Anne C. Lang

Community assembly during secondary forest succession in a Chinese subtropical forest

Subtropical broad-leaved forests in southeastern China support a high diversity of woody plants. Using a comparative study design with 30 × 30 m plots (n = 27) from five successional stages ( 1 m in height in each plot and counted all woody recruits (bank of all seedlings ≤1 m in height) in each central 10 × 10 m quadrant of each plot. In addition, we measured a number of environmen...

Mixed afforestation of young subtropical trees promotes nitrogen acquisition and retention

Summary 1. Afforestation is globally increasing to produce timber and pulp wood, but also to enhance ecosystem services such as carbon sequestration, nutrient retention or groundwater recharge. In China, large areas have been and will be afforested in order to compensate for the negative impacts of former clear-cuttings and to make use of the ecosystem services associated with afforestation. In order to further optimize these services with regard to balanced nutrient (particularly nitrogen) cycles, it is important to know whether the use of mixtures of native tree species in afforestation projects promotes the acquisition and retention of nitrogen compared with the currently established large-scale monocultures. 2. To test the effect of species richness on system N retention and tree sapling N uptake, we conducted a 15 N tracer experiment in a young tree plantation. To this end, saplings of four abundant early successional tree species were planted in monocultures, in two- and four-species mixtures and as single trees. 3. Nitrogen retention increased with higher species richness due to enhanced N pools in sapling biomass. These species richness effects strengthened over time. 4. Species-specific differences in 15 N recoveries over time revealed below-ground niche differentiation with regard to N uptake, which is likely to result in complementary resource use among coexisting species. 5. Synthesis and applications. This study provides evidence that mixed afforestation promotes N retention from the sapling stage. To further improve ecosystem services associated with afforestation, we strongly suggest the use of mixtures of native tree species instead of monocultures. Mixtures of four species may reduce system N losses and thus may lessen groundwater contamination due to N leaching. We encourage further investigations to find optimal species combinations that promote a wide range of ecosystem services related to more closed nutrient cycles and minimized soil erosion. In our study, the plantations’ capability to retain N could be optimized by means of both increasing tree species richness and by choosing the optimal species combinations.

Strong positive biodiversity-productivity relationships in a subtropical forest experiment

Forest ecosystems contribute substantially to global terrestrial primary productivity and climate regulation, but, in contrast to grasslands, experimental evidence for a positive biodiversity-productivity relationship in highly diverse forests is still lacking1. Here, we provide such evidence from a large forest biodiversity experiment with a novel design2 in subtropical China. Productivity (stand-level tree basal area, aboveground volume and carbon and their annual increment) increased linearly with the logarithm of tree species richness. Additive partitioning3 showed that increasing positive complementarity effects combined with weakening negative selection effects caused a strengthening of the relationship over time. In 2-species mixed stands, complementary effects increased with functional distance and selection effects with vertical crown dissimilarity between species. Understorey shrubs reduced stand-level tree productivity, but this effect of competition was attenuated by shrub species richness, indicating that a diverse understorey may facilitate overall ecosystem functioning. Identical biodiversity-productivity relationships were found in plots of different size, suggesting that extrapolation to larger scales is possible. Our results highlight the potential of multi-species afforestation strategies to simultaneously contribute to mitigation of climate change and biodiversity restoration.

Impacts of species richness on productivity in a large-scale subtropical forest experiment

Tree diversity improves forest productivity Experimental studies in grasslands have shown that the loss of species has negative consequences for ecosystem functioning. Is the same true for forests? Huang et al. report the first results from a large biodiversity experiment in a subtropical forest in China. The study combines many replicates, realistic tree densities, and large plot sizes with a wide range of species richness levels. After 8 years of the experiment, the findings suggest strong positive effects of tree diversity on forest productivity and carbon accumulation. Thus, changing from monocultures to more mixed forests could benefit both restoration of biodiversity and mitigation of climate change. Science, this issue p. 80 In a replicated experiment in a subtropical forest, higher tree species diversity promoted productivity and carbon storage. Biodiversity experiments have shown that species loss reduces ecosystem functioning in grassland. To test whether this result can be extrapolated to forests, the main contributors to terrestrial primary productivity, requires large-scale experiments. We manipulated tree species richness by planting more than 150,000 trees in plots with 1 to 16 species. Simulating multiple extinction scenarios, we found that richness strongly increased stand-level productivity. After 8 years, 16-species mixtures had accumulated over twice the amount of carbon found in average monocultures and similar amounts as those of two commercial monocultures. Species richness effects were strongly associated with functional and phylogenetic diversity. A shrub addition treatment reduced tree productivity, but this reduction was smaller at high shrub species richness. Our results encourage multispecies afforestation strategies to restore biodiversity and mitigate climate change.