甘肃臭草型退化草地优势种群空间格局及其关联性

In the process of grassland degradation the spatial pattern and spatial association of dominant species

空间格局和空间关联性是研究种群扩散和群落演替的重要方法。在石羊河上游高寒退化草地,运用点格局分析法,对不同演替阶段甘肃臭草和阿尔泰针茅的格局及关联性进行了研究。结果表明:甘肃臭草在没有形成斑块(CK)和斑块形成阶段(A),所有尺度上为聚集分布,在斑块扩散(B)、稳定(C)和衰退阶段(D)分别在0—90 cm、0—70 cm和0—40 cm上为聚集分布,90—100 cm、70—150 cm和40—150 cm为随机分布;阿尔泰针茅在CK阶段所有尺度上为随机分布,在A、B、C阶段分别在0—47 cm、0—75 cm、0—130 cm上为聚集分布,在47—50 cm、75—100 cm和130—150 cm上为随机分布,D阶段在所有尺度上为聚集分布;从CK—D阶段,甘肃臭草和阿尔泰针茅之间的关联性由显著负关联向关联性不显著转变,负关联显著程度先增强,后减弱;甘肃臭草种群从CK到D样地,种群领地密度先增大后减小,阿尔泰针茅种群领地密度逐渐减小。优势种替代过程中,种内竞争和种间竞争的相互转化影响格局的分布类型,竞争的不对称性影响关联性程度的强弱。

Spatial pattern and succession. Melica przewalskyi spatial association are important methods to study population diffusion and community is a kind of perennial rhizomatous clonal herbs with strange taste, which is not edible for grazing animals. With the infuluence of climate change and overgrazing, Melica przewalskyi gradually replaced Stipa Krylovii and became a single dominant specie in the northern slope of Qilian Mountains. It is very important to understand their distribution patterns and spatial association in the process of patch formation and recession, which is critical for revealing the mechanism of the replacement of the dominant species and the relationship between Melica przewalskyi and Stipa Krylovii in the process. The experiments were conducted in Yue ya ai grasslan the upper reaches of Shi yang river in Sunan country Gansu provin d （38°47＇15.8＂ N,99° 43＇ 35.9＂ E） which is located in ce, China. In early August, 2010, four different patches in different recession stages, such as formation stage, diffusion stage, stable stage and recession stage, were respectively selected in the study area, and a sample with no patch was selected as control plot（CK）. The measured value L（d） and the value of upper and lower envelopes were calculated by the Visual Fortran 6.5 based on the coordinate getting by GetData Graph Digitizer 2.22. Origin 7.5 was used as the plot software. This plot in the lower left corner coordinate origin to the intersection, using the step of 5 cm, the number of MonteCarlo stochastic simulation is 20 times, dashed line are the 95% confidence envelops for the same process. The results showed that：the aggregation of Melica przewalskyi population was intensely decreased and the spatial distribution pattern transfered from clumped to random, Melica przewalskyi population showed clumped pattern at all scale in the no patch stage（CK） and the patch formation stage（ A）, while it showed clumped pattern at 0--90 cm, 0--70 cm and 0--40 em and random pattern at 90--100 cm, 70--150 cm and 40--150 cm in the diffusion stage（B）, stable stage（C） and recession stage （D）. The aggregation of Stipa Krylovii population was intensely increased, the spatial distribution pattern transfered from random to clumped. Stipa Krylovii showed random pattern at all scale in the CK stage, while it showed clumped pattern at 0--47 cm, 0--75 cm, 0--130 cm scale and random pattern at 47--50 cm, 75--100 cm and 130--150 cm scale in the A,B and C stage, and in the D stage,it showed clumped pattern at all scale. The spatial association of Melica przewalskyi replacing Stipa Krylovii gradually transferred from negative to no association. Negative correlation increased significantly in the beginning, and then weakened. Territory density of Melica przewalskyi first increases, and then decreases. As to Stipa Krylovii,the territory density gradually reduce. Competition is a internal factor causing the formation and change of the population spatial distribution pattern. The population spatial distribution pattern changes with the intraspecific competition and the interspecific competition changing into each other. The distribution pattern tend to clumped as the interspecific competition was the mainly factor, while the pattern was random or regular as the form tend to intraspecific competition. The competition showed unsymmetry. When the change of Melica przewalskyi population pattern was mainly caused by interspecific competition, Stipa Krylovii population pattern could change owing to intraspecific competition or intraspecific competition. Negative correlation was very significant when interspecific competition tends to be predominant in both populations.