内蒙古高原温带稀树草原生态系统特征与成因

内蒙古高原分布的温带榆树稀树草原生态系统在中国乃至世界上都是一种特殊的生态系统,对于它的研究可加深对植被分布规律的理解,且有利于该系统的保护。本文分析了该生态系统的地理分布、气候特点、土壤状况、物种组成、群落结构及天然更新状况等,比较了草原、森林和稀树草原3个生态系统的特征,提出了在内蒙古高原分布的温带榆树稀树草原生态系统是在独特的气候、土壤和地形条件下形成的经度(水分梯度)地带性顶极植被,决定其存在的最关键因素首先是降水量和土壤的水分条件,其次才是沙质土壤。这种生态系统既不是草原,又不是森林,而是介于落叶阔叶林和草原之间的一种生态系统类型。在此纬度带上,从东到西分布的经度地带性植被谱应为:温带森林、温带稀树草原、典型草原、荒漠草原等。在同一纬度带上,沙质土壤的基质并不完全被稀树草原生态系统所覆盖,还有沙漠等生态系统类型。建议《中国植被》增加一个新的植被类型,温带稀树草原。     

元谋干热河谷植被的类型研究 Ⅰ.群丛以上单位

本文主要用法瑞植物社会学学派的方法对元谋干热河谷植被的群丛以上单位进行划分和研究。经分析,确定了从群目(order)到群丛(association)的一个分类等级系统。整个河谷区的植被可以归入到扭黄茅、坡柳群目(Dodonaeo-Heteropogonetalia contorti)中,下面再分出两个群属(alliance)和九个群丛。经使用模糊聚类分析数学方法验证,分类基本合理。 经研究表明元谋干热河谷1600米以下地区的气候及植被特点与热带的稀树草原(savanna)十分相似,可以称为半自然稀树草原或次生性稀树草原(semi-natural savanna or secondarysavanna)。     

云南潞江坝怒江干热河谷植被研究

应用法瑞地植物学派的理论和方法,将云南潞江坝1300m以下地区干热河谷植被确定为1群目、3群属、6群丛、4亚群丛。通过对植被外貌、结构、区系组成、分布特点的分析,认为本区现存植被主要由河谷季雨林长期破坏所至,目前较典型的干热河谷灌草丛植被类型属于次生性稀树草原或半自然性稀树草原。     

植被生态系统恢复及其在华南的研究进展

介绍了恢复生态学常用的理论,并指出恢复生态学研究大多涉及植被生态系统恢复。植被恢复的目标就是要恢复植被的合理结构、功能和动态过程,从而为人类提供生态系统服务。植被恢复可以把区域的地带性植被生态系统作为参考生态系统,但目前的植被恢复工作绝大部分只是恢复了植被生态系统的部分组成、结构和功能。植被生态系统恢复研究主要从退化的原因与过程、恢复的过程与机理,以及从生境恢复、种群恢复、群落恢复、生态系统和景观恢复等不同尺度上的恢复开展。在介绍华南地区的植被生态系统现存问题的基础上,对华南地区开展的植被生态系统恢复,尤其是华南植物研究所(园)开展的植被生态系统恢复研究进行了介绍。最后,提出了华南地区植被生态系统恢复的方向及发展趋势。     

基于CSCS和RegCM3模型的21世纪末中国潜在植被

潜在植被作为陆地生态系统的重要组成部分,能够真实反映立地气候环境,对其分布特征的研究可为生态工程评价提供依据。本文以综合顺序分类系统理论为基础,选取RegCM3模型及A2情景下的预测数据,模拟了2071—2100年中国潜在植被的空间分布。结果表明,21世纪中国潜在植被均发生了不同程度、不同方向的变化,具体表现为:温带森林和冻原高山草地向冷干方向变化,其中温带森林为中国主体潜在植被;亚热带森林向较冷地区演替;温带荒漠、热带森林及热带稀树草原向冷湿方向迁移;半荒漠向暖湿地区集中分布;干草原、温带湿润草地及热带荒漠向暖干方向变化,其中温带湿润草地和热带荒漠的空间分布重心迁移显著。本文揭示了21世纪中国潜在植被的变化规律,可为我国21世纪生态建设战略提供参考。     

论沙丘植被过程的基本生态关系

沙丘生态系统常常被认为是一种退化生态系统,自然植被恢复和稳定人工植被构建是沙丘生态系统恢复的基本手段。本文基于对沙丘生态系统长期研究结果,依从对立统一、动态变化哲学原理,结合相关生态学理论,从沙丘生态系统的独特性出发,提出了进行植被塑造过程研究需要注意的若干生态关系。论述了尺度-格局-过程的耦联关系和协同-权衡关系的转化在植被塑造过程研究中的必要性,阐释了区分沙丘流动与沙丘固定、干扰与胁迫、风蚀与沙埋在植被过程研究中的重要性,并探究了生态位法则或中性法则在沙丘植被过程研究中的应用价值,从适沙性与耐旱性、生理与繁殖过程、有性与无性繁殖等方面论述了沙丘植被塑造过程研究应关注的问题,旨在为沙丘生态系统植被自然恢复和稳定植被建设搭建理论构架。     

疏林草原榆树种子-幼苗更新过程研究进展

榆树疏林草原曾广泛分布于我国北方农牧交错区,是科尔沁沙地、浑善达克沙地和呼伦贝尔沙地特有的原始景观,景观特征类似于热带稀树草原——萨瓦纳,乔木种类单一,草灌木植被发达,是遏制沙漠扩张的重要屏障。但目前榆树疏林的生长状况大都不良,树龄老化,自然消亡长期得不到更新,特别是种子-幼苗时期更新过程受到人为因素和自然环境的影响,使得榆树疏林生态系统处于崩溃边缘。本文基于国内主要的榆树疏林草原分布区榆树种子-幼苗更新过程研究,列举了榆树疏林种子-幼苗的分布特征以及影响其生长发育的主要因素,并且提出进行榆树种源保护、长期定位观测,开展多学科交叉研究和榆树固沙效果分析的展望,对于榆树疏林植被恢复和重建具有重要的理论价值。     

2001-2018年中国-老挝交通走廊核心区植被稳定性对极端干旱的响应

中国-老挝交通走廊核心区干旱事件的频繁发生威胁着该区域生态系统的稳定性。基于Palmer干旱指数（PDSI）和增强型植被指数（EVI）数据量化了中老交通走廊核心区不同植被类型的稳定性（年均EVI与其标准差之比）及其对干旱的抵抗力（干旱期间植被结构和功能保持其原始水平的能力）和恢复力（植被恢复到干旱前水平的速度）。结果表明：（1）2001-2018年间,中老交通走廊核心区共发生5次极端干旱事件,出现极端干旱的年份有2005年、2010年、2015年、2016年和2017年,以上年份极端干旱面积占总面积的比例分别为13.37%、47.46%、10.41%、12.00%和3.05%;（2）不同植被类型对极端干旱的响应不同,中老交通走廊核心区内常绿阔叶林的稳定性显著高于其他植被类型,和其他植被类型相比,常绿阔叶林虽然暴露在干旱环境中的时间更长,但其具有更高的稳定性,在维持中老交通走廊核心区的生态系统稳定性上发挥着重要作用;（3）常绿阔叶林和木本稀树草原对极端干旱的抵抗力和恢复力显著高于混交林、草地和农田,研究区内各植被类型对极端干旱的抵抗力与温度和降水呈显著正相关关系。     

金沙江河谷苏铁天然植物群落的研究

近年在金沙江干热河谷及其邻近地区陆续发现的苏铁天然植物群落,为本属植物在欧亚大陆内陆分布的最北边缘。其中,面积最大和保存较好的是渡口市攀枝花苏铁(Cycas panzhihuaensis)植物群落。本文研究了这个群落的分布与生境、生长状况、外貌、种类组成以及群落的综合特征等。认为具有稀树草原的特点,而这里的稀树草原是次生性质的,苏铁群落是其中幸存的残遗植被类型。这对研究我国植物地理有着重要意义。     

塔吉克斯坦的生态系统和植物多样性

本文在查阅资料的基础上,结合野外考察对塔吉克斯坦生态系统和植物多样性进行研究。塔吉克斯坦生态系统有12种——积雪冰川生态系统、高山荒漠生态系统、高山草甸草原生态系统、中部山地针叶林生态系统、中部山地的肉叶森林生态系统、中部山地疏叶旱生森林生态系统、中低部山区的亚热带稀树草原生态系统、山麓的半荒漠和荒漠生态系统、湿地生态系统、农业生态系统、城市生态系统和杂草生态系统;多样的生态系统分布植物9 771种,其中藻类2 145种,菌类2 233种,地衣524种,苔藓植物358种,蕨类植物22种,裸子植物35种,被子植物4 454种。     

Long range lateral root activity by neo-tropical savanna trees

The extent of water uptake by lateral roots of savanna trees in the Brazilian highlands was measured by irrigating two 2 by 2 m plots with deuterium-enriched water and assaying for the abundance of deuterium in stem water from trees inside and at several distances from the irrigation plots. Stem water of trees inside the irrigation plots was highly enriched compared to that of control trees, whereas stem water of trees just outside the plot was only slightly enriched compared with that from control trees. Therefore, bulk water uptake in the savanna trees studied occurred in a horizontally restricted area, indicating that their rooting structure was characterized by a dense cluster of short roots associated with the main trunk and a few meandering long range lateral roots. This root architecture was confirmed by extensive excavations of several species. The same deuterium labeling pattern was observed in an Amazonian tropical forest. The savanna ecosystem, however, differed from the tropical forest ecosystem by having a greater proportion of trees outside the irrigation plots having stem water with deuterium levels significantly above background. This leads us to the conclusion that savanna trees have more or longer lateral roots compared to tropical forest trees. The greater lateral root development in savanna trees may be an adaptation for more efficient nutrient absorption.     

Edge influence on plant litter biomass in forest and savanna in the Brazilian cerrado

Edge influence, characterized by differences in ecosystem characteristics between the edge and the interior of remnants in fragmented landscapes, affects a variety of organisms and ecosystem processes. An important feature that may be affected by edges is the amount of plant litter, which provides important habitat for a large variety of organisms and influences ecological processes such as fire dynamics. We studied edge influence on plant litter and fine woody debris in the cerrado of São Paulo state, south‐eastern Brazil. We collected, sorted, dried and weighed plant litter along 180 m‐long transects perpendicular to three savanna and eleven forest edges adjacent to different anthropogenic land uses, with four to five transect per edge. There tended to be less biomass of the finer portions of fine woody debris at both savanna and forest edges. Graminoid litter at savanna edges was greater than in the corresponding interior areas, whereas other litter portions were either unaffected by edges or did not show consistent patterns in either savanna or forest. Edge influence was usually restricted to the first 20 m from the edge, was not influenced by edge characteristics and exhibited no clear differences between savanna and forest areas. Several mechanisms may have led to the variable patterns observed including variation in the plant community, plant architecture, and invasive species. The edge‐related variation in plant litter may putatively lead to, for example, increased fire frequency and intensity at the savanna edges and altered trophic dynamics at forest edges; the mechanisms and consequences of this edge influence should be addressed in future studies.     

Fire in Australian savannas: from leaf to landscape

Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km²) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management.     

Ecological thresholds at the savanna-forest boundary: how plant traits, resources and fire govern the distribution of tropical biomes

Fire shapes the distribution of savanna and forest through complex interactions involving climate, resources and species traits. Based on data from central Brazil, we propose that these interactions are governed by two critical thresholds. The fire-resistance threshold is reached when individual trees have accumulated sufficient bark to avoid stem death, whereas the fire-suppression threshold is reached when an ecosystem has sufficient canopy cover to suppress fire by excluding grasses. Surpassing either threshold is dependent upon long fire-free intervals, which are rare in mesic savanna. On high-resource sites, the thresholds are reached quickly, increasing the probability that savanna switches to forest, whereas low-resource sites are likely to remain as savanna even if fire is infrequent. Species traits influence both thresholds; saplings of savanna trees accumulate bark thickness more quickly than forest trees, and are more likely to become fire resistant during fire-free intervals. Forest trees accumulate leaf area more rapidly than savanna trees, thereby accelerating the transition to forest. Thus, multiple factors interact with fire to determine the distribution of savanna and forest by influencing the time needed to reach these thresholds. Future work should decipher multiple environmental controls over the rates of tree growth and canopy closure in savanna.     

Anthropogenic disturbance and the formation of oak savanna in central Kentucky, USA

Aim To deepen understanding of the factors that influenced the formation of oak savanna in central Kentucky, USA. Particular attention was focused on the link between historical disturbance and the formation of savanna ecosystem structure. Location Central Kentucky, USA. Methods We used dendrochronological analysis of tree‐ring samples to understand the historical growth environment of remnant savanna stems. We used release detection and branch‐establishment dates to evaluate changes in tree growth and the establishment of savanna physiognomy. We contrasted our growth chronology with reference chronologies for regional tree growth, climate and human population dynamics. Results Trees growing in Kentucky Inner Bluegrass Region (IBR) savanna remnants exhibited a period of suppression, extending from the establishment date of the tree to release events that occurred c. 1800. This release resulted in a tripling of the annual radial growth rate from levels typical of oaks suppressed under a forest canopy (< 1 mm year^?1) to levels typical of open‐grown stems (3 mm year^?1). The growth releases in savanna trees coincided with low branch establishment. Over the release period, climatic conditions remained relatively constant and growth in regional forest trees was even; however, the growth increase in savanna stems was strongly correlated with a marked increase in Euro‐American population density in the region. Main conclusions Our data suggest that trees growing in savanna remnants originated in the understorey of a closed canopy forest. We hypothesize that Euro‐American land clearing to create pasturelands released these trees from light competition and resulted in the savanna physiognomy that is apparent in remnant stands in the IBR. Although our data suggest that savanna trees originated in a forest understorey, this system structure itself may have been a result of an unprecedented lack of Native American activity in the region due to population loss associated with pandemics brought to North America by Euro‐Americans. We present a hypothetical model that links human population dynamics, land‐use activities and ecosystem structure. Our model focuses on the following three land‐use eras: Native American habitation/utilization; land abandonment; and Euro‐American land clearance. Ecological understanding of historical dynamics in other ecosystems of eastern North America may be enhanced through recognition of these eras.     

Coastal Forest in Eastern Southern Africa has Savanna Bush-clump Origins

Ecosystems - The extensive coastal forests in eastern southern Africa persist as a putative alternative stable state in an open ecosystem mosaic that includes grassland and savanna. We examine two...     

Vegetation,herbivores and fires in savanna ecosystems: A network perspective

The dynamics of savanna ecosystems depends on the interplay between multiple factors such as grazing, browsing, fires, rainfall regime and interactions between grass and woody vegetation. In most modelling applications this interplay may not be fully understood because some of these drivers enter the models as dynamically independent factors. In this paper we consider such factors as dynamic variables. To analyze their interplay we focus on the structure of the interactive network of variables and exploit the properties of signed digraphs using the algorithm of Loop Analysis. Qualitative signed digraphs for the savanna ecosystem are developed and their predictions used to interpret patterns of abundance observed in case studies selected from the literature. The outcomes of this exercise unveil that: 1) the structure of the interactions is appropriate locus for the explanation of patterns observed in savannas; 2) signed digraph can help disentangling causative mechanisms by linking correlation patterns, source of change and network structure. This study highlights that central to the understanding of savanna dynamics is our ability to diagram the important relationships and understand how they interrelate with sources of variations to cause ecosystem change.     

Functional significance of ungulate diversity in African savannas and the ecological implications of the spread of pastoralism

The African savanna biome supports a higher diversity of ungulate species than is found in any other biome or continent. This exceptional faunal diversity and herbivore biomass density is directly linked to the high spatial heterogeneity of African savanna ecosystems. The dependence of herbivore dietary tolerance on body size translates into important size-related differences between savanna ungulate species in terms of habitat specificity, geographical range, and the share of community resources exploited. Intact savanna ungulate communities, with species distributed across body size classes and feeding guilds (grazer/browser), have strong regulatory influences on savanna ecosystem structure and function. Replacement with livestock systems of low diversity and high biomass density within a narrow body size range has occurred through the removal of competitors, pathogens, and predators, and the widespread provisioning of water. Overgrazing by livestock, coupled with episodic droughts, has caused widespread rangeland degradation and loss of floristic and faunal diversity which, by current models, is unlikely to recover to 'climax conditions even with destocking. In selected regions where potential still exists, African savanna biodiversity and human economic development will both be best served by the integration of sustainable wildlife utilization into multispecies animal production systems.     

Myxobacterial Biodiversity in an Established Oak-Hickory Forest and a Savanna Restoration Site

The purpose of this study was to establish the myxobacterial biodiversity of an established oak-hickory forest and a savanna restoration site that has been cut and subsequently burned on four occasions between 1993 and 1998 in an attempt to restore the land to the native savanna ecosystem. Soil and bark samples were processed through standard methods specifically for myxobacteria and numbers and types of species were recorded for both locations. Species were identified through morphology of fruiting bodies, SDS-PAGE of whole cell protein profiles, and 16S rRNA gene sequences. Statistical analyses were employed and suggested that significantly greater numbers and types of myxobacteria are present on the bark of the trees in the established oak-hickory forest than the bark of trees in the savanna restoration site, while little difference in numbers and types of species were observed between the soil samples of the two locations.     

Heatwave implications for the future of longleaf pine savanna understory restoration

The longleaf pine (LLP) savanna ecosystem once covered?~?92 million acres of the Southeast USA, but due to anthropogenic activities such as logging and fire suppression, only 3% of its once widespread historic range remains. While many restoration efforts are underway to conserve this biodiverse ecosystem, restoration must be done in the context of climate change. In the last few decades, heatwaves have increased in frequency and intensity across the Southeastern USA with further increases predicted. To expand our understanding of LLP savanna restoration in light of these changes, we ran a series of three simulated heatwave greenhouse experiments through a Course-based Undergraduate Research Experience (CURE) incorporating?~?150 undergraduate researchers per experiment. We measured plant growth metrics for four understory grasses commonly used in LLP savanna restoration efforts. We found that while most grass plug individuals survived heatwave conditions, aboveground production was reduced due to heatwaves. This productivity decrease could result in less biomass available for the essential vegetation fire feedback loop, where fire increases grass biomass, and in turn, more grass provides more fuel for fire. These results imply that land managers can proactively compensate for biomass loss due to heatwaves by planting more grass plugs during initial restoration.