Spectral Analysis of Dynamics of Rare Eremophyte Helianthemum ordosicum Population

Based on plot survey data at different slope positions,the dynamics of Helianthemum ordosicum population were analyzed using the spectral analysis method.Results showed that the natural regeneration dynamics of H.ordosicum population were presented as fluctuation of the distribution of individuals by age classes determined from the ground diameter.The quantitative dynamics of H.ordosicum population at different slope positions were greatly affected by the base wave.The apparent mid-and small-scale periodic fluctuations also existed.The mid-scale periodic fluctuations were about half of the base waves in the 12 mm-15 mm increment of ground diameter,and the small-scale periodic fluctuations were reflected in the 2.00 mm-6.25 mm increment of ground diameter regardless of slope positions.The mid-and small-scale periodic fluctuations were related to the environment pressure,interspecific competition and the intrinsic physiological characteristics.Because of the different habitat conditions,the small-scale periodism in the increment of ground diameter decreased from the lower slope position to the upper slope position in H.ordosicum population.Human disturbance also affected the periodic fluctuations.The periodic fluctuations of the quantitative dynamics maintained and sustained the self-stability in H.ordosicum populations.