The four-line model of the Triangular Running Skyline system: Scale model test

The four-line model of the Triangular Running Skyline (TRS) system is the theory generalized from the previous TRS theory to treat the main and slack-pulling lines separately. The previous theory,i.e., the three-line model, treated the main and slack-pulling lines as a single line to simplify the solution. The first part of this study developed numerical procedures for the four-line model. In this paper, to empirically ascertain the accuracy of the four-line model theory, a series of static equilibrium tests was carried out using a reduced scale model of the TRS system. The result proved that the theory of the four-line model has the same accuracy as that of the three-line model. However, the result also proved that the carriage may have to be located lower than the designated height. Thus, it has been proved that the development of a certain adjusting method is necessary to move the carriage of the TRS system closer to the designated point. A part of this paper was orally presented at the Second Annual Meeting of the Japanese Forest Engineering Association, November 18, 1995, Tokyo. This English title is a tentative translation from the original Japanese by the authors of this paper.     

Agroforestry pathways for the intensification of shifting cultivation

As a system of land use which entails the deliberate association of trees with herbaceous field crops in time, shifting cultivation is one of the most ancient, widespread and, until recently, ecologically stable forms of agroforestry. However, under pressure of population and competing uses for land and labour, traditional swidden systems have been observed historically to undergo more or less predictable processes of intensification. Since shifting cultivation is an indigenous form of agroforestry, scientific agroforestry is not, strictly speaking, an alternative to shifting cultivation, but rather a systematic approach to the recombination of its basic elements into more intensive, sustainable and politically viable forms of land use, whenever pressures signal the need for change in traditional swidden systems.Different agroforestry options open up from different stages of intensification in swidden systems. A review of evolutionary typologies of shifting cultivation gives rise to a framework for the identification of agroforestry interventions and development pathways appropriate to specific systems. technological proposals are limited to a short list of the most promising agroforestry interventions in main sequence swidden systems. These include integral taungya, economically and biologically enriched fallows, variations on the alley cropping theme, and various tree crop alternatives to annual cropping systems. Examples and quantitative data are cited to substantiate the main hypotheses behind the proposals.     

Crown projection area of young Pinus sylvestris: A model and its test

In this study we applied a theoretical model for determining the projection area of a Scots pine (Pinus sylvestris L.) crown in different directions. The model is based on the assumption that the foliage elements (shoots) are randomly distributed within a symmetrical crown envelope. The model was tested using photographically measured data for three young Scots pine crowns. The compatibility between calculated and measured values was satisfactory.     

Study on half-scale model test for light-frame shear wall

A half-scale model of a light-frame shear wall was developed to evaluate the racking performance of a fullscale shear wall (prototype). The effect of nail size on the performance of the shear wall was also investigated using models constructed with three types of nail. Materials for the model were determined through experimental methods, which included nail-head push-through, stud-to-sheathing nail connection, and static bending tests. Materials with which the model was made to be in similarity to the prototype were three-layer 4.8-mm plywood, 39.72-mm long nails, and 1 × 2 lumber cut from 2 × 4 studs. In accordance with ASTM E 72 and ASTM E 564, racking resistance tests were conducted on 20 shear walls. The results showed that the maximum load capacities of the prototype walls could be evaluated by the model without significantly different failure modes. Tests on the effect of nail size revealed that increasing the nail head diameter may improve the performance of shear walls.Parts of this paper were presented at the International Conference on Effective Utilization of Plantation Timber (ICEUPT'99), Chi-Tou, Taiwan, May 1999; and the World Conference on Timber Engineering (WCTE2000), Whistler, Canada, July–August 2000     

A retrieval and validation method for shelterbelt vegetation fraction

Shelterbelts are important in defending against natural disaster and maintaining ecological balances in farmland. Understanding of the shelterbelt vegetation fraction is fundamental to regional research of shelterbelts using remote sensing. We used SPOT5 imagery with 10×10m spatial resolution in combination with knowledge of the characteristics of shelterbelts to develop a method for retrieval of the vegetation fraction of shelterbelts by the pixel un-mixing model. We then used the method to retrieve values for shelterbelts in study area. By combining the parameters of photographic images with characteristics of shelterbelts, we developed a method for measuring the vegetation fraction of shelterbelts based on an advanced photographic method. We then measured the actual values to validate the retrieval result. The multiple correlation coefficients between the retrieved and measured values were 0.715. Our retrieval and measuring methods presented in this paper accurately reflect field conditions. We suggest that this method is useful to describe shelterbelt structure using remote sensing.     

Assessment of tree response to drought: validation of a methodology to identify and test proxies for monitoring past environmental changes in trees

A thinning experiment stand at Avoca, Ballinvalley, on the east coast of the Republic of Ireland was used to test a developed methodology aimed at monitoring drought stress, based on the analysis of growth rings obtained by coring. The stand incorporated six plots representing three thinning regimes (light, moderate and heavy) and was planted in the spring of 1943 on a brown earth soil. Radial growth (early- and latewood) was measured for the purpose of this study. A multidisciplinary approach was used to assess historic tree response to climate: specifically, the application of statistical tools such as principal component and canonical correlation analysis to dendrochronology, stable isotopes, ring density proxy, blue reflectance and forest biometrics. Results showed that radial growth was a good proxy for monitoring changes to moisture deficit, while maximum density and blue reflectance were appropriate for assessing changes in accumulated temperature for the growing season. Rainfall also influenced radial growth changes but not significantly, and was a major factor in stable carbon and oxygen discrimination, mostly in the latewood formation phase. Stable oxygen isotope analysis was more accurate than radial growth analysis in drought detection, as it helped detect drought signals in both early- and latewood while radial growth analysis only detected the drought signal in earlywood. Many studies have shown that tree rings provide vital information for marking past climatic events. This work provides a methodology to better identify and understand how commonly measured tree proxies relate to environmental parameters, and can best be used to characterize and pinpoint drought events (variously described using parameters such as like moisture deficit, accumulated temperature, rainfall and potential evaporation).     

对当前西部退耕还林政策中有关做法的思考

退耕还林政策是一项关系国家前途命运的大事 ,涉及千千万万农民的切身利益 ,有必要深入调查研究。对退耕还林政策中“以粮代赈”、“报账制”、“无偿提供种苗”、“个体承包”等问题提出自己的看法。     

A generic process-based SImulator for meditERRanean landscApes (SIERRA): design and validation exercises

Understanding the interrelationship that exists between landscape patterns and fire history requires a great range of case studies to reduce the effects of substrate and climate. The lack of such data has led to an increasing need for spatially explicit models dealing with vegetation dynamics. The challenge is to find a compromise between process complexity, realism and landscape applications. In this paper, we describe a simulation approach (SIERRA) focussed on the particular case of Mediterranean-type communities subjected to large recurrent fires. Firstly, disturbance response strategies used in “vital attributes models” are used to simulate the influence of fire on vegetation dynamics, focussing in particular on the integration of specific regeneration abilities of Mediterranean species. Next, the model takes a functional approach towards carbon and water budgets to drive competition and simulate the seasonal vegetation water status to estimate fire risk. Spatial processes of seed dispersal, surface water fluxes depending on topographic convergence, and fire spread are used to accurately simulate landscape heterogeneity. The model offers a spatial representation of the annual course of vertical structure of biomass and carbon fluxes coupled with the weekly soil water budget and evapotranspiration rates. Some simulation and validation exercises are presented to illustrate both the functional properties on a Quercus ilex stand, and the fire-prone community dynamics of a maquis shrubland. These initial results will form a strong basis for using the model to test hypotheses about fire-prone landscape patterns.     

Building on traditional shifting cultivation for rotational agroforestry: Experiences from Yunnan,China

Under population pressure, the transition from the long-fallow shifting cultivation to short-fallow shifting cultivation with associated land degradation has been claimed to be unavoidable and sedentary cultivation would be advocated as the only future to replace the unsustainable short-fallow shifting cultivation in the mainstream research and development. The recent development of the shifting cultivation system in Yunnan, Southwest China demonstrates how local peoples hybridize elements of the traditional shifting cultivation and the new agriculture and forestry technologies as a new and dynamic rotational agroforestry system for economic development without losing the natural resource base. Comparing experiences in other regions and under some conditions, the rotational agroforestry system may be promoted as a viable option for development of the shifting cultivation system in the mountainous areas where the introduction of sedentary agriculture is much constrained.     

A global model for the hot-pressing of MDF

The hot-pressing operation is the final stage in medium-density fiberboard (MDF) manufacture, where the mattress of fibers is compressed and heated to promote the cure of the resin. In MDF hot-pressing, many physical, chemical and mechanical processes are involved; the complexity of this operation arises from the fact that they are coupled. A global model is presented for this operation that integrates all mechanisms involved in the panel formation (heat and mass transfer, chemical reaction and mechanical behavior). This approach results in a two-dimensional unsteady state problem, which involves the knowledge of the polymerization kinetics of the resin, the transport properties and material properties, which are position and time dependent. This dynamic model was used to predict the evolution of the variables relating to heat and mass transfer (temperature, moisture content, gas pressure and relative humidity), as well as the variables relating to mechanical behavior (pressing pressure, strain, modulus of elasticity and density). The model performance was analyzed using the typical operating conditions for the hot-pressing of MDF and the results were compared to the experimental data from an industrial MDF press. We concluded that the model could predict in an acceptable way the behavior of the key variables for the control of the pressing cycle, as well as some physico–mechanical properties of the final product. The improvement of this model will permit the scheduling of the press cycle to fulfill objectives of minimization of energy consumption, better quality of the board and increased process flexibility.     

CamFlores: A FLORES-type model for the humid forest margin in Cameroon

A FLORES-type model in the Simile modelling environment is being developed for three villages in the Humid Forest Benchmark area of southern Cameroon. The modelling project seeks to investigate the effects of introduction of new crop varieties and improved farming systems on the long-term maintenance of stable mosaics of forest and agriculture, within the context of the international Alternatives to Slash and Burn programme. Biophysical data have been collated, and socio-econnomic and tenure data have been acquired in spatially-explicit ways. Maps of land-cover at village and benchmark scale are being prepared from detailed and semi-detailed satellite imagery, using a nested legend system that allows linking of maps at different scales. These data enable the initial construction and parameterisation of the model, and will permit the extrapolation of the results of modelling from the villages to the benchmark, and ultimately to the whole of the Congo Basin humid forests. The prototype version of the model involves 10 households and about 500 land patches, and includes the three agricultural systems dominant in the southern more forested portion of the Benchmark (mixed food-fallow systems, forest melon fields, cocoa plantations) with no rental, sale or other transfer of land. Decision-making at the household level is essentially modelled deterministically, and labour productivity is assumed to be constant between households. This model is now complete, and once it has been adjusted and suitably parameterised, it will be applied to real data from the three test villages. This will require the addition of new farming systems, the introduction of modes of permanent or temporary transfer of land, and modification of the decision model to render it more realistic. The work described in this paper is a part of a project funded by the European Union through ICRAF and hosted at the IITA Humid Forest Ecoregional Centre, Cameroon. The assistance of Valentina Robiglio (JPO GIS specialist), especially in preparation of land-cover maps and in collection of socio-economic data, is gratefully acknowledged, as is the work of IITA ASB village facilitators in collection of field data. The cooperation of IITA, IRAD, CIFOR and ICRAF scientists in providing data for the model and periodically reviewing progress with the modelling process was essential to the progress achieved thus far.     

退耕还林的实践与思考——陕西省延安市宝塔区姚店镇案例分析

1999年退耕还林工程在全国开始启动时 ,各地纷纷出台许多退耕还林的办法和政策以保证田能退得下来林能还得上。而陕西省宝塔区姚店镇却已在描绘已退耕的林地上如何培养后续资源 ,使农民手中有更多的钱可用的蓝图。姚店镇从 1 986年开始退耕还林 ,到 1 999年 ,已发展经济林 2 .4万多亩 ,人均 2亩多 ,林业已成为当地主导产业之一。从 1 997年以来 ,苹果价格每年以 0 .1元 /ｋｇ的速度下滑 ,但当地农民对林业的发展仍充满信心。纵观姚店镇退耕还林的历程 ,给我们留下了许多值得思考的问题。1　姚店镇退耕还林的实践1 1　退耕还林的发展阶段消…     

A diagnostic survey of shifting cultivation in northern Laos: targeting research to improve sustainability and productivity

About 25% of Laos' four million people practise shifting cultivation (mainly of rice) on a third of the country's cropped area. Official policy is to eliminate shifting cultivation by the year 2000. Diagnostic surveys of shifting cultivation were conducted in Luang Prabang and Oudomsay Provinces in northern Laos to understand the practice from a farmer's perspective, to observe fields, and to identify and give priority to problems and research to address problems. Weeds, low and possibly declining soil fertility, intensification of the cropping cycle, rats (plus birds, wild pigs), and insects lowered rice yields or reduced system sustainability. The forest ecosystem has been degraded by logging, burning, and rice monocropping; and potentials for environmental rehabilitation through natural succession are minimal. Farmers cannot adopt high labor and cash cost innovations; and improved fallow is needed as an intermediate step prior to crop diversification, adoption of agroforestry technologies, and sedentary agriculture.     

Quantitative validation and comparison of a range of forest growth model types

Predictions from a range of model types (simplified process-based, a statistical state space, statistical difference, and a hybrid model) were compared to 969 measurements of forest growth across an environmental gradient. The models compared were 3-PG, CANTY, CanSPBL(1.2), and CanSPBL(water). The study made an objective comparison and validation of model types, with the main criterion for comparison being each model's ability to match actual historical measurements of forest growth in an independent data set. A number of stand level forest growth variables were compared including basal area, mean top height, and stocking over 14,058 ha of plantation-grown Pinus radiata in south-eastern New Zealand. Stand variable predictions at 195 permanent plot locations covering a range of elevations from 0 to 660 m were highly correlated with field estimates derived from plot data. The hybrid model CanSPBL(water) on average was the most accurate model in the study where predictions of stocking, basal area, and mean top height were 96%, 96%, and 96% efficient. The statistical-difference equation model CanSPBL(1.2) was equally efficient but on average 3% less accurate and slightly more biased in predictions suggesting that the hybrid model explained differences in growth due to differences water availability and soil type. The process-based model 3-PG predicted stocking and basal area 89% and 88% efficiently. Finally, the statistical state-space model CANTY predicted stocking, basal area, and mean top height 96%, 87%, and 87% efficiently. Results quantify the amount of precision that can be expected from the three model types, and suggest that each approach has strengths and weaknesses.     

An experimental test of a nitrogen uptake and partitioning model for young trees

Simulation models of nitrate uptake and total nitrogen partitioning during the exponential growth phase of one-year-old peach trees (Prunus persica (L.) Batsch.) were tested in an experiment with 88 plants grown in soil-filled containers. Plants were fertilized with (15)N-NO(3) (-) and nitrate uptake estimated by periodic destructive analysis of plants for excess (15)N. Partitioning of N within the trees was followed by the analysis of plant parts for total N and (15)N. The nitrate uptake model, which provides one of the main inputs to the partitioning model, is based on a simplified form of the Michaelis-Menten equation adapted to describe uptake by roots growing in soil layers. The nitrogen partitioning model considers each plant part (e.g., roots, trunk, shoots, leaves) as either a sink or a source for nitrogen. The model uses a flow equation, which is the same for all plant parts, to model the dynamics of nitrogen partitioning in the tree using increases in dry matter of various plant parts as driving force variables. The experiment demonstrated an error in the compartment organization of the partitioning model as a result of which the model failed to simulate changes in root N. A modification of the partitioning model structure to take account of the importance of trunk nitrogen reserves for root growth at the beginning of the growing season, which was indicated by the (15)N data, greatly improved prediction of root N. This modification is discussed in relation to the modeling approach.     

A model of tree-crop competition for windbreak systems in the Sahel: description and evaluation

A model was developed to simulate the effects of competition for soil water and radiation between windbreaks and pearl millet crops in the Sahel. These effects on millet (Pennisetum glaucum (L.) R. Br.) growth were simultaneously simulated for each millet row parallel to the windbreak with small time steps for soil water processes, radiation availability and crop assimilation. The crop routine of the model was based on an existing semi-deterministic model. The soil-water flow was simulated in two dimensions to account for horizontal gradients. Competition for water was expressed by distributing the available soil water between trees and millet in proportion to its uptake rates in a non-competitive situation. Competition for light was incorporated as light reduction through a two-dimensional (windbreak) barrier with time-increasing height and density. Tree parameters were introduced as fixed values or as time-dependent forcing functions. Crop, windbreak trees (Bauhinia rufescens Lam.), and soil data inputs were either field-determined or obtained from literature. Reasonable agreement between simulated and measured soil water content and dry matter production was obtained under the conditions in Niger. Global radiation intensities and soil water contents were simulated satisfactorily as a function of time and the distance from the windbreak. Hence, the model is appropriate to analyse competition for light and water between windbreaks and crops.     

A MCDM-based model for vendor selection: a case study in the particleboard industry

We investigated procurement of raw materials for particleboard to minimize costs and develop an efficient optimization model for product mix.In a multiple-vendor market,vendors must be evaluated based on specified criteria.Assuming sourcing from the highest-scoring vendors,annual purchase quantities are then planned.To meet procurement needs,we first propose a model to describe the problem.Then,an appropriate multi-criteria decision making(MCDM) technique is selected to solve it.We ran the model using commercial software such as LINGO and then compared the model results to a real case involving one of the largest particleboard manufacturers in the region.The model run based real data yielded a procurement program that is more efficient and lower in cost than the program currently in use.Use of this procurement modelling approach would yield considerable financial returns.     

四川省沐川县退耕还林与产业化协调发展成效与作法

沐川县是全国首批 174个退耕还林工程试点县之一 ,近年来 ,已在退耕还林与产业化协调发展方面作了有益偿试 ,找到了生态与经济的最佳结合点 ,形成了“公司 +基地 +农户”等产业化发展模式。通过对沐川县退耕还林与产业化发展的调查 ,总结了沐川县退耕还林与产业化协调发展的成效 ,并对存在的问题进行了剖析 ,提出了建议。