Effects of plant species diversity on soil conservation and stability in the secondary succession phases of a semihumid evergreen broadleaf forest in China

Abstract

One of the most studied aspects of ecosystems in recent years has been the relationship between plant species diversity and ecosystem functions; however, the relationship with one such ecosystem function, soil conservation, has been less well studied. We established forest plots in the secondary succession phases of a semihumid evergreen broadleaf forest in China. The plots differed in plant species richness but had otherwise similar soil-erosion factors, observed surface runoff, sediment, and total phosphorus (P) loss. We analyzed the relationship between plant diversity and soil conservation and stability. Results indicated that the frequency and volume of surface runoff, sediment, and total P loss in the test plots, as well as their CV (coefficients of variation), present significant negative correlations with increasing species richness. The plot with the lowest richness in Yunnan pine, African boxwood, and running mountaingrass (Ass. Pinus yunnanensis, Myrsine africana, and Oplismenus compositus [APMO]) yielded the highest runoff rates, with runoff occurring a total of 77 times: 23, 32, and 22 times in 2001, 2002, and 2003, respectively. The average values for surface runoff, sediment, and total P loss over the three-year study period were, respectively, 960.20 m³ ha⁻¹ y⁻¹ (13.72 thousand ft³ ac⁻¹ yr⁻¹), 11.40 t ha⁻¹ y⁻¹ (4.54 tn ac⁻¹ yr⁻¹), and 127.69 kg ha⁻¹ y⁻¹ (113.82 lb ac⁻¹ yr⁻¹). The CV values for the three parameters were, respectively, 287.6, 534.21, and 315.47. However, in the plot with the highest richness in a native oak species, Evelyn keteleeria, and a species of viola (Ass. Cyclobalanopsis glaucoides, Keteleeria evelyniana, and Viola duelouxii [ACKV]), surface runoff only occurred 9 times: 2, 4, and 3 times, respectively in the three years. The average values for surface runoff, sediment, and total P loss were 75.55 m³ ha⁻¹ y⁻¹ (1.08 thousand ft³ ac⁻¹ yr⁻¹), 0.28 t ha⁻¹ y⁻¹ (0.11 tn ac⁻¹ yr⁻¹), and 4.71 kg ha⁻¹ y⁻¹ (4.20 lb ac⁻¹ yr⁻¹). The CV values for the three parameters were, respectively, 57.93, 187.94, and 59.2. Plant density increased linearly in herb, shrub, and tree layers with increasing plant species richness, whereas plant cover increased logarithmically. Plant species diversity can enhance soil conservation, but this effect was comparatively weak relative to the contributions of plant cover and density to soil conservation. Plant species diversity increases plant density and cover in the local community, indirectly regulating and enhancing soil conservation. Competition and niche theories can explain, to some extent, the increases in plant density and cover. Our results challenge the view of a negative relationship between plant species diversity and productivity.