SourCeBook oN remoTe SeNSiNg aND BioDiverSiTy iNDiCaTorS

Chapter 4. Trends in Selected Biomes, Habitats, and Ecosystems: Forests
Chapter 4. Trends in Selected Biomes, Habitats, and ecosystems: Forests
Authors: James Strittholt 1 , Marc Steininger
Contributors: Colby Loucks 3 , Ben White 4
Reviewers: Mette Løyche Wilkie 5 , Manuel Guariguata 6
1 Conservation Biology Institute, 2 Conservation International, 3 World Wildlife Fund (WWF-US), 4 Global Land Cover Facility,
University of Maryland, 5 Food and Agriculture Organization of the United Nations, 6 Center for International Forestry Research
Remote sensing based indicators for forests:
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Extent of component ecosystems
Forest change
Rate of deforestation/reforestation
Forest intactness
Area and number of large forest blocks
Forest fragmentation
Carbon storage
Area and location of old-growth forests
Area and location of plantations
Forest degradation
Area and location of sustainable forestry
Alien species
Fire occurrence
The physical characteristics of forest ecosystems reflect sunlight in the visible, near-infrared, and middleinfrared
regions of the light spectrum in ways that are easily distinguished from other types of vegetation
cover. Thus, remote sensing has become an important tool for evaluating forest ecosystems at multiple
spatial and temporal scales to examine and monitor forest composition, structure, and function (Kerr
and Ostrovsky 003).
4. 1 Delineating Cover and estimating Change in extent
Leaves are full of pigments that absorb visible light. Therefore, because of their dense leaf cover, forested
areas tend to reflect less light from the visible region of the spectrum (and thus appear darker than)
other vegetation types. In contrast, leaves strongly reflect near-infrared light — which is not visible to our
eyes — and thus they appear brighter when near-infrared data are mapped. Water in forest leaves absorbs
near-infrared light, and thus forests tend to appear dark when middle-infrared images are displayed.
The middle-infrared is also best able to reveal “canopy shading.” This is caused by the canopy geometry
(i.e., the uneven tree and branch height) of forests. In general, taller forests with more uneven canopies,
such as old-growth forests, appear darker in the middle-infrared than shorter forests with more even
canopies, such as young secondary regrowth, because of a combination of canopy shading and the water
absorption of leaves. This darkening trend is also seen in the near-infrared, although less so. Inundated
forests usually appear even darker still, because of even more light absorbed by standing water or wet
soils beneath the canopy. The brightness in all of these spectral regions also depends on the colour of
the background underneath the canopy, which is a mix of soil and vegetative litter. The influence of the
background colour is more obvious when leaf cover is lower, such as in areas of more open vegetation
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