Individual-based simulation of the diffusion process of Eupatorium adenophorum

In order to investigate the diffusion patterns of Eupatorium adenophorum, this study uses a computer to simulate various plant diffusion processes under different environments. The study develops binary cellular automata as a framework reflecting the growth and semination of plants by the change of cellular state and transition function. This model allocates 16 integers, namely 1 to 16, to indicate a life history of plant starting from seed. In each iteration (a year), Monte-Carlo simulation is applied to decide whether an individual survives into the next year, the probability of which is estimated from previous literature. If a plant survives youth, mature or senile period, its propagation will also be considered and short-tailed dispersal kernel was employed. Applying this basic model, this study also simulates the diffusion process of E. adenophorum under four typical ecological environments. Examining the age structure of the four populations, we found that, although with significantly different numbers of plants left, most individuals were in the infancy period. Besides, their dispersal velocity showed different periodic law. These observations provided reasonable suggestions on what control strategies to be taken respectively.     

森林采运作业的计算机模拟

从机械模拟、集运材作业、森林作业规划设计的开发和应用等方面阐述了计算机模拟技术在森林采运作业领域应用的基本原理和思路。     

Delphi在排队论仿真中的应用

在服务行业中由于顾客到达和服务时间的随机性，排队现象几乎是不可避免的，作为服务行业的物流企业也面临相应的问题。为了解决物流企业在提供服务时的排队现象，进行物流系统规划时可以用仿真语言或者商用的仿真软件进行仿真分析，也可以将数学模型转化成计算机仿真语言，用Delphi语言实现其仿真模拟，为决策提供相应的依据。     

Application of the SB distribution to the simulation of correlated lumber properties data

Summary With the emergence of probabilistic design procedures, the need for precise knowledge of the entire probability distributions of load effects and material resistance has never been greater. In order to evaluate these distributions, simulation techniques have provided a reliable and cost and time effective alternative to large scale destructive testing. With the use of the Johnson's S_B probability distribution, a closed-form, analytic procedure has been developed to model the inherent variability in strength, given some nondestructively evaluated parameter. This modeling procedure serves as the basis of a verified simulation process to predict a strength distribution, given a probability distribution of the NDE parameter. The approach presented here, represents a closed-form, analytic solution to a problem which has heretofore been treated in a more subjective fashion. This simulation procedure is complemented by a stratified sampling scheme.The author wishes to recognize Engineering Data Management, Inc. for the use of their computer software, STADMAN, and the Mc Intire-Stennis Research Program for the financial support of this study     

Improving the simulation of stand structure in a forest gap model

There is currently great interest in improving the applicability of forest gap models to changing environmental conditions, in order to facilitate the assessment of possible impacts of climatic change on forest ecosystems. Moreover, for the development of mitigation strategies, it is necessary to include forest management options in the models. Both the simulation of transient effects of climatic change and of forest management regimens require a realistic representation of stand structure in gap models, since tree species respond to variations in stand density in characteristic ways, depending on their ecological strategies.In this study, we compared the effect of five different height growth functions that are sensitive to stand density on simulated stand structure of the FORSKA forest gap model. We used long term observation data from a beech thinning trial at Fabrikschleichach, Bavaria, to test the alternative functions. First, we compared simulation results of the original FORSKA model with measured stand development from 1870 to 1990. Whereas simulated stand level variables (e.g. biomass, mean diameter and height) showed good correspondence with observations, individual tree dimensions and simulated stand structure were quite unrealistic. After calibrating parameters of the height growth functions with data from a lightly thinned plot at Fabrikschleichach, we ran the model with data from a heavily thinned plot for validation. All five functions considerably improved the simulation of height/diameter relationships and stand structure. However, there were distinct differences between functions. The best correspondence with measurements was shown by a function which uses the relative radiation intensity in the centre of a tree crown as an indicator of the competition status of the tree. This function is rather simple and needs only two growth parameters, which can be derived for different functional types of species, according to their shade tolerance.With the new, flexible height growth function it should be possible to extend the applicability of gap models to more realistic simulation experiments including forest management and natural disturbance. To our knowledge, this was the first attempt to employ long term forest observation data for the calibration and validation of a forest gap model. The results suggest that such data could be very useful in model testing and improvement.     

基于整体化理论的林木、林分生长模型模拟系统开发

以森林模型整体化理论思路为基础,利用vb6.0编程软件开发出独立的林木林分生长和收获模型模拟系统,在解决不同水平模型之间相容性、一致性及内部结构的问题,在生态模拟中有一定的应用价值。     

森林生态系统生物量的模拟

森林生态系统定位研究的成果,将会为森林经营管理者提供决策的理论基础和最佳的实施方案.如若对系统中各成分和功能过程全面了解,通过系统的计算机模拟,可以表示出系统内各成分相互作用以及整个系统对不同干扰、环境污染和经营管理措施的反应,将对实现林业向生态化转变,为森林多效性的稳定和永久利用发挥作用.     

FDS火灾模拟与应用

利用FDS(Fire Dynamics Simulator)对火灾模型的设置进行了探讨和分析。结合作者多年应用FDS的实践经验,给出了FDS在室外燃烧实验方面的一些使用方法,并指出了FDS的应用限制。     

森林火灾的计算机仿真研究

建立森林防火仿真系统，通过给出建立仿真系统的一般步骤，结合林火行为、气象条件和可燃物条件等建立森林防火的防真系统。通过仿真，可以直观地掌握林火的发生，发展和蔓延的过程，以及林火蔓延的方向等，为森林防火部门的火灾预测、指挥扑救提供很好的支持。     

中国南部区域地表变化对气候的反馈模拟

将1990年和2000年2期遥感图像按照BATS类别分类作为RegCM3区域气候模式耦合的陆面过程类型,模拟研究了中国南部区域2种实际地表对2000年气候的反馈。模拟结果表明,地表状况分类与模拟气候数据在时间上的一致能够提高气候模拟的准确性;实际地表的变化对区域温度、径流和蒸发都造成了显著影响,2000年地表模拟结果与1990年地表模拟结果相比,区域温度降低0.314℃,表面径流减小0.4 mm.d-1,蒸发增加了0.315 mm.d-1,地表植被的恢复在一定程度上有益于减小全球变暖的负面影响。     

A simulation of the development and restoration of old-growth structural features in northern hardwoods

Thinning treatments in second-growth forest may be a practical means of accelerating the development of certain old-growth structural features in regions where old stands are presently uncommon. We used CANOPY, an individual-tree model calibrated with data from thinned and unthinned stands, to simulate effects of thinning on growth rates and development of old-growth structural features in second-growth northern hardwoods. Three simulated, moderately heavy thinnings over a period of 45 years nearly doubled the predicted mean radial increment of canopy trees, percent of stand basal area in large trees, and area of canopy gaps. Compared to untreated stands, thinned stands had fewer dead trees per ha, but the dead trees were larger in size and the overall volume of snags and logs was little affected. In a 77-year old even-aged stand, moderately heavy thinning was predicted to reduce the time needed to attain the minimum structural features of an old-growth forest from 79 to 36 years. Simulated treatments in an older, uneven-aged stand gave mixed results; the moderately heavy treatment stimulated individual tree growth, but the removal of some medium-sized canopy trees in conjunction with natural mortality delayed the development of old-growth structure. Total volume of dead wood may still be deficient under the thinning regimes investigated in this study, but predicted live-tree structure 45 years after moderately heavy thinning was typical of stands in the advanced transition and steady-state stages of old-growth development. Results suggest that thinning can substantially accelerate the development of old-growth structure in pole and mature northern hardwoods, but response in older, uneven-aged stands is more modest, and treatments in these stands may need to be more conservative to achieve restoration goals.     

Improved simulation of poorly drained forests using Biome-BGC

Forested wetlands and peatlands are important in boreal and terrestrial biogeochemical cycling, but most general-purpose forest process models are designed and parameterized for upland systems. We describe changes made to Biome-BGC, an ecophysiological process model, that improve its ability to simulate poorly drained forests. Model changes allowed for: (1) lateral water inflow from a surrounding watershed, and variable surface and subsurface drainage; (2) adverse effects of anoxic soil on decomposition and nutrient mineralization; (3) closure of leaf stomata in flooded soils; and (4) growth of nonvascular plants (i.e., bryophytes). Bryophytes were treated as ectohydric broadleaf evergreen plants with zero stomatal conductance, whose cuticular conductance to CO(2) was dependent on plant water content. Individual model changes were parameterized with published data, and ecosystem-level model performance was assessed by comparing simulated output to field data from the northern BOREAS site in Manitoba, Canada. The simulation of the poorly drained forest model exhibited reduced decomposition and vascular plant growth (-90%) compared with that of the well-drained forest model; the integrated bryophyte photosynthetic response accorded well with published data. Simulated net primary production, biomass and soil carbon accumulation broadly agreed with field measurements, although simulated net primary production was higher than observed data in well-drained stands. Simulated net primary production in the poorly drained forest was most sensitive to oxygen restriction on soil processes, and secondarily to stomatal closure in flooded conditions. The modified Biome-BGC remains unable to simulate true wetlands that are subject to prolonged flooding, because it does not track organic soil formation, water table changes, soil redox potential or anaerobic processes.     

Multi-agent simulation of alternative scenarios of collaborative forest management

International calls for sustainable development advocate that forest management should be carried out in a multi-stakeholder environment. The importance of community participation is acknowledged in theIndonesian Act No. 41 on Forestry (1999). However, it is not clear how to achieve this in areas already allocated to a concession holder. Current regulations offer little flexibility for concessionaires to develop site-specific management, or to involve local communities in forest management. The research reported here examines the application of simulation techniques to explore scenarios of sustainable forest management addressing those limitations. Several scenarios have been developed using multi-agent simulation to examine social and biophysical issues. Of the four scenarios examined in this study, collaborative forest management involving both the concessionaire and the local community appears to offer the most promising pathway toward sustainability. The authors wish to acknowledge that this paper has been produced with financial support from Department for International Development of the UK, and the Asian Development Bank under RETA Grant 5812 and CIFOR. The views expressed here are those of the authors and can in no way be taken to reflect the official opinion of the donors or of CIFOR. The authors also thank Bruce Campbell for his inputs to the paper.     

Forest modelling: the gamma shape mixture model and simulation of tree diameter distributions

? Key message

New types of distribution functions are needed to model the dynamics of stands where important age classes are represented by few trees. In this study the gamma shape mixture model and two simulation methods were used for generating tree diameter data.

? Context

To analyse forest dynamics, it is necessary to know distribution of the characteristics (mainly tree diameters) of trees forming particular developmental phases. In many forest inventories, the measurement of large diameter at breast height (DBH) samples is practically impossible. In this case, DBH distributions can be generated using theoretical models.

? Aims

The aim of this study was to assess the precision of the approximation of empirical DBH data using the gamma shape mixture (GSM) model and kernel density estimation. The strengths and weaknesses of the two simulation methods were presented and discussed.

? Methods

The GSM model was adopted to approximate empirical DBH data collected in 20 near-natural stands. Two simulation methods were used: (a) the procedure based on a multimodal distribution and gamma random numbers (MDGR procedure) and (b) MCMC techniques with Metropolis–Hastings sampling (MH method).

? Results

The GSM model precisely fitted the investigated DBH distributions. The MDGR procedure was slightly more precise than the MH method, especially in the case of the samples of 250 DBHs. The level of homogeneity within the drawn DBH sets was similar for all samples.

? Conclusion

The GSM model is very flexible. The DBH random variates, generated with the use of analysed procedures, represented all tree generations being significant from a biological point of view.

     

竹材宏观微观力学性能试验与数值模拟

竹材是一种力学性能优异、可再生和环保的结构性材料,具有广阔的工程应用前景.准确掌握竹材各组分的力学性能参数对于竹材的工程应用具有重要意义.结合细观力学和材料力学方法得到了一种确定竹材纤维和基体材料力学性能参数的计算方法:首先通过竹材试件的准静态压缩、拉伸和弯曲试验,获得了竹材在不同加载条件下的宏观力学性能;然后结合细观...     

THE DYNAMIC SIMULATION MODEL OF MANAGEMENT FOREST RESOURCES SYSTEM

INTRODUCTIONThemanagementofforestresourceisalargescalesystemwiththecharactCristicsofdpondcs,non-linearityandmulticircuits.ltrelatestoagreatnumberoffactors,includingnotonyplantationsandnatUralresourcesec-tors,butalsosomeotherfactorsaboutmap-ageInentandutilization.Thesefactorsaremu-tUaldePCndenceandinterachononeanotherwithsomesortsofdpodricfeedbackprocc-uurs.fossystCm,whichisconstantlychange-ableastiInepasses,hasaheavilyrelationtootherSystCms.ItisimPossibletoclearIyunder-standsuchaconti…     

动磁式直线冰箱压缩机数值模拟与分析

建立了动磁式直线冰箱压缩机的理论数学模型,采用描述函数法对气缸内非线性气体力进行了线性化.气缸直径与活塞行程比值、永磁体充磁厚度、以及电压源驱动频率等3个参数分别对压缩机比推力、系统弹性刚度和阻尼、系统功率因素的影响进行了数值模拟和分析.在保证压缩机排气量稳定和高效的前提下,提出了合理选择和确定压缩机主要结构和性能参数的方法.     

美国的森林生长与收获混合模拟系统

充分发挥森林生态效益是当前森林经营管理工作的重点,森林生长模拟系统是森林经营管理的常用工具。介绍了美国的森林生长混合模拟系统FVS-BGC(FVS-Bio-Geochemical Cycles),该系统是由经验生长收获模型(FVS:Forest vegetation simulator)与林分生物地球化学循环过程模型(STAND-BGC:Stand Bio-Geochemi-cal Cycles)组成的混合模拟系统,可以基于生理过程、气候变化等环境条件来模拟单木和林分两个水平在日和年时间尺度上的生长过程;还介绍了该系统的功能、结构、运行流程以及输入输出结果3个方面,并以一块美国火炬松(Loblolly pine)林分为例进行了模拟预测。