Spatial Structure of An Old-growth Oak Forest on Karst Terrain
[Objective]To investigate the distribution pattern,species association and marker characterist-ics of karst oak old-growth forests,and to explore the role of vertical stratification in maintaining biod-iversity in karst forests.[Method]A 200 m×110 m fixed plot was established in an old growth karst forest(>300 years)in the Nanpanjiang River basin,southwest China.Trees were divided into overstory and un-derstory based on height and species composition.Relationships between diameter class and species abundance,and between diameter class and richness were analyzed by negative exponential function.The distribution patterns of overstory,understory and their main populations were analyzed by pair correla-tion function g(r),and spatial correlations between overstory and understory,and their main populations were also analyzed.The mark character of tree species and tree size were detected by mark correlation function kmm(r).[Result](1)The diameter distribution of the stand,over-story and understory all showed an inverted J-shaped pattern.Species richness of the stand and understory decreased with increasing dia-meter classes,while that of the overstory increased first and then decreased;(2)The overstory exhibits regular or random distribution on most scales,and only exhibits aggregation distribution on small scales(r = 0～1 m,4～6 m).The understory had higher aggregation intensity at large scale when compared to the overstory;(3)Random correlation dominated the overstory and understory,and their major populations.Only a few pairs had positive or negative correlation at small scale(r = 0～2 m);(4)The stand and under-story shared a characteristic of conspecific aggregation at all scales,and their intensity were obviously higher than that of the overstory.Tree sizes of the stand and overstory differentiated obviously and small trees were strongly aggregated.The understory contained a similar size of small trees that were randomly distributed at most scales.[Conclusion]These results suggest that vertical stratification largely determine species composition,abundance,distribution pattern and the spatial association of overstory and under-story,which plays an important role in species coexistence and diversity maintenance.
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