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941.
Evaluating the durability of wood-based panels using internal bond strength results from accelerated aging treatments 总被引:1,自引:0,他引:1
In this study, the durability of wood-based panels was evaluated by comparing the internal bond (IB) strength retention after
five different laboratory-based accelerated aging tests with the IB retention after 5 years of outdoor exposure in Shizuoka
City. In each accelerated aging test, the IB retention of MDI-bonded panels showed high retention compared to other panels.
Outdoor exposure in Shizuoka City resulted in an IB retention value for particleboard (PF) and oriented strandboard (aspen)
of less than 10% after the 5-year exposure period. Medium-density fiberboards maintained their initial IB strength over the
same period. Calculation of the mean IB retention for all board types allowed comparison of the severity of aging between
the accelerated test methods and outdoor exposure. The ASTM six-cycle test method was the most severe among the standard treatment
cycles applied. 相似文献
942.
The spruce bark beetle, Ips typographus, is one of the most extensively studied European forest pests. Gaps exist in the knowledge about second generation breeding
performance in bivoltine populations. In this study, the breeding performance of the second generation was evaluated in three
bivoltine populations of I. typographus in the SE Alps. Length of the maternal galleries (from 40.5 to 44.8 mm), population growth rate (PGR; from 0.7 to 3.6), and
emerged adults per m2 (from 669 to 1,570 insects/m2) varied among populations and were negatively correlated with bark colonisation density. Pheromone traps set up in the three
investigated forests differed in the number of trapped beetles, with mean captures ranging between 5,310 and 19,850 insects
per trap. The populations giving the highest captures in the traps showed the lowest bark colonisation density (248 vs. 489
maternal galleries per m2) and the best breeding performance. The populations of parasitoids and predators corresponded to just 1–9 and 2–10% of the
emerging I. typographus adults, respectively, and phloem temperature never reached thresholds lethal to I. typographus. Interspecific competition was negligible, whereas intraspecific competition was found to be the main factor affecting the
breeding performance of the second generation, although with different intensity according to the colonisation density. It
is hypothesised that competition with the first generation and spring precipitation influence the number of suitable hosts
available to the second generation. 相似文献
943.
研究了位于印度加瓦尔海平面(950~1100m)上的亚热带森林的再生生长状况。对生长在不同方位(东、西、北、南)研究地的植被进行了定量分析。研究结果表明:宽叶榆绿木(Anogeissus latifolia)的树木、幼树和幼苗层在研究地点的所有方位显生长优势。长叶松(Pinusroxburghii)和毛白杨(Terminalia tomentosa)的树木、小树在研究地点的北部显生长优势。树木层的最高(380株·ha-1)和最低密度(260株·ha-1)分别出现在南坡和北坡。幼树的最高(1790株·ha-1)和最低密度(970株·ha-1)分别出现在东坡和西坡。树木和灌木层的多样性分别为0.846~1.710和1.943-2.847。与其它种的相比较(4%~33%),宽叶榆绿木(Anogeissus latifolia)的相对剪枝强度较高(45%-57%),此种是在北坡中最重要的树种。目前研究表明,如果不合理开采继续进行,宽叶榆绿木(Anogeissus latifolia)就有可能被其他种代替,在树种的成分和森林重建方面会发生剧烈的变化。人类活动的压力,地理方位和土壤营养已引起了树种的成分和森林重建方面的变化。 相似文献
944.
A semi-greenhouse study was conducted to understand the effects of soil burial depth on seed germination and seedling development.
The seeds of wild apricot (Prunus armeniaca) were buried at the soil depths of 0-cm, 4-cm, 8-cm, and 12-cm, respectively, to simulate the seed hoarding behavior of rodents
in the field. The results revealed that the rates of seed germination and established seedlings from buried seeds were both
the highest in 4-cm burial depth group, and then decreased with increasing soil depth. The number of rotten seeds increased
in deeper burial depth. It is unfavourable for seed germination at 0-cm burial depth (i.e., seeds were laid on soil surface).
There was insignificant effect of burial depth on growth of established seedlings. The results from this study indicated that
proper burial depth in soil would be helpful for the seed germination and seedling growth. The seedlings derived from buried
seeds at shallower depth (4 cm) in this research have advantage in their early development. 相似文献
945.
The effect of uncertainty on the cost-effectiveness of alternative chains of stand establishment in northern Finland was examined.
The data were from a reforestation study of Scots pine (Pinus sylvestris L.) consisting of 288 sample plots, which were measured with respect to regeneration success. The study design included four
site-preparation methods (patch scarification, ploughing, prescribed burning and disk trenching) combined with three reforestation
methods (sowing, planting with containerized seedlings and planting with bare-rooted transplants). Initial reforestation density
was 2,500 spots or seedlings per hectare, and the regeneration success was modeled as probability with two thresholds, namely
500 and 1,100 saplings. On formerly spruce-dominated as well as pine-dominated sites the most cost-effective chain was ploughing
and planting with containerized seedlings, when threshold was 1,100 saplings per hectare. However, with threshold of 500 saplings
the best performer was ploughing and direct sowing on both sites. 相似文献
946.
Lloyd C. Irland 《European Journal of Forest Research》2010,129(5):777-786
The UN’s Millennium Development Goals (MDGs) and other regional and national policy commitments have motivated an upsurge
of interest in concepts and practical methods for monitoring forest conditions and trends at very wide geographic scales.
Two approaches to sustainability assessment at a global level are reviewed here. One consists of monitoring change in forest
conditions over time—the so-called Criteria and Indicators (C&I) approach. Another approach compares nations at a given point
in time. An example is the Yale Environmental Performance Index (EPI). Both approaches yield insights. It is widely recognized,
though, that severe data weaknesses afflict forest information over much of the world. These weaknesses include weak or absent
information on wood consumption in many regions, poor area estimates, and weak or absent information on key ecological conditions
in forests. The purpose of this essay is to introduce these efforts at global assessment, and to argue that an entirely new
discipline is needed to supply the information needed. The focus of this new discipline would be to design an ecologically
based set of definitions for forest and related ecosystems, and then to build and implement the optimum combination of satellite
measurements, air photo interpretation, and field plot measurements needed to measure world forest resource conditions and
trends. Examples of this new approach are already appearing. This argument is addressed to members of the global forest policy
community concerned with assessment, and to scientists, technologists, and managers in the many technical fields already engaged
on one or another aspect of measuring and monitoring forest conditions at a national and regional scale. 相似文献
947.
948.
949.
950.
Pascale Affolter Ulf Büntgen Jan Esper Andreas Rigling Pascale Weber Jürg Luterbacher David Frank 《European Journal of Forest Research》2010,129(3):289-298
Tree rings from the Alpine area have been widely used to reconstruct variations in summer temperature. In contrast, estimates
of changes in the hydrological cycle are rather scarce. In order to detect altitudinal and species-specific patterns of growth
responses to anomalous dry and wet conditions, a large network of 53 tree-ring width site chronologies along the Rhone valley
(Valais, Switzerland) covering the 1751–2005 period was compiled and analyzed. A total of 1,605 measurement series from four
conifer species—pine, larch, spruce, fir—were detrended to allow inter-annual to multi-decadal scale variability to be preserved.
Site chronologies were combined to four altitudinal (colline: <800 m asl, sub-montane: 800–1,000 m asl, montane: 1,000–1,450 m
asl, sub-alpine: >1,450 m asl) and species-specific mean time-series. These records were compared with temperature, precipitation,
and drought (scPDSI) data. Among the altitudinal records, the colline chronologies showed highest correlation with June precipitation
and scPDSI (0.5 and 0.7). Altitudinal effects, via control on climatic conditions, were superimposed upon species-specific
characteristics in affecting tree growth and response to moisture variations. In particular, species-specific differences
affected the significance level of drought response, with decreasing drought sensitivity towards higher elevations. Growth
conditions were found to be optimal at ~1,300 m asl, with precipitation/drought limiting tree growth below and temperature
above. Common years of extreme drought and low growth for the colline sites occurred in 1921, 1944, 1976, 1992, and 1998.
Our results demonstrate the potential of lower elevation conifers for reconstructing long-term changes in Alpine hydro-climate. 相似文献