Eco-Hydrological Studies On Subtropical Evergreen Broad-leaved Forest In Xiaokeng

Rainfall is a main source of nutrient inputs to the forest ecosystems,which has been drawn greater attention to researchers.Therefore,it is particularly important to study on the relationship between forests and water.Rainfall redistribution and nutrient inputs through forest canopy is one of the most important fields in the ecological researches on structure and functioning of forest ecosystem,which is great meaningful to understand the regional hydrological and biogeochemical processes.Rainfull passing through a multi-layered canopy usually cause its redistribution and great changes in quantity and chemical constituents.In this study,an investigation on rainfull partition in a subtropical evergreen broad-leaved forest was conducted in Xiaokeng,Southern Anhui,during two-year period.The major objectives of the study are as follows.(1)To determine the features of ranifall partitioning for the different aged stands of a subtropical evergreen broad-leaved forest;(2)To reveal the impact of the different aged stands on rainfall chemistry;(3)To reveal the chemical relationship between the throughfull,stemflow and rainfull;(4)To compare the differences in soil properties and water conservation function among different stage of the subtropical evergreen broad-leaved forest.Thus,the results from the study can provide basic methods for restoration and sustainable management of subtropical evergreen broad-leaved forest.The followings are the main results obtained from the study.1.Rainfall partitioningDuring the study period,rainfall mainly concentrated from May to September,contributing more than 80%of the total annual rainfall.The average annual bulk precipitation was 1226.4 mm.The mean amounts of throughfall in the mid-aged and young stands were,respectively,1159.2 mm and 850.8 mm,which contributed 94.5%and 69.4%of the annual bulk precipitation for the two different aged stands.The result indicates that there exists great difference in rainfall partitioning among the mid-aged and young stands of Xiaokeng subtropical evergreen broad-leaved forest.2.pH value and nutrient dynamicsIn the course of experiment,pH value of rainfull didn't appear small in 5.6 of sample,the average pH value was 6.16.For all sampling stands,the mean pH value ranked as follow:throughfull>stemflow.The mean pH value of throughfall was higher in the young stand than in the mid-aged stand.The lowest mean pH appeared in bulk precipitation.During the experiment,the pH of bulk precipitation and throughfall showed weak acid,and have a significant seasonal variation,with the lowest pH value of 5.3 in the winter and the highest value of 7.79 in the summer.Compared with rainfall,the chemical components of throughfull and stemflow changed greatly,of which concentrations of NH4+-N and Fe were ranked:throughfall>bulk precipitation>stemflow;while P,K,Ca,Mg,NO3--N showed:stemflow>throughfall>bulk precipitation.The concentration of Na showed:bulk precipitation>throughfull>stemflow.With comparison to nutrient concentrations in 2006,all bio-elements measured in the study were increased somewhat except for Ca and Fe,of which P increased most greatly.Many factors,including rainfall intensity,forest characteristics,atmospheric conditions,human activities etc,can cause these changes.3.Soil water conservation functionSoil physical properties,water-holding capacity of forest floor and soil for the different age-stages of the subtropical evergreen broad-leaved forest had obvious differences During the forest rehabilitation,the forest floor was developed,soil physical properties were improved,and their water conservation functions were enhanced gradually along with the stand development.Based on the total and effective water-holding capacity of litter and soil(0?40 cm),the order of the water conservation function for the forest stands studied was:pre-matured stand(2152 and 244 t·hm-2)>mid-aged stand(2010 and 227 t·hm-2)>young stand(1883 and 186 t·hm-2),indicating that the hydrological effect of soil was greater significantly in the pre-matured stand than in the young stand.