Studies On Spatial Heterogeneities Of Subtropical Hilly Evergreen-Deciduous Broad-leaved Forest

Abstracts: As 0patial heterogeneity becomes a major theme in a wide range of ecological studies, the concepts of scale and hierarchy become increasingly important in ecology in general. This confirms, and is indicative of, the rapidly rising awareness of the importance of scale and hierarchy by ecologists. Since structures of forest communities, functional heterogeneity and its spatially and temporally dynamic varieties which expresses by many approaches, it is difficult to quantity community heterogeneity. In this research, one sampling in sizes of 100 m×100 m were established in subtropical hilly evergreen-deciduous broad-leaved forest in Baisha River of southwestem Sichuan province, and expanded the researches of forest spatial heterogeneity by many statistics methods. The results were as following:(1) To simulate stand structures of different forest layers using two-parameter Weibull function, it can prefer to elucidate the structures of tree sizes. And the results demonstrated that H≥10m layer was important layer that controlled the forest stand structure, in simultaneity, we obtained better simulated forest stem density by Weibull function, and this reflected continuous distributions about nature forests at certain spatial ranges.(2) Spatial patterns of different layers which included whole stand, H＜10m layer and H≥10m layer represented Regularity distribution tending to randomness, and the same as different tree species at the distance interval 75m. By analysis of Ripley's K function, inflexions in multi-scales were presented in spatial patterns of different forest layers and tree species that indicated the affinities between forest structures and exterior conditions.(3) By analysis of semivariogram function, diameter at breast height and basal area of forest stand show spatial autocorrelations in strict ranges, further more, they represented spatial varieties only in orientations of 45 degree.(4) Time series equations of basal area increment of each tree species were established, and AR (2) was suit for many tree species. By analysis of semivariogram function, basal area increment of each tree species showed spatial varieties only in orientations of 45 degree during 1986-1991, 1986-1996, 1986-2001, 1986-2006. In addition, trees biomass represented spatial varieties only in orientations of 45 and 97 degree.(5) There were robust linear relationships between diffuse of Photosythetically active Flux Density under canopies (PPFDDiffuseU) and gapfraction, openness as well as leaf area index (LAI) (R²=0.9836, P＜0.00001), moreover, PPFDDiffuseU had positive linear correlations with gapfraction, openness, and had negative linear correlation with the LAI. By analysis of semivariance PPFDDiffuseU and LAI had obvious spatial heterogeneities, however gapfraction, openness had weak spatial variability. Our results confirm importance of examining spatial dependence of light availability in studies of forest canopy, but they also underscore the limitations of a single period of data collection. Long-term studies as well as experimental manipulations of light availability are needed to establish causal relationships between light availability and stand-level patterns.(6) Organic matters contents which were in hilly evergreen-deciduous broad-leaved forest, second forest of hilly evergreen-deciduous broad-leaved forest and plantation forest such as Japan cedar and fir forest, showed evidently different. Organic matters contents in hilly evergreen and deciduous broad-leaved forest represented spatial autocorrelations in large ranges, and tended to distributions of patchiness varieties, at same time, represented spatial varieties only in orientations of 45 and 97 degree.(7) Linear models for isotropy were optimal models by simulating Shannon-Wiener diversity indices (H) , Pielou evenness indices (E) ; and for anisotropy linear model was optimal model to H, as well as Gaussian model to E. moreover, the ratio of C/(C₀+C) showed that anisotropic heterogeneities was not obvious, namely isotropy of H and E was effective to spatial pattern of tree species diversity, and appeared steady variances in whole scales; in sampling scales, H and E represented negatively spatial autocorrelation, and its spatial autocorrelation presented not remarkable in regional scales (-0.6386,-1.0902＜-1.96)(8) Under all scales, principal coordinates of neighbour matrices (PCNM) analysis was best approach to spatial analysis of ecologically environment data, by means of PCNM varieties in fine scale of OM contents, DBH, stem densities, gapfraction and openness were very outstanding, Moreover, diversity indices, OM contents, BA, stem densities, gapfraction and openness in middle scales showed very outstanding.(9) By analysis of canonical correlation, the results showed that they had obvious correlations among forest structures, canopy structures and light environment factors, additionally, they represented high affinities with PCNM variables.(10) From above analysis, we know that forest stand represent continuous change situations in space and time, and this confirms that forest stand structures factors can simplify regional continuous variables, and this proved that previous hypothesises were correct.