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81.
Walter Seidling 《European Journal of Forest Research》2007,126(4):529-544
Crown transparency estimates of Scots pine, Norway spruce, common beech, pedunculate and sessile oak, annually surveyed between
1990 and 2004 within a grid over Germany, provide a suitable response variable to study drought effects on forest trees. Major
climatic factors, available on a monthly basis as plot-specifically interpolated values and parameters of site and stand conditions,
biotic and other relevant factors were used as predictors in different cross- and length-sectional, and longitudinal models.
Stand age is a considerable and most constant driver of crown transparency in all species. Pine, spruce and beech responded—mainly
with a delay of 1 year—with some foliar loss in areas where there was a surplus of temperature after the generally hot and
dry summer of 2003. Parallel time-series analyses delivered species-specific geographic large-scale patterns with delayed
or recent precipitation deficits or temperature surpluses. Even if beech is partly responding in current years with leaf loss
towards precipitation surpluses, defoliation is especially high 1 year after hot summers, partly a result of high seed sets
after such summers. Crown condition of oak responds in dry and warm areas according to the drought stress hypothesis, however,
in cool and wet mountainous ranges oak responds after wet summers with higher defoliation. Longitudinal approaches revealed
for all 4-tree species significant relationships between crown condition and deviations from the long-term means of temperature,
precipitation but also global radiation and wind speed. Results do not always match the drought stress hypothesis, however,
this is not to expect considering the heterogeneous site, stand and climatic conditions across Germany. Complex interactions
of climatic and biotic factors also impede simple relationships. Soil-related clusters reveal higher sensitivity of spruce
and beech towards climatic drought factors on more acid soils with thin humus layers. Also clusters constructed from plot-specific
courses of defoliation reveal groups with rather closer relationships like a group of pine plots in the Oberpfalz, which seems
to be especially sensitive to summer drought. 相似文献
82.
杉木苗根系打泥浆后造林不仅能提高造林成活率,而且与当年生幼树的根系地径和树高的生长关系密切,在不同的造林时间或造林后的不同时间,其影响程度是不同的。 相似文献
83.
Effect of particle shape on linear expansion of particleboard 总被引:2,自引:0,他引:2
Hinoki (Japanese cypress) strand with 0.6mm thickness was hammer-milled to prepare three types of particles that had the same thickness but different lengths and widths. Screen analysis and image analysis were conducted to evaluate the shape and distribution of the particle dimensions. Laboratory-scale particleboards were fabricated at three density levels using these particles. To determine the true effect of particle shape on the linear expansion (LE) of the board, these boards exhibited almost the same temperature behavior during pressing, the same density profile, and the same bending properties at each board density level. LE at 40°C and 90% relative humidity of the board was found to be affected by the particle shape. The board composed of small particles showed a larger LE at the same density level. It was considered that the out-of-plane orientation angle of the particles affected the LE of the boards. Thickness swelling and internal bond strength were also affected by the particle shape.Part of this report was presented at the 50th annual meeting of the Japan Wood Research Society, Kyoto, April 2000 相似文献
84.
根据1993年省森林资源清查、森林资源消耗量及消耗结构的调查资料,以可持续发展的理论为指导,采用线性规划对我省的林种结构进行了研究。研究结果:河南省现阶段的林种结构应为:用材林∶防护林∶经济林∶薪炭林∶特用林=349∶159∶237∶211∶44。 相似文献
85.
高分辨率遥感图像均值调整法分割技术研究 总被引:1,自引:1,他引:1
遥感图像分割是将以像元为基础的图像转化为以对象为基础的过程,因此,遥感图像分割是遥感图像高级分析的基础.对于中、低分辨率遥感图像来说,单个像元的面积较大,且混合像元现象严重,图像分割会产生较大的误差.高分辨率遥感图像单个像元的面积较小,分割后图像上单个对象内含若干像元,便于分析和提取信息.以高分辨率遥感图像Q u ickB ird和IKONO S为研究对象,采用均值调整法对图像进行分割和精度检验.结果表明:采用均值调整法进行高分辨率遥感图像分割具有较好的效果,图像分割的速度和精度均较高. 相似文献
86.
Guillermo Trincado Curtis L. VanderSchaaf Harold E. Burkhart 《European Journal of Forest Research》2007,126(2):253-262
A height–diameter mixed-effects model was developed for loblolly pine (Pinus taeda L.) plantations in the southeastern US. Data were obtained from a region-wide thinning study established by the Loblolly
Pine Growth and Yield Research Cooperative at Virginia Tech. The height–diameter model was based on an allometric function,
which was linearized to include both fixed- and random-effects parameters. A test of regional-specific fixed-effects parameters
indicated that separate equations were needed to estimate total tree heights in the Piedmont and Coastal Plain physiographic
regions. The effect of sample size on the ability to estimate random-effects parameters in a new plot was analyzed. For both
regions, an increase in the number of sample trees decreased the bias when the equation was applied to independent data. This
investigation showed that the use of a calibrated response using one sample tree per plot makes the inclusion of additional
predictor variables (e.g., stand density) unnecessary. A numerical example demonstrates the methodology used to predict random
effects parameters, and thus, to estimate plot specific height–diameter relationships. 相似文献
87.
Charles J. KREBS 《Integrative zoology》2015,10(3):233-240
Population ecology is the most mature of the three subdisciplines of ecology partly because it has a solid mathematical foundation and partly because it can address the primary questions of distribution and abundance with experimental protocols. Yet there is much left to do to integrate our population knowledge into community and ecosystem ecology to help address the global issues of food security and the conservation of biodiversity. Many different approaches are now being developed to bring about this integration and much more research will be necessary to decide which if any will be most useful in achieving our goals of explaining the changes we see in the distribution and abundance of animals and plants. Food web ecology would appear to be the best approach at present because it uses the detailed information of the population ecology of particular species in combination with data on consumer–resource interactions to apply to the applied problems of biodiversity conservation, food security, pest management and disease prevention. If we can use our understanding of population ecology to address the practical problems of our time in a creative way, we will benefit both the human population and the Earth's biodiversity. Much remains to be done. 相似文献
88.
针对树材气体渗透性与气体在管胞中的流动特性和规律紧密相关,研究管胞的气体渗透流阻,可以获得关于针叶树材气体渗透性更深入的认识。本文从针叶树材管胞解剖结构出发,运用流体力学理论,导出了管胞3个纹理方向渗透气体流阻的数学表达式,并由此计算了针叶树材管胞的气体渗透系数。计算结果表明,管胞流阻可以描述气体渗透阻力的分布情况,反映气体渗透性在3个纹理方向的差异,在木材细胞层次揭示针叶树材气体渗透性的机制。 相似文献
89.
云南玉溪市老城中心面临着传统商业衰退以及城市化进程中对中心商业区升级的矛盾,通过引入城市网络的概念,将原本集中布置的商业区延展为一个连续的商业网络,并设计穿越整个地块的开放绿地空间,将保留的历史建筑融合在绿地网络之中,以此保持和发展该地区原有的文化和经济氛围,并形成多元化的土地利用方式。 相似文献
90.
茶叶等级评价是检测茶叶品质的一项重要技术指标。通过提取红茶高光谱成像技术下的图像特征和光谱特征,构建一种基于图谱融合方法、适用于英德红茶等级评价的快速无损判别模型。首先制备3种不同等级的红茶样本,采用t分布-随机近邻嵌入和主成分分析对光谱数据进行降维可视化分析,然后从影响内在品质角度用连续投影法提取每种化学值的特征波长,通过多模型共识策略和竞争性自适应重加权算法-连续投影法筛选得出表征其内在品质的最佳特征波长组合,并建立基于遗传算法优化支持向量机的等级判别模型;其模型的训练集准确率为88%,预测集准确率为78.33%。为了融合外形纹理差异,先提取最佳特征波长组合对应的高光谱图像;采用图像掩膜消除背景的干扰和采用图像主成分分析消除多波长图像间的冗余信息,然后采用灰度共生矩阵和局部二值化算法提取主成分前三维主成分图像与特征光谱融合,并建立基于特征融合的遗传算法优化支持向量机等级判别模型,且基于第三主成分图像特征融合模型判别效果最佳,训练集准确率提升至98%,预测集准确率提升至96.67%。 相似文献