Abstract:

The quantity, composition and monthly pattern of litter-fall in Pinus massoniana forests were investigated in fixed plots at Tieshanping of Chongqing during growing season ( March to November in 2009) to study damage by long-term acid rain to the forests, and correlation analyses were conducted among litter-fall characters and the relevant environmental factors. Results showed that the total production of litter-fall was 4 704.27 kg ·hm^-2, which mostly consisted of needles (53.68%) and twigs (25.69%), whereas inflorescences, barks, cones and other-litters accounted for 8.29%, 5.12%, 1.71% and 5.51%, respectively. The litter-fall peak appeared earlier in damaged forests than in healthy ones. The total monthly quantity of litter-fall was significantly influenced by the wind speed of the same month (P＜0.05), and the soil moisture in 0-40 cm layers in the previous month (P＜0.01). There was a one-month time lag of the monthly litter-fall in response to soil moisture variation. When the topsoil moisture decreased, the needle litter-fall increased rapidly and continuously. However, the twig-fall did not rise markedly until the soil moisture content was low enough. Inflorescence-fall was affected by wind speed (P＜0.01) and cone-fall by rainfall (P＜0.05); Bark-fall was influenced by a combination of the air temperature, rainfall and evaporation (P＜0.05). In summary, the forests damaged by the acid rain reduced their resistance against soil drought, due to reduced fine roots, especially the fine roots in deeper soil layers.

Key words: acid rain region, Pinus massoniana forest, litter-fall, soil moisture, Chongqing