Diversified land conversion deepens understanding of impacts of rapid rubber plantation expansion on plant diversity in the tropics

Understanding the status and changes of plant diversity in rubber (Hevea brasiliensis) plantations is essential for sustain-able plantation management in the context of rapid rubber expansion in the tropics, but remains very limited at the continental scale. In this study, we investigated plant diversity from 10-meter quadrats in 240 different rubber planta-tions in the six countries of the Great Mekong Subregion (GMS)-where nearly half of the world's rubber plantations are located-and analyzed the influence of original land cover types and stand age on plant diversity using Landsat and Sentinel-2 satellite imagery since the late 1980s. The results indicate that the average plant species richness of rubber plantations is 28.69 +/- 7.35 (1061 species in total, of which 11.22 % are invasive), approximating half the species rich-ness of tropical forests but roughly double that of the intensively managed croplands. Time-series satellite imagery analysis revealed that rubber plantations were primarily established in place of cropland (RPC, 37.72 %), old rubber plantations (RPORP, 27.63 %), and tropical forests (RPTF, 24.12 %). Plant species richness in RPTF (34.02 +/- 7.62) was significantly (p < 0.001) higher than that in RPORP (26.41 +/- 7.02) and RPC (26.34 +/- 5.37). More importantly,species richness can be maintained for the duration of the 30-year economic cycle, and the number of invasive species decreases as the stand ages. Given diverse land conversions and changes in stand age, the total loss of species richness due to rapid rubber expansion in the GMS was 7.29 %, which is far below the traditional estimates that only consider tropical forest conversion. In general, maintaining higher species richness at the earliest stages of cultivation has sig-nificant implications for biodiversity conservation in rubber plantations.

Automated summary

Understanding plant diversity in rubber plantations is crucial for sustainable management, but knowledge at a continental scale is limited. This study analyzed plant diversity in 240 rubber plantations in the Great Mekong Subregion and found that the average species richness is about half of tropical forests and double that of croplands. The establishment of rubber plantations mainly replaced croplands, old rubber plantations, and tropical forests, and species richness was highest in the latter. The maintenance of high species richness and the reduction of invasive species with stand age are important for biodiversity conservation in rubber plantations.