Lateral strength of nailed timber connections with decay

Loading tests were conducted on nailed connections with decay due to a brown rot fungus. The effect of the decay on the lateral strength of nailed connections was investigated. After loading tests, the sound and decayed regions of a nailed connection were observed in the cross section, which was cut parallel to the grain through the nailed point. The nailed connections with decay showed a low load during initial deformation when the main and side members had a decayed region in the boundary between them. The nailed connections showed low load after yielding when the sound region in the main member decreased. The yield load of nailed connections with decay was calculated based on the yield theory. The model of calculations had sound and decay regions within a member. The yield load of nailed connections obtained by the calculation based on the yield theory agreed with the results obtained by experiments when significant decay in a direction parallel to the grain was observed in the main and side members. This result indicates that the yield theory can estimate the yield load of nailed connections not only with a sound member, but also a member that is partly or wholly decayed.     

Serial exposure technique for assessing performance of wood preservatives

Summary The performance of copper-chrome-arsenate (CCA) and two quaternary ammonium compounds as wood preservatives was compared using a serial exposure technique, involving successive 10-week exposures in conventional soil jars. All preservative treatments were successful in preventing decay of Pinus radiata sapwood after the first exposure, but successive 10-week exposures clearly distinguished those treatments likely to offer long-term protection. The progressively increasing times of exposure with test fungi overcame the time lag for decay initiation in wood treated to preservative retentions above the toxic threshold established by conventional laboratory methods. Consequently, an additional and higher toxic threshold could be calculated. Examination of data from field stake tests suggested that a series of toxic thresholds established by a serial exposure technique could be related to preservative retentions which protect wood in the field from decay for increasing periods of time. Results of all tests are discussed in relation to the development of a laboratory procedure which may predict field performance of wood preservatives.     

非线性模型对数回归的偏差校正及与加权回归的对比分析

本文结合大样本的立木生物量实测数据,对非线性模型对数回归的偏差校正问题进行了探讨,并与加权回归结果进行了对比分析。首先,分析了对数回归产生偏差的内在原因,并提出了一个新的校正因子,同时对另外3个偏差校正因子一并进行了检验,结果表明本文和Baskerville(1972)提出的校正因子,能保证与加权回归估计结果趋于一致;然后,对非线性加权回归中基于普通回归残差推导的权函数与通用权函数(W＝1/f(x)²)的拟合效果进行了对比分析,结果表明二者基本相当,而通用权函数更具有广泛的适应性。建议对带有异方差的非线性模型,最好直接采用加权回归进行估计;当按照通用权函数进行估计其总相对误差超出一定范围时,应该根据普通回归估计的残差推导效果最佳的权函数后再进行加权回归。     

Fungal decay resistance of wood impregnated with parahalophenyl para-tolyl sulfonamides

Summary We are investigating wood decay biocides that are both effective in protecting wood from decay and more environmentally compatible than other biocides. A series of halophenyl sulfonamides were synthesized and characterized by infrared and neuclear magnetic resonance spectroscopy. Wood impregnated with these compounds was tested for resistance to decay as well as water leaching. Wood impregnated with para-iodophenyl or para-fluorophenyl para-tolyl sulfonamides resisted decay by brown- and white-rot fungi. For wood impregnated with para-iodophenyl para-tolyl sulfonamide, threshold retention with the brown-rot fungus Gloeophyllum trabeum was 9.1 mmol/ 100 g solution for unleached blocks. For leached blocks, weight loss was very high (24.6%), which indicated that threshold retention will be substantially higher than 9.1 mmol/100 g solution. With the white-rot fungus Coriolus versicolor, threshold retentions were 2.9 and 5.6 mmol/100 g solution, respectively, for unleached and leached blocks. Leaching of the blocks treated with the iodo compound slightly decreased resistance to decay by C. versicolor. For wood impregnated with parafluorophenyl para-tolyl sulfonamide, threshold retentions with both G. trabeum and C. versicolor were very close to 9.0 and 9.2 mmol/100 g solution, respectively, for leached and unleached blocks. Leaching had a little effect on resistance to decay by both fungi. Wood impregnated with parachlorophenyl or bromophenyl para-tolyl sulfonamide was ineffective in resisting decay by both fungi.     

Estimation of GPS positional accuracy under different forest conditions using signal interruption probability

We proposed a signal interruption probability (SIP) value indicating the frequency of global positioning system (GPS) signal interruption or the fragmentation of GPS data, and used it to estimate the success probability of ambiguity resolution in carrier-phase differential GPS (DGPS) as well as the horizontal precision of code-phase DGPS under different forest conditions. In field tests, a rover was set up at four observation points, each representing a different condition within a forest. At each observation point, static surveying was conducted for four periods of 30 min, and data from the first 1, 5, 15, and 30 min from each observation point were extracted for analysis. The position of each point was calculated by baseline analysis using three types of GPS data, i.e., dual-frequency (L1 and L2), single-frequency (L1), and code-phase DGPS data. The results showed that ambiguity resolution was a key factor in determining the horizontal accuracy of carrier-phase DGPS, and that the success probability of ambiguity resolution differed greatly according to forest conditions, which were well explained not by the index of the canopy opening but by the SIP. Furthermore, estimation of the success probability of ambiguity resolution was made based on the SIP and the observation period using a logistic regression model. The horizontal precision of code-phase DGPS was also estimated based on the SIP and the observation period. In conclusion, the SIP was found to be an effective indicator of GPS positional accuracy under different forest conditions.     

A probability model for root and butt rot in Picea abies derived from Norwegian national forest inventory data

Root rot in Norway spruce (Picea abies (L.) Karst.) causes substantial economic losses to the forestry sector. In this study, we developed a probability model for decay at breast height utilizing 18,141 increment cores sampled on temporary plots of the Norwegian National Forest Inventory. The final model showed a good fit to the data and retained significant relationships between decay and a suite of tree, stand and site variables, including diameter at breast height, stand age, altitude, growing season temperature sum (threshold 5°C), and vegetation type. By comparing model predictions with recorded decay at stump height in an independent data set, we estimated a proportionality function to adjust for the inherent underestimation of total rot that will be obtained by applying a probability model derived from increment cores sampled at breast height. We conclude that the developed model is appropriate for national and regional scenario analyses in Norway, and could also be useful as a tool for operational forestry planning. This would however require further testing on independent data, to assess how well the new model predicts decay at local scales.     

Manganese in tree rings of Norway spruce as an indicator for soil chemical changes in the past

Element concentrations in tree rings can be used to monitor changes in environmental quality. With regard to the detection of incipient soil acidification, the manganese concentration in soils and plants is a significant marker for the switch of acid buffering in soils mainly with the exchange of base cations or with the dissolution of aluminium oxides. This is a site-specific non-linear event, indicating the onset of Al³⁺ dominance in the soil solution, were damages to vegetation due to acid stress become possible. This turning point is also a marker for the attainment of pH 4.2 in soils, the critical threshold used for critical load calculations. On a plot of the German environmental monitoring in forests the element concentrations in tree rings of 60-year-old spruces reveal a distinct decline in the Mn concentration, beginning in the late 1960s ending in the late 1970s. With this information it was possible to assume a base saturation in the soil of about 15–20% in the late 1960s, and to model the development of the base saturation of the site. A decline from 17.5 to 6% within one decade could be related to the deposition. This is in accordance with the base saturation of 6.5%, measured in 1993 for this site, but also for adjacent spruce sites on the same geological substrate. The knowledge of the time span were this site-specific non-linear event occurred is essential for the reconstruction of the soil chemistry of a site. Moreover, it enables the assignment of observations like ‘forest damages’ to the onset of changes in environmental quality.     

基于TM数据的森林植物碳储量估测方法研究

以广东省第六次森林资源连续清查样地数据为基础，根据TM数据及其非线性组合的光谱信息，结合地学信息及林分信息，建立了森林植物碳储量估测的多元线性回归方程及神经网络模型。分析结果表明，神经网络模型的估测精度高于回归模型估测精度，但用它们估测落实到样地的森林植物碳储量误差仍然较大，还不能满足样地调查精度的要求。     

三种国外木材防腐剂室内防腐防霉防白蚁性能评价

不含铬和砷的TanalithCuAz、Tanalith CY和Totim B是目前国外广泛应用的环保型木材防腐剂产品.本文报道了这3种国外木材防腐剂产品的首次国内室内防腐性能评价试验的结果.结果显示,用少量Tanalith CY和Totim B产品即可有效地抑制腐朽菌对木材的侵害;Tanalith CuAz对腐朽菌的抑制效力随其浓度的增加而快速增大;Tanalith CuAz和Totim B分别显现出良好的抑制白蚁、防止蓝变菌及霉菌侵染的功效.     

油茶F1代试验林树高、冠幅、产果量的相关性分析

为给良好树形结构的设定及产量预测提供参考,根据2003～2005年闽侯桐口林场的油茶杂交F1代试验林连续3a的生长量调查数据,对49个处理的树高、冠幅、单株产果量的平均数据进行相关性分析和主成分分析。结果表明冠幅与单株产果量间存在显著相关性。对两者进行一元非线性回归模型分析得到回归曲线和回归方程,进一步了解两者间的相关性,同时作出产果量的预测。     

川西亚高山针叶林生物量遥感估算模型研究

利用野外实测68个样地的森林生物量数据、TM影像的单波段数据、植被指数数据以及地形数据在内的18个自变量建立了川西亚高山针叶林生物量的回归估算模型。研究表明:在建立的一元线性回归、一元非线性回归和多元线性回归生物量模型中,以多元线性回归模型在森林生物量估算中有较好的精度。     

林火碳排放研究进展

火是森林生态系统主要的干扰因子, 森林火灾的频繁发生不仅使森林生态系统遭到破坏, 同时也造成了含碳温室气体的大量释放。综述了火烧面积、森林可燃物以及燃烧效率等主要因子对森林火灾排放碳量估计的影响, 分析了这一领域未来研究发展趋势。大量研究表明:1)卫星遥感是估测大尺度上森林过火面积的主要手段, 随着高分辨率卫星的应用, 森林火灾面积的估计精度不断得到提高。目前的研究主要集中于大尺度上林火面积的估计和估算方法的改进。2)遥感数据是目前估计大尺度可燃物燃烧量的有效手段, 利用遥感数据的同时结合有效可燃物计算模型, 运用多元线性与非线性分析结合等方法提高对可燃物燃烧量的估计。3)燃烧效率是决定可燃物消耗量的主要因子, 也是估计森林火灾释放含碳气体量的关键。未来的研究是利用高分辨率的遥感数据, 结合复杂的可燃物计算模型, 更精确地估计林火碳排放。     

Use of GIS-derived environmental factors in predicting site indices in Japanese larch plantations in Hokkaido

The objectives of this study were (1) to evaluate the effects of environmental factors derived from GIS on tree-height growth of Japanese larch (Larix kaempferi) and (2) to develop a best-fit regression model for its site index. Based on data from 40 sample plots situated in an even-aged (38 years), pure, and undamaged Japanese larch stand, multiple regression models for a site index of Japanese larch were constructed using environmental factors as independent variables. The average slope gradient, effective relief, distance from ridge, flow accumulation, degree of exposure, shading, solar radiation index, and gravitational water index were used as environmental factors and calculated on GIS using digital elevation model data. These factors were related to the Japanese larch site index through multiple-regression analysis. The result showed that the most effective factor for estimating site index was the degree of exposure. Through a backward stepwise procedure, the degree of exposure, shading, and average slope gradient were selected for a best-fit regression model. This model explained 72% of the variance in site index, with standard error estimates of 1.75 m. This strong relationship suggests that GIS-derived environmental factors can be used to predict site indices of Japanese larch. This study was supported by the experimental forest of Kyushu University.     

Using optimization for fitting individual-tree growth models for uneven-aged stands

A convenient model type for simulating the dynamics of uneven-aged and uneven-sized stands of Finland is individual-tree model. This is because the stand structures are complex due to the presence of several tree species and irregular size distributions of trees. The required minimum set of models in this approach consists of species-specific individual-tree diameter increment models, individual-tree survival models, and ingrowth models. The development of these models needs data in which the diameter and survival of each tree of the sample plots is known for at least two time points. For this, the trees need to be numbered, which is tedious in uneven-aged forests due to the great number of small trees and the continuous ingrowth process. This study proposes a modelling approach that fits the above models but requires only the diameter distributions of the plots in the beginning and at the end of the measurement interval. The method uses non-linear optimization to derive such values for model parameters that, when the models are applied to the initial diameter distribution, the simulated stand development results in a diameter distribution which agrees with the measured ending distribution. The study showed that the method produces similar models and model parameters as regression analysis. Since the method is less demanding in terms of modelling data, it brings new data sets available for modelling the dynamics of uneven-aged stands and reduces the cost of collecting new data. The models fitted by the proposed optimization method were rather similar to the models developed earlier for Finnish uneven-aged forests.     

A model to calculate ex ante the threshold value of interaction effects necessary for proposed intercropping projects to be feasible to the landowner and desirable to society

This article describes an approach to evaluate the difference in net present valued economic returns that would be expected from temperate intercropping as compared to annual cropping or tree farming alone. This tool can be used by landowners to provide a threshold level of the value of interaction effects required for a proposed intercropping project to break even, based on current data. The landowner would then need to consider, using information from other sources, whether the threshold is realistic for given site conditions. The threshold value is useful to agricultural policy-makers to consider economic instruments that would induce landowners to adopt intercropping, if it should be considered socially beneficial to do so. The approach measures the financial gap that exists between intercropping and annual cropping alone and compares this gap to the beneficial interaction effects that are associated with intercropping. The approach is demonstrated using experimental results from an on-going intercropping study at the University of Guelph, Guelph, Canada. A base model scenario using black walnut trees with annual crops is set up with a 5% discount rate, 96 trees per hectare, and sawlog prices for black walnut of $1066 per 1000 bdft as a base case. The base model predicts that black walnut and corn intercropping returns $555 per hectare less than the annual crops alone, over the entire rotation of trees. This amounts to about $42 per hectare per year in annual terms, at a 6% rate of discount. This is the threshold that would need to accounted for by the net present value (NPV) of on-farm interaction effects. This estimate depends on the specific assumptions made and the experimental situation, and should not be interpreted as reflecting returns possible in other circumstances. This revised version was published online in June 2006 with corrections to the Cover Date.     

A statistical thinning model for initialising large-scale ecosystem models

Abstract

Large-scale ecosystem models are important tools for carbon assessment at national scales. Many of these models are not initialised with known field data from any particular time, but simulate the growth of each stand from its estimated germination year up to the present or future. The models will overestimate current-day standing volume or biomass unless historic stand management (biomass removal due to thinning) is taken into account. The full management history of each stand is rarely known, and must be somehow estimated. One possibility is to build statistical thinning models based on data in a National Forest Inventory, which could then be integrated into the ecosystem models. If the harvesting model is constructed using only variables that are also used within the ecosystem model, then the management impacts can be included in the ecosystem model for the entire simulated life of the stand. In the case of most flux dynamics models, this precludes the use of the tree-level data that harvesting models have traditionally relied on. In this article, we develop a novel means to interrogate a subset of the Austrian National Forest Inventory based on deriving probability density functions for particular combinations of stand and site variables. We determine the parameters of a probabilistic model to estimate historic patterns of timber removals and validate it against inventory estimates. Our procedure can establish supportable estimates of historic management regimes suitable as input data for subsequent modelling of national-scale forest carbon stocks, sources and sinks.     

The potential of moisture content measurements for testing the durability of timber products

Traditionally, the durability of timber is determined in laboratory decay tests or ground contact field tests. Since it is commonly accepted that results from those tests are not directly transferable to less severe above-ground exposures, this study aimed at assessing alternative durability measures related to the moisture performance of wood. Results from above-ground tests including continuous wood moisture monitoring were analyzed. Decay ratings determined in double-layer field tests were compared with time of wetness, and temperature- and moisture-induced dose according to a dose–response model for above-ground decay. Significant differences between European wood species were found in façade, decking, sandwich, lap-joint, and double-layer tests with respect to their moisture performance. It is concluded that for many wood-based products intended for above-ground use, a combination of short-term laboratory decay tests and mid-term moisture performance field tests may serve as time-saving alternative to long-term decay tests in the field.     

The effect of taper on the MOE of log stringers

Load sharing between the stringers in gravel-decked log bridges is an important design factor when small- diameter stringers are used with thin gravel decks. In order to estimate the load sharing between the stringers, it is necessary to consider the deflection of the stringers; therefore, accurate estimates of the apparent modulus of elasticity (MOE) for full-size log stringers are required. In this paper, load and displacement data from the full- size bending tests are used to demonstrate that taper near midspan has the greatest effect on the MOE used in common log bridge design methods, where the logs are assumed to have constant cross sections. This paper proposes a method to estimate a MOE that can be used in a constant cross-section model given the geometry of the particular log of interest, and the MOE from full-size bending tests calculated when considering actual log geometry.     

利用度量误差模型方法建立海南省桉树、木麻黄、马占相思重量与材积相容性模型

利用海南省按树、木麻黄、马占相思实测数据,采用度量误差模型方法,研究建立树干去皮材积与重量相容性联立方程,并对使用普通非线性回归方法和度量误差模型方法得到的重量估计结果进行对比分析。结果表明：对于带有度量误差的重量模型,使用度量误差模型方法进行估计效果更好;所建立的树干去皮材积与重量相容性联立方程拟合效果均较好,且二元明显优于一元,采用一元材积的重量模型预估精度达到96％以上,采用二元材积的重模型预估精度达到98％以上。     

Segmented models for stress-strain diagrams

Summary Tension and compression stress-strain data from tests of wood specimens were mathematically described by 2- or 3-segment models, respectively. Three or four parameters are required by the segmented models, but these are easily obtained from regression analysis of the digitized data. One required parameter is Young's modulus. The model parameters varied with moisture content, and it was possible to regenerate typical stress-strain diagrams at a variety of moisture levels for use in a finite-element program. This form of analysis makes it possible to demonstrate statistically that wood stress-strain diagrams have an initial linear segment, and that the stress-strain diagrams are not entirely curvilinear as some have proposed. The author gratefully acknowledges the discussions with Dr. T. E. McLain which helped to simplify these models