Naturalized Development And Biological Characteristics Of Pinus Tabulaeformis Plantation On The Loess Plateau In North Shaanxi

In this paper, Pinus tabulaeformis plantation were taken as the research object in the different regions, and growth, reproductive and regeneration characteristics, community structure were studied across environmental gradients on the Loess Plateau, in order to confirm the main factors affecting the natural regeneration and reproduction of Pinus tabulaeformis, to explore the evaluation method for the plantation communities naturalized development based on fuzzy membership function synthetic evaluation model, to present the boundary of natural regeneration and naturalized cultivation way, to provide theoretical bases for planting and management. The main results were as follows:(1) Sexual reproduction process was complete in southern and middle Loess Plateau in north Shaanxi. Mother tree rate accounted for more than 30%. Cone yield, length, width, average seed number per cone, seed length and width was higher in the south and middle region than that in the north region. Full seed rate was 67.32 %-77.60 % in the northern region, which was higher than that in the southern and middle region (59.12 %-62.76 %). Annual precipitation and average temperature of January had the most influential effect on reproduction characteristics, while annual evaporation and frostless period took the second place。(2) The weight per 1000 seeds was higher in the south and middle region than that in the north region. The viability of seeds was the lowest in Shenmu. There was not significant difference in the viability and the germination of seed. The optimum temperature of seed germination was 20-25℃, the lowest temperature was 8℃. The lowest soil moisture of seed germination was 8 %.(3) Seed did not germinate after falling to the ground in Shenmu, Wuqi and Suide. There were few of saplings in the forest edge in Zhidan, Yanchuan and Yanchang. There were abundant seedling and sapling in Huanglong and Yichuan, and maximum age of sapling was 10. Seedling and sapling aggregately distributed mother tree around. Annual precipitation, annual temperature and≥10℃annual accumulated temperature had the most influential effect on regeneration.The region of annual precipitation more than 550 mm was suitable cultivation region. Potential regeneration region was that of annual precipitation between 550 mm and 500 mm, which was mild suitable cultivation region. The region of annual precipitation less than 500 mm was not suitable cultivation region.(4) Families, genera and species of indigenous plant gradually increase from north to south, 70% plant belonged to temperate distribution genera. The minimum of species diversity was in Shenmu. Latitude and annual precipitation had the more effect on species diversity herb layer, latitude, annual precipitation, annual sunshine hour and average temperature of January had the more effect on species diversity shurb layer. Cody index (β_C) present increasing trend from north to south, which explained species replacement rate increase with decreasing latitude, andβ_C was able to reflect the community changes as the latitude alters. Whittaker index (β_WS),Jaccard index (C_j) and Sorenson index (C_S) changed irregularly and salutatory, which community similarity had great difference. C_j and CS had the same change trend.(5) Pinus tabulaeformis grew normally, and average DBH, height, crown width and crown height gradually increased from north to south. There was significant difference among growth index in the 8 sites. The diameter and the height distribution of Pinus tabulaeformis artifical forest obey described normal distribution function in Huanglong and Yichuan. Latitude, annual precipitation and average temperature of January had the most influential effect on growth, while frostless period took the second place.(6) Based on fuzzy membership function synthetic evaluation model, the plantation community naturalized development was evaluated. The result show that Huanglong>Yichuan>Zhidan>Yanchang>Yanchuan>Suide>Shenmu>Wuqi.(7) Stem diameter, height, crown height and crown width in the shady slope were significantly greater than that in the sunny slope. The community species richness and diversity index were shady slope>sunny slope; evenness index was sunny slope>shady slope. Species richness, evenness index and diversity index of the herb layer were higher than that of the shrub layer in the shady slope. Shannon-wiener index and Pielou index(Jsw) were shrub layer>herb layer in the sunny slope.Because of individual competition, mortality increased and death age, stem diameter, height, crown height and crown width decreased with increasing of density. Species richness, evenness index and diversity index in the shrub layer were higher than that in the herb layer in the different density plots. The community species richness and diversity index were densityⅢ>densityⅡ>densityⅠ; evenness index (Jsw, Ea) was densityⅠ>densityⅢ>densityⅡ, but Jsi was densityⅢ>densityⅠ>densityⅡ.(8) Pinus tabulaeformis what grow in the shady slope and the region of annual precipitation more than 550 mm on the Loess Plateau in north Shaanxi preceded than in the other place. The optimum stand density of Pinus tabulaeformis is 2800-3000 stocks/ hm2.