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1.
《农业工程》2021,41(6):524-536
This study was conducted during 2018–19 to evaluate the floristic composition and ecological characteristics of vegetation of Pashat valley, Bajaur. Floristic list of the valley contains 385 species distributed in 291 genera and 102 families. The dicotyledons having 83 families with 311 species and monocotyledons with 12 families contains 61 species. Pteridophytes having 05 families with 11 species and gymnosperm with a single family of two species. The leading family was Asteraceae with 42 species (10.90%) followed by Poaceae with 39 species (10.10%), Papilionaceae (Fabaceae) with 24 species (6.23%), Lamiaceae with 20 species (5. 19%) and Rosaceae with 15 species (3.90%). Therophytes 180 species (46.80%), hemicryptophytes 53 species (13.80%), nanophanerophytes 51 species (13.20%) and geophytes 35 species (9.09%) were the dominant life form groups. Leaf size class was dominated by microphylls (138 species, 35.84%) followed by nanophylls (124 species, 32.21%) and mesophylls (89 species, 23.12%). Habit wise the vegetation was mostly herbs (289 species) followed by shrubs (54 species), trees (38 species) and lianas (4 species). According to flowering phenology, most plants (62.30%) bloomed in spring followed by in summer (34%), in autumn (1.82%), in the whole year (1.30%) and in winter (0.52%). Based on chorological affinities, most of the species were bioregional in distribution (170 species, 44.15%) followed by mono-regional (157 species, 40.78%), pluri-regional (43 species, 11.17%) and cosmopolitan (15 species, 3.89%). The ecological characteristics like life form and leaf size spectra of the vegetation have a strong correlation with the prevailing environmental conditions such as altitude, slope, precipitation and temperature.  相似文献   

2.
Floristic inventory of village Sherpao, District Charsadda comprised of total 104 plant species belonging to 46 families and 95 genera. The leading families included Fabaceae, Asteraceae, Poaceae and contributed by 8 species one (7.69%).The most pre-dominant life form was therophytes having 35 species (33.65%). Most dominant habit of flora were herbs having 77 species (74%) followed by trees contributed by 18 species (17.30%) and shrubs having 9 species (8.65%). Leaf size spectra of the flora showed that the most dominant leaf size class were microphyll having 38 species (36.53%) followed by nanophyll contributed by 32 species (30.76%), mesophyll represented 22 species (21.15%) and leptophyll contributed by 12 species (11.53%). Based on habitat 77 species (74%) were xerophytic in nature followed by 14 species (13.46%) in wet condition and 13 species (12.5%) were present in both conditions. In 104 plant species 85 were non spiny and 19 were spiny. Plant growth and distribution are having strong correlation with environment. Therefore, it is important to understand the environmental aspects that affect plant growth and distribution.  相似文献   

3.
《农业工程》2020,40(3):190-196
A study was conducted to explore the plant biodiversity, phenology, life form and leaf size spectra of the vegetation of Biha Valley, District SWAT. The study area was surveyed thoroughly in different seasons of the year. Floristic diversity of the area consists of 202 plant species belonging to 154 genera and 70 families. There were two flowering seasons, 85.15% plant species flowers during May to August while 14.65% plant species flowers during the September to November. Biological spectrum of the area indicated that Therophytes (46.60%) was the dominant life form class, followed by Hemicryptophytes having 15.53%, Nanophanarophytes (11.65%), Megaphanerophytes (8.25%), Chamaephytes (7.77%), Geophytes (5.34%), Liana (2.91%) and Mesophanarophytes (1.94%). Leaf spectra of study area revealed that Microphylls was dominant with (41.26%) followed by Nanophylls (32.04%), Mesophylls (15.53%), Leptophylls (8.85%) and Megaphylls (2.91%).  相似文献   

4.
Topsoil translocation has been used for vegetation restoration throughout the world, but it has been poorly tested within savannas. This study describes Brazilian savanna (cerrado) regeneration for the first 3 years following topsoil translocation. The topsoil was stripped from 2.5 ha of savanna and spread on 1 ha of an abandoned laterite quarry in the Federal District, Brazil. We assessed vegetation structure and species composition in 18 circular plots (3.14/m2) after 5 and 15 months and in 30 circular plots after 37 months. In the last floristic survey, the coverage of herbs was estimated using the step‐point method. To verify the source of regeneration, a total of 181 shrubs and trees were excavated over the first 2 surveys. After 3 years, 24, 40, and 21 species of herbs, shrubs, and trees, respectively, had been recorded by the surveys. Of the 33 families found, Fabaceae, Poaceae, and Asteraceae were the most representative. At 5 and 15 months, 91 and 83% of the individuals (shrubs and trees combined) were derived from resprouting, respectively. Shrub and tree stem density reached 3.2/m2 at 5 months, but declined to 0.5/m2 at 37 months. By the final survey, native and exotic grasses completely covered the ground. Topsoil translocation was effective for the propagation of native herbs, shrubs, and trees, despite the need to control invasive grasses. The large number of shrub and tree resprouts from roots suggests that the bud bank is an important component of the topsoil for savanna restoration.  相似文献   

5.
Floristic inventory of wild plants comprised of total 129 plant species belonging to 42 families and 101 genera. Location wise UAP contributed greater amount of plant species (53%), followed by PFI (29%), UoP (15%) and Islamia College (3%). Majority of the plants were annual herbs (58%), followed by perennial herbs (29%), trees (10%) and shrubs (3%), respectively. The leading families included Poaceae, contributed 18% of all the plant species. Habitat wise, 44% of them grew in grassy plains, abandoned lands and mismanaged lawns, followed by roadsides (34%), undulating grassy plains (15%) and stony grounds with uneven topography along with stream banks and drainage ditches (7%). Still some of plant species were used as ornamentals, while some shrubs were use in fencing around fields; others were utilized as green manure, for fishing, sheltering and religious purposes. Exploring and identifying the wild flora of the campus and compiling as a handbook would help to monitor new plants introductions particularly of noxious invasive weeds in the campuses in future.  相似文献   

6.
We aimed to determine which factors explain the relative abundances of climbing plants in a tropical sandy coastal plant community, locally called restinga, in SE-Brazil, where facilitation is an important mechanism controlling shrub and tree diversity. The factors examined were: associations with host trees and shrubs, environmental conditions, associations with herbs and space. We surveyed a total of 84 vegetation patches within two hectares of open restinga vegetation. Climbers, trees, shrubs and herbs were sampled using an adapted cover pin frame approach. Partial constrained ordination (pRDA) was used to partition the variation of climber species relative abundances into four sources: trees and shrubs relative abundances, herb species relative abundances, environmental variables (patch architecture and size), and the spatial coordinates. Linear models were used to model the relationship of climber diversity as a function of the environmental factors. A total of 12 climber species belonging to 5 families were recorded. Associations between climber species with subordinate trees and shrubs were the major determinants of climber presence in these vegetation patches. The support for growth created by these trees and shrubs had a secondary role in explaining these patterns. We found no relationship between tree dominance and climber species dominance in each patch. However, most climbers were associated with subordinate shrubs. Trellis availability at the first stratum was related to greater climber diversity suggesting that subordinate trees and shrubs may be crucial to promote climber diversity in this plant community. Space and associations with herbs had a minor contribution to overall variation. While 15 years of research in the site associated local floristic diversity to dominant trees, our results demonstrate that climber diversity in this community is governed by interactions with subordinate host woody species related to the environmental support for growth created by such trees and shrubs.  相似文献   

7.
确立了滨河河道硬度与滨河土地硬度两个指标,用以研究城市化地区河岸带的植物构成、多样性与均匀度、优势植物等特征与河岸硬度的关系。选定晋江市都市区12条主要河流作为研究对象,通过样地调查收集数据,并采用相应指数进行数据处理分析,结果表明:(1)调查河流的河岸带植被物种共计70科143属159种,其中乔木20科30属41种,灌木15科15属20种,草本35科98属98种,草本居主导地位,河流间种类分布不均衡;(2)河岸带植物乔灌草区系均以广义热带性成分居多,其次为世界性成分、温带性成分,无中国特有分布类型,乔木中广义热带成分占绝对主导,直观反映地带性特征,灌木与草本中的温带成分多于乔木中的温带成分,类型趋于多元,种类更丰富;(3)从河岸植被优势植物构成来看,主要优势乔木与灌木基本为本土植物,而主要草本中外来植物入侵严重,对地带性植物景观的指示显然不及乔木与灌木;(4)从河岸植被的人工美学属性来看,灌木优势植物中园林观赏植物的种类数显著多于乔木、草本优势植物,反映出晋江人工审美主导的滨河景观空间主要改变与塑造了灌木层植被景观;(5)从河岸植物的人居需求属性来看,龙眼、杨桃等多见于庭院林、水岸林的水果树种也在河岸植被中频繁出现,反映出人口密集区由于对植物生产用途的重视而对河岸植被产生的影响;(6)滨河土地硬度与河道硬度对河岸带灌木植物的影响最强烈,二者均对河岸带植物多样性造成威胁,且前者具有更大的影响力,而后者直接影响了河岸植物的分布形态,出于生产与审美目的的人为干扰对河岸带植物优势种的影响力随滨河硬度的增加而加强,低滨河硬度有助留存原生植被群落;(7)天然弯曲的河流形态对河流植被特征具有积极影响,有助于保留更多本土植被类型,并能在某种程度上丰富乔灌草的植物种类,但这种缓和作用无法根本扭转河岸硬化对植物多样性的胁迫影响。研究表明,城市化地区河流的岸带植被特征与沿线人为干扰类型和强度密切相关,恢复与塑造河岸生态景观要以乡土植被为主,通过乔木景观塑造地带性景观,并以灌木与草本丰富植被景观。  相似文献   

8.
This first ever study was carried out to explore the floristic composition of protected and unprotected forests of Sathan Gali, District Mansehra, KP, Pakistan. The study area being the part of the Western Himalayas harbours rich floristic diversity. In the current investigation, an effort was made to record primary data about floral diversity of the area. The study area was visited recurrently during 2013 and 2014. Plants were collected from different sampling sites, identified, preserved and deposited in Herbarium of Hazara University, Mansehra. A total of 127 plants species including 59 common and 68 different were found in 13 stands of reserved forest. The different species were only confined with this forest whereas common plant species were distributed in both forests. The dominant family was Asteraceae (13 species, 10.7%) followed by Labiateae (10 species, 7.75%), Poaceae and Rosaceae (8 species, 6.2%) each, Polygonaceae and Pteridaceae by (5 species, 3.87%) each. Angiosperms were represented by 118 (92.91%), plant species, Pteridophytes 5(3.93%) species and Gymnosperms 4 (3.14%) species were recorded in reserved forest. Only single species of climber was documented. The number of herbs, shrubs and trees species recorded were 73.64%, 13.17% and 10.07% respectively. A total of 103 plant species of 55 families including 61 common in both forest types and 42 species different to guzara Forest. These plant species were recorded from 22 sampling stands. Angiosperms by (92.3%) plant species, Gymnosperms (2.88%) and Pteridophytes (4.8%) were recorded. The dominant family was Poaceae by 11 plant species followed by Asteraceae and Rosaceae each represented by 10 species and Pteridaceae by 5 plant species. Habit wise 69.23% were herbs, 14.42% shrubs and 16.34% species of tree were reported. This study will assist ecologists, botanists, taxonomist, conservationists and policy makers to mend, and manage the current vegetation status and sustainability for upcoming generations. The present investigation will also serves as base line for future researches on the Himalaya regions.  相似文献   

9.
Globally, riparian zones along river banks are widely recognized for their vital role in water regulation and conservation of biodiversity. Here, we specifically investigated the floristic and functional diversity of the vegetation of the riparian zones of protected forests in Kashmir Himalaya, India. A random sampling method was used for site selection while a transect method was used for data collection. Data obtained from the field was subjected to taxonomic and functional classification. Floristic analysis revealed a total of 78 species belonging to 68 genera in 40 families, suggesting an unequal distribution of species among families. Nine families contributed half of the species: Rosaceae was the dominant family with nine (12%) species followed by Asteraceae with eight species (10%), while 23 families were monotypic. In terms of functional trait diversity, herbaceous and perennial taxa dominated, and the biological spectrum showed a dominance of the therophytic life form, indicative of disturbed vegetation. The phenological spectrum revealed that the maximum flowering periods starts in March and extends into May, in which a total of 61% of the species were observed to flower. The leading leaf size spectra were mesophyll with 35%, followed by microphyll (31%). Most (64%) of the species had a simple leaf lamina type. The results of the present study serve as a means to evaluate best management practices, assess restoration and mitigation projects, prioritize riparian related resource management decisions, and establish aquatic life use standards.  相似文献   

10.
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.  相似文献   

11.
Diversity and distribution of trees [≥5 cm diameter at breast height (dbh)], shrubs and herbs was assessed in thirty 0.05‐ha (10 × 50 m) plots of a tropical high forest in the Ssese islands of Lake Victoria, central Uganda. The aim was to determine the floristic richness and composition of the forests. We recorded 179 species belonging to 70 families and 146 genera. Of these, nine families had five species or more. Rubiaceae was the richest with fourteen species followed by Euphorbiaceae (thirteen), Apocynaceae (ten) and Moraceae (nine). The majority of the families (35) were represented by one species each. Fifty‐eight herbaceous species, 39 lianas, ten shrubs and 72 species of trees were recorded. The commonest species recorded in the forest included: Uapaca guineensis Mull. Arg., Tabernaemontana pachysiphon Stapf., and Aframomum luteoalbum (K Schum.) K. Schum. Among the rare species encountered were Ficus densistipulata De Willd., Englerophytum oblanceolatum (S. Moore) Pennington, and Afromomum zambeziacum (Bak.) K. Schum. The present study has shown that the Ssese islands are floristically rich in species and compare well with other mainland forests. Species richness, rarity and uniqueness of habitats can be considered as approaches in the prioritization of conservation sites within the fragmented forests of Ssese islands.  相似文献   

12.
Abstract. Grazing by domestic livestock in native woodlands can have major effects on ecosystem functioning by the removal of plant species that form important functional groups. This paper documents the changes in floristics in a large group of remnants of native woodland left after agricultural clearing in southwestern Australia. Species richness and diversity were significantly reduced in remnants and the proportion of exotic species increased. Detrended Correspondence Analysis (DCA) was used to identify floristic and environmental patterns among plots and identified two distinct groups based on grazing intensity. This indicated that the significance of the relationship between grazing effects and DCA floristic axes was greater than edaphic characteristics that normally influence floristic patterns. Floristic characteristics of sites that were influencing the position of plots on the ordination diagram included proportion of exotic species and proportion of native perennial shrubs and herbs. Numbers of species of native shrubs and perennial herbs were significantly reduced in grazed plots and numbers of exotic annual grasses and herbs were significantly higher. Other life form groups such as native perennial grasses and geophytes were not significantly affected by grazing. Reproductive strategies of perennial species showed a significant decrease in numbers of resprouters and a significant increase in numbers of facultative seeder/sprouters. Exclosure plots showed increases in number and cover of perennial shrubs and herbs after three years whereas number and cover of exotic species did not change. Time series DCA showed that the floristic composition of exclosure plots in grazed sites became closer to that of the ungrazed sites.  相似文献   

13.
《农业工程》2020,40(4):296-299
Tiaret massif forest offers a very interesting model for studying the evolution of the flora in the region, with a variety of very remarkable vegetation distribution conditioned by a significant number of ecological factors (climate and anthropogenic activities). A floristic study was carried out in Tagdempt sector, characterized by semi-arid Mediterranean climate and forming a natural barrier against steppe development.The floristic analysis based on the method of Braun-Blanquet with a minimum surface of 100 m2 allowed us to draw up a list of 126 species belonging to 100 genera of 40 families. The most dominant family was Asteraceae with 23 species (18.3%), followed by Fabaceae and Poaceae with 12 (9.5%) and 9 species (7.1%), respectively. Among life forms, annual herbs represented 53.2%, followed by perennial shrub species (32.5%) and finally trees (14.3%). Biogeographically, the Mediterranean was the most dominant type (49.6%), whereas other types had low percentages. Moreover, out of the plants identified, six with different status were rare (4.76%), nine were endemic (7.14%) and only five of the taxa have official protection status under the Algerian legislation (3.96%).  相似文献   

14.
蒙古栎群落叶型的分析   总被引:15,自引:1,他引:14  
1 引  言叶的大小即叶型是群落的重要外貌特征之一 ,与群落的生产率有关 ;叶子的形态与气候有密切的关系 ,一个扩展着的叶片所能达到的最大程度 ,受温度和湿度有效性的影响 ;大的叶片经常地出现于热带温暖而潮湿的气候中 ,而小的叶片则是十分干燥和寒冷地区植物的特征[1] .对于不同的群落的叶型分析 ,前人已做了一些研究 ,如对常绿阔叶林和季雨林的群落学研究[2~ 4 ] 及北方落叶林的群落学研究[5,6] .另一个与气候相关联的叶子特征是叶子的叶缘 ,有关方面的研究资料比较少 .据研究 ,在一个植物区系的双子叶乔木中全缘叶植物种的百分率 ,…  相似文献   

15.
Traditional cultural and religious beliefs and practices in the form of sacred groves play a crucial role in environmental conservation and biodiversity. The present study was conducted to explore plant resources, their biological spectrum, leaf size spectrum, sacred grove conservation status, locally known as Kankabati Sitabala Than (KST) in the district of West Midnapore, West Bengal in India. The study's floristic list revealed that the KST vegetation was diverse and composed of 277 species of 238 genera distributed over 77 families under 36 orders according to APG IV classification, of which 87 species were aliens. Poales (23.40%) and Poaceae (15.38%) were the dominant order and family in terms of species wealth. Biological spectrum shows the study area was classified as “thero-crypto-chamaephytic” type of phytoclimate. Leptophyll (26.60%) and ovate (18.91%) were found to be high in the leaf size spectrum and lamina. The vulnerable climber and tree species are Cayratia pedata and Pterocarpus indicus. The vegetation phenology, observed during different seasons revealed that most of the species were dominant in rainy seasons (99.68%), followed by winter (69.87%) and summer (29.81%). The study area being a sacred grove remains fairly undisturbed. For the long-term conservation of germplasm of the grove some recommendations have been suggested.  相似文献   

16.
Aim To carry out (1) a floristic survey of endemic flowering plants of the Western Ghats occurring in Goa, (2) identify their habitat preference and diversity of life‐form type, (3) observe flowering phenology of the endemics and (4) to correlate factors that affect their phenological pattern. Location Goa state is located between 15°48′ N and 14°53′54′′ N and 74°20′13′′ E and 73°40′33′′ E, in the northern part of the Western Ghats, India. Method A list of endemic plants from the study area was prepared using available floristic works and checklists of endemic plants of India. Based on preliminary field observations carried out in the study area, major habitats such as plateaus, moist deciduous forests, semi‐evergreen forests, evergreen forests and mangroves were identified for the subsequent intensive survey of endemics. Voucher specimens for all the endemic species were collected, processed using conventional herbarium techniques and deposited in the Herbarium, Department of Botany, Goa University. Species were identified using local and regional floras and their identity was confirmed at various herbaria along the Western Ghats. Data on their life‐form types, habitat and phenology was recorded in the field. Phenological observations were made every fortnight. A computerized data base was generated incorporating details on their life‐form type, phenology and habitat. Results A floristic survey of endemic plants of the Western Ghats in Goa resulted in the collection of 113 endemic species. Life‐form analysis reveals that herbaceous endemics are the most dominant followed by trees, shrubs and climbers. Plateaus in the study area harbour the largest number of endemic species, especially herbs. Endemic trees are distributed in the semi‐evergreen and evergreen forests. Endemic species in the study area show different peak and lean seasons of flowering depending on their life‐form type, habitat and ecological factors like temperature and rainfall/moisture content in the soil. Main conclusions The plateaus in the northern part of the Western Ghats are unique, being species rich with herbaceous endemics. These ephemerals are closely associated with the rainfall patterns thus; any change of moisture regime over the long‐term will have an impact on the distribution of these endemics.  相似文献   

17.
A botanical inventory and diversity of trees, shrubs (≥5 cm diameter at breast height [dbh]), herbs, climbers and lianas was assessed in plots (154) of 20 × 5 m in Mt. Marsabit forest, northern Kenya. We recorded 52 species of trees and shrubs, twelve species of herbs and six species of climbers and lianas. They belonged to 35 families and 64 genera. Rubiaceae was the richest family with nine species followed by Euphorbiaceae (six), Oleaceae (five), Rutaceae (four), Capparaceae, Labiatae and Leguminosae (three each). The rest of the families were represented by one or two species. Rinorea convallarioides (Bak.f.) Eyles ssp. marsabitensis Grey‐Wilson (Violaceae), an endemic species, and Drypetes gerrardii Hutch. (Euphorbiaceae), were the two most important species, accounting for more than third of the combined importance value. Species diversity indices were 2.735 (Shannon–Wiener), 0.88 (Simpson's) and 0.296 (Evenness). There was a strong evidence of disturbance arising from anthropogenic and wildlife foraging activities. This inventory has affirmed Mt. Marsabit forest as a unique habitat for several endemic, rare, threatened or vulnerable plant species, which should be conserved.  相似文献   

18.
We examined the initial response of the quantity and distribution of fine roots to the creation of an experimental canopy gap with a diameter of 50 m in a mature managed Norway spruce forest. Under the canopy, the fine root length densities of trees, shrubs, and grasses and herbs were 3207, 707 and 2738 m m–2, respectively. The fine root biomass of trees, shrubs, and grasses and herbs were 182, 47 and 52 g m–2, respectively. Two growing seasons after gap creation hardly any fine tree roots were found in the middle part of the gap. The living tree roots in the gap edge zone were mainly located within a 5-m distance from the standing edge trees. The indices developed here to show the influence of trees on fine root lenght density clearly revealed the effect of the vicinity of living trees on fine root lenght density. The root densities of grasses, herbs and dwarf shrubs did not show a clear response to gap creation despite the increase of their foliage. Our results suggest that in boreal spruce forests a gap disturbance creates a distinct tree root gap and that the gap edge trees do not extend their root systems rapidly into the formed root gap.  相似文献   

19.
This study was conducted to assess the floral composition of the Alno communal mixed forest in the Philippines. A quadrat method of vegetational analysis was used for the assessment of trees, shrubs, saplings, and seedlings. A total of 78 species belonging to 43 families were identified in this communal forest. For the assessment of grasses, herbs, ferns, and other low-lying vegetation, the line intercept method was used. A total of 31 species belonging to 20 families were found using this method. The diversity (Shannon–Wiener) indices of this communal forest are 3.2129 and 2.3870 for the quadrat method and line intercept method, respectively. The most dominant species in this area is Pinus kesiya Royle ex Gordon (Benguet pine) with an importance value of 64.19 %. Endemic species in the area also connote ecological importance, being considered a good indication of the status of habitats and ecosystems of this communal forest.  相似文献   

20.
We updated the floristic checklist of the Nizanda region, Isthmus of Tehuantepec (southern Mexico), characterized the occurring plant communities based on dominant species, and described the region’s flora according to life form, growth form, growth type, and growth habit spectra. Ten years of botanical exploration, along with surveys in 188 100-m2 samples from different vegetation types, provided the baseline floristic information. Ordination and classification analyses were performed to examine the degree of differentiation between communities. Geographical ranges of all species were used to assess biogeographical relationships of this flora. The inventory includes 920 species (553 genera, 124 families). More than one-third of the families were represented by a single species, whereas the 10 richest families had 43% of the species richness. Dendrograms showing plot classification at three taxonomic levels (species, genus and family) revealed savannah as the most strongly differentiated community amid seven vegetation types. Regarding growth forms, forbs and trees prevailed. Phanerophytes were the most common life form category, whereas herbs and woody plants were the dominant growth types. The largest richness for all taxonomic levels was recorded in the tropical dry forest. The expanded floristic knowledge gained for the Nizanda region provided better criteria to revise the classification scheme of its vegetation. Our preliminary biogeographical analysis illustrates the role of the Isthmus of Tehuantepec as a corridor for thermophilous floras between two oceanic watersheds, and as a natural distributional limit for several Mesoamerican plant species.  相似文献   

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