Mapping the Harapan Rainforest - how we did it
We have done a lot of work collecting data in the Harapan Rainforest, in lowland Sumatra. In this blog we present an overview of how all that data is used to produce a vegetation map.
Our focus was to summarize the condition of the Harapan Rainforest. Satellite imagery (taken by the French satellite SPOT in 2009) was used to generate a very basic classified image. These pictures were three years old, but were the most recent high resolution images that we could find of the entire Harapan Rainforest boundary, with low cloud cover (it is very wet and cloudy there).
In general, we view forests in shades of red, as a false colour composite (FCC). This is where the image colours are shifted to allow us to use near infra-red. Healthy vegetation reflects the near infra red (making it look red in the resultant image). The naked eye can discriminate more shades of red than any other colour.
In this map, the darker the red the more developed the forest (or at least this is the theory we wanted to test).
A quick classification of the SPOT imagery gave us an indication of vegetation differences that we might be able to identify on the ground within the forest. We were not entirely sure what those differences were and that was why we needed to verify them with ground-based observations.
At each plot we collected the following data:
- location coordinates
- environment eg hill slope, swamp, etc.
- percentage forest cover
- size of trees
- dominant tree species
- dominant understory vegetation
Periodically, we sent data up to the server whenever we had a WiFi connection back at base camp. Back at Kew the data was collated and published on the GIS Unit Expedition Maps webpage. Geotagged tweets as well as our ODK datasheets were mapped in near-real-time.
It was a very successful field campaign and we surveyed over 300 plots assessing detailed canopy measurements and environmental variables with associated geo-locations, photographs and videos.
Back at Kew
Back in the office at Kew we cleaned up the data, filled-in blanks and attached photos taken with our own cameras. The field data was broken into thirds. One third was used to train the satellite imagery into defined forest categories and the last two-thirds to test the classification.
The forest categories we used were: Old Secondary Forest/Disturbed, Young Secondary Forest/Disturbed, Very Young Secondary Forest (Thicket/Disturbed), Scrub, and Cleared. After a few iterations a base map was produced for the area. Our results show that all forest levels showed good potential for regeneration by species identified in the field. There was a lot more intact forest than we had suspected from our initial work with the satellite imagery. See some of the results shown on the map here.
We are finishing up this phase of the project, but are still updating our online expedition maps with geo-located photographs and our next blog will show you some of the highlights.
- Jenny -