing how important they are for our future
Ongoing Blog Theme: climate change on Earth: past and present – the things that have and will change and what we can do about it
What was the talk about?
The talk was about the creation of a global mangrove restoration map which can be used in the future for assessing potential sites that would benefit from restoration, and areas where degradation could be reduced. The talk also discussed why mangroves are important and why they need to be safeguarded, as they have many ecosystem services that are beneficial to humans and the environment.
What is a mangrove?
The coastal zone is the most heavily influenced by humans with high levels of human industry and agriculture located there e.g. the United Arab Emirates (see Figure 1). Along the coastlines is also where mangroves are located, and in recent years there has been a battle between humans and mangroves for valuable coastal land, which the mangroves are sadly losing.
Mangroves contain a mix of shrubs and trees, with more than 70 species and their hybrids adapted to live in the interface where the land meets the tides and the sea (see Figure 2 and 3). They are also adapted to high salinity concentrations.
There were an estimated 150,000 km² of mangroves in the year 2000, predominantly occurring in tropical climates (see Figure 4).
Mangrove forests once covered more than 200,000 km² of land. Sadly, annual mangrove loss rates are as high as 1-2% (this data is from the 1970s and 1980s) (see Information Box 1 for more facts). This was in part due to the stigma surrounding them about how hot, sweaty, insect ridden and uninhabitable they were.
Mangroves occur at the coast where many humans congregate. In places like Singapore, mangroves were removed and replaced by aquaculture e.g. shrimp farms. In Indonesia, aquaculture is the predominant reason for mangrove loss. In most of Eastern Asia and Myanmar mangroves are removed for rice paddy fields.
Areas with large mangroves also tend to be located in areas of the world with large expanding cities and growing populations. But, even though mangroves are shunned and destroyed for other land use purposes, they actually have many positive ecosystem benefits, which can be seen in Figure 5.
Mangroves provide important habitat for marine life, serving as sheltered nurseries for fish and providing food for human populations. For small local populations, mangrove wood is a valuable resource as it is resistant to rot. Mangroves prevent coastal erosion by stabilising lots of sediment in their vast root systems. Mangroves also act as a protective barrier to storms and hurricanes. Mangroves are diverse and beautiful places to visit, and so have become important for tourism as local populations can benefit from offering snorkelling, fishing and boat tours (WWF, 2019). The density of mangroves means that they have the potential to store vast amounts of carbon in the soil, something that is vital for combating climate change. In fact, mangroves account for 10-15% of global carbon burial. Mangroves also purify water through their vast root systems (Smithsonian, 2019).
Restoration of mangroves has become very popular in the last few decades with a focus on planting saplings to re-grow mangroves. However, long-term successes with this form of restoration are very low (usually 10-20%) due to saplings being planted below sea level and the use of inappropriate species e.g. the wrong species are planted in the wrong locations. All of this adds up to a big waste of time, resources and money while damaging natural habitat instead of conserving it. To top this, the success of these projects focuses on the number of trees planted and not on the long-term success and survival of the restored mangrove. In the end these projects don’t really give us much return on our investments. Therefore, another way to restore mangroves must be sought.
Restoration can be achievable if done properly to achieve conservation goals and this links in to what Tom and his team were working on. Tom’s research identified areas where restoration can be feasibly be achieved to benefit the local populations with ecotourism (see Information Box 2).
If you’d like to read more about mangrove restoration or the importance of mangroves you may find these links interesting:
The Smithsonian article is a good read: https://ocean.si.edu/ocean-life/plants-algae/mangroves
Also: The Mangrove Alliance ( http://www.mangrovealliance.org/) and Mangroves for the future (https://www.mangrovesforthefuture.org/)
Methods
Different mangroves differ from each other – there are 4 main types that the project identified:
1. Lagoon
2. Deltaic
3. Estuarine
4. Fringing (sheltered bay/behind a coral reef)
Each type has different restoration and ecosystem values. The project then categorised each mangrove type based on many different variables:
· River outlet No. (Deltas have the most outlets to the sea)
· River outlet length
· Angle of mangrove to coast (Lagoons are parallel to the coast while other types are perpendicular)
· Catchment area size (More precipitation with a larger catchment)
· Precipitation volume (riverine based types have more precipitation e.g. deltaic and estuarine)
Deltas and lagoons were hard to categorise from coastline maps as deltas are split into many different mangroves and lagoons are hard to spot.
The mangroves, once assigned, were defined further based on their sediment type e.g. Carbonate (organic) or Terrigenous (inorganic). The project was then able to build up a picture of individual mangroves and their variables on a very small scale.
Results
The main results showed that 40% of the mangroves the study categorised were deltaic, with the Brazilian coast having the most concentrated deltaic mangroves. Using the mangrove data that the study obtained, the project then moved onto the creation of a global mangrove map.
Before this project, there was only a snapshot of global mangrove populations from the year 2000. The project worked with the Global Mangrove Watch to produce a time map of mangrove loss. Using this map the project could then find key areas to restore.
(Find out more about Global Mangrove Watch and view their maps here: https://www.globalmangrovewatch.org/ )
Overall, lagoon-type mangroves had the worst losses while South and North America had lost the most mangroves of all the countries studied.
Worldwide, 6.6% of mangroves were lost since 1996, with an annual loss rate of 0.21%.
The project also studied mangrove degradation, something which is often overlooked in relation to loss. Degradation is driven by a number of factors which can be seen in Figure 6.
Using the Global Mangrove Watch maps, the project actually identified new areas containing mangroves that had not previously been recorded. The project highlighted areas where there were huge losses in mangroves due to degradation.
Restoration Map
To identify which mangrove areas would succeed from restoration, the project looked at several key variable environmental factors:
1. Tidal range
2. Sea level rise
3. Sediment regime
4. Timing of loss
5. Mean patch size
6. Patch contiguity
Areas that were the most restorable had no historic sea level rise, increasing sediment catchment and a predicted low sea level rise.
The project found that:
· 8,120 km² of mangroves were restorable
· These mangrove areas were located across 105 different countries/territories
· 6,630 km² of the restorable mangroves were rated as highly restorable
Ecosystem Services
If all of the 8,120 km² of mangroves are restored, then:
· 69 megatons of carbon could be stored in these areas by the plants
· 1000 trillion fish and invertebrates could be added to fisheries each year
· 12.5 Ma people would be protected from coastal surges/tsunamis etc
To view the project’s finished map and to have a play around with the data it contains follow this link: https://maps.coastalresilience.org/mangrove-restoration/ and here (since the first link can be unavailable at times): https://oceanwealth.org/explore-the-mangrove-restoration-potential-mapping-tool/
The project wants the map to become freely available for public use and public editing so that conservation projects can use the data when considering places to restore and then update the map. For the time being, the map is only available through the link, above, and cannot be edited by anyone outside the project. The data on the map will also not be updated until 2020, at the earliest, so that any sea level rises, or mangrove losses cannot be updated.
Limitations of the Techniques Used
The main techniques used were:
· GIS
· Landsat Radar Images
· Normalised Difference in Vegetation Index (NDVI)
· Google Earth Engine Data Catalog
GIS
Geographical Information Science is a technique that allows projects to gather data and analyse in various formats such as maps and 3D scenes. GIS is a very versatile and suitable technique for identifying relationships between geomorphology and mangroves, enabling the advancement of the project. Through the use of GIS mapping, the project is able to monitor changes in the landscape and apply this to mangrove restoration (esri, 2019).
Landsat Radar Images
Landsat is a satellite imaging system that images the human and natural changes that take place on the planet’s surface and has been doing so continuously since 1972 (NASA, 2016). The technique was very suitable for the project as it allowed it to utilise worldwide images showing the human and environmental changes that have affected mangroves. However, cloud cover cannot be controlled and so this reduces the data available from the images greatly and will always impact the use of the images. Also, Landsat images did not cover the globe fully until the 1990s and so there are gaps in the image record that would hinder studies looking at mangrove change over the last 5 decades.
NDVI
The index identifies patches of land that contain high amounts of vegetation based on the reflected wavelengths of light produced by the plants present. If there is dense vegetation present, then there will much more reflected radiation from near-infrared wavelengths compared to visible wavelengths. Sparse vegetation is indicated by a similar reflected radiation from both near-infrared wavelengths and visible wavelengths.
Most of the satellite systems use the NDVI to assess the density of plants on Earth. The scale produced by the index is between +1 and -1. A score closer to +1 indicates healthier and denser vegetation, while scores of less than zero indicate sparse to no vegetation (see Figure 7). The index is a suitable technique and gives a good score for density of vegetation in an area and this can be related to previous scores to show mangrove degradation while also being used to highlight areas that could benefit from restoration.
Google Earth Engine Data Catalog
The Earth Engine data is powered by Google and a free to use public data set. The engine provides data for temperature, climate, satellite imagery and geophysical imagery as well as much more (Earth Engine Data Catalog, 2019). The technique is very suitable as Google analyses data sets for free using their high-performance computers giving very detailed high-resolution images and data that can be utilised.
How did the Talk Advance our Knowledge?
The talk highlighted how precious mangroves are to our planet and to humans – they have so many ecosystem services that are vital to reducing the impact of climate change and benefiting and protecting humans. However, given the rapid losses of this underrated resource, restoration and conservation of mangroves is vital. Tom’s project helped create a global mangrove restoration map that will be an important tool for restoration projects to understand the type of mangrove and consequently the restoration considerations and ecosystem benefits that each mangrove type has. To help lower carbon emissions and protect marine habitats for future generations, the restoration and protection of mangroves is essential.
If you would like to read more about Tom’s work you can follow this link here: https://www.researchgate.net/project/Mangrove-Restoration-Potential-Map and to read his story map click here: https://www.researchgate.net/deref/https%3A%2F%2Fuploads.knightlab.com%2Fstorymapjs%2F1cbea3f748012e49b6ae12df3b1e0db8%2Fmangroves-restoration-opportunities%2Findex.html
Thanks for reading!
Continue next time with my blog relating to the climate and ice interactions of Patagonia - an important topic relating to the theme of climate change.
References:
Earth Engine Data Catalog. (2019). A planetary-scale platform for Earth science data & analysis. Available at: https://developers.google.com/earth-engine/datasets/ [Accessed: 28/03/2019]
esri. (2019). What is GIS? Available at: https://www.esri.com/en-us/what-is-gis/overview [Accessed: 28/03/2019]
NASA. (2000). Normalized Difference Vegetation Index (NDVI). Available at: https://earthobservatory.nasa.gov/features/MeasuringVegetation/measuring_vegetation_2.php [Accessed: 28/03/2019]
NASA. (2015). United Arab Emirates, Persian Gulf. Available at: https://earthobservatory.nasa.gov/images/87245/united-arab-emirates-persian-gulf [Accessed: 26/03/2019]
NASA. (2016). Landsat Science. Available at: https://landsat.gsfc.nasa.gov/imaging-the-past/ [Accessed: 28/03/2019]
Ocean Wealth. (2019). Explore the Mangrove Restoration Potential Mapping Tool. Available at: https://oceanwealth.org/explore-the-mangrove-restoration-potential-mapping-tool/ [Accessed: 28/03/2019]
Science World. (2018). Mapping Mangroves. Available at: https://scienceworld.scholastic.com/issues/2018-19/100818/mapping-mangroves.html#1120L [Accessed: 28/03/2019]
Smithsonian. (2019). Mangroves. Available at: https://ocean.si.edu/ocean-life/plants-algae/mangroves [Accessed: 28/03/2019]
WWF. (2013). Sinks and Sources - Awesome Mangroves. Available at: http://wwf.panda.org/?210971/Sinks-and-Sources---Awesome-Mangroves [Accessed: 26/03/2019]
WWF. (2019). Mangrove Importance. Available at: http://wwf.panda.org/our_work/oceans/coasts/mangroves/mangrove_importance/ [Accessed: 28/03/2019]
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