【作者】 郑丽凤；

【导师】 周新年；

【作者基本信息】 福建农林大学 ， 森林经理学， 2008， 博士

【摘要】 常绿阔叶林是闽北的地带性植被,其植物区系组成十分丰富,蕴藏着极其丰富的生物基因,生态功能显著,但由于不适当的人为干扰,现除了几个自然保护区外,严格意义上的常绿阔叶林不多了,基本沦为天然次生林,在景观和林分水平上均表现出不可持续性,急需采取科学合理的经营策略。择伐能充分发挥每棵树木生长潜力,最大限度利用林地生产力,增加林分组成以及结构上的多样性,提高抗病能力,保持生态系统稳定性。因此从生态采运角度出发,按可持续经营原则,对现有闽北天然次生林因地因林实行择伐是其最合理的经营方式。天然次生林择伐与更新定位研究基地位于福建省建瓯市大源林业采育场,试验林分于1996年11月进行不同强度(弱度13.0%、中度29.1%、强度45.8%、极强度67.1%)择伐作业试验(伐后天然更新),并设未采伐和皆伐作业进行对照,于2006年7月再次进行伐后跟踪调查。以群落学方法调查林地植被,收集林地凋落物和取土壤剖面并以常规方法进行植被、凋落物养分含量和土壤理化性质分析,比较不同的择伐强度对林地生态因子的影响,探讨闽北天然次生林择伐强度的阈值,并对采伐作业的环境成本定量化评价。在此基础上,通过闽北森林资源清查固定样地资料,分析现实天然次生林林分结构特征,探讨择伐的各个技术要素的选择与确定,旨在探索适合闽北天然次生林可持续经营的理论与技术。主要研究结果如下:(1)择伐作业基本上能保持原有的林分结构和种的数量,随着择伐强度的增大,各树种重要值的改变也随着增大,弱度、中度和强度择伐对优势种的影响不大,极强度择伐后,各树种地位有了一定程度的变化,而皆伐引起树种地位的变化最大。(2)伐后10 a弱度择伐乔木层物种丰富度最大,随择伐强度增大,物种丰富度度减少:各择伐样地在10 a后物种多样性指数均超过伐前,而皆伐样地物种多样性比伐前下降。(3)伐后10 a各择伐样地直径分布均为左偏,中小径阶林木居多,中度和强度择伐样地林分直径分布符合负指数分布,而Weibull分布具有较强的灵活性和适应性,基本可以用来拟合不同择伐强度作业后的林分直径分布。(4)各样地大中小径级结构和蓄积结构距离理想林分均有一定差距,尤其是极强度择伐,形成了过伐的残次林。未采伐样地q值为1.404,除极强度择伐外,其余各择伐样地q值在1.2～1.4之间,说明只要择伐强度不超过强度择伐,林分的q值还是合理的。(5)随择伐强度的增大,蓄积量生长率呈增大趋势,平均年生长量和总收获量则呈凸形抛物线变化,平均年生长量在强度择伐最大,达到6.08m~3/(hm~2·a)。(6)从伐后10 a林分空间结构分析,弱度和中度择伐有利于林分空间结构的优化。弱度择伐后林木的平均混交度最大,中度择伐次之;不同择伐强度对林木的大小分化程度影响不大,但各主要树种的地位都有一定程度变化;采伐并未改变林木的空间分布格局,各样地林分整体和主要树种均为聚集分布。(7)在择伐经营的前提下,天然更新良好,且随着择伐强度的增大,林分更新密度增大;不同择伐强度对伐后10 a主要种群更新格局的类型没有影响,主要种群更新格局均为聚集分布,但择伐强度不同,各种群集聚程度和平均拥挤度都呈不同的变化趋势。(8)不同强度择伐作业10 a后林地凋落物现存量和养分总量均下降,且下降幅度随采伐强度的增大而加大。强度择伐和极强度择伐10 a后林地凋落物及其养分含量仍未恢复,弱度择伐和中度择伐则与未采伐林地比较接近。(9)弱度和中度择伐林地经过10 a的恢复,土壤结构稳定性、水分、孔隙状况和养分含量得到恢复,并有所改善,而强度择伐、极强度择伐和皆伐后迹地土壤各项指标仍未恢复,其破坏程度均随采伐强度的增大而加剧。经主成分分析得出全K、速效K、速效P、有机质、全N、非毛管孔隙度、土壤密度、最小持水量、最大持水量、总孔隙度10项指标变化率,能较好地反映林地土壤理化性质的变化状况,不同强度采伐作业对林地土壤理化性质的干扰程度依次为:皆伐作业＞极强度择伐＞强度择伐＞中度择伐＞弱度择伐。(10)综合择伐强度对林地生态因子的影响结果,闽北天然次生林宜采取弱度和中度择伐,择伐强度的阈值不宜超过40%。(11)从涵养水源价值、保持水土价值、固碳释氧价值3方面对伐后10 a采伐经营的环境成本进行了研究。结果表明,弱度择伐环境成本较小,仅1.7元/m~3,中度、强度择伐环境成本分别为弱度的5.1、12.2倍,极强度择伐的环境成本最大,达到25.3元/m~3,是弱度择伐的16.2倍;皆伐由于收获量大,其单位采伐量环境成本为弱度择伐的14.9倍,低于极强度采伐。(12)根据闽北地区天然次生林2次森林清查固定样地资料,分析现实天然次生林林分结构特征,将样地划分为4个不同的蓄积水平,分析各水平的直径结构,蓄积结构,以期为择伐策略的选择提供基础。(13)在综合各种研究成果的基础上,提出适合闽北天然次生林的择伐技术模式。模式包括培养目标、择伐方式、择伐强度、择伐周期、集材方式、清林方式等技术指标与要求,为闽北天然次生林的可持续经营提供参考。更多还原

【Abstract】 As the climax forest ecosystem in northern Fujian Province, evergreen broad-leaved forests, which have rich flora composition and biological gene, play an important role in ecological function, and are of great benefit to local economy and society. However, under the unsuitable human intervention, most natural forests in Fujian Province tend to be degraded, and the situation is getting severer. Presently, except several nature conservations established by government, most evergreen broad-leaved forests have been degraded to natural secondary forests. In the levels of landscape and the specific stands, the traditional management has been proved to be unsustainable for these forests. To meet the need of practical management, it is necessary to do more research on management tactics for these natural secondary forests. As a major harvesting method, some previous researches showed that selective cutting following natural regenerating may be sound compared with clear cutting and shelterwood cutting, because it may make every tree in the stand necessary space to grow potentially, and increase species diversity and ability of resistance against diseases, and make the ecosystems more stable. Therefore, from the point of harvesting and regeneration, selective cutting may be a good selection for harvesting method of natural secondary forests.The sample plots for this study on selective cutting were set up in Dayuan Forest Logging and Regeneration Station located in Jian’ou County, Fujian Province. The experimental stands were harvested by selective cutting of different intensities (low intensity of 13.0% in volume, medium intensity of 29.1%, high intensity of 45.8%, over-high intensity of 67.1%) in November, 1996. The un-cutting and clear cutting plots were set as controls. All the cutting areas were recovered by means of natural regeneration following cutting operation. The regeneration investigation was conducted again in July, 2006. Vegetations in these plots were investigated adopting the regular methods of community ecology. Forest litters within plots were collected for further analysis, and soil sections were examined in every plot as well. The effects of different intensity selective cutting on the forest ecological factors, including stand structure, species diversity, regeneration, litter nutrient content, physical and chemical properties of soil, were investigated to determine the sound threshold of selective cutting intensity of these natural secondary forests. Environmental costs of logging operations were evaluated quantitatively also. Based on the results of investigation of these fixed plots, as well as the realistic structural characteristics of other natural secondary forests as comparison, the strategies of selective cutting operation for natural secondary forests were put forward to provide guidance for the management of natural secondary forests in northern Fujian. The main conclusions of this study are as follows:1) Selective cutting may preserve original stand structure basically, while the clear cutting results in great destruction in it. The more intensive of cutting, the more changes of tree species diversity and importance value of species in stands. Low, medium and high intensity selective cuttings caused a light variation to the tree layer flora, while the over-high intensity selective cutting changed it greatly.2) Species richness of tree layer peaked after 10 years of low intensity selective cutting, and the higher intensity of selective cutting, the less species richness. Diversity indexes of all the selective cutting plots after 10 years of cutting are more than the original ones. Selective cutting operation is beneficial to the development of tree layer species diversity, but the clear cutting results in the greatest decline of species diversity.3) All the skewnesses of diameters distribution of selective cutting plots after 10 years are negative, which suggests that the small-size trees dominate in the stands. The diameters of medium and high intensities cutting stands are distributed in negative exponential distribution. And Weibull distribution models are suitable for all the diameter distributions in the experimental natural forests after selective cutting.4) Diameter-class and stock structure of all plots are away from the ideal stand structure, particularly the over-high intensities selective cutting which led to a defective forest. The value of q on non-cutting plots is 1.404, while in other selective plots it is between 1.2 and 1.4. This suggests that if the selective cutting intensity is no more than that of high intensity cutting, i.e., 45.8%, the q value will still be reasonable.5) With selective cutting intensity increases, the volume growth rate is increasing, and the average annual growth and the total harvest volume inclines to change as a convex parabolic trend. For the high intensity selective cutting plots the average annual growth is the highest, i.e., 6.08m~3/(hm~2·a).6) The low and medium intensity selective cuttings may enhance the stability of forest community spatial structure effectively. The forest mingling intensity is the biggest in low selective cutting plots, that of medium intensity cutting ranks the secondary. Selective cutting intensity exerted little influence on diameter differentiation, but the positions of dominant species changed with different extents. Selective cutting did not change the spatial distribution of species. Aggregation distribution was the spatial pattern of either the forest as a whole or the dominant species, regardless of what selective cutting intensity is.7) The natural regeneration has been well on the way after selective cutting operation. The regeneration density goes up with the increasing intensity of selective cutting. All the distribution patterns in the five dominant populations follow the clumped pattern regardless of selective intensity, but the assemble intensity and mean crowding index varied with different trends.8) Biomass of forest litter and total nutrient contents were generally reduced with the cutting intensity increasing. Biomass of forest litter and total nutrient contents in high and over-high intensity selective cutting sites have not been recovered after 10 years, while that in low and medium intensity selective cutting sites were close to that of uncutting areas. It showed that vegetation in the low and medium intensity selective cutting plots have been recovered after 10 years.9) The soil aggregate stability, moisture content, porosity and nutrient of low and medium selective cutting plots have been recovered basically; furthermore some indexes have been partly improved after 10 years of cutting. But those in high intensity, over-high intensity and clear cutting plots, the physic-chemical properties of soil haven’t recovered yet. And with the felling intensity increasing, the properties of soil deteriorated much more. By means of principle component analysis (PCA), the main indexes including variations of total K, available K, available P, organic matter, total N, non-capillary porosity, bulk density, maximum moisture capacity, minimum moisture capacity, total porosity, which responds most of the impacts of soil by cutting, were analyzed quantitatively. The orders of the disturbance degree are as followings: clear cutting>over-high intensity selective cutting>high intensity selective cutting>medium intensity selective cutting>low intensity selective cutting.10) Comprehending the research results, we concluded that for harvesting and management, the natural secondary forests in northern Fujian could be taken the selective cutting with low or medium intensities, and the intensity threshold should be no more than 40%.11) From the conversed values of water and soil conservation, carbon sequestration and oxygen releasing, the environment cost of selective cutting operating were evaluated as well. The results show that environmental cost of low intensity selective cutting is the least, only 1.7 Yuan/m~3, while that of medium and high intensity cutting were 5.1 Yuan/ m~3, 12.2 times of that of low intensity. Over-high intensity selective ranks the highest, which is 27.6 Yuan/m~3, and is 16.2 times of that of low intensity selective cutting. Due to its more timber volume harvesting, the cost of clear-cutting is lower than that of over-high selective which is 14.9 times of that of low intensity.12) According to fixed-plots survey data of natural secondary forests in northern Fujian, the realistic structural characteristics were analyzed, which can be divided into 4 different levels. The diameter and stock structure of each level were studied also.13) Based on the integration of research results, techniques model of selective cutting for natural secondary forests in northern Fujian is put forward, which contains the management objectives, determination of selective cutting methods, selective cutting intensity, selective cutting cycles, sound skidding methods and clean-up techniques for harvesting operations.更多还原