Continental Gradient Research Articles

Distribution and habitat niches of 37 peatland Cyperaceae species across a broad geographic range in Canada

The presence and absence of 37 Cyperaceae species found on 498 peatlands across Canada were examined along surface water chemistry, shade, height above the water table, and climatic gradients. A canonical correspondence analysis of the species distribution along the environmental gradients indicated that surface water chemistry and climate were highly correlated with the first and second axes and were the two most important gradients distinguishing among groups. The climatic gradient was further subdivided into western oceanic continental and eastern oceanic continental gradients. Height above the water table and shade were correlated to the third canonical correspondence analysis axis and were of secondary importance in explaining species distributions. A TWINSPAN analysis of the species separated them into eight groups: (1) widespread, obligate rich fen, wet, shade-tolerant species; (2) widespread rich fen preferential species; (3) continental and eastern oceanic, rich fen preferential, wet, shade-intolerant species; (4) widespread fen, wet, shade-intolerant species; (5) widespread bog or fen, shade-tolerant species; (6) widespread subcontinental and oceanic, bog or fen, shade-intolerant species; (7) eastern subcontinental and oceanic, poor fen preferential species; (8) western oceanic, bog and poor fen preferential, shade-intolerant species. Response surfaces were generated by quantifying the frequency of occurrence of representative species in each group along pH and height above the water table, shade and mean annual temperature, and mean annual total precipitation gradients. Frequency of occurrence values for several of the rarer species indicated that they were not limited by the number of suitable habitats analyzed in this study but by other factors such as competition, failure to establish, or dispersal. This study emphasizes the importance of habitat and climate in determining the local and regional diversity and distribution of the most common Cyperaceae on peatlands in Canada.Key words: sedges, Carex, peat lands, response surfaces, climate, water chemistry.

A Global Dynamic Model for the Neolithic Transition

During the Holocene strong gradients in the distribution of technologyincluding subsistence ways emerged on a global scale.These patterns were further amplified in historic times and are stillvisible through worldwide differences in national wealth.In order to evaluate major factors responsible for the shift fromforaging to food production we here employ quantitative methods bydeveloping a deterministic but simple model. After compiling existing maps of potential vegetation at 5000 BP theinhabited world is split into 197 regions with homogeneous environmentalconditions. Suitable variables for the macro-economic and culturaldevelopment in the Neolithic period are found to be farming to hunting-gatheringratio, number of agricultural economies and a technological development index.The model explicitly describes economic adaptation, growth and migrationof human populations together with the spread of their cultural characteristics; it accounts for over-exploitation of natural resources, crowdingmortality and the climate variability on a millennium scale.In a thorough model validation region specific trajectories are compared toarchaeological evidence revealing a high correspondence. Major parts of the knownsequence of Neolithic centers including the timing differences are robustlyreproduced. A series of known problems in prehistory is discussedcomprising the lag between domestication and full scale farming, the off-levelingof the technological boost following the transition, the emergence ofdistinct migration waves and sensitivity to climate fluctuations.Not mere population pressure but continuous innovation and competition betweensubsistence strategies is identified as a prime mover of agricultural development.The results suggest that few aspects of biogeography may have determined theobserved continental gradients in the number of domesticable species ultimatelyleading to an increasing differentiation in technology and demography.

Флористическое районирование и синтаксономия

The advantages of using floristic subdivision of the area for syntaxonomic purposes are discussed. The analysis of changes in floristic composition of East-European broad-leaved forest communities along the West-East continentality gradient shows that floristic differences between the adjacent provinces correspond to changes in species composition at the association or the alliance level. A new association, Lathyro nigri—Quercetum roburis (all. Aceri tatarici—Quercion Zolyomi 1957, order Quercetalia pubescenti-petraeae Klika 1933), is established for the Southern Non-Chernozem region of European Russia.

Phytogeographical relationships among high mountain areas in the Baetic Ranges (South Spain)

ABSTRACTThe Mediterranean area is regarded nowadays as one of the hot‐spots of world biodiversity. The Baetic ranges in Spain have such a large number of endemic plant taxa that the territory has been recognized as a well‐defined biogeographical unit. These endemic taxa tend to concentrate on disjunct highland areas that have been described consequently as ‘highland islands’. Despite the importance and complexity of these sites, the research carried out so far has produced only descriptive classifications. These approaches overlook the relationships between the sites and do not serve to identify the main centres of endemism. Herein, multivariate analysis techniques (cluster analysis and reciprocal averaging) and the parsimony analysis of endemicity (PAE), applied to the 222 orophilous endemic taxa of the Baetic ranges, have been used to reveal the floristic similarities between the areas involved, to identify the centres of endemism and to re‐assess the previous classifications. Four centres of endemism are defined, one siliceous and three calcareous. The most outstanding feature in the Baetic ranges is precisely the floristic difference between siliceous and calcareous mountains. Calcareous territories extend along a SW–NE axis in line with the oceanic–continental gradient. The nature of the soil in the vast siliceous and calcareous–dolomitic territories of the Sierra Nevada is probably the cause of the remarkable floristic diversity. Not surprisingly, in our analysis these areas stand out as centres of endemism. We conclude that previous biogeographical classifications of the ranges are too rigid and do not properly reflect the floristic similarities of the area under study.

Bird conservation in fragmented Mediterranean forests of Spain: effects of geographical location, habitat and landscape degradation

The effects of habitat fragmentation on forest bird assemblages were analysed in 214 holm oak ( Quercus ilex) remnants spread across the northern and southern plateaux of central Spain. Bird richness was highly dependent on fragment area for all species regardless of isolation, and barely affected by habitat traits. Geographical location was associated with high differences in richness of bird assemblages, which included 17 species exclusive to northern remnants and one exclusive to southern remnants. This supports the hypothesis that habitat suitability deteriorates sharply from north to south for forest birds in Spain. The species-area relationships of bird assemblages sampled in fragmented forests along a broad continental gradient (from Norway to southern Spain) showed that true forest birds only nest in woodlands >100 ha in southern Spain, whereas the full complement of forest species occurs in much smaller fragments in central-western Europe. Loss of species that are particularly sensitive to habitat fragmentation accounts for these differences between dry Spanish and mesic European woodlands. These results are explained by the low habitat suitability of Spanish woodlands, associated with the restrictive conditions for plant regeneration in the Mediterranean climate and long-standing human usage. There is, therefore, a particular need to develop management strategies that conserve birds, and probably other forest organisms, in Mediterranean regions by preventing habitat deterioration and decreases in fragment size, and by conserving all woods >100 ha.

Typology and ecology of Californian serpentine annual grasslands

Abstract. A first classification for serpentine annual grasslands distributed throughout northern and central California is proposed. This study has followed the Braun‐Blanquet phyto‐sociological system based on floristical, biogeographical and bioclimatic features of the sampled areas. Numerical analyses of classification and ordination were applied to the floristic relevés. Minimum Variance Clustering grouped relevés into basic classification units that allowed us to define low‐hierarchical syntaxonomical units (associations) and ‘communities’. A Principal Coordinate Analysis was used to extract those ecological parameters related to the axes that separate those classification units from the previous dendrogram. The results showed that differences in species composition was mainly due to a continentality gradient and the shady effect of an overstory vegetation. On the basis of both analyses we propose a first syntaxonomic scheme on ultramafic (mainly serpentine) annual plant communities of the biogeographical Californian Region that comprises four associations, two subassociations and some provisional communities.

Transect Studies of Pine Forests Along Parallel 52°N, 12–32°E and Along a Pollution Gradient in Central Europe: General Assumptions, Climatic Conditions and Pollution Deposition

This research program describes the response of pine forest to changing climate and environmental chemistry. All 15 selected pine forest stands belong to the Dicrano–Pinion alliance and include two associations of pine forest: sub-continental pine forest Peucedano–Pinetum and sub-oceanic pine forest Leucobryo-Pinetum, as well as mixed forest of the Querco–Pinetum type. This program consists of two transects following pollution and continentality gradients across Poland: one from the western border to the eastern border (in the area of Bialowieza National Park) along the 52nd parallel, and the second from industrial Upper Silesia (SW Poland) to the same point in the Bialowieza area. We assumed that the first west-to-east transect of sites followed a gradient of cooling and continentality. The western–eastern site difference in mean annual temperature averages is 1.8°C (from 8.5 to 6.7°C); average differences between July and January for most western sites are 18.8°C and for the eastern site is 22.3°C. Extension of the continental transect to the west (Germany) and the east (Belarus) became possible two years after the program had been initiated. This so-called ‘large transect’ spans 20° (from 12°25′ to 32°60′E) of latitude, with a difference in mean annual temperature of 3.5°C (from 5 to 8.5°). The second transect was established along a decreasing pollution gradient of sulphur deposition. The content of sulphur in Scots pine needles varied between 0.17% dry mass in Upper Silesa to 0.12% in Bialowieza National Park. In each forest stand climatic elements (temperature and precipitation), the rate of radial growth of pine trees, diversity of plant species and forms, some measures of biomass, organic matter turnover measured by litter fall and decomposition, and diversity of selected groups of epigeic and soil fauna (invertebrates) were measured. Detailed descriptions of important measurements will be presented in two subsequent papers included in this volume.

Application of a forest succession model to a continentality gradient through Central Europe

The forest succession model FORSKA was applied to a west-east transect across Central Europe using points from a global climate data set. Climate change experiments were undertaken for two general circulation model scenarios and two different site classes. The simulated climate changes lead to reduced forest productivity and a changed species composition on most sites. Under current climate, the broad scale pattern of the climatically driven distribution of forest communities is quite realistically reproduced. However, the resolution of climate data imposes limitations on the simulation of forest dynamics in subcontinental climate, because climate variability and extreme events are not well represented.

P-wave velocities of main upper mantle minerals at high temperature and high pressure and its geological implication

At 0 - 5.0GPa and room temperature to 1400℃, the P-wave velocities of olivine, clinopyroxene and orthopyroxene, which are three common minerals from upper mantle, are measured under both simulated oceanic and continental geothermal gradients. The experimental results indicate that the P-wave velocities of these minerals increase with depth under both geothermal gradients. This implicates that pressure is more important than temperature in deep earth in controlling the P-wave velocities of mantle minerals, but the increase of temperature has greater effect on P-wave velocities of main mantle minerals at greater depth than at smaller depth. At low pressure, the measured P-wave velocities of mantle minerals are smaller than their true values due to fracturing, compaction process and recrystallization of mineral powder. The true P-wave velocities of mantle minerals can be obtained at lower pressure by the extrapolation of measured velocities at a high pressure. At higher depth, all these three minerals show local decreases of velocities at their Vp-D curves, which may be related to phase transformation, softening effect and melting effect of minerals. The depth range of the local velocity decreases of these minerals is nearly consistent with that of low velocity zone (LVZ) in North China and can explain the origin of LVZ in this area.

Eocene continental climates and latitudinal temperature gradients: Comment and Reply

Eocene continental climates and latitudinal temperature gradients: Comment and Reply

古気候変動史から見た現在

The history of global climate on the earth during these 600 million years is presented based on the oxygen isotope data of fossil shells. The paleoclimatic curves clearly show the cyclic changes with different frequencies, such as, glacial-interglacial cycle of 0.1 Ma and Fischer-Arthur cycle of 32 Ma, and Greenhouse-icehouse cycle of 300 Ma. Today is located in the interglacial period of icehouse state. There are essential differences of the environmental systems and conditions between the greenhouse and icehouse states. The greenhouse state characterized by no continental ice sheets, simple climatic zones, more carbon dioxide in atmosphere, small annual temperature range, warmish and humid poles, high sea level, wide continental shelves, low latitudinal and vertical gradients of seawater temperature, warm oceans, slow circulation of bottom currents, anoxic oceans, abundant marine organisms, black shale deposition of oil raw material, sulfide deposits on oceanic ridges, manganese deposits on continental shelves, active magmatism, first spreading, magnetic quiet and active orogeny. A modern greenhouse warming was also compared with the warming after the “Younger Dryas Event” in the postglacial age.

Modelling Distributional Patterns of Woodland Birds along a Continental Gradient

There are several ways to approach the question of how distributions of species are determined, including field experimentation and computer or mathematical modelling. If large numbers of species are to be considered simultaneously, modelling is the most practicable method. The current paper examines the relative capacities of a set of models to account for patterns of distributions of 92 species of forest and woodland birds along a 250—km transect in southeastern Australia. Multivariate analyses of habitat ordinations (nonmetric, multidimensional scaling: NMDS) were used to characterize the habitat breadth and habitat position of each of the avian species. Breadth is the range of structural types of habitat that a species occupies. Position is a measure of the “representativeness” of the typical habitat type occupied by a species relative to the entire sample of habitat types. There was a significant inverse correlation between breadth and position (r = —0.70). The models were used to try to account for this inverse relationship and related statistics, including the amount of co—occurrence between species. Three models based on the geographic proximity of sites provided reasonable representations of the observed patterns, except for co—occurrence, which all models consistently underestimated. Several more complicated techniques were used to try to increase the explanatory power of the models, but only one of these methods provided a justifiable improvement. The modelling demonstrated that many of the distributional patterns observed for this avifauna could be accounted for by using simple site—selection algorithms, and by assuming that species behaved independently. The major source of variation unaccounted for by the models was a consistent underestimation of levels of co—occurrence between avian species, which may mean that further modelling may require interdependence rather than independence of species.

Geographic Variation of Flowering Phenology in Twenty-six Common Shrubs in SW Spain.

Summary The relationships between flowering phenology and both altitude and continentality are studied for 26 wellrepresented taxa in southwestern Spanish shrublands. For most species, flowering date is delayed when altitude increases, but at different rate in each species. However, flowering length is not reduced in the higher altitudes. The continentality gradient is less important than the altitude explaining changes in flowering phenology. Nevertheless, for a few species there is no correlation between phenology and altitude or continentality. The flowering behaviour of species groups is discussed with regard to different reproductive strategies and the environmental features of the study sites.

The Relationship between Habitat Breadth, Habitat Position, and Abundance in Forest and Woodland Birds along a Continental Gradient

Multivariate analyses of habitat ordinations (nonmetric, multidimensional scaling) were used to characterise the habitat breadth ([) and habitat position (y) of 92 species of forest and woodland birds along a 250 km transect in south-eastern Australia. Abundances were estimated on the basis of excluding zero-density sites (viz, absence), leading to the notion of average density at sites at which a species occurs. There was a significant inverse correlation between 5 and y. This result, when used in conjunction with the distributions of P and y, proved incompatible with existing models of habitat occupancy patterns. The correlation between ,3 and average density, and between y and average density, each was approximately zero, results that differed from the findings of other studies at the range-level geographic scale. These differences are interpreted in light of the insensitivity of range-based studies, which do not explicitly account for habitat structure, to the geographic distributions of preferred habitat types of individual species of animals.

Articles Deuterium and Oxygen-18 in Central European Groundwaters

A general view of deutrium and oxygen-18 content found in modern groundwaters in Central Europe is presented. Both nuclides show a characteristic continental gradient of depletion in precipitation and modern infiltration waters from west to east and north to south: σD between –5 … –10‰ to –1.5‰per 100 km and –10‰per 100 km, respectively. An additional depletion is given in the mountain belt in dependence on the elevation. Old groundwaters are depleted in deuterium up to 12 ‰ in relation to modern infiltration waters. Such groundwaters are well known from Central Europe and other parts of the world. The use of natural deuterium variations of groundwaters in the GDR is considered in connection with the dry-weather Glow in this region.

Deuterium and oxygen-18 in European groundwaters — Links to atmospheric circulation in the past

A thorough discussion of deuterium and 18O isotope ratios found in modern infiltration waters and in old groundwaters recharged during the final stages of the last glaciation in Western and Central Europe is presented. Old European groundwaters are depleted in deuterium by ∼ 12%. when compared to modern infiltration waters. The continental gradient in deuterium content found in these waters is very similar to that presently observed in infiltration waters and in precipitation. This fact strongly suggests a constant circulation regime of the atmosphere over Europe for the past 35,000 yr. Relative constancy of atmospheric circulation during that time makes a quantitative interpretation of the depletion in heavy-isotope content of glacial waters meaningful in terms of changes in surface air temperature over Europe at the transition from the last ice age to the Holocene climate. The shift in air temperature deduced from the above-mentioned depletion in deuterium content reaches ∼ 7°C. This value is in good agreement with previous estimates based on simulation of the ice age atmosphere and on measurements of noble-gas contents in European groundwaters. The relation between δ D- and δ 18O-values found in old European groundwaters is essentially identical with the well-known relationship δ D = 8δ 18O + 10, which is proved to be valid for modern precipitation and infiltration waters. It means further that deuterium excess in European meteoric waters, defined as d = δ D − 8δ 18 O did not undergo substantial changes for at least 35,000 yr. This fact provides a strong argument in favour of the hypothesis that the increase in relative humidity by ∼ 1090 over the glacial ocean, which is a widely accepted opinion nowadays, was probably not a world-wide phenomenon.

Fennoscandia ? A short outline of its geodynamical development

Based on the strong heat flow in the Archaean and Proterozoic a concept for dynamical processes is developed that agrees with observation of low and high pressure metamorphism in ensialic belt of the Precambrian in Scandinavia and other old shield areas. Heat release is considered to have taken place predominantly at fast spreading oceanic ridges, some of them certainly adjacent to continental margins. Thinner, warmer, lighter, and faster oceanic plates descended with very small dip below the continent, leading to an underplating, to a decrease of the continental thermal gradient, and to a compressive stress with the tendency to keep the growing Archaean supercontinent together. Ensialic belts may have partly been created by a shallow secondary back-arc creep pattern. The general decrease of heat production and heat release continuously slowed all creep processes. At around 1000 ± 300 Ma, oceanic plates must have reached critical values of thickness, weight, and density to perform a real steep angle subduction, reinforced by sediment loads and phase transition at depth. A well developed plate tectonic pattern with an opening and closing of the lapetus ocean, with subduction, and a subsequent continent-continent collision can be inferred for the forming of the Caledonian-Appalachian mountain range. Even today, dynamical movements at asthenospheric levels below Fennoscandia are still present as indicated by observations of seismic travel time residuals, deep seismic soundings, gravity, compressive stresses, and theoretical calculations of temperature and viscosity.

Were Archaean continental geothermal gradients much steeper than today?

Were Archaean continental geothermal gradients much steeper than today?