Effects of fire regime shift in Mediterranean Basin ecosystems: changes in soil seed bank composition among functional types

We studied the soil seed bank in a possible scenario of fire regime shift and asked: (1) Does high fire frequency impact the density of seeds stored, species richness and evenness? (2) Overall, does high fire frequency produce changes in the presence–absence and abundance of species? The study was implemented in a Mediterranean Basin ecosystem in plots with increasing fire frequency (unburned, burned once and burned twice in the last 66 years). The number of seeds increased with fire frequency for all life forms (shrub, scrub, perennial forb, annual forb and perennial graminoid). Species richness of annual forbs also increased. Evenness of shrubs diminished because the number of seeds in all the species decreased, except C. albidus, which increased. Overall, differences in the abundance of species were found, mainly by depleting shrubs and increasing forbs. There were no differences in the presence–absence data. In conclusion, high fire frequencies act as a filtering factor for species of a larger size and advanced maturity age. In contrast, life forms of small size and rapid onset of reproductive maturity can be enhanced. This community conversion from woody to herbaceous soil seed banks is fundamental to identify vegetation changes in future regimes of high fire frequency.     

Fire frequency and tree canopy structure influence plant species diversity in a forest-grassland ecotone

Disturbances and environmental heterogeneity are two factors thought to influence plant species diversity, but their effects are still poorly understood in many ecosystems. We surveyed understory vegetation and measured tree canopy cover on permanent plots spanning an experimental fire frequency gradient to test fire frequency and tree canopy effects on plant species richness and community heterogeneity within a mosaic of grassland, oak savanna, oak woodland, and forest communities. Species richness was assessed for all vascular plant species and for three plant functional groups: grasses, forbs, and woody plants. Understory species richness and community heterogeneity were maximized at biennial fire frequencies, consistent with predictions of the intermediate disturbance hypothesis. However, overstory tree species richness was highest in unburned units and declined with increasing fire frequency. Maximum species richness was observed in unburned units for woody species, with biennial fires for forbs, and with near-annual fires for grasses. Savannas and woodlands with intermediate and spatially variable tree canopy cover had greater species richness and community heterogeneity than old-field grasslands or closed-canopy forests. Functional group species richness was positively correlated with functional group cover. Our results suggest that annual to biennial fire frequencies prevent shrubs and trees from competitively excluding grasses and prairie forbs, while spatially variable shading from overstory trees reduces grass dominance and provides a wider range of habitat conditions. Hence, high species richness in savannas is due to both high sample point species richness and high community heterogeneity among sample points, which are maintained by intermediate fire frequencies and variable tree canopy cover.     

Understory response to varying fire frequencies after 20 years of prescribed burning in an upland oak forest

Ecosystems in the eastern United States that were shaped by fire over thousands of years of anthropogenic burning recently have been subjected to fire suppression resulting in significant changes in vegetation composition and structure and encroachment by invasive species. Renewed interest in use of fire to manage such ecosystems will require knowledge of effects of fire regime on vegetation. We studied the effects of one aspect of the fire regime, fire frequency, on biomass, cover and diversity of understory vegetation in upland oak forests prescribe-burned for 20 years at different frequencies ranging from zero to five fires per decade. Overstory canopy closure ranged from 88 to 96% and was not affected by fire frequency indicating high tolerance of large trees for even the most frequent burning. Understory species richness and cover was dominated by woody reproduction followed in descending order by forbs, C3 graminoids, C4 grasses, and legumes. Woody plant understory cover did not change with fire frequency and increased 30% from one to three years after a burn. Both forbs and C3 graminoids showed a linear increase in species richness and cover as fire frequency increased. In contrast, C4 grasses and legumes did not show a response to fire frequency. The reduction of litter by fire may have encouraged regeneration of herbaceous plants and helped explain the positive response of forbs and C3 graminoids to increasing fire frequency. Our results showed that herbaceous biomass, cover, and diversity can be managed with long-term prescribed fire under the closed canopy of upland oak forests.     

放牧干扰下高寒草甸物种、生活型和功能群多样性与生物量的关系

为明晰放牧强度对高寒草甸物种、生活型以及功能群多样性和生物量的时间累积作用以及对多样性与生物量之间相互关系的影响。选择青藏高原东北缘高寒草甸,在6个放牧强度样地连续4 a(2012—2015)进行物种、生活型、功能群多样性和生物量调查。采用重复测量方差分析和线性回归法分析放牧强度和放牧年份对物种、生活型、功能群多样性以及多样性与生物量之间的相关关系的影响。结果表明:(1)放牧强度和放牧年份均对生物量产生显著影响。随放牧强度增加,生物量显著降低。但随放牧年份延长,不同放牧强度区生物量无一致的变化规律。(2)放牧年份对物种、生活型和功能群丰富度、均匀度和优势度的影响均达到显著水平。但放牧强度和放牧年份只对物种丰富度产生交互作用,放牧强度对物种丰富度的影响具有时间的累积效应。(3)放牧干扰下不同层次多样性,仅物种丰富度与所有多样性指数显著相关,物种丰富度可以作为物种多样性测度的代表性指标。(4)多样性与生物量关系的研究,对丰富度而言,仅低放牧强度样地(Plot2)中物种丰富度随生物量增加而显著降低,其余放牧强度样地的物种、生活型和功能群丰富度均与生物量无关。对均匀度而言,高放牧强度样地(Plot4、Plot5、Plot6)生活型均匀度随生物量的增加而显著降低。对优势度而言,高放牧强度样地生活型优势度随生物量的增加而显著增加。生活型多样性可作为放牧干扰下生物量变化快速预测的有效指标。     

Effects of fire on forest dynamics in southern Switzerland

Abstract. We analysed the influence of fire on species composition, floristic diversity and indicator values of the vegetation in forests of the Canton Ticino (South Switzerland). Both frequency of fire and time since last fire were taken into account using variance analysis. Results show a strong interaction of these two parameters, i.e. the reaction of the vegetation after a fire depends on the frequency of past fires. A rapid recovery is generally observed after fire, involving both herbaceous and woody species. However, a long-term tendency towards floristic and edaphic impoverishment is observed with increasing frequency of fires. This phenomenon appears to be linked to the progressive dominance of a few fire-tolerant species.     

Effects of fire frequency on plant species composition of sandstone communities in the Sydney region: Inter-fire interval and time-since-fire

Abstract Fire frequency is the number of fires experienced by a particular community within a given time period. This concept can potentially be resolved into a number of interacting variables, including: time since the most recent fire, the length of the inter-fire intervals, and the variability of the length of the inter-fire intervals. We estimated the effects of these three variables on the floristic composition of 65 samples from dry sclerophyll vegetation with different fire histories in Brisbane Water, Ku-ring-gai Chase and Royal National Parks near Sydney. Our analyses suggest that fire frequency may account for about 60% of the floristic variation among our samples. They confirm the hypothesis that the recent (<30 years) fire frequency produces effects on floristic composition of fire-prone communities that can recognizably be attributed both to the time since the most recent fire and to the length of the intervals between fires. These effects are equal in magnitude but are different in the nature of the floristic variation they are associated with. Increasing time-since-fire is associated with a decline in the evenness of fire-tolerant species, indicating that fewer of these species come to dominate the community in the prolonged absence of fire. Herbs and small shrubs decrease in abundance, while larger shrubs increase in abundance. Inter-fire intervals of decreasing length are associated with a decrease in the evenness of the fire-sensitive species, particularly those large Proteaceae shrubs that often dominate the community biomass in dry sclerophyll shrublands of southeastern Australia. Furthermore, the variation associated with inter-fire intervals is not necessarily solely related to the shortest inter-fire interval, but is related to combinations of inter-fire intervals through time. Thus, increasing variability of the length of the inter-fire intervals is associated with an increase in the species richness of both fire-sensitive and fire-tolerant species, implying that it may be variation of the inter-fire intervals through time that is primarily responsible for maintaining the presence of a wide variety of plant species in a particular community. Our results also suggest that the floristic variation associated with different inter-fire intervals decreases with increasing time-since-fire.     

Herbaceous species responses to long-term effects of prescribed fire, grazing and selective tree cutting in the savanna-woodlands of West Africa

Grazing, fire and selective tree cutting are major disturbances that shape species diversity in savanna ecosystems, yet their effects are highly variable. We carried out a factorial experiment with two levels to examine the effects of grazing, fire and selective tree cutting on herbaceous species richness, abundance and diversity on two sites in the Sudanian savanna-woodlands of Burkina Faso for 10 years (1994–2003). The results showed significant inter-annual variation in species richness, abundance and diversity at both sites (p<0.001), while main or combined effects of fire, grazing and selective cutting were very limited and varied between life forms and sites. Grazing tended to favour the diversity of perennial grasses; fire tended to influence the richness of annual grasses and abundance and diversity of perennial grasses while selective tree cutting had no effect on any of the vegetation attributes assessed. The combined effect of grazing, fire and selective cutting tended to increase the diversity of forbs. In many cases, the responses of herbaceous species to treatments were clearer on the site with deeper soils than the one with shallow soils. Depending on the site and treatments, the inter-annual variation in vegetation attributes was partly related to amount and/or frequency of rainfall and partly to inter-annual variation in grazing or fire intensity. It can be concluded that both disturbances and climatic condition influence the structure and diversity of herbaceous flora in the Sudanian savanna-woodland ecosystem. The responses were site-specific, which accentuates the importance of landscape-scale approaches to understand the impacts of disturbances on composition, structure and diversity of savanna ecosystems.     

Long-term patterns of shrub expansion in a C4-dominated grassland: fire frequency and the dynamics of shrub cover and abundance

Worldwide, grassland ecosystems have experienced a major shift in growth-form dominance as woody plant species have expanded and replaced native grasses. In the C(4)-dominated grasslands of central North America, a reduction in fire frequency is the most cited cause of this shift in growth forms as fire both enhances grass productivity and constrains the establishment and expansion of native woody vegetation. Using an 18-yr plant species composition data set, we quantified patterns of change in shrub cover, frequency, and species richness associated with three distinct fire regimes. During the study period (1983-2000), shrub cover increased most dramatically in sites in which the frequency of fire was once every 4 yr (intermediate frequency; 28.6%) followed by sites in which fire occurred only once during the 18-yr period (low frequency; 23.7%). Annual fire effectively prevented the recruitment of new woody species, but even with this high fire frequency, shrub cover increased slightly (3.7%). Comparatively, shrub species richness increased by three and six, respectively, in the intermediate- and low-frequency fire sites. These data indicate that within this grassland, periods without fire are necessary for recruitment of both new individuals and additional shrub species; however, once established, shrub cover will increase regardless of fire frequency and even annual fire will not reduce shrub abundance.     

Recurrent fires and environment shape the vegetation in Quercus suber L. woodlands and maquis

The effects of fire recurrence on vegetation patterns in Quercus suber L. and Erica-Cistus communities in Mediterranean fire-prone ecosystems of south-eastern France were examined on stands belonging to 5 fire classes, corresponding to different numbers of fires (from 0 to 4) and time intervals between fires since 1959. A common pool of species was identified among the plots, which was typical of both open and closed maquis. Fire recurrence reduced the abundance of trees and herbs, whereas it increased the abundance of small shrubs. Richness differed significantly between the most contrasting classes of fire recurrence, with maximal values found in control plots and minimal values in plots that had burned recurrently and recently. Equitability indices did not vary significantly, in contrast to Shannon's diversity index which mostly correlated with richness. Forest ecosystems that have burnt once or twice in the last 50 years were resilient; that is to say they recovered a biomass and composition similar to that of the pre-fire state. However, after more than 3-4 fires, shrubland communities displayed lower species richness and diversity indices than unburned plots. The time since the last fire and the number of fires were the most explanatory fire variables, governing the structure of post-fire plant communities. However, environmental factors, such as slope or exposure, also made a significant contribution. Higher rates of fire recurrence can affect the persistence or expansion of shrublands in the future, as observed in other Mediterranean areas.     

Fire frequency has a contrasting effect on vegetation and topsoil in subcoastal heathland,woodland and forest ecosystems,south-east Queensland,Australia

Ecosystems managed with contrasting fire regimes provide insight into the responses of vegetation and soil. Heathland, woodland and forest ecosystems along a gradient of resource availability were burnt over four decades in approximately 3- or 5-year intervals or were unburnt for 45–47 years (heathland, woodland), or experienced infrequent wildfires (forest: 14 years since the last fire). We hypothesized that, relative to unburnt or infrequent fires, frequent burning would favour herbaceous species over woody species and resprouting over obligate seeder species, and reduce understorey vegetation height, and topsoil carbon and nitrogen content. Our hypothesis was partially supported in that herbaceous plant density was higher in frequently burnt vegetation; however, woody plant density was also higher in frequently burnt areas relative to unburnt/infrequently burnt areas, across all ecosystems. In heathland, omission of frequent fire resulted in the dominance of fern Gleichenia dicarpa and subsequent competitive exclusion of understorey species and lower species diversity. As hypothesized, frequent burning in woodland and forest increased the density of facultative resprouters and significantly reduced soil organic carbon levels relative to unburnt sites. Our findings confirm that regular burning conserves understorey diversity and maintains an understorey of lower statured herbaceous plants, although demonstrates the potential trade-off of frequent burning with lower topsoil carbon levels in the woodland and forest. Some ecosystem specific responses to varied fire frequencies were observed, reflecting differences in species composition and fire response traits between ecosystems. Overall, unburnt vegetation resulted in the dominance of some species over others and the different vegetation types were able to withstand relatively high-frequency fire without the loss of biodiversity, mainly due to high environmental productivity and short juvenile periods.     

Vegetation dynamics across a chronosequence of created wetland sites in Virginia, USA

Plant species composition, dominance, richness, and diversity were measured across a 15-year chronosequence of created wetland sites in Virginia, USA. Using an age-class categorization (1?C2?years, 3?C5?years, 6?C10?years, or 11?C15?years), all classes had a predominance of herbaceous species with perennial life history strategy, and perennials contributed 68.6?% to the overall dominance measure (importance value; IV) averaged across all sites. There was no significant difference in species richness or diversity among age classes. Analysis of Similarity (ANOSIM) indicated that herbaceous species composition was similar between the youngest and oldest age classes, but not the intermediate classes. For woody shrubs and saplings, planted species were more prevalent in the youngest age classes, and volunteer species predominated in the oldest age classes. These results suggest that perennial herbaceous species are important in early plant development on created wetland sites, and may be influential in observed patterns of species composition over time. In the context of plant development in newly created wetlands, dominance shifts from planted to volunteer woody species suggest that planting early successional species, or species with reproductive strategies attuned to created wetland site management, may favor survivorship and recruitment of other species over time.     

Impact of two wildfires on endemic granite outcrop vegetation in Western Australia

Abstract. In seasonally dry regions of the world fire is a recurring disturbance but little is known of how fire interacts with granite outcrop vegetation. We hypothesize that the floristic composition in granite vegetation, usually attributed to the edaphic environment, may also reflect the impact of disturbances such as fire. Dramatic differences in floristic composition and cover over 13 years and two fires were observed in vegetation on a Western Australian granite outcrop. This was very marked in the first year following the two fires, with annuals and geophytes showing the greatest turnover of species. Even among the perennial shrubs there was considerable turnover in a number of obligate seeders. After the first fire the number of species declined for woody perennials, herbaceous perennials and annuals, remained unchanged for perennial grasses and sedges, and varied with highest richness 4 yr after fire for geophytes. Demographic studies of two endemic woody obligate seeders and three endemic mallee eucalypt resprouters similarly showed dramatic differences within and between species in seedling recruitment following the two fires. Fire does have a significant impact on the floristic composition of semi‐arid granite outcrop vegetation communities. Studies on other granite outcrop systems are needed to test the generality of this conclusion.     

Spatial relationships between the standing vegetation and the soil seed bank in a fire-prone encroached dehesa in Central Spain

Postfire vegetation regeneration in many fire-prone ecosystems is soil seed bank dependent. Although vegetation and seed bank may be spatially structured, the role of prefire vegetation patterns and fire in determining postfire vegetation patterns is poorly known. Here, we investigated the spatial patterning of species abundance and richness in the vegetation and seed bank of a Mediterranean encroached dehesa in Central Spain. The seed bank was studied with and without a heat shock simulating a spatially homogeneous fire. Semivariograms and cross-semivariograms showed that species richness in the vegetation was aggregated in patches, mainly of herbs, with highest values corresponding to high herb cover and low tree cover. Species richness in the seed bank was also structured in patches, but the spatial pattern was weak. Seedling density of germinates in the seed bank also showed weak spatial pattern. Heating increased overall germination and species richness, and the intensity of the spatial pattern of species richness, particularly of herbaceous species. However, seed bank density patterns disappeared after heat shock because of increased germination of shrubs without spatial pattern. Our results document that the spatial structure of plant richness in the vegetation may persist after fire due to the spatial patterns of herbaceous species in the seed bank, and that postfire species richness patterns can arise independently of fire intensity patterns. However, the spatial structure of the vegetation after fire can be altered by the feedback between shrub encroachment and an eventual fire because of the ubiquitous germination of shrubs.     

Early post-fire succession in California chaparral: Changes in diversity, density, cover and biomass

For four consecutive years, following the fires in November 1993, temporal variations in species richness, cover and biomass of component plant groups in early post-fire chaparral succession were monitored on different aspects at the Stunt Ranch Santa Monica Mountains Reserve, southern California. Plant groups were categorized based on growth form, life form, ability to fix nitrogen, geographic origin and regeneration strategies. North-facing slopes exhibited higher species richness, higher species turnover rate over time and faster vegetation recovery in terms of biomass accumulation and return to pre-fire species composition. This was probably due to higher species richness and biomass of nitrogen-fixing species found on north-facing slopes in comparison to south-facing slopes. On both north- and south-facing slopes, annuals had the highest species turnover rate, followed by herbaceous perennials and shrubs. In the first four post-fire years, annual species were the largest floristic group, but herbaceous perennials and shrubs were the major contributors to community biomass. Nitrogen-fixing species and exotics contributed significantly to early post-fire community structure. Although the general trends in post-fire succession are clear in terms of temporal changes in the relative proportions of different plant groups, environmental variation and the nature of plant life histories of component species, especially dominant species, could alter such trends significantly.     

Plant diversity patterns in the Aljibe Mountains (S. Spain): a comprehensive account

The Aljibe Mountains are located in the southern tip of the Iberian Peninsula and have a remarkable biogeographical interest. The complete plant species list (trees, climbers, shrubs, perennial and annual herbs, ferns, lichens, bryophytes and macroscopic algae) was recorded in four 0.1 ha plots from each of the most representative community types (Quercus suber woodland, Q. canariensis forest, open heathland and Q. coccifera shrubland). Up to 119 plant species were found in total in the Q. suber woodland plot. The diversity of woody plants was analysed from 44 samples of cover (100 m line), and the herbaceous layer was explored in 200 quadrats (of 0.5 × 0.5 m). Three biodiversity components (species richness, endemism, and taxonomic singularity) were evaluated in both shrub and herbaceous layers. Open heathlands showed the highest richness of endemic species, both woody and herbaceous. The highest number of woody species was found in the evergreen Q. suber woodland, and of herbaceous species in the semi-deciduous Q. canariensis woodland. Taxonomic singularity was higher in Q. canariensis woodlands and Q. coccifera shrublands for woody species, but there were no significant differences in the herbaceous layer. Local species diversity of heathlands in this region resembles that of South African heathlands (fynbos), despite the obvious geographic and floristic distance, and contrasts with the low diversity of biogeographically closer, European temperate heathlands. The Aljibe Mountains show high diversity values for different life forms (from trees to mosses) and spatial scales (from community to region), and are rich in endemic species. Thus, this area should be recognised as a relevant unit within the Mediterranean plant diversity hot spots.     

Composition,size and dynamics of the seed bank in a mediterranean shrubland of Chile

Abstract Analysis was performed of the richness and abundance of woody species, forbs, and annual grasses in the easily germinating soil seed bank (henceforth seed bank) in a mediterranean shrubland of central Chile. The effects of successional development after fire and by microsite type (underneath or outside shrubs) on the density of seeds in the soil, and the relationship of species abundance in the seed bank with its abundance in the above‐ground vegetation was examined. A total of 64 plant species were recorded in the seed bank, of which 44 were annual or biannual. Eight species were woody and another eight were perennial herbs. Four could not be identified to species level. The highest richness of established herbaceous species was recorded in late spring, with 31 species. The regeneration of the herbaceous vegetation was driven by the annual production of seeds and by a reserve of short‐lived propagules in the soil. Density of all germinating seeds was significantly higher during late spring and late summer. Density of grass seeds was greater during late spring, while that of all other species was greater during late summer. Annual grass seeds accumulated in higher proportion at exposed microsites rather than under woody canopy, and in young (< 5 years old) and intermediate‐age patches (10–20 years old) rather than in mature vegetation (30–50 years old). The abundance of established woody and herb species was uncorrelated with that of the seed bank.     

Fire-type and forestry management effects on the early postfire vegetation dynamics of a Pinus pinaster woodland

The objective of this research was to study the effects of type of fire, prefire-, and postfire-management on the postfire vegetation dynamics of a Pinus pinaster woodland in Central Spain, burned at 15 yr of age. The effects of type of fire (crown-, or surface-fire), prefire-management (thinning out of trees and clearing of brush or no such actions) and postfire-management (removal of burned trees one year after the fire or no such action) on the postfire vegetation were studied during the first three years after the fire. Herbaceous plant abundance, species richness, and diversity, as well as abundance, growth and density of the dominant shrub species (Cistus ladanifer) were measured during the first three years after the fire. Our results show that the effects of the type of fire on the vegetation were minimal. Prefire-management effects were significant on the abundance of herbaceous species, mainly during the second and third year after fire, in particular for the Leguminosae species. Prefire managed areas were more diverse in species, and produced higher plant biomass than unmanaged areas. Postfire-management effects on the shrubs and herbs were minimal, except for the Leguminosae, which increased their cover where the trees had been removed. Plant dynamics were marked by the interaction between prefire-management and fire-type through the dynamics of the shrub cover. On most occasions, plots that resulted in lower cover of C. ladanifer had greater abundance of herbaceous plants and, in particular, of the Leguminosae. In general, our results show that irrespective of fire-type, prefire-, or postfire-management all areas tended to be very similar in their vegetation three years after the fire.     

Effects of late growing-season and late dormant-season prescribed fire on herbaceous vegetation in restored pine-grassland communities

Abstract. We compared the effects of late dormant-season and late growing-season prescribed fires on herbaceous species in restored shortleaf pine- (Pinus echinata) grassland communities in the Ouachita Highlands of western Arkansas. Herbaceous species richness, diversity, and total forb and legume abundance increased following fire. Late growing-season burns reduced distribution and abundance of panicums (primarily Panicum boscii, P. dichotomum, and P. linearifolium) while late dormant-season burns increased Panicum distribution and abundance. Density of legumes (such as Stylosanthes biflora) increased following frequent or annual dormant-season fires. However, season of fire influenced the distribution and abundance of fewer than 10 % of the species. Fire plays an essential role in pine-grassland communities by creating and maintaining open canopy conditions that perpetuate understory herbaceous plant communities.     

Ecology of pollination in a tropical Venezuelan savanna

Pollination modes ecology of a total of 164 plant species was evaluated according to habitats and plant life forms in the Venezuelan Central Plain. Frequency distribution of nine pollination modes showed that, at the community level bee pollination (38.6%) was dominant. Butterfly (13.9%), fly (12.7%), and wasp (10.8%) pollination were the second most frequent. Moth (6.2%) and wind (10.4%) pollination occurred with similar frequency, and the least common were bird (3.1%), beetle (2.3%) and bat (1.9%) pollination. There was a significant interaction effect indicating that pollination mode was affected by the type of habitat. Bee pollination was the most common pollination mode in all habitats with butterfly, fly and wasp pollination being secondary for forest and forest-savanna transition; and butterfly, wasp, wind and fly pollination being secondary for savanna. Wind, butterfly and fly pollination were found in disturbed areas as secondary pollination modes. Pollination modes were significantly associated and affected by life forms. Bee pollination was dominant in all life forms with wasp, butterfly and fly pollination being the secondary for trees, shrubs, and lianas; and butterfly and wind pollination being the secondary for herbaceous species. The number of pollination modes (richness) among life forms ranged between four and nine for epiphytes and perennial herbs respectively. The highest values of diversity indexes among life forms were found in trees and shrubs. The richness and diversity indices of pollination modes were statistically higher for more structured habitats, forest and forest-savanna transition, than herbaceous habitats, savanna and disturbed areas, which is associated with the highest values of diversity indexes in trees and shrubs. Equitability was higher for forest and disturbed areas than forest-savanna transition and savanna. The results of comparative richness, equitability, diversity indices, and the frequency distribution of pollination modes of 19 samples from tropical and temperate communities indicated that richness of pollination modes may be different between tropical and temperate communities. The proportion of each pollination mode suggests four grouping: (1) rain forests and their strata, (2) grassland savanna, and associated disturbed areas, (3) temperate communities, and (4) the most heterogeneous group, contained mostly neotropical communities, including the four habitats of the Venezuelan Central Plain. The frequency of pollination modes, richness, diversity and equitability of communities, habitats, successional stages, and vegetation strata varies with respect to geography, vegetation structure, and plant species richness.