Effects Of Gap On The Regeneration Of Quercus Liaotungensis Koidz In The Ziwuling Mountains

The forests in the Ziwuling Mountains were the most complete natural secondary forest and water conservation forest and ecological forest in the loess platau region in northwest China. The forest of Quercus liaotungensis Koidz was a main forest formation in Ziwuling Mountains. According to field investigation, we found that Q. liaotungensis population's natural regeneration was mainly depended on mother tress'sprouts. There were few seedlings in forest of Q. liaotungensis. That might lead to the population recession.54 different gaps were investigated in Q. liaotungensis population in the Ziwuling Mountains. The results were as follows:1. The important values of main tresses were used to compare the difference in composition of main tresses in shrubs between gaps and control stands. There were total 62 species in the shrubs of gaps and control stands, common species 21, which had a significant change in the important value of the order in the different habitats. Except Q. liaotungensis' order being ranked number two, while the remaining 40 species were all changed. And the important value of tress were calculated and sorted in different size gaps. The results showed that the same tree species had different dominance in the same size gaps. And the same tree species also had different dominance in different size gaps. With the size of gaps increasing, some trees' dominance increased, however some declined.2. Q. liaotungensis' number of seedlings and saplings and older saplings declined with the height of tress increasing in the gaps and control stands. However there were a lot of seedlings, but also many saplings and older saplings were survived in the gaps. That was good to maintain stability of community and to achieve natural regeneration in the forest of Q. liaotungensis. And the gap sizes had an effect on the growth status and original method of Q. liaotungensis. The results showed that the density of all seedlings and saplings and older saplings were higher in the medial gaps than them in the small gaps and in the large gaps. The community of Q. liaotungensis only had a better stable population structure in medial gaps than in small gaps and in the large gaps.3. The density and growth status of seedlings and saplings and older saplings between gaps and control stands were compared and analyzed. ANOVA showed:â‘ The density of seedlings had no significant difference ( F = 1.186,P > 0.05). And there were obvious difference in the density and the height and the basal diameter of seedlings and saplings ( P < 0.05 ). In the gaps the growth status of seedlings and saplings were better than in the control stands. Moreover the density of seedlings and saplings were almost a time than in the control stands.â‘¡There were a significant difference in the height and the basal diameter of Q. liaotungensis and in the height of sprouts ( P < 0.05 ). But there were no obvious difference in both the height and the basal diameter of saplings and older saplings ( P > 0.05 ). The seedlings, the saplings and the older saplings grew better in the medial gaps than them in the small gaps and in the large gaps.4. The growth status and the density of Q. liaotungensis and the environmental factors were correlatively analyzed. The results showed that the altitude and the thickness of litter and the slope had little effect on the height and the basal diameter and the number of Q. liaotungensis ( r < 0.1 ). There was a positive correation between the height and the basal diameter of Q. liaotungensis and the temperature and ground temperature. But there was a negative correlation on the density. The number and the height and the basal diameter were a significant positive correlation with light intensity and soil moisture ( r > 0.4,P < 0.05 ).5. According to values of niche breadth based on gap sizes, the species were classified into 4 types, i, e, species of the narrow amplitude of niche having 26 kinds, species of the wide niche having 7 kinds, species of the middle niche species having 6 kinds, few of the comparatively narrow niche species.6. The main tresses' niche overlap values were analyzed in the different size gaps. The results showed that the niche overlap values of main tree species were low in different gaps, even the highest values were no more than 0.1. The similarity degrees of all tress utilizing resources were lower in the 100-200 m2 gaps than that in the other size gaps. The niche overlap values of trees in the 0-100 m2 were similar to that in the 200-300 m2 gaps.7. The aggregation indexes of Q. liaotungensis were calculated in different size gaps. The results showed that the seedlings and the saplings were aggregation distribution in different size gaps. And the aggregation indexes in the medial gaps were lower than them in the small gaps and in the large gaps. But the trend of the aggregation indexes of the saplings was complex and not consistence.