Swamp Communities Research Articles

A palynological investigation of Holocene vegetation change in Torres Strait, seasonal tropics of northern Australia

The islands of Torres Strait occupy a shallow area of submerged continental shelf narrowly separating Cape York Peninsula, Australia, from New Guinea. The human history of Torres Strait is unique with respect to mainland northern Australia. Island vegetation, however, exhibits a strong affinity with the environments of the western lowlands regions of Cape York Peninsula and with the vegetation of seasonal tropical Australia in general. Cape York Peninsula is both climatically and biologically diverse, yet few pollen studies have been carried out in its seasonally tropical environments. A summary presentation of palynological results, tracing the nature of vegetation change in Torres Strait, offers a possible framework for vegetation changes in similar environments on mainland Australia and also provides an opportunity to explore the relationship between Quaternary change in humid–tropical Australian environments and their seasonal–tropical counterparts. Six pollen records from Torres Strait provide evidence of vegetation change and fire history over approximately the last 8000 years. Near-shore sediments reveal a Holocene succession in vegetation incorporating lower-tidal mangrove, upper-tidal mangrove, saltmarsh and freshwater swamp communities. Extensive stable mangrove communities dominated coastal Torres Strait between approximately 6000 and 3000 radiocarbon years before present (yr BP). Inland, the strongest Myrtaceae-forest and rainforest representation occurs around the mid-Holocene only to be replaced by open sclerophyll woodlands, as tree density and diversity decline in the last 3000 years. The development of continuous island freshwater swamp conditions, at the coast and inland, is similarly restricted to the late Holocene (c. 2600 yr BP) and fire, as a prominent feature in the Torres Strait environment, is also a relatively recent phenomenon. Comparisons with regional mainland Australian palynological records reveal a degree of consistency in results from Torres Strait suggesting a similarity in late Quaternary trends through Australian humid and seasonally tropical environments. A number of differences, however, are also apparent, highlighting a degree of diversity which warrants further attention.

Seasonal Influences on the Ecology of Testate Amoebae (Protozoa) in a Small Sphagnum peatland in Southern Ontario, Canada

Testate amoebae (Protozoa) were studied in spring, summer, and fall from the same microhabitats in a small Sphagnum-dominated peatland in southern Ontario, Canada. A total of 32 sampling stations were established in two wetland plant communities, 19 in an open Ericaceae low-shrub community and 13 in a closed Picea mariana and Larix laricina swamp community. Sphagnum was collected in each station for analysis of testate amoebae and measurement of soil water content parameters and water table depth in May, August, and October 2001. pH and dissolved oxygen of the groundwater under the Sphagnum were measured also. A total of 52 taxa including the rotifer, Habrotrocha angusticollis, were identified. Soil water content and water table variables emerged as the primary factors separating testate amoebae between the open bog/fen community and swamp community. Testate amoebae in the open bog/fen community showed a clear separation between the May sampling period and the August and October sampling periods. Sampling stations in May had much higher water table and were wetter than those in August and October. Conversely, testate amoebae in the swamp community did not show a clear difference between sampling periods. Soil moisture and water tables appear to be more constant in the swamp communities. Biological factors or other microscale environmental factors may need to be considered to explain seasonal changes in testate amoebae. A greater understanding of relationships between testate amoebae and microenvironmental factors is necessary to track seasonality in testate amoebae distributions.

Spatial and temporal analysis of vegetation mosaics for conservation: poor fen communities in a Cornish valley mire

AbstractAim Biogeographers increasingly realize the importance of seeing plant communities as spatial mosaics and understanding the spatial and temporal heterogeneity of a site is often a key to successful conservation. The aim of this paper is to examine the approaches to the description and analysis of spatial and temporal variation in sub‐communities within patch mosaics of vegetation in order to inform conservation management. The activities of the tin streaming industry in Cornwall over the last century have created a highly varied mosaic of poor fen vegetation on Goss Moor National Nature Reserve (NNR). The wetland mosaics comprise dry hummocks and different sized wet pools. The size and depth of the pools determines the rate and type of vegetation that develops, as does the nature of boundary or edge. The ergodic hypothesis is used to describe the various plant sub‐communities and their boundaries to identify pathways of hydroseral succession. A further aim was to test the use of Ellenberg Indicator (EI) values as a tool for the rapid description of spatial and temporal environmental change on wetland sites with a view to their management.Location Goss Moor National Nature Reserve, Cornwall, UK.Methods An extensive survey of the whole wetland complex was undertaken to identify patches of poor fen vegetation containing Potentilla palustris (L.) Scop. and Menyanthes trifoliata L. At each patch, species abundance data were collected as well as associated environmental information such as depth of the organic layer and standing water depth, patch location, patch size and boundary type. The plant sub‐communities present were defined using techniques of numerical classification [two‐way indicator species analysis (twinspan)] and ordination [detrended correspondence analysis (DCA)] and these were ordered using the ergodic hypothesis in order to characterize the stages of the hydrosere. Floristic and environmental relationships were examined using canonical correspondence analysis (CCA). Further environmental differences between the poor fen sub‐community types were characterized by weighted EI values for acidity (R), moisture (F), nitrogen (N) and light (L).Results and conclusions Twelve poor fen sub‐community types were described and found to be distributed along a primary environmental gradient of organic matter depth, surface water height and bare substrate. Separation of the poor fen communities by a moisture gradient was considered as spatial evidence for hydroseral succession, which begins with the colonization of open‐water pools created by tin excavations. High water levels were associated with the swamp communities, increased organic depth was associated with poor fen, and the type of boundary was shown to affect the resulting community composition. Weighted Community Ellenberg Indicator values for nitrogen, light, reaction and moisture are recommended as an effective tool for indicating differences between plant (sub‐)communities. The importance of examining sub‐community mosaics in the study of hydroseral development is stressed and the manner in which both sets of information may be used to underpin the conservation management of the site is demonstrated.

Composição florística de veredas no Município de Uberlândia, MG

Foram estudadas quatro comunidades vegetais de veredas no Municipio de Uberlândia, MG, durante dois anos com o objetivo de conhecer sua composicao floristica. As veredas foram percorridas por meio de trilhas estabelecidas, ao acaso, passando pela borda (local de solo mais seco), meio (solo medianamente umido) e fundo (solo saturado com agua). A frequencia de visitas a cada vereda foi mensal e o material botânico coletado foi incluido no Herbarium Uberlandense (HUFU). A identificacao das especies foi feita utilizando-se chaves analiticas, consultas a especialistas de varias familias e/ou comparacao com exsicatas devidamente identificadas e depositadas nos herbarios HUFU, IBGE e UB. No levantamento floristico foram registradas 526 especies, 250 generos e 89 familias. As cinco familias com maior numero de especies foram Poaceae (64), Asteraceae (63), Cyperaceae (54), Melastomataceae (27) e Fabaceae (23). Na zona de borda da vereda foram amostradas 361 especies sendo 168 exclusivas deste ambiente. Um total de 300 especies ocorreu na zona de meio, sendo 75 exclusivas. Na zona de fundo ocorreu a menor riqueza especifica, compreendendo um total de 136 especies com 52 exclusivas desta area. A grande riqueza floristica encontrada nas veredas amostradas deve-se, possivelmente, as diferencas edaficas, especialmente aquelas relacionadas com a umidade.

Low atmospheric CO(2) levels during the Permo- Carboniferous glaciation inferred from fossil lycopsids.

Earth history was punctuated during the Permo-Carboniferous [300-250 million years (Myr) ago] by the longest and most severe glaciation of the entire Phanerozoic Eon. But significant uncertainty surrounds the concentration of CO(2) in the atmosphere through this time interval and therefore its role in the evolution of this major prePleistocene glaciation. Here, I derive 24 Late Paleozoic CO(2) estimates from the fossil cuticle record of arborsecent lycopsids of the equatorial Carboniferous and Permian swamp communities. Quantitative calibration of Late Carboniferous (330-300 Myr ago) and Permian (270-260 Myr ago) lycopsid stomatal indices yield average atmospheric CO(2) concentrations of 344 ppm and 313 ppm, respectively. The reconstructions show a high degree of self-consistency and a degree of precision an order of magnitude greater than other approaches. Low CO(2) levels during the Permo-Carboniferous glaciation are in agreement with glaciological evidence for the presence of continental ice and coupled models of climate and ice-sheet growth on Pangea. Moreover, the Permian data indicate atmospheric CO(2) levels were low 260 Myr ago, by which time continental deglaciation was already underway. Positive biotic feedbacks on climate, and geotectonic events, therefore are implicated as mechanisms underlying deglaciation.

Paleoecological Analysis of Two Early Pennsylvanian Mineral-Substrate Wetlands

Abstract The biomass within two Early Pennsylvanian (Langsettian [Westphalian A] equivalent) penecontemporaneous swamp communities was sampled quantitatively to obtain an estimate of the taxonomic contribution to each assemblage. Blocks of organic-rich shale were removed from a clastic parting within the Black Creek Coal, and ∼0.5-m2 siltstone quadrats were chain-sawed from a clastic swamp community directly above the Bear Creek Coal. Bedding planes were exposed, and the surface areas for each taxon per bedding surface were measured and used as proxies for biomass contribution in each locality. Biomass over a combined area of 5.47 m2 was assessed for the Black Creek Coal parting; biomass covering an area of 9.70 m2 was evaluated for the assemblage preserved above the Bear Creek coal. In addition to calculating standard diversity indices, this data set was analyzed using cluster analyses and non-metric multidimensional scaling (NMDS) to differentiate variations within the general flora. Low species diversi...

Outlying haymaking lands at S lendet, central Norway: effects of scything and grazing

Sølendet Nature Reserve, situated 700-800 m a.s.l., covers 306 ha. Sølendet mainly consists of calcareous fens and wooded grasslands that were mown for hay for several centuries; the hay was vital for keeping the livestock through the winter. A vegetational succession commenced as soon as haymaking ceased (c. 1950), the most obvious change being the formation of scrub and a heavy litter layer in the tall fen and swamp communities. Mowing recommenced in the nature reserve in 1974, and the vegetation and landscape is being restored. Permanent plot methods have been applied to follow the effects of scything and cattle grazing on the flora and vegetation, with emphasis on the rich fen vegetation.

Galium aparine L.

Galiun L., Section KOLGYDA Dumort. (Section Aparine Koch). An annual herb with prostrate or, more usually, scrambling-ascending diffusely branched stems 15-300cm, stout and hairy at the nodes, the four angles very rough with downwardly directed prickles. Leaves 12-60 x 3-8 mm, in whorls of 6-9, narrowly to widely oblanceolate or elliptical, mucronate, 1-veined, glabrous or with hooked bristles above, margins rough with backward-pointing prickles. Flowers 1.5 mm diameter in 2-5-flowered axillary cymes, their peduncles topped by a whorl of 4-8 bracts; hermaphrodite, sometimes male (andromonoecious). Calyx a minute annular ridge; corolla 1.5-1.7 mm in diameter, whitish, with four acute lobes. Stamens 4, exserted; styles 2, short, connate below; stigmas capitate. Two-seeded fruits with length of longest axis 3-5 mm (excluding setae), wider than the corolla, olive or purplish, covered with white hooked setae with tuberculate bases, their stalks divaricate. Mature fruit a dry mericarp with length of longest axis 2-3 mm, and a mean airdry mass of 9.65 mg ? 0.33 (10 samples of 100 from a hedgerow population). Salisbury (1974) reports the average mass of seed from shade-tolerant woodland and hedgerow plants as 3.7 mg, and Grime et al. (1988) record a mean seed mass of 7.25mg for a hedgerow population. Galiumn iparine is a highly variable species owing to a combination of phenotypic plasticity and genecological variation. The species has different responses to the environment corresponding to different environmentally conditioned life cycles [see VI (e)]; plasticity in the timing of seed germination, productivity, growth form, freezing tolerance, and the light and temperature dependence of photosynthesis enable G. apa7ine to establish itself in a wide variety of habitats. Potential variability concealed in the higher polyploid conditions, especially in the widespread hexaploids [see VI (d)], enabling them to respond to changing environmental conditions, is probably also the basis of their success. Among plants of G. apariine raised from seed collected from various sites in continental Europe, B6cher etal. (1955) distinguished at least five different climatic ecotypes or races that either may be discrete or more probably ranges of a large clinal variation: mediterranean, summer-annual (seed germinates in the spring) with accelerated development from Portugal; mediterranean, biennial from Spain; southern, winterto summer-annual from France; northern, rather late flowering winterto summerannual from Denmark and Poland; and northern, very late flowering winter-annual (seed germinates in autumn) from Denmark and Sweden. Ecotypes of G. aparine have been demonstrated by Berkefeld (1988), differing in shape of cotyledons, hairiness of stems, colour of stem edges and length of fruit spines in plants grown under uniform garden conditions from seed collected in several different habitats. In Britain, two discrete ecotypes of G. apa7i71e exist, one found in arable fields or open situations and the other growing in hedgerows (FroudWilliams 1985); the two ecotypes are very similar morphologically but differ markedly in seed dormancy and germination requirements [see VIII (d)]. Bain & Attridge (1988) provide evidence of genotypic differences in shade strategies between hedgerow and field populations [see VI (e)]. Two forms have been recognized, the rarer G. aparine f. interimediwan Bonnet, with smooth or tuberculate fruits without spiny hairs, and the common form G. apar-ine f. apari71e with spiny fruits (Moore 1975). Variants of G. spur-ium with setose fruits, apart from the flower characters and the diploid chromosome number, are often not easy to distinguish from G. caparine and have been described as G. spuritini ssp. infestlin (Hanf 1983). Galiuiml apariine is native on maritime shingle beaches, in primary tall-herb fen communities, and in primary alderwood in natural hydrarch successions, but is also a very variable cosmopolitan weed found in hedges, waste places, drained fen peat, on limestone scree, roadside verges, river and stream banks, and is a major arable weed, especially of cereal crops. *Abbreviated references are used for standard works, see Jolurnal of Ecology (1975), 63, 335-344. Nomenclature of vascular plants follows Florca Euri0opaea and Stace (1997) for British species.

Habitat Relationships of Small Mammals at Port Campbell National Park, Victoria.

Habitat relationships of six species of small mammals was investigated in eight vegetation communities at Port Campbell National Park, Victoria. The dispersion of 317 trap captures over 10 months was used to assess the relationships of small mammals with different vegetation communities. Rattus fuscipes showed a strong affinity for dense, structurally complex vegetation, particularly a disused softwood plantation and to a lesser extent a closed-heath/low open-forest community. Captures of Rattus lutreolus were most frequent in the wetter communities which provided adequate cover, particularly the swamp community. A possible relationship between captures of this species and the abundance of sedge food resources is suggested. Antechinus swainsonii was captured in greatest numbers in tussock-grassland/low open-shrubland where dense ground cover was present. However, areas with dense mid-storey cover which were considered to be favourable habitat supported few individuals. Sminthopsis leucopus, although captured at low rates in only two communities, favoured more open vegetation than both A. swainsonii and A. minimus. The later species was captured rarely, but exclusively in open-heath, although more favourable habitat appeared to be present elsewhere in the Park. The low abundance of Mus musculus was attributed to a lack of habitat available at an early successional stage. A mammal species list for the Park of 15 species has been compiled based on trapping, incidental observations and indirect traces. Key areas for conservation of small mammals within the Park are identified.

Interface ecosystems with an oil spill in a Venezuelan tropical savannah

Frequent oil spills associated with oil operations in tropical savannas are developing new ecosystems that may be symbiotic interfaces between industry and environment. This paper describes these developments, the role of restoration efforts and uses ‘emergy’ to evaluate the changes. In April 1991, an estimated 36 000 barrels (5724 m 3) of 40 gravity crude oil were released into 4600 ha of tropical grassland-scrub and palm swamp communities from the blowout of a Venezuelan Oil Company well (Corpoven MUC-21) in Monagas State in eastern Venezuela. Ecologic and economic impacts of the oil spill were estimated using emergy analysis. The oil spill, its damages, and subsequent clean up were evaluated by comparing the emergy flows associated with each aspect of the spill and ecological restoration. Using emergy measures of solar emjoules (sej) and converting to macro-economic dollars (emdollars), total damages (including cleanup and spilled oil) amounted to 48.5 E18 sej or 11.3 E6 US emdollars. Environmental damages to ecosystems and agro-ecosystems amounted to about 22% of the total, while economic losses and costs of restoration were about 78% of the total. The area affected by spilled oil was divided into four zones based on post spill treatments and amount of spilled oil. The largest ecological impact was to a lightly oiled zone (about 4500 ha) but was relatively short lived having recovered ecological productivity (GPP) within 30 days. A zone where heavily oiled soil was removed (9 ha) and a third zone where heavy surface oil was burned (80 ha) made up a smaller fraction of total losses. The zone with soil removal was estimated to require about 15 yrs to recover, while the area that was burned was estimated to recover in about 10 yrs. A fourth zone that was heavily oiled but received no further treatments (11 ha) exhibited the smallest total losses and recovery was estimated to require only 5 yrs. A method is suggested for evaluating the benefit/cost ratio of ecological restoration projects using the four zones for comparative purposes.

Fitogeografía y vegetación del Sector Aljíbico (Cádiz-Málaga, España)

Se analiza la flora y vegetación del sur de la Península Ibérica (Andalucía, provincias de Cádiz y Málaga) con el fin de delimitar y subsectorizar la unidad fitogeográfica Aljíbica. Hemos reconocido 4 subsectores en base a la bioclimatología, flora y vegetación: Aljíbico, Algecireño, Marbellí y Sidonense. Incluímos el sector Aljíbico en la provincia Tingitano-Onubo-Algarviense. Dicha provincia forma parte de la superprovincia lberomarroquí-Atlántica que enlaza las regiones Eurosiberiana y Macaronesica con la Mediterránea. Las series de vegetación reconocidas en el sector Aljíbico han sido las siguientes: alcornocales de Myrto-Querceto suberis S y Teucrio-Querceto suberis S, quejigares de Rusco-Querceto canariensis S, robledales de Cytiso-Querceto pyrenaicae S, acebuchales de Tamo-Oleeto sylvestris S, algarrobales de Clematido-Ceratonieto siliquae S, alisedas de Arisaro-Alneto glutinosae S, hojaranzales de Frangulo- Rhododendreto baetici S, fresnedas de Ficario-Fraxineto angustifoliae S, brezales higrófilos de Genisto- Ericeto ciliaris S, choperas de Crataego-Populeto albae S, tarajales de Polygono-Tamariceto africanae S y de Agrostio-Tamariceto canariensis S y adelfares de Rubo-Nerieto oleandri S. Se lectotipifican Tamo-Oleetum sylvestris oleetosum y fraxinetosum angustifoliae y Polygono- Tamaricetum africanae aretosum italici. Como nuevos sintaxones se proponen Crataego-Populetum albae, Rusco-Quercetum canariensis quercetosum broteroi, Asparago-Calicotometum villosae juniperetosum turbinatae, Equiseto-Salicetum pedicellatate salicetosttm albae y Asperulo-Ulicetum scabri anthyllidetosum cytisoidis. Se describen nueve comunidades caracterizadas cada una por: Juniperus oxycedrus, Quercus lusitanica e Ilex aquifolium, Dianthus lusitanus, Potamogeton nodosus, Potamogeton pectinatus, Myriophyllum altermflorum,Callitriche stagnalis, Callitriche regis-jubae y Ranunculus tripartitos. Se cita como nueva serie para el subcontinente europeo Cytiso-Querceto pyrenaicae S y se propone una nueva serie, Crataego-Populeto albae S. Se incluye la alianza Campanulion velutinae en Tinguarrenalia siculae a la cual se le asigna el rango de suborden.

Late Quaternary vegetation dynamics and hydroseral development in a Thuja occidentalis swamp in southern Ontario

Palaeoecological data from a small swamp in southern Ontario are used to reconstruct postglacial upland and wetland vegetation dynamics and assess the relative importance of autogenic and allogenic factors in wetland development. The inferred upland forest dynamics are comparable in timing and trend with lake records from the region. During the early Holocene, the shallow open water body became increasingly colonized by aquatic plants, until at around 8000 BP when the shallow open water community was replaced by a Larix swamp. At around 5600 BP, there was an apparent reversal in the wetland progression and Typha was locally dominant. There is a possible hiatus in the sedimentary record at around this time. Thereafter, a Thuj–Abies–Picea swamp community developed. The data suggest that internal factors and local events such as beaver activity could be equally or more important than regionally acting factors such as climatic change in controlling the hydroseral progression. The changing nature of the wetland community led to a 40-fold variation in sediment accumulation rate during the Holocene, emphasizing the importance of establishing a good chronology and using a multiple-core approach in such systems.

The Upper Pennsylvanian Duquesne Coal of Ohio (USA): Evidence for a dynamic peat-accumulating swamp community

An outcrop of the Duquesne Coal (Conemaugh Cyclothem) has the only significant occurrence of coal balls in Upper Pennsylvanian (Stephanian B equivalent) sediments of the Appalachian Basin. Excellent preservation of plant debris within autochthonous peat has permitted a more refined reconstruction of the source plant community than reported in published studies of other coals. Coal balls were quantitatively sampled for whole-plant species and mineralogical content. Shoot-root ratios were extremely high compared with values reported for other coals. The samples were analyzed using cluster analyses and non-metric multidimensional scaling (MDS) in order to differentiate microhabitats and stages of ecological succession within the general flora. Cluster analysis produced 5 stable clusters, which agreed with the sequence of ecological succession as determined in a previous study, and with microhabitat differentiation in contemporaneous seral stages. Three dimensions of the MDS analysis provided the best fit to the data. The dimensions are interpreted as representing: (1) ecological time or succession; (2) increasing dominance of Psaronius tree ferns in the plant community; and (3) an increase in microtopological variation (probably hummock formation). The initial stages of succession (oldest layers of permineralized peat) are characterized by aerial debris from Mesoxylon, Sigillaria and Calamites, followed by an assemblage dominated by Chaloneria. This was succeeded by more species diverse assemblage, dominated by Neuropteris seed ferns and Psaronius tree ferns, with numerous subcanopy plants, including lianas, epiphytes and ground herbs. Late seral stages (youngest layers of permineralized peat) were dominated by Psaronius tree ferns.

An ordination study of mangrove swamp communities in West Africa

Mangrove vegetation and soil were analysed with a view to understanding the community structure and soil relationship in mangrove ecosystems. Coverage values of all plants, frequency, density and basal area for trees were obtained. Soil properties measured included pH, field moisture, bulk density, organic carbon, Al3+, SO4 2- and Cl-. Principal components ordination of the vegetation data established six mixed mangrove community types. All soil properties varied significantly between the community types, but was most marked in the cases of CO3 2- and SO4 2+. Several tree species showed variation in dominance and density across the community types. Rank correlation of soil with vegetation ordination axes revealed greater correlation along Axis 1 than higher order axes. Soil Cl- was observed to markedly correlate with hyperspace locations of Nypa fruticans, Avicennia africana, Rhizophora mangle and Acrostichum aureum communities. Soil classification showed that several soil properties could serve as indicators for community type differentiation. Additional environmental factors influencing mangrove distribution were inferred from the ordination patterns.

A Geochemical Appraisal of Oil Generation in the Taranaki Basin, New Zealand

From a basin-wide evaluation of organic geochemical data, it has been possible to characterize and differentiate various source rock units and to establish the genetic relationships of oils. Most of the oils are primarily terrestrially sourced, and it is possible to recognize varying contributions from source rocks within the Paleogene Kapuni Group and late Cretaceous Pakawau Group. This distinction is attributable to the rise to dominance of angiosperms over gymnosperms in coastal plain swamp communities by the Eocene. Apart from the Maui family (i.e., Maui field, Maui-4, and Moki-1) oils, the inferred relative contributions from the main source rock types generally correlate with the relative proportions of suitably thick and mature units near reservoirs, given that mos Cretaceous-sourced oil appears to have escaped prior to trap development. Maui family oils do appear to be primarily sourced by Rakopi Formation (late Cretaceous) coals. In the northern part of the Taranaki Peninsula, where heat flows are highest, Mangahewa/Kaimiro Formation (Eocene) coals are the chief sources of oils. Farther south, in the Kapuni and Kupe South fields, Farewell Formation (Paleocene) coals appear to be the main oil source rocks. Biomarkers suggest that the onset of oil expulsion from coals occurs at a maturity level corresponding to a vitrinite reflectance of ca. 0.8% Ro, and may be aided by the evolution of large volumes of carbon dioxide. The terrestrial influence on Paleogene source rocks diminishes to the north-northwest of the basin and increasing marin contributions to oils are observed. A late Paleocene marine black shale is the source of oil in the Kora volcanic structure. It is possible that shales interbedded with coals, reflecting periodic marine incursions of coastal flood plains, also contribute to oil generation throughout much of the basin.

Pollination biology in a palm swamp community in the Venezuelan Central Plains

RAMIREZ, N. & BRITO, Y., 1992. Pollination biology in a palm swamp community in the Venezuelan central plains. In a palm swamp community that differs strongly from the surrounding savanna in the Venezuelan central plains, the pollination and floral biology of 33 plant species were studied during three years: 1983, 1984 and 1989. The most frequent flower colours were white, pink, yellow, and in a lesser proportion green, brown, purple and red. Floral symmetry was found in roughly equal proportion for actinomorphic and zygomorphic flowers. Most flowers were short-lived (6–12 hours); in monoecious species the female flowers were longer-lived than the male flowers. The most frequent rewards were pollen and nectar (36.4%) and pollen (30.3%). At the community level, bee- and wasp-pollination prevailed in 57.1% of plant species studies, followed by wind- (14.3%), fly- (11.4%), butterfly- (8.6%), bird- (5.7%) and beetle-pollination (2.9%). Between one and five plant species were simultaneously visited by the visitor species. The vast majority of the pollinating species displayed a high degree of load specificity: 26 pollinator species (65.0%) carried pollen from only one plant species, eight (20.0%,) carried pollen from two plant species, three (7.5%) carried pollen from three plant species and one (2.5%) carried pollen from five plant species. Visitor specificity and pollen transportation were similar amongst the visiting agents. Plant pollination-system specificity and pollen transportation were statistically significant among plant species with different pollinator types, but plant pollination system and pollen transportation were not different among floral symmetry, floral longevity, reward type, plant sexuality, breeding system and plant life form. The visitor species/plant species ratio was 1.6, and the pollinator species/ plant species ratio was 1.3. Among different guilds, birds, Coleoptera and Lepidoptera showed the highest pollinator species/plant species ratio, and wind pollination exhibited the lowest.

Successional Patterns of the Gran Sabana (Southeastern Venezuela) Vegetation During the Last 5000 Years, and Its Responses to Climatic Fluctuations and Fire

Three Holocene palynological records from the Gran Sabana region were studied from an ecological per- spective, in order to examine and to compare the responses of plant communities to external disturbances, i.e. climatic changes and fire. Attraction domains were defined using modern surface samples to build a multidimensional space, in which successional trends (deduced from palaeoecologi- cal data) were plotted. Both dryness and fire produced the substitution of forest by open savanna, but at different time scales. Forests did not recuperate at any time interval of this study, though a humid climate returned. In its place, morichales (swamp communities dominated by Mauritiaflexuosa (Palmae)) de- veloped in a general landscape of open savanna. More de- tailed palaeoecological studies using fine resolution techniques, with emphasis on transitional phases, are recommended.

A Multivariate Analysis of Vegetation Patterns in Tidal Freshwater Swamps of Lower Chesapeake Bay, U.S.A.

RHEINHARDT, R. D. (School of Marine Science, College of William and Mary, Gloucester Point, VA 23062). A multivariate analysis of vegetation patterns in tidal freshwater swamps of lower Chesapeake Bay, U.S.A. Bull. Torrey Bot. Club 119: 192-207. 1992.-The woody and herbaceous vegetation of 23 tidal freshwater swamps was sampled along the Pamunkey River, a tributary of the York River (a subestuary of Chesapeake Bay). Tidally driven water level fluctuations were monitored and recorded in selected swamps. Four vegetative life-forms were examined and ordinated with Detrended Correspondence Analysis: trees (canopy and sapling sized), woody subcanopy (shrubs and understory trees), vines, and herbs. Species distribution patterns were compared in relation to edaphic factors, a flooding index, and duration of flooding in the root zone. On the basis of the canopy composition, two tidal swamp communities were found, both subjected to a tidally forced hydroperiod regime within the upper 15 cm of their root zones, the approximate height of the hummocks. Nyssa biflora-Fraxinus spp. dominated swamps are best developed toward the more downriver reaches in the wetter sites, which contain more hollows, a higher organic matter content, and higher calcium levels. In contrast, Acer rubrumLiquidambar styraciflua-Nyssa biflora dominated swamps are more common throughout the mid- to upriver reaches at less wet sites with lower organic matter and calcium levels. Taxodium distichum was found to co-dominate in two swamps that may represent relic conditions for the wetter sites. Although low in canopy diversity, the tidal swamps are floristically rich in herbaceous and subcanopy species, ranking them among the most speciose in temperate North America. The microtopographic complexity (the hummocks vs. hollows pattern) appeared to be strongly related to species distribution patterns in the canopy, vine, and herbaceous strata. Although the ordinations segregated canopy and herbaceous strata similarly, the woody subcanopy did not segregate into the same two communities established by the canopy and herb strata, suggesting that the canopy may be partitioning different resources than the woody subcanopy.

Feral Pig (Sus Scrofa) Rooting in a Monsoon Forest-Wetland Transition, Northern Australia.

A grid of 447 cells (each 50x50 m) was set up in a wet monsoon rain forest on a gradual slope above the Adelaide River floodplain in the Australian Northern Territory. Surveys of pig (Sus scrofa) rooting were carried out at approximately 3-month intervals from November 1988 to September 1989. The pigs had only limited effects on the forest in both the wet and dry seasons. The seasonally flooded swamp communities (Melaleuca forest and sedgeland) were primarily exploited in the dry season; dryland communities ([Eucalyptus] and Lophostemon forests) were exploited during the wet season. Rainfall during the previous wet season may have influenced the pattern of rooting in the dryland forests. Rooting and ground cover were weakly positively related in 3 out of the 4 surveys.

Reproductive Biology of a Tropical Palm Swamp Community in the Venezuelan Llanos

The reproductive biology of a tropical palm swamp community, called morichal in the Venezuelan Central Llanos, was studied. Of the 128 woody and herbaceous species of plants recorded, 99 (77.34%) were hermaphrodites, 25 (19.53%) were monoecious, and four (3.13%) were dioecious. The morichal is characterized by a low number of species with obligate cross-fertilization. The frequencies of species with different breeding systems in a subsample of 26 species showed that eight (30.77%) were self-incompatible, 14 (53.85%) were self-compatible, and four (15.38%) were agamospermous. Ten of 14 self-compatible species were autogamous. Regardless of the self-incompatibility level estimated, seed and fruit set were greater in self-fertilized flowers than in hand-pollinated flowers in three of the nine self-incompatible species. These results are related to the facts that: 1) the relative isolation of the plant population limits the gene flow among similar communities and enforces the intrapopulation pollen flow; 2) the overlapping flowering patterns and infrequent and unspecialized pollinators may be enforcing self-compatibility and agamospermy; 3) self-compatibility is the rule among short-lived species in the morichal; and 4) three out of four agamospermous species are of the Melastomataceae family.