Complex interactions shaping aspen dynamics in the Greater Yellowstone Ecosystem

Loss of aspen (Populus tremuloides) has generated concern for aspen persistence across much of the western United States. However, most studies of aspen change have been at local scales and our understanding of aspen dynamics at broader scales is limited. At local scales, aspen loss has been attributed to fire exclusion, ungulate herbivory, and climate change. Understanding the links between biophysical setting and aspen presence, growth, and dynamics is necessary to develop a large-scale perspective on aspen dynamics. Specific objectives of this research were to (1) map aspen distribution and abundance across the Greater Yellowstone Ecosystem (GYE), (2) measure aspen change in the GYE over the past 50 years (3) determine if aspen loss occurs in particular biophysical settings and (4) investigate the links between biophysical setting and aspen presence, growth, and change in canopy cover. We found that aspen is rare in the GYE, occupying 1.4% of the region. We found an average of 10% aspen loss overall, much lower than that suggested by smaller-scale studies. Aspen loss corresponded with biophysical settings with the lowest aspen growth rates, where aspen was most abundant. The highest aspen growth rates were at the margins of its current distribution, so most aspen occur in biophysical settings less favorable to their growth.     

Clones No 1333 of Populus alba×P.davidiana and No 1132 of P.davidiana×P.alba×P.daviana

IntroductionAspen(Populus~anaDode)isapioneeringspecieswhichiswidelydistributed,welIadapted,andhasgoodqualityoftimber.ItdistributesfromXimalayaMoun-tains,toDaxing'anMountainsandXiaoxing'anMoun-tainsandfromAhaiMountainstoWusulijiangriver,coVerin23provineeso…     

In vitro propagation of European aspen (Populus tremula L.) from axillary buds via organogenesis

Axillary buds from 1-year-old twigs of European aspen (Populus tremula L.) were used for propagation of indigenous aspen clones for further phytoremedial studies. The most intense bud development was seen after the break of dormancy, i.e. from the middle of February until mid-March. Lower infection rates were observed from the axillary buds collected at an urban forest border in comparison to a forest location, accompanied by higher percentages of browning. The optimal medium for shoot induction primarily via callus cultures was Murashige and Skoog mineral salts medium (MS) supplemented by 20 μM zeatin riboside and 1 μM indol acetic acid. The shoots were rooted in half-strength MS medium supplemented by the same hormones, after which they were successfully transferred to a commercial soil mixture. The protocol for aspen propagation is proposed.     

Aspen patch and migratory bird relationships in the northern Yellowstone ecosystem

We evaluated the effects of aspen patch area and orientation (relative to North and an elevational gradient) on the early breeding season abundance and species richness of migratory and resident birds in the northern ungulate winter range of the Yellowstone ecosystem, USA. Using an information-theoretic model selection approach, we found patch area and basal area of aspen to be the most important covariates for long distance migrants, and patch orientation relative to elevational gradient the most important covariate for residents/short-distance migrants. Basal area of live aspen and aspen snags was marginally important for both migratory strategies, likely because aspen snags are an important habitat for most cavity-nesting species. Landscape ecological theory postulates passive interception of dispersing or migrating organisms by patches of suitable habitat. Our results suggest that residents/short-distance migrants are intercepted by patches that are oriented perpendicular to the elevational gradient of our study region resulting in greater abundances and species richness in those patches. However, long-distance migrants appear to use aspen patches without regard to orientation, but rather to patch area.     

Response of aspen stands to forest tent caterpillar defoliation and subsequent overstory mortality in northeastern Ontario,Canada

Overstory mortality, understory tree recruitment, and vegetation development were assessed in trembling aspen (Populus tremuloides Michx.) stands following two recent episodes of forest tent caterpillar defoliation (Malacosoma disstria Hbn.) in northeastern Ontario. The results suggest that poplar (aspen and balsam poplar (Populus balsamifera L.)) mortality increased with consecutive years of insect defoliation occurring from the mid-1980s to mid-2000s and the proportion of poplars in the overstory, but decreased with improved pre-defoliation tree vigour (DBH increment). The first outbreak, which lasted from the mid-1980s to early 1990s, was more severe in terms of insect defoliation and contributed more to poplar mortality and decline. The decline began in the late 1990s and peaked in early 2000s. Poplar regeneration and understory shrubs responded rapidly to foliage loss to insect defoliation and mortality of overstory poplars. The regenerated poplars were able to maintain their growth under developing shrubs and residual overstory canopy and numbers were sufficient to compensate for the poplar trees lost to insect infestation. The defoliation-induced overstory decline will accelerate the transition of aspen stands to conifer dominance through enhanced conifer recruitment and growth, and reduced hardwood overstory in aspen-dominated stands, while hardwood dominance will persist in pure aspen stands. From a timber supply perspective, the decline caused by forest tent caterpillar defoliation could delay the availability of aspen stands for harvesting by 40–50 years.     

沼气混合制冷剂循环液化流程与设备分析

以天然气液化设备为模型,利用Aspen HYSYS软件,设计小型混合制冷剂液化沼气流程,对该流程进行数值模拟,根据PR方程计算出沼气的泡点与露点以及液化率、能耗等。在热力学分析的基础上,计算流程各设备损失,分析产生设备损失的原因,提出降低设备损失的方法。依据模拟结果,建立实验平台对降低损失方法进行验证,结果表明:小型混合制冷剂液化沼气流程具有可行性,液化过程中能耗和损失最大的设备是压缩机,利用储液罐上端的闪蒸气预冷混合制冷剂的方法可使压缩机和冷却器的损失分别减少12.2%和27.2%。     

沼气混合制冷剂循环液化流程与设备火用分析

以天然气液化设备为模型,利用Aspen HYSYS软件,设计小型混合制冷剂液化沼气流程,对该流程进行数值模拟,根据PR方程计算出沼气的泡点与露点以及液化率、能耗等.在热力学分析的基础上,计算流程各设备(火用)损失,分析产生设备(火用)损失的原因,提出降低设备(火用)损失的方法.依据模拟结果,建立实验平台对降低(火用)损失方法进行验证,结果表明:小型混合制冷剂液化沼气流程具有可行性,液化过程中能耗和(火用)损失最大的设备是压缩机,利用储液罐上端的闪蒸气预冷混合制冷剂的方法可使压缩机和冷却器的(火用)损失分别减少12.2％和27.2％.     

阔叶材（山杨和速生杨）纤维素的形态结构

采用日立Ｓ－１５０型扫描电镜观测了山杨和速生杨纤维素的形态结构。通过观测发现，漂白浆样和未漂浆样显示了各自的某些特点。同时，探讨了原浆和水解后浆样纤维素形态结构的变化状态。     

向日葵籽壳-杨木刨花板制造工艺研究

试验采用向日葵籽壳和向日葵籽壳与杨木刨花混合物为原料,分别压制脲醛胶刨花板。结果表明,向日葵籽壳刨花板的物理力学性能,达不到刨花板国家标准（ＧＢ／Ｔ４８９７－９２）的要求,加入杨木刨花可提高向日葵籽壳刨花板的物理力学性能。当向日葵籽壳在向日葵籽壳－杨木混合刨花中所占的比例由７５％下降至５０％时,向日葵籽壳－杨木刨花板的物理力学性能由Ａ类刨花板的二等品上升为特等品。     

Suitability of boreal mixedwood clearcuts as wood bison (Bison bison athabascae) foraging habitat in north-central Alberta,Canada

Plant species composition (n = 95) and biomass (n = 62) samples from harvested and natural stands were analyzed to determine if forest clearcutting increased forage abundance for wood bison (Bison bison athabascae) in north-central Alberta. The sampled stands ranged from 1 to 28 and 50 to 100 years old, respectively, and were members of a Populus tremuloides/Rosa-Viburnum vegetation-type, which is a common forest community on upland sites in the boreal mixedwood zone of western Canada. In addition, a five-stand chronosequence was monitored from May to September, inclusive, to measure seasonal variation in forage abundance and nutrient content. Three-fourths of clearcuts were mechanically treated after harvesting. The data showed that clearcutting increased forage availability, but not quality. Peak summer biomass production occurred in 2–12-year-old clearcuts (∼944 kg/ha, S.D. 511, n = 30), with forage availability decreasing to natural stand levels (∼228 kg/ha, S.D. 147, n = 10) 25–30 years after harvesting. Mechanical site treatment increased forage availability by 26% above untreated clearcuts (P = 0.002). No major differences relevant to bison nutrient requirements occurred between forbs and graminoids in summer, or among age-classes within a monitored chronosequence. Crude protein content declined and fiber content increased during the growing season. Peak forage availability and maximum crude protein content occurred in July among monitored stands. Species with fair forage quality dominated the vegetation in 1–16-year-old clearcuts, with the proportion of forbs increasing as stands aged. Maximum summer carrying capacity of natural stands averaged 0.57 animal unit month per hectare (AUM/ha), depending upon the applied assumptions, with lower winter values (0.01–0.03 AUM/ha). In 2–12-year-old clearcuts, maximum summer and winter carrying capacities were <0.67 and <0.29 AUM/ha based on 25% seasonal usage, respectively. The application of a safe-use factor, down-weighting of forbs to account for dietary preferences, and adjustments for forage quality reduced summer (≤0.30 AUM/ha) and winter (≤0.07 AUM/ha) carrying capacities. Wood bison carrying capacity typically decreased when stands were >8 years old. Clearcuts provide adequate forage for wood bison during the summer, but owing to low graminoid biomass they are not suitable as winter habitat.