基于哑变量的湖南栎类次生林直径分布研究

文章以湖南省188个栎类次生林样地为研究对象,利用Kolmoglov-Smirnov检验法对6种分布密度函数在直径分布拟合中的适用性进行检验。以林分变量为自变量,采用参数预测法构建Weibull函数3个参数的逐步回归参数模型和以林分类型为哑变量的哑变量参数模型,并对比两类模型的直径分布预测精度。结果表明,Weibull函数更适合于栎类直径分布的拟合(接受率为91.7%);与逐步回归参数模型相比,参数b、c的哑变量模型的R~2分别提高了0.104和0.134,且应用于直径分布预测时的精度显著提高(P=0.025)。研究基于林分类型哑变量构建参数模型,并用于栎类次生林的直径分布预测,预测精度较高。     

哑变量在云杉地上生物量模型中的应用研究

基于150株样木的生物量数据,采用常规回归方法和哑变量模型方法,构建了黑龙江、吉林两省云杉地上总生物量与各分项生物量的一元、二元以及三元模型。结果表明:2种方法建立的模型中,地上总生物量模型预估精度最高,在96%以上;树叶生物量最低,仍达87%以上;其他生物量预估精度均在91%以上;总相对误差均控制在±5%的范围内。通过对一元、二元和三元模型对比分析,发现随着解释变量增加,2种方法生物量模型的预估精度和确定系数都有所提高。引入地域哑变量后,一元、二元和三元模型的预估精度和确定系数都比常规模型有所提高,估计值的标准误差和总相对误差有一定下降,哑变量可以提高模型的拟合优度和预测效果。     

基于无人机激光雷达的银杏人工林有效叶面积指数估测

【目的】精确估测银杏人工林有效叶面积指数(eLAI),以更好了解银杏人工林的生长和竞争、理解人工林生态系统的功能和生产力。【方法】基于多旋翼无人机激光雷达(LiDAR)系统获取的点云数据,结合45块地面实测样地数据,使用孔隙度模型法(通过计算点云的冠层穿透率,根据Beer-Lambert定律计算有效叶面积指数)和统计模型法(首先通过地面实测的有效叶面积指数和所提取的LiDAR特征变量建模,然后借助拟合的模型估测有效叶面积指数)对我国典型银杏人工林进行样地尺度的有效叶面积指数估测。【结果】1)使用统计模型法估测eLAI时,仅利用LiDAR高度特征变量估测精度为R2=0. 38(rRMSE=54%),引入其他特征变量(冠层密度特征、冠层容积比以及强度特征变量)后精度分别达到R2=0. 64(rRMSE=26%)、R2=0. 61(rRMSE=28%)、R2=0. 74(rRMSE=23%); 2)根据Cover将样地分组建模后发现,分组建模的精度优于不分组建模的精度;3)孔隙度模型法估测有效叶面积指数的精度为R2=0. 71(rRMSE=32. 0%)。【结论】结合多组LiDAR特征变量估测有效叶面积指数能够充分挖掘LiDAR数据包含的冠层结构特性,从而提升估测精度;同时,使用孔隙度模型法可以有效估测银杏人工林有效叶面积指数。无人机LiDAR点云在估测银杏人工林有效叶面积指数上具有较好的潜力。     

基于ALS数据和哑变量技术森林蓄积量估测

基于机载LiDAR数据,分析哑变量对林分蓄积量估测精度的影响。以广西高峰林场为研究对象,借助机载激光雷达点云数据和96个样地数据,将样地数据按7∶3的比例随机划分为建模样本和测试样本,采用随机森林模型(RFR)和支持向量机模型(SVR)对建模样本与对应的点云特征回归建模,将树种组(针叶林和阔叶林)和龄组分别作为哑变量引入到回归模型。利用测试样本的估测精度评价模型的估测精度,引入树种组哑变量,随机森林模型决定系数R2从0.59提高到0.64,支持向量机模型决定系数R2从0.49提高到0.50。引入龄组哑变量,随机森林模型决定系数R2从0.59提高到0.65,支持向量机模型决定系数R2从0.45提高到0.55。根据模型的建模精度和验证精度结果得出,引入哑变量对蓄积量估测模型的精度提升是相对有效的。龄组哑变量对模型精度提升效果优于树种组哑变量。     

基于哑变量的高山松蓄积量反演模型研究

基于Landsat TM和地面实测样地数据,采用传统线性回归和引入哑变量的线性回归两种建模方法构建香格里拉高山松蓄积量反演模型,并对模型进行验证。研究表明,传统一元和多元线性回归模型的相关系数分别为0.280和0.365,引入哑变量的线性回归模型相关系数为0.602;结合实测检验数据,传统一元、多元线性模型和引入哑变量的模型预测精度分别为61.1%,74.9%和80.3%,引入哑变量的高山松森林蓄积量模型反演精度明显提高,研究结果可为今后基于哑变量的遥感森林蓄积量反演提供一定的依据和参考。     

黄土高原半干旱区油松人工林枯落物截留雨量模拟研究

为建立合适的枯落物截留雨量预估模型,利用2008-2011年定位观测数据,采用回归分析方法对黄土高原半干旱区油松人工林枯落物对降雨的截留与林外降雨量(P)、林内穿透雨量(TF)之间的关系进行建模研究;运用Bootstrap方法,对模型进行参数特征分析.结果表明:枯落物截留与林内外降雨量均可用非线性模型Ic=aPb进行回归模拟,回归方程分别为Ic=0.499P0.627和Ic=0.717TF0.513.该模型不仅具有较高的拟合精度,且拟合方程参数稳定性良好,经检验方程均达到显著性要求,可用于预估该区域油松人工林的枯落物截留量.     

毛竹生长动态模拟预测新模型

本文以影响毛竹生长的6个主要气象因子为输入变量，以毛竹平均胸径为输出变量，首次运用人工神经网络方法建立毛竹生长动态模拟预测模型。结果表明：该模型模拟精度高达93．91％，从而为人工神经网络方法的应用和毛竹科学研究开辟新的思路。     

用泛化改进的BP神经网络估测森林蓄积量

介绍主成分变换和经规则化调整法进行泛化改进的BP神经网络在森林蓄积量建模估测中的应用,比较普通BP神经网络与泛化改进的BP神经网络对蓄积量预报的差异,分析直接用中心标准化的观测值建立仿真模型和进行主成分变换后再建立模型的效率问题.结果表明:泛化改进的BP神经网络比普通BP神经网络具有更高的预报精度,利用主成分得分作为仿真模型的变量比直接用观测值作变量具有更快的速度,并保证了预报精度.     

基于机载小光斑全波形LiDAR的亚热带林分特征反演

【目的】研究通过集成波形信号处理、空间解析和重构建模以及综合波形信息提取方法,探索基于小光斑全波形LIDAR特征变量高精度反演林分特征的新方法。【方法】以江苏南部丘陵地区的亚热带天然次生林为研究对象,在预处理和分析小光斑全波形 LIDAR 数据的基础上,首先基于体元空间框架分解和提取波形的振幅能量信息,并构建伪垂直波形模型;然后,从中提取空间位置信息(即点云)及几何辐射变量,计算 LiDAR点云和波形特征变量,并通过相关性分析筛选特征变量;最后,结合地面实测林分特征参数构建反演模型并验证精度。【结果】1)各 LiDAR特征变量对 Lorey’s树高的敏感性最高,对蓄积量和地上生物量次之,对胸高断面积最低,而返回脉冲总能量和返回脉冲峰值点数对胸高断面积的敏感性却高于其他林分特征因子;在点云特征变量组中,平均高、高度百分位数及冠层上部的返回点云密度与各林分特征之间的相关性较高,而在波形特征变量组中,能量中值高度的均值、返回脉冲长度的标准差和冠层粗糙度的标准差与各林分特征之间的相关性较高;2) Lorey’s 树高的模型估算精度最高( RMSE为实测均值的7.26%),而蓄积量、地上生物量和胸高断面积的模型估算精度略低且较相近( RMSE为实测均值的15.91%～19.82%);模型自变量的数量都在3个以内,选中的自变量为高度百分位数、冠层返回点云密度、返回脉冲长度和冠层粗糙度的标准差;3)各林分特征实测值与交叉验证估算值的拟合结果表明, Lorey’s树高的拟合效果最好(R2=0.85),地上生物量(R2=0.68)和蓄积量(R2=0.59)次之,而胸高断面积(R2=0.45)最低;4) Lorey’s 树高、蓄积量和地上生物量的空间分布状况基本一致,源于它们内在的相关性;相比其他3个特征变量,胸高断面积的空间分布不够连续,这可能是由于其预测模型精度较低所致。【结论】各林分特征综合回归模型的拟合效果和精度都高于仅使用点云特征变量拟合模型的精度,表明了波形特征变量提取森林中下层信息的潜力。点云特征变量描述了森林冠层及上部的三维结构及密度信息,而波形特征变量则获得了森林冠层及以下部分完整的垂直分布和能量信息,二者互补可提升林分特征反演的精度。     

思茅区森林生物量分层抽样调查设计

基于普洱市思茅区森林资源二类调查数据,以森林起源、地类、龄组、优势树种作为分层变量,在95%的可靠性下,设置95%,90%和85%的抽样设计精度分层抽样进行森林生物量估测,将抽样调查结果与系统抽样方法进行比较。结果表明:1)分层抽样具有样本数量少、抽样精度高的明显优势,在普洱市思茅区,按85%的设计精度,按优势树种的分层抽样比系统抽样的效率约提高了52%;2)采用单变量进行分层抽样,优势树种具有显著优势。按85%的设计精度,在样本数量为44个的前提下,其实际抽样精度达到87.82%。     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Growth of Mixed Birch-Coniferous Stands in Relation to Pure Coniferous Stands at Similar Sites in South-eastern Norway

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.     

Defoliation by the Needle-shortening Pine Gall Midge,Thecodiplosis brachyntera,on Pines in Central Sweden

An outbreak of the needle-shortening pine gall midge, Thecodiplosis brachyntera , occurred on Scots pine, Pinus sylvestris (L.) and lodgepole pine, P. contorta (Dougl.) in central Sweden during 1995-1998. The larval feeding of T. brachyntera kills current-year needles and heavy infestation causes severe defoliation. A pattern of fluctuating defoliation among years and sites was found on both pine species. Defoliation was evenly distributed in the crown of P. sylvestris during years of high as well as low infestation; apical whorls had as much defoliation as basal whorls. In P. contorta , however, there was a tendency for defoliation to be concentrated on branches in the most apical whorls. Growth ring increments on P. sylvestris with high levels of defoliation (71%) did not differ from trees with moderate levels (26%) of defoliation. Shoot lengths were significantly shorter, however, on heavily infested trees the year after defoliation.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Biogeochemical impacts of clearfelling and reforestation on blanket-peatland streams: II. major ions and dissolved organic carbon

Streams and drains in blanket-peatland forest in western Ireland were sampled weekly over 5 years, 1996–2000, using continuous, depth-proportional passive sampling. Analysis was for pH, alkalinity by Gran titration, anions by IC, metals by ICP, aluminium speciation by loaded-resin exchange, and dissolved organic carbon (DOC) by absorbance at 320 nm.

Effects of felling are identified graphically from two forest drains whose catchments (both about 1 ha) were clearfelled, and partial clearfelling of one larger catchment (somewhat over 1 km²), in summer 1999. Calcium concentrations and alkalinity were increased in the drain- and streamwater from the felled areas. The pH was increased in drains, while in the larger stream, pH range decreased while the mean increased. Phosphorus increased markedly with clearfell, in the absence of recent fertilising, and also increased with fertilising; these results are reported in an accompanying paper. Ammonium-nitrogen concentrations were increased in the two drains with felling, and temporarily decreased in the larger stream. Nitrate increased in some cases. Potassium and manganese concentrations also increased. Concentrations of DOC and organic monomeric aluminium increased gradually, subject to a continuing strong annual cycle. There were no clearfelling effects on concentrations of solphate, suspended solids or inorganic monomeric aluminium. In the two drains (fully clearfelled), concentrations of sodium, chloride and magnesium, and conductivity, were all reduced after felling. Fertilising effects other than for phosphorus were indistinct.

Effects of the combined clearfell–reforestation treatment were testable statistically, using randomised intervention analysis, between two larger streams (1 km²) as a treatment–control comparison. There were statistically significant positive responses in streamwater concentrations of nitrate, potassium, calcium, DOC and aluminium fractions. The implications for management practice depend on whether the loss of nutrients is sustainable for future crop productivity, and whether critical limits and loads of receiving ecosystems are exceeded.     

Effect of Drought on Growth and Mortality of Actively Growing Norway Spruce Container Seedlings Planted in Summer

Survival, root egress and height growth of 13-month-old actively growing Norway spruce ( Picea abies (L.) Karst.) container seedlings exposed to preplanting drying treatments (0, 4, and 8 days) and postplanting drought periods (1, 2, 3, and 4 weeks) were studied in the field between 5 July and 18 August 1999. The mortality of seedlings increased and the height growth and root egress decreased throughout the postplanting drought period. Postplanting performance was also affected by preplanting drying treatments. The results indicate that no risk of excessive mortality and growth restrictions occurs when actively growing seedlings are planted in summer, provided that seedlings are well watered before planting and the drought period does not exceed 3 weeks.     

Rehabilitation of diseased cacao fields in Peru through shade regulation and timing of biocontrol measures

The objective of this case study was to test the effectiveness of biocontrol for the rehabilitation of abandoned, diseased (moniliasis, witches' broom and black pod) cocoa and to develop testable hypotheses regarding the effect of shade and biocontrol timing. Three trial fields differed in their shade regimes. Biocontrol was administered starting either at flowering or pod filling. Disease incidence and yield were compared with cultural control alone. Biocontrol reduced moniliasis from 49% to 25%, independent of the shading regime and application time. Witches' broom was most severe without shade and unaffected by biocontrol. No significant effects on black pod were observed. Although biocontrol increased percentage healthy fruit independent of shading and timing, only the shaded plot with biocontrol from flowering onwards responded with increased yield. Our hypothesis is: 'In the rehabilitation of abandoned cacao, only fields under sustainable shade management and early onset of biocontrol can realise their production potential.' This revised version was published online in June 2006 with corrections to the Cover Date.