Leaf area increases with species richness in young experimental stands of subtropical trees

Aims: Most biodiversity–ecosystem functioning research has been carried out in grassland ecosystems, and little is known about whether forest ecosystems, in particular outside the temperate zone, respond similarly. Here, we tested whether productivity, assessed as leaf area index (LAI), increases with species richness in young experimental stands of subtropical trees, whether this response is similar for early-season leaf area (which is dominated by evergreens) and seasonal leaf area increase (which is dominated by deciduous species), and whether responses saturate at high species richness. Methods: We used a planted tree biodiversity experiment in south-east China to test our hypotheses. LAI was determined three times by digital hemispheric photography in 144 plots that had been planted with 400 trees each, forming communities with 1, 2, 4, 8 or 16 tree species. Important Findings: LAI increased significantly with tree species richness in the fifth year of stand establishment. Similar, but weaker, statistically non-significant trends were observed 1 year before. We did not observe leaf area overyielding and the presence of particularly productive and unproductive species explained large amounts of variation in leaf area, suggesting that selection-type effects contributed substantially to the biodiversity effects we found in this early phase of stand establishment. Effects sizes were moderate to large and comparable in magnitude to the ones reported for grassland ecosystems. Subtropical (and tropical) forests harbor substantial parts of global net primary production and are critical for the Earth’s carbon and hydrological cycle, and our results suggest that tree diversity critically supports these ecosystem services