Measurements of the natural frequencies of trees

Recent theoretical work has suggested that tree natural frequencyis an important indication of tree stability in windy conditions.This paper reports natural frequency measurements on a largenumber of urban trees using a remote laser-based method. Themajority of the measurements were made on healthy lime trees,and showed a consistent variation of natural frequency withtree size, with out-of-leaf, winter frequencies being substantiallygreater than in-leaf, summer frequencies. These measurementsalso revealed that different tree geometries can produce significantchanges in natural frequency. A number of measurements weremade on diseased lime trees (crown die-back, rot, etc.) andthese displayed natural frequencies that were very differentfrom those for the healthy trees. Key words: Trees, stability, natural frequencies     

Population structure and fruit production of Pyrus bourgaeana D. are affected by land-use

The Iberian wild pear (Pyrus bourgaeana D.) is a rare, fleshy-fruited tree restricted to dehesas and evergreen sclerophyllous Mediterranean forests in the southwestern Iberian Peninsula. It produces palatable fruits and leaves attractive to different species groups, playing an important trophic role in the ecological networks of Mediterranean ecosystems. However, the intensification in the traditional land-use linked to these areas could threaten the stability of the wild pear populations in the short/medium-term. In order to determine the population dynamics of this relevant species in relation to the land-use history, we selected two populations (southern Spain) subjected to different land-use management, dehesa (D) and abandoned olive grove (AOG). An analysis of 122 adult trees reported an overall density of 0.6 trees ha⁻¹. The tree age was estimated by tree-rings analysis in all adult trees. Dendrometric parameters, reproductive features, and germination rates were also measured. Regeneration was clearly biased, as evidenced by the truncated age structure. A low correlation (R² = 34%) between age and DBH (diameter at breast height) (244 cores analysed) showed that diameter seems not to be a reliable predictor of tree age. Trees from AOG populations had significantly-higher values of DBH, height and crown diameter, but were less productive in terms of fruits and seeds. Nested analysis of variance showed significant variation in fruit production, fruit size, dry mass, water content and seed viability. There were also significant differences in masting. No evidence was found to demonstrate that fruit production, seed viability, or germination rate influence the low natural recruitment of this species. These findings indicate that the traditional agrosilvopastoral practices carried out in the study area for decades, and its subsequent intensification, have strongly influenced the ecological structure of the Iberian wild pear populations at the local scale, which could compromise its stability in the near future.     

佛山市主要城市园林植物滞尘效益分析

研究了佛山主要园林植物净化大气环境的生态效应,测定了佛山市15种主要城市绿化植物滞尘能力,采用相关的指标和评价分析方法,建立相关模型,同时对影响植物叶片滞尘能力的有关因子进行了分析和探讨。研究表明,不同地点及不同种类的植物的滞尘量差异显著,乔木树种滞尘量最大,说明乔木植物是滞尘的主体。不同植物滞尘能力的差异与叶片的表面特性(皱纹、粗糙、绒毛、油脂等)及其湿润性有密切关系,滞尘量的多少与树冠总叶面积、枝干分枝角度、树冠形状等有关。     

基于绿视率的城市生态舒适度评价模型构建

城市生态系统服务指人类从城市生态系统中获取的利益,城市绿色空间是提供城市生态系统服务的主要载体。而城市化进程的加快对城市绿色空间的存量造成威胁,城市生态系统服务难以达到居民需求。传统的城市绿色空间评价指标集中于对城市绿地面积的评价,指标偏向整体性和二维化,忽视了三维绿量,也鲜少关注生态系统服务质量。基于以上背景提出了一个城市生态系统服务功能评价指标——城市生态舒适度,通过人体的主观感受对城市生态系统服务功能做出质量反馈,并结合灰色关联分析法构建了该指标的评价模型。通过样本的条件对比分析得出,当绿视率水平低于30%时,城市生态舒适度的主要影响因子为绿视率;当绿视率水平高于30%时,则是湿度、PM2.5浓度和风力等级。将评价模型的模拟结果与实测值进行对比验证,结果显示二者的变化趋势基本相同,表明评价模型科学有效。     

The effects of tree characteristics on rainfall interception in urban areas

Trees in urban areas have significant effects on the urban ecosystem. They can be used to improve the water cycle in urban areas by increasing evaporation and reducing runoff through rainfall interception. Street trees placed in planters on impervious areas reduce runoff by intercepting rainfall and by temporarily storing raindrops on leaves. Therefore, understanding tree canopy geometry and the effect of rainfall interception is important in urban hydrology. In this study, we assessed the effect of tree canopy morphology on rainfall interception using four major street tree species, Sophora japonica L., Ginkgo biloba L., Zelkova serrata (Thunb.) Makino, and Aesculus turbinata Blume, in Seoul, South Korea. We measured throughfall for each tree and also derived three-dimensional data of tree canopy morphology with a terrestrial laser scanner. Tree height, canopy crown width, leaf area index (LAI), leaf area density, mean leaf area, and mean leaf angle were used to determine canopy morphology. The interception rate was mostly affected by the LAI; a higher LAI tended to result in a higher interception rate. Leaf area affected the rainfall interception rate when trees had similar LAIs. These findings on individual tree canopy rainfall interception can help us to understand the importance of rainfall interception in hydrology and for ecological restoration when planning urban green spaces.

     

长白山西坡风灾区森林恢复状况

以长白山西坡风灾迹地（阔叶红松林、云冷杉林、岳桦林）的样地调查资料为基础,研究了各林型森林群落遇灾23年后的恢复特征.结果显示：3种林型的恢复速度为阔叶红松林>云冷杉林>岳桦林,并且它们与各自对照的群落共有度指数分别为0.49、0.44、0.33.风灾对各林型的乔木组成和多样性的影响不同：阔叶红松林中,风灾显著增加了乔木总数量,但对乔木种数和α多样性指数没有显著影响（P>0.05）;云冷杉林中,风灾仅显著降低了Shannon多样性指数和Simpson优势度指数;岳桦林中,除Pielou均匀度指数,其余多样性指数都因风灾而显著降低.各林型优势树种组成变化及更新情况对风灾的响应也与林型相关：阔叶红松林与对照区的优势树种组成显著不同,而云冷杉林及岳桦林受灾前后的优势树种组成差异均不大;阔叶红松林的幼树更新情况较好,云冷杉林有少量更新,岳桦林带几乎没有林木更新.表明风灾对森林群落的影响在23年后仍未消除,森林在风灾干扰后的恢复需要一个漫长的过程.     

台风“布拉万”对东北近天然落叶松云冷杉试验林的影响

台风是重要的森林干扰因子之一,会对森林生态系统的结构和功能产生较大的影响。2012年的台风"布拉万"对我国东北地区局部森林造成了严重的破坏。以受灾最重的吉林省汪清林业局的近天然落叶松云冷杉林为对象,采用方差分析和相关分析方法,研究林分结构和地形条件对林木株数损伤率的影响。结果表明:(1)林木损伤类型可分为折断、连根拔起、搭挂、压弯4种,其中连根拔起为最主要的损伤类型,占总损伤株数的52%,台风灾害造成的林木株数损伤率平均为14.09%。(2)径级大小对林木株数损伤率的影响显著。损伤主要发生于径级较小林分处,径级越大,其株数损伤率越小。(3)林木株数损伤率随林分密度的增加有减小的趋势,但在统计学上它们的关系不显著。(4)不同树种间的林木株数损伤率差异显著,落叶松、冷杉等针叶树种损伤株数最多。(5)林分的树种多样性指数与林木株数损伤率无显著的相关性。(6)海拔、坡度和坡位对林木株数损伤率的影响不显著,但坡向的影响显著,东北坡向林分的林木株数损伤率最大。研究结果可以为灾后森林恢复和减少风灾影响的森林培育措施提供依据。     

Mechanical stability of trees under dynamic loads

Tree stability in windstorms and tree failure are important issues in urban areas where there can be risks of damage to people and property and in forests where wind damage causes economic loss. Current methods of managing trees, including pruning and assessment of mechanical strength, are mainly based on visual assessment or the experience of people such as trained arborists. Only limited data are available to assess tree strength and stability in winds, and most recent methods have used a static approach to estimate loads. Recent research on the measurement of dynamic wind loads and the effect on tree stability is giving a better understanding of how different trees cope with winds. Dynamic loads have been measured on trees with different canopy shapes and branch structures including a palm (Washingtonia robusta), a slender Italian cypress (Cupressus sempervirens) and trees with many branches and broad canopies including hoop pine (Araucaria cunninghamii) and two species of eucalypt (Eucalyptus grandis, E. teretecornus). Results indicate that sway is not a harmonic, but is very complex due to the dynamic interaction of branches. A new dynamic model of a tree is described, incorporating the dynamic structural properties of the trunk and branches. The branch mass contributes a dynamic damping, termed mass damping, which acts to reduce dangerous harmonic sway motion of the trunk and so minimizes loads and increases the mechanical stability of the tree. The results from 12 months of monitoring sway motion and wind loading forces are presented and discussed.     

Canopy tree mortality depends on the proportion of crown exposed to sunlight,but this effect varies with species' wood density

Understanding what drives changes in tree mortality as well as the covariates influencing trees' response is a research priority to predict forest responses to global change. Here, we combined drone photogrammetry and ground-based data to assess the influence of crown exposure to light (relative to total crown area), growth deviations (relative to conspecifics), tree size, and species' wood density (as a surrogate for light-demanding and shade-tolerant life-history strategies) on the mortality of 984 canopy trees in an Amazon terra firme forest. Trees with lower wood density were less prone to die when their proportion of crown was more exposed to sunlight, but this relationship with relative crown exposure weakened and slightly reversed as wood density increased. Trees growing less than their species average had higher mortality, especially when the species' wood density decreased. The role of wood density in determining the survival of canopy trees under varying light conditions indicates differential responses of light-demanding versus shade-tolerant species. Our results highlight the importance of accounting for life-history strategies, via plant functional types, in vegetation dynamic models aiming to predict forest demography under a rapidly changing climate. Abstract in Spanish is available with online material.     

Short-term Effects of Harvest Technique and Mechanical Site Preparation on Arthropod Communities in Jack Pine Plantations

Arthropods play a key role in the functioning of forest ecosystems and contribute to biological diversity. However, the influence of current silvicultural practices on arthropod communities is little known in jack pine (Pinus banksiana) forests, a forest type comprising a major portion of the Canadian boreal forest. In this study, the effects of silvicultural treatments on arthropod communities were compared to identify those treatments that minimize ecological impacts on arthropods. The influence of harvesting techniques and mechanical site preparations on insect family richness and abundance of arthropods (total, by orders and by trophic groups) was examined in young (three-year-old) jack pine plantations of northern Ontario. Each of the following treatments were conducted in three plots: (1) tree length harvest and trenching; (2) full tree harvest and trenching; (3) full tree harvest and blading; and (4) full tree harvest and no site preparation. Arthropods were collected using sweepnets and pitfall traps over two years. Blading significantly reduced insect family richness, the total abundance of arthropods, abundance of Orthoptera, Heteroptera, Hymenoptera, Diptera, insect larvae, and plant feeders when compared to the other treatments. The use of either full tree or tree length harvesting had similar short-term effects on family richness and the abundance of arthropods. Arthropod diversity declined with increasing post-harvest site disturbance. These results suggest that arthropod communities in the understory and on the ground are reduced most on sites mechanically prepared by blading, but are similar under conditions immediately following either full tree or tree length harvesting. The implications for regenerating jack pine in the boreal forest are discussed.     

Wind-induced tree sways

Conclusions The question of how the results of investigations on wind-induced tree sways can be used in practice is often posed. First, it must be said that, according to information in the literature, no tree species can survive violent storms (with mean wind speeds over a period of 10 min higher than 30 m/s) without any damage. This threshold value for wind speed is related to the height near the top of a forest stand. Taking the results of the spectral method as a basis for the reduction of storm risk of vital conifers, necessary silvicultural action must be: (1) to influence the amount and frequency distribution of the wind force in such a way that its shere of action becomes more and more unsuitable for tree sways, and (2) to raise the characteristic frequencies of the trees' primary sways because then effective wind force takes on lower and lower values due to narrow-band energy transfer.Numerous silvicultural methods for achieving these objectives, such as cutting off the tops of crowns or chaining trees together, are described in detail by Rottman (1986).     

Estimating mean windflow in hilly terrain from tamarack (Larix lancina (Du Roi) K. Koch) deformation

The deformation of tamarack, including crown deformation and tree ring asymmetry, was calibrated against the mean wind speed and direction at seven meteorological stations in Newfoundland. The indices, based on regression equations, showed that tree deformation is caused primarily by summer southwesterlies. A crown deformation ratio, D, gave a good estimate of mean windflow in complex terrain. A compression index, C, describing tree-ring asymmetry, gave a reasonably good estimate of mean wind flow over flat terrain but was unreliable for estimating wind flow over hilly terrain.     

新疆生态质量变化趋势遥感分析

新疆是我国西部生态环境问题比较突出的区域,开展生态状况调查评估、及时掌握生态质量状况及其变化特征是环境保护的一个研究重点。以遥感数据为基础,根据构建垂直干旱指数(Perpendicular Drought Index, PDI)的思想,改变土壤基线所经过的原点,提出表征土壤湿度的垂直湿度指数(Perpendicular Moisture Index,PMI)。基于代表绿度的垂直植被指数(Perpendicular Vegetation Index, PVI)、代表湿度的垂直湿度指数PMI和代表热度的地表温度(Land Surface Temperature, LST),利用空间几何原理创建了植被-湿度-温度生态指数(Vegetation-Moisture-Temperature Ecological Index, VMTEI)。利用MODIS数据计算了新疆2000—2018年的VMTEI,并进行趋势分析。结果表明:VMTEI集成了植被、湿度和热度的信息,能很好地反映新疆生态质量的空间分布和时间变化趋势。新疆生态质量状况总体空间分布格局变化不大,与植被分布特征比较一致,呈现出纬向伸展的变化,不同生态系统VMTEI均值差异明显,湿地生态系统生态质量状态最好,VMTEI均值为0.43左右,其次为森林生态系统;最差的是荒漠生态系统,VMTEI仅为0.28。近20年来,新疆生态状况总体上得到改善,其中,生态状况明显改善的区域占2.332%,主要集中在塔里木河干流、伊犁河、额敏河和天山北坡绿洲经济带,以农田、聚落生态系统为主,主要原因为三北防护林建设、风沙治理、城市绿地面积增加造成的生态质量状况改善;生态状况严重退化的区域占0.430%,主要集中在塔克拉玛干沙漠外围、博斯腾湖、艾比湖以及零星分布于新疆的不同地区,以湿地生态系统为主,主要由于人为因素和气候变化造成平原湖泊以及部分水库的生态退化。     

浙江天童常绿阔叶林演替阶段共有种的树木构型

树木构型是木本植物为响应光照变化在其空间建造结构上的配置模式和形态体现。研究演替不同阶段共有种构型的变化可以剔除植物谱系的影响, 反映植物构型特征与光资源供给性的关系。该研究在浙江宁波天童、南山和北仑3个次生演替序列上选择了5个演替共有种, 分4个群落高度层级, 对照分析了树高、冠幅深度和面积、枝条伸展方向、基径、叶片盖度和聚集度构型性状随演替的变化, 并分析了与冠幅曝光指数的线性关系。结果表明: 1)随着演替进行, 冠幅厚度和面积、叶片盖度、叶片聚集度和基径逐步增加, 但在个别相邻演替阶段增加不显著; 2)随着演替进行, 植物的垂直枝比例降低, 水平枝比例增加; 3)演替过程中植物冠幅曝光指数在各层级内都呈现出减小趋势; 4)构型性状和植物冠幅曝光指数间存在显著的线性回归关系(p < 0.001)。总之, 随着常绿阔叶林演替进行, 演替共有种构型的变化反映了物种功能类群由阳性先锋植物向耐阴植物的转化, 其中, 植物对光资源的适应是导致构型变化的主要原因。     

森林的风/雪灾害研究综述

风／雪灾害不仪极大影响木材生产,同时对森林生态系统的稳定性也造成很大影响。森林风／雪危害的主要类型有树干弯曲、干(冠)折、掘根以及后续危害等;其发生主要依赖于气象条件、立地因子、树木和林分特征及其之间的相互作用。其中．林木尖削度(胸径／树高)和林分结构特征(树种、组成、密度等)是控制树木和林分对风／雪荷载抵抗的主要特征量。因此．通过造林、调整林分结构．加强林分管理如间伐、施肥等措施一直是用来减少林木的风／雪灾害的主要措施。另外．林木或林分发生风／雪害的模型分析研究也取得了很大进展,但由于森林风／雪害受诸如地形、天气等多种因素影响、目前所建立的模型系统在实际应用中普适性较芹。通过综述以往研究结果认为：在气象和立地条件难以控制的情况下．通过改变可控因子林分结构来减少森林风／雪害是可行的。因此．研究如何加强森林经营管理,尤其是不同形式的间伐技术和不同处理的造林措施与风／雪灾害发生的关系、如何增加林木和林分抵抗风／雪灾害的能力等是今后该研究领域的重点和难点。与此同时．应加强风／雪灾害危险率评估研究．进而对森林进行风／雪灾害危险率管理;并注重对受灾前后林地内生态效应的研究,以便为灾后的森林经营管理和调控提供坚实的理论依据。     

突变级数法在厦门城市生态安全评价中的应用

针对港湾快速城市化地区存在的潜在突变特性,基于P-S-R(压力-状态-响应)框架和突变级数法,构建了评价城市生态安全的突变模型,并对1996—2006年厦门城市生态安全进行了评价.结果表明：1996—1998年,快速城市化对厦门市区域生态安全的影响不大,研究区生态安全状况呈上升趋势;1998—2001年,由于大范围高强度的填海造地、人口激增等生态干扰远远超过了生态系统自身的修复能力,导致厦门城市生态安全状况呈快速下降趋势;2001—2006年,厦门城市生态安全整体水平回升,主要受其海湾型生态城市重大战略转变的影响;2006年,研究区系统压力安全级别为Ⅲ,说明厦门市还存在着生态安全隐患.突变级数法反映了单一指标极值情况对生态系统突变的影响,弥补了现有方法在此方面的不足,它既减小了权重赋值的主观性,又避免了主观判断安全标准的不确定性,可准确地反映城市生态安全的发展趋势.     

城市生态风险管理关键问题与研究进展

我国目前正处于社会经济转型和城市化进程加快时期,随着城市化发展和城市人居环境的变化,城市生态风险受到越来越多关注。在综述国内外城市生态风险管理研究进展,总结风险源与受体特点和风险评价方法的基础上,结合城市生态风险管理的需求,明确了城市生态风险的管理目标,将管理目标系统归纳划分为控制目标、调控目标和规划目标3个层次;在解析城市生态风险管理特点的基础上,结合风险管理目标从弹性力、动态管理性和空间异质性3个方面对生态风险管理措施与方案进行了总结分析,并进一步探讨了风险管理保障机制。从生态风险管理目标制定、构建城市生态系统特点的风险管理体系及其管理机制等方面提出了建议与展望,以期推动我国城市生态风险管理的发展。     

北京昌平区城镇化过程与空间特征研究

城市化作为一种巨大而又毫无计划的蔓延过程,强烈地影响着全球的大面积土地,而且产生了深刻的社会和生态效应,因此全面了解城市化的生态学效应的研究已成为国际城市生态学研究的前沿领域.基于昌平区1989、1996和2001年3期土地利用景观数据提取城镇用地信息,采用城镇扩展强度指数和景观格局指数对昌平平原区城镇化过程与空间特征进行了深入研究.结果表明,昌平平原区有3种主要的城镇化模式,即都市边缘带状城镇扩展模式、交通主轴线状城镇扩展模式和卫星城面状城镇扩展模式.昌平区城镇化过程主要集中在研究时段的前期(1989～1996年).都市边缘带状城镇扩展区内,前期以城镇斑块面积独立扩展和新的城镇斑块不断产生2种方式为主,而后期以城镇斑块面积的合并扩展为主;交通主轴线状城镇扩展区则为城镇斑块面积独立扩展、合并扩展,以及新城镇斑块的产生3种方式同步进行;最后,在卫星城面状城镇扩展区,前期以城镇用地的合并扩张为主,后期则表现为卫星城周边新的城镇用地不断涌现.城镇扩展强度指数和城镇景观格局指数结合使用,能较好地揭示昌平城镇化过程与空间特征.     

城市生态基础设施管理研究进展

城市生态基础设施作为城市生态系统的重要组成部分,在维持自然生态过程稳定、促进社会经济发展、保障人居环境质量方面发挥着重要的作用。在快速城市化进程中,对城市生态基础设施进行科学的管理显得尤为重要。在重新明确城市生态基础设施管理概念和内涵的基础上,归纳提炼了4项管理原则,并对现有管理类型进行了梳理。对生态基础设施管理涉及的3个关键问题的常见解决方法进行了总结、分类,并对每类方法的优劣进行了分析讨论。针对此领域的工作做了展望。对于现有城市生态基础设施管理问题与方法的整合研究既有利于明确今后研究重点,也为城市生态基础设施管理提供了科学依据和案例参考。     

The Nature of Urban Soils and Their Role in Ecological Restoration in Cities

Current and predicted trends indicate that an increasing proportion of the world’s population is living in urban and suburban places. The nature of the urban environment becomes an important factor if we are concerned with the restoration and preservation of biodiversity and ecosystems in and around cities. This article highlights the varied impacts of cities on soils and their implications for restoration planning and expectations of restoration “success.” Urban soils exist in different historical and formational trajectories than their local nonurbanized counterparts due to direct anthropogenic disturbance and indirect environmental impacts from urbanization. Therefore, urban soils often exhibit altered physical, chemical, and biological characteristics in comparison to local nonurbanized soils. Several unique features of urban soils and urban ecosystems pose particular issues for ecological restoration or the improvement of degraded soil conditions in cities. The creation of novel soil types, conditions that promote invasion by non‐natives, the strong influence of past land use on soil properties, and the presence of strong interactions and alternative stable states set up unique difficulties for the restoration of urban soils. Soils in urban restorations are a medium that can be deliberately manipulated to improve site conditions or in the monitoring of soil conditions as indices of ecosystem status. Including an explicit role for strong manipulations of soils in urban ecosystems changes how we approach baselines, management, and reference conditions in urban ecological restoration. With an understanding of urban soil ecological knowledge, we can guide aspects of urban ecological restoration toward successful outcomes.