The Forest Transformation: Tropical Planted Tree Cover Shows Inconsistent Regional Patterns of Gain and Loss
Sloan, S., P. Meyfroidt, T. K. Rudel, F. Bongers and R. Chazdon (2019). The forest transformation: Planted tree cover and regional dynamics of tree gains and losses. Global Environmental Change 59, 101988. https://doi.org/10.1016/j.gloenvcha.2019.101988
Planted tree cover is on the rise, particularly in the world’s tropical regions. Growing populations demand more food and fiber from planted trees, while forest restoration schemes widely promote tree planting across vast areas that have been stripped of their native forest vegetation.
But what is the significance of planted tree cover in terms of its temporal dynamics? The forest-transition concept depicts areas of planted tree cover as remaining indefinitely as tree cover. Alternatively, planted areas may follow a more dynamic process, whereby planted tree cover is unstable and actively used, and where tree cover gains occur alongside tree cover losses. Which of these two narratives is more prevalent in tropical regions? The answer directly affects trajectories of global tree-cover-change and the relevance of planted tree cover for forest-landscape restoration schemes. We investigated this question by identifying recent planted areas across the tropics in 2014 and observing their historical changes in tree cover between 1990 and 2010.
We examined tree-cover change dynamics across 46.7 million hectares of currently planted areas across 11 tropical countries (Brazil, Cambodia, Colombia, Indonesia, Laos, Liberia, Malaysia, Panama, Peru, Thailand, and Vietnam). We characterized tree-cover change dynamics in the planted areas as one of four temporal sequences: simple (monotonic) increase in tree cover, simple decrease, dynamic (fluctuating) increase, or dynamic decrease. We also compared historical tree-cover change dynamics in planted areas with adjacent agricultural-forest mosaic areas. Finally, we examined whether the commercial export orientation of current planted areas was associated with historical trends in their tree-cover dynamics or patch size.
Contrary to the forest-transition narrative, we found that tree-cover decreased more often than it increased within planted areas, with simple decreases being particularly prevalent in Southeast Asian countries. For example, in Indonesia, Malaysia, and Cambodia, 18.2% of planted areas exhibited simple decreases in tree cover from 2000-2010, more than twice the percentage of areas that showed simple or dynamic increases combined. In contrast, South America exhibited simple and dynamic tree-cover increases in over 14% of planted areas, with simple increases being most prevalent. Also, the planted areas with simple and dynamic increases were greater than or equal to the combined areas of simple and dynamic decreases for major South American countries. Still, across the tropics, planted areas were only moderately distinguishable from non-planted areas in terms of their respective tree-cover change dynamics. Tree cover losses in planted areas were not clearly associated with higher export orientations or larger plantation areas.
These trends support a forest-transformation narrative in which major planted-area expansion occurs alongside minor net tree-cover change. Dynamic tree-cover changes are particularly common in Southeast Asia, where planted areas are most extensive and expansive but where net tree cover gains are tenuous, reflecting political-economic shifts in forest management and the devaluation of degraded natural forests. In this regard, the treadmill-like dynamics of tree plantations in many tropical regions more closely resemble agricultural cropping systems than forest systems. Without careful planning and regulations, the promotion of planted tree-cover expansion to address climate change or forest degradation may perversely lead to further forest losses and carbon dioxide emissions.
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This study was conceived at the final workshop of the Forest Transitions working group at Rutgers University in May 2017.