| Acer mono is a rare broadleaf tree species with high landscape and economic value, and is also an important component of polar birch secondary forests. As a typical forest type in the mountainous areas of northern Hebei province, China, polar birch secondary forests is the primary timber forest in this area. However, these stands often exists such unhealthy characteristics as monotonous vertical structure and poor understory regeneration, etc. Acer mono has a great potential of regeneration. As a result of long growth cycle and slow cost-effective response, little attention was paid to the tending and management of polar birch secondary forest. Therefore, how to take advantage of Acer mono's regeneration potential to improve the poor understory regeneration condition of polar birch secondary forest, has been an important research aspect in this area. Based on the study of Acer mono regeneration characteristics, we furtherly analyzed its spatial distribution pattern and the spatial correlation association between Acer mono and other tree species at different altitude level, in order to provide references on the growing techniques of Acer mono. Meanwhile, after investigating and analyzing the damage situation and sprouting reaction of Acer mono undergone disturbance(intermediate cuttings), we summarized the rational and practical rejuvenating techniques for Acer mono seedlings, in order to lay the foundation of special tree species cultivation, enrich tree species composition and cultivate multiple layered forests.Acer mono under polar birch secondary forest was the research object of this paper. Firstly, two sample plots of 100m*100m were set at Taoshan forest farm, which is the subordinate body of Mulan paddock administration of state-owned forest farms in Hebei province. And then, on the basis of sample plot investigation, we calculated and analyzed the tree species composition of polar birch secondary forest and the regeneration characteristics of Acer mono. Lastly, we studied the spatial distribution pattern using point pattern methods. The main research results are as follows:1. The stand structure characteristics of polar birch secondary forestThe holistic tree diameter distribution of the stand appeared approximately reverse “J”type,with birch ranging from 4 to 34 cm, showing normal distribution, and polar ranging from 6 to 20 cm, without obvious distribution characteristics.The stand showed obvious and simple stratification. It could be divided into two layers based on tree height, the upper layer being 14 meters high and lower layer 4 meters. According to amount, the populations were classified into birch, polar, Acer mono and other species.Point pattern analysis showed that polar, birch and Acer mono exhibited aggregate distribution, while other tree species present aggregate distribution at small scale and stochastic distribution at large scale. The maximum aggregate intensity was that other tree species5.41> polar2.58> Acer mono 2.03>birch1. 39. The growth of birch, polar and other tree species had significant positive correlation with Acer mono. The maximum correlation intensity was that birch 2.41>polar 2.35>other tree species 0.7. In the sample plots, birch, polar, Acer mono and other tree species had formed stable composition and interspecific relationship.2. The spatial structure of Acer mono at different altitude levelAccording to tree height, Acer mono was classified into four levels:samplings, small trees, medium trees and big trees.In the researched spatial scale scope, samplings, small trees and medium trees showed aggregate distribution, while big trees present aggregate distribution at small scale and stochastic distribution at large scale.Samplings was positive correlated with small trees and big trees, and was not correlated with medium trees. Small trees showed significant correlation with medium and big trees separately. Medium trees and big trees was positive correlated mutually. The maximum aggregate intensify was small trees 5.71>big trees 3.76>medium trees 3.59>sampling 2.69.3. The spatial structure of different-level Acer mono and other tree speciesIn the researched spatial scale scope, birch had no correlation with samplings and medium trees, but has positive correlation with small trees and big trees. Polar had negative correlation with samplings at small scale and had no correlations at large scale; polar had negative correlation with small trees and had no correlations with medium trees; it also had positive correlation with big trees at small scale, but had no correlation at large scale. Other species had no correlation with samplings at small scale, while positive correlation at large scale; other species had negative correlation with small trees and medium trees, and had positive correlation with big trees at small scale, while had no correlation at large scale.4. The damage reaction of Acer mono after disturbanceIn the process of polar birch secondary forest management, adaptive tending and thinning methods were often used to facilitate its healthy and orderly growth.After tending and thinning, the damage ratio of Acer mono was 98.72%. The occurrence frequency of different damage types was that bending>spike top>bark torn>branches breaking=pest damage>no damage. Branches bending, spike top and bark were main damage types. The extent of damage was extremely severe.Meanwhile, at sample plot without thinning, the damage ratio of Acer mono was 70.25%. The occurrence frequency of different damage types was that no damage > bending >bark torn>spike top=pest damage >branches breaking. Samplings bending was main damage types. The extent of damage was slight.5. Rejuvenation techniques for samplings and small treesFor those Acer mono with bad growth condition(mostly samplings and small trees around big trees), trunk cutting is suggested, minimum reserving diameter being 2 cm.After trunk cutting, many seedlings would shoot out on the stump. In this situation, reserve one seedling that grows the best. The retention of seedling should execute in the early growth period. After that, more later-stage management methods such as weeding, bush cutting, stem cutting and planning hole extending would contribute a lot to the final rejuvenation effects. |
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