Differential water and soil conservation capacity and associated processes in four forest ecosystems in Dianchi Watershed, Yunnan Province, China

Abstract

The soil and water conservation capacity of forest ecosystems is closely associated with precipitation, runoff, sediment delivery, and the export of the nutrients nitrogen (N) and phosphorus (P) from forest soil. Research has investigated the potential for decreasing runoff pollution from watersheds by improving the function of forest ecosystems in conserving soil and water. Four typical forest ecological systems, including Pinus armandii forest, Yunnan pine forest, mixed broadleaf-conifer forest, and broad-leaved forest, were compared for vegetation community structure and species diversity; water-holding capacity in canopy, litter and soil layers; and the relationship with surface runoff and the export of sediment, N, and P during the 2013 rainy season. The species number and species richness were in the range of 10 to 22 and 4.68 to 7.94, respectively. The Shannon-Wiener Index, Simpson Index, and Pielou Index were 0.95 to 1.67, 0.43 to 0.68, and 0.50 to 1.04, respectively. Canopy interception rate increased with decreasing precipitation. The linear correlation equation of the two parameters was described as I = −2.768x + 64.318, where I = the canopy interception rate (mm) and x = rainfall amount (mm). The broad-leaved forest had the greatest interception rate because of its dense canopy. Litter storage in the four forest ecosystems ranged from 7.31 to 11.98 t ha⁻¹ (6,527 to 10,698 lb ac⁻¹); the highest litter yield was found in the broad-leaved forest. In this ecosystem, both the undecomposed and semidecomposed litter had the most water retention capacity (14.02 t ha⁻¹ [12,519 lb ac⁻¹] and 14.71 t ha⁻¹ [13,136 lb ac⁻¹], respectively) and effective water interception rate (8.18 t ha⁻¹ [7,304 lb ac⁻¹] and 9.01 t ha⁻¹ [8,045 lb ac⁻¹], respectively). In the 0 to 60 cm (0 to 23.6 in) soil layer, the broad-leaved forest had the greatest soil field capacity of 188.80 t ha⁻¹ (168,598 lb ac⁻¹) and 18.88 mm (0.74 in) water depth equivalent. The amount of surface runoff, sediment yield, and export of N and P increased with rainfall amounts, but the four forest ecosystems differed significantly in these properties. The ranges of sediment yield and export of total N and P were 13.1 to 344.2, 0.16 to 1.55, and 0.02 to 0.10 mg m⁻², respectively. The broad-leaved forest formed an extremely dense canopy and had the highest maximum water-holding capacity, porosity, and soil field capacity. These properties made this ecosystem highly suitable for decreasing surface runoff and the export of sediments, N, and P from the forest soil.