Phytosociological Structure Research Articles

Graph theoretical analysis of the phytosociological structure of plant communities: The theoretical basis

A method employing samples of variable size is assumed and shown to be useful in the detection of unidirectional associations of one species with another, whether caused by direct influence or by coincidence of ecological requirements. The pattern of these associations from a signed digraph (directed graph), the graph theoretical properties of which give insight into the phytosociological structure of the plant community. The properties of transitivity, balance, homogeneity, reachable sets and types of subgraphs are examined.

A Phytosociological Study on the Weeds of Wheat Fields at Samsun City Boundaries

The phytosociological structure of weeds in the wheat fields at Samsun city boundaries has been investigated by the method of Braun-Blanquet, and associations have been classified according to differential and characteristic species. The following associations have been described: a) Convolvulo-Polygonetum convolvuli Nova b) Cerastio-Poetum annuae Nova c) Lolio-Avenetum sterilis Nova

Black alder swamps on forested peatlands in Latvia

The black alder (Alnus glutinosa (L.)Gaertn.) stands occupy 2.5% of the forest area in Latvia. The majority of its communities lie on peatlands; they have been studied in the whole of latvia using the Braun-Blanquet approach. One hundred and fifty alder dominated releves selected from 334 forest areas have been analysed. Three associations (Carici elongatae-Alnetum, Sphagno squarrosi-Alnetum, andCircaeo-Alnetum), one with four subassociations have been recognized; these belong to the Eurosiberian alder swamps (cl.Alnetea glutinosae) and the European broad-leaved forests (cl.Querco-Fagetea). The phytosociological structure, distribution in Latvia and floristic features of these communities are reported. Results are compared with similar communities in the Baltic Sea states and neighbouring countries.

Vegetation analysis of some wadis in the Egyptian Mediterranean desert With 2 Figures and 3 Tables

AbstractThe present study determines the variation in the phytosociological structure of wadi Washka and wadi Nethely in the western Mediterranean region of Egypt.Four vegetation groups were recognized in wadi Washka (A: Hammada scoparia‐Plantago albicans, B: Scorzonera alexandrina‐Hammada scoparia, C. Scorzonera alexandrina‐Launaea resedifolia, D: Suaeda pruinosa‐Salsola tetrandra) and five in wadi Nethely (I: Gymnocarpos decandrum‐Helianthemum stipulatum, II. Scorzonera alexandrina‐Plantago albicans, III: Arisarum vulgare‐Thymelaea hirsuta, IV: Anabasis oropediorum‐Scorzonera alexandrina, V: Salsola tetragona‐Pancratium maritimum). Two phytosociological groups were recognized in addition to those identified in the previous studies. The first is codominated by Anabasis oropediorum and Scorzonera alexandrina and characterizes the plateau of wadi Nethely and the second is codominated by Arisarum vulgare and Thymelaea hirsuta and characterize the lower position near the cultivated bed of the wadi. Among soil factors affecting the distribution of vegetation groups are moisture content, Clay, CaCO3%, Ca++ and K+.Nomenclature follows Täckholm (1974).

Pine‐birch forest communities on nondrained peatlands in Latvia With 2 Figures and 2 Tables

AbstractResearch carried out on pine‐birch forest communities on excessively moistened peatland in Latvia gives a detailed notion on phytosociological structure of forested bogs and mires in the western part of the East‐European Plain at the Baltic Sea.The paper reflects one of the aspects of swamp forest investigation results in Latvia on plant communities, biodiversity and its preservation.129 sample plots from Cl. Vaccinio‐Piceetea Br.‐Bl. 39, O. Vaccinio ‐ Piceetalia Br.‐Bl. 39, All. Dicrano ‐ Pinion LIBB. 33 belonging to two associations and one subassociation have been described according the to BRAUN‐BLANQUET tablework methodology.Distribution in Latvia and floristic features of pine‐birch forest communities on nutrient‐poor bogs and medium‐rich mires have been analysed. Results are to be compared with similar investigations in the Baltic Sea region states and neighbouring countries.

Weed community structure in spring-seeded crops in Manitoba

The phytosociological structure of weed communities in spring wheat, barley, oats, flax, and canola was investigated using data collected during a 3-yr survey of 1384 fields in Manitoba. Fields were surveyed during July and August, after the application of all herbicides. Association and cluster analysis techniques, using the presence or absence of species in a field, were employed to distinguish co-occurring groups of species. Only a small number of significant positive and negative associations were found between species and only minor clusters with a few species were formed at low similarity levels. These results indicated that the weed community was composed of species responding to conditions more or less independently of each other. A comparison of weed associations among the five crops and four geographic regions in the province indicated that the weed community structure was determined largely by climatic variables. The pattern of weed association in the four geographic regions was correlated with differences in temperature and precipitation during the spring and summer. The lack of floristic differentiation was attributed to the fact that production practices were similar for the five spring-seeded crops. Key words: Weed communities, weed ecology, cluster analysis, association analysis

Vegetation?environmental relationships in the bed of Wadi El-Sheikh of Southern Sinai

This study deterines the magnitudes of variation in the phytosociological structure in the bed of Wadi El-Sheikh of Southern Sinai. It evaluates the relationships between its vegetation and environment. Vegetation and soil were sampled in 68 stands representing physiographic variations in the study area. Relative frequency, density and coverage were determined for each perennial and were added to provide an estimate of its importance value. The stands were classified by the mutual information method. The principal components analysis was applied to achieve a two-dimentional ordination of stands. Determinations of the percentages of surface sediments of different size classes, soil pH, conductivity, moisture content, water-holding capacity, CaCO3 and organic matter were carried out. The classification and ordination resulted in a clear demonstration of the vegetation pattern in the study area in quantitative terms. Other phytosociological groups were characterized in addition to those identified in previous studies. Vegetation analysis indicated that it is dominated by Artemisia judaica, Zilla spinosa, Fagonia tristis var. boveana and Lygos raetam. Factors influencing the distribution of vegetation fall into two important groups, one includes the moisture factors and the other includes factors of soil fertility.

Estrutura fitossociológica de uma associação natural de parque Inhanduvá com quebracho e cina cina, no Rio Grande do Sul

The phytosociological structure of a park's natural vegetation located in the south-west of Rio Grande do Sul State, in a Quarai Chico River neighbouring area, and under ciliary forest influence, was studied. The vegetation is characterized by the existence of Aspidosperma quebracho-blanco Schlecht. (quebracho) and Parkineonia aculeata L. (cina-cina), as well as by the presence of numerous species of ciliary forest, associated with the three typical species of the Inhanduva Park. Since this is a rare association in Brazil and because it constitutes a very fragile ecosystem, we suggest its preservation.

Graph theoretical methods for comparing phytosociological structures

This paper describes some methods that can be used to compare the phytosociological structure of plant communities using some graph theoretic properties of the directed graphs that represent them. In such a graph, the species are represented by points and the association of species A with species B is represented by a directed line segment going from B to A. Two communities can be compared using simple indices to measure the similarity of their species-lists (point similarity) and of the species associations in them (line similarity). A more sophisticated and informative measure of line similarity is the probability that, given the number of points shared by two graphs, they have at least as many lines in common as they are observed to have. A formula for calculating that probability is given here. The graphs of community structure can also be compared with respect to the homogeneity of the distribution of the lines among the points, a property related to the number of species that are important in determining the composition of the community. These techniques are illustrated using the graphs of the phytosociological structure of intertidal seaweed communities on the southeast coast of Nova Scotia.

Phytosociological structure of seaweed communities and the invasion of Fucus serratus in Nova Scotia

A method for analyzing the phytosociological structure of seaweed communities using measured line transects, or line transects with subsidiary point sampling, is described. The methods are applied to communities on the shores of Nova Scotia to investigate the spread of the introduced species, Fucus serratus L., which has been rapid in some areas but slow in others. The study found no evidence that its invasion into new areas has been slowed by competition from Chondrus crispus Stackh., but it did find evidence that competition from Fucus edentatus Pyl. has probably been an important factor.

Graph theoretical analysis of the phytosociological structure of plant communities: An application to mixed forest

A sampling method, compatible with the theory elaborated in the previous paper, was used to investigate the mixed-forest community of a woodlot in Southern Ontario. The results provide an illustration of the graph theoretical methods developed for the elucidation of a community's phytosociological structure. Certain conjectures about the community are tested and it is found that Goodall's hypothesis concerning the nature of a plant community is supported. The tests also show that the vegetation of the study area forms a single natural grouping despite the disparity of the position ofAcer saccharum and the polarity evident among the other tree species.

The Distribution of Asphodelus Microcarpus and Associated Species on the Western Mediterranean Coast of Egypt

This study is a quantitative analysis of the distributional behavior of Asphodelus microcarpus in relation to the main environmental factors. Its abundance was estimated in 40 stands covering most of the apparent physiographic and edaphic variations in an area extending about 500 km along the western Mediterranean coast of Egypt. In each stand, the number of shoots of A. microcarpus was counted in fifty 1—m2 quadrats, and its density and frequency were calculated. Variations in these two phytosociological characters were then evaluated in different types of habitat. Associated perennials were recorded in each quadrat and their relative frequencies estimated. These frequencies were used in ordering stands along there different axes according to the degrees of dissimilarity between them. This three—dimensional ordination was used to illustrate the phytosociological behavior of A. microcarpus and its relationship with other species. Quantitative estimations of conductivity and percentages of CaCO3, organic carbon total nitrogen, sand, silt, and clay were made for the soil in each stand. Also, the nature of surface, depth of soil, and physiographic position of each stand was rated. Variations in each of these environmental parameters, or their combinations, were then correlated with the distributional behavior of A. microcarpus. Variations in the abundence of A. microcarpus within each of the major types of habitat were found to be at least as significant as those between them. This indicated that local environmental variations had a substantial role in determining the distributional pattern of that species. The position of A. microcarpus in the ordination, which represented the phytosociological structure of the vegetation, was intermediate. The conclusion is that abundance of A. microcarpus is controlled mainly by the moisture availability and the total nitrogen and CaCO3 percentage in the soil. The moisture availability correlated significantly with more than 85% of the variation in its abundance. Its ecological amplitude in relation to local variations in this factor conformed roughly to that based on an geographical scale. Along the gradient of total nitrogen, the abundance of A. microcarpus exhibited a significant abrupt increase at the category of the highest value. In relation to the CaCO3 gradient A. microcarpus increased in abundance at medium categories and decreased toward low, as well as high ones. However, significant variation with either nitrogen or CaCo3 percentage was less than one—third of that with moisture availability, implying that moisture is ore important in controlling A. microcarpus distribution.

THE PRAIRIE, MEADOW, AND MARSH VEGETATION OF NELSON COUNTY, NORTH DAKOTA

The objectives of the study were to determine the general phytosociological structure of the native prairies, meadows, and marshes of Nelson County, North Dakota; to establish relationships between this structure and factors of the physical environment; and to evaluate the relationships between the vegetation of Nelson County and the True and Mixed prairies. Frequency values and environmental measurements on soil texture, salinity, pH, and an estimate of the drainage regime were obtained in 100 stands selected to represent the vegetational diversity within the County. The drainage regime proved to be the most important single environmental factor in determining the vegetation. A phytosociological drainage regime gradient was then established by assigning indicator values to selected species, and the behaviors of all species and environmental factors were displayed along this gradient. The vegetational display was then divided into six units: the uplands into high prairie, mid prairie, and low prairie and the lowlands into meadow, marsh, and cultivated depressions. Each vegetational unit is described. Comparisons are made between each unit and the related vegetation in surrounding areas. It is concluded that Nelson County should be considered to be within the geographical area of the True Prairie, although the frequent occurrence of western grassland types and western species suggests that the County is within the tension zone between the True and Mixed prairies.

Eine begrabene Solifluktionsdecke und ihr Einfluß auf die heutige Vegetation: Beobachtungen auf einer Bliesterterrasse (Saarland)

Abstract. In the lower Blies valley the author discovered a periglacial mudflow consisting of white marl and fragments of limestone, surmounted by 25-30 cm river-sand belonging to a Riß-terrace. The surface of these deposits was covered by fossil ice-wedges. The changes in the phyto-sociological structure of the vegetation cover permitted to fix the exact extension of the periglacial mudflow.