退化沙质草场群落特征及功能群生物量的空间变异性

Spatial Variability of Community Characteristics and Above-ground Biomass of Functional Group in Degraded Sandy Grassland

科尔沁沙地草地退化、沙漠化发展中的沙质草场阶段，植被丰富度、盖度可很好地拟合为球状模型，都具有明显的空间结构特征，在所研究范围内，盖度变异幅度明显高于丰富度，但在变程范围内植被丰富度空间变：异性强，盖度的空间变异性弱，依赖性强。群落生物量及各功能群生物量的空间自相关范围在9．390～252．690m范围内变化，相差近30倍，表明影响功能群生物量的生态过程和格局起作用的尺度效应明显。多年生草本和中生植物生物量的结构方差与基台值的比值小于60％。不具有空间结构特征，随着距离的增大，半方差函数值达到一个稳定的极限值后，开始下降并呈现出减小的趋势，但是受牲畜活动等随机因素影响，在5m取样尺度内不存在局部格局，而可能受更大尺度的格局控制。群落中其它功能群生物量表现出随着距离的增大空间变异性增强的趋势，但超过其变程后半方差函数值稳定在一个极限值附近。群落中生态功能群旱生植物的波动变化不仅对群落盖度、草场的生产力有直接的影响，而且对草场群落及其生态系统的稳定和生态功能的发挥具有重要作用。

Geostatistical theory and methods were used for describing spatial variability of community characteristic and above-ground biomass of functional group in sandy grasslands of the Horqin Sand. Results showed that vegetation richness and coverage had distinct degree and scale changes in spatial variability. Vegetation richness had the high spatial variability, while coverage had a high dependence in study area. The above-ground biomass of functional groups and community in sandy grasslands had a different spatial auto-relation range from 9.39 m to 252.69 m. This showed that factors, affecting ecological processes and patterns of above-ground biornass of different functional groups, played their ecological roles on different scales. The semi-variogram values of above-ground biomass of perennial herbs and Mesophytes, following the increase of spatial distances, showed decreasing trends when semi-variogram values exceeded the effective range. However, semi-variogram values of above-ground biomass of other functional groups, following the increase of spatial but semi-variogram values were no longer changed when distances, showed a trend of increasing spatial variability, exceeding the effective range. The above-ground biomass of perennial herb and intermediate xerad, owing to the effects of human disturbance and livestock activities and topographic condition, had no spatial difference in a range of five meters. It may be controlled by a process on larger scale. So, the above-ground biomass of different functional groups had the more complex mechanism and processes corresponding to disturbance and effects from human, livestock and nature. Moreover, changes on xerad not only influenced community＇s coverage, but also played an important role in maintaining ecological functions and the stability of grassland ecosystem.