| Pinus tabulaeformis is the main afforestation tree species in Shaanxi Loess Plateau.This research takes different development stages of P. tabulaeformis plantation inShaanxi Loess Plateau as the research object, through the typical sample plot surveymethod, diameter-class structures, height-class structures, seedlings regeneration, speciesdiversity, soil physical and chemical characteristics were analyzed; the ecological factors,the age structure, height, diameter, length of needles, dry biomass of roots, stems andneedles of one to ten year-old seedlings in different habitats were studied; path analysisand stepwise regressing analysis were conducted in the environmental factors influencedseedlings regeneration and growth. Different field seeding experiments and differentthickness litter and different concentration litter leach liquor of P. tabulaeformis seedgermination indoor control experiments, further discussed the influent factors of P.tabulaeformis seed germination, providing scientifical basis for P. tabulaeformisplantation sustainable management.The main results were as follows:1. In10-year-old P. tabulaeformis plantations the plantation structure, seedlingnatural regeneration and community characteristics had no significant difference. On theopposite, in30-year-old P. tabulaeformis plantations （thinned once） the growth situation,species diversity, the contents of available P, NH+4-N and NO-3-N had significantdifferences, meanwhile shady aspect was higher than sunny aspect. In the50-year-old P.tabulaeformis plantations （thinned twice） the trees diameter had no significant difference,while there were big-diameter individuals on the shady aspect. Average tree height,seedling natural regeneration, species diversity and soil chracteristics of50-year-old P.tabulaeformis plantations on the shady aspect were obvious better than on the sunnyaspect. P. tabulaeformis was suitable for planting both on the sunny and shady aspects in Huanglong forest region, but in the perspective of sustainable development, the shadyaspect had better site condition. Timely tending was a wonderful measurement that canpromote the sustainable development of P. tabulaeformis plantation.2. Lacking above three year-old seedlings in the understory, lacking above sevenyear-old seedlings in small gap, the number of five and six year-old seedlings were alsosmall in big gap. One to ten year-old seedlings could be divided into three periods, one tothree year-old, four to seven year-old, eight to ten year-old seedlings, among which one tothree year-old seedlings were critical for the establishment and growth of the population.The growth situation of seedlings in order of medium gap size>small gap size>understory, in medium gap size the shady aspect>sunny aspect,while in small gap sizeand understory the sunny aspect> shady aspect. In shady aspect, with the gap sizeincreasing, the root of seedlings growing better, and with the age of seedlings rising, thepromote effects became more significant; in sunny aspect, the root growth of seedlings insmall gap was better than in medium gap.3. The ecological factors and soil characteristics had significant difference indifferent gap size in shady aspect and sunny aspect. The light intensity and airtemperature in sunny aspect were higher than shady aspect, but air humidity was belowthan shady aspect. With the gap size increasing, the light intensity increased,while theair humidity decreased; there were no significant difference of air temprature in differentgap size. The dry quality of fall and humus in gaps were higher than in understory. Withgap size increasing, the coverage of shrub and herb increased, in the same gap size thecoverage of shrub and herb layer on sunny aspect was greater than on shady aspect.Forest gap enhanced the effectiveness of soil resource, the content of available P,NH+4-N and NO-3-N in the same soil layer was highest in small gap then medium gapthen understory both in shady and sunny aspect. Light intensity, shrub and herbcoverage, litter thickness were the main factors of influencing P. tabulaeformis seedgermination and seedling growth.4. P. tabulaeformis plantation litter significant influenced on seed germination andseedling survival of P. tabulaeformis. sowing patters had significant effects on the seedgermination and seedlings growth of P. tabulaeformis, the germination rate in order ofclear shrubs herbs and litters> clear herbs and litters> clear shrubs and litters> clear shrubs and herbs; the height, the bascal diameter,the root and stem biomass of seedlingswere highest when sowed after clearing shrubs herbs and litters and clearing shrubs andherbs.1cm and2cm thick litter had no significant influence on P. tabulaeformis seedgermination, but3cm thick litter and first layed litter than sowed significantly reducedthe germination ratio of P. tabulaeformis seed and the beginning time of germination.Different litter water extract liquor had no significant influence on P. tabulaeformis seedgermination. Those mean litter mainly through physical obstacles affected the P.tabulaeformis seed germination.5. Timely tending and thinning were wonderful measurments that can promoteindividuals growth and the sustaninable development of P. tabulaeformis plantation. The10year-old and30year-old P.tabulaeformis plantations in HuangLongShan shouldtending and thinning respectively. At the same time pay attention to the protection of thespecies diversity, perfect the stratified structure, improve the ecological benefit andcommunity of sustainable development ability. Reasonable thinning strength combinedwith clearing forests shrub and herb can provide suitable conditions for seedling naturalregeneration and growth, promote P. tabulaeformis seed germination, guarantee seedlingsurvival and growth. |
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