| Land cover classification | (see Section 2.2) |
Brief definition of the land cover classes used in the pan-tropical survey of forest resources based on high resolution satellite data
| Homogeneous Land Cover Classes | average height | canopy coverage | description |
| Closed Forest | > 5 m | > 40 % | Continuous tree formation of natural origin |
| Open Forest | > 5 m | 10–40 % | Continuous tree formation of natural origin |
| Shrubs | 1–5 m | > 10 % | Low woody vegetation of natural origin |
| Other Land Cover | < 10 % | Land with woody vegetation below 10 % | |
| Plantations | > 1 m | (dense) | (synonymous of Man-made Woody Vegetation) Forestry or agricultural plantation |
| Water | Sea, lakes, reservoirs, rivers | ||
| Composite Land Cover Classes | |||
| Fragmented Forest | (forest) > 5 m | (forest) > 10 % | Mosaic of forest and non-forest with forest fraction between 10 and 70% of total area (estimated average 33%) |
| Long Fallow | variable | variable | Mosaic of mature forest, secondary forest, various stages of natural regrowth and cultivated areas with cultivated areas covering between 5 and 30 % of total area |
| Short Fallow | variable | variable | Mosaic of young secondary forest, various stages of natural regrowth and cultivated areas with cultivated areas covering between 30 and 50 % of total area |
Other specifications:
Scale: the scale of the interpreted satellite images is 1: 250 000.
Minimum mapping unit = 3 × 3 mm, approximately 50 ha, or 2 mm width for linear features.
A forest class is considered continuous or non fragmented when the non-forest elements (below minimum mapping unit) present in it are less than 30 % of the class.
A forest class is considered fragmented when the non-forest elements (below minimum mapping unit) present in it are more than 30 % of the class and the forest fraction is between 10 and 70 %.
The composite classes (Fragmented Forest, Long Fallow, Short Fallow) are used where individual elements are below minimum mapping unit (< 3 × 3 mm).
| Definitions of forest | (see Section 2.2.1) |
Three different definitions of forest have been adopted in the analysis and presentation of survey results:
F1 = closed forest
F2 = closed + open forest + 2/3 fragmented forest
F3 = closed + open forest + fragmented forest + long fallow
F1 represents forest in the strictest sense, mostly dense, not fragmented nor (heavily) degraded.
F2 is a definition aimed at matching the concept of forest used in FORIS (Forest Resources Information System) by FAO in its periodic assessments based on existing information. According to the FORIS definition the class long fallow is excluded; the reduction factor applied to fragmented forest is due to two factors: (i) forest blocks smaller than 100 hectares are not included, according to FORIS definition, but, in practice, (ii) composite forest/non-forest classes have been considered when more detailed classes were not available, and a certain forest fraction has been estimated and included in FORIS statistics, which is fairly common.
F3 represents forest in its broadest sense, including all types and phases of degradation (but still with the connotation of forest). This definition of forest, that allows for the most detailed differentiation among changes, has been used in the analysis of change processes presented in the Section 4, “Results and Findings”, unless otherwise specified.
| Definitions adopted in the estimation of deforestation and degradation rates | (see Section 2.2.1) |
Gross Deforestation has been calculated as the sum of all area transitions from natural forest classes (continuous and fragmented) to all other classes.
Net Deforestation has been calculated as the area of Gross Deforestation minus all area transitions into natural forest classes from all other classes.
In all cases concerning partial deforestation or afforestation, involving the class fragmented forest, the area considered was that of the estimated forest or non-forest fraction.
Net Degradation of Natural Forest has been calculated from the area transitions among natural forest classes, by adding all changes corresponding to degradation minus those corresponding to amelioration.
Balance between natural forest and man-made woody vegetation has been calculated as the algebraic sum of the areas, and changes, of natural forest and of man-made woody vegetation at 1980 and 1990.
Other Technical Terms
| Biomass | (see Section 2.8) |
The data sources used for the present study define biomass as: the total above ground biomass density of trees of 10 cm diameter (breast height) or larger, including main stems, branches, bark, twigs, leaves and fruits. In the present study an attempt has been made to estimate, by inference, the biomass of woody vegetation at less than 10 cm diameter, such as that of shrubs and young secondary regrowth.
Co-registration
The spatial, or geometric co-registration of two satellite images implies that both images are geometrically corrected according to a common projection or that one image is corrected according to the geometric features of he other one which is used as reference; in all cases the co-registration will result in spatial matching and will allow perfect superposition of the two images. The radiometric co-registration of two images consists of common radiometric correction of atmospheric effects and uniform enhancement; images radiometrically co-registered will have similar tonal and chromatic characteristics.
| Interdependent interpretation | (see Section 2.3) |
“Interdependent interpretation” indicates the visual interpretation of two satellite images, acquired at two different dates (in this study some ten years apart), within a single interpretation process. This approach secures the highest level of thematic and spatial consistency between historical and recent image classification. This procedure is the most important element of the methodology since it reduces the error associated to the estimate of changes and make the production of change matrices possible.
Multi-date or multitemporal
Multi-date, or multitemporal, satellite data indicates two or more images acquired at different dates and covering the same portion of Earth's surface.
