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951.
Urban forests are important for the health of cities. These forests face high anthropogenic pressure, including demands on their multi-functional role. Therefore, the impact of pests-induced disturbances may be greater for urban forests than forests outside of cities. Monitoring of pests in their native environment is an important tool for the management of urban forests. To better understand how pest population density is affected by the forest environment, we used the Oak bark beetle, Scolytus intricatus, as a model organism. The study was carried out in 2014–2015 in the urban forests of Pardubice City, Czech Republic. Pest population density was studied at three levels: branch, tree and patch. The increasing branch diameter was identified as an important variable with a threshold of 70 mm for entrance holes and 45 mm for emergence holes. Increasing host tree diameter at breast height with a threshold of 46.8 cm was statistically significant at the tree level in terms of the number of entrance holes. Increasing spring canopy openness was identified as an important variable at the patch level with a threshold of 50.78% and had a decreasing trend for the number of reared adults and their total body size. Big oak trees with thick branches under closed spring canopy are the most susceptible to attack by S. intricatus. Based on our findings, we propose that the maintenance of mature oaks under open canopies is important for urban forest management. Avoiding mixed plantings of oaks and conifers should promote these open canopies and lead to multiple advantages regarding oak silviculture. 相似文献
952.
Accurately measuring the biophysical dimensions of urban trees, such as crown diameter, stem diameter, height, and biomass, is essential for quantifying their collective benefits as an urban forest. However, the cost of directly measuring thousands or millions of individual trees through field surveys can be prohibitive. Supplementing field surveys with remotely sensed data can reduce costs if measurements derived from remotely sensed data are accurate. This study identifies and measures the errors incurred in estimating key tree dimensions from two types of remotely sensed data: high-resolution aerial imagery and LiDAR (Light Detection and Ranging). Using Sacramento, CA, as the study site, we obtained field-measured dimensions of 20 predominant species of street trees, including 30–60 randomly selected trees of each species. For each of the 802 trees crown diameter was estimated from the aerial photo and compared with the field-measured crown diameter. Three curve-fitting equations were tested using field measurements to derive diameter at breast height (DBH) (r2 = 0.883, RMSE = 10.32 cm) from the crown diameter. The accuracy of tree height extracted from the LiDAR-based surface model was compared with the field-measured height (RMSE = 1.64 m). We found that the DBH and tree height extracted from the remotely sensed data were lower than their respective field-measured values without adjustment. The magnitude of differences in these measures tended to be larger for smaller-stature trees than for larger stature species. Using DBH and tree height calculated from remotely sensed data, aboveground biomass (r2 = 0.881, RMSE = 799.2 kg) was calculated for individual tree and compared with results from field-measured DBH and height. We present guidelines for identifying potential errors in each step of data processing. These findings inform the development of procedures for monitoring tree growth with remote sensing and for calculating single tree level carbon storage using DBH from crown diameter and tree height in the urban forest. 相似文献
953.
为研制精 度较高、 更符合客 观实际 的 林分 材种 出 材率 表, 利用 毛白 杨 林分 标准 地 及造材木资 料, 对毛 白杨单株 木树皮 率的变化 规律进 行了研究 。结果表 明, 树皮 率与 胸径、 树高、年龄呈 显著负相 关, 与林 分密度 呈显著正 相 关, 树 皮 率与 胸径 和 年龄 的单 因 子模 型以 及 树皮率与胸 径、树高 、年龄、林 分密度 的多元线 性模 型, 均 具 有 较高 的 估测 精 度; 在同 一 造 材木上, 树 皮率随材 长段的不 同而变 化, 在相 对长度 70 % 树 高以 下 范围, 树皮 率 随材 长段 增 长而迅速降 低, 但在0 ~20 m 树高 范 围内 , 树 皮率 常出 现 反弹 , 因 此, 应分 材 长 段测 算 树皮 率,进而编 制材种与 出材量 表; 树干 各部位皮 厚 与所 在部 位 直径 具 有十 分密 切 的关 系, 其 相 关模型可用 于立木造 材中树 皮率的估 测。 相似文献
954.
楠木人工林优树选择标准和方法 总被引:7,自引:2,他引:5
本文分别应用小样地法、平均木标准差对比法、综合评分法、优势木对比法对4株预选树(nm-20、nm-19、nm-18、nm-06)进行分析,制定选优标准,确定nm-20为优树。分析结果表明:应用小样地法进行楠木人工林选优最客观、正确,工作量较少。若预选树生长量指标md>40%、mh>30%、mv>140%且形质指标符合,则可确定为优树。 相似文献
956.
景洪农场1998年对1.4 万hm 2 割胶树推广减少割胶刀次、使用复方刺激剂(ET+ CRM)、增加割胶株树、减少胶工人数的新型割胶制度。根据品系、树龄不同,分别采用s/2d/3、(s/4+ s/4↑)d/3+ ET+ CRM、(s/2+ s/4↑)d/3+ ET+ CRM 等割制,同时建立了一套相应的生产、技术管理制度。1998 年比1997年干胶增产3.72% ,胶工人均产干胶比1997 年增加50.86% ,新增经济效益2 188.5 万元 相似文献
957.
本文全面地介绍了国际上在树木年代学和树木气候学的理论和研究方法方面的研究概况,以及近年来取得的进展,并以沃罗涅什州欧洲赤松为例,阐明了年轮宽度与太阳活动的关系,为在我国进一步开展树木气候研究提供信息和借鉴。 相似文献
958.
959.
A broadscale land evaluation program to assess the potential for growing particular trees in Africa 总被引:1,自引:0,他引:1
T. H. Booth 《Agroforestry Systems》1998,40(2):125-138
960.
Single-node leafy and leafless cuttings harvested from one-year-old, 1.3 to 1.5 m tall Leucaena leucocephala seedlings were
successfully rooted in a non-mist propagator which is suitable for use in the rural tropics. Cuttings with a leaf attached
rooted more successfully than those without a leaf (71% and 39% respectively) and clones differed significantly (43% to 71%).
There was also a clear pattern in rooting ability of cuttings collected sequentially down the main stem. Cuttings rooted most
successfully when taken from node five to 13, counting from the apex; this was the region where internodes were longest (64
to 109 mm) of moderate diameter (2.9 to 5.5 mm) and all cuttings had a leaf attached.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献