| Forest is an important production and life supply of humans. With the increasing of human's demanding, more forest suffered destructive interference, and part of virgin forests gradually degenerated into secondary forests. In China, secondary forest has become predominance of the forest resources, and occupied nearly half of the total forest. In mountainous region of northern Heibei, zonal vegetation-temperate deciduous forests have suffered disturbance by man-made or natural, and gradually formed a large area of secondary forest dominated by Populus and Behula. In the study, a Poplar-Birch natural secondary forest plot was settled in Beigou forestry station. The research based on data of vegetation and soil in the plot, the characteristics of forest community, spatial heterogeneity of vegetation and soil, the relationship of spatial heterogeneity of vegetation and soil components were analyzed. The paper aims to reveal the characteristics of spatial patterns and heterogeneity of the secondary forest, and provide quantitative relationship of spatial heterogeneity of vegetation and soil. The research findings could extend the theories of pattern and process, and provide some references to secondary forest conservation and management. The main results are as follows:1. The characteristics of the Poplar-Birch natural secondary forestThere were 16 arbor species,18 bush species and 71 grass species in the forest. The dominant species were Populus davidiana, Betula platyphylla, Larix gmelinii, Corylus mandshurica and Carex rigescens et al. The diameter structure of pioneer trees—Populus davidiana, Betula platyphylla showed there were fewer seedlings, the populations were in recession. The height structure showed arbors have no obvious vertical structure. The diameter distribution of bush presented approximate inversed"J". The height distribution showed bushes have no obvious vertical structure. Interspecific association in the community was significantly positive. Association coefficient between species indicated that association between arbor pairs was strongly positive, while association between arbor and bush pairs was more strongly negative.Grass species have the largest richness; arbors have the highest diversity index and evenness index. Niche breadth of arbors from big to small were as follows, Acer truncatum, Larix gmelinii, Sorbus pohuashanensis, Betula platyphylla et al. The biggest niche breadths of bush and grass species were Corylus mandshurica and Carex rigescens. The bigger niche overlap index of species pairs were Betula platyphylla-Quercus mongolica, Betula platyphylla-Picea wilsonii; Larix gmelinii-Acer truncatum, Larix gmelinii-Sorbus pohuashanensis:Corylus mandshurica-Swida bretchneideri, Corylus mandshurica-Weigela florida; Carex rigescen-Maianthemum bifolium, Carex rigescen-Vicia unijuga, Carex rigescen-Saussurea japonica, et al.Arbors were weakly mingling and in middle state, the number of cluster unites decreased with the measuring diameters increasing. Whereas the mingling of bushes were lower, and in transition of middle to inferior state, and mainly dominated by cluster unites. In the research scale, aggregating was the main distribution in arbors and bushes populations. The relationship of main species pairs indicated that Betula platyphylla vs. Populus davidiana, Betula platyphylla vs. Larix gmelinii, Betula platyphylla vs. Corylus mandshurica were negatively associated at most of the scales, while species pairs among Larix gmelinii, Populus davidiana, Corylus mandshurica were positively associated.2. The characteristics of vegetation spatial heterogeneityExponential model was the optimum model for spatial heterogeneity of arbors, bushes and litter amount, while spherical model was the fittest model to spatial heterogeneity of leaf area index (LAI) and grass coverage. The range of arbor, bush, grass, LAI and undecomposed, semi-decomposed, decomposed litters were 11.4 m,5.7m,8.7m,73.1m,31.5m,27.9m and 41.4m. The structure ratio of arbor, bush and grass, undecomposed and semi-decomposed litter amount showed strongly spatial correlated, respectively, the values were 0.92,0.89,0.92,0.89 and 0.87. Whereas structure ratio of LAI and decomposed litter showed moderately spatial correlated, the values were 0.52 and 0.72. In spatial distribution patterns, arbor, shrub and grass were obviously patchy. The basal area less than 3×103 cm2 of arbor individuals occupied a large percentage. Fragmentation level of bush was much higher than arbor, the basal area less than 15 cm2 individuals were the most. The pattern of grass was more complicated, the patches of 30%-60% of coverage took a large percentage. The pattern of LAI was simple, the patches of 0.8-1.2 occupied the largest percentage. The litter amount of semi-decomposed distributed obviously patchy while undecomposed and decomposed distributed continuous. The patches of 0.1-0.2 kg of litter amount took the largest percentage in the 3 levels of decomposition.3. The characteristics of soil spatial heterogeneityExponential model was the fittest model to spatial heterogeneity of topsoil water content (SWC). The range of SWC was 40.2 m, and structure ratio (0.94) showed the strong spatial correlation. In vertical soil horizon, spatial distribution patterns of soil pH value and soil nutrients were continuous, and the patterns were similar in different soil horizons, especially, in 0-20 cm and 20-40 cm. The range of pH value from the shallower to the deeper horizons were 46.1 m,37.1 m and 27.4 m. The range of nutrients were quite different in each soil horizons, the range of 0-20 cm soil horizon were 36-164 m, 20-40 cm were 53-115 m,40-60 cm were 36-108 m. From different soil nutrients indexes, range of total nitrogen was the smallest, while range of soil organism matter was the largest. The range of phosphor was larger than nitrogen and potassium. In spatial structure ratio, the total content of nitrogen, potassium showed strong spatial correlation at the research scale, whereas organic matter, available phosphorus and potassium showed moderate spatial correlation. In spatial distribution pattern, the area of 15%-30% patches of topsoil water content was the largest. With the increase of the depth of soil, the areas of patches of 5.9-6.1,5.9-6.1,6.1-6.3 pH value,60-80 g/kg,40-60 g/kg,20-40 g/kg organic matter, less than 6 mg/kg available phosphorus,200-250 mg/kg,150-200 mg/kg,100-150 mg/kg available potassium,4-6 g/kg,2-4 g/kg,4-6 g/kg total phosphorus,16-18 g/kg,16-18 g/kg,18-20 g/kg total potassium,2-3 g/kg,1-2 g/kg,1-2 g/kg total nitrogen occupied the largest percentage in each soil horizons.4. The relationship of spatial heterogeneity between vegetation and soilIn the Poplar-Birch natural secondary forest,15%-30% topsoil water content was suitable for arbor and bush, and has a great influence on LAI; 25%-30% topsoil water content was suitable for grass, and have a close relationship with litter amount.5.9-6.3 pH value was suitable for arbor; 5.9-6.1 pH value was suitable for bush and grass, and closely related to LAI and litter amount.40-60 g/kg organism matter was suitable for arbor, bush and grass, and greatly influenced LAI; 40-50 g/kg organism matter has a close relationship with litter amount.6-12 mg/kg available phosphorus was suitable for arbor and bush, and greatly influenced LAI; 6-8 mg/kg available phosphorus was suitable for grass, and closely related to litter amount.100-250 mg/kg available potassium was suitable for arbor; 150-200 mg/kg available potassium was suitable for bush and grass, and has a close relationship with LAI and litter amount.0.3-0.5 g/kg total phosphorus was suitable for arbor; 0.3-0.4 g/kg total phosphorus was suitable for bush and grass, and closely related to LAI and litter amount.16-20g/kg total potassium was suitable for arbor, bush and grass, and has a close relationship with LAI and litter amount.1.5-2.5 g/kg total nitrogen was suitable for arbor and grass; 1.5-2.0 g/kg total nitrogen was suitable for bush, and closely related to LAI and litter amount. |
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