In their recent letter in Trends in Ecology and Evolution, Loarie, Joppa and Pimm express their doubts about the long term future importance of satellite imagery with high spatial resolution (HSR) in environmental studies. I share the concerns of the authors that commercial HSR satellites cannot fulfill the need for uninterrupted global coverage to detect environmental and climatic changes. On the other hand, the bird’s eye view on the world offered by free online platforms such as Google Earth and Live Search Maps, creates novel opportunities to analyze fine-scale features over large spatial scales.
Church forest north of Lalibela, Ethiopia. Left image by R. Aerts, right image © DigitalGlobe – see online image here
Habitat fragmentation typically yields fine-scale features and is a key driver of global species loss, especially in formerly forested areas. With the ever rising competition for land forest patch sizes continue to decrease, and forest fragmentation studies worldwide are likely to become increasingly dependent of HSR data. Small fragments are essential for the conservation of biodiversity when large fragments are no longer available, and are therefore an environmental priority. Commercial HSR images should not replace courser earth-observing products, but as these are becoming
progressively more available for free, environmental scientists must not hesitate to peruse them to tackle the problems related to small
fragments or relictual vegetation.
Striking examples of small fragments are the Ethiopian Orthodox church forests. In northern Ethiopia, church forests and other sacred groves
represent the majority of all remaining patches of Afromontane forest in a landscape of degraded semiarid savanna. Previous studies in the
region only covered few fragments. To illustrate the power of free images on Google Earth, I digitized 394 church forests in an area of half a million hectares by systematically scanning HSR images in eight blocks at an eye altitude of 6-8 km. Results are harsh: while most sources estimate the current forest cover in Ethiopia at a meager 4%, the actual cover is even lower: 0.2%, which is virtually zero. This has dramatic consequences for remaining forest species in the region – many of them are probably lost, only, they don’t know it yet.
What other ‘more coarse’ methods for detecting environmental changes (particularly in forests) are preferable over HSR? I don’t imagine every acre of forest can be monitored and/or policed. Just curious.
Also, I thought I’d send you a link to an ongoing discussion on my blog about Amazon deforestation here
I’d be interested to hear your thoughts considering your perspective from another part of the world.
Thanks for your comments Nicholas.
Some of the ‘more coarse’ remote sensing methods for detecting environmental changes in forests are the standard normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI) which can be obtained from the Land Processes Distributed Active Archive Center (LP DAAC). The amount of data that is available is just incredible (global! coverage, every 16! days), but compared to HSR, it ‘only’ has a spatial resolution of 250 meters.