不同高寒退化草地阿尔泰针茅种群的小尺度点格局

Fine-scale spatial point patterns of Stipa krylovii population in different alpine degraded grasslands

种群空间格局是种群自身特性、种间相互关系及环境条件综合作用的结果。采用草地群落学调查与点格局分析方法,在祁连山北坡选择未退化、轻度退化、中度退化和重度退化等4种高寒草地,分析了阿尔泰针茅(Stipa krylovii)种群斑块特征、株丛结构和点格局特征。结果表明:阿尔泰针茅在衰退过程中种群密度和种群领地面积减小,空斑面积增大,领地密度先增大后减小,小株丛(株丛径0.1—1.0 cm)比例增加,大株丛(株丛径2.1—7.0 cm)比例减小;不同草地梯度中阿尔泰针茅种群的空间格局存在明显差异:未退化草地中阿尔泰针茅种群在0—64 cm尺度上为均匀分布,64—100 cm尺度上为随机分布;中度退化草地中阿尔泰针茅种群在0—70 cm尺度上为随机分布,而在70—100 cm尺度上为聚集分布;轻度退化和重度退化草地中阿尔泰针茅种群在0—100 cm尺度上均为随机分布。在放牧干扰和种间竞争作用下,阿尔泰针茅种群斑块从中心开始破碎,并逐渐向四周辐散,引起小尺度上种群斑块间分布格局出现"随机分布-聚集分布-随机分布"转变,促使原有斑块被分割为多个直径较小的"岛"状小斑块并进一步分化,最终种群斑块完全破碎、草毡层逐步消失,从而造成阿尔泰针茅种群的衰退。

Spatial distribution pattern is important in plant ecology as it affected the dynamics of plant populations,communities and ecosystem processes,which can reveal the dynamic and stability of population and community structure.Stipa krylovii,the zonal vegetation in alpine degraded grassland,has a great significance for understanding ecological processes and sustainable utilization of grassland resources with studies on population patterns of S.krylovii.Study sites locates in the MaChangtan grassland in SuNan country of the north Qilian Mountain（38°47′22.1″—38°52′11″ N,99°45′11.7″—99°57′41.2″ E）.with the altitude of 2610—2632 m,the annual temperature of the region is 1—2 ℃,the annual precipitation varies within a range of 270—350 mm,the soil is mainly consisted of mountain chestnut soil,the dominant native vegetation in the region is consisted of perennial grasses and forbs.In July 2010,we recorded fine-scale（0—100 cm） spatial patterns of S.krylovii from 2 m × 2 m grids（2 cm × 2 cm quadrats） in four plots under four kinds of degradation gradients according to community characteristics,population characteristics of S.krylovii,and grassland stocking rate for nearly 10 years： no degradation（90%）,light degradation（105%—125%）,moderate degradation（123%—138%） and heavy degradation（135%—150%）.The point pattern analysis and Monte Carlo stochastic simulation method were used to quantitatively analyze S.krylovii population patterns by the software of GetData Graph Digitizer 2.22,VisualFortran 6.5 and Origin 7.5.Based on life history traits,bunch structure,patch characteristics and strategies of ecological adaptation in the community,the mechanisms generating and maintaining these patterns were discussed.The results showed that： First,there were significant effects on patch characteristics of S.krylovii population under the different degradation gradient.The density and population territory area of S.krylovii population in heavy degradation was significantly lower than no degradation,but its total area of hole in heavy degradation was greater than no degradation,and territory density increased firstly and then reduced.Second,the bunch structure of S.krylovii population existed complicated relationships.The small bunch of 0.1—1.0 cm in heavy degradation was greater than no degradation.At the same time,the proportion of big bunch was significantly higher than others in no degradation.Third,there was a difference at different scales.Under no degradation conditions,the spatial patterns of S.krylovii were regular at 0—64 cm scales,but aggregated at 64—100 cm scales;under light degradation conditions they were random at 0—100 cm scales;under moderate degradation conditions,the spatial distributions were random at 0—70 cm scales,but aggregated at 70—100 cm scales;under heavy degradation conditions,there was random as a whole and the scale ranges was from 0 cm to 100 cm.In contrast,the population patch is the basic functional unit of S.krylovii,which can decide the status and role of S.krylovii in the community.Under the role of grazing and interspecies competition,population patches may crumble from center to the edges gradually,and it lead to the spatial patterns changed.Finally,S.krylovii declined in alpine degraded grassland along with population patch broken and mattic epipedon disappeared.