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Stand structure and diversity of research for improving forest productivity and play functions of forests has important guiding role. The Loess Gully Pinus tabulaeformis as the research object, using sample surveys and canopy analyzer, research and analysis of stand structure and understory plant diversity of Pinus tabulaeformis (Pinus tabulaeformis) plantation reached the following conclusions: (1) oil under a pine plant a total of 87 species belonging to 25 families and 56 genera; herbaceous layer 70, a total of 17 under the 17 families and 38 genera, shrub layer, under the 11 families and 17 genera. Northwest Stipa plants (Stipa sareptana), alfalfa (Medicago sativa), the Altai Gouwa flowers (Heteropappus altaicus), trouble grass (Muhlenbergia hugelii), Geranium (Geranium sibiricum), the Mao berry (Rubus parvifolius), yellow Artemisia (Artemisia annua), capillaris Artemisia (Artemisia capillaris) Burnet (Radix Sanguisorbae), Lactuca (Artemisia apiacea), caregiver fescue (Festuca parvigluma,), madder (Rubia cordifolia), northwest needle Mao alfalfa, the Altai Gouwa flowers, caregiver fescue niche breadth and niche overlap was relatively large. (2) oil pines high-16a before slow growth, after the age of growth gradually accelerated, 35a slow growth to stop growing; DBH growth slow in 16a before, has accelerated after a slow growth after 40a of P. tabulaeformis DBH and tree height growth basic synchronization. (3) shady slope density of 1800 / hm ~ 2 about middle-aged forest DBH distribution more reasonable, sunny slope density around 1500 / hm ~ 2 the DBH distribution more reasonable. Shady slope density of 2,150 / ha of tree height high distribution more reasonable, the sunny slope density of about 1800 / hm ~ 2 tree height distribution is more reasonable. (4) exist between the DBH growth of young forest stand density was significantly positively correlated; the DBH growth with the presence of stand density was significantly negatively correlated. The presence of young the Lin Shu high and stand density was significantly negatively correlated; middle-aged forest and mature Lin Shu-high density of the existence of a significant positive correlation. (5) With the increase in stand density, the Pinus tabulaeformis leaf area index increase, the transmittance decreases; site coefficient, direct light 立地 coefficient of scattered light in the case of the same forest age, and the coefficient of integrated optical site with The decrease in density is increased. (6) shady slope, slope, gentle slope and low-altitude conditions, high species richness index, is conducive to the growth of understory plants. Slope and gentle slope woodland understory plants evenly distributed. Forest age phases understory shrub layer species richness are less than the herbaceous layer; most species-rich middle-aged forest diversity index and evenness index higher than the young forest and mature forest understory for shrub and grass to survive.
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