退化土地植被恢复群落物种多样性与生物量分配格局

研究了湘西北女儿寨小流域7种典型植被恢复群落生物量的空间分配格局、物种多样性特征及其相互关系。结果表明:1)润楠次生林乔木层生物量最高,马尾松天然林灌木层生物量最大,油桐人工林草本层生物量最高,乔木层最低,毛竹-杉木林灌木层与草本层生物量最小,群落总生物量以马尾松天然林群落最高,荒草灌丛群落最低。2)乔木层物种以润楠次生林最丰富,多样性指数最高,物种分布最均匀;灌木层物种丰富度以毛竹-杉木混交林最高,油桐人工林多样性与均匀度指数最大,优势度最小,荒草灌丛群落的物种丰富度、多样性及均匀度最低;草本层物种丰富度以油桐人工林最高,马尾松天然林最低,杉木人工林草本层多样性指数与均匀度指数最大,润楠次生林优势度最高;群落总体物种丰富度以油桐人工林最高,润楠次生林群落的多样性指数最高,种群分布最均匀,荒草灌丛群落的多样性、均匀度与优势度都最低。3)女儿寨小流域退化土地物种丰富度与群落生物量之间的关系可用"S"曲线较好地描述,双曲线能较好地描述群落多样性指数、群落均匀度指数与生物量之间的关系,而生态优势度与生物量之间为非性线关系。     

北京九龙山植物群落物种多样性特征对比分析

根据对北京九龙山植物群落的样地调查数据,采用Shannon-Wiener多样性指数、群落均匀度和生态优势度指标研究了九龙山封育植被乔灌草各层的物种多样性,并分别就阳坡和阴坡进行了乔木材、灌价群落的指标对比分析,结果表明,这3种指标能够有效地表征暖温带植物群落的组成结构特征,在九龙山封育植被中,阴阳坡的灌丛群落与乔木材相比,其灌木层的物种多样性Shannon-Wiener指数D高于乔木林中乔木层,而低于其灌木层;灌丛群落的草本层Shannon-Wiener指数小于乔木材中草本层;乔木材的草本层的物种多样性Shannon-Wiener指数大于灌木层,灌木层又大于乔木层,而生态优势度系数C在上述3种比较中与Shannon-Wiener指数表现相反,而群落均匀度指数J在比较中阴阳坡的表现不同,最后讨论了九龙坡地区植被演替序列及加速其进展演替的恢复措施。     

长江三峡地区退化生态系统植物 群落物种多样性特征

以三峡地区退化生态系统植物群落样地资料为基础,研究了不同退化类型、不同退化程度植物群落的物种多样性特征,分析了植物群落物种多样性与人为干扰和演替的关系。结果表明：受干扰较轻的退化类型,群落物种多样性比自然生态系统高,受干扰较严重的退化类型,群落物种多样性比自然生态系统低。随着生态系统的退化,群落物种丰富度先升高后又逐渐降低。从不同层次来看,乔木层物种多样性逐步减低,灌木层和草本层物种多样性则表现出先升高后又逐渐降低。退化森林生态系统各层次的物种多样性表现为灌木层、草本层＞乔木层,和地带性生态系统常绿阔叶林的灌木层（包括乔木幼苗和幼树）＞乔木层＞草本层的格局有显著差别。若以空间代替时间,则表现出随着演替进程群落物种多样性升高后又降低。从群落各层次来看,乔木层随着演替进程物种多样性逐步升高,灌木层、草本层则先升高后又降低。     

四川大巴山巴山水青冈群落的物种多样性特征

巴山水青冈(Fagus pashanica)是川、陕、鄂、渝四省市交界处的特有植物。巴山水青冈林集中分布在四川省东北部的大巴山区。目前关于巴山水青冈群落的资料极其匮乏。作者在大巴山区通过对7个样地39个样方调查数据的分析, 探讨了巴山水青冈群落的物种多样性特征。主要结果有: (1) 巴山水青冈群落物种组成丰富, 共记录到维管束植物77科142属217种。乔木层物种集中于壳斗科、杜鹃花科、蔷薇科、山矾科等科; 灌木层物种集中于蔷薇科、忍冬科、壳斗科、槭树科等科; 草本层植物个体数量以苔草属(Carex)植物和普通鹿蹄草(Pyrola decorata)占绝对优势。(2) 群落乔木层物种多度对数呈倒“J”型分布, 灌木层与草本层的物种多度近似对数正态分布。群落物种丰富度由大到小依次为灌木层>草本层>乔木层; Shannon指数与Simpson指数的顺序为灌木层>乔木层>草本层; 均匀度指数的顺序为乔木层>灌木层>草本层。(3) 东坡、南坡的植物物种多样性高于北坡。乔木层Shannon指数与土壤第二层厚度回归关系显著; 草本层Shannon指数与土壤第一层厚度的回归关系显著; 灌木层的物种数和Shannon指数与土壤第一层有机质回归关系显著。(4) 群落建群种和乔木层主要树种重要值与物种多样性主要表现为负相关关系, 但与灌木层的物种多样性关系不显著(P≥0.05)。结果表明, 灌木层物种多样性主要受到环境因素的影响, 而乔木层和草本层物种多样性受到环境因子和群落自身特征的双重影响。     

岷江冷杉林皆伐后次生群落结构和物种多样性的演替动态

为阐明岷江冷杉林皆伐后次生群落的演替过程,采用空间代替时间的方法,在川西米亚罗林区海拔3100—3600 m的阴坡选择岷江冷杉林皆伐后次生演替10、20、30、40和50a阶段的次生群落作为研究对象,对其群落结构和物种多样性的动态进行了研究。不同演替阶段的树木均呈显著聚集分布。按群落中优势种的重要值将该演替序列划分为3个类型:悬钩子-蔷薇灌丛、白桦阔叶林和桦木-岷江冷杉针阔混交林。随次生演替,乔木和灌木种的物种丰富度趋于增加,而草本种的物种丰富度趋于减少;乔木和灌木种的Shannon-Wiener多样性指数趋于增大,而草本的Shannon-Wiener多样性指数趋于减小;乔木、灌木和草本层的Pielou均匀度指数均趋于增大;乔木层的Simpson优势度指数趋于减小,灌木和草本层的Simpson优势度指数在演替0—40年阶段趋于增大,而在演替50a阶段趋于减小。在该演替序列中,乔木、灌木和草本层的物种组成均呈耐荫种替代非耐荫种的趋势。     

四川小寨子沟森林群落物种多样性的环境梯度分析

运用去势典范对应分析法(DCCA),分析了四川小寨子沟自然保护区森林群落物种多样性指数与环境因子的关系.结果表明,群落物种多样性表现为草本层>灌木层>乔木层;海拔高度是群落乔木层物种多样性分布格局的主导因素,随着海拔高度的上升,乔木层物种丰富度和多样性下降,而均匀度没有明显变化;土壤有机质和土壤全氮代表的土壤养分状况决定着灌木层和草本层物种多样性的分布格局.地形因子(如坡度、坡向等)与物种多样性没有明显的关系.     

鼎湖山植物群落多样性的研究

根据鼎湖山自然保护区１６个植物群落的样地调查资料,从种丰富度和不同类型的物种多样性指数、均匀度与植被类型、人为干扰程度、演替阶段等方面的关系进行了分析。本区植被类型的多样性指数、均匀率指数变化反映了其结构复杂程度、生境的差异。物种丰富和多样性随着人为干扰程度的增强而降低。群落内各层的物种丰富度的大小的顺序为“灌木层＞草本层＞乔木层”,而群落多样性指数的大小顺序为“灌木层＞乔木层＞草本层”。群落多样     

不同火烧强度迹地林下灌草层物种多样性及其与土壤因子的关系

为揭示胶东丘陵区麻栎黑松混交林过火后林下灌丛群落结构和多样性变化,探究群落物种分布和多样性指数与土壤因子之间的相互关系,该研究以威海仙姑顶中度、轻度、未过火林地为研究对象,对不同火烧强度林地进行土壤的定量分析和植物物种多样性调查,并运用典范对应分析法(CCA)和冗余分析法(RDA)进行排序,以明确影响不同火烧迹地林下灌丛群落物种多样性的关键土壤因子。结果表明:(1)各林地丰富度、多样性、均匀度指数在群落垂直方向上均表现为草本层大于灌木层。灌木层丰富度、多样性、均匀度指数均随火烧强度的增加先升后降,轻度火烧达到最大值,是灌丛群落特征变化的关键转折期;草本层Patrick、Shannon-Wiener和Simpson指数逐渐降低,Margalef指数先降低后微弱上升,均在未过火林地达到最大值,均匀度指数各林地无显著差别(P0.05)。(2)未过火与中度火烧地之间的Morista-Horn指数在灌木层、草本层和灌草层中均为最小,β多样性最高,林下物种组成差别迥异;轻度与中度火烧地在灌木层次上物种异质性较高,未过火与轻度火烧地在草本层次上拥有较高异质性的物种更替。(3)中度和轻度火烧地林下灌丛群落大致均可分为3个类群,未过火林下灌丛植物疏离分散,则未形成类群;中度火烧影响植物物种多样性的正向主要因子为碳氮比(C/N),逆向主要因子为全磷(TP)、全钾(TK);轻度火烧正向因子为氮磷比(N/P),逆向因子为pH;未过火林地物种多样性受多种土壤因子的共同作用。(4)火烧提高了林下灌丛群落物种更替速率,增加了灌木层物种多样性,降低了草本层物种多样性,轻度火烧地的物种丰富度水平较高,火烧迹地影响群落物种多样性的因子既有相似性又存在差异性,TK和TP是火烧迹地物种多样性的共同影响因子,磷(P)是火烧迹地物种多样性的共同限制性元素。     

浙江古田山常绿阔叶林演替序列研究:群落物种多样性

采用较为成熟的“空间差异代替时间变化”的研究方法,应用相邻格子样方法调查了16个典型样地,利用Shannon-Wiener指数、Pielou均匀度指数、Simpson生态优势度指数计算了浙江古田山自然保护区常绿阔叶林演替序列4种群落的物种多样性。结果表明,从针叶林到针阔叶混交林、木荷林和甜槠林的演替过程中,4种群落乔木层的Shannon-Wiener指数分别为1.9670、2.4975、2.6140和2.4356,呈现先增大后变小的趋势;灌木层物种多样性以针阔叶混交林最高,Shannon-Wiener指数为2.8625;针叶林的草本层Shannon-Wiener指数为1.5334,高于其它3种群落。在群落的垂直结构中,演替序列中的针叶林、针阔叶混交林、甜槠林物种多样性均表现为灌木层>乔木层>草本层,而木荷林物种多样性大小则表现为乔木层>灌木层>草本层。演替过程中,乔木层、灌木层和草本层的物种多样性的变化幅度以草本层最大,H、JSW、JSI、D的变异系数分别为0.1572、0.0806、0.0899和0.1884;灌木层变化幅度最小,其H、JSWJ、SI、D的变异系数分别为0.0482、0.0385、0.0142和0.1553。     

青藏东缘岷江上游亚高山针叶林人工恢复过程中物种多样性动态

通过对不同林龄(10～70年)的人工云杉(Picea asperata)林及自然恢复的桦木(Betula utilis var. sinensis)林和天然原始冷杉(Abies faxoniana)林的调查研究,采用Margalef指数、Simpson指数、McIntosh指数、Shannon-Wiener指数、Pielou的均匀度指数、Hurlbert均匀度指数等多样性指数及物种数、个体数和盖度分析了群落乔木层、灌木层、草本层及总体的物种多样性,结果发现1)人工云杉林的物种多样性随着林龄的增加逐渐上升,林冠郁闭前后上升最快,在50～70年间下降;其中乔木层物种多样性先上升,郁闭后下降;灌木层物种多样性郁闭前下降,郁闭后骤然上升,后来缓慢下降;草本层物种多样性在早期阶段很高,随着郁闭度的增大而下降,郁闭后又缓慢回升.2)均匀度的变化幅度不大,变化的趋势基本上与物种多样性相反. 3)次生桦木林与同林龄的人工云杉林及天然原始林相比,原始冷杉林的物种丰富度、群落总体、乔木层、草本层优势度(Simpson指数和MacIntosh指数)和多样性(Shannon-Wiener指数)最高,灌木层均匀度最低;人工云杉林的物种丰富度、优势度、群落总体、乔木层、草本层多样性最低,但灌木层的均匀度和多样性最高. 4)物种多样性的变化与群落盖度特别是乔木层盖度呈负相关,影响人工云杉林物种多样性恢复的主要因素是其乔木层的盖度过大. 5)人工云杉林的物种多样性不仅低于同龄的自然恢复的桦木林,远远低于天然原始林,而且经过70年的发育,灌木层和草本层的盖度很低,水土保持和水源涵养的生态效益很差.迫切需要调整人工云杉林的群落结构,以恢复其生物多样性,增强其生态效益的发挥.建议在人工云杉林郁闭以后,采取适当的人工干扰如间伐等,降低乔木层的盖度,以促进林下灌草层的发育,既可增强水土保持功能,又可加速物种多样性的恢复.     

百山祖自然保护区主要植被类型概述

对近20年来多次调查的资料进行系统整理,将百山祖植被主要划分成6个植被类型：常绿阔叶林、常绿落叶阔叶混交林、针阔叶混交林、针叶林、山地矮林和山地灌草丛,其下可分为22个群系：同时对群落的种类组成、结构和演替趋势作了概述。。     

Species composition and diversity of small Afromontane forest fragments in northern Ethiopia

In the highlands of northern Ethiopia, remnants of the original Afromontane forest vegetation are largely restricted to church yards and other sacred groves in a matrix of cropland and semiarid degraded savanna. To assess the potential for natural forest regeneration, species composition and diversity of all forest fragments (10) in a study area of 13,000 ha were analyzed in relation to environmental and soil variables. Using a random design and a density of approximately one plot per 2 ha in all fragments, 31 20×20 m plots were sampled. Indicator species analysis and MRPP tests yielded five communities representing two forest types and one degraded savanna habitat. The forest fragments had a species-poor tree and shrub community in which plots were rather homogeneous and most species abundant. NMDS and analysis of variance indicated that a topographical gradient correlated to soil phosphorus, soil depth, stoniness and the proximity to the river system explained the major differences in species composition and separated moist and dry Afromontane forest communities. The grazing intensity further partitioned the habitats. Present communities and their environmental correlates indicate that the secondary climax forest in the area probably consisted of dry Afromontane forest interlaced by broad strips of moist Afromontane forest along rivers and streams and not a continuous, mono-dominant Juniperus forest as is often presumed. Negative effects of the degraded matrix on forest fragments increased with decreasing patch area and increasing shape irregularity. Nevertheless, all remaining fragments are important for their role in the landscape ecology of the region as refuges and species pools and should be protected and managed accordingly. If seed dispersal from forest fragments into exclosures and subsequent tree recruitment are both successful, the vegetation type most likely to establish is Afromontane savanna woodland, and if managed properly, eventually dry Afromontane forest may arise. Increasing the size of small patches and placing forest plantations and exclosures in the vicinity of small forest fragments is expected to yield the most immediate results. This approach may increase the likelihood of patch colonisation by frugivorous forest birds and thus foster the regeneration of native woody species.     

不同密度格木幼林的土壤理化与林下植被特征

为探索适合格木(Erythrophleum fordii)人工林在幼龄阶段的种植密度,在不同林分密度(2 m×1 m、2 m×2 m、2 m×3 m、3 m×3 m)的6 a生格木人工林下设置标准样地,采用土壤质量评价和灰色关联度等方法,探究不同密度下格木幼林的土壤理化与林下植被特征。结果表明,密度2 m×3 m下的林木胸径、树高最优,较最低水平高16.7%、27.9%;土壤总孔隙度最大,全N、硝态N、铵态N含量最高,灌木草本多样性最高。相关性分析表明土壤化学性质对灌木草本的多样性影响最大。不同林分密度下格木幼林土壤理化性质及林下植物多样性有显著差异,因此,选择合适的林分密度对人工林土壤肥力的可持续利用及林分的经营培育至关重要。     

Classification and ordination of communities of soil arthropods in an urban park of Osaka City

To assess the effect of management of a park on soil arthropods, communities of Oribatida and Collembola were analyzed at 11 sites of different vegetation in Tsurumi Park, an urban park of Osaka City. The type of canopy layer and soil density strongly affected the community parameters, such as species diversity. Ordination revealed that soil density, contents of organic matter, and shrub layer were important for variety in the oribatid community; the shrub layer was important for the collembolan community. Species richness of both arthropod groups was highest in a mixed forest and lowest on bare land, while the abundance of Collembola was highest on a lawn site. Areas of a common vegetation type had a similar oribatid community;Trichogalumma nipponica dominated in deciduous forests,Eohypochthonius crassisetiger in mixed forests and one of coniferous forests. On the other hand, collembolan communities did not correspond with the vegetation.Sminthurinus sp. was collected from every site, and the most abundant species wasCryptopygus thermophilus that exhibited an outbreak on lawn sites. A significant correlation existed between species diversities but not between abundances of Oribatida and Collembola.     

树种组成对北亚热带11年生常绿阔叶人工林碳储量的影响

以中国北亚热带退化灌木林改造而来的木荷-青冈栎混交林和杜英纯林为对象,研究树种组成对常绿阔叶人工林生态系统碳储量的影响。结果表明:(1)退化灌木林改造成两种人工林生长11年后,生态系统植被、土壤碳储量均显著增加;植被碳储量的增加主要来自乔木层。(2)两种人工林碳积累能力有差异。杜英林植被碳储量比木荷-青冈栎林高99.4%,其中杜英林的乔木层碳储量比木荷-青冈栎林高27.75t·hm-2,是后者的2倍;杜英林土壤有机碳储量(0~50cm)显著高于木荷-青冈栎林10.17t·hm-2,其中在0~10、20~30cm土层杜英林均显著高于木荷-青冈栎林。研究表明,退化灌木林人工改造成常绿阔叶林后生态系统碳储量显著增加,杜英纯林碳蓄积能力明显高于木荷-青冈栎混交林,说明在以增加碳储量为目的的退化生态系统改造过程中,树种选择非常重要。     

环境因子对山西太岳山典型森林类型物种多样性及其功能多样性的影响

该研究采用典型样地法,调查群落内物种分布并测量植物功能性状(叶面积和植株高度),对山西太岳山不同坡位华北落叶松-白桦混交林以及辽东栎次生林物种多样性及其功能多样性进行比较分析,探究环境因子对不同群落层次(乔木、灌木、草本)物种多样性及其功能多样性的影响机制,以及环境因子与群落构建之间的联系,为森林生态系统多样性研究以及经营管理提供理论依据。结果显示:(1)华北落叶松-白桦混交林的物种分布更加均匀,物种多样性和功能多样性(乔木层)均显著高于辽东栎次生林。(2)华北落叶松-白桦混交林乔木层功能均匀度与功能分散指数显著高于辽东栎次生林,但灌木草本层低于辽东栎次生林。(3)不同群落层次的物种多样性与功能多样性均呈正相关关系,影响物种分布和性状分布的环境因子存在差异,物种多样性受多种环境因子的综合影响,而单个环境因子对功能多样性影响较大,环境解释力与林分类型和群落层次相关。(4)乔木层物种多样性主要受土壤pH、冠层结构(MLA、林分开度)以及光照影响,灌木层物种多样性与土壤pH和MLA密切相关,林下总辐射、土壤养分(SOC、STN)、土壤相对含水率是影响草本层物种分布的主要环境因子;冠层结构(MLA、林分开度)是影响乔木层功能多样性最主要的环境因子,土壤pH和坡位分别是华北落叶松-白桦混交林和辽东栎次生林灌木层功能多样性的主要影响因子,影响草本层功能多样性的主要环境因子是土壤相对含水率与LAI。研究表明,在垂直分层的森林生态系统中,不同群落层次竞争的主要环境资源存在差异,乔木层通过改变冠层结构和林内环境限制林下物种分布和性状分布。     

杉木林改造成乡土阔叶林对林下植物物种组成和多样性的影响

把杉木林改造成乡土阔叶林,不仅能提供高价值木材,而且能够提升生态系统服务功能,是我国目前改造退化针叶林最常见的经营模式之一,但这些改变对其林下植物物种组成和多样性的影响及机制我们尚知之甚少。以南亚热带杉木林采伐迹地上重新种植的杉木林、红锥林和米老排林为研究对象,调查研究其灌木层和草本层植物物种组成和多样性,结果表明：（1）和杉木林相比,改造后的红锥林和米老排林灌木层的植物物种丰富度和多样性均呈极显著降低（P<0.01）,但其草本层植物只有物种丰富度极显著降低（P<0.01）,多样性均无显著变化（P>0.05）;（2）主成分分析（PCA）表明改造后的林分灌木层和草本层的植物物种组成发生明显的变化,冗余分析（RDA）确定导致林分灌木层植物物种组成发生变化的主要原因是杉木林改造成红锥林和米老排林后的冠层透光率、土壤碳氮比、土壤含水量和凋落物碳氮比的显著变化,而冠层透光率和土壤碳氮比的显著变化是导致其林下草本层植物物种组成发生明显变异的主要因子;（3）方差分解结果显示微地形、乔木特性和土壤理化性质的独立效应对灌木层和草本层植物物种组成的影响高于它们的交互效应。该研究为科学经营管理人工林和提高人工林生态系统多功能性提供科学依据。     

Vegetation Changes in a Native Forest Produced by <Emphasis Type="Italic">Atta vollenweideri</Emphasis> Forel 1893 (Hymenoptera: Formicidae) Nests

Herbivory is an important factor to generate spatial mosaics with variations in a plant community composition and organization. The objective of this work was to determine the impact of Atta vollenweideri Forel 1893 nests on herbaceous and shrub vegetation in a degraded native forest of the Espinal ecoregion. The study was carried out in the Protected Area and Multiple Use Nature Reserve called Estancia “El Carayá” (Entre Ríos, Argentina). Ten A. vollenweideri nests were selected by simple random sampling through internal roads, and two transects were drawn from the center of the nest (0 m) up to 60 m away in opposite directions. The line intercept method was used to quantify the percentage of vegetation cover of herbaceous and shrub species, while the floristic composition was estimated by the Canfield method. Afterwards, a nonparametric test between positions and a conglomerate analysis to evaluated distance were applied. Grass species, legumes, and sedges fell in the adjacent areas to nests, highlighting the bare soil at the crest and base of the nests. Fifteen plant species were identified, and two families correspond to monocotyledonous and dicotyledonous species. In conclusion, the nests of A. vollenweideri affect the community of herbaceous and shrub vegetation of the studied degraded native forest of the Espinal ecoregion since these ants perform a high selection of herbaceous species considered as pioneers of plant successions.     

我国南方4种常见人工林林下植物多样性特征及影响因素

为了解长期植被恢复的成熟人工林林下植物组成与多样性特征及其影响因素,基于广东鹤山生态系统国家野外科学观测研究站的南亚热带人工林生态系统,对环境相似(坡度、坡向、海拔)、30 a生4种类型人工林(桉树混交林、马占相思纯林、乡土混交林、针叶混交林)进行调查研究,分析林下植物组成和物种多样性(Shannon-Wiener指数、Simpson指数、Pielou指数)特征。结果表明,人工林林下植物类型丰富,均可形成乔-灌-草垂直结构;4种林型林下植物组成既有相似性,也有差异性,桉树混交林与针叶混交林、马占相思纯林与乡土混交林的灌木层组成相似;桉树混交林与马占相思纯林、乡土混交林与针叶混交林的草本层组成相似,而桉树混交林与针叶混交林的草本层组成极不相似。林分类型影响林下植物多样性,马占相思纯林林下灌草多样性显著低于其他3种混交林(P<0.05),灌木物种数、个体数最少;针叶混交林林下物种丰富度最高。林分郁闭度与林下植物多样性呈正相关(P<0.001),林下植物分布与土壤养分含量相关,桉树混交林、马占相思纯林林下植物多样性与不同形态氮含量相关,有效磷、全磷影响乡土混交林林下物种的分布,针叶混交林受土壤酸碱度、全钾的影响较为明显。在4种人工林林下植物群落中,乡土混交林多样性,均匀度最高,优势度最低,具有更佳的保育和维持林下生物多样性功能。因此,乡土树种混交林更适用于生态公益林构建或对一些针叶林及外来树种纯林进行林分改造。     

The vegetation of the forest-steppe region of Hustain Nuruu, Mongolia

The vegetation of a forest-steppe region in Hustain Nuruu, Mongolia, was studied by a phytocoenological approach. Eleven plant communities were recognized, comprising four steppe communities, two meadow communities, a tussock grassland, two shrub communities, a scrub community and a woodland community. The botanical and ecological characteristics of the different communities are discussed, with reference to the existing classification of Mongolian plant communities. Analysis of the present data indicates that a refinement or extension of the classification system is desirable, especially concerning the steppe(-related) communities. Discussion of the relative distribution of steppe and forest reveals that in the relatively dry location of Hustain Nuruu grassland and shrubland dominate the natural vegetation (88% of the area). Forest covers ca. 5% of the area, it is limited to sites where ground water is within rooting depth: north slopes above 1400 m (Betula platyphylla woodland) and along erosion gullies (fragmentary Ulmus pumila gallery woodland). Under natural conditions forest cover might reach 12%, but it is speculated that wild ungulates could maintain its extension at a lower level. The importance of forest is greater in forest-steppe regions with higher rainfall, but the factors determining the distribution of grassland and forest are expected to be similar.