Observing succession on aspen-dominated landscapes using a remote sensing-ecosystem approach

In the North American upper Great Lakes region, forests dominated by the aspens (Populus grandidentata Michx. – bigtooth aspen, and P. tremuloides Michx. – trembling aspen), which established after late 19th and early 20th century logging, are maturing and succession will create a new forest composition at landscape to regional scales. This study analyzed the capabilities of Landsat ETM+ remote sensing data combined with existing ecological land unit classifications to discriminate and quantify patterns of succession at the landscape scale over the 4200 ha University of Michigan Biological Station (UMBS) in northern Lower Michigan. In a hierarchical approach first multi-temporal Landsat ETM+ was used with a landscape ecosystem classification to map upland forest cover types (overall accuracy 91.7%). Next the aspen cover type was subset and successional pathways were mapped within that type (overall accuracy 89.8%). Results demonstrated that Landsat ETM+ may be useful for these purposes; stratification of upland from wetland types using an ecological land unit classification eliminated confounding issues; multi-temporal methods discriminated evergreen conifer versus deciduous understories. The Landsat ETM+ classifications were then used to quantify succession and its relationship to landform-level ecological land units. Forests on moraine and ice contact landforms are succeeding distinctly to northern hardwoods (95% and 88% respectively); those on outwash and other landforms show greater diversity of successional pathways.     

Poor recruitment is changing the structure and species composition of an old-growth hemlock-hardwood forest

Anthropogenic factors such as elevated deer populations, invasive earthworms or climate change may alter old-growth forests of the Upper Midwest region of the United States. We examined demographic trends of woody species across all size classes over 35 years in a late-successional forest dominated by hemlock (Tsuga canadensis), sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis) in Michigan's Upper Peninsula using two sets of permanent plots. For the duration of the study period, species that were less-preferred white-tailed deer (Odocoileus virginianus) forage, especially sugar maple, comprised a much higher fraction of all seedlings and saplings compared to overstory trees. The density of small sugar maple declined across the study period, but no other species became more abundant, creating a more open forest understory. By the most recent census, preferred species for deer browse had been nearly eliminated from the understory, and declines in unpreferred species such as sugar maple were also apparent. We found small changes in temperature (<0.5-1 °C rise in minimum and maximum temperatures depending on season) and precipitation (±28 mm depending on season) and little evidence of invasive earthworms impacts. Our results suggest that the sustained elevated deer density is shifting the structure and composition of this old-growth forest. A demographic model showed that if current recruitment, growth and mortality rates were to continue for 500 years the forest would eventually reach a new equilibrium with virtually no hemlock or yellow birch remaining.     

长江上游低中山常绿阔叶林区森林的生态功能和恢复对策

本文论述了长江上游中低常绿阔叶林区森林的生态功能,认为该区的森林在维持生物多样性,涵养水源,保持水土和农业生态屏障等方面具有不可替代的重要的生态作用;提出了七个恢复对策;（1）改良“杂木林”观念,确立常绿阔叶林的不可替代地位;（2）建立常绿阔叶林自然保护区;（3）积极进行现有人工林的改造;（4）搞好农林结构调整。促进退耕还林;（5）突出流域单元的恢复重建的示范作用;（6）加强科学研究;（7）加强教育,严格执法。     

A crown profile model for Pinus radiata D. Don in northwestern Spain

A crown profile model was developed for radiata pine (Pinus radiata D. Don) in Galicia (northwestern Spain). Data from 443 trees located in 56 permanent plots, established by the Unidade de Xestión Forestal Sostible (UXFS) of the University of Santiago de Compostela in plantations of this species in the region, were used. The crowns of the trees were measured by a visual method based on similar triangles. Both simple geometric shapes and mathematical equations were used to describe the crown profiles. As crown profile models usually require variables that are expensive to measure, equations to estimate the maximum crown radius and the height to the maximum crown radius were also developed, using other easily measured tree and stand variables. Several models were fitted using a system of equations approach and accounting for an autocorrelated, heteroscedastic error structure. The selected crown profile model consists of a system of two allometric equations for the crown below (primarily shade needles) and above (primarily sun needles) maximum crown radius. The model explained 88% of the variability in crown radius with a mean error of 0.24 m.     

采收方式对烤烟上部叶香味品质的影响

研究了不同采收方式对上部叶香味品质的影响.结果表明:上部6片叶成熟后集中一次采收和带茎秆采收,烤后烟叶的香味品质均优于常规采烤方法,其中以打顶后68 d带茎采收处理表现最优.与对照相比,打顶后68 d带茎采收处理明显提高了挥发性香气物质总量,新植二烯、类胡萝卜素降解产物、芳香族氨基酸代谢产物量和西柏烷类降解产物等4类致香物质总量均有不同程度的提高,美拉德反应产物总量略低;同时,该处理烤后烟叶颜色橘黄,组织结构疏松,油分足,色度强,化学成分含量适宜,比例协调,显著降低淀粉、蛋白质含量,烟叶的平衡含水率、叶质重、填充值均得到改善且在适宜范围内,显著提高了烟叶均价及产值.表明上部叶带茎秆烘烤能够提高大多数香气物质的含量,改善烟叶品质.     

轮式拖拉机侧置变速操纵机构设计

介绍3种侧置变速操纵机构的结构特点和传动原理,对比分析各自的优劣势。     

1960—2009年图们江上游湿地景观变化的遥感监测

基于景观生态学原理,在地理信息系统和遥感技术的支持下,利用地形图、Landsat影像数据,提取图们江上游1960年、1977年、1985年、1999年和2009年的湿地信息,分析了该地区近50 a来湿地的分布状况和变化特征。结果表明:从湿地面积的变化特征上,该区域湿地面积减少一半,天然湿地的比例在降低,沼泽变化最大,减少了68.17%,人工湿地比例增大。从湿地景观格局的变化特征上,近50 a,该区域湿地景观斑块个数减少了近2/3,平均斑块面积增加1倍,景观多样性指数、景观破碎化指数及景观均匀性指数均在一定程度上减少。其中人类活动是图们江上游天然湿地减少的主要因素。     

川金丝猴的上肢肌

金丝猴上肢的三角肌锁骨部不及猕猴发达,肱二头肌除具有长短两头外,短头内侧还分出一条细长肌束,以细长腱止肘内侧筋膜。大猩猩、猕猴的背上滑车肌和长臂猿的背阔髁肌是同一肌肉的不同名称,金丝猴有与上述相同的起点,但不止于肱骨内上髁,而与肱三头肌止腱相连,并止于前臂筋膜,可与家畜的前臂筋膜张肌相当。肘肌不显著,并具有肘关节肌。指总伸肌腱越过伸肌支持带后立即裂成三支,每支又分别裂成内、外两支。除外侧腱的外支和内侧腱的内支分别单独止于第二和第五指远节指骨外,其余的以相邻腱的两支相合并后各止于第3和第4指。不同于猕猴指总伸肌腱分四支,分别到第2—4指,每一腱无分支存在。第二及第三指伸肌与人的示指伸肌相当,但分为两长腱分别与指总伸肌到第2、3指的腱相连。第四及第五指伸肌与人和长臂猿的小指伸肌相当,但它还分出一细腱至第4指。拇短伸肌不存在。金丝猴具有掌短肌,位于小鱼际皮下,肌纤维横向,肌束内夹有少量脂肪,属已退化的皮肌。     

2014-2017年赣江上游稀土矿区典型流域水质污染变化及成因

[目的] 分析赣江上游稀土矿区典型流域水质的时空分布特征,揭示水质污染状况和成因,为该流域的水环境治理提供理论依据和数据支撑。[方法] 采用2014-2017年赣江上游桃江流域10个监测断面的6项水质指标,运用描述性统计分析、水污染指数法、相关性分析等方法分析该流域水质污染现状及其成因。[结果] ①桃江流域各监测断面不同水文时期的污染状况均存在差异,以氨氮含量的时空差异最为明显。②水污染指数评价结果表明水质类别为Ⅱ类和Ⅲ类所占比例分别为55%和29%,龙头滩断面的水质状况最差,以劣Ⅴ类为主。[结论] 水质污染成因解析揭示出氨氮为桃江流域最主要的污染物,降雨对流域内水环境的影响较大,农业活动和以稀土采选为主的工业活动是造成水环境污染的重要人为活动。