林分直径结构的Weibull研究

摘要：日本落叶松直径服从Weibull分布,本研究编制了直径分布预估概率表;其形状参数C取不同的值时,其分布曲线形状类型即不同,当1.8＜C＜3.1时,分布图形为正偏,中小径阶的林分为多数。     

樟树苗期直径结构Weibull分布的研究

应用Weibull分布函数对樟树苗期直径分布进行了拟合，结果表明Weibull分布的拟合效果很好。探讨直径分布规律对于樟树的科学管理具有重要的意义。     

林分直径结构的Weibull研究——以日本落叶松为例

日本落叶松直径服从Weibull分布,本研究编制了直径分布预估概率表;其形状参数C取不同的值时,其分布曲线形状类型即不同,当1.8相似文献   

使用Weibull分布对人工油松林直径分布的研究

使用三参数维泊尔函数拟合人工油松林直径分布，根据χ^2－检验结果，三参数维泊尔分布与正态分布的拟合效果基本上一样。在本文中，改进了Issos求解维泊尔直径分布的方法，并取得了等效的结果。另外，利用20块标准地资料，采用Issos方法所求得的参数值与林分特征因子建立回归方程，并建立了维泊尔分布参数的予估方程，即根据林分平均直径，直径变动系数，平均高，年龄以及单位面积林木株数（0．1公顷）予估维泊尔直径分布，但其效果并不太好。对于拟合人工油松林分的直径分布，那个分布更适合，这个问题有待于进一步的研究。     

基于Weibull分布的林分结构可视化模拟技术研究

林分结构是林分生长和林分经营的理论基础,具有重要的生产实践和科研价值。以杉木人工林为研究对象,以30 m×30 m样地大小为例,以Weibull分布拟合林分直径结构,并进行x2检验。在已知林木算术平均胸径和林木株数的前提下,以C#语言为基础,结合Weibull分布模型、测树因子间关系模型、生物量估计模型、GDI+技术与MOGRE技术,实现了林分结构统计图表可视化模拟,并对林分进行了2维3维可视化模拟。结果表明:Weibull分布可有效拟合林分直径结构分布,可视化模拟技术使林分结构得到了更加直观高效的表达,为研究林分结构提供了新的技术手段,为提高森林经营管理水平提供了可视化决策平台。     

Logistic分布预测林分直径结构的研究

著名的Ｌｏｇｉｓｔｉｃ方程作为生物种群动态模型和生长曲线方程,在生态学和林学中得到了广泛应用;但它作为一种概率分布函数,却一直鲜为人知。林学上,对林分直径分布的研究,从６０年代以后,开始采用分布函数来描述林分的直径结构情况。如正态分布、对数正态分布、...     

Weibull分布的参数估计在蒙古栎天然林直径分布研究中的应用

林分内的树木并非杂乱无章地生长着，在未遭受人为破坏的情况下，林分内部始终都维持着一些比较稳定的结构规律，特别是直径的结构规律，它是林分结构的最基本内容，研究和探讨这些规律，对森林经营和森林调查有着重要的意义。该文通过Ｗｅｉｂｕｌｌ分布的参数估计，利用“查算法”比较容易地拟合了蒙古栎天然林的直径分布，获得了令人满意的效果。     

杜仲人工林林分直径分布研究

以偏度、峭度为指标杜仲林分直径分布特征，分别采用韦布尔函数和Ｌｏｇｉｓｔｉｃ函数模拟了杜促林分的直径分布，分析了分布参数估计了值与有关测检因子的相关性，建立了分布参数预测模型。精度检验和比较表明，本文提出的Ｌｏｇｉｓｔｉｃ回归预测模型模拟杜仲林分直径分布效果较好。     

Characterizing Diameter Distributions by the use of the Weibull Distribution

The well known Weibull distribution is fitted to sampled diameterdistributions from 120 Sitka spruce stands and 90 stands ofother conifer species, these being spread throughout Great Britainand having a wide range of ages. The parameters of the Weibulldistribution, estimated by the method of Maximum Likelihood,are then regressed, using weighted least squares, upon meandiameter at breast height, d say hence yielding a family ofWeibull distributions indexed by d. The effect of using minimumsampled dbh as an additional index is also examined. The resultsare compared with the Forestry Commission's Stand Tables andare found to be an improvement.     

Diameter distributions in Picea ables described by the Weibull model

The three‐parameter Weibull function met specified statistical standards for goodness of fit as a model for the diameter distribution of moderately thinned Norway spruce stands in Denmark. Weibull distributions estimated by percentile estimators fit the majority of 522 observed diameter distributions (material made available by the Danish Forest Experiment Station) at the 10% level of significance in the Chi‐square and Kolmogoroff‐Smirnow tests. The Weibull distribution was less suited to describe the diameter distribution in unthinned stands and heavily thinned stands. Weibull parameter predictions were developed and used in connection with a Danish yield table for Norway spruce on clay‐rich coastal soils. The use of the Weibull distribution to predict stem frequencies in different diameter classes before and after a specified thinning of stands is demonstrated.     

Fitting irregular diameter distributions of forest stands by Weibull, modified Weibull, and mixture Weibull models

Irregular diameter frequency distributions of forest stands include multimodal structure of mixed-species stands, highly skewed and highly irregular shapes of uneven-aged stands, and rotated sigmoid form of old-growth stands. In this study, a traditional two-parameter Weibull model, a modified two-parameter Weibull model, and a finite mixture of two-parameter Weibull models were used to fit four artificial example plots. The model fitting and comparison results indicate that the mixture Weibull model is more flexible to fit various irregular diameter distributions, while the traditional Weibull model fails in every case to adequately describe these frequency distributions. The modified Weibull model is a good choice for fitting the “rotated-sigmoid” diameter distribution of an uneven-aged old-growth stand. However, it may not be sufficient when a diameter frequency distribution is multimodal or highly irregular in shape.     

Modelling soil nitrogen levels under acacia/sorghum rotations

A mathematical model is formulated and implemented for the nitrogen (N) cycle, on a yearly time scale, in an arid-zone fallow system. The model is generally applicable to such systems; by combining data from a number of sources, its behaviour is investigated for a genericsorghum bicolor — Acacia senegal system. The model reproduces such observed effects as the initial fall in soil N early in theAcacia rotation, and provides support for the hypothesis that the N fixing potential ofAcacia roots is less important than their ability to take up otherwise inaccessible mineral N through deep roots.     

Intake and relative palatability indices of acacia species fed to sheep and goats

An experiment was conducted to determine preference intake and relative palatability indices of Acacia karroo, Acacia nilotica, Acacia tortilis, Acacia sieberiana and Acacia rhemniana in sheep and goats using a completely randomized design. The size of Experimental Farm from which the browses were harvested was 1842.75 ha. The leaf samples were randomly collected from various young trees. The samples were analysed for proximate composition, measured for intake and relative palatability indices of sheep and goats. Dry matter (DM) content ranged from 917.4 to 936.8 g/kg DM and organic matter from 822.9 to 892.2 g/kg DM. All acacia species contained crude protein content (CP) of more than 7–17% required for grazing animals. The content of neutral detergent fibre (ADF) and acid detergent fibre ranged from 372.8 to 658.1 and 150.0 to 464.6 g/kg DM, respectively and were significantly (P < 0.05) different among the species. All of the acacia species had low levels (0–5.57 g/kg DM) of condensed tannins. The intakes of all feeds except A. karroo and A. rhemniana were high in both sheep and goats. The leaves from A. sieberiana had the highest palatability indice (Pi) while those of A. rhemniana had the lowest Pi in both sheep and goats. It was concluded that there was an effect of acacia species on intake and relative palatability indices. Species A. sieberiana, A. nilotica and A. tortilis have potential as livestock fodder, based on moderate to high CP value, low ADF, low tannins, high intake and relative palatability indices.     

Relationship between salt tolerance and proline accumulation in Australian acacia species

 The effects of salinity on the seedlings of five acacia species, Acacia ampliceps, A. salicina, A. ligulata, A. holosericea, and A. mangium were studied with respect to mortality, growth, and proline accumulation. There was marked variation among the species in their response to salinity. A. ampliceps showed the highest level of salt tolerance among the five acacia species. In contrast, A. holosericea and A. mangium were classified as the least tolerant. The concentration which caused 100% mortality in 2-week-old seedlings during 1 week of treatment was 2.5% (w/v) and 1.5% NaCl for A. ampliceps and A. holosericea, respectively. The dry weights of whole plant of two acacia species decreased markedly under the above salt stress conditions. Proline accumulation was found in leaves and roots after NaCl treatment. The maximum level of proline accumulation in A. holosericea was about twice as great as that in A. ampliceps throughout the stress period. Thus, the level of proline accumulation was not related to the degree of salt tolerance in these acacia species, although a positive correlation between the extent of salt stress and the accumulation of proline was found. Received: July 18, 2002 / Accepted: October 10, 2002 Acknowledgments The author thanks Dr. Kiyoshi Tazaki for his technical advice on the quantitative analysis of proline and Toshiro Sumizono for use of the phytotron. He is also grateful to Dr. Kenji Shinohara for reviewing the language. This work was supported by a grant from the Science and Technology Agency of Japan to the Forestry and Forest Products Research Institute (Encouragement of Basic Biology).     

刺槐人工林林木地径与胸径关系的分析

通过对采伐后伐区刺槐人工林林木蓄积量的调查,建立了地径和胸径相关关系的数学模型,编制出了地径与胸径对应表。