排序方式： 共有14条查询结果，搜索用时 31 毫秒
1.
用50%甲胺磷、25%灭幼脲Ⅲ号悬浮剂、10%灭百可乳油对国槐进行树干注射防治害虫试验.结果表明:3种药剂对槐蚜和国槐尺蠖均有较好的防治效果,田间持效期达43 d和50 d.3种药剂的建议使用浓度为50倍液. 相似文献
2.
3.
4.
对不同规格的母竹苗造林与出笋率关系的调查结果表明 :农地毛竹出笋率是山地的 2 0 9倍 ,竹苗规格以A3 B3 C2 组合的出笋率最高 ,其次为A3 B3 C1和A1B1C2 组合。 相似文献
5.
Vindhya Prasad Tewari K. M. Mariswamy A. N. Arunkumar 《Journal of Sustainable Forestry》2013,32(3):213-229
Tectona grandis (teak) is one of the most important timber species worldwide and India is one of the major teak growing countries. Though some volume equations were developed in the past in India, merchantable volume equations (any top diameter or bole length) are not available. Moreover, the models developed were neither quantitatively and qualitatively evaluated nor validated with independent data sets. Hence, the objective of this study was to develop appropriate volume equations to predict total tree volume and merchantable volume for teak in Karnataka. Linear and non-linear equations were used to model the relationship of the volume with respect to diameter at breast height (dbh) and total height. Merchantable volume equations for estimating merchantable volume to any minimum top diameter or bole length have also been constructed. The equations tested mostly fitted well to the data. Other models developed elsewhere tended to underestimate the volume, especially at dbh ≥ 23 cm. The geometric cylinder volume equation, in combination with a stem form factor of .40, is widely used for teak in Karnataka but they were found to be less precise compared to regression equations when applied to the present data set. Model validation indicated that models should be calibrated with local data for greater accuracy in the prediction. 相似文献
6.
枫香（Liquidambar formosana）是我国闽北林区重要的乡土树种,生长迅速、适应性强,在观赏、药用、用材等方面都有着重要作用。单木模型是林分模型的基础,通过建立单木生物量生长模型,在时间维度上分析林木生物量生长的动态变化,以期为全面评价森林的固碳能力提供科学依据。采用典型抽样的方法,从广东省9个地区的一类样地附近抽取枫香样木40株（天然起源25株,人工起源15株）,破坏性实测各组分的生物量并进行树干解析得到样木的生物量生长数据。基于逻辑斯蒂（Logistic）、坎派兹（Gompertz）和理查德（Richards）3种基础生长方程,利用哑变量的方法,建立分起源和立地等级的枫香干材生物量生长模型,以决定系数R2、均方根误差RMSE、总相对误差TRE和平均预估误差MPE 4个指标来评价各模型,进而分析枫香干材生物量的生长过程。结果表明,Richards方程在基础模型中效果最佳（R2=0.61,RMSE=50 kg）;与Richards方程相比,哑变量模型R2提高了11%,RMSE降低了7.95 kg;起源与立地等级对枫香干材生物量均产生了较大影响,在天然起源的高立地等级条件下,枫香干材理论最大连年生长量和平均生长量分别在其生长的第23年和第38年到达。 相似文献
7.
Roger F. Walker Robert M. Fecko Wesley B. Frederick Watkins W. Miller Dale W. Johnson 《Journal of Sustainable Forestry》2013,32(6):469-492
Variability of postfire injury and stand and individual tree factors that affected survival responses of eastern Sierra Nevada conifers to wildfire were examined. Prefire measurements served as a basis of comparison for postfire conditions in a mixed conifer stand located in the eastern portion of the Lake Tahoe Basin and provided insight into predisposing influences on survival. Species composition consisted primarily of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and California white fir (Abies concolor var. lowiana [Gord.] Lemm.) along with a minor component of sugar pine (Pinus lambertiana Dougl.). Postfire survival was higher in Jeffrey pine than white fir but was highest overall in sugar pine. Catastrophic crown loss occurred less frequently in Jeffrey pine than in the fir but was least common in sugar pine. Survival generally increased with tree size, but this relationship did not extend to the largest trees in the stand. Among an array of regression models used to evaluate selected variables for their predictive capacity regarding postfire survival, prefire stand density was found to negatively influence that of Jeffrey and sugar pine, and survival of Jeffrey pine and white fir was negatively correlated with bole char. These results provide natural resource managers guidance in the selection of viable trees for retention during the salvage harvesting operations that often follow wildfire events. 相似文献
8.
《Scandinavian Journal of Forest Research》2012,27(6):571-581
A method and algorithm for reconstructing the three-dimensional (3D) surface of stems based on terrestrial laser scanner data from standing trees is presented. Laser scanning delivers a dense cloud of points, and this raw point data are filtered for deriving a digital terrain model and subsequent fitting of a parametric stem model. The stem model is made up of a sequence of successive cylinders that overlap in space; each cylinder is parameterized by its orientation and radius. The model is estimated iteratively from a given starting point and by adding cylinder segments. Successive segments are added whenever criteria on deviation in orientation and radius relative to the previous cylinder and a fit statistic to the point data are met. The method has proven applicable when applied to a European beech tree and a wild cherry tree from dense forest stands. The use of the resulting 3D reconstruction of tree stems in respect to diameter in breast height and height of crown base calculation, as well as taper, sweep and lean assessment of standing trees, is described. Finally, desirable future improvements to the basic algorithm are discussed. 相似文献
9.
10.
Pessimistic forecasts often suggest that widely spaced trees enjoying free growth (no competition with other trees) will fail
to provide high quality timber. This challenges the temperate agroforestry practice of planting widely spaced trees to produce
high quality timber. We analyse tree growth data from recent temperate agroforestry plantations aged three to eight years,
featuring low tree plantation densities (50 to 400 stems ha−1), the association of trees with intercrops (silvoarable systems)
or animals (silvopastoral systems), and the use of plastic shelter tubes to protect trees (1.2 to 2.5 m high) and avoid damage
by cattle or sheep in pastures or facilitate maintenance in silvoarable systems. The plantations are located in climates ranging
from Mediterranean, dry central temperate plains, cold and wet central uplands to mild oceanic areas. Some plantations included
a forestry control (high density of plantation, no tree shelter, no intercropping nor grazing). Trees were evaluated for height
and diameter growth and stem form (straightness and absence of knots). Trees in most agroforestry plots grew satisfactorily,
often faster than in forestry control plots. In some experimental plots, average annual height increments as high as 1 m and
diameter increments as high as 1.5 cm were observed. Few agroforestry plantations were unsuccessful, and the reasons for the
failures are discussed: animal damage in silvopastoral plots, but also a wrong choice of tree species unsuitable for local
soil and climate characteristics. From these early results we can formulate some guidelines for designing future agroforestry
plantations in temperate climates, concerning tree density, use of tree shelters and care required for widely spaced trees.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献