Study On Elm Woods Ecology In Sandy Land In The Songliao Plain

The elm woods ecosystem was the clamix community type in sandy land in Songliao Plain and could be divided into Hemipelea davidii woods、Ulmus pumila woods and U. macrocarpa var. mongolica woods based on the construted species. The ecosystem had a unique species and ecological process which constitute the forest-steppe landscape and played an important role maintaining regional ecological balance as well as the quality of northeastern grassland ecological environment. At present, the elm woods had degraded seriously such as the community regeneration slowly, the distribution area shrinkage and need to carry out population and community ecology basic research. In this paper, the typical located plot of the three elm woods were used to investigated the population characteristics （such as the quantative characteristics of leaf modules, branch modules, thorn modules and fruit modules） and the community characteristics （such as the scpecies composition and quantative characteristics of arbor layer and herbal layer）. The coefficient of variation, mathematical models, the important value and species diversity indexes were applied to analyze the phenotypic plasticity of mudules, seed rain dynamics and community structure characterization respectively. We aimed to discover the structure and dynamics of elm woods population and community. This paper has important theoretical and practical significance and can create some degree of new perspective of plant population and community research, as well as provide scientific evidences and technical supports for the elm woods management and restoration in Songliao Plain.1 Research of H. davidii woods Ecology1)Population EcologyThe variation degree of H. davidii modules varied greatly in different age-class branches. The regulation was as follows: the variation degree of modules biomass is greater than the modules numbers. Furthermore the variation degree of 1a and 2a branches were higher than 3a branches commonly, which indicated that the effect of external factors on modules biomass （in particular branches biomass） was relatively large, but little effect on the modules numbers.Regression analysis showed that there were significant regression between the biomass, modules numbers of 1a and 2a branches and the total biomass of branches. Furthermore, the regression function determination coefficient （R2） of 1a and 2a branches were higher than those of 3a branches commonly, which indicated that the contribution of 1a and 2a branches to the capacity of population regeration and expansion were higher than those of 3a branches. Correlation analysis showed that the modules of 1a and 2a branches all growed at the same rate, and the modules of 3a branches except of thorn modules showed the same growth rate too.2)Seed rain and the patterns of the seed dispersal in H. davidii woodsThe quantitative characteristics of the H. davidii seed rain in the understory and at the woodsides, as well as the seed dispersal patterns at the woodsides and of the isolating trees were analyzed. The results indicated that among three smpling plots, the average density of the seed rain in the understory was the highest (13732.5±3106.2 seeds·m^-2). For isolating trees, the seed rain had the highest density (5449.4±1429.3seeds·m^-2) in southeast transect, being significantly higher than that in other directions, and the lowest one (650.2±631.6 seeds·m^-2) in the northwest transect, being significantly lower that in other directions. At the woodsides, the seed rain density was significantly higher in the east and south transects than in the west and north transects. The variation of the seed density was greater, with the variation coefficient being 25.7%-106.3% in different directions in the two plots of isolating trees and woodsides. Same as other anemochorous plants, H. davidii had the characteristies of seed dispersal away from the seed source. In the eight sampling transects, there existed diversity in the patterns of the dispersal away from the seed source in per unity area and in accumulated area, including linear, power, exponential, quadratic parabola and logarithmic functions.3)The synecologyThere were not shrubs in H. davidii woods and the arbor layer could be divided into two inferior layers, which the height of upper-arbor layer was 4.05-7.86 m and the lower-arbor layer height was 2.05-3.20 m. There were totally 32 herbal species belonging to 13 families and 27 genera, which were dominant by Poaceae, Fabaceae and Compositae. There were 11 areal type, most of which were Mongolian-Northeastern China-Dahuricia-North China accounting for 34.38%, and the Northeastern China- North China areal type taking up 12.5%. The species of mesophyte dominated three water ecological types, making up 59.37%, and the mesoxerophyte and xerophyte species occupying 25% and 15.63% respectively. Most plants among the six life forms belonged to the hemicryptophyte which accounted for 31.25%. The H. davidii community had the typical characteristic of temperate steppe.The species diversity of herbal layers in H. davidii woods were correlated to the extent of arbor layer development, the decrease of camopy would lead to the increase of ecological dominant diversity of herbaceous layer and decrease of eveness and species diversity. There were no significantly correlations between the community production and species number within functional group, but with the individuals within functional group showed a significant positive correlation （p <0.05）.4)The impact of grazing on species diversity of H. davidii woodsWith the increase of grazing intensity, the life form structure showed a significant change. The dominance type of life form was hemicryptophyte under moderate and medium disturbance, and under the heavy disturbance the dominance type was therophyte. The change of the species diversity indicated that the community under moderate disturbance had the highest richness, evenness and species diversity, particularly there were sigmificant difference between richness （p<0.05）. With the increased of the disturbance extent, the species diverstiy of community decreased linearly. H. davidii woods showed the degraded characteristic such as species number decrease, community structure simplified and xerotic trends.2 Research of Ulmus macrocarpa var. mongolica woods Ecology1)Population ecologyThe variation degree of U. macrocarpa var. mongolica modules varied greatly in different age-class branches. The regulation was as follows: the variation degree of modules numbers is greater than the modules biomass. Furthermore, contrast to H. davidii, the variation degree of 1a and 2a branches were lower than 3a branches commonly, which indicated that the effect of external factors on modules numbers was relatively large, but little effect on the modules biomass. These may be determined by the spcies biological characteristics.Regression analysis showed that there were significant regression between the biomass, modules numbers of different age-class branches and the total biomass of branches. The order of regression function determination coefficient （R2） of different age-class branches was 1a <2a<3a, which was accordance with the coefficient of variation. The results showed that the contribution of 1a and 2a branches to the capacity of population regeration and expansion were decreased. Correlation analysis showed that the modules of 1a, 2a and 3a branches all growed at the same rate, the numbers and biomass of modules in different age-class branches were correlated with the total biobass significantly, which indicated the coincidence of modules in resource utilization.2)The synecologyThe canopy of arbor layers was 40-60%, the height 5.83-9.33m, DBH 0.13-0.19m, Under branch height 2.16-2.63m, row distance 3.72-8.16m. The total number of herbal species were 47 and belonged to 2 families and 39 genuses, The main families embraced Poaceae, Fabaceae and Compositae. Most areal type were Mongolian-Northeastern China-Dahuricia-China north within 13 areal types.The area has the influx characteristics of 4 areal type. The species of mesophyte dominated three water ecological types, the rest was xerophyte and mesoxerophyte, which had the trends of dried habitat condition. The life forms of most of the plants belonged to the therophytes, followed by hemicryptophytes. There were no significantly correlations between the community production and species number within functional group, but with the individuals within functional group showed a significant positive correlation （p <0.05）.3 Research of U. pumila woods Ecology1)Population ecologyThe regulation of U. pumila modules in different age-class branches was as follows: the variation degree of modules biomass is greater than the modules numbers. Furthermore, coincide with macrocarpa var. mongolica, the variation degree of 1a and 2a branches were lower than 3a branches commonly, which indicated that the effect of external factors on modules numbers was relatively large, but little effect on the modules biomass. Regression analysis showed that there were significant regression between the modules biomass, modules numbers of different age-class branches and the total biomass of branches. The order of regression function determination coefficient （R2） of different age-class branches was 1a <2a<3a. The results showed that the contribution of 1a branches to the capacity of population regeration and expansion were decreased under the impact of human disturbance and external factors. As the result the population regeneration and community structure were unsustainable. Correlation analysis showed that the modules of 1a, 2a and 3a branches all growed at the same rate, the numbers and biomass of modules in different age-class branches were correlated with the total biobass significantly, which indicated the coincidence of modules in resource utilization.2)The synecologyThe U. pumila woods structure was relatively simple, there were only arbor and herbal layers without shrub layers , furthermore there were not typical temperate forest species but steppe species. Usually there were higher species richness of herbal layers. The dominant species were Celeistogenes squarosa, Pottentilla sp., Leymus chinensis, et al.. There were also Prunus armeniaca and Securinega suffruticosa shrubs in some local topography.View from the composition of ecological and areal type structure, compared to the survey by Li jiandong in 1981, the hemicryptophyte and geophyte decreased and the therophyte increased dramatically. The hygrophilous disappeared and Xerophytes decreased dramatically. In terms of the areal type, most areal type were Mongolian-Northeastern China-Dahurica-China north. The area has the influx characteristics of 4 areal type but the number of areal type decreased dramatically too. In addition, there were no significantly differences between three plots, which indicated that there were seriously human disturbance and lead to homogenization in species composition and community structure.