3. Results

3.1 Extent of land use categories in year 2000

Table 2. Overall extent of land use categories in year 2000, with data sources

3.2 Area transitions for year 2000

Forest transitions

FAO (2006a) gives the total loss of forest area at 130 000 km² per year for the period 1990-2005, which is used here for year 2000. There is no distribution given as to which categories these forests are converted into, however it is well know that conversions into agriculture is most common, see e.g. FAO (2001). Further, conversions into cattle ranching (woodland/grassland in this paper) as well as degradation of forests (also into woodland/grassland) are common. Conversions into urban areas are dealt with below. By expert estimate, the distribution of the losses of forests is therefore (‘000 km²):

- into agricultural crops 98

- into woodland / grassland 30

- into urban areas 2

FAO (2006a) gives the total gain of forest area at 57 000 km² per year for the period 2000-2005, which is here applied for year 2000. These gains appear either as planted forests or as naturally expanding forests (typically on abandoned agricultural land). Most gains occur on former agricultural land, but considerable planting of woodlands/grasslands are also done. By expert estimate it is assumed that 75% of the gains are from former agriculture land, and 25% from former woodland/grassland, i.e. (‘000 km²):

- from agriculture crops 43

- from woodland/grassland 14

Transitions to and from Other land/water also occur, in some cases with considerable ecological consequences (e.g. conversion of mangroves to fish farming, mining or hydroelectric dam constructions) but are considered area-wise negligible at the global level.

Urban area transitions

Angel et al. (2005) provides a global and well controlled estimate of urban area dynamics. The study is limited to urban areas with more than 100,000 inhabitants and does not include infrastructure developments. Presumably, smaller cities take up considerable areas, but perhaps it is the larger cities that represent the bulk of overall growth of urban areas. Obviously, infrastructure expansion is considerable, but no documentation of this could be obtained. Lacking further documented information on the topic, this study uses the figures directly from Angel et al. (2005).

The global urban expansion rate is estimated at 20 000 km² per year. Most of this intrudes on agricultural land. It is assumed for this paper that 80% of urban expansion occurs on agricultural land, 10% into forests and 10% into woodland/grassland. Other conversions to and from urban areas were considered negligible at the global level.

I.e. (000 km²):

- from agriculture crops 16

- from forest 2

- from woodland/grassland 2

Agricultural crop area transitions

FAO (2006b) provides time series for land use areas. For the period 1995-2002 the agricultural crop area expanded by 31 000 km² per year, however there is no information in FAOSTAT about the distribution between losses and gains that lead to this overall net area change figure.

Gains of agricultural land from forests was estimated above to 98 000 km² per year. Further, woodland/grassland is converted into agricultural cropland in many areas, but the rate seems not well known. It is here assumed that the rate is about 10 000 km² per year. The total gains of agricultural cropland is thus about 108 000 km² per year.

Losses of agricultural land to urban areas was estimated above to 16 000 km² per year, and conversions into forests to 43,000 km² per year. In addition, agricultural land is lost due to degradation, for example salinization and erosion into woodland/grassland. Lacking documented global statistics, it is here assumed that the losses are 20 000 km² per year, brining the total losses of agricultural land to 79 000 km² per year.

The balance between losses and gains is then 29 000 km² per year, which is close to the net change obtained from FAOSTAT above.

Woodland / Grassland transitions

All transitions to and from woodland/grassland have been covered in the previous sections and result in a net increase of 24 000 km² per year. This can be compared with the FAOSTAT estimate for 1995-2002 (FAO 2006b)which is an increase of 13 000 km² per year.

3.3. Area changes for year 2000

The above results are brought together in Tables 3. and 4. showing the overall land use area change for year 2000. Table 3 shows all transitions to and from the land use categories as well as the areas remining in each. Table 4 shows the losses and gains for each category. Note that the Other land category is excluded as there were no significant changes identified for this category.

Table 3. Global land use area change matrix for year 2000, ‘000 km²

Table 4. Global losses, gains and net changes of land use areas in year 2000