What is it about?
Focusing on China’s Loess Plateau, one of the world’s largest afforestation areas, we employed the equilibrium behavior theory to identify the area suitable for forests. Through a systematic survey of 4,875 field sites and 80,000 km of transects, we explored the alternative vegetation states in the Loess Plateau and explained the maintenance mechanism, thereby confirming the area suitable for forests and developing a more scientific theoretical framework for afforestation.
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Why is it important?
For decades, afforestation planning has relied on “hard” thresholds of precipitation, often assuming forests can only survive where mean annual precipitation exceeds 500-600 mm. These traditional models assume a linear relationship between precipitation and forest. However, this thinking overlooks the complex, nonlinear relationship of dryland ecosystems, i.e., alternative stable states. This oversight could affect the prediction of suitable areas for afforestation and hinder large-scale afforestation success. Based on the systematic field survey data and remote sensing data, we identified that instead of a single predictable outcome, ecosystems at the 350-500 mm precipitation level can exist in three distinct states: treeless, open woodland, or forest. With a minimal mathematical model, we identified that forests can actually persist at a much lower threshold of 350 mm, provided that positive feedback between vegetation and precipitation is maintained. The existence of alternative stable states means that regime shifts, for example, the sudden collapse from a forest to a treeless state, could result in massive losses of carbon stock, impacting global climate goals. Therefore, we suggest that afforestation is not just about planting trees but about steering ecosystems toward the right state. Our findings offer a new theoretical framework for afforestation policymakers: 1. Recognize the value of open woodland as a rational ecological state, rather than blindly pursuing high-density forest cover. 2. Limit afforestation in regions below 350 mm. 3. Pay more attention to the vegetation in alternative stable state zones, where management interventions may mean a lot.
Perspectives
From my perspective, the most interesting message of this publication is the important effect on the practical implementation of equilibrium behavior theory. By identifying the existence of alternative vegetation states, we have fundamentally updated the precipitation thresholds for forest persistence across the Loess Plateau. This demonstrated that equilibrium behavior theory is not merely an abstract concept; rather, it possesses significant applied value in shifting afforestation strategies from a traditional pattern to a more scientific framework.
Xuan Li
Lanzhou University
Read the Original
This page is a summary of: Alternative vegetation states on the Loess Plateau and implications for large-scale afforestation success, Proceedings of the National Academy of Sciences, May 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2527794123.
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