资源环境科技发展态势分析平台

Extensions of forest-transition theory to the tropics often depict sustained expansions of planted tree cover and corresponding long-term net gains in total tree cover. To explore the patterns and implications of continued tropical planted tree-cover expansion, we profiled sequences of tree-cover change over 1990-2010 according to Landsat imagery for recently observed (ca. 2014) planted tree-cover areas in 11 tropical countries. Alternative patterns of change emerged from these analyses. Termed the 'reforestation treadmill' and 'forest transformation' narratives, planted tree-cover change featured relatively ephemeral planted covers, modest net gains, and similar tree-cover change dynamics compared to nearby agricultural-forest mosaics. Planted areas were characterised not by unambiguous reforestation but rather combinations of tree-cover losses and gains, with losses typically being more prominent. Contemporary gains and losses during 5-10-year periods regularly distinguished planted areas from non-planted areas, with losses being 1.5-2.3 times more common than gains. Planted areas were only moderately distinguishable from non-planted areas overall with respect to tree-cover change dynamics. Relationships between tree-cover change and the export orientations of planted tree/tree-crop commodities were also examined. Greater export orientations did not significantly associate with tree-cover loss or larger planted patches, with partial exceptions for Southeast Asia. Regional disparities in planted tree-cover dynamics were apparent. In Southeast Asia, dominated by Indonesia, tree-cover declines in planted areas since 1990 were relatively pronounced (20% of planted areas), particularly with respect to progressive transitions from tree cover to cleared lands. Planted areas there were generally indistinguishable from nearby non-planted areas with respect to historical tree-cover change dynamics. In contrast, in South America, dominated by Brazil, tree-cover increases in planted areas since 1990 were more appreciable (at least 14% of planted areas), with most being progressive, stable, 'net' increases (10% of planted areas) and the remainder being dynamic increases entailing short-term losses since 1990 (4% of planted areas). Total tree-cover increases within South American planted areas were equal to or greater than total decreases since 1990. These patterns suggest a forest-transformation narrative in which major planted-area expansion occurs alongside minor net tree-cover change. This narrative appears particularly well suited to Southeast Asia, where planted areas are extensive and expansive but where net tree cover gains are tenuous, reflecting political-economic shifts in forest management and the devaluation of extensive, degraded natural forests.