[Effect of thinning intensities on fruiting regularities of Quercus liaotungensis forests in Huang-long and Qiaoshan mountains.] / é—´ä¼å¼ºåº¦å¯¹é»„æ¡¥æž—åŒºè¾½ä¸œæ Žæž—ç»“å®žè§„å¾‹çš„å½±å“.

In order to clarify the impact of thinning intensities on fruiting regularity of Quercus liaotungensis forests, we took the Q. liaotungensis half-mature forests in Huanglong and Qiaoshan mountains on south of the Loess Plateau as the object of study, which were under close-to-natural management of different thinning intensities (CK, 10%, 20% and 30%). An analysis was made on stand density and percent of seed trees, seed number of sample tree and unit area, seed spatial distributions, seed characteristics of the Q. liaotungensis forests after 5 years of thinning. The results showed that, percent of seed trees, seed number per sample tree and percent of developed seeds of Q. liaotungensis forests increased with the increasing intensity, and showed a pattern of 30%>20%>10%>CK. Seed number per area reached the maximum number under 20% thinning, and showed a pattern of 20%>30%>CK>10%. From the seed spatial distribution in the canopy, the upper accounted for 73.6%, while the lower had 26.4%. The sunny side of canopy layer set relatively the most fruits of 65.8%, shady side only had 34.2%. Under thinning, further improving was geater under lower canopy than under upper canopy and so was on shady side than on sunny side. The seed long diameter, seed short diameter and 1000-seed mass of Q. liaotungensis forests increased with the increasing intensity, which reached the maximum under 30% thinning. 10% thinning did not significantly impact Q. liaotungensis fruiting, the thinning intensity of 20% was most conducive to the seed quantity and quality improvement of Q. liaotungensis, while the thinning intensity of 30% did not improve the fruiting, and lowered the total number of seeds. It was proposed that 20% thinning should be chosen (canopy density of 0.7) to effectively improve fruiting and quality of Q. liaotungensis.

[Evaluation of the tree form quality of middle-aged Pinus tabuliformis plantation under different canopy densities in Huanglong Mountains, Northwest China].

To clarify the effects of different canopy densities on tree form quality of Pinus tabuliformis, a hierarchical indicator system was structured, which brought about a set of grading criteria to evaluate tree form quality of the middle-aged P. tabuliformis plantation under four canopy densities in Huanglong Mountains by using the analytic hierarchy process (AHP). Plots were divided into four classes according to the stand canopy density (CD) : CD<0.65 (type 1), 0.65≤CD<0.75 (type 2), 0.75≤CD<0.85 (type 3) and CD≥0.85 (type 4). The results indicated that, by comprehensive analysis of ten related indicators, i.e., diameter at breast height (DBH), tree height, diameter height ratio, taperingness, stem straightness, forking ratio, height under living branch, number of branches, max-branch base diameter and average base diameter of branches, the tree form quality could be evaluated. Among these factors, stem straightness, forking ratio and DBH were the most important ones influencing the tree form quality with a total weight of 0.7382. So, these three indicators were the major determinants of tree form quality. The comprehensive scores of the tree form quality evaluations fluctuated as the canopy density decreased and topped at 90.28 when CD was valued at 0.75 (type 2). The indicators and evaluation system developed in this study were easy to operate, and quite fit for solving the quantity problem of the tree form quality evaluation. Our system would be capable for applications in evaluating the tree form quality of other tree species on the Loess Plateau.

[Effects of forest gap size on the architecture of Quercus variablis seedlings on the south slope of Qinling Mountains, west China].

Typical sampling method was conducted to survey the effects of forest gap size on branch architecture, leaf characteristics and their vertical distribution of Quercus variablis seedlings from different size gaps in natural secondary Q. variablis thinning forest, on the south slope of Qinling Mountains. The results showed that gap size significantly affected the diameter, crown area of Q. variablis seedlings. The gap size positively correlated with diameter and negatively correlated with crown area, while it had no significant impact on seedling height, crown length and crown rates. The overall bifurcation ratio, stepwise bifurcation ratio, and ratio of branch diameter followed as large gap > middle gap > small gap > understory. The vertical distribution of first-order branches under different size gaps mainly concentrated at the middle and upper part of trunk, larger diameter first-order branches were mainly distributed at the lower part of trunk, and the angle of first-order branch increased at first and then declined with the increasing seedling height. With the increasing forest gap size, the leaf length, leaf width and average leaf area of seedlings all gradually declined, while the average leaf number per plant and relative total leaf number increased, the leaf length-width ratio kept stable, the relative leaf number was mainly distributed at the middle and upper parts of trunk, the changes of leaf area index was consistent with the change of the relative total number of leaves. There was no significant difference between the diameters of middle gap and large gap seedlings, but the diameter of middle gap seedlings was higher than that of large gap, suggesting the middle gap would benefit the seedlings regeneration and high-quality timber cultivation. To promote the regeneration of Q. variabilis seedlings, and to cultivate high-quality timber, appropriate thinning should be taken to increase the number of middle gaps in the management of Q. variabilis forest.