Study Of The Natural Development And The Characteristics Of Artificial Pinus Tabuleaformis Forest In Ziwuling Region

The species diversity, Size-class structure, nutrient pool and organic carbon pool of the Pinus tabulaeformis were studied in the different site conditions in Ziwuling area on the Loess Plateau. The results are as followed:1. The results showed that the artificial Pinus tabulaeformis and natural Pinus tabulaeformis both had the quite rich species composition. This two forest types had similar trends of the community diversity as shrubs>herbs> trees. In order to measure the whole community diversity, the average of the relative thickness of the leaf layer and the relative coverage of each living from were used as weighting parameters. The results showed that the artificial Pinus tabulaeformis in shade slope had the highest community diversity. The result of similarity comparison indicated that there had the highest comparability indices of natural Pinus tabulaeformis forests in different slopes. Regardless of the species composition and the community spatial structure of the natural forest and the artificial forest, this two forest types had the high similarity. It was proved that the proper artificial measures can increase both the quantity and the coverage of the forestland and the development of the artificial forest.2. The results showed that in this region the average of C﹑N and P content of P. tabulaeformis needles were 499.5±63.75 mg/g, 8.53±0.50 mg/g and 0.94±0.64 mg/g, respectively. The C content of plant leaves was decreased in the order of natural forest on sunny slope> natural forest on shade slope> plantation on shade slope> plantation on sunny slopes. The N,P content of plantation leaves in sunny slopes was obviously higher than that of the natural forest in sunny slope. There were significant differences in the C/N,C/P,N,P,and N/P of leaves among four kinds of Pinus tabulaeformis which differed in site conditions. But there was no significant difference in the C content of leaves. The C of leaves had negative correlation with the N,P of leaves. And the N of leaves had observably positive correlation with the P of leaves. The result of N/P<14 in Pinus tabulaeformis leaves showed that Pinus tabulaeformis forest is easily influenced by the limit of N in the nature growth process. There was no significant difference in the C,N content in the 40～60 cm soil layer, but in the other soil layers, the C and N content of the plantation soil was significantly higher than that of the natural forest. The C and N content of plantation on sunny slope soil was significantly higher than that on shade slope soil. Soil C both in the 0～20 cm and 20～40 cm soil layer were positively correlated with soil N,the plant N and P. Not only leaves nutrients was the maximum in the plantation sunny slope, but also soil communities in this region was the greatest soil nutrient pools and carbon pools. The obvious correlation of soil C and N with the C,N and P in Pinus tabulaeformis leaves showed that interaction relations between Pinus tabulaeformis and soil.3. The analysis of the size structure of three populations of Pinus tabulaeformis showed that most individuals were concentrated in the 0～4㎝,12～16㎝,16～20㎝ and 20～24㎝ size classes. Younger and older individuals were dramatically few. Because of different environmental conditions, different populations developed their own characteristic size structure. Valley in the cloudy slop showed a stable development tendency. However, uphill position in sunny slope showed obvious declining tendencies. The result showed that the density decreased with the increasing of size-class structure. The analysis of life tables and survival curves showed that even under different environmental conditions, survival curves of Pinus tabulaeformis populations belonged to Deevey type III, and death peaks of different populations were the in period of I-II size classes and IV-VII size classes. Time sequence prediction models of different populations after 4, 8, 16, 24 years indicated that the numbers of old individuals would increase in the beginning and finally decrease, giving rise to difficulties for maintenance of these populations, most of the individual would be adult after 20 years. The investigations indicate that Pinus tabulaeformis population in Ziwuling area develops and renewals well. Pinus tabulaeformis population is able to maintain the stability through self-regulating without human interference. However, younger individuals of Pinus tabulaeformis population in uphill position in Sunny slope were dramatically few, if it would not be improved, the Pinus tabulaeformis population will lose its balance. Different counter-measures for fostering species should be made according to different site conditions, so as to create the environmental condition for development of young seedlings of T Pinus tabulaeformis .