High-elevation rock outcrop vegetation of the Southern Appalachian Mountains

Abstract. Species composition patterns and vegetation-environment relationships were quantified for high-elevation rock outcrops of the Southern Appalachian Mountains, an infrequent and insular habitat in a forested landscape. Outcrops occur over a wide geographic range encompassing extensive variation in both geology and climate. Geographic-scale factors interact with site-scale factors to produce variation in vegetation among outcrops. Similarly, site-scale factors interact with micro-scale factors to produce variation in vegetation within outcrops. To provide a quantitatively-based classification of outcrop vegetation we used a TWINSPAN analysis of 154 100-m² plots. We recognized nine communities that primarily correspond to different combinations of elevation, bedrock type, geography, and moisture. Within outcrops of a single bedrock type, vegetation composition of 100-m² plots was consistently correlated with elevation and solar radiation, but relationships to soil nutrients varied with bedrock type. Both site-scale (100 m²) factors (e.g. elevation, slope, aspect, and bedrock type) and plot-scale (1-m²) microsite factors (e.g. soil depth, vegetation height, soil nutrients) were strongly correlated with species composition at the 1-m² level. Environment can be used to predict composition more effectively for 100-m² plots on a single bedrock type than either across bedrock types or at a 1-m² scale. Composition-environment relationships resemble those described for outcrop systems from other regions with pronounced topographic relief more than they do those described for the nearby but flatter and lower-elevation outcrops of the Southeastern Piedmont. There is strong spatial autocorrelation in this community, perhaps owing to dispersal limitation. Consequently, a comprehensive conservation strategy must include reservation of both a range of geologic types and a range of geographic locations.     

Typology of macrofaunal assemblages: a tool for the management of running waters in The Netherlands

A survey was carried out at 156 sites, situated in streams in the province of Overijssel (The Netherlands), to describe the macroinvertebrate assemblages and their environments. Fifty-six environmental variables were measured once at each sampling site. The main aim was to describe a typology of stream for this region.Different multivariate analysis techniques (clustering and ordination) were used in combination with ecological information on individual taxa to derive and describe site groups in terms of taxonomic composition and mean environmental conditions. The resulting site groups were termed cenotypes.Eleven cenotypes were distinguished. Differences between cenotypes were attributed to (combinations of) environmental key factors, namely, dimensions (width and depth), morphological (profile shape) and hydraulic stream characteristics, duration of drought and load of organic material.The typology offers a basis to be used for regional stream management and nature conservation. Efforts to improve stream ecosystems should be directed at the physical and hydraulic conditions.Typological studies are needed (especially in semi-natural landscapes) if we are to better understand, manage and conserve freshwater biota.     

Composition and spatial heterogeneity of submersed vegetation in a softwater lake in Wisconsin

Big Muskellunge Lake, a softwater lake (pH 7.5–8.0, alkalinity 0.36 meq/L) in northern Wisconsin, harbors a diverse (25 species) submersed macrophyte vegetation. The present submersed flora combines species generally thought distinct in their ecological affinities, and is very similar to that reported in 1935. The only differences are the apparent loss of three previously infrequent Potamogeton species, and the addition to the flora of two infrequent Potamogeton species and the now abundant Elodea canadensis. Dramatic differences in composition and pattern of the vegetation occurred between sites of contrasting exposure and sediment type. Substantial compositional variation, at scales ranging from tens of centimeters to tens of meters, occurred along transects of contiguous quadrats at uniform depth and exposure. Analyses of species sequences along line transects detected significant segregation of species that is most plausibly explained by biotic factors such as colonization, clonal growth, and competition. Heterogeneity at small scales of a few meters or less is common in Big Muskellunge Lake. Such pattern has been neglected in macrophyte ecology, in spite of its significance for neighbor relationships which may critically influence growth and reproduction of aquatic plants.     

On the integrated interpretation of indirect site ordinations: a case study using semi-arid vegetation in southeastern Spain

The need for rigorous methods of interpreting indirect site ordinations is discussed and the problem of oblique habitat and phytosociological trends is emphasized. A sequential approach, termed integrated interpretation, is introduced to overcome this problem. It first involves a technique termed rotational correlation a linear form of trend surface analysis, which locates the best fit between a habitat variable and the coordinates of a pluridimensional ordination. The coordinates at positions of best fit are then used to produce two-way site-species tables (seriation arrays) which summarize floristic variation in relation to each major habitat trend. The seriation arrays can also be used to identify groups of differential species. Integrated interpretation is demonstrated using semi-arid vegetation from Murcia Province, SE Spain. A two-axis site ordination of vegetation data by non-metric multidimensional scaling is shown to have two oblique trends related to aspect-induced topoclimates and types of past anthropogenic disturbance. Rotation of the configuration to maximum linear correlation achieves very high levels of explanation for each factor. Rotated ordination coordinates from the correlation analysis are used to obtain two seriation arrays and floristic noda which relate directly to the two underlying habitat trends. A floristic discontinuity is revealed on the topoclimate continuum and it is hypothesized that temperature conditions are a major determinant of floristic composition, but that moisture partly determines vegetational cover and phytomass. Several patterns of past cultivation are detected and associated with five main kinds of geomorphological unit, together with some evidence that the rate of succession is partly determined by topoclimate. The integrated approach to interpretation is compared with visual methods and other multivariate techniques. A case is made for increased interpretational rigour in site coordinate studies, especially the discontinuation of trend-seeking using individual unrotated ordination axes.Nomenclature of vascular plants follows Tutin et al. (1964–1980) Flora Europaea 5 Vols. Cambridge University Press, Cambridge. Nomenclature of syntaxa follows Rivas-Goday & Rivas-Martinez (1967).I am indebted to J. A. Michel, Dr M. A. Abdelrahman and Monica M. Dargie for field assistance. Field discussion with Dr R. L. Wright, Dr M. P. Austin and Professor F. Esteve Chueca was most helpful; the latter assisted with confirmation of vascular plant voucher specimens. Non-vascular taxonomy was determined by Dr C. Humphries (mosses and one alga) and Dr O. L. Gilbert (lichens). An anonymous referee suggested an approximation of the analytical solution to rotational correlation, and Dr N. R. J. Fieller assisted with its confirmation. The project was assisted by a grant from the University of Sheffield Research Fund.     

Changes in vegetation patterns on the margins of a constructed wetland after 10 years

Summary A constructed urban wetland in Adelaide was surveyed 18 months and 10 years after construction to see how shoreline vegetation, soil electrical conductivity (EC), texture and pH changed over time and to provide data for future site management. Multivariate analysis detected four plant associations at 18 months: salt‐tolerant taxa on conductive clays; a weed‐dominated community on lower EC soil; and two smaller waterlogged, low EC clusters dominated by Common Reed (Phragmites australis) and Sea Club‐Rush (Bolboschoenus caldwellii), respectively. At 10 years, site cover and heterogeneity was higher, with the margins dominated by Phragmites and salt‐tolerant species. EC was much lower and more uniform, and the soils were heavier and more alkaline. Managed storm water flushing apparently lowered soil EC, but possibly also disturbed the shoreline. However, weeds were still common, and the potential for domination by Phragmites at the expense of other native shoreline species means that ongoing monitoring and hydrological and vegetation management are essential to maintain site habitat diversity.