Late pleistocene deposits at Wretton, Norfolk. I. Ipswichian interglacial deposits

Interglacial deposits found in the low terrace at Wretton, Norfolk, were formed in the zones II and III of the Ipswichian interglacial. The variety of sediments found is associated with the fluviatile environments of a meandering river. During zone II there was a regional mixed oak forest, with the local development of alder carr, fen, reedswamp and open water communities. During zone III the regional vegetation was more open and Carpinus became an important woodland tree. Locally, fen, reedswamp and open-water communities persisted, but alder carr was absent. The plants give some indication that the climate may have been more continental than at present, a number of species occurring which are not native to the British post-glacial flora but which have a wide distribution on the Continent. A brief comparison of the vegetational history is made with that of other Ipswichian interglacial sites in England and with the correlative Eemian interglacial on the Continent. The interglacial sections at Wretton form one of the richest Ipswichian sites for non-marine Mollusca so far found in England. The presence of a few more southern or more continental species, not now living in England, confirms that the climate was probably slightly warmer than at present, at least in summer. Numbers are large enough for satisfactory analysis in almost all sections, so that the environmental conclusion they suggest can be checked against those deduced from the plants. In general, these conclusions match and indicate a series of deposits laid down by a plant-rich Fenland river, a true ancestor of the present river Wissey, in its channel and neighbouring parts of its floodplain. The occurrence of brackish water species of Mollusca allows levels of marine influence to be clearly integrated with the vegetational history. Brackish horizons occur between - 1.95 m and +0.45 m O.D. in zone II b deposits, giving an indication of sea-level at this stage. The zone III deposits, although at a lower level, show no trace of brackish influences and a possible oscillation of sea-level is inferred.     

Recent developments at Dungeness

FINDON, R. A., 1989. Recent developments at Dungeness . The most significant development pressures at Dungeness over the last three years are discussed, namely military training, aggregate winning, water industry, electricity generation, recreation and tourism. The future prospects for Dungeness are briefly reviewed, as are the changes to the area notified as a Site of Special Scientific Interest.     

A CONCEPTUAL MODEL OF A SILTATION SYSTEM IN SHALLOW LAKES WITH LITTORAL VEGETATION

SUMMARY

In shallow lakes a siltation system develops when wind driven water turbulence erodes the lake floor, silt is resuspended and transported by means of waterdrift into the littoral vegetation. Here, due to the resistance of the vegetation, the turbulence is reduced and the silt deposited. Through this mechanism, the prevailing winds have a major rôle in the erosion and siltation pattern, lake morphology, vegetation pattern and in the mixing of water and nutrients from the open water and the reedswamp and vice versa. The model explains the uneven distribution of vegetation at the lakes Neusiedlersee (Austria) and Chilwa (Malawi) satisfactorily, if one assumes a positive correlation between siltation and reedswamp growth and spread.     

Why are there so many species of bumble bees at Dungeness?

WILLIAMS, P. H., 1989. Why are there so many species of bumble bees at Dungeness? Dungeness is unique in the British Isles in that it has more species of bumble bees than any other locality. Three ideas about what governs the number of species at a locality are examined by locking at patterns of flower visits at Dungeness in comparison with those at Shoreham, a species-poor locality also in Kent. The species of bumble bees that are present at Dungeness but absent from Shoreham show no association in their distributions among 2 km grid-squares in Kent with the species of food-plants that they prefer at Dungeness, nor is there any correlation between the diversity of bees and diversity of food-plants at Dungeness and Shoreham. From the information available, Dungeness is most likely to have more species of bumble bees because it has a particularly high density of the more nectar-rich flowers that bumble bees can use. Bumble bees feed most profitably from deep flowers because these contain more nectar than shallow flowers, although direct access to deeper flowers is ultimately limited by the length of each bee's proboscis. The distribution of worker proboscis lengths among species in the species-pool in Kent is clumped about a median of 7.9 mm. The best foraging conditions for the maximum number of species should be provided when flowers of similar depths are present in sufficiently large numbers for all foragers to make near-optimal flower choices. Although there is no difference in median between the distributions of the bees' proboscis lengths and the depths of the flowers they use at Dungeness, at Shoreham the flower depths used are shorter than the proboscis lengths. Among the food-plants at Dungeness, high densities of Teucrium scorodonia and Echium vulgare are likely to be especially important.     

Late holocene history and vegetation dynamics of a floodplain alder carr: A case study from eastern Bohemia, Czech Republic

Vegetation development in the lowland floodplain alder carr “Na bahně” (eastern Bohemia, the Czech Republic) has been studied by means of pollen and macrofossil analyses and combined with vegetation analysis performed over the last 70 years. Local successional changes started with an oxbow lake (160 cal BC) which has later terrestrialised (630 cal AD). Then it changed from a typical alluvial fen into aSphagnum-dominated spring mire (950 cal AD) supplied by water arising from a river terrace surrounding the locality from three sites. In the centre of this wetland a small patch of alder carr developed (100 cal. AD), showing some tendency towards cyclic succession. The alder carr alternated several times with an openCarex fen (1100 cal AD to recent). The last fen-to-alder carr transition has been documented by direct observation during this century. Possible autogenic and allogenic factors driving the succession are discussed. The model of autogenic cyclic succession corresponds well with direct field observations and can be used to interpret alder carr structure, its dynamics, and function.     

Orfordness and Dungeness: a comparative study

FULLER, R. M., 1989. Orfordness and Dungeness: a comparative study . Dungeness originally developed as a shingle spit from Winchelsea, across the bay which now forms the Romney Marshes and, 700–800 years ago, probably had its distal end between New Romney and Hythe. The structure seems to have been very similar to present-day Orfordness. Then a breach at the spit's origin produced an abrupt change in accretion and erosion patterns with the eventual development of the present-day cuspate foreland. It would seem that Orfordness is on the verge of such a breach, which is prevented by coastal defence works. Much can be learned by comparing physiographic and ecological processes at Orfordness with those at Dungeness, using Orfordness as an historical model for early Dungeness. This paper considers some of the evidence for these conclusions, examines the structures which survive to the present-day and discusses the ecological significance of the features, especially in terms of plant successional developments.     

Ectomycorrhizal root development in wet Alder carr forests in response to desiccation and eutrophication

Effects of desiccation and eutrophication on ectomycorrhizal (ECM) root development in wet Alder carr forests in The Netherlands were studied. In northwestern Europe, wet Alder carr forests are found mostly in peatlands and along streams, forming an important component of wetland ecosystems. The dominant tree species in wet Alder carr forests is Alnus glutinosa (L.) Gaertn. (Black alder), which associates with ectomycorrhizal fungi. During recent decades, wet Alder carr forests in Europe have declined because of desiccation and eutrophication, particularly in The Netherlands. In the present study, the number of root tips of A. glutinosa trees was highest in an undisturbed wet Alder carr forest in a peatland area. Eutrophication in the peatland area significantly inhibited ectomycorrhizal (ECM) root development of A. glutinosa. In the eutrophied forest, ECM root tips were observed only close to A. glutinosa trees growing on hummocks. The concentrations of nitrate and potassium in soil water of the eutrophied forest were significantly higher than in the undisturbed forest, while magnesium and iron concentrations and the pH were significantly lower. The number of ECM root tips of A. glutinosa in a desiccated forest along a stream was generally lower than in an undisturbed wet Alder carr forest on waterlogged soil in the same area. The sulphate concentration in soil water in the desiccated forest was significantly higher than in the forest on waterlogged soil. ECM root development of A. glutinosa may have been negatively affected by the chemical composition of the soil water.     

The structure and diversity of the animal communities in a broadland reedswamp

The fauna of a Phragmites reedswamp at Alderfen Broad, Norfolk, is described in terms of structure and diversity. Three transects were laid parallel to the water's edge at 1 m ( T1 ), 10 m ( T2 ) and 25 m (T3) from the reedswamp/open water interface. Twenty samples were taken randomly along each transect in July and all the macroinvertebrates in the samples were collected. The pH at each site was measured. The pH fell from 8–4 at T1 to 6–4 at T3 .
The fauna of the three transects was analysed by recurrent groups and by plotting the log abundance against the frequency for each species and dividing the resulting graph into units in terms of abundance and frequency. Both methods gave very similar results but the recurrent groups analysis only gave information on the most frequent species. The recurrent groups of the three transects had no common elements. The abundance/frequency analysis is simple to perform and could be of considerable use in evaluating sites for conservation purposes.
Transect T2 had the greatest species diversity, equitability and evenness, T3 the least. Reasons for this are discussed.     

The competitive and predatory impacts of the nonindigenous crab Carcinus maenas (L.) on early benthic phase Dungeness crab Cancer magister Dana

We evaluate the potential competitive and predatory impacts of nonindigenous European green crab Carcinus maenas on native Dungeness crab Cancer magister in the northeast Pacific. The coastal estuaries of Washington State, USA, provide appropriate habitat for recently introduced green crab, yet these areas are important nursery grounds for Dungeness crab and contribute greatly to the coastal crab fishery. Juvenile Dungeness crabs are dependent on limited intertidal epibenthic shell for refuge habitat during early benthic life and experience increased mortality on open sand and mud as a result of predation by fish and birds. Early juveniles throughout the subtidal are similarly at risk due to predation by fish and especially adult conspecifics. Laboratory experiments and infrared video observations revealed that juvenile green crab displace Dungeness crab of equal size from shelters during one-on-one competition. Green crab also consistently win nocturnal foraging trials in which the species compete for fresh, damaged clams. Field and laboratory enclosure experiments show that juvenile Dungeness crab emigrate from oyster shell habitat as a result of competition and predation by adult green crab. Depending on the extent to which the two species overlap, interactions with the dominant nonindigenous species could have a negative influence on juvenile Dungeness crab survival and could conceivably impact recruitment to the fishery. However, current evidence indicates that the distribution of green crab in Washington State is far removed from nursery areas of Dungeness crab.     

Marshland vegetation of the class <Emphasis Type="Italic">Phragmito-Magnocaricetea</Emphasis> in northwest Croatia (Krapina river valley)

Marshland vegetation of the class Phragmito-Magnocaricetea in the Krapina river valley was investigated during 2006 and 2007, and some sporadic investigations were made earlier. Phytosociological studies were carried out in accordance with the standard Braun-Blanquet methodology. As a result of the field work, and a small amount of data from the literature, 120 relevés were collected and 18 communities were established. For the purposes of comparison, the relevés were also classified using numerical methods. The clusters obtained mostly correspond to specific associations, but do not confirm the division into traditional vegetation alliances and orders. In the analysis of the ecological factors it is established that separation of the relevés is influenced by nutrient content, soil reaction, soil moisture, depth of water, and type of management. Analysis of the plant life forms shows, in all marshland communities, a prevalence of hemicryptophytes, geophytes and hydrophytes. The most widespread marshland communities of the investigated area are: Phalaridetum arundinaceae, Phragmitetum australis and Galio palustris-Caricetum ripariae. Furthermore, Carex randalpina community is recorded for the first time in Croatia. The most threatened marshland communities could be considered to be: Carex randalpina community, Caricetum vesicariae, Leersietum oryzoidis and Oenantho-Rorippetum. They are selected because of their very small surfaces in the investigated area and the small number of known localities within the territory of Croatia. The most invasive alien plant species in the Krapina river valley is Solidago gigantea. It spreads in potential habitats of marshland vegetation, and it is recorded in the species composition of many marshland communities. For the preservation of marshland vegetation, and especially threatened types, it is necessary to maintain the water regime of the habitats, to not remove natural plant cover due to spreading of neophytes, and to provide occasional mowing and burning.     

Short-Term Vegetation Dynamics of Alnus Dominated Peatlands: a High Resolution Palaeoecological Case Study from Western Pomerania (NE Germany)

Actual ecological research postulates for alder carrs a cyclic alternation of Alnus tree vegetation with open fen or Salix dominated vegetation. Such cycles are also indicated in palaeo-ecological studies, but normally the temporal resolution of these studies is insufficient to resolve the duration of short-term cycles in vegetation development. This paper presents a high resolution palaeoecological study (including pollen, macrofossils and non-pollen palynomorphs) of a Late Holocene wood peat section from the small, long-term Alnus dominated peatland ‘Heger Soll’ in the ‘Rodder Forst’ in Western Pomerania (NE Germany) to reconstruct short-term vegetation changes. During a time-span of ca. 800 years, sedge-dominated fen vegetation types alternated with two phases of Alnus carr and one phase of Salix shrubland. The alder carr decline coincided with the beginning of intensified human activity in the surroundings of the mire and was probably connected to increased water discharge resulting from large-scale deforestation, after which willow scrub and sedge fen became established. Growth of Alnus trees was associated with prolonged phases of reduced human impact and probably less water supply. This study shows that human impact on the uplands surrounding the mire and on the alder carr itself may explain the observed “cyclic” vegetation development of alder carrs, willow scrubs and sedge fens in Central Europe.     

Management plan for the Royal Society for the Protection of Birds reserve at Dungeness, Kent

THOMAS, G. J., GLOVER, J. & MAKEPEACE, P., 1989. Management plan for the Royal Society for the Protection of Birds reserve at Dungeness, Kent . A synopsis of a new management plan for RSPB Dungeness reserve is presented.     

Distribution patterns of boreal marshland birds: modelling the relationships to land cover and climate

Aim The aims of this work were (1) to study how well land‐cover and climatic data are capable of explaining distribution patterns of ten bird species breeding and/or feeding primarily on marshes and other wetlands and (2) to compare the differences between red‐listed and common marshland species in explanatory variables, and to study the predictability of their distribution patterns. Location Finland, northern Europe. Methods The data of the bird atlas survey carried out in 1986–89 using a 10 × 10 km uniform grid system in Finland were used in the analyses. Land‐cover data based on CORINE (Coordination of Information on the Environment) classification and climatic variables were compiled using the same 10 × 10 km grid. Generalized additive models (GAM) with a stepwise selection procedure were used to select relevant explanatory variables and to examine the complexity of the response shapes of the different species to each variable. The original data set was randomly divided into model training (70%) and model evaluation (30%) sets. The final models of common and red‐listed bird species richness were validated by fitting them to the model evaluation set, and the correlation between observed and predicted species richness was calculated. We assessed the discrimination ability of the binary models (single species) with the area under the curve (AUC) of a receiver operating characteristic (ROC) plot and the Kappa coefficient. Results Cover of marshland, shoreline length and mean temperature in April–June were significantly (P < 0.01) related to the common marshland species richness. Cover and clumping of marshland and mean temperature and precipitation in April–June were selected in the model of red‐listed marshland species richness. The level of discrimination in our single species models varied in ROC from fair to excellent (AUC values 0.70–0.95). Cover of marshland was included in all GAM models built for the target species, but clumping of marshland, shoreline length and cover of mires also appeared as important predictors in single species models. Seven species had statistically significant relationships with climatic variables in the multivariate GAMs. Cover of marshland was highest in squares in which the red‐listed bittern Botaurus stellaris, marsh harrier Circus aeruginosus and great reed warbler Acrocephalus arundinaceus and the water rail Rallus aquaticus were observed. Main conclusions Cover of marshland was the only variable which was included in all the models, reinforcing the close connection between the studied species and marshlands. Broad‐scale clumping of marshlands was important for the red‐listed species, probably due to the much lower population sizes of red‐listed species than those of common species. Land‐cover data produced in CORINE seems to be well suited for modelling the distribution patterns of marshland birds. Although climatic variables also strongly affect the studied marshland birds, habitat availability plays a crucial role in their occurrence. The distribution patterns of marshland birds at the scale of 10 × 10 km reflect the interplay between habitat availability and direct climatic variables.     

Uptake of DOM by Nemertean Worms: Association of Worms with Arthrodial Membranes

SYNOPSIS. Carcinonemertes errans is a nemertean worm, the juvenilesof which are found as epibionts on the Dungeness crab, Cancermagister, in close association with the arthrodial membranesof the crabs. The juvenile nemerteans appear to have no meansof taking in particulate food but survive for many months onthe surface of the host. We show that the juvenile C. erransare capable of removing amino acids from dilute solution insea water, that the water near the arthrodial membranes wherethe worms are found contains high concentrations of primaryamines, and that there is a low resistance pathway for low molecularweight amino acids across the arthrodial membrane examined invitro.     

The shingle ridge succession at Dungeness

FERRY, B. W., BARLOW, S. L. & WATERS, S. J. P., 1989. The shingle ridge succession at Dungeness . The range of plant communities which have colonized both intact shingle ridges and areas of disturbed shingle on Denge Beach, Dungeness, are described. An attempt is made to place these communities into categories of the National Vegetation Classification scheme, and further to relate them to physical and chemical gradients and variations in the shingle substrate.     

A remnant New Zealand carr

Carr vegetation was once extensive in New Zealand. It can be divided into Cordyline australis I Carex secta carr, comprising an open wood with scattered large herbs and an abundance of Carex species, and podocarp carr, dominated by tall conifers. Both have been almost eliminated by agricultural development. We studied a remnant of Cordyline australis I Carex secta carr in South Island, which graded at one end into salt marsh. Eight communities were recognized, including one pure salt marsh and two more with saline influence. Near the stream that provided moisture and alluvium for the area were herbaceous communities. In the poorly-drained area away from the stream were communities dominated by shrubs and small trees. The soil environment is similar to that of many European carrs, though generally less organic. A number of the exotic species are also found in European carrs.     

Marshland vegetation of the class <Emphasis Type="Italic">Phagmito-Magnocaricetea</Emphasis> in Croatia

The marshland vegetation of the class Phragmito-Magnocaricetea in Croatia is presented in a single place for the first time. All the available relevés from the literature have been assembled and supplemented with the results of field research. Thirty-three communities have been established, shown in a synoptic table drawn up on the basis of 486 relevés. The communities are understood according to the traditional syntaxonomic system based on the dominant or diagnostic species. For the purposes of comparison, the marshland vegetation is classified using numerical methods as well. The results obtained show that most clusters correspond to specific associations, but do not confirm the division into vegetation alliances and orders. The marshland communities with the most relevés in the dataset, and that therefore can be considered the most widespread in Croatia, are: Phragmitetum australis, Caricetum gracilis, and Galio palustris-Caricetum ripariae. The marshland vegetation is also analysed from the standpoint of nature conservation. In the dataset studied, 59 taxa from the Red Book of Vascular Flora of Croatia are identified as threatened, the 15 most endangered marshland communities are separated, and 10 neophytes and one neophyte association are registered. The diversity of marshland vegetation, and of the associated plant species, is considerably higher in inland Croatia than along the Adriatic coast, which is probably a result of the geological bedrock, climate and, in some places, halophile conditions.     

A trematode metacercaria encysted in the nerves of the dungeness crab, Cancer magister

Of 188 Dungeness crabs, Cancer magister, 8 contained unidentified trematode metacercariae encysted in various components of the nervous system, including the thoracic ganglion, brain, lamina ganglionaris of the eyestalk, and major nerves arising from the thoracic ganglion. A single cyst was present in the available tissue sections of 7 of the crabs and no behavioral abnormalities were exhibited. One crab with multiple cysts in major nerves near the thoracic ganglion was markedly ataxic. The cysts and included worms distorted, compacted, and destroyed nervous tissue, and occupied most of the nerves where present. Host response was minimal, but some cysts invoked massive hemocytic accumulations near the infection site. Infections probably seriously affect nerve impulse transmission and accounts for the lethargic behavior of the crab with multiple cysts in major nerves. The present report is the first record of digenetic trematode infections in the Dungeness crab and the apparent restriction of the worm to nervous tissue is unusual if not unique in the Digenea. Because of the absence of grossly recognizable lesions and the small samples excised at necropsy, both the incidence and intensity of infection in Dungeness crab populations are almost certainly higher than indicted by our data.     

Migration studies at Dungeness Bird Observatory

McMINN, S., 1989. Migration studies at Dungeness Bird Observatory . The part played in the study of bird migration by the Dungeness Bird Observatory is outlined. Information concerning blackbird ( Tardus merula ) and robin ( Erithacus rubecula ) migration is presented as well as notes on migration over the sea.