LITTER ACCUMULATION AND NUTRIENT FLUXES IN PINUS MASSONIANA STAND AND ITS MIXED FORESTS WITH BROAD-LEAVED TREES

One-year seedlings of six broad-leaved tree species, Michelia macclurei, Castanopsis fissa, C. sclerophylla, C. kawakamii, Cyclobalanopsis myrsinaefolia and Castanopsis lamontii, were separately planted in 25-year-old artificial forest of Pinus massoniana, wihich developed into different closed mixed forests after 16 years. Litter accumulation and its nutrient fluxes were analyzed for the above 6 mixed forests and the P. massoniana stand planted with no broad-leaved trees. Data from two-year field collection showed that annual litter accumulation in the 6 mixed forests were 7 137.3 kg hm~-2, 6 741.1 kg hm~-2, 8 041.7 kg hm~-2, 7 151.3 kg hm~-2, 7 533.2 kg hm~-2 and 6 149.1 kg hm~-2,respectively, but only 3 442.8 kg hm~-2 in pure stand P. massoniana. Difference existed among forests in their litter compositions, with fallen leaves accounting for 49.7%~71.5% of the total, branches 5.7%~26.1%, barks 7.7%~18.9%, fruits 0.7%~2.0% and others 5.5%~17.1%. In the mixed forests, 50.4%~58.0% of the total litter came from P. massoniana trees and 42.0%~49.6% from planted broad-leaved trees, with great difference among their litter compositions. The dynamics of litter in the mixed forests showed significant seasonal patterns, with the first peak occurring between February and April, and the second in August or September. Nutrient concentrations in the litter varied with forest types, litter components and shedding times, with N ranging from 3.25 to 12.98 g kg~-1, P from 0.23 to 0.97 g kg~-1, K from 0.42 to 4.02 g kg~-1, Ca from 7.34 to 32.57 g kg~-1 and Mg from 1.34 to 5.58 g kg~-1. Annual fluxes of the five nutrient elements via litter in the seven forests consistently decreased in the order: CaNMgKP. From annual litter accumulation the total fluxes of the five nutrient elements were 204.95 kg hm~-1, 223.93 kg hm~-1, 304.12 kg hm~-1, 288.46 kg hm~-1, 213.77 and 238.05 kg hm~-1, respectively for the six mixed forests, and 142.01 kg hm~-1 for the pure stand P. massoniana. Fig 3, Tab 4, Ref 13