Coexistence and divergence of tropical dry forests and savannas in southern Mexico

Aim The purpose of the study was to assess the degree of floristic differentiation between tropical dry forest (TDF) and savanna occurring in a single landscape. This comparison provides information on the responses of vegetation to the prevailing environmental conditions, while it also allows us to make inferences about large‐scale events and processes, both biogeographical and evolutionary. Our approach included three levels of analysis: (1) taxonomic, (2) morphological and (3) vegetational. Location The seasonal dry tropical landscape in the Nizanda region, Oaxaca State, southern Mexico. The landscape comprises a complex vegetation mosaic in which tropical dry forest and savannas are the most conspicuous components. Methods Comparisons between TDF and savanna were based on inventories for these communities produced after 8 years of botanical survey. At the taxonomic level, the relative representation of taxa of different hierarchical levels in each community was examined. Morphological analyses required the classification of species on each of three criteria: (1) growth form, (2) life form and (3) growth habit. Vegetation level analysis was based on the frequencies of taxa in one hundred 100‐m² composition plots with which matrices of binary data were constructed for species, genera and families. These were subjected to classification analysis with Ward's method and using Euclidean distances as the dissimilarity algorithm. Results The combined flora for both communities comprised 600 species, 375 genera and 94 families; between them they shared 31, 40 and 34 taxa, respectively. The corresponding Sørensen similarity values were 10%, 21% and 72%, respectively. Ranking genera and families according to their species richness displayed large differences between savanna and TDF. Large differences between these communities were observed for Acanthaceae, Cactaceae, Euphorbiaceae and Mimosaceae, whereas Fabaceae and Asteraceae had similar high ranks according to the species richness in the two systems. The growth form spectrum diverged between the two communities, with TDF having more trees, shrubs and climbers. Savanna was characterised by forbs and graminoid herbs. Growth habit spectra revealed a clear dominance of herbaceous and suffruticose plants in savanna, and of woody elements and epiphytes in TDF. Regarding Raunkiaer's life forms, savanna had relatively more hemicryptophytes, and TDF more phanerophytes. Classification analyses showed that savanna and TDF forest samples kept their identities, regardless of taxonomic level (species, genera and families) at which the analyses were performed. Main conclusions The TDF and savanna of Nizanda represent two floristic systems with a large degree of differentiation at all taxonomic levels and patterns of morphological attributes. This suggest that the two floristic sets have evolved independently for extended periods of time, despite their close proximity. One important implication of this floristic differentiation is the large joint contribution made by these communities to the regional flora.     

Plant families as predictors of plant biodiversity in Mexico

Three speciose plant families (Asteraceae, Fabaceae s.l. , and Poaceae) are evaluated for their appropriateness as predictors of overall regional patterns of plant diversity in Mexico. These families fulfil criteria for usefulness as indicators advocated by several authors, such as adequate taxonomic knowledge, wide geographical distribution, and occurrence in different plant communities. Known richness was determined from a database including 17,903 species from floristic inventories, review of taxonomic literature, and the study of herbarium specimens. Mexico was divided into 253 cells, each 1° latitude by 1° longitude; for each cell, total plant diversity and number of species in each predictor's family were determined. In addition, each species was categorized by 'preferred' vegetation type (temperate forest, dry tropical forest, humid tropical forest, xerophytic scrubland). Both multiple and simple regression models show that the three families are good predictors of total vascular floristic richness. Fabaceae s.l. has the highest semipartial correlations for all multiple models except with the xerophytic scrubland data set, for which it shares the highest values with Poaceae. Univariate models also predict satisfactorily the vascular floristic richness, especially when Fabaceae s.l. is used as the predictor, and the effect of vegetation type is included. Our results indicate that these three families can be used as potential predictors for total vascular plant species richness in Mexico although Fabaceae s.l. is the best predictor.     

Heterogeneity of xerophytic vegetation of limestone outcrops in a tropical deciduous forest region in southern México

The heterogeneity of xerophytic vegetation developing on limestone outcrops immersed in a tropical deciduous forest matrix was studied in Nizanda (S México). The study units comprised three clearly distinct communities based on their physiognomy and substrate, representing a gradient of edaphic aridity: (1) xerophytic scrub (XS); (2) tropical deciduous forest on rock (TDFr); and (3) tropical deciduous forest on deeper soil (TDFs). Structural and floristic variables were gathered in nine 100 m² plots by community. In the 0.27 ha sampled 211 plant species were recorded. Total floristic richness by community decreased with increasing edaphic aridity: 159 species in TDFs, 107 in TDFr, and 36 in XS. Although significant differences were observed between the three communities for only four structural variables (total and upper stratum species densities, and relative monocotyledon density and cover), other variables confirmed the differences between the two forest communities and the XS (total and upper stratum cover, density, and basal area). TDFr and XS also differed from TDFs with respect to lower stratum species density, and absolute monocotyledon density and cover. The results showed the importance of monocotyledons and the prevalence of clonality in TDFr and XS. A comparison between limestone outcrop and inselberg vegetation indicated a virtual absence of therophytes, graminoid herbs, cryptogamic crusts, and desiccation-tolerant and carnivorous plants in the former, whereas the prevalence of monocotyledon mats, and xerophytic and succulent plants is the most striking similarity between these rocky environments. Xerophytic vegetation of limestone outcrops in Nizanda may be seen as analogous of relictual communities that existed during a northbound migration of Neotropical flora, towards the arid zones of North America.     

Flora and vegetation of rocky outcrops/cliffs near the Hyrcanian forest timberline in the Mazandaran mountains,northern Iran

Due to their numerous endemic/sub‐endemic and rare plant species, rocky outcrops and cliffs, particularly those occurring at the timberline and forest/steppe ecotones of the Hyrcanian area, are considered as among the most important and fragile ecosystems in Iran. As a representative of such ecosystems, one of the last remnants of relatively undisturbed timberline and ecotone areas of the central Hyrcanian region was selected for phytogeographical, floristic and vegetation analyses. The flora and vegetation of rocky outcrops and crevices at altitudes of 2500–3000 m a.s.l. was surveyed by 40 relevés of 25 m² surface area. A total of 215 vascular plants belonging to 55 families and 150 genera were identified in the different vegetation types. Hemicrytophytes (55.8%) were the dominant life form and Euro–Siberian/Irano–Turanian biregional plants (28.2%) were the most common chorotype at the study sites. A phytogeographical analysis indicated that Euro–Siberian elements (including Hyrcanian endemics) precede other uniregional chorotypes in the timberline and upper‐mountain parts of the central Hyrcanian area. The Caucasus, an important biodiversity hotspot close to Iran, has a considerable number of taxa in common with the Irano–Turanian floristic regions. Five vegetation types were identified using a modified TWINSPAN procedure and subsequently analysed by indirect gradient analysis applying both species‐related (species richness, life form and phytogeographical elements) and topographic/bedrocks features of the studied relevés. The analysis revealed that the vegetation of the area is mainly affected by altitude, heat index, northness, slope inclination and bedrock features.     

香港长洲岛野生植物物种多样性与植被的研究

长洲岛共有野生维管植物237种,隶属于73科184属.植被类型以次生常绿阔叶林为主,其次为灌丛群落.植物区系以热带亚热带植物地理成分占优势,热带性质明显.该岛的植物区系与邻近岛屿植物区系具有极大的相似性,在香港植物区系组成中占有一定地位.由于人为活动和外来植物的影响,其植物多样性及植被的保护应引起注意.     

新疆焉耆盆地种子植物区系特征分析

焉耆盆地位于新疆天山中段南麓,在植被地理区划上属于新疆暖温带灌木、半灌木荒漠区,其独特的自然地理位置和生态环境孕育了较为丰富的植物资源,研究其种子植物区系多样性分布特点对该区植物资源保护及可持续开发利用具有极其重要的意义。本研究通过野外实地调查及查阅相关文献资料,对新疆焉耆盆地的种子植物区系分布特点进行了系统分析。结果显示,该区种子植物约有1035种,隶属于80科373属,其中新疆特有种有38种,占新疆特有种总种数的14.18%。区系地理成分中,在科级水平上,焉耆盆地种子植物80科可划分为6个分布区类型和7个变型,并以温带地理成分为主(共有22个科),占该区非世界分布科总科数的57.89%;在属级水平上,焉耆盆地种子植物373属可划分为12个分布区类型和17个变型,并以温带地理成分为主(共197属),占非世界分布属总属数的62.54%。焉耆盆地种子植物生活型中,草本植物占优势,共有901种,占该区种子植物总种数的87.05%;灌木有110种(占10.63%),乔木17种(占1.64%),藤本7种(占0.68%)。焉耆盆地种子植物生态类型中,中生类型676种,占该区种子植物总种数的65.31%;旱生类型有191种(占18.45%),湿生类型123种(占11.88%),水生类型45种(占4.35%)。     

Observations on the floristic,life-form,leaf-size spectra and habitat diversity of vegetation in the Bhimber hills of Kashmir Himalayas

Vegetation analysis provides the prerequisites to understand the overall community structure and function of any ecosystem and is a fundamental requirement for the precise evaluation of biodiversity. Although many studies have assessed floristic attributes of specific areas, there are still unexplored regions, as is the case of the mountain region in the Kashmir Himalayas. Current research highlighted the recent findings of the scientific characterization of floristic and ecological aspects on the forest flora found in the Bhimber hills, Pakistan. Floristically, a total of 93 species belonging to 80 genera in 41 families were recorded. The species distribution patterns across the families were disproportionate with half of the species contributed by 8 families and 25 families were monotypic. Based on the floristic analysis, Asteraceae was the largest family with 12% of species followed by Poaceae with (11%) species. PAST software, a multivariate ecological community analysis was used to classify the species similarities and differences among the different habitat types. According to the habitat wise distribution, 21% of species were growing in the natural forest habitat, while 15% of species were dispersed in highly distributed habitats along roadsides and 8% on pedestrians. In terms of functional diversity, the herbaceous growth form was dominant (58%). The biological spectrum revealed therophytes as the dominant life form as it indicates the disturbed habitat vegetation. The phytogeographical analysis revealed that the maximum (69%) species were native, while the minimum (31%) species were exotic. Thus, the study of these functional and habitat diversity patterns can significantly improve our understanding of the ecological aspects of the flora in the geographical location. This information may additionally be useful in devising management plans to ensure sustainable utilization and better management of forest landscapes in this Himalayan region.     

Classification and ordination analysis of herbaceous flora in district Tor Ghar,western Himalaya

District Tor Ghar is phytosocilogically unexplored region in the western Himalaya. Present study was conducted in district Tor Ghar during the summers of 2012 and 2013 to study floristic diversity of herbaceous flora in the region. The district Tor Ghar is located on 34° 32′ - 34° 50′ N, and 72° 48′ - 72°58′ E. A total of 229 herb species belonging to 168 genera and 66 families were identified. Herbaceous vegetation was sampled from 1 × 1 m quadrats. For vegetation classification into plant communities, presence, absence (1,0) data on 229 herbaceous species and 64 locations were analyzed in PCORD version 5 via Cluster and Two Way Cluster Analyses. Six plant communities were established. Plant abundance data were treated in CANOCO version 4.5 to measure the ecological gradient of plant species and communities of the region. Detrended Correspondence Analysis (DCA) a type of indirect gradient analysis reconfirmed the results of Cluster and Two way Cluster Analysis. Moreover the study furnishes useful information for improvement, protection and management of present vegetation status for future generation. A comprehensive conservation measure with practical implementation is utmost necessary for conservation of rapidly depleting plant resources of the area.     

安徽湿地维管植物多样性及植被分类系统

通过野外实地调查并结合相关文献资料,对安徽湿地维管植物多样性进行了研究,系统地分析了安徽主要的湿地植被类型及分类系统。结果表明:(1)安徽省湿地维管植物共有95科303属682种(含种下分类单位),其中蕨类植物10科11属16种,种子植物85科292属666种;种子植物中裸子植物2科5属7种,被子植物83科287属659种(其中双子叶植物62科208属451种,单子叶植物21科79属208种);湿地维管植物主要是由草本植物组成,科、属的优势现象明显,以莎草科(Cyperaceae)、禾本科(Gramineae)、菊科(Compositae)和蓼科(Polygonaceae)为优势科;以蓼属(Polygonum)、苔草属(Carex)、眼子菜属(Potamogeton)、飘拂草属(Fimbristylis)、莎草属(Cyperus)等为优势属,属的组成相对较为分散,寡种属和单种属占总属数的93.4%;(2)从分布区类型看,在科级水平上有7个类型,在属级水平上有13个类型,表明该区系地理成分复杂,分布区类型多样;总体上温带成分略多于热带成分,说明了安徽湿地维管植物的分布与本地所处的气候带相适应,反映出从热带向温带过渡的区系特点;(3)依据中国湿地植被的分类原则和分类系统,结合安徽湿地植被的生境特征和群落学特征,可将安徽湿地植被划分为3个植被型组、7个植被型、7个植被亚型和141个群系。     

湖北恩施地区蕨类植物区系研究

蕨类植物是森林植被中草本层的重要组成部分,对森林的生长发育有重大影响。本研究在搜集文献、野外调查和采集标本的基础上,对湖北恩施地区蕨类植物区系成分及特点进行研究。结果显示:(1)恩施地区蕨类植物共有39科96属380种,其中中国特有种106种;该地区蕨类植物起源古老,物种分化水平较高,优势科属明显、物种丰富、组成多样,是蕨类植物物种多样性的典型代表地区之一。(2)该地区稀子蕨属、荚果蕨属、黔蕨属和骨牌蕨属种类齐全、分布广泛,是这些属的分化和分布中心。(3)该地区蕨类植物生活类型齐全,以土生为主(占81.36%)。(4)恩施地区在中国蕨类植物地理区系中占有重要地位,该地区蕨类植物科属以泛热带区系成分相对较多,总体偏热带区系成分;物种以温带亚洲、东亚和中国特有分布型为主(占60.79%),具有显著的亚热带性质。(5)恩施蕨类植物区系与其他地区联系广泛,过渡性比较明显,尤其与四川地区联系紧密。     

外马廊山岛植被特性与植物多样性

该研究对无居民海岛舟山外马廊山岛进行初步踏勘,了解该岛植被特征与植物多样性,探讨海岛植被与大陆植被的差异性,并对海岛植物的主要植物组成、生活型结构、地理成分、群落类型以及多样性和相似性进行了分析。结果表明:外马廊山岛面积小,共有33科51属55种植物,植物种类偏少,留存有普陀狗哇花,滨柃,厚叶石斑木等具有滨海特色植物,具有开发潜力。外马廊山岛热带成分较为明显,与附近地区较为相似。岛上群落优势种或建群种的科为山茶科,大戟科,松科等,与大陆的常绿阔叶林的优势种或建群种的优势科如樟科,金缕梅科,壳斗科,山茶科等不大相同。岛上植物主要以高位芽植物为主(58.18%),但较大陆常绿阔叶林的高位芽植物比例要低。外马廊山岛植物群落结构简单,植物多样性相对较低,物种丰富较低,主要原因在于生态适应性和演替过程的差异,岛上植物群落演替至稳定群落还需要相当一段时间。外来种比例占9.09%,外来种如黑松和红鸡竹能形成群落或在群落中具有较为明显的优势,并可能会造成一定的生态干扰。     

青藏高原东南部察隅河流域种子植物区系研究

在野外植被调查、标本采集和资料查询整理的基础上,汇总了察隅河流域种子植物名录,并对流域内植物物种的组成、优势科属、区系地理成分及性质进行分析。运用R语言在属水平上与其周边16个地区的植物区系进行聚类及主成分分析,探讨察隅河流域种子植物区系与其他区系之间的关系。结果表明：(1)察隅河流域共含种子植物138科、689属、2 771种(含变种),其中裸植子物4科12属56种,被子植物134科677属2 715种,被子植物中双子叶植物112科531属2 270种占绝对优势。(2)区内地理成分联系广泛,科的区系划分除世界分布类型外,热带分布型53科(55.21%),温带分布型43科(44.79%);属的区系划分中所有类型均有分布,温带分布型396属(62.07%),热带分布型230属(36.05%);属的分布型与科相比具有更明显的温带性质;植物种类丰富度高但特有成分低,无特有科,仅含12特有属。(3)流域内植被垂直地带性分布较为明显,保留了较多古老孑遗植物,如裸子植物的西藏红豆杉(Taxus wallichiana)、察隅冷杉(Abies chayuensis)和云南松(Pinus yunnanensis)等;由于青藏高原的上升运动,成为杜鹃花属(Rhododendron)、虎耳草属(Saxifraga)、龙胆属(Gentiana)和报春花属(Primula)等新生高山植物区系成分分化繁衍的摇篮。(4)察隅河植物区系属喜马拉雅山南侧热带成分向温带成分过渡的区系性质,与珠峰自然保护区植物区系更为相似。     

Factors affecting the diversity of flora and vegetation in central European settlements

Published data on the number of plant species and/or communities were gathered for 77 European cities and 85 villages. The relationships between the floristic and vegetation diversity and some environmental variables were analysed. Species number in cities showed log linear increase with city size (expressed as the population size or city area). A linear increase in the species number with size was found in the village flora. The richness of both city and village flora was not significantly related to any climatic variable. On the contrary, the number of communities in both villages and cities was correlated not only with settlement size but also with altitude and mean annual temperature. The diversity of village vegetation was closely related to the climax type of the respective region. The features of human settlements that make it possible to consider them as landscape islands are discussed.     

山西庞泉沟国家自然保护区种子植物区系研究

庞泉沟自然保护区共有种子植物89科359属809种,其中裸子植物2科6属7种,被子植物87科353属802种。含5属以上的科15科,单、寡种属共330属,这些科、属在植物区系组成中具有重要作用。种子植物科、属、种的区系地理成分复杂多样。科的分布区类型中,世界分布型40科,北温带分布型24科,分别占总科数的44.94%和26.97%。属的分布区类型中,温带成分256属,占总属数的82.05%,反映出该区植物区系的温带性质。种的分布区类型中,中国特有分布种居首位,尤以华北成分占优势,其中华北落叶松、黄刺玫、油松等为该区植被建群种或优势种。科、属、种的特有现象不平衡,没有中国特有科,中国特有属、特有种分别为7属、325种。     

南京市加拿大一枝黄花入侵地群落的物种组成与多样性特征研究(附表)

为探究外来植物加拿大一枝黄花(Solidago canadensis)入侵与南京市本土植物多样性的关系,该文采用踏查及样方调查对其入侵地群落的物种组成与多样性进行研究。结果表明:(1)入侵地群落中共有维管植物200种(含种下单元),隶属于62科156属,其中被子植物195种,裸子植物1种,蕨类植物4种; 数量最多的是菊科(Asteraceae)和禾本科(Poaceae)植物,分别有25种和24种; 从生活型来看,草本植物占多数,有133种,占所有种的66.50%; 此外,群落内尚有其他外来植物29种。群落中重要值最大的是加拿大一枝黄花,为40.00%; 其次是救荒野豌豆(Vicia sativa),为7.00%。(2)从植物区系看,非入侵地中植物科的区系分布型共4个,而入侵地植物科的区系类型仅有3个,其中泛热带分布、世界分布和北温带分布为两者均有,东亚和北美间断分布型仅在非入侵地中存在。非入侵地植物科的区系以世界分布型为主,有13科,占该类型群落中所有科的39.39%; 入侵地则以泛热带分布型为主,有16科,占总科数的45.71%。非入侵地中植物属的区系分布型有10个,而入侵地有12个,两者区系成分相近,旧世界热带型和热带亚洲至热带大洋洲分布型仅在入侵地中出现。北温带分布型和世界分布型同为两者中最主要成分。入侵地及非入侵地群落属的区系R/T值分别为0.58和0.38,种系分化度分别为3.29和3.11。(3)重度入侵群落的Margalef指数(E)与非入侵及轻度入侵群落相比,显著降低; 此外,重度入侵群落的Simpson指数(D)、Shannon-Weiner(H'')指数和Pielou指数(J)均显著低于非入侵、轻度入侵、中度入侵群落。(4)不同生境之间加拿大一枝黄花群落的E、D、H''和J均无显著性差异。该研究可为南京地区的加拿大一枝黄花入侵地的治理防控和生态恢复,以及进一步的科学研究提供强有力的理论支撑。     

A transect study of the Eucalyptus forests and woodlands of a dissected sandstone and laterite plateau near Darwin,Northern Territory

Tabletop Mountain in the Northern Territory is a sandstone plateau topped in part by a residual laterite soil. The vegetation of the plateau was mapped and transects placed to cover the mapping units in which eucalypts were dominant or shared dominance. A polythetic divisive classification of the transect floristic data was largely congruent with the mapping units, which also differentiated the dominants. Topography and soils have an apparently strong influence on the nature of the vegetation through their influence on the periodicity and intensity of drought and Waterlogging. However, differences in soil fertility and understorey flammability are postulated to be important in discriminating several of the mapped vegetation types. The flora of Tabletop more closely resembles that of the Alligator Rivers region than that of the Mitchell Plateau or Weipa. Some of the communities differentiated at Tabletop are related floristically to some of the communities differentiated in the Alligator Rivers region and at Gove.     

Geological History,Flora, and Vegetation of Xishuangbanna,Southern Yunnan,China1

Xishuangbanna of southern Yunnan is biogeographically located at a transitional zone from tropical Southeast (SE) Asia to subtropical East Asia, and is at the junction of the Indian and Burmese plates of Gondwana and the Eurasian plate of Laurasia. The flora of the region consists of a recorded 3336 native seed plant species, belonging to 1140 genera in 197 families, among which 83.5 percent are tropical genera and 32.8 percent are endemic to tropical Asia, suggesting a strong affinity to tropical Asian flora. The vegetation of Xishuangbanna is organized into four forest types: tropical rain forest, tropical seasonal moist forest, tropical montane evergreen broad‐leaved forest, and tropical monsoon forest. The tropical rain forest in Xishuangbanna has the same floristic composition of families and genera as some lowland equatorial rain forests in SE Asia, and is dominated (with a few exceptions) by the same families both in species richness and stem dominance. The exceptions include some deciduous trees in the canopy layer, fewer megaphanerophytes and epiphytes, and a higher abundance of lianas and microphyllic plants. We consider the tropical rain forest of Xishuangbanna as a type of tropical Asian rain forest, based on their conspicuous similarities in ecological and floristic characteristics.     

Diversity and ecological distribution of macrofungi in the Laojun Mountain region,southwestern China

Surveys of the macrofungi associated with eight different vegetation types in the Laojun Mountain region of southwestern China yielded approximately 520 species belonging to 175 genera. Species richness and diversity were highest in mixed conifer and broadleaf forests and deciduous broadleaf forests. In typical forests of temperate regions of the world, there are five dominant genera of ectomycorrhizal macrofungi. The distribution patterns of species in these genera for the different vegetation types indicate that they are able to associate with a wide variety of different trees. Analysis of data for common macrofungal species and taxonomic similarity of the communities present in the eight vegetation types suggest that the greater the differences in the plant species that comprise the vegetation, the less similar are the common macrofungal species associated with the most common host plants. These same data also show that some species of macrofungi occur only in one or two vegetation types. There were 156 species of edible fungi recorded from the different vegetation types, and these fungi appear to be abundant in the Laojun Mountain region. At different positions along the elevation gradient, positive correlations existed with respect to the relationship between species richness and diversity, and the general trend was for macrofungal species richness and diversity to decrease with increasing elevation, with the numbers of species recorded being significantly lower at the very highest elevation. The relative dominance of certain taxa in the assemblage of species present was found to increase with increasing elevation, and variation in the evenness component of diversity was slight. As such, the differences in dominance and evenness were also not significant (P > 0.05). Macrofungal species richness was slightly more diverse on shaded slopes than on more exposed (sunny) slopes, and the differences in species diversity, dominance and evenness were relatively minor. This suggests that slope aspect may only weakly influence the distribution of macrofungal species in the Laojun Mountain region.     

The Austral floristic realm revisited

The classification of the Earth's flora into floristic regions has been the major goal of plant geography since the 19th century. A detailed revision of 19th and 20th century classifications is presented herein, with particular emphasis on the delimitation of the Austral floristic realm. A comparison between Chile, New Zealand, and the Cape Floristic Region is made at the genus level. Using the vascular flora of these biogeographical regions, the analysis revises previous attempts to define the Austral realm, while also assessing differences made by changes in taxonomic delimitations from recent molecular phylogenetic studies. The results indicate that the Austral floristic realm can nowadays be better described as a circum-Antarctic generalized track, composed of some 60 genera and 15 families restricted to South America and Australasia, possibly including South Africa.     

Isolated Pasture Trees and the Vegetation under their Canopies in the Chiapas Coastal Plain,Mexico1

The Coastal Plain of Chiapas (southern Mexico) was formerly covered by large tracts of subhumid tropical forests but is heavily deforested at present. In this region, 15 pastures were selected to characterize species composition of isolated trees, as well as to describe species composition, growth form patterns, and patterns of dispersal units in the vegetation growing under their canopies. The 65 recorded pasture trees belonged to 20 species and 11 families, of which Fabaceae and Moraceae were the most species-rich. Coccoloba barbadensis (Polygonaceae) and Enterolobium cyclocarpum (Fabaceae) were the most abundant and frequent trees in the studied pastures. More than half (55%) of isolated tree species were fleshy-fruited. In the vegetation sampled under pasture trees, 134 species and 45 families were found. Fabaceae and Poaceae had the largest numbers of species. Herbs were the predominant growth form (46.3%), followed by shrubs (23.9%), trees (23.1%), and lianas (2.2%); 6 species could nor be placed in any growth form category. Most species of this flora were fleshy-fruited (43.3%), followed by heavy, gravity-dispersed fruits (17.9%). The analysis of dispersal units by growth form category confirmed the prevalence of fleshy fruits, although their predominance was not so obvious among herb species. Almost half (49.2%) of the flora under pasture trees was typical of secondary vegetation; this pattern was true for herbs but not for most woody species, which were typical of primary vegetation. A numeric classification of the vegetation samples taken under pasture trees produced eight floristic groups, all of which were independent of the specific identity of pasture trees. No significant effect of dispersal unit type of pasture tree on the characteristics of the vegetation growing under them was found. Future attempts to re-create the original forest cover using isolated trees in pastures as regeneration foci should pay more attention to the maintenance of a large specific diversity independently of the dispersal types among these components of tropical landscapes.