森林种群径阶转移模型中转移概率的估算方法

基于统计分析理论和微分方程理论,给出了森林种群径阶转移模型中估算转移概率的方法：第一种是在有两次样地观测数据,不考虑林分环境因子等因素的条件下估算转移概率;第二种是在已知林分环境因子条件下,不需要对样地有两次观测数据来估算转移概率.实例验证结果表明,两种估算转移概率的方法具有计算简单和实用性强的特点,对森林经营与管理有一定的理论指导和实际应用价值.     

蒙古栎红松林演替模型FOROAK的研究

以森林动态斑块理论为基础建立了蒙古栎（ＱｕｅｒｃｕｓｍｏｎｇｏｌｉｃａＦｉｓｃｈ．）红松（ＰｉｎｕｓｋｏｒａｉｅｎｓｉｓＳｉｅｂ．ｅｔＺｕｃｃ．）林动态变化的林窗模型ＦＯＲＯＡＫ,该模型包括对树木生长的生物学过程和影响树木生长的环境因子模拟两部分。用两种不同面积大小的样地分析森林动态,确定蒙古栎红松林林窗面积为０．０５ｈｍ２。以实际调查数据检验模型,证明所得模型能合理预测森林变化过程,在预测树种组成上精度很高,实际调查和预测的树种断面积组成比在６０、１００和２７０年非常接近,在森林发育后期观测样地的树种组成与预测结果吻合程度良好。对裸地上森林模拟,表明森林的动态过程规律是,蒙古栎和白桦（ＢｅｔｕｌａｐｌａｔｙｐｈｙｌａＳｕｋａｃｚ．）在林分发育开始占优势,中期形成阔叶树和针叶树混交,但以阔叶树为主的森林,后期渐被红松取代。对现实原始林预测显示,森林未来３００年变化稳定,红松株数和生物量变化很小。     

基于抚育间伐效应的长白落叶松人工林两阶段枯死模型

1972和1974年分别在黑龙江省江山娇林场及孟家岗林场设置10块长白落叶松人工林固定样地(8块抚育间伐样地、2块对照样地),采用连年复测数据,分析抚育间伐对人工长白落叶松样地枯死与单木枯死的影响.基于二分类变量Logistic回归,建立了样地枯死及样地内单木枯死概率的两阶段模型(Ⅰ:抚育间伐后样地水平枯死概率模型;Ⅱ:枯死样地中单木水平枯死概率模型),采用广义估计方程(GEE)方法对模型参数进行估计.根据敏感度和特异度曲线相交点确定枯死概率最优临界点.结果表明: 样地数据按照抚育间伐次数分为4组分别建模(模型1～模型4).在模型1中,地位指数、林分年龄的自然对数、抚育间伐年龄及强度为显著自变量;模型2～模型4采用主成分分析法建模,主成分包含林分年龄、每公顷株数、平均胸径及抚育间伐因子,说明抚育间伐因子对样地枯死概率有显著影响.抚育间伐对枯死样地中单木枯死概率无显著影响,单木枯死概率模型中显著性自变量为林分初植密度、年龄、林木胸径的倒数及林分中大于对象木的所有林木断面积之和.样地枯死概率模型及单木枯死概率模型Hosmer和Lemeshow拟合优度检验均不显著,模型AUC均在0.91以上,估计正确率均超过80%,说明模型拟合效果较好.     

基于8hm2样地的天山云杉林蒸腾耗水从单株到林分的转换

为准确地估算天山北坡中部雪岭云杉森林的林分蒸腾耗水量,本研究设置了8hm2固定样地,在每木调查的基础上,通过对7株标准木连续晴天液流的观测,分别得到胸径与液流速率和边材面积的拟合方程,最终计算得到了林分的蒸腾耗水量,确定了估算该森林群落蒸腾耗水的最小取样面积,并且讨论了最小取样面积随样地位置的变化。结果表明：①在自然生长系,雪岭云杉林分最大蒸腾耗水量、平均蒸腾耗水量同植株密度呈Extrem函数分布;当种植密度达到1200株/hm2时,林分最大蒸腾耗水量达到最大,为77.27 t/hm2d;②对林分蒸腾耗水量的测算存在明显的最小取样面积,最小取样面积随取样点的不同而略有差异,取样起始点在本样地的海拔上边界和下边界处时最小取样面积为4 hm2,取样起始点在本样地的中部时最小取样面积为2.56hm2。本研究为更精确地估算天山北坡雪岭云杉森林的蒸腾耗水量提供了理论依据。     

基于知识粒度的森林生态系统健康评价指标赋权方法

依据系统科学原理,从影响森林健康包括的系统活力、系统组成、系统恢复力和林地环境等方面筛选13个指标构建森林健康评价指标体系;针对健康评价取值未知(无决策属性)的状况,利用粗糙集理论的属性重要度分析各指标因子对森林健康的影响程度,提出将基于知识粒度和属性重要度的森林健康评价指标赋权法。根据二类调查和样地调查数据,以湖南省大围山自然保护区8个次生林群落和2个人工林样地为应用实例,结果表明:森林健康评价指标体系的林分郁闭度、林分蓄积量、叶面积指数等13个指标在大围山自然保护区森林健康评价中的权重与专家打分法得到的结果基本相符,并且对样地进行了评价,其中只有1个处于健康,7个处于亚健康,2个处于不健康。与层次分析法、主成分分析法等赋权方法相比,基于粗糙集的森林健康评价指标赋权法不需要提供任何先验信息,以森林健康系统相关信息为分析依据,直接从反映森林健康的指标数据中挖掘各因子之间的相关性及其重要度,不依赖专家经验,信息量越大,所得权重越客观。该评价指标赋权法真实有效,评价结果更符合客观实际,为森林健康评价和健康经营提供理论依据。     

基于地统计学丰林自然保护区森林生物量估测及空间格局分析

摘要： 基于丰林保护区1997年样地调查数据,根据一元生物量估测模型,计算样地生物量,在此基础上,利用ArcGIS地统计插值方法得到整个研究区森林生物量分布,并从林分结构（林型、林龄组）和地形因子（海拔、坡度、坡向）两个方面对保护区森林生物量空间格局进行了分析。结果表明,利用地统计插值得到区域水平的森林生物量是可行的,保护区森林平均生物量水平为171.5t/hm2,总生物量为3.08Tg(1Tg=1012g);不同林分结构（林型、林龄组）有不同的生物量水平;地形因子与生物量有显著的相关性,并得到它们之间的回归方程,为保护区森林生态系统的可持续经营提供了科学依据。     

森林碳计量方法研究进展

森林是陆地生态系统的主体,不仅是巨大的碳库而且对减缓气候变暖具有积极作用。科学有效的森林碳计量方法,有助于加深对全球碳循环过程的理解。然而,由于森林生态系统结构复杂,对森林碳计量的估算结果普遍存在精度低、不确定性高的问题。近年来,国内外发展了大量对森林碳计量进行估算的方法,主要有基于样地清查的森林植被和土壤碳估算、基于生长收获的经验模型估算、基于定量遥感雷达观测的遥感估测、基于多尺度森林生态系统网络的通量观测和陆地生态系统过程模型模拟等方法。在实际的森林碳计量中,根据不同的森林类型特征和数据获取情况,往往采取不同的碳计量方法,甚至不止一种。以生态过程模型模拟、遥感反演和数据同化技术为主要手段,基于碳通量观测数据、控制实验数据和遥感影像数据,发展多学科、多过程、多尺度的综合联网观测,充分认识森林碳循环过程中碳源/汇的时空分布特征,开展区域、洲际乃至全球尺度碳循环及其对全球变化和人类活动响应的系统性、集成性研究,以便建立高效、可靠的碳计量体系是未来林业碳计量的发展趋势。随着世界各国温室气体排放清单的编制,中国迫切需要科学的方法体系计量森林碳源/汇,提升我国在生态环境问题上的国际发言权和主导权,同时对我国森林可持续经营、生态环境保护以及美丽中国建设提供建议与支持。分析了各类森林碳计量方法的主要特征、优缺点,同时探讨了目前的森林碳计量方法存在的问题和未来的发展趋势,为不同时空尺度下森林碳计量提供参考。     

不同立地条件下昆虫群落对松毛虫密度影响的估计(英文)

天敌在松毛虫种群动态中起重要作用,但把天敌的作用加入系统管理模型中却很困难。本文试图用林分因子代替天敌的作用,因为林分条件可以方便地用于系统模型中。通过对浙江省衢县、常山县和龙游县不同立地条件的222块样地的调查数据的分析,从70多科的昆虫群落中选择了16个关键种（科）,并对林分因子和各样地关键种的种数、个体数、多样性之间的关系进行了典型相关分析。结果表明郁闭度和植被条件（灌木层盖度、灌木层高度、草木层盖度、草木层高度、总盖度）是刻划昆虫群落功能的关键林分因子。根据郁闭度的变化和植被条件用系统聚类方法可以把林区分为四种类型,这四种类型林地的昆虫多样性指数、种数、个体数量和松毛虫的密度都存在明显差异;在每种林地都建立了松毛虫密度的变化率与关键林分因子间的回归模型,所有的回归的相关系数都相当高（0．924－0．964）,因此可以认为对林地的分类是合理的,而且用林分因子评估天敌的影响在实践中是可行的。     

海南甘什岭白藤土壤种子库特征及幼苗更新能力

为探究海南甘什岭地区白藤土壤种子库的储备状况及幼苗更新能力,按公里网格设置样地30块(20 m×20 m),于各样地内沿对角线设置7个1 m×1 m小样方,对白藤种子和天然更新幼苗(≤40 cm)的分布状况进行调查,比较不同样地环境条件下种子储备和幼苗更新能力的大小,并采用随机森林方法,对影响种子和幼苗数量的立地环境因子进行分析。结果表明:甘什岭地区白藤土壤种子分布不均匀,土壤种子库种子主要集中在枯落物层;白藤更新幼苗中Ⅰ级(0~9 cm)幼苗占比最高,达61.63%,是更新幼苗的主体,但Ⅰ级幼苗、Ⅱ级幼苗间的转化率较低(39.18%),是制约白藤幼苗天然更新关键环节;立地环境因子中,林冠高度、林分郁闭度、凋落物厚度和林分密度是影响种子分布和幼苗数量的主要环境因子;总之,在自然状态下,白藤天然更新能力不足,应采用人工干预和调控措施促进更新;在白藤更新抚育过程中,应通过林内疏枝除冠、间苗等措施,调节立地环境因子,改善种子的着地环境,提高白藤幼苗转化率,达到促进白藤自然更新的目的。     

亚热带常绿阔叶林林分结构对物种组成变异的驱动作用:从局域到区域尺度

林分结构可以表征森林群落光的可利用性和光环境的异质性,对群落物种组成的变异具有重要驱动作用。然而,目前还鲜有研究将林分结构用于解释群落物种组成的变异。本研究以哀牢山亚热带中山湿性常绿阔叶林20 ha森林动态监测样地及其周边区域按公里网格设置的19个1 ha森林动态样地为研究对象,将林分结构参数、环境因子和空间结构变量共同作为解释变量,采用基于冗余分析的变差分解和层次分割方法,在局域和区域尺度上同时解析群落物种组成变异的驱动因素。结果表明,在局域和区域尺度上,纳入林分结构后均提高了对物种组成变异的解释率。在局域尺度上,加入林分结构作为解释变量后,单纯的空间结构的解释率明显下降,林分结构与环境因子累计贡献了41.0%的解释率。在区域尺度上,林分结构与环境因子累计贡献了23.0%的解释率。从局域到区域尺度,环境过滤的相对作用明显增强。林分结构指示的光的可利用性对林冠下方的树种组成具有较强的塑造作用,今后的研究应进一步探讨林分结构对亚热带常绿阔叶林物种组成变异的驱动机制。     

Forest transition in Vietnam and its environmental impacts

This study assesses the presence of a forest transition – that is, a shift from net deforestation to net reforestation – in Vietnam during the 1990s, and describes its key attributes relevant for global environmental change issues. Using Fuzzy Kappa and other indicators, we compared forest cover estimates and spatial patterns from global and national land cover maps from the early and late 1990s, and compiled other available statistics for years before and after that period. This showed that a forest transition indeed occurred in Vietnam: the forest cover dropped to 25–31% of the country area in 1991–1993, and then increased to 32–37% in 1999–2001. The reforestation occurred at a higher rate than deforestation in the previous decades, and was due in similar proportions, to natural forest regeneration and to planted forests. The carbon stock in forests followed a similar transition, decreasing to 903 (770–1307) Tg C in 1991–1993, and then increasing to 1374 (1058–1744) Tg C in 2005. However, forest density declined during the same period, with an increasing proportion of young and degraded forests. The effects on habitats measured with landscape pattern indices were contrasted: in several regions, the reforestation decreased forest fragmentation, while in others, clearing of old‐growth forests continued and/or forest fragmentation increased. This shows that a transition in forest area is not sufficient to rehabilitate the different ecosystem functions and services of forests. Other forest transitions exist in Tropical Asia and in Latin America. Knowledge about the causes, pattern and environmental impacts of the forest transition in Vietnam is therefore relevant to understand possible emerging regional trends that would have implications for global environmental change.     

A statistical mechanical study of helix-coil transition in concentrated solutions of polypeptides and proteins

The helix–coil transition in polypeptides was studied by methods of statistical mechanics, taking account of interaction between “melted” amide groups through hydrogen bonds. The statistical sums are calculated in the explicit form for two limit cases: (1) the dilute solution when the main contribution is given by collisions of two particles; (2) “condensation” when contacting macromolecules form a united aggregate. In the first case the transition enthalpy was shown to decrease linearly when the concentration increases, while at the appropriate choice of theoretical parameters, melting temperature and range are almost independent of the concentration. In the second case the structural transition parameters were shown to be independent of the concentration (the saturation effect). These results agree with the experimental data on synthetic polypeptides reported by other authors and with data on some globular proteins (serum and egg albumin) reported in this paper.     

Forest transition in an ecologically important region: Patterns and causes for landscape dynamics in the Niger Delta

The influence of human related actives such as oil and gas exploration, intensified logging of trees and over exploitation of forest resources for food, have negatively impacted the once flourishing and ecologically diverse forest system of the Niger Delta region in Nigeria. Relevant information on the transitional changes of forested landscapes in the delta is poor compared to other tropical forests such as the Brazilian and Columbian Amazonian forest where numerous research studies have been conducted. Consequently, this study aimed at investigating the spatial extent and rates of forest transition in the Niger Delta region taking into consideration the patterns, causes and implications of the landscape dynamics. The study determined the spatial extent and rates of forest transition in the study area using remotely sensed data from 1986 and 2007. The results indicated that the spatial extent of deforestation, unchanged forest cover and afforestation were 1.38, 2.39, and 1.15 million hectares, respectively, while the annual deforestation and afforestation rates were 0.95 and 0.75% which are high compared to other areas in the humid tropics. The annual rate of change in forest cover was determined as ?0.13% indicating an overall reduction in the spatial extent of forest cover for the entire delta. Changes in the spatial structure of forests were investigated using landscape metrics and the results showed there was a substantial increase in forest fragmentation. The variations in population dynamics and poverty indicators between different states of the Niger Delta were unable to explain the observed patterns of forest change. Instead, the authors observed that the main determinants of forest dynamics were the variations in state forest management policies and the influence of the oil and gas industry on the economies of the states. High rates of afforestation were found in states that have limited oil resources and were more economically dependent on forest products, while states with high deforestation rates were found in the main oil-producing parts of the study site. Using the present trend of forest transition dynamics, a 20-year forward simulation was generated using the Markov algorithm. The results concerning forest transition in the study area point to the urgent need for appropriate environmental policy development and implementation for the Niger Delta region.     

Moderate disturbances accelerate forest transition dynamics under climate change in the temperate–boreal ecotone of eastern North America

Several temperate tree species are expected to migrate northward and colonize boreal forests in response to climate change. Tree migrations could lead to transitions in forest types, but these could be influenced by several non‐climatic factors, such as disturbances and soil conditions. We analysed over 10,000 forest inventory plots, sampled from 1970 to 2018 in meridional Québec, Canada, to identify what environmental conditions promote or prevent regional‐scale forest transitions. We used a continuous‐time multi‐state Markov model to quantify the probabilities of transitions between forest states (temperate, boreal, mixed, pioneer) as a function of climate (mean temperature and climate moisture index during the growing season), soil conditions (pH and drainage) and disturbances (severity levels of natural disturbances and logging). We further investigate how different disturbance types and severities impact forests' short‐term transient dynamics and long‐term equilibrium using properties of Markov transition matrices. The most common transitions observed during the study period were from mixed to temperate states, as well as from pioneer to boreal forests. In our study, transitions were mainly driven by natural and anthropogenic disturbances and secondarily by climate, whereas soil characteristics exerted relatively minor constraints. While major disturbances only promoted transitions to the pioneer state, moderate disturbances increased the probability of transition from mixed to temperate states. Long‐term projections of our model under the current environmental conditions indicate that moderate disturbances would promote a northward shift of the temperate forest. Moreover, disturbances reduced turnover and convergence time for all transitions, thereby accelerating forest dynamics. Contrary to our expectation, mixed to temperate transitions were not driven by temperate tree recruitment but by mortality and growth. Overall, our results suggest that moderate disturbances could catalyse rapid forest transitions and accelerate broad‐scale biome shifts.     

Partitioning an elevation gradient of vegetation from southeastern Ethiopia by probabilistic methods

Vegetation and environment have been analyzed along an altitudinal gradient in Harena Forest, Bale Mountains National Park, southeastern Ethiopia. Vegetation data include numbers of each tree and shrub species and cover-abundance values of each herbaceous species. Environmental data comprise edaphic factors, altitude and topography. The two vegetation layers data were analysed separately.Probabilistic similarity coefficients were computed between the relevés, and these values were used in subsequent computations for classification and ordination. Two sets of stratocoena, comprising 6 types each, derived on the basis of separate analyses of tree-shrub and herb layers of the forest were recognised. A combination of the two sets of stratocoena produced a total of 11 vegetation types. Environmental fuzzy set analysis was applied to determine the strength of the relationship of the relevés to the environmental factors. Autocorrelation analysis was applied to the eigenvectors of probabilistic similarity matrices and environmental data. Altitude appears to be more important thant the other environmental factors in controlling the zonation of the forest. Other important environmental influences on the vegetation include pH, organic matter content and texture of the soil. It is suggested that the whole forest be included in the National Park to create suitable conditions for adequate protection.Abbreviations EFS Environmental fuzzy sets - PROSIM Probability similarity index - PCA Principal components analysis     

Folding of a LysM domain: entropy-enthalpy compensation in the transition state of an ideal two-state folder

Protein-engineering methods (Φ-values) were used to investigate the folding transition state of a lysin motif (LysM) domain from Escherichia coli membrane-bound lytic murein transglycosylase D. This domain consists of just 48 structured residues in a symmetrical βααβ arrangement and is the smallest αβ protein yet investigated using these methods. An extensive mutational analysis revealed a highly robust folding pathway with no detectable transition state plasticity, indicating that LysM is an example of an ideal two-state folder. The pattern of Φ-values denotes a highly polarised transition state, with significant formation of the helices but no structure within the β-sheet. Remarkably, this transition state remains polarised after circularisation of the domain, and exhibits an identical Φ-value pattern; however, the interactions within the transition state are uniformly weaker in the circular variant. This observation is supported by results from an Eyring analysis of the folding rates of the two proteins. We propose that the folding pathway of LysM is dominated by enthalpic rather than entropic considerations, and suggest that the lower entropy cost of formation of the circular transition state is balanced, to some extent, by the lower enthalpy of contacts within this structure.     

Environmental drivers of species composition and functional diversity of dung beetles along the Atlantic Forest–Pampa transition zone

Human activities are causing a rapid loss of biodiversity, which impairs ecosystem functions and services. Therefore, understanding which processes shape how biodiversity is distributed along spatial and environmental gradients is a first step to guide conservation and management efforts. We aimed to determine the relative explanatory importance of biogeographic, environmental, landscape and spatial variables on assemblage dissimilarities and functional diversity of dung beetles along the Atlantic Forest–Pampa (i.e. forest–grassland) transition zone located in Southeast South America. We described each site according to their biogeographic position, environmental conditions, landscape features and spatial patterns. The compositional dissimilarity was partitioned into turnover and nestedness components of β‐diversity. Mantel tests and generalised dissimilarity models were used to relate β‐diversity and its components to biogeographic, environmental, landscape and spatial variables. Variation partitioning analysis was used to estimate the pure and shared variation in species composition and functional diversity explained by the four categories of predictors. Biome domain was the main factor causing dung beetle compositional dissimilarity, with a high species replacement between Atlantic Forest and Pampa. Biogeographic, environmental, landscape and spatial distances also affected the patterns of dung beetle dissimilarity and β‐diversity components. The shared effects of the four sets of predictors explained most of the variation in dung beetle composition. A similar response pattern was found for dung beetle functional diversity, which excluded biogeographic effects. Only the pure effects of environmental and spatial predictors were significant for species composition and functional diversity. Our results indicate that dung beetle species composition and functional diversity are jointly driven by environmental, landscape and spatial predictors with higher pure environmental and spatial effects. The forest–grassland transition zone promotes a strong species and trait replacement highly influenced both by environmental filtering and dispersal limitation.     

不同生态修复措施和环境因素对亚热带红壤区针叶纯林坡面水土保持功能的影响

使用"地理探测器（GeoDetector）"对亚热带红壤区水土流失影响因素的定量分析结果可为当地森林生态修复和侵蚀模型完善提供科学依据。基于福建省龙岩市新罗区龙门溪小流域森林调查数据和径流小区监测数据，利用地理探测器探测不同生态修复措施和环境因素对针叶纯林坡面水土保持功能的影响及交互作用，结果表明：（1）对比中幼龄针叶纯林，补植阔叶树使针阔混交比例为7 ： 2可减少46%的径流量和76%的泥沙量，生态修复效果较好。对重侵蚀区"老头树"少量施肥难以产生效果。（2）影响坡面径流的因素由强到弱依次是：降雨因子（0.53），土壤容重、林分密度、灌草层盖度、树高和针阔比（均在0.08左右）；影响泥沙流失的因素依次是：地表径流量（0.84），降雨因子（0.2），林分密度、土壤容重、灌草层盖度、土壤含水率、灌草层生物量（均在0.12左右）。（3）各影响因素交互后主要呈增强作用；林分密度、灌草层盖度和土壤容重还可与其他因子产生强烈非线性增强作用（交互后影响力>0.9），是在森林修复和模型参数优化时需重点关注的对象。     

Evidence of incipient forest transition in southern Mexico

Case studies of land use change have suggested that deforestation across Southern Mexico is accelerating. However, forest transition theory predicts that trajectories of change can be modified by economic factors, leading to spatial and temporal heterogeneity in rates of change that may take the form of the Environmental Kuznets Curve (EKC). This study aimed to assess the evidence regarding potential forest transition in Southern Mexico by classifying regional forest cover change using Landsat imagery from 1990 through to 2006. Patterns of forest cover change were found to be complex and non-linear. When rates of forest loss were averaged over 342 municipalities using mixed-effects modelling the results showed a significant (p<0.001) overall reduction of the mean rate of forest loss from 0.85% per year in the 1990-2000 period to 0.67% in the 2000-2006 period. The overall regional annual rate of deforestation has fallen from 0.33% to 0.28% from the 1990s to 2000s. A high proportion of the spatial variability in forest cover change cannot be explained statistically. However analysis using spline based general additive models detected underlying relationships between forest cover and income or population density of a form consistent with the EKC. The incipient forest transition has not, as yet, resulted in widespread reforestation. Forest recovery remains below 0.20% per year. Reforestation is mostly the result of passive processes associated with reductions in the intensity of land use. Deforestation continues to occur at high rates in some focal areas. A transition could be accelerated if there were a broader recognition among policy makers that the regional rate of forest loss has now begun to fall. The changing trajectory provides an opportunity to actively restore forest cover through stimulating afforestation and stimulating more sustainable land use practices. The results have clear implications for policy aimed at carbon sequestration through reducing deforestation and enhancing forest growth.