Study on the Points Pattern Characteristics and Negative Density Dependence of Dodonaea viscosa of Jinsha River Dry-Hot Valley

Based on the explanation of the community construction rules with the negative density restriction hypothesis, the distribution pattern of mulberry in the dry-hot valley(DHV) of Jinsha River basin, the process of negative density dependent on(NDD) were studied, which provides a reference for revealing the maintenance mechanism of community in the DHV eco-zone. Ripley's o−ring(R), a pairwise correlation function in point pattern analysis, and random-labeling were used to analyze the point pattern characteristics and density-restriction effect of D. viscosa population. The pattern aggregation frequency of D.viscosa population is inverted J type(nearly L type) with spatial scale, and random distribution on medium-large scale. The aggregation distribution of the mulberry population was strong from 0−5 m, and weak from 5−22 m. The aggregation distribution of the mulberry population was random at the > 22 m.O12(r) > 0.04 was strongly correlated with common woody associated species at 0−9 m scale, weakly correlated at 12−30 m scale, and had no correlation or weak negative correlation at 30−72 m scale. The self-thinning effect of density restriction was not obvious at the scale of 0−40 m, but the distance restriction was more obvious at the small tree stage than at the middle tree stage. At the same time, the large trees showed stronger sheltering effect to the same kind of small trees within 1m distance. There was no difference in the order habitat utilization patterns among the subpopulations, but the extra aggregation degree of small trees was significantly higher than that of medium trees, showing obvious sparsity effect at the scale of 0−22 m. The Ripley's O−ring function for point pattern can clearly describe the relationship between pattern and scale of mulberry population, and eliminate the cumulative effect. There is no difference in habitat utilization of different age class structure of D. viscosa population, but there are different degrees of density restriction in different age class structure, and different age class populations can coexist well in medium and large scale. On the medium and small scale, density restriction is another important factor for the community skeleton structure and species coexistence of D. viscosa, which provides space for species coexistence. The density restriction of mulberry population is in the ecotone of the upper edge of the Jinsha River's DHV. Density restriction is one of the potential driving forces for the construction of D. viscosa community and the dynamic maintenance of biodiversity stability.