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Productivity and site data from 187 temporary sample plots wereanalysed by multiple regression analysis to derive models inwhich site variables accounted for 78–86 per cent of thevariation in Sitka spruce productivity (General Yield Class,GYC). Climatic variables (accumulated temperature and windiness)extrapolated from meteorological data and tatter flag resultsaccounted for up to 78 per cent of the variation, the contributionof edaphic factors being small. The best regression models wereassociated with confidence limits of about ± 2.5 m3 ha–1y–1 and the mean error for predicting GYC for a forestblock (acquisition) was calculated to be ±1 m3 ha–1y–1 These figures were confirmed by the results of a validationsurvey and the application to field prediction of productivityis described. 相似文献
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An experiment in Helmsdale Forest (Highland Region, Scotland)examined the effects of shelter and weed competition on Sitkaspruce (Picea sitchensis (Bong.) Can.) and lodgepole pine (Pinuscontorta Douglas ex Loudon). Different levels of shelter fromwind were achieved by using netting and were measured usingtatter flags. Three treatments compared weed competition byremoving no vegetation, heather (Calluna vulgaris L.) only orall ground vegetation respectively. Results indicate a definiterelationship between material lost from tatter flags and treedry weight at five years. Even the smallest increase in shelterresulted in increased growth of Sitka spruce and the beneficialeffect of shelter became most apparent 4 to 5 years after planting.Tree dry weight was found to be correlated with root collardiameter and height but not fifth year height increment. Resultsfrom weeding treatments were unclear and differed between species.This was because bird damage interacted with weeding, the completelyweeded plots being most heavily damaged; and because the methodof hand weeding (pulling out the whole plant including roots)damaged fine tree roots. Bird damage was prevented by nettingbut in unnetted plots it was found impossible to separate birddamage from other factors although it was clearly more seriouson lodgepole pine. 相似文献
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Accurate and reliable evaluation of site suitability for the cultivation of selected species and availability of potential timber yield information is vital for the assessment of afforestation projects. This study examined the relationship between site index and environmental factors in Douglas-fir (Pseudotsuga menziesii var. menziesii) plantations in the province of Firenze (central Italy). The aim was to predict site index by readily measurable factors. The influence of climatic (temperature and rainfall), topographic (elevation, aspect, topographical exposure, etc.) and soil (pH, texture, etc.) on Douglas-fir site index was evaluated by multiple regression analysis exploiting data from 71 plots distributed across the study area. Approximately 58% of the observed site index variation is explained by annual rainfall, water surplus, clay content, calcium-carbonate content and east–west component of aspect. Climatic factors directly related to water balance have a greater influence on the productivity of examined Douglas-fir plantations than examined topographic and soil factors. Results of the study are ecologically sound and of practical value for field foresters, with reference to the study area. The precision of the model may be only indicative for assessing site index for single sites. At a landscape mapping level, estimate reliability is quite appropriate. 相似文献
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Intraspecific variations in the water relations and stomatal response of Quercus ilex L. were analyzed under field conditions by comparing trees at two locations within a Mediterranean watershed (l'Avic, Catalonia, NE Spain). Distinct environmental gradients exist between the two sites (referred to as ridge top at 975 m and valley bottom at 700 m) with greater soil depth for water storage, reduced radiation, reduced wind and higher water vapor pressure deficits at the valley bottom than at the ridge top. Osmotic adjustment and changes in tissue elasticiity did not significantly increase drought resistance in the trees studied. The leaf-to-air vapor pressure difference (Deltaw) threshold for inducing stomatal closure was higher at the ridge top (15.6 kPa MPa(-1) +/- 0.5 SE) than at the valley bottom (9.8 kPa MPa(-1) +/- 1.0 SE). However, increases in Deltaw beyond the threshold were followed by greater reductions in leaf conductance of trees at the ridge top than at the valley bottom. At both sites, maximum leaf conductance was related to predawn shoot water potential which, in turn, was related to watershed stream flow. The effects of water deficits during the dry summer of 1989 were more severe in trees at the valley bottom than at the ridge top. During periods of high evaporative demand, site-specific differences in the control of water loss led to more conservative water use by trees at the ridge top and, thus, to even greater drought avoidance (higher predawn water potentials) in late summer. 相似文献
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【目的】研究定向刨花板(OSB)的各向异性,探讨OSB面内剪切模量动态和静态测试方法,以提供一种快速、简便、重复性好、精度高的动态测试方法测量和分析OSB弹性常数。【方法】应用ANSYS程序计算OSB自由板和悬臂板试件的振形系数,给出振形系数依赖于板长宽比和宽厚比的关系式,通过仿真计算、动态试验和方板静态扭转试验验证其正确性。动态试验测试OSB剪切模量试件从一块整张OSB上下料制作,分为3个方向,即沿整板纵向下料制作的试件(0°或x向)、横向方向下料制作的试件(90°或y向)和沿与纵向呈45°方向下料制作的试件;方板扭转试验测试OSB剪切模量试件沿整板纵向或横向下料制作;动态测试OSB纵向、横向和45°方向弹性模量以及面内剪切模量和45°方向剪切模量。【结果】OSB实测纵向弹性模量是横向弹性模量的2.89倍,45°方向剪切模量小于面内剪切模量。正交各向异性材料方板扭转试验测试剪切模量推算公式需用±45°方向应变测量值的差值进行推算,将其用于OSB,测得的静态剪切模量与动态测试的剪切模量相当吻合。【结论】OSB弹性模量具有方向性,纵向最大,横向最小,45°方向介于二者之间;自由板扭转振形法和悬臂板扭转模态法适用于动态测试OSB面内剪切模量,其正确性得到方板扭转试验验证;0°和90°OSB动态测得的剪切模量几乎相等,可作为OSB面内剪切模量Gxy的估计值;OSB不宜按单向复合材料处理,在理论分析时宜按正交各向异性处理,OSB45°方向的剪切模量G45°相似文献
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This paper compares five different methods of wind exposureassessment in an attempt to identify a method that could servein windthrow hazard assessment. The candidate methods that wereselected are: a wind tunnel simulation, two numerical modelsbased on air flow behaviour (MC2 and Strongblow) and two empiricalmethods (Topex and Topex-to-distance). Best correlations withthe wind tunnel results were observed with Strongblow and Topex-to-distance.For MC2, significant correlations were obtained at high windspeedsbut not at lower windspeeds. Ranking of windiness by topographicposition was identical for the wind tunnel, Strongblow and Topex-to-distance.Wind direction estimation by MC2 showed little sensitivity totopography, especially at higher windspeeds. This fact can beattributed both to the version of MC2 used and the conditionsin which the simulations were performed. The estimation of windspeedby direction obtained with Strongblow also appeared not to bevery reliable. The satisfactory performance of Topex-to-distanceand the ease with which this method can be calculated wouldmake it appropriate for inclusion in a windthrow hazard ratingsystem. 相似文献
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Plantation forestry is one of the most important approaches to restoring forest cover in China. Of the remaining sites suitable for afforestation in China, 52?% are considered harsh and only 13?% considered good, which indicates that successfully establishing a plantation in the future will become more and more difficult. Seedling quality in terms of morphology, physiology, and viability is a critical aspect for successful plantation establishment. Due to a large area in need of afforestation, and because of its diverse harsh sites, many studies have focused on nursery techniques of promoting seedling stress resistance, including inoculating ectomycorrhizal fungi, applying plant growth regulators, use of fall fertilization, induced water stresses, or a combined use of these methods. Most of relevant results of this research have been published in Chinese, and are unknown to researchers from other countries. Moreover, no comprehensive review of stress resistance research in forest tree seedlings in China has been completed. Therefore, this review intends to provide a concise synthesis of literature related to plant manipulation techniques that offer seedling stress resistance in Chinese nurseries, discuss potential shortcomings of these studies, and define priorities for future seedling stress resistance research. With this paper we hope to enhance communication about nursery and plantation seedling culture among researchers from China and other countries. 相似文献
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《Forest Ecology and Management》1998,111(1):15-22
We examined the floristic significance of soil seed banks in relation to valley, midslope and ridge sites in a 70–90-year old forest in northeastern Connecticut. A-horizon mineral soils were collected to 5 cm depth in the early spring from forest understory sites across the topography. Samples from each of the sites were exposed to full sun within a greenhouse. Records of germination were made at regular intervals over a 60-day period. These showed significant differences among sites in number of species and total number of germinants. Greatest numbers of species and germinants were recorded from valley sites and these progressively declined from midslope to ridgetop. Twenty-five different species were identified. Species were grouped into growth habits – graminoids, herbs, shrubs, trees, and vines. Over 61% of all germinants across all sites were graminoids. Seventy-four percent of all germinants in the valley sites were graminoids, with over 93% of them represented by two sedge species, Carex glaucodea and C. lupulina. On the ridgetop sites graminoids were more evenly distributed among six different species. The percentage in each growth habit changed rank across topographic position with germinants of graminoids and trees most abundant on valley sites; herbs, on midslopes, and shrubs, on ridgetops. All germinants, except for those of the trees, Carex spp., and two herb species were weedy species that were not characteristic of the existing vegetation. Germinants of the trees, Carex spp., and herbs that were characteristic of the existing vegetation were mostly confined to soils from the valley sites. Two weedy herbs, Plantago major and Verbascum thapsus, are exotic introductions that originally came from Europe. Only one vine, Vitis aestivalis, from a midslope site germinated. Species diversity is higher on midslope sites than valleys and ridgetops. The significance of these findings in relation to site productivity and disturbance history is discussed. 相似文献
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P. Charles Goebel Kurt S. Pregitzer Brian J. Palik 《Forest Ecology and Management》2006,230(1-3):43-54
We examined the distribution of ground-flora species (herbaceous and woody species <1 m tall) across riparian areas of northeastern Wisconsin in an effort to understand how hierarchical landscape properties, such as the physiographic system (ground moraine and outwash plain), valley system (constrained and unconstrained), and valley floor landforms influence distribution patterns of ground-flora species and functional plant guilds across riparian areas of small streams and rivers in a glacial landscape. A total of 162 species were recorded on 417 (1 m2) plots stratified by four different valley types that reflect the dominant physiographic system and valley system (constrained ground moraine, constrained outwash plain, unconstrained ground moraine, unconstrained outwash plain) and transverse geomorphic structure (valley floor landforms including floodplains, terraces, slopes, and adjacent uplands). Although distribution patterns of individual ground-flora species are highly variable among the four valley types, canonical correspondence analyses (CCA) of individual valley types indicate that ground-flora vegetation is related strongly to hierarchical landscape properties, including valley type and the transverse geomorphic structure of the stream valley. Vegetation ultimately reflects the influence of hydrogeomorphic processes that shape valley floor landforms. Constrained valley types tend to be characterized by diverse floodplain ground-flora communities dominated by graminoids and pteridophytes, while the terraces and slope plant communities are comprised of facultative upland and obligate upland perennial forb and woody species whose distribution appears to be a function of topographic features, such as aspect. However, ground-flora communities of unconstrained valley types appear to be responding not only to changes associated with the transverse geomorphic structure of the riparian ecotone, but also to more localized changes in environmental conditions associated with flooding and hydrologic regime. As a result, floodplain, terrace, and slope ground-flora communities tend to be diverse, dominated by a mixture of obligate wetland, facultative wetland, and facultative species. Thus, variation in riparian plant community characteristics can be explained using a nested, hierarchical landscape framework to organize and group different riparian settings based on the underlying geomorphic processes shaping stream valleys. Based on these results, we suggest that riparian management zones (RMZs) designed to maintain riparian function should be variable in width rather than fixed, encompassing variation in valley floor landforms and valley walls, regardless of the physiographic system. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(2):185-195
Abstract To enable use of round Scots pine timber in structural frameworks it is necessary to estimate the mechanical properties of the material. This paper presents data on density, bending strength and modulus of elasticity (MOE) of 533 debarked Scots pine logs with diameter from 75 mm to 250 mm sampled from 10 sites in southern Norway. The results show that round timber can have high values of bending strength and MOE, depending on the sites from which the trees have been collected. Some of the variation in bending properties can be explained by visual characteristics, but since a significant proportion of the residual variance is related to sites, criteria for visual strength grading have to be conservative to be valid across all sites. The potential for machine grading based on measuring MOE is better since this model is more accurate and the random effect of site is smaller. 相似文献
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The aim of this study was to estimate a basal area growth model for individual trees in uneven-aged Caspian forests. A survey was conducted in order to find a natural forest without any harvesting activities, a so called ‘untouched forest’ and an area was selected from the Iranian Caspian forest. Three sample plots in the same aspect and of the same forest type were selected. In each plot, total tree height, diameter at breast height, distance of neighbor trees and azimuth were measured. Thirty trees were selected and drilled with increment borer to determine the increment model. Regression analysis was used to estimate the growth model. Results show that, for individual trees, there is a significant nonlinear relationship between the annual basal area increment, as the dependent variable, and the basal area. The results also show that the basal area of competing trees has a positive influence on growth. That the increment is higher with more competing neighboring trees is possibly because plots with higher volume per hectare and more competition, most likely also have higher site index or better soil or better site productivity than the plot with lower volume per hectare. 相似文献
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吴章文 《中南林业科技大学学报(自然科学版)》1989,(2)
1986年4～8月,在油桐重点产区湖南、湖北5县12个地段65个测点,对油桐纯林内的太阳辐射分布进行观测研究,结果表明:油桐林内太阳辐射的垂直分布与树冠形状有关,塔形树冠内的太阳辐射分布均匀,到达量多;水平分布与树冠的方位和枝条的部位有关,南向方位或下坡方向所在方位的到达量多,枝条外端的到达量多;油桐叶片对太阳辐射的吸收率与品种有关,葡葡桐大于小米桐。 相似文献
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立地质量评价和林分生产力预估对于树种选择、森林经营决策至关重要。目前常利用优势高直接估测立地指数以评价同龄纯林立地生产力,而对于混交林、异龄林、无林地以及随时间不断变化的立地则很难用该方法进行立地质量评价,往往通过立地指数—环境因子模型模拟,应用环境因子预测立地指数。文中简述了环境因子与立地指数关系研究概况,从研究尺度、数据来源、关键环境因子选择、预测模型及其拟合评价等方面进行综述,并讨论和展望了立地指数—环境因子的未来研究重点,以期为我国人工林立地质量评价和科学经营提供参考。 相似文献
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Timothy J. Albaugh Johan Bergh Tomas Lundmark Urban Nilsson José Luiz Stape H. Lee Allen Sune Linder 《Forest Ecology and Management》2009
We developed site specific component (stem, branch, and foliage) biomass functions for two sites in Sweden (64° and 57° North latitude) where four treatments (control, irrigated, fertilized, irrigated plus fertilized) were applied in the existing Norway spruce stands (Picea abies L. Karst.) for 17 years. We tested for site effects in the component biomass equations and compared site specific biomass estimates to those generated using published functions ( 19 and 39). Site effects were significant for all components and indicated it would be unlikely to generate equations that well estimate biomass across the Norway spruce range as implicitly indicated in our efforts to generate species biomass expansion factors. We rejected our hypothesis that the published functions would well estimate component biomass for control plots. The published functions did not compare well with site specific component biomass estimates for the other treatments; both published functions well estimated stem mass up to stem mass of 25 Mg ha−1, beyond which stem mass was overestimated, and both functions over and under estimated foliage and branch mass. Nor did the published functions compare well with each other, with stem, foliage and branch mass estimate differences of 12, 55, −8% and 11, 77, and 59% for the southern and northern sites, respectively, when averaged over all treatments and years. Adding limiting resources through fertilization increased stem, foliage and branch mass 57, 11, 18% and 120, 37, and 69% at the southern and northern sites, respectively, which would increase carbon sequestration and available stemwood and bioenergy materials. We recommend that more effort is spent in process-based modeling to better predict mass at a given site and ultimately provide better estimates of carbon sequestration and bioenergy material production changes. 相似文献
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Aitor Gastón Juan I. García-Viñas Alfredo J. Bravo-Fernández César López-Leiva Juan A. Oliet Sonia Roig Rafael Serrada 《New Forests》2014,45(5):641-653
An expert on local flora usually is the best option for plant species selection in most ecological restoration projects; although species selection often needs to be dealt with swiftly as well as on a limited budget, and obtaining the opinion of a local expert may not always be an economically viable alternative. In such cases, species distribution models (SDM) may offer a faster and more cost effective alternative. We asked six experts to rank native tree species according to their suitability at 24 forest sites. The predictive performance of the suitability rankings was evaluated by assessing their ability to discriminate present from absent species in the observed tree assemblages at each evaluation site. We used the area under the receiver operating characteristic curve to calculate the probability that the estimated suitability for a species present at a particular evaluation site is greater than the estimate for an absent species (both picked at random). Suitability rankings were also obtained from the predictions of SDM and the same procedure was used to estimate the predictive performance of the set of models at each site. The experts offered concordant suitability rankings at almost every evaluation site. There were no significant differences in the predictive performance of the SDM and four of the experts, although the SDM performed slightly better than the other two experts. Our results point to the suitability of the proposed species distribution modeling approach to obtain fast and cost effective recommendations for species selection in forest restoration projects. 相似文献
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利用９个生长较好的马尾松种源区域试验点测定材料,建立２４个种源在不同纬度上９年生树高的Ｇａｕｓｓｉａｎ反应函数,发现３个反应函数参数（模式纬度、内稳定性参数和尺度参数）具有显著的地理变异模式。北部种源大多在其原产地以南３～６个纬度的区域内生长表现最佳,而南部种源的原产地大致也是其生长的最适地。一般来讲,南部种源较北部种源具有较高的内稳定性和遗传可塑性,适宜栽植的区域较广。根据优良种源在不同纬度上的生长优势,并考虑到气候等安全因素,为几个马尾松优良种源确定了适合的推广栽植范围。 相似文献
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森林生产力与立地条件的相关性分析——以宁明县的马尾松和桉树森林生产力为例 总被引：1，自引：0，他引：1
以广西主要树种马尾松和桉树在宁明县的森林生产力为例,采用生物量连续函数法求算林地生物量,据此推算样地生产力,利用高精度的1：10000数字高程模型（DEM）求算研究区域的坡向、坡度、海拔,运用TPI指数求取坡位和地貌类型,利用P值检验法分析研究不同树种的森林生产力与立地条件的相关性。结果表明：立地因子与马尾松、桉树生产力相关性较高,但相关性在树种间存在差异性;海拔、坡位和土壤种类这三个因子均对马尾松与按树的生产力有制约作用;地貌类型和土层厚度因子对马尾松影响明显,而坡向和成土母岩因子则对桉树影响明显;坡度对两树种生长的影响均较小。由此可见,森林生产力与立地条件的相关程度取决于森林树种,不同树种的相关性结果不一致。研究结果为正确地构建森林生产力的预测估算模型和合理地进行营造林树种布局规划提供理论依据。 相似文献