北京西山地区油松元宝枫混交林生物量和营养元素循环的研究

本试验测定了25年生人工油松元宝枫混交林和油松纯林的现存生物量、生长量、枯落物层蓄积量和一年内的逐月凋落量,并分析了它们各组分的氮、磷、钾和灰分含量,土壤中速效性氮、磷、钾的含量,进而求出林分的元素年归还量和年存留量,得到了不同林分主要营养元素循环及改土性能方面的总概念。结果表明,油松元宝榈混交林对于油松纯林的优越性主要表现为:生长量高44.46％,枯落物层元素累积量高12.82—26.83％,元素的归还量和存留量分别高13—142.47％,林下土壤速效性养分含量比对照高22.5—222.7％。元宝枫凋落物分解速度快,单位胸高断面积的元素归还量比油松高1.8—4.2倍,是个良好的土壤改良树种。其结论是:选择元宝枫作为伴生树种是恰当的,在试验地条件下的这种混交组合是适宜的。

BIOMASS AND NNTNENT CYCLING STUDIES IN SOME MIXED STANDS OF PINE AND MAPLE IN XISHAN AREA BEIJING

The biomass and its net increment of a 25-year old pine-maple mixed stand was compared with that of a pure pine stand.The total mass of the litter layer from both stands and the monthly yield of litter production during one year were measured.The contents of nutrient elements (N,P,K and other ash elements)in all parts of the trees,in the fallen litter at different periods and those of the soils were determined.From these data,estimations of the annual amount of nutrient elements.absorbed,remained and returned to the soil,in the stands studied were made.The results give evidence to show the superiority of the mixed stand in some respects,as compared with the pure stand.In the mixed stand,the volume increment is 44.46% higher,the nutrient elements accumulated in fallen litter is increaced by 12.82-26.83%,and the amounts of nutrent elements,remained and returned to the soil,are 142.47%and 13% larger respectively.The amount of available nutrient elements in the soil under mixed stand is also greater than that of the pure stand.Litter of maple is more readily decomposed than that of pine,and the amount of nutrient elements so returned is 1.8-4.2 times larger (with equal basal areas).Maple is,therefore,considered to be a right species for soil enrichment.A pine-maple mixture is accordingly a good choice of stand composition under the natural conditions of xishan area.