Ecological Functions Of Forest Litter In Karst Region, Centre Of Guizhou Province

Forest litter layer is one of the main layers of the three vertical structures about forest ecosystem.It plays an important role not only in conserving water,delaying surface runoff,inhibiting the evaporation of soil moisture and preventing soil erosion,but in maintaining fertility of forest soil,promoting normal material recycling of forest ecosystem and sustainable use of resources as a central aspect of material recycling of forest ecosystem.As a fragile ecosystem,Karst area is lack of soil and water.So the ecological functions of litter are particularly important.Four kinds of natural secondary forests of the karst landform in central Guizhou Province were chosen as the object of the study during June 2007 to September 2008:Celtis sinensis and Ligustrum lucidum forest, Carpinus pubescens forest,Pinus massoniana forest and shrub.Litter reserves,litter quantity,litter dynamics,water-holding properties, decomposition and nutrient return of the four kinds of forest were studied systematically.The results indicated that:(1) The water-holding capabilities of these four kinds of forest litter layer were different.The maximum water-holding percentage ranged from 221.50%to 256.00%.The order was Carpinus pubescens forest＞Celtis sinensis and Ligustrum lucidum forest＞shrub＞Pinus massoniana forest.The maximum water-holding capacity changed from 8.72×10~3 kg /hm~2to 17.54×10~3 kg /hm~2.The effected interception fluctuated from 5.99×10~3 kg /hm~2 to 11.41×10~3 kg /hm~2.Variation pattern of effected interception of litter showed the same as that of the maximum water-holding capacity,the order was Pinus massoniana forest＞shrub＞Celtis sinensis and Ligustrum lucidum forest＞Carpinus pubescens forest.(2) During the whole process of water holding of litter layer,the water-holding capacity in the first 2 h was superior to that of other time. The water absorption speed declined rapidly and the rate of increase of water-holding capacity became smaller after 2 h,especially after 6 h.The equation between the water-holding capacity of litter layer and the immersion time was found by study:W = a ln t+b.The equation between the water absorption speed of litter layer and the immersion time was found by study:V=kt~n.(3) The effection of inhibiting the evaporation of soil moisture was obvious in the four kinds of litter layers.The evaporation of litter-covered soil cut back from 13.6%to 70.49%than litter-free covered soil in two months.The effect on decreasing runoff and sand and increasing infiltration of litter layer was also very significant,but the performance of Celtis sinensis and Ligustrum lucidum forest was the best.(4) Annual amounts of litter-fall were different among the four kinds. The amount of the litter-fall about Pinus massoniana forest was the largest:6.886×10~3kg / hm~2,followed by Celtis sinensis and Ligustrum lucidum forest(5.945×103kg/hm~2) and shrub(4.928×103kg/hm~2). Carpinus pubescens,the smallest,was only 3.958×103kg / hm~2.The pattern of monthly variation of the litter-fall about the Celtis sinensis and Ligustrum lucidum forest was consistent with that of the shrub.Both of them showed "bimodal".Pinus massoniana forest showed "three peak". Carpinus pubescens forest showed "unimodal".(5) Because of differences in litter and nutrient content,the four kinds of forest were significantly different in annual nutrient return amount.The order was Celtis sinensis and Ligustrum lucidum forest＞Pinus massoniana forest＞shrub＞Garpinus pubescens forest. Seasonal dynamics of nutrient return in Pinus massoniana forest was not obvious.The other three kinds of forest were mainly in autumn.(6) The return amounts of five nutrient elements about the four types of forest were different.Nutrient return amounts of the five elements in the four kinds of litter-fall showed consistency:Ca＞N＞K＞P＞Mg. Returned amount of Ca was the largest.It constituted more than 50%.It showed that Ca was on the top in the nutrition of karst species.(7) It showed exponential relationship between leaf-fall decomposition rate and time in both stands,which showed fast stage of decomposition at first,and slow stage after that.The decomposition rate of Celtis sinensis and Ligustrum lucidum forest was the fastest,followed by Carpinus pubescens forest,and the differences between Pinus massoniana forest and shrub were little.