| Starting with the geographic distribution, basic biological characteristics and the species composition, stand structure, interspecies relationship, population structure, spatial pattern, fecundity and population regeneration in different habitat, the community feature, population dynamics and reproduction characteristics of Pinus tabulaeformis f. Shekannesis were studied systematically based on the detailed plot investigation, which provided the basis of making reasonable conservation and management measures for protecting the present P. tabulae-formis f. Shekannesis natural forest effectively and expending its distribution scope. The main conclusions were as follows:1. P. tabulaeformis f. Shekannesis was an ecological forma group of P. tabulaeformis in the Loess Plateau. The concentrated distribution area of it, which belonged to Heshangyuan forest farm located in the north of Ziwuling, was narrowness. This area was located in the northwest of P. tabulaeformis distribution area. The seedling of P. tabulaeformis f. Shekan-nesis relatively grew rapid, the DBH of it grew fast in 6～22 a, height growth increased in 6～18 a, volume grew rapid in 18～40 a, and the age of volume maturation>46 a.2. There were 162 species of seed plants in P. tabulaeformis f. Shekannesis community, belonging to 120 genera, 52 families. The florae of seed plants presented a diversified and complicated composition, including 12 types and 9 variants, among which the north temper-ate distribution compositions made significant dominant and it accounted for 49.51% in total genera, and the tropic elements took some percentage. Based on the species important value, the P.tabulaeformis f. Shekannesis community in Qiaobei forest area could be divided into 5 community types: P.tabulaeformis f. Shekannesis+Quercus wutaishannica-Cotoneaster mul-tiflorus-Carex sp. Community, P.tabulaeformis f. Shekannesis-Ostryopsis davidiana-Carex sp. Community, P.tabulaeformis f. Shekannesis-Cotoneaster multiflorus-Carex sp. Commu-nity, P.tabulaeformis f. Shekannesis-Rosa hugonis - Carex sp. Community, and P.tabulaeformis f. Shekannesis- Spiraea salicifolia - Carex sp.+Anemone upehensis Commu-nity. The species composition and stand structure of different community types showed dif-ference. And the community environment, in which P.tabulaeformis f. Shekannesis was dominant species, had some similarity. The overall association among 20 main species in the community was not significant, 82.4% species-pairs showed insignificant association and low interspecific association index, which mainly indicated the species composition and commu-nity structure tended to be stable. In different community types, the numbers of species un-correlated with P.tabulaeformis f. Shekannesis increased along with the enhancement of light conditions in community, meanwhile, the numbers of in positive association with P.tabulaeformis f. Shekannesis gradually decreased.3. Seedlings of 5 P.tabulaeformis f. Shekannesis populations all showed aggregated dis-tribution pattern, the saplings and large tree in different population fitted into aggregated dis-tribution or random distribution, in addition, the aggregated intensity of these two develop-ment stage was lower than that of seedlings. The area with the highest aggregated intensity was 25 m2 in seedling and sapling, and 100 m2 in large tree. Except population A, the age structure of other populations belonged to progressive type, and the survival curve of them belonged to Deevey III, all these indicated that most population could keep stable state, and further develop without artificial destruction. The analysis of PCA showed that the main fac-tors that affecting the population structure were slope site, altitude, slope face, water content and the pH value of soil.4. The quantity of cones and seeds per individual of different population had no signifi-cant difference. The natural germination rate of P.tabulaeformis f. Shekannesis was very low, and the highest one among 5 populations was only 1.203‰(population C). Generally benefi-cial conditions for germination were higher pH soils with lower coverage of shrub and herb plants. The numbers of 1-year-old seedlings in population showed the status of population D (5.00 Ind./100 m2)> population C (2.00 Ind./100 m2) >population B (0.75 Ind./100 m2). There was no 1-year-old seedling in population A and E. The growth of basal diameter and height of aerial stem of 1～10 year old individuals in population C and D was higher than that in other population, this indicated that young individuals grew well under the habitat with mod-erate light condition, however, south slope with strong light condition was not the suitable environment for natural generation.
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