Ecological Sectors Research Articles

Influence of small climatic variations on the species composition of roadside grasslands

Relations between the distribution of Arrhenatheretalia species from roadside grasslands of southern Belgium and variations in climatic parameters are described on the basis of a statistical sampling procedure integrating multivariate techniques (cluster analysis and DCA-ordination). The authors examine the influence of small macroclimate features, such as mean annual rainfall (1100-1400 mm), mean annual temperature (7.0-8.2 °C), mean annual number of frost days (90-120) and mean annual number of snow days (28-35), on the floristic composition of roadside grasslands from High Ardennes (525-570 m a.s.l.) (19 samplings) and Middle Ardennes ecological sectors (330-500 m a.s.l.) (26 samplings). Cluster analysis revealed two distinct clusters of vegetation samples which are likely to be arranged along a climatic gradient. Sample scores on the first DCA-axis were significantly correlated with climatic parameters. Mean annual number of frost days was the factor which best explained the differences between plots, when analysed with a linear regression. These results indicate that very small macroclimate variations in general and in the number of frost days in particular, are determinant of compositional variation in roadside plant communities.

SPECIAL SECTION: LAND USE OPTIONS IN DRY TROPICAL WOODLAND ECOSYSTEMS IN ZIMBABWE:: Introduction, overview and synthesis

The articles included in this special section focus on the ecological and economic interactions of woodland use in Western Zimbabwe. One of the aims was to investigate the use of modelling to achieve integration among disciplines. The integrated model draws on the models in the different papers comprising the special section. The model has five ecological sectors, five sectors covering woodland use by local people and the state forestry organisation, two sectors to cover agriculture, one sector for population growth and land use, a sector to cover carbon sequestration, and a sector to calculate net present values of the various uses. The state has usually attempted to keep people and their livestock out of the state forest. We show that the private benefits of cropland may be greater than those related to state or local use of the woodland, but further work is required to incorporate the public costs of subsidies to cropland, and the public benefits of woodland services. Livestock production in the woodlands is compatible with woodland management, both from economic and ecological perspectives. Expulsion of forest 1 The vegetation formation in these areas is, strictly speaking, woodland, but the areas gazetted under the Forest Act are officially termed state forests. We use the term ‘forest dwellers’ for illegal inhabitants within the state forests. 1 dwellers from the state forest makes little ecological impact on the woodland, and does not improve the economic value of the woodland to the state. However, if the Forestry Commission relaxes the current control on in-migration, it is likely that the woodland will be rapidly depleted in the face of massive in-migration. Modelling is seen as a framework for integration of ecological and economic issues, but further work is required to incorporate institutional perspectives from the sociological and anthropological disciplines.

Study of the roadside vegetation in the Walloon region (South Belgium) and in particular in the Upper Ardennes: phytosociology, ecology, pedology

of PhD thesis Study of the roadside vegetation in the Walloon region (South Belgium) and in particular in the Upper Ardennes :phytosociology, ecology, pedology by Sandrine Godefroid Laboratoire de Botanique systematique et Phytosociologie, Universite libre de Bruxe/les, avenue Franklin Roosevelt 50, C.P. 169, B-1050 Bruxelles Key-words: roadvergesremnant semi-natural vegetationecological network -linear elementsArrhenatheriongrassland vegetation. Mots-des : bermes de routes vegetation semi-naturelle relictuelle reseau ecologique elements lineaires Arrhenatherionvegetation prairiale. The study of roadside vegetation in south Belgium was carried out with the help of 233 phytosociological releves scattered in 20 ecological sectors. The analysis has demonstrate that it was possible to appreciate the syntaxonomical position of the phytocoenosis by using the Braun-Blanquet system. The results have made conspicuous that roadside verges, as well communal, agricultural as motorways, are a refuge for precious relics of the ancestral vegetal landscape, which was fashioned by a rural population living in a subsistence economy and which characterised the rural landscape of south Belgium till the beginning of the 20th century. So, quite the contrary of a widespread idea, roadside phytocoenosis are not always characterised by the dominance of one or a small number of species without any distinct phytogeographic and syntaxonomic affinities. Our study has thus revealed a strong correlation between ecoand phytogeographic characteristics of a region and the differentiation and the sync horology of roadside vegetation. 26 syntaxa, corresponding to well known units of the Braun-Blanquet classification, have been identified and belong to the Mesobromion erecti (Braun-Blanquet & Moor 1938) Knapp 1942 ex Oberdorfer (1950) 1957, Xerobromion erecti (Braun-Blanquet & Moor 1938) Moravec in Holub et a/. 1967, Arrhenatherion elatioris W. Koch 1926, Polygono Trisetion jlavescentis Braun-Blanquet & Tiixen 1943 ex Marschall 1947 n. inv. Tiixen & Pre sing 1951, Molinion caeruleae W. Koch 1926, Lotio Potentillion anserinae R. Tiixen 1947, Agropyro Rumicion crispi Nordhagen 1940 em. R. Tiixen 1950, Thera -A irian R. Tiixen 1951, Call uno Genistion pilosae Duvigneaud 1944 and Aperion spicae-venti Tiixen in Oberdorfer 1949. D ow nl oa de d by [ 21 3. 12 9. 11 0. 38 ] at 0 8: 57 2 2 M ar ch 2 01 4

Spatial patterns of phytoplanktonic pigments and primary production in a semi-enclosed periantarctic ecosystem: the Strait of Magellan

The spatial patterns of nitrate, phytoplankton size-fractionated chlorophyll a, photosynthetic pigments detected by HPLC and primary production were studied at the end of the austral summer (February–March 1991), in the Strait of Magellan to provide insight into the mechanisms governing this seemi-enclosed periantartic ecosystem. Climatological peculiarities, hydrodynamic constraints, runoff and land forcing were considered. The most important features identified for this area were the confinement of the microphytoplankton fraction to the external parts of the Strait and the rather uniform dimensional structure of the phytoplankton communities (< 5 μm) within the internal sectors. In particular, the nanoplanktonic fraction (10-2 μm) comprised 33%, while the picoplanktonic one (2-0.5 μm) represented 62% of the total. The concentration of active Chl. a and plant pigments detected by HPLC, nitrate and primary production showed an uneven but similar distribution, allowing for the characterization of different sectors within the Strait, according to different types and intensities of forcing factors. The different ecological sectors identified along the Strait were associated with distinct hydrographic typologies: an oligotrophic, wind-mixed coastal area, adjacent to the Pacific opening; a high runoff fjord and a divergence zone in the Andean sectors; a stratified inland sea in the basin-like part of the channel (Paso Ancho) and a shallow, tidally mixed system in the Patagonian sectors. Areas of relatively low and high phytoplankton biomass and primary production alternate along the Strait, according to the hydrographic structures of the different sectors. Phytoplankton biomass, in terms of active Chl. a (spectrofluorometric determination) ranged between 10 and 51 mg m −2 and primary production between 275 and 1170 mg C m −2 d −1. The assemblage of plant pigments detected by HPLC indicated that the high levels of phytoplankton pigments and production were most likely attributable to Chlorophytes, Prasinophytes, Prymnesiophytes and/or Gyrodinium and Gymnodinium-like Dinoflagellates that were submitted to natural senescence and to superfluous feeding activity; while, when Diatoms, Cryptomonads and Prymnesiophytes were dominant, efficient zooplankton grazing occurred and characterized a balanced food chain. The spatial distribution of the parameters considered was related to hydrologic conditions indicating a Pacific water influence in the entire channel.

Ecosystem analysis using fuzzy set theory

Ecosystem studies of environmental quality are complicated by the imprecise nature of many ecological interrelationships and the subjectivity which is inherent in judgements by field observers. Many analyses of ecosystems require hierarchical decision-making processes which involve variables from social, economic and ecological sectors that are seemingly incompatible. Fuzzy set theory has been developed for and applied to problems involving complex systems like ecosystems. For example, government agencies who make habitat evaluations for wildlife can use techniques developed in fuzzy set theory for the combination of disparate variables that are required for decision-making at an ecosystem level. Another application of fuzzy set theory has generated a classification scheme for wetlands which is based on the knowledge of wetland experts. Fuzzy compartmentalization of ecosystem components allows greater diversity of behavior tha deterministic or probabilistic methods.

Functional taxonomy: An immodest proposal

The thesis is presented that classical taxonomy is of limited value to ecosystem science, and that the further development of ecosystem theory may actually be hindered by a reliance on the biological (phylogenetic) species as the basic functional unit of ecosystems. It is further argued that this situation could be improved if ecologists could agree on a system of functional classification in which ecological taxa would be distinguished solely on the basis of what they do in the context of an ecosystem, and not on their evolutionary relationships. A functional classification system is proposed in which functional taxa for specific ecosystems (ecological sectors) are defined as broad trophic groups of organisms in common vertical habitat zones, and with common inputs and outputs (ecosystem commodities and services). This system is envisioned as potentially useful in the development of comparative ecosystem theory, for constructing simulation models, for ongoing research in economic versus ecological values, and for cataloging new functional information as it becomes available. The proposed system is tentatively applied to the salt marsh estuarine ecosystem in the southeastern U.S.A. and to the swampforest ecosystem in Louisiana (U.S.A.). Twenty-five sectors are identified in the former and twenty in the latter. “It is by endless subdivisions based upon the most inconclusive differences, that some departments of natural history become so repellingly intricate”. Melville (1851), Moby Dick.