"Abiotic variables Because of the elevational zonation of vegetation shifts with latitude (the elevation of characteristic plant species and communities decreasing slightly with increasing latitude; Peet 1978a; Allen et al. 1991) in the southern Rockies, we examined relationships between vegetation and elevation using both actual (sampled) plot elevations and a latitudinally adjusted measure of elevation. Allen et al. (1991) found that floristically similar vegetation zones declined by 106.6 m per degree of latitude between the Wet Mountains and Rocky Mountain National Park (RMNP), between which all of our samples are located. "
[Show abstract][Hide abstract] ABSTRACT: Objective: Our purpose was to characterize vegetation compositional patterns, tree regeneration, and plant diversity, and their relationships to landscape context, topography, and light availability across the margins of four stand-replacing subalpine burns. Location: Four 1977 to 1978 burns east of the Continental Divide in Colorado: the Ouzel burn, a burn near Kenosha Pass, the Badger Mountain burn, and the Maes Creek burn. Methods: Vegetation and environmental factors were sampled in 200 0.01-ha plots on transects crossing burn edges, and stratified by elevation. We utilized dissimilarity indices, mixed-effects models, and randomization tests to assess relationships between vegetation and environment. Results: Three decades after wildfire, plant communities exhibited pronounced compositional shifts across burn edges. Tree regeneration decreased with increasing elevation and distance into burn interiors; concomitant increases in forbs and graminoids were linked to greater light availability. Richness was roughly doubled in high-severity burn interiors due to the persistence of a suite of native species occurring primarily in this habitat. Richness rose with distance into burns, but declined with increasing elevation. Only three of 188 plant species were non-native; these were widespread, naturalized species that comprised <1% total cover. Conclusions: These subalpine wildfires generated considerable, persistent increases in plant species richness at local and landscape scales, and a diversity of plant communities. The findings suggest that fire suppression in such systems must lead to reduced diversity. Concerns about post-fire invasion by exotic plants appear unwarranted in high-elevation wilderness settings.
"Multivariate methods can reveal patterns in species assemblages that elude the sequential single species approach. Gradient analysis involving Detrended and Canonical Correspondence Analysis (DCA and CCA) has been applied to biogeographical data in order to extract the dominant biogeographical patterns by ordinating species and geographical areas and by relating them to some environmental variables (Peet, 1978; Heliovaara, Vasanen & Immonen, 199 1 ; Vaisanen; Heliovaara & Immonen, 1992). Furthermore, patterns in the geographical distribution of species can also be studied on the basis of changes in the environmental conditions existing in the whole system (on any time or space scale). "
[Show abstract][Hide abstract] ABSTRACT: Two methodological approaches are compared with regard to their usefulness for providing explanations of observed faunal differences along Atlantic-Mediterranean coasts. A set of distribution data of ascidians containing 519 species and 80 genera was used for this purpose. Similarity methods were applied to establish the faunal affinities between distribution areas, and the measurement of β diversity and ecological distances along unidimensional gradients by non-lineal rescaling (using Detrended Correspondence Analysis) was undertaken for determining the steepness of ecotones existing along spatial gradients; these were analysed to detect the principal faunal changes, as well as their concordance with the commonly accepted limits for the classical biogeographical areas. There are fewer widely distributed species of shallow-water ascidians than in the Indo-Pacific region. Marked environmental changes within the Atlantic Ocean translate into significant differences in the composition of ascidian assemblages both in a latitudinal range and between the western and eastern sides. Few species show an amphi-Adantic range and most of these correspond with typically cosmopolitan species which are in general associated with shipping traffic or other forms of man-made transport. Three main endemism areas can be distinguished for Adantic-Mediterranean ascidian fauna involving genera and species: Caribbean, Mediterranean and south-west African. The rest of the shallow-water regions act as transitional or buffer zones where the genetic flows are generally maintained, although an increase in the number of certain species is found in some areas. This transitional role is mosdy found in the European Adantic coasts from the British Isles towards the Senegalian subregion, where gradual changes in ascidian populations occur: cold-water and tropical species at their southern and northern boundaries are substituted by temperate and subtropical species at the entrance of the Mediterranean.
Biological Journal of the Linnean Society 01/2008; 64(2):151 - 177. DOI:10.1111/j.1095-8312.1998.tb01539.x · 2.26 Impact Factor
"Topography facilitates the compression of biotic communities into relatively constricted vertical spaces (McLaughlin 1994), where areas of higher topographic complexity support higher species richness (Felger and Wilson 1994). Limited data suggest that species turnover (b-diversity) in Sky Islands is high relative to other forest types in western North America (Whittaker and Niering 1965; Peet 1978), though data only exist for the Santa Catalina Mountains in the Sierra Madre Occidental. The study builds on the limited knowledge of the relationship between the dominance and diversity of woody plant species and environmental variation in the American Southwest. "
[Show abstract][Hide abstract] ABSTRACT: The Sky Island archipelagos of the Sierra Madre Occidental contain diverse, highly endemic, and topographically complex ecosystems,
yet the local and landscape-scale controls on woody plant dominance and diversity patterns are poorly understood. This study
examines variation in woody plant species composition in relation to a suite of environmental variables (i.e., elevation,
potential soil moisture, soil type, geologic substrate, and heat load) in the Chiricahua National Monument, Arizona (CHIR).
Nine vegetation types were identified using cluster analysis that varied by species composition and plant life form. Non-metric
multidimensional scaling and correlation analyses identified significant relationships between vegetation composition and
elevation, potential soil moisture, and heat load. Rarefied species richness varied among vegetation types, and in relation
to topography, with higher species richness occurring on more topographically complex sites. β (species turnover) and γ (landscape) diversity were also high in CHIR compared to other temperate forests. This study highlights the importance of
local- and landscape-scale environmental controls on species diversity and vegetation patterns in Madrean evergreen woodlands.
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