Structure And Plant Diversity Of Robinia Pseudoacacia Stands In The Gully Region Of Loess Plateau

Based on the field investigation of Robinia pseudoacacia plantation, by the method of space altered from time, this study analyzed the characteristics of plantation stand structure , composition and diversity of Robinia pseudoacacia plantation in Chunhua county. The result as followings:1. There are rich of undergrowth species in the Robinia pseudoacacia plantation, which includes 108 species belonging to 36 families 80 genera., comprising 22 species, 13 families 19 genera of shrub and 86 species, 23 families, 62 genera of herb. In shrub layer, rosaceae, leguminosae, caprifoliaceae, fagaceae plant communities accounted 59.1% of total plants. and compositae, gramineae, leguminosae, rosaceae families accounted for 64.0% in genera and 58.1% in species.2. Cryptophytes take a high percentage only in the stage of young plantation. Annual plant species decreases in quantity and dominance with the increasing of plantation age; Generally chamaephytes are not more than 10% of total species in quantity; hemicryptophyte and phanerophytes increasingly get added finally up to more than 30%.3. Diameter rank distribution and peak were bigger in sapling stand stage; the partial degrees and stand diameter one-order partial embodiment were small and had a flat distribution in mid-maturation forest stage. Average DBH of Robinia pseudoacacia increased with the increase of plantation age. But growth rates were different, sapling and mid-maturation forest were higher than embodiment. Sapling forest between average DBH and density were positive correlation, negative in the mid-maturation forest. Lower density (less than 1,500 plants/hm2) is conducive to DBH growth.4. The height skewness of young stage forest was larger than the middle stages forest and mature stages forest. The height distribution kurtosis was sharper in young forest stage (kurtosis value greater than 0), and was flatter in the middle stage. Robinia pseudoacacia's average height was increased with its stand age. The average tree height was increased faster in the young stage and the middle stages, 0.1669m per year. The average tree height of mature stages was decreased, 0.0797m per year.The canopy density of Robinia pseudoacacia was increased with the growth of forest age, reached the maximum (0.75) in its 20 age. After that, the canopy density was reduced and stabilized at around 0.45.5. With the increasing of forest age, overall species richness of under gross species was increased, the middle stages forest had a highest richness index; the Shannon-Wiener diversity index and Simpson diversity index were increased from young stage to middle stages, and significantly reduced in middle stages. The pielou index was lower in young stage and higher in middle stages and middle stages. The Richness of herb layer, Shannon-Wiener index and Simpson index were higher than shrub layer.6. After middle stage, the density could be controlled at 1000-1500 strains/hm2, which would increase the diversity of undergrowth plant, and improve the community stability.