Global Landuse Modeling (GLM) Data

To accurately assess the impacts of human land-use on the Earth System, information is needed on the current and historical patterns of land-use activities. The Global Landuse Modeling (GLM) Data collection provides the first global gridded estimates of the underlying land conversions (land-use transitions), wood harvesting, and resulting secondary lands annually, for the period 1700-2000. Using data-based historical scenarios, our results suggest that 42-68% of the land surface was impacted by land-use activities (crop, pasture, wood harvest) during this period, some multiple times. Secondary land area increased 10,000,000 to 44,000,000 km2 ; about half of this was forested. Wood harvest and shifting cultivation generated 70-90% of the secondary land by 2000; permanent abandonment and relocation of agricultural land accounted for the rest. This modeled data provides important estimates of global land-use activities for studies attempting to assess the consequences of changes to the Earth's surface over time. For this study, six major factors were evaluated that influence land-use transitions and the resulting amount, distribution, and age of secondary lands. Because the details of each of these factors are important but generally not well known historically, a scenario approach was performed to bracket the uncertainty of model estimates.

The two focal scenarios chosen for detailed analyses were based on three criteria: quantity of data inputs, the reasonableness of model assumptions, and comparisons of estimates of secondary land area to independent estimates published by the Food and Agriculture Organization (FAO 1998). One scenario was based the detailed land-use history reconstruction of Hyde (H1), and the second on Sage-Hyde (H2). Both scenarios were driven with the FAO-based wood harvest reconstruction (L1). Both concentrated wood harvesting activities in grid-cells with land use (Z1); a recent FAO study on forest accessibility found that about half the world's forest was within 10 km of major transportation infrastructure (roads, railways, rivers), and about three-quarters within 40 km (FAO, 2001). Both scenarios applied minimum transitions outside the tropics and non-minimum transitions (e.g. shifting agriculture) in the tropics (T3), roughly corresponding to the distribution of shifting cultivation in the mid-late 1900s (Butler, 1980; Lanly, 1985).

For details of the remaining model assumptions, data values and parameters, consult the Detailed data Guide at the EOS-WEBSTER data distribution site. Since the model settings for the focal scenarios are sub global, we chose to refer to them simply as "Hyde" and "Sage-Hyde". Other scenarios will be added in the future. Currently, only the two focal scenarios are available for beta testing. (Please contact User Support if you are interested in obtaining data for the other scenarios.) Missing data values are set to "-1".