Putting Comorian landscapes on the map

By Katie Green (BCSF)

While the community team have been busy working on agricultural development and natural resource management activities, the ecological monitoring team have been scaling the steep Comorian mountains searching for and recording the islands’ unique biodiversity and monitoring forest habitats. Click here to read more about our ecological monitoring and research work.

The arrival of Merlijn Jocque, a field biologist employed by Durrell to support the ecological monitoring programme, brings the team up to five people. Surveying all three islands in detail twice a year (dry and wet season) is pretty exhausting so an additional pair of highly-skilled hands is going to make things a lot easier. It also means that I am now able to devote some time to completing the first high-resolution land cover maps of the Comoros.

Detailed and accurate land cover maps are essential for assessing the extent of forest cover, mapping species distributions, and identifying areas for protection. These data can then be used as a baseline to monitor changes and the impact of the community work on forest and biodiversity.

We’re producing the maps from specially commissioned satellite images of the three islands. Imagery software can classify each pixel of these images, depending on how the land cover at that point reflects sunlight into space. To be able to do this, the software first needs to be ‘trained’ using field data. The collection of field data is called ‘ground truthing’ and involves taking detailed descriptions of land cover at specific points and using a hand held GPS unit to record locations.

Just before Merlijn got here, field technician Ishaka Saïd and I completed the ground-truthing work in Grande Comore. We covered the island from top to bottom and walked a total of 120km, including climbing the highest point in the Comoros, the active volcano Mount Karthala, at 2344m above sea level.

The long trek took us through an array of habitats: coconut and banana plantations cover the lower slopes which gradually make way for lush cloud forest higher up. Higher still, the path breaks out into an open heathland reminiscent of a windswept moor in the UK, complete with a population of common stonechats. Finally, we were greeted at the summit by a lunar landscape of volcanic sand and rock interspersed with the charred remains of vegetation blasted by the last eruption.

Other highlights of our travels around the island included beautiful orchids and butterflies, tenrecs, geckos, chameleons (all pictured), several confusing paths not shown on the map, and warm Comorian hospitality. But what also became very clear to us was the extent of deforestation on the island. Natural forest remains only in fragments in La Grille mountain range in the North and on the higher slopes of Mount Karthala. Apart from these areas, the majority of the island is covered by plantations and open grassland. Forest-dependent species are now restricted to small areas at high altitudes where human activities are low, threatening their long term survival prospects. This includes the endemic Karthala scops owl (Otus pauliani), which is listed as Critically Endangered on the IUCN’s red list.