Xinbao Zhang

South China Karst faces the challenge of balancing ecological conservation and regional development, a task made more intricate by the geological limitations of carbonate formations. Large‐scale conservation and restoration initiatives have mitigated rocky desertification and positioned South China Karst as a global hotspot for vegetation regrowth over the past two decades. However, challenges stemming from geological constraints and oversights in recognizing the synergies within social‐ecological systems remain. Here, we propose a social‐ecological framework that integrates the extended timescale of both historical and recent human impacts with the corresponding processes of forest evolution. The framework elucidates the enduring and continuous progression of “forest‐deforestation‐reforestation,” offering applicability for optimizing ecological space across diverse social‐ecological contexts. Moreover, it serves to enhance the sustainability of reforestation efforts when faced with geological constraints.

Understanding the forest evolution is vital to answering the reforestation potential in karst areas. Here, we present the first‐ever pollen record in karst depression sediment, combined with comprehensive dating methods (¹³⁷Cs, ²¹⁰Pb_ex, and ¹⁴C) and historical documents, to reveal plant change history in southwest Guangxi, a severe rocky‐desertification region. We inferred three stages of “virgin forest–deforestation–sparse tree planting” over the past three centuries. Before the 1780s, the barren mountains used to be a lush mixed broadleaf forest probably. However, maize cultivation, along with explosive population growth and migration, accelerated mountain reclamation and deforestation, leading to severe rocky desertification since the 1780s, featured by the co‐occurrence of Zea pollen appearance and Dicranopteris spore surge from 0.92% to 12.18%. Since the 1930s, sparse tree planting began, as Cupressaceae/Taxodiaceae pollen abruptly increased by 32%. Our study is significant in understanding the rocky desertification causes and guiding ecological restoration in the region.

Suspended sediment yields in the Upper Yangtze River and its four headwater tributaries (i.e. Jinsha, Min, Jialing and Wu) have declined significantly during recent decades. Compared with 1956–1970, mean annual suspended sediment yield during 2001–2011 was reduced by 84% in the Upper Yangtze River at Yichang, by 34% in the Jinsha at Pingshan, by 84% in the Jialing at Beibei, by 75% in the Wu at Wulong, and by 48% in the Min at Gaochang. Linking these observed decadal changes of runoff discharge and suspended sediment load to dam construction and multiple environmental rehabilitation projects (e.g. soil-water conservation, reforestation) during the past decades, it can be concluded that the construction of large dams on the main stem and major tributaries of the Upper Yangtze River has played a principal role in the reduction of fluvial suspended sediment yields, while the environment rehabilitation projects may make limited contributions to the changes in suspended sediment yields, except for the Jialing River.

Karst depressions represent important sinks for sediment, and such sediment can provide a valuable record of the impact of environmental change on soil erosion rates. However, the sediment dynamics of karst depressions are not well understood. This contribution reports a study of the small catchment of a karst depression in Southwest China, with a drainage area of 0.054 km², aimed at using the sediment deposits in the depression to reconstruct the erosional response of the catchment to land‐use change and, more particularly, the deforestation which took place in 1979. ¹³⁷Cs and ²¹⁰Pb_ex are used as both chronometers and as tracers. Five cores, collected from the bottom of a depression, with an area of 2652 m², showed similar ¹³⁷Cs depth distributions, with a single ¹³⁷Cs peak, which was attributed to the 1979 deforestation. The ¹³⁷Cs activity associated with the peaks varied between 5.68 ± 0.64 and 9.19 ± 0.99 Bq kg^–1. The average depth of sediment deposition between 1979 and 2008 deduced from the depths of the 1979 ¹³⁷Cs peak was 74.1 cm. The existence of relatively high ²¹⁰Pb_ex activity of 66.33 ± 8.44 Bq kg^–1 in the upper section (0–16 cm) of the core analyzed for ²¹⁰Pb_ex suggests that recent sedimentation has been very limited. Net erosion rates on the hillslopes contributing runoff and sediment t to the depression were estimated to be 5258 t km^–2 year^–1 from 1979 to 1990 and 256 t km^–2 year^–1 from 1991 to 2008, respectively. The high sediment yield in the first period was associated with the severe soil erosion triggered by the 1979 deforestation, which resulted from the changes in land ownership immediately after the Cultural Revolution. Soil erosion has been very limited since 1990 because the thin soils had been totally removed from many parts of the karst slopes and the soils remaining on the other parts of the slopes have been protected by terracing or vegetation rehabilitation. Copyright © 2012 John Wiley & Sons, Ltd.