The histology of dermal glands of mating Breviceps with comments on their possible functional value in microhylids (Amphibia: Anura)

During mating male and female Breviceps become ‘glued’ together. The distribution of multicellular dermal glands varies between the sexes. The mate has a large number of holocrine glands on the ventrum, while the female has similar glands on the dorsum of the back. II thus appears that both sexes contribute to the ‘glueing’ mechanism. New hypotheses to explain the adhesion between the sexes are proposed, viz., that the shift to terrestrial habils and subterranean laying in Breviceps have secondarily resulted in male si2e diminution. In other microhylids which adhere during aquatic oviposition, yet demonstrate a terrestrial morphology and habits, bouyancy is suggested to be of primary functional value.     

Grassland bird response to vegetation structural heterogeneity and clearing of invasive bramble

Spatial and temporal patterns of disturbance and the subsequent heterogeneity are critical in maintaining biodiversity within grassland ecosystems. Grassland birds have evolved within this ‘shifting mosaic’ to become reliant on specific habitat characteristics maintained under varying levels of both natural and anthropogenic disturbance. Unfortunately, grasslands in South Africa have been extensively transformed and remain poorly conserved, threatening grassland avifauna. Mistbelt grassland is a threatened vegetation type endemic to the province of KwaZulu-Natal, of which only 0.3% is formally protected. This study investigated seasonal and patch type heterogeneity in a Mistbelt grassland avian community by determining avian community structure and composition in four patch types, i.e. i) untransformed open grassland, ii) burnt grassland, iii) bramble-invaded and, iv) bramble-cleared grassland, during winter and summer. Avian assemblages were significantly different between the different patch types for each season. The bramble patch type negatively affected grassland bird species diversity. Bramble-cleared grassland and untransformed grassland had similar vegetation structure and avian communities in the summer, suggesting that the grassland bird community benefitted soon after the clearing of invasive vegetation. This study provides further evidence that bird diversity is enhanced in structurally heterogeneous grassland landscapes. Furthermore, the protection and appropriate management of privately owned Mistbelt grassland, conserved in the form of rangeland, is an important refuge for threatened and endemic avifauna, such as the globally-threatened blue swallow (Hirundo atrocaerulea) and wattled crane (Bugeranus carunculatus).     

Anthropogenic Influences on Wild Nutmeg Fruit Crop in the Western Ghats of India

Myristica dactyloides is characteristic of the mid- and high-elevation evergreen forests of the Western Ghats of India. Aril and seeds of the species are valuable nontimber forest products and are harvested extensively. We made visual estimates of fruit crop size in nine populations. We assessed disturbance using five variables: distance from road, method of harvesting fruits, nonforest matrix around the population, seedling regeneration, and protected area status. Unsustainable harvest and proximity to road impacted fruit crop, as did the nonforest matrix (F = 38.17 df = 5,102, p < .001). While high protection and measures against harvesting keep some populations safe, the harvest method plays a crucial role in determining total fruit production and seedling recruitment in the species.     

Human Impacts on Forest Biodiversity in Protected Walnut-Fruit Forests in Kyrgyzstan

We used a spatially explicit model of forest dynamics, supported by empirical field data and socioeconomic data, to examine the impacts of human disturbances on a protected forest landscape in Kyrgyzstan. Local use of 27 fruit and nut species was recorded and modeled. Results indicated that in the presence of fuelwood cutting with or without grazing, species of high socioeconomic importance such as Juglans regia, Malus spp., and Armeniaca vulgaris were largely eliminated from the landscape after 50–150 yr. In the absence of disturbance or in the presence of grazing only, decline of these species occurred at a much lower rate, owing to competitive interactions between tree species. This suggests that the current intensity of fuelwood harvesting is not sustainable. Conversely, current grazing intensities were found to have relatively little impact on forest structure and composition, and could potentially play a positive role in supporting regeneration of tree species. These results indicate that both positive and negative impacts on biodiversity can arise from human populations living within a protected area. Potentially, these could be reconciled through the development of participatory approaches to conservation management within this reserve, to ensure the maintenance of its high conservation value while meeting human needs.     

中烈度火干扰后喀纳斯泰加林火成演替群落的稳定性

【目的】 分析中烈度火干扰后,不同火后时间喀纳斯泰加林群落在火成演替过程中的稳定性状态,加深对其火干扰后群落演替和恢复过程的科学认识。【方法】 运用采用数学模型改进的Gordon稳定性测度方法,计算并判定中烈度火干扰后不同火后时间喀纳斯泰加林通过火成演替其群落所达到的稳定性状态。【结果】 受到中烈度火干扰后,随着火后时间的增加和森林群落的持续恢复,喀纳斯泰加林火成演替群落的稳定性由低逐渐升高,并在火后60 a达到相对持续稳定。【结论】 喀纳斯泰加林群落的稳定性受火干扰的深刻影响,在中烈度火干扰后,大约需要60 a群落才能通过演替恢复到相对持续稳定的状态。中烈度火干扰后森林群落达到相对稳定状态的演替恢复时间为通过计划火干扰恢复退化泰加林提供参考。     

耕地植被人为干扰格局动态变化特征及其尺度效应

为探究耕地植被人为干扰格局动态变化特征及其尺度效应,该研究以黑龙江省大庆市为研究区,通过遥感与地理信息系统相结合的方法计算和识别耕地植被人为干扰,分析5个时段(1990-1995年、1995-2000年、2000-2005年、2005-2010年和2010-2016年)耕地植被人为干扰格局动态变化特征;并采用滑动格窗法和ISODATA聚类算法,对耕地植被人为干扰格局的尺度效应进行了研究。结果表明:1)当耕地植被受到的人为干扰增多时,研究区耕地植被人为干扰的分布趋向于集中;反之则趋向于分散。2)研究期内占耕地植被人为干扰面积50%以上的地区的尺度效应并不明显,但仍有占面积11.81%～18.33%的地区人为干扰的尺度效应十分显著,这些地区是人为干扰分布最集中和最不均匀的地区。3)在耕地植被人为干扰尺度效应显著地区中,土地利用类型未发生变化的地区所占的面积比例呈上升趋势,说明耕地保护政策产生了较好的效果;但耕地植被人为干扰的主要来源是农业生产行为,应将未来政策关注的重点转为对耕地土壤理化性质稳定性的维护。4)从多尺度空间聚类类型可以看出,在大部分尺度效应显著地区,尺度越小耕地植被人为干扰越显著,说明发展适度规模农业是降低人为干扰、提高粮食产量的有效途径。研究对于实现耕地保护和粮食稳定生产具有重要意义。     

考虑主轴扭转变形的轴系振动模型

针对大型水力发电机组传统上忽略轴系扭转变形的假设可能导致轴系振动分析出现较大偏差的问题,采用Lagrange方法建立轴系振动方程和含轴系扭转效应的转子运动方程,通过定义广义动量,将这2个方程构建为统一形式的一阶微分方程组.以发电机转子上的阻力矩和水轮机转轮上的动力矩为纽带,构建包括水力系统、发电机、励磁、调速系统在内的完整水力机组模拟运行系统,并采用二阶Runge-Kutta法进行仿真计算.计算结果表明,在机组故障扰动条件下,计入轴系的弹性对轴系横向振动的影响不大,主轴扭转刚度对稳定工况下轴的扭转变形影响较大;故障扰动下,发电机转子和水轮机转轮之间的扭转角变化趋势与有功变化趋势基本一致.仿真表明,所建立的轴系扭振模型能反映轴系振动的基本特征,模型是合理的.     

基于离散元软件的大豆垄上深松铲仿真试验分析

为了合理优化大豆垄上深松铲的作业性能和作业效果,对传统大豆垄上圆弧式深松铲进行理论分析,通过分析深松铲正常作业时的耕作阻力以及对土壤的作用确定深松铲结构参数,并借助计算机离散元软件对深松铲进行仿真试验,研究深松铲结构参数对于其耕作阻力及土壤扰动面积的影响,从而优化深松铲结构。理论分析得到深松铲切削角范围为30°~60°,入土角范围为19°~23°。2因素5水平正交旋转组合离散元仿真试验得到:影响深松铲耕作阻力的主次因素为切削角、入土角;影响深松铲土壤扰动面积因素的主次顺序为深松铲切削角、入土角;理论上当深松铲切削角34.39°、入土角20.24°时,耕作阻力为804.799 N,扰动面积为418.42 mm^2。验证试验结果表明,优化后的深松铲与理论值相比,耕作阻力增加7.92%,土壤扰动面积增加7.54%,均与理论值偏差较小,仿真优化结果可靠。优化后的深松铲作业性能与作业效果优良,为大豆垄上深松铲的优化设计提供一定依据。     

城市森林降温效应影响因素研究进展

城市森林是缓解城市热岛效应的重要绿色基础设施。本文探讨影响城市森林降温效应的内、外因素及作用机制,为优化城市森林结构、缓解城市热岛效应提供参考。影响城市森林降温效应的内部因素从单木尺度上主要有树种、树冠结构和树冠形状,从林分尺度上主要有林分类型、林分结构、绿量、林分面积和形状,城区尺度主要应用遥感方法对城市森林降温效应进行研究,主要指标有归一化植被指数、叶面积指数和景观格局指数;影响城市森林降温效应的外部因素有气候、地面类型和经营措施等;内部因素及外部因素通过影响林内外能量的流动和交换,共同影响城市森林降温效应。缓解城市热岛效应,一方面要加强理论研究,重视温度场理论,结合地面观测与遥感解译,充分研究林分结构与城市森林能量传输的关系,另一方面需加强城市森林的经营管理,从促进热量交换的角度优化林分结构,合理布局城市建筑、森林和水体等基础设施,实现降温效应最大化。