Foraging patterns of breeding Grey Herons were studied in the Camargue. Most individual birds used several different and widely dispersed feeding sites during the season. Some birds abandoned certain foraging sites but no seasonal trends were detected. There was evidence of both flock and territorial feeding at different sites. Birds were observed feeding in a number of different food patches (discrete feeding sites). There was evidence that the biomass intake rate influenced how long a bird would remain in a patch. When this was high, birds remained in patches, conversely when the rate was low birds left to feed elsewhere. Departures from a breeding colony to the feeding grounds were clumped. Birds leaving the colony together were likely to go to the same feeding site more often than birds leaving successively, but not together. I t is argued that the colony may have been used as an information centre. The diet of chicks in different colonies was compared. The proportions of the important prey types from different colonies and from different broods were different. There was evidence that adults sometimes pre-digest large prey so that their small chicks can consume prey that would normally be too large for them to eat. An experiment on prey selection provided evidence that chicks could select between two prey types which differed only in the irrelative profitability. The chicks consumed the most profitable prey type first. When the relative profit ability of the prey types was reversed, the chicks reversed their selection. This may be an adaption to maximise prey intake rate in the face of sibling competition. The results are discussed in relation to the success of the birds at different stages of their life cycle. The implications for the conservation of the species are considered.

The aim of this study has been to investigate the different responses of vegetation to the major environmental disturbances and discontinuities in Kordofan region of the Sudan. Data used have been obtained from fieldwork survey, aerial photographs and a landsat image in combination with existing maps and statistics on vegetation, climate, agriculture and population. Results obtained have shown that most plant species are neither randomly distributed nor indications of the postulated regularity of distribution were detected. Such a distributional pattern was explained through the pattern of surface properties. These have included rainfall, soil characteristics, micro-topography and the type of vegetation itself. The different types of vegetation identified were shown to reflect various succession stages following either excessive cultivation, grazing or both. Climatically conditioned natural vegetation is virtually absent as the effect is almost entirely masked by man's activities. Evidence presented showed that various types of woodland were formerly more extensive and that they have been replaced by secondary shrubland, bushland and grassland. Most plant communities have been explained by their history of cultivation and grazing pressure. These two were found to interpret the process of successional changes, to radically alter its dynamics and to set plant species on a wide variety of paths which is largely controlled by the pressure exerted. Achieved result indicated that vegetation in the area has persisted to exist and to re-establish itself after virtual elimination. This is shown to reflect a high degree of resilience in the system. Evidence were shown that if the vegetation is protected and the climatic and edaphic conditions were favourable, it will eventually be succeeded by a richer type of vegetation. It has not been possible to prove neither to reject the claim often found in literature that the vegetation zones in this region are constantly shifting southward as a result of overgrazing, overcultivation and accelerated soil erosion. However, it has been possible to recognise a process of successional changes which varies from one place to another in terms of nature and intensity depending largely on site characteristics.

An account is given of the use of a computerised database approach to the study of the chemistry and botany of streams with a pH at and below 4.0. the SIEUR (Stream Information Entry, Update and Retrieval) system was designed and implemented on the Northumbrian Universities IBM System 370 computer running under the M.T.S. operating system. SIEUR has been used to store approximately 2500 water chemistry and 2700 biological records. Of these, 269 chemistries and 125 biologies were collected from 10 m reaches from four countries where the pH was at or below 4.0 on the day of sampling. Principal component and cluster analyses of the acid chemistries suggested that they may be grouped together, based on the level of the various cations measured. This grouping follows closely a geographical breakdown of the sites and is probably a reflection of the mining associations of the majority of the sites. There was no similar grouping of the biological samples. Detailed examination of the distribution of 30 photosynthetic species which occurred live suggested that four patterns of reaction to low pH existed. In the design and practical application of the SIEUR system to the investigation of the acid datasets several problems and some solutions were identified. The need to date, time and location stamp all data at all stages of the analyses was apparent. SIEUR provides an "expansion facility" to overcome the problem of chemical and biological sampling not necessarily occurring together on the same day. By the use of this facility the user can specify the leeway by which chemical and biological samples from the same site are linked to each other in terms of date of sampling. A major design consideration was the need to identify structure in the data and to be able to store and retrieve this as data. During the use of the system the need for comprehensive statistical and graphical facilities was apparent. The decision to provide interfaces to existing packages to do this, rather than provide integral facilities was fully justified in terms of the flexibility obained.

<p> Since European settlement, clearing for agriculture, changes in hydrology, and urbanization have reduced the coverage of bottomland forest (BLF) in the Upper Mississippi Valley (UMV) by 46%. Recently, emphasis has been placed on restoring BLF, which provides vital ecosystem services (e.g., enhanced water quality, nutrient cycling, and wildlife habitat). Beginning in 1998, the US Army Corps of Engineers has restored BLF on many sites in the UMV, ranging in area from less than 1 ha to 120 ha. Root production method (RPM^&reg;) seedlings of three species of bottomland oaks and pecan have been planted to rapidly establish large-seeded species that are not regenerating under current conditions, with the expectation that light-seeded species (e.g., silver maple, green ash, eastern cottonwood, elm) will colonize passively. A chronosequence of nine restoration sites, ranging in age from 1 to 23 yr since planting, and two mature BLF reference sites was used to assess restoration success. Five 0.1-ha circular plots were randomly located at each site. Planted trees and natural recruits with a diameter at breast height (DBH) greater than or equal to 2.5 cm were identified, tagged, and their basal diameter, DBH, and height were measured. Density of shrubs was assessed in belt transects with a total area of 100 m² and cover of herbaceous species was estimated in twenty 0.5 m2 quadrats. Tree variables by species (mean basal diameter, mean height, density, and dominance) and community variables (richness and Simpson diversity of each stratum, total tree dominance, total shrub density, total herbaceous cover and the percent exotic herbaceous species cover) were calculated at the plot scale. Trajectories of change in tree size and community structure were examined using generalized linear modeling, relative to their values in reference sites. Tree height and diameter increased with time since restoration for all species. <i> Quercus palustris, Q. macrocarpa,</i> and <i>Q. bicolor</i> are all on track to achieve dimensions typical of mature BLF within 27 to 37 yr since planting. However, the dominance models for these trees show general declines which may indicate decreasing survivorship among planted trees and no recruitment of new seedlings. Pecan has suffered high mortality and without replanting it will be underrepresented in the restored forest. Tree dominance, richness, and diversity peaked and then decreased. Both total shrub density and total herbaceous cover showed no trend with time, although diversity of both shrubs and herbaceous vegetation slightly increased. Comparison with reference sites suggest that the shrub density, although there is no trend with time, is still in line with reference plot values. Exotic cover peaked between 10 to 15 years and began to decline to levels similar to reference plots. Overall, the results indicate some restoration success (tree growth rates, shrub diversity, herbaceous richness and diversity, and declines in exotic species cover) but suggest that replanting will be necessary in most sites to overcome mortality due to prolonged flooding and other factors (e.g. white-tailed deer browsing, inhibition of tree recruits by dense grass cover). Accurate mortality data for planted tree species is necessary to evaluate and improve the success of future USACE restorations. Ideally, a subset of trees should be tagged immediately after planting and these trees should be monitored at regular intervals. Frequently updated records will allow the USACE to make site-to-site management adjustments.</p>

No description available.

No description available.

The successional changes in a new. lowland reservoir in Leicestershire, England, were investigated, with particular refere~ce to larvae of the Chironomidae. During the first four years major changes in water chemistry were the result of the different sources of water used to fill the reservoir and the release of nutrients from the inundated terrestrial vegetation. Phytoplankton populations showed erratic changes in species composition and standing crop during the first year of filling. Seasonal fluctuations, similar to those observed at other eutrophic reservoirs, occurred in subsequent years. Chironomid species composition and temporal and spatial variation in the larval populations were investigated. Orth6cladiinae larvae were particularly abundant in mats of algae in shallow water in the second year after filling commenced. This was probably the result of a stable water level, warm weather conditions and high nutrient concentrations. In the third year Chironomus p lumosus and Polypedi tum nubeculosum larvae were numerically do~nant. Populations of these spec~es declined the following year and Tanytarsus species predominated. Temporal changes of the fauna were lnfluenced by climate and the filling regime of the reservoir. Chironamid larvae did not indicate any marked differences in water quali ty be tween the two arms of the reservoir. Populations were generally found to be contagious ly dis tributed. Chironomids in rainbow and brown trout diets were investigated during the first two fishing seasons. The species composition of larvae and pupae in the diets suggested different feeding zones for the two trout species. The behaviour of chironomid larvae and not their numerical abundance determines their occurrence in the diets. The results from this study are discussed in relation to management of the reservoir. Due to the importance of chironomids in trout diet it may be beneficial to base stocking policy on a knowledge of the seasonal population fluctuations of the chironomids.

No description available.

No description available.

No description available.