六盘山区辽东栎林分结构对各植物层生物量的影响

The Effects of Stand Structure of Quercus wutaishanica Forests on the Biomass of Different Plant Layers in the Liupan Mountains of Northwest China

[目的]量化宁夏六盘山区辽东栎次生林各植物层(乔木层、林下植物层(草本和灌丛)、枯落物层)生物量随郁闭度及林分密度的变化,确定能使各层生物量均维持在较高水平的最佳林分结构,以充分发挥森林多种功能。[方法]基于野外调查样地数据,利用上外包线分析法确定辽东栎林各层生物量对林分密度和郁闭度的响应规律,并经综合权衡后确定最佳郁闭度范围。[结果]随郁闭度和林分密度增加,乔木层生物量先快速增加,在郁闭度0.75和密度1050株∙hm^(−2)时分别达到292.3和296.9 t∙hm^(−2),分别为其外包线最大值的80%和82%,之后增速变缓;林下植物层生物量先缓慢下降,在郁闭度0.75和密度1150株∙hm^(−2)时分别达到9.08和9.17 t∙hm^(−2),分别为其外包线最大值的89%和86%,之后快速减小;枯落物层生物量先逐渐增加,在郁闭度0.75时达到33.34 t∙hm^(−2),为外包线最大值的97%。综合分析各层生物量随郁闭度的变化表明,需维持林冠郁闭度在0.75~0.79左右,才能使林分各层生物量都保持在各自上外包线最大值的80%以上。[结论]在宁夏六盘山区,要使辽东栎林的乔木层、林下植物层、枯落物层的生物量均维持在较高水平,需维持林冠郁闭度在最佳范围0.75~0.79左右,这可用于指导该地区及类似地区的辽东栎林多功能经营。

[Objective]To quantify the effects of stand density and canopy density on the biomass of different plant layers(overstory tree layer,understory plant layer,and litter layer)of Quercus wutaishanica secondary forests in the Liupan Mountains of Ningxia in northwest China,and to determine the optimal stand structure that can maintain the biomass of each layer at a relatively high level for fully using the multiple forest ecosystem services.[Method]Using sample plot data obtained from field survey,the response of biomass in each layer of Quercus wutaishanica forests to stand density and canopy density were determined by upper boundary lines(UBL)analysis.Then these UBLs were superimposed to find an optimal canopy density range.[Result]With the increase of canopy density and stand density,the overstory tree layer biomass increased rapidly at first,reaching 292.3 and 296.9 t·hm^(−2)when the canopy density was 0.75 and the density was 1050 trees∙hm^(−2),respectively(80%and 82%of the UBL predicted maximum),and then the growth rate slowed down;the understory plant biomass decreased slowly first,and reached 9.08 and 9.17 t∙hm^(−2)when the canopy density was 0.75 and the density was 1150 plants∙hm^(−2),which were 89%and 86%of the maximum value of UBL,respectively.Then it decreased rapidly;the litter layer biomass increased rapidly at first,and reached 33.34 t∙hm^(−2)when the canopy density was 0.75,which was 97%of the maximum value of UBL.Therefore,the canopy density should be maintained at about 0.75-0.79 in order to keep the biomass of each layer of the stand above 80%of the maximum value of UBL.[Conclusion]In order to maintain the biomass at relatively high level for all different plant layers of Quercus wutaishanica forests in Liupan Mountains,the canopy density should be maintained at about 0.75-0.79,which will be helpful for guiding the multifunctional management of Quercus wutaishanica forests in the study region and similar areas.