bluuebunny/crossref_metadata_2025_split huggingface dataset:
Community dynamics of desert grasslands: influences of climate, landforms, and soils
Authors: Wondzell Steve , Ludwig John A. 
Published: May 2006

Abstract. Permanently marked vegetation transects in Big Bend National Park, Texas, USA were monitored to follow temporal dynamics of desert grassland communities on a variety of landforms and soil types over a 26‐yr period after the removal of domestic livestock. Historic records indicate that the park area was severely overgrazed prior to its establishment, and our results show that the species present increased in both cover and density after the removal of livestock. However, the timing of recovery corresponded to multiyear periods of above‐average precipitation. Little change was observed in between 1955 and 1960, a period dominated by several consecutive years of drought. The cover of two large shrubs common to the Chihuahuan Desert, Larrea tridentata and Flourensia cernua, increased from 1960 to 1967, a period dominated by summer drought and frequent wet winters. The cover and density of forbs, perennial grasses, and most shrubs increased on nearly all landforms between 1967 and 1981, when summers were wetter than average. In contrast, the cover of Larrea tridentata decreased during this period. Comparisons among the plant communities on each landform showed that they diverged through time after domestic livestock were removed. Presumably, differences in topographic position and soil texture influence water availability which was reflected in the species composition on each soil series.Unfortunately, we cannot isolate the effects of recovery from grazing from the effects of climate because the study design did not include control plots located within grazed pastures. Certainly, the directional trajectory of change and the regrowth of grasses into inter‐shrub spaces, must, at least in part, be the result of recovery from grazing. However, our data also indicate that the desert grassland communities are sensitive to multi‐year periods of above‐ or below‐average precipitation. Clearly, the dynamics between shrubs and grasses cannot be explained by a simple successional paradigm that views increased shrub dominance as retrogression from a climax grassland. Many alternate hypotheses have been forwarded to explain the dynamics that control the vegetation composition in the desert and desert grassland region of North America. Experimental tests of these hypotheses are needed to indentify the interactions between biotic and abiotic factors that control dominance by shrubs or grasses.
The vertical distribution of below‐ground biomass in grassland communities in relation to grazing regime and habitat characteristics
Authors: Rodríguez Miguel A. , Brown Valerie K. , Gómez‐Sal Antonio 
Published: May 2006

Abstract. 40 sites, representing different pasture types in Northwest Spain, were sampled in respect of their floristic composition, distribution of above and below‐ground biomass and environmental and physical variables. Five plant community types were identified by classification techniques of plant species composition. These communities were then characterized in terms of the percentage of ground covered by herbaceous and shrub vegetation, stones, rocks and gaps as well as their topographic location and characteristics of the shallow soil (pH, organic matter, nitrogen and calcium content). Bio‐mass was assessed in terms of above‐ground structures, surface crowns and three below‐ground layers to a depth of 10 cm. Three types of grazing regime were distinguished: Concentrated Intense Grazing in early spring (CIG), Extended Intense Grazing throughout the spring (EIG), and Non‐Intense Grazing (NIG). Grazing regime showed the highest association with plant community type and three broad categories were identified: xeric stressed pastures, which nevertheless received CIG, mesic pastures with EIG, and three kinds of NIG mesic pastures.The xeric communities had the highest proportion of aboveground biomass, as a consequence of their greater proportion of woody perennials. These xeric communities displayed a more gradual reduction in below‐ground biomass with depth than mesic pastures, a likely consequence of the low water content in the upper soil layers. The mesic communities had a high concentration of below‐ground biomass in the upper layers when they were intensely grazed. However, when grazing was low (i.e. NIG situations), these communities had greater variability in biomass profiles than any of the other pasture types. Possible causes of the patterns in biomass distribution of the intensely grazed pastures are discussed.
Shoot and leaf demography of Carex curvula ssp. Curvula and Carex curvula ssp. rosae in the Central Alps
Authors: Erschbamer Brigitta , Winkler Josef 
Published: May 2006

Abstract. Populations of Carex curvula ssp. curvula, C. curvula ssp. rosae and their intermediate form were investigated in the Central Alps over a three‐year period. The closely related taxa showed a different dominance behaviour in their respective communities. This may be caused by different growth strategies and a different reproduction biology. Therefore, the main aim of the study was to compare the demography of the three taxa. Shoot and leaf turnover, flower and seed production and population half‐lives were determined.Differences in growth dynamics were less pronounced between the two species of Carex curvula than between these taxa and their intermediate form which showed the highest shoot turnover, highest number of fertile inflorescences and highest number of seeds per inflorescence. Carex curvula ssp. rosae showed a slightly higher shoot and leaf production but a lower reproduction capacity than Carex curvula ssp. curvula.Recruitment of populations of the three Carex‐forms was only by vegetative shoots. Flowering had a striking effect on the shoot dynamics of the species grown in the grassland sites: up to about 70 % of all dead shoots could be identified as dead flowering shoots from the previous year.The different dominance behaviour of the three taxa could not be explained by their demographical features. Interspecific interactions and the occurrence of microniches might affect the growth and reproduction processes of the taxa.
A vegetation map of tropical continental Asia at scale 1:5 million
Authors: Blasco F. , Bellan M.F. , Aizpuru M. 
Published: May 2006

Abstract. A vegetation map at scale 1:5 million is presented.* It covers Bangladesh, Burma (Myanmar), India, Cambodia, Laos, Thailand, Vietnam and Sri Lanka and fills a conspicuous gap in the cartography of tropical vegetation, following the publication of vegetation maps of South America, Africa and Malaysia. For conformity, it is presented as one sheet at a scale of 1:5 million. It uses the basic map of the American Geographical Society (1942; bipolar oblique conformal projection) which forms the base for FAO's Soil map of the world. Basic information was obtained from many published maps, unpublished observations and satellite data. The limits of the main vegetation types have been updated with a complete set of Landsat MSS images (369 scenes) with a mosaic of Landsat TM data for 1991 and with recent forest maps from Asia.Nine main vegetation units, which are groups of forest formations, have been identified and mapped, including woodlands, thickets and wooded savannas. Agricultural land has been shown in a uniform pale green colour in order to clearly express the extent of human impacts on woody vegetation.In spite of the necessary oversimplification of the ground data, this map is probably the most explicit expression of the remaining forest stands and of the regression of natural vegetation in the region. It can be considered as a benchmark for future monitoring of tropical vegetation.
The vegetation of the Farasān Islands, Red Sea, Saudi Arabia
Authors: El‐Demerdash M.A. 
Published: May 2006

Abstract. Classification of the vegetation of the Farasān Islands using TWINSPAN technique resulted in the recognition of seven community types associated with seven different habitat types: silty runnels, palm orchards, rocky plains, rocky plateau crevices, coastal sand dunes, sand plains, and mangroves. These communities were dominated or co‐dominated by 13 perennial species; 87 associate species were recorded in the study area with chamaephytes dominating the life‐form spectrum. Canonical Correspondence Analysis (CCA) indicated that organic carbon, soil moisture, silt, electrical conductivity and calcium carbonate were the major edaphic gradients controlling the distribution of the plant communities on the Farasān Islands.Higher species richness was recorded in the plant communities inhabiting the palm orchards, the crevices of the rocky plateau, silty runnels, rocky plains and rocky plateau, while those of the mangrove and sand formations (dunes and plains) showed a lower species richness.Soil texture and organic matter are the main factors promoting species diversity in the more diversified habitats, while high salinity and calcium carbonate are the main factors associated with lower species diversity in the less diversified habitats of the study area.
Variation in species richness on small grassland quadrats: niche structure or small‐scale plant mobility?
Authors: Van Der Maarel Eddy , Noest Vera , Palmer Michael W. 
Published: May 2006

Abstract. In this study we make clear that the significance of deviations from an expected variance in species richness as demonstrated in alvar grassland, is a function of spatial pattern at the scale richness was measured, i.e. 10 cm2. If corrected for spatial dependence, more than half of the significant cases become nonsignificant. As regards cases of significant variance deficit, which has been interpreted as an indication of niche limitation, we suggest that there may be a simple physical limitation to the number of species on the scale of observation in the form of a low number of plant units which can find a place because of the modal plant size of the species involved. In most cases of significant variance deficit the modal size of the plant units involved was probably bigger than average.Insofar as a significant variance deficit can be demonstrated, the resulting species richness distribution curve should be analyzed and we propose a skewness test, enabling us to differentiate between significantly left‐skewed curves (‘niche limitation’), significantly right‐skewed curves (‘niche facilitation’) and symmetrical curves. We present results obtained with the G‐test, a log‐likelihood ratio goodness of fit test. Only few cases of significantly left‐skewed curves and a majority of symmetrical curves were found.Attempts to demonstrate guild proportionality in grasslands suffer from the heterogeneity of usually distinguished guilds, such as annuals vs. perennials or graminoids vs. dicotyledons.We observe that niche limitation may occur in alvar grassland, but indications for niche facilitation are stronger. Finally, we conclude that deviations in species richness variance are interesting indications of community structure, but only of spatial structure. Niche structure resulting from assembly rules should be investigated through experiments.
Changes in landscape structure in the northwestern Alps over the last 7000 years: lessons from soil charcoal
Authors: Carcaillet Christopher , Brun Jean‐Jacques 
Published: May 2006

Abstract. Current land‐use a bandonment and the current rise in temperature in the Alps both suggest that tree limits may change. When it is assumed that the climate of the early mid‐Holocene between 8000 and 5000 yr before present is analogous to that of the predicted climate of the late 21st century, palaeo‐ecological studies of the early Holocene may provide data for the prediction of the vegetation pattern in a century from now. It appears that mid‐Holocene charcoal assemblages can be used to reconstruct the spatial patterns of the vegetation before, or during, the practice of slash‐and‐burn.Correspondence analysis (CA) of charcoal assemblages shows that an important ecological gradient is determined by elevation. However CA also shows that charcoal assemblages in profiles between 1700 and 2100 m a.s.l. are roughly stratified: the more recent assemblages from the topmost centimetres of soil are intermediate between the lowermost assemblages and assemblages from higher elevations. This suggests that the woody communities at the highest elevation were located at lower elevations at a later date. The taxonomic diversity of the soil charcoal assemblages has been compared to that of present‐day phytosociological relevés after transformation to charcoal‐equivalent data. This comparison revealed that the vegetation pattern along the altitudinal gradient in the mid‐Holocene was different from that at present. The assemblages indicate that some communities disappeared, that Picea is a late‐Holocene invading species, and that there is no strict modern analogue for the vegetation structure prior to that of 3000 yr ago. The past structure of the woody vegetation was also different from that of today. Although past vegetation is not a good analogue for predicting future vegetation patterns, it still has potential as an indicator for the potential presence of tree species where there is none today. If we assume a temperature rise, and take into account current trends of landscape use abandonment, then we can expect strong vegetation dynamics at the upper tree line in the future: Abies alba may expand to occupy elevations of ca. 1800–2000 m in mixed communities with Picea abies, Pinus sylvestris and hardwood species, and Pinus cembra may expand up to 2500–2700 m a.s.l.
Slow‐motion population dynamics in Mojave Desert perennial plants
Authors: Cody Martin L. 
Published: May 2006

Abstract. To investigate survivorship and regeneration in desert perennial plants, individual shrubs were mapped, measured and tagged on a nearly level 360 m2 plot of diverse Mojave Desert vegetation in 1981, they were re‐mapped and measured 15 years later, in 1996. A large majority of the shrubs persisted between censuses. Modest birth (establishment) and death rates indicate that plants are replaced approximately every century, while the median longevity of several species is much longer. A 15‐yr intercensus interval, appropriate for most species (i.e. birth and death rates were measurable), is too short for several larger shrubs (including Larrea divaricata, Ephedra nevadensis, Yucca schidigera and the larger Opuntia spp.) in which virtually no births or deaths occurred and in which longevity must be extremely high.While individuals of most species grew over the 15‐yr interval, others did not, and some individuals shrank in size. In a number of species, individual growth rates were significantly reduced according to the number of neighbouring plants rooted 0.5–2.0 m distant. Even Larrea tridentata, one of the largest species, showed significant effects of growth rate reduction where crowded by allospecific plants, despite the generally much smaller sizes of these neighbours.
Acidification and eutrophication of deciduous forests in northwestern Germany demonstrated by indicator species analysis
Authors: Diekmann Martin , Dupré Cecilia 
Published: May 2006

Abstract.A new method of indicator species analysis is suggested that can be used to demonstrate changes in the species composition of forests resulting from atmospheric deposition of acidifying substances and nitrogen. The method is not dependent on an exact re‐localization of sites. 2162 published relevés ofFagus sylvaticaandQuercus robur‐Carpinus betulusforests from two study areas in Germany (S Niedersachsen and Nordrhein‐Westfalen) were compiled and divided into relevés from before 1975 and more recent relevés. Weighted averages of Ellenberg indicator values for light (L), moisture (M), reaction (R), and nitrogen (N) were calculated and for each of the four data sets ‐ mesic and dry sites in two areas ‐ N was regressed on R to give a predicted value (Npred) for any given R. The differences between observed values Nobsand Npredwere calculated separately for old and new relevés (Ndev‐old and Ndev‐new). The same analysis was applied to model data including 16 different scenarios of acidification and/or eutrophication.The model runs resulted in six different types of regression plots for Ndev and R. All models had in common that the regression lines for Ndev‐new lay, completely or largely, above the zero line ofno change and above the lines for Ndev‐old. Also, in the four data sets, Ndev‐newwas generally larger than Ndev‐old, and particularly so in Nordrhein‐Westfalen. The values of Ldev‐oldand Ldev‐newindicate that the differences in Ndevare unlikely to be caused by altered forest management, but must result from atmospheric pollution.
Competition between Quercus petraea and Carpinus betulus in an ancient wood in England: seedling survivorship
Authors: Le Due M.G. , Havill D.C. 
Published: May 2006

Abstract. Age structures of populations of canopy trees in Wormley Wood are consistent with reports that successional change is occurring, with Carpinus betulus replacing Quercus petraea as the dominant species. TWINSPAN analysis of data from a vegetation survey identifies three communities (described in earlier work), the ‘Bracken’, ‘Bramble’, and‘Bareground’ societies, characterized by increasing prominence of C. betulus and loss of species diversity.An experiment was set up in which C. betulus, Q. petraea and Betula pendula seedlings were explanted into each of the communities. Survival of seedlings was monitored over 860 days and differences investigated. Cohort survivorship differed between species and sites. C. betulus seedlings survived longer than Q. petraea in Bracken and Bramble communities.Species‐ and site‐specific variation in the types and effects of herbivory were found. Herbivory did not appear to be a critical factor in the survival of Q. petraea seedlings. The photosynthetic light response of the seedling species was measured in the field. The light compensation point for Q. petraea seedlings (77 μmol photon m‐2 s‐1) is higher than the maximum available light under the main tree canopies in the wood. In contrast, seedlings of C. betulus have a lower light compensation point (15 μmol photon m2 s‐1) and the mature tree casts a deeper shade than Q. petraea. It is suggested that the invasion of the canopy by C. betulus, following the cessation of coppicing, is creating light levels too low for Q. petraea seedling banks to persist.
BOOK REVIEWS
Authors: Meijer Willem 
Published: May 2006

Book Reviewed in this article:Anhuf, Dieter. 1997. Satellitenbildgestützte Vegetationklassifikation der Côte d'Ivoire. Mannheimer Geographische Arbeiten 45. ix + 190 pp. ISBN Price:Anhuf, Dieter (ed.). Forschungen im französischsprachigen Ausland. Mannheimer Geographische Arbeiten 43. 179 pp. ISBN Price:
Ecological requirements of Abies alba in the French Alps derived from dendro‐ecological analysis
Authors: Rolland C. , Michalet R. , Desplanque C. , Petetin A. , Aimé S. 
Published: May 2006

Abstract. We used dendro‐ecological techniques to investigate fundamental relationships between climate and growth of Abies alba (silver fir) in eastern France. Seven Abies forests in the Trièves region of the French Alps were chosen to represent a wide range of ecological conditions based on the results of previous forest vegetation surveys. In each forest, four trees were sampled in each of five different stands with two cores per tree. These 280 cores were studied using two separate dendro‐ecological methods: the pointer years method (based on extreme growth events), and correlation functions between tree ring‐widths and monthly climatic data. Data from 11 meteorological stations were combined to provide a regional analysis of precipitation and minimum and maximum temperatures. The two dendro‐ecological methods appear to be complementary, as the first technique emphasizes common and low intensity linear correlations between ring‐widths and climatic variations, and the second method emphasizes extreme and unusual climatic events such as exceptionally cold or dry years.Across all sites, drought in the previous year was consistently correlated with a low growth rate; however, other climatic variables varied substantially among sites. For example, drought in the current year reduced growth more in the low elevation sites than in the high elevation sites and severe winter frost reduced growth the most in the high altitude sites and the driest site. Moreover, certain growth responses are better correlated with the age of the stands, the canopy closure and the floristic composition of the community than the abiotic factors, emphasizing the value of dendro‐ecological sampling based on phytosociological units.
Effects of soil texture and precipitation on above‐ground net primary productivity and vegetation structure across the Central Grassland region of the United States
Authors: Lane Diana R. , Coffin Debra P. , Lauenroth William K. 
Published: May 2006

Abstract. A potentially important organizing principle in arid and semi‐arid systems is the inverse‐texture hypothesis which predicts that plant communities on coarse‐textured soils should have higher above‐ground net primary productivity (ANPP) than communities on fine‐textured soils; the reverse is predicted to occur in humid regions. Our objectives were: (1) to test predictions from the inverse‐texture hypothesis across a regional precipitation gradient, and (2) to evaluate changes in community composition and basal cover on coarse‐ and fine‐textured soils across this gradient to determine how these structural parameters may affect ANPP. Sites were located along a precipitation gradient through the Central Grassland region of the United States: mean annual precipitation ranges from 311 mm/y to 711 mm/y, whereas mean annual temperature ranges from 9 °C to 11 °C.For both coarse‐ and fine‐textured sites in 1993 and 1994, August ‐ July precipitation in the year of the study explained greater than 92% of the variability in ANPP. Soil texture did not explain a significant proportion of the variability in ANPP. However, soil texture did affect the proportion of ANPP contributed by different functional types. Forbs and shrubs made up a larger proportion of total ANPP on coarse‐ compared to fine‐textured sites. Shrubs contributed more to ANPP at the drier end of the gradient. Basal cover of live vegetation was not significantly related to precipitation and was similar for both soil textures. Our results revealed that across a regional precipitation gradient, soil texture may play a larger role in determining community composition than in determining total ANPP.
Shrub facilitation of Quercus humilis regeneration in succession on calcareous grasslands
Authors: Rousset Olivier , Lepart Jacques 
Published: May 2006

Abstract. In southern France, the natural invasion by Quercus humilis of calcareous grassland takes place in a mosaic of herbaceous and scrubby patches. We hypothesized that the presence of the shrubs Buxus sempervirens and Juniperus communis alter the rate and the pathway of the succession by facilitating the regeneration of Q. humilis. To infer the process of facilitation at a large scale, the spatial distribution of Q. humilis was studied in relation to acorn sources and the type of plant cover in grazed and ungrazed sites.Abundant recruitment up to 80 m from the wood margins and from isolated oak trees in grassland shows that acorns are dispersed effectively. At the three study sites, the density of Q. humilis individuals was higher under shrubs than in grassland, suggesting that facilitation may occur. This density difference was much higher in the grazed sites than in the ungrazed site. Moreover, before grazing by livestock, the distribution of first‐year seedlings is independent of vegetation cover. Thus, shrubs improve Q. humilis regeneration by protecting individuals from grazing. The high density of individuals at the northern edge of shrubs suggests that a second facilitation mechanism may exist, probably related to improved germination conditions. Facilitation by shrubs appears to be very important for Q. humilis dynamics.