Nondestructive detection of decay in living trees

We used a four-point resistivity method to detect wood decay in living trees. A low-frequency alternating current was applied to the stem and the induced voltage measured between two points along the stem. The effective resistivity of the stem was estimated based on stem cross-sectional area. A comparison within a group of trees showed that trees with butt rot had an effective resistivity that was at least a factor of two lower than that of healthy trees. In tests on several groups of Norway spruce (Picea abies (L.) Karst.) comprising more than 300 trees in total, the method detected butt rot with high accuracy. We validated the method both by measurements and by finite element modeling and simulations.     

苹果低产的因素及其应对措施

在当前生产条件下成龄苹果园 ,每公顷产量应达到 3.4 5万公斤 ,但由于立地条件、管理水平不同、单位面积产量差别很大。多数果园达不到理想的产量 ,在藁城市每公顷产量不足 750 0 kg的果园并不少见 ,因此开发低产园是迅速提高苹果产量的有效途径。1　果园低产的原因1 .1　土壤的肥力低施肥量少土壤养分消耗大现有的结果苹果园大部分是土层薄、肥力低 ,土壤有机质含量低 ,果树根浅 ,容易受干湿变化和气温高低的影响 ,根系寿命短 ,且树体生长缓慢 ,新梢生长量小 ,枝条细弱 ,芽瘦小 ,不能形成花芽。低产园由于没进行树穴改良和深翻熟化 ,只是表…     

The persistence and function of living roots on lodgepole pine snags and stumps grafted to living trees

In Alberta, Canada, pairs of grafted lodgepole pine trees were selected to study the longevity and location of live roots of snags that were grafted to living trees, to determine the impact of these live residual roots on the diameter growth of the living tree. In a second study, dense groups of grafted trees were manually thinned and one leave tree was left to grow for two growing seasons. For both studies, roots were excavated. Results indicate that more live roots were maintained on snags connected to living trees with a large graft and that roots located within 90° of the root grafted to the live tree persisted longer. Also, tree ring index in the living trees significantly increased following manual thinning, but was unaffected when the grafted partner died naturally. Grafts with large phloem connections maintained a higher number of live roots on snags, than grafts with small connections.     

Natural decline of volatile acids due to aging of living trees

Wood age, i.e., number of years that have passed after the annual rings of xylem tissue developed from cambium, had a strong negative impact on the volatile acid content of wood of the two oak species, Quercus petraea and Q. frainetto. Up to 80% of acetyl groups were cleaved off in the heartwood zones close to the pith if the living oak trees were about 200 years old.     

Occurrence and significance of bacteria in living trees of Populus nigra L.

On the occurrence and significance of bacteria in living trees of Populus nigra L. Eleven strains of bacteria were isolated from sapwood and heartwood of living poplar trees (Populus nigra L.) and identified mostly as Erwinia, Xanthomonas, Agrobacterium and Acinetobacter. Most of them were able to attack milled wood and the wood components pectin, hemicelluloses and holocellulose; α-cellulose and lignin were not consumed. The capillary liquid in the xylem of poplar served as a nutrient for the isolated bacteria. The significance of these bacteria for wetwood formation is discussed.     

城市街路园林树木生存环境剖析

通过对沈阳市城市街路园林树木所处的生存环境调查研究,详细、客观分析了影响树木生存的主要环境因素,有针对性的提出相应对策和建议.     

Defense mechanisms in the sapwood of living trees against microbial infection

When pathogenic microorganisms invade living sapwood of woody plants, a series of defense responses occurs at the lesion margin. Putative active defense mechanisms include constitutive and induced inhibitory compounds, cell wall alterations, and occlusion of xylem elements. Active defenses play an important role in the sapwood, while constitutive and induced microenvironmental conditions in the wood might also constrain pathogen development. It is necessary to develop a unified understanding, in which these factors could act synergistically and provide effective defense barriers.     

Detection of wetwood in living poplar trees by electrical resistance measurements

Wetwood was detected in living trees by determining the electrical resistance patterns across the stem with a Shigometer. The resistance of wetwood to a pulsed electric current was low compared with that of healthy sapwood. Bacteria were isolated from wood with low resistance, but rarely from wood with high resistance. Provided that drilling and measurements were performed in a stepwise fashion, the extent of wetwood could be assessed with little damage to the trees tested. This procedure may be useful in identifying trees containing wetwood, particularly in the early stages before crown symptoms become apparent.     

桤木优树选择研究

论述了桤木优树选择应遵循的基本原则，包括目标性原则、一致性原则、优中选优原则等。根据这些原则，针对桤木短周期工业用材林(纸浆材)这一选择目标，提出了桤木优树选择的方法，包括五株优势木比较法、绝对生长量法及标准差法，同时提出了相应的选择标准。     

Risk-based selection of forest regeneration methods

A stochastic optimization model is developed to select between planting and seed-tree regeneration methods. The model considers the uncertainty of, and the legal requirement on, the stocking level of the established seedlings in a given year after regeneration. Uncertainty is quantified as a variation of the mortality rate of the planted seedlings for the planting method and as the prediction error for the seed-tree method. The objective of the forest landowner is assumed to maximize the expected net present value (NPV). Numerical simulations show that the landowner should select the seed-tree method rather than planting for a sample site with a Scots pine stand. In addition, if a risk-free selection model is used, it over-estimates the financial return by about +1.8%. Sensitivity analysis shows that a less restrictive forest act may improve the expected NPV for both planting and the seed-tree method. Sensitivity analysis also shows that a decrease in the variation of the mortality rate (or prediction error) increases the expected NPV. Since these results are obtained only for the sample site, more work is needed to be done until a general conclusion has been drawn.     

Estimating water use by sugar maple trees: considerations when using heat-pulse methods in trees with deep functional sapwood

Accurate estimates of sapwood properties (including radial depth of functional xylem and wood water content) are critical when using the heat pulse velocity (HPV) technique to estimate tree water use. Errors in estimating the volumetric water content (V(h)) of the sapwood, especially in tree species with a large proportion of sapwood, can cause significant errors in the calculations ofsap velocity and sap flow through tree boles. Scaling to the whole-stand level greatly inflates these errors. We determined the effects of season, tree size and radial wood depth on V(h) of wood cores removed from Acer saccharum Marsh. trees throughout 3 years in upstate New York. We also determined the effects of variation in V(h) on sap velocity and sap flow calculations based on HPV data collected from sap flow gauges inserted at four depths. In addition, we compared two modifications of Hatton's weighted average technique, the zero-step and zero-average methods, for determining sap velocity and sap flow at depths beyond those penetrated by the sap flow gauges. Parameter V(h) varied significantly with time of year (DOY), tree size (S), and radial wood depth (RD), and there were significant DOY x S and DOY x RD interactions. Use of a mean whole-tree V(h) value resulted in differences ranging from -6 to +47% for both sap velocity and sap flow for individual sapwood annuli compared with use of the V(h) value determined at the specific depth where a probe was placed. Whole-tree sap flow was 7% higher when calculated on the basis of the individual V(h) value compared with the mean whole-tree V(h) value. Calculated total sap flow for a tree with a DBH of 48.8 cm was 13 and 19% less using the zero-step and the zero-average velocity techniques, respectively, than the value obtained with Hatton's weighted average technique. Smaller differences among the three methods were observed for a tree with a DBH of 24.4 cm. We conclude that, for Acer saccharum: (1) mean V(h) changes significantly during the year and can range from nearly 50% during winter and early spring, to 20% during the growing season;(2) large trees have a significantly greater V(h) than small trees; (3) overall, V(h) decreases and then increases significantly with radial wood depth, suggesting that radial water movement and storage are highly dynamic; and (4) V(h) estimates can vary greatly and influence subsequent water use calculations depending on whether an average or an individual V(h) value for a wood core is used. For large diameter trees in which sapwood comprises a large fraction of total stem cross-sectional area (where sap flow gauges cannot be inserted across the entire cross-sectional area), the zero-average modification of Hatton's weighted average method reduces the potential for large errors in whole-tree and landscape water balance estimates based on the HPV method.     

辽西山地乡土树种开发利用的种类与方法

文章研究了乡土树种的分布及影响因子,从辽西山地5个自然保护区的树种天然分布中,筛选出分布较广且可以开发利用的59个乡土树种;筛选了辽西山地主要的天然植被类型12个,为人工营造混交林提供了主要依据。     

An evaluation of scarification methods for seeds of two leguminous trees

Twenty different methods of seedcoat scarification were tested on Gleditsia triacanthos L. and Robinia pseudoacacia L. to find an alternative to acid scarification for these species. For germination testing, nicking or burning were best, and these same methods could be used in small nurseries with adequate labor. For larger quantities, hot water soaks or heat shock soak treatments yielded satisfactory, though lower, germination.     

Decay development in living sapwood of coniferous and deciduous trees inoculated with six wood decay fungi

Development of decay and/or discoloration was assessed in the functional sapwood of one coniferous and three deciduous trees after wounding and artificial inoculation with six wood decay fungi. Living stems of mature Douglas fir, beech, oak, and sycamore trees were wounded in spring 2002 and immediately inoculated with brown, white, and soft rot fungi. Extent of discoloration and decay, wood weight loss, and total phenols in the reaction zone (zone of active response at a dynamic interface between living sapwood and wood colonized by decay fungi) were assessed 16 and 28 months after inoculation.     

北京市不同环境功能区绿化树种选择与配置的探讨

根据环境功能分区的原则及内容,将北京市划分为7个不同的环境功能区,依据不同的环境功能区特点以及树种配置原则,把树种选择与生态效应相结合,并针对性的提出可供选择树种与配置的建议,以期为北京的绿地规划建设提供可借鉴的理论依据。     

南阳市银杏资源调查和优树选择

南阳市现有 2 0年以上树龄的银杏 1182 1株 ,2～ 8年生新植银杏 2 988179株。所选优良单株 9棵 ,其中 8株为果用型优树 ,每kg种核均在 4 0 0粒以下 ;另一株为速生用材型优树 ,胸径年平均生长量 1 6cm。     

杉木促进开花结实方法的探讨

试验通过对 １、２、３年生杉木苗施用赤霉素 １００ ｐｐｍ、细胞分裂素、北林激素 １０倍水稀释、北林激素２０倍水稀释等不同药品的处理,以及与对照的比较,发现以上药品对１年生杉木处理无效果,没有开花现象;对２、３年生杉木苗,北林激素２０倍水稀释后对提前雄花开花结实时间效果很明显。     

陇南大红袍花椒优良栽培类型及其优树选择

在对陇南大红袍花椒优良栽培类型调查的基础上，进行优树选择。并应用性状综合评分法结合绝对产量（生长量）法对初选的20株优树进行综合评价、分级，从中复选了9株Ⅰ级优树和8株Ⅱ级优树作为繁育推广的重点，通过嫁接建立了优良品种花椒基因库，进行无性系测定。