Effect of light on germination of seven species of cacti from the Zapotitlán Valley in Puebla, México

Seed germination of seven species of cacti from Zapotitlán Valley, Puebla, Mexico, were compared at four different light treatments (red light, far-red light, white light and darkness) at a constant temperature of 25°C, and at two light treatments (white light and darkness) at two fluctuating temperatures (15–30°C and 20–30°C). Results allowed us to divide the studied species into two groups: positive photoblastic and indifferent to light. Positive photoblastics were barrel cacti and indifferent to light species were columnar cacti. Although barrel cacti had a light requirement for germination, they germinated in far-red light. Probable relationships among life-form, species distribution and light requirements for germination are discussed.     

Factors affecting the distribution, abundance and seedling survival of Mammillaria gaumeri , an endemic cactus of coastal Yucatán, México

The population status of an endemic cactus (Mammillaria gaumeri) was assessed in coastal Yucatán, México. Similar numbers of mature plants were found in open and full sun microhabitats. Plants in full sun had more ramets and were of larger diameter. There was a correlation between M. gaumeri abundance and the biomass of a disturbance indicator, Myrmecophila tibicinis (Orchidacea). Higher seedling survival in shade microhabitats and aggregated distribution of adults suggests that shrubs serve as nurse plants. Initial mortality rates of seedlings were many times higher in full sun microhabitats than in shade conditions. Herbivory had no effect on seedling survival.     

Temporal variability in the maternal environment and its effect on seed size and seed quality in Flourensia cernua DC. (Asteraceae).

The biological phenomenon commonly referred to as maternal effect occurs whenever the environment exerts an influence upon the mother that is later expressed in characteristics of her offsprings. For example, the environmental conditions experienced by a mother plant during flowering and fruiting can modify the quality of her descendants (seeds), and even interrupt their development. Between-year variation in minimum temperature and the classic, between-year variation in precipitation represent an unpredictable environment for winter blooming plants in arid zones. In this study, we investigated the effect of maternal environment (temperature and precipitation) on seed size and seed quality in F. cernua, over a 5-year period. Results indicated that the proportion of filled seeds, as well as their size, increased with higher absolute minimum temperatures during seed formation, and that, to a lesser extent, both the precipitation occurred during the same period and the annual precipitation also have a positive influence on seed size. In this way, environmental conditions prevailing during seed formation exerted a strong maternal effect on the size and quality of seeds produced and, probably also, in the developmental possibilities of F. cernua seedlings. This effect was subject to important, between-year variation.     

Beach–dune interactions on the dry–temperate Danube delta coast

Beach–dune seasonal elevation changes, aeolian sand transport measurements, bathymetric surveys and shoreline evolution assessments were used to investigate annual and seasonal patterns of dune development on Sfântu Gheorghe beach, the Danube delta coast, from 1997 to 2004. Dune volume increased consistently (1.96 m³ m^− 1 y^− 1 to 5.1 m³ m^− 1 y^− 1) over this 7-year period with higher rates in the southward (downdrift) direction. Dune aggradation is periodically limited by storms, each of which marks a new evolutionary phase of the beach–dune system. As a consequence of the variable beach morphology and vegetation density during a year, foredune growth occurs during the April–December interval while between December and April a slightly erosive tendency is present. The pattern of erosion and deposition shown by the topographical surveys is in good agreement with the sand transport measurements and demonstrates the presence of a vigorous sand flux over the foredunes which is 20–50% smaller than on the beach. This high sand flux, due to low precipitation and sparse vegetation cover, creates an aerodynamically efficient morphology on the seaward dune slope. The seaward dune face accretes during low to medium onshore winds (5.5–12 m s^− 1) and erodes during high winds (> 12 m s^− 1).     

Soil–vegetation relationships in a coastal desert plain of southern Sinai, Egypt

The present study provides an analysis of soil, vegetation types as well as structure and species distribution in 19 sites in El-Qaa plain along the Gulf of Suez (south Sinai, Egypt), and focuses on the environmental factors that control the species distribution. A total of 203 species belonging to 39 families of the vascular plants are recorded. Asteraceae, Fabaceae, Chenopodiaceae and Poaceae are the largest families. Grasses constitute only 9% of the recorded species, while the woody perennials (shrubs and sub-shrubs) are highly dominated (46%). Therophytes and chamaephytes are the most frequent, denoting a typical desert life-form spectrum. Floristic composition in the different geomorphologic landscape units showed differences in species richness. The highest mean species richness of 19.7±1.7 is recorded in the wadi channels. The lowest species richness values are recorded in the coastal shore and playas (6.0±1.4) and in the alluvial fans (mean of 8.4±1.6 species). Chorological analysis revealed that 46% of the studied species are uniregional, being native to the Saharo-Arabian region. On the other hand, about 50% of the recorded species are biregional and pluriregional, extending their distribution all over the Saharo-Arabian, Sudano-Zambezian, Irano-Turanian and Mediterranean regions. Classification of the vegetation is analysed using two-way indicator species analysis (TWINSPAN) techniques resulted in the recognition of five vegetation groups, each of definite vegetation and soil characters, and could be linked to a specific geomorphologic unit. Capparis spinosa var. spinosa occupied the terraces, Cornulaca monacantha, Convolvulus lanatus and Deverra tortuosa inhabited the alluvial plains, Launaea nudicaulis and Artemisia judaica characterized the wadi channels, Acacia tortilis subsp. raddiana and Leptadenia pyrotechnica characterized the alluvial fans and Tamarix nilotica, Zygophyllum album and Nitraria retusa on the playas and the coastal shore. Ordination techniques as detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) are used to examine the relationship between the vegetation and studied soil parameters. Nine soil variables are included: electrical conductivity, pH, calcium carbonate, gypsum, organic matter, gravel, fine soil fractions and soil saturation percentage. Analysis with DCA gave results similar to CCA, suggesting that there is a relatively high correspondence between vegetation and soil factors. DCA axis 1 showed significant positive correlation with CaCO₃, pH, soil saturation and organic matter, and interpreted as a calcium carbonate—soil saturation gradient. DCA axis 2 showed significant correlation with pH, gypsum and electric conductivity, and interpreted as an electric conductivity—gypsum gradient. Application of CCA indicated that soil surface sediment, CaCO₃, soil saturation, pH and organic matter are the main operating edaphic gradients in the area. These gradients are related closely to the first three canonical axes, and accounted for 67% of the species–environment relationship among the sites.     

Clay slides in the Målselv valley, northern Norway: Characteristics, occurrence, and triggering mechanisms

The distribution of a large number of clay slides in the Målselv valley, northern Norway, is analysed and put into context with the stratigraphic organization of the valley-fill sediments. About 32% of the landslides larger than 10⁴ m³ occur close to the valley margins, where mud is either exposed or at shallow depth. About 57% of the landslides occur mid-valley, where relatively thin (< 15 m) coarse-grained deltaic sediments overlay fine-grained marine and glaciomarine sediments, and about 11% of the landslides occur in front of ice-contact deposits. The slide-prone areas are all characterized by the occurrence of heterogeneous sediments (interbedded clay, silt and sand), in addition to the presence of steep slopes eroded by rivers. The heterogeneous nature of the sediments probably enhanced groundwater drainage and leaching of salts from the clay, increasing sensitivity. Thus, the distribution and organization of the valley-fill sediments and groundwater drainage probably controlled the position of the slide scars and sliding planes. Since deglaciation of the valley (11,500 BP–present), isostatic rebound has enhanced fluvial incision and the creation of steep slopes due to a fall in relative sea level of up to 80 m.Arcuate-shaped, ‘bottleneck’ landslide scars ranging from c. 10⁴ to 10⁷ m³ in size is the dominant morphological signature of the slides, typical for quick clay slides or earth flows involving fluid mud. Their most common triggering mechanism is probably erosion at the toe slopes by the river Målselv or its tributaries. River erosion close to the valley margin, where glaciomarine and marine sediments are present, seems to give the most severe slides. The overall valley-fill organization controls the distribution of clay slides, which may apply to other fjord valleys having similar sediment distribution.     

Effect of plant species on shrub fertile island at an oasis–desert ecotone in the South Junggar Basin, China

Shrub fertile islands are a common feature in arid ecosystems. To examine the effect of plant species on the spatial patterns of soil chemical and physical properties surrounding individual shrubs, two deciduous shrub species with different morphologies (Tamarix spp. and Haloxylon ammodendron Bge.) were studied at an oasis–desert ecotone in South Junggar Basin. Soil samples were collected under the shrub crown (canopy), at the vertically projected limit of shrub crown margin (periphery), and in the space between shrub crowns (interspace) at two depths, 0–10 and 10–20 cm, to analyze their physical and chemical properties. The results show that the fertile islands of Tamarix spp. are enriched with more soil nutrients (significantly higher, P<0.05; soil organic matter (SOM); total nitrogen (TN) and available nitrogen (AN); to a deeper depth (>20 cm) and in a larger area (beyond the canopied area) compared to that of H. ammodendron (significantly higher, P<0.05, soil nutrients detected only for AN; <20 cm in depth; smaller than the canopied area). Soil texture patterns surrounding the shrubs of the two species are even more different, with more coarse particles under the Tamarix spp. canopies compared to the interspace between shrubs but fewer under the H. ammodendron canopies compared to the interspaces. These variations are attributed to the difference in morphology of the two studied species: the Y-shaped crowns of H. ammodendron are less capable of capturing and maintaining litter under them than the hemispheroidal crowns of Tamarix spp., which leads to the less well developed fertile islands surrounding H. ammodendron shrubs.     

Variations in some physico-chemical parameters in a hypersaline coastal lagoon of Baja California,Mexico

San Jose lagoon is a hypersaline body of water located in Mexico in the Baja California Peninsula. The lagoon belongs to a system that lies between the fault ridge known as San Jose Creek. Because of its marine origin, it can be considered as thalassohaline, but its isolation from the ocean has brought about changes in its salt composition. It has an area of 13,500 m², a mean depth of 80 cm and a total volume of 10,000 m³. It does not desiccate and can be considered as a permanent lagoon. Seasonal variations are small. TheArtemia population in San Jose produces cysts all year. To determine the physico-chemical conditions inducing permanent production of cysts, temperature, salinity, dissolved oxygen, and pH of the lagoon were monitored, as well as relative humidity and wind conditions in the region in different seasons of the year. From spring to summer, differences of 1 mg L^–1 of O₂, 1°C in water temperature, and 8 g L^–1 in salinity were observed, and from summer to winter differences of 3.3 mg L^–1, 6.5°C, and 14 g L^–1, respectively. Despite small seasonal variations, the lagoon exhibits strong spatial and daily changes that are important for cyst production.     

Status of an endangered subspecies: the peninsular pronghorn at Baja California

During November 1993, we traversed by ground and by air the Vizcaíno Desert, the last redoubt of the peninsular pronghorn (Antilocapra americana peninsularis). A total of 29 h of aerial census was performed and a total of 1900 km²were covered by ground, totalling 400 man hours of survey. At present the peninsular pronghorn population consists of 175 individuals, and inhabits an area of approximately 5000 km². Because of the impossibility of controlling its activities over such an area and because of the present small population size, we propose to manage part of the population in semi-captivity at Mesa de la Choya island, with the objective of assuring the survival of this subspecies, the most endangered mammal in Mexico.     

Local- and watershed-scale controls on the spatial variability of natural levee deposits in a large fine-grained floodplain: Lower Pánuco Basin, Mexico

This study examines spatial variations in natural levee deposits within the lower reaches of a large coastal plain drainage system. The Pánuco basin (98,227 km²) drains east-central Mexico, and is an excellent setting to examine the influence of watershed and local controls on the morphology and sedimentology of natural levees. Although many fluvial systems in the U.S. Gulf Coastal Plain have been investigated, the rivers in the Mexican Gulf Coastal Plain have received comparatively little attention. Lateral and downstream characteristics of natural levee morphology and sediment texture are considered within the context of meandering river floodplain deposits. Data sources include total-stations surveying, sediment samples of surficial levee deposits, topographic maps (1:50,000), and aerial photographs (1:40,000). The slope of natural levees average 0.0049 m/m, whereas the texture (D₈₄) of levee deposits averages 0.12 mm. Natural levee characteristics vary due to local- and watershed-scale controls. The lateral reduction in levee height displays a curvilinear pattern that coincides with an abrupt change in sediment texture. The downstream pattern of natural levee texture exhibits the influence of local-scale perturbations superimposed upon a larger watershed-scale trend. Disruption to the fining trend, either by tributary inputs of sediment or reworking of Tertiary valley deposits, is retained for a limited distance. The influence of the channel planform geometry on levee morphology is examined by consideration of the radius of curvature (R_c) of meander bends, and is inversely related to natural levee width. This suggests that the planform geometry of river channels exerts a control on the dispersal of flood sediments, and is responsible for considerable local variability in the floodplain topography. The average width of natural levees increases with drainage area, from an average of 747 m in the Moctezuma to an average of 894 m in the Pánuco. However, in the lower reaches of the Pánuco valley the width of natural levees rapidly decreases, which is associated with fining of the suspended sediment load. Thus, the reduction in natural levee width signifies an abrupt change in the directionality of cause–effect relationships at the watershed-scale. Findings from this study elucidate linkages between meandering river channels and floodplains for a large lowland alluvial valley.     

Landscape evolution and origin of Lake Fúquene (Colombia): Tectonics, erosion and sedimentation processes during the Pleistocene

The Basin of Ubaté–Chichinquirá (5°28′N, 73°45′ W, c. 2580 m altitude) includes the Fúquene Valley and is located in the central part of the Eastern Cordillera of Colombia. Rocks and sediments were folded and faulted during the Miocene, uplifted during the (late) Pliocene, and affected by glaciers during the Pleistocene. Successive glacial and interglacial periods left significant marks in the landscape which were used to reconstruct six stages in the development of the landscape along a relative chronology. During early Pleistocene episode 1 glaciers formed U-shape valleys. Evidence of the impact of ice sheets has been found as far downslope as ca. 2900 m elevation. During episode 2 moraines developed which were cut by the present San José River. During episode 3 abundant sediment was produced by glacial erosion. It accentuated the sculpturing of hard rock and deepening of the drainage basin. The ancestral Ubaté–Suarez River constituted a dynamic erosive system that gave rise to deep V-shaped valleys and progressively formed a set of intricate valleys with a high sediment production. Finally, intense glacial and fluvio-glacial erosion led to a geomorphological system with high energy levels and intensive sediment transport leading to wide valleys. During episode 4 the Ubaté–Suarez River eroded and deepened its valley until it captured the old El Hato–San José Valley. It caused intense erosion of the moraine and the fluvio-glacial gravels. Deep V-shaped valleys stabilized in the high areas of the main drainage system and these valleys form the present-day fluvial sub-basins. During episode 5 the deep valley in the northern part of the Basin of Ubaté–Chichinquirá developed. During middle Pleistocene episode 6 colluvial sediments formed the Saboya dam and a lake was formed in the river valley of which the present Lake Fúquene is only a small remnant. Lithological changes indicate fluctuating water levels and Lake Fúquene must have expanded periodically up to an area 5 to 10 times the present-day surface.     

Late Holocene development of a floodplain along a small meandering stream, northern Québec, Canada

This paper describes the activity of a small meandering stream and the development of its floodplain during the last 4600 years (calendar years BP) in the northern boreal zone of Québec. Three trenches were excavated across the floodplain's full width and permitted the interpretation of morphosedimentary units in relation to modern analogs. Chronological controls within trenches was provided by the dendrochronological and radiocarbon dating of buried tree trunks. From 4600 to 2900 cal. BP and from 1000 to 120 cal. BP, the channel migrated and constructed its floodplain at very slow rates, mostly because of low flow velocities, vegetated streambanks and the cohesive texture of marine sediments reworked by the channel. Vertical accretion rates were extremely variable on the floodplain, with high rates proximal to the modern channel and low rates over distal (also older) portions of the floodplain. Following a major channel shift (meander cut-off or avulsion) around 2900 cal. BP, channel migration appears to have been constrained to a narrow zone adjacent to the modern channel. Within this constrained zone, the migrating channel has reworked its own sediments leading to a marked unconformity between 2900–1000 cal. BP. It is thought that underlying marine sediments protrusions, and perhaps the forested banks, protected older alluvial sediments from being eroded during the last three millenniums. Our study shows that small boreal floodplains may contain, in a very small area, abundant and diversified archives of their evolution.     

Vulnerability to environmental hazards in the Ciudad Juárez (Mexico)–El Paso (USA) metropolis: A model for spatial risk assessment in transnational context

The purpose of this paper is to present a geographic information system (GIS)-based method for mapping risk to environmental hazards. Framed by the hazards literature, the method has been developed to specifically overcome issues of data compatibility associated with transnational contexts. The approach is elaborated in reference to a project in which risk was spatially characterized, using a suite of biophysical and social indicators, for the Ciudad Juárez (Mexico)–El Paso (USA) metropolis. Results reveal clear spatial disparities in hazard vulnerability, both within and between the two cities, based on the differential allocation of selected risk factors. The case indicates that future international analyses will be advanced by the clear definition of concepts, the systematic mining of compatible variables, and the selection of valid risk indicators based on criteria that balance the need to incorporate contextual specificity with general comparability.     

Primary production and decomposition in the coastal zone of the northern part of the Aral Sea near the delta of the Syr Dar'ya

Data are given on the concentration of suspended organic carbon and chlorophylla in seston, the quantity of organic carbon in bottom sediments, and other environmental characteristics. The results of experiments determining daily quantitites of total and net primary production and aerobic decomposition in plantonic and bottom communities are discussed.     

Soil physico-chemical properties affecting the distribution of biological soil crusts along an environmental transect at Zapotitlán drylands, Mexico

The composition of cyanobacteria, mosses, and lichens of biological soil crusts were correlated with soil characteristics and sun exposure along an environmental transect. The study was conducted in Zapotitlán drylands, a locality within the Tehuacán–Cuicatlán Valley, central Mexico, where a great variety of environments for crust development exist due to landscape fragmentation. Data were analyzed with redundancy and Sorensen analysis. Soil crusts consisted of different combinations of cyanobacteria (7 species), mosses (19 species), and lichens (8 species). The relative frequencies of these groups were positively correlated with soil apparent density and lichens were also positively correlated with soil pH. However, there were no significant correlations with sun exposure.     

On the river–lake relationship of the middle Yangtze reaches

The geological and meteorological setting of the Jianghan–Dongting lake area leads to high precipitation and siltation, but poor water discharge, thus the area is frequently flooded. In the past the river–lake relationship of the Middle Yangtze has been variable but has deteriorated recently under increasing human influence. The Jianghan Plain of the Middle Yangtze becomes a waterlogged lowland under the constant threat of flooding from the perched Jingjiang River. Due to siltation and land reclamation the Dongting Lake has lost most of its regulatory function for the river and has become increasingly vulnerable to flood disasters. The Middle Yangtze River has been undergoing siltation, resulting from a downstream decline of sediment transport capacity, resulting in the elevation of the flood level above the lowlands. Heightening of the levees has caused further siltation of the channel.The Three Gorges Reservoir will provide a buffering period of 50–80 years, during which much of the silt will be trapped in the reservoir and scouring downstream may occur. We should utilize this period to work out an overall resolution to the problem. Construction of a water and silt diversion project in the Honghu Lake and surrounding areas may resolve this problem in the dangerous Chenglingji–Wuhan Segment of the Yangtze. Widening the canals connecting the Middle Yangtze and Han Rivers may function as a discharge-dividing channel of the Yangtze, which may prove to be beneficial.     

10 Myr evolution of sedimentation rates in a deep marine to non‐marine foreland basin system: Tectonic and sedimentary controls (Eocene,Tremp–Jaca Basin,Southern Pyrenees,NE Spain)

The propagation of the deformation front in foreland systems is typically accompanied by the incorporation of parts of the basin into wedge‐top piggy‐back basins, this process is likely producing considerable changes to sedimentation rates (SR). Here we investigate the spatial‐temporal evolution of SR for the Tremp–Jaca Basin in the Southern Pyrenees during its evolution from a wedge‐top, foreredeep, forebulge configuration to a wedge‐top stage. SR were controlled by a series of tectonic structures that influenced subsidence distribution and modified the sediment dispersal patterns. We compare the decompacted SR calculated from 12 magnetostratigraphic sections located throughout the Tremp–Jaca Basin represent the full range of depositional environment and times. While the derived long‐term SR range between 9.0 and 84.5 cm/kyr, compiled data at the scale of magnetozones (0.1–2.5 Myr) yield SR that range from 3.0 to 170 cm/kyr. From this analysis, three main types of depocenter are recognized: a regional depocenter in the foredeep depozone; depocenters related to both regional subsidence and salt tectonics in the wedge‐top depozone; and a depocenter related to clastic shelf building showing transgressive and regressive trends with graded and non‐graded episodes. From the evolution of SR we distinguish two stages. The Lutetian Stage (from 49.1–41.2 Ma) portrays a compartmentalized basin characterized by variable SR in dominantly underfilled accommodation areas. The markedly different advance of the deformation front between the Central and Western Pyrenees resulted in a complex distribution of the foreland depozones during this stage. The Bartonian–Priabonian Stage (41.2–36.9 Ma) represents the integration of the whole basin into the wedge‐top, showing a generalized reduction of SR in a mostly overfilled relatively uniform basin. The stacking of basement units in the hinterland during the whole period produced unusually high SR in the wedge‐top depozone.     

Late Cenozoic uplift of the Amanos Mountains and incision of the Middle Ceyhan river gorge, southern Turkey; Ar–Ar dating of the Düziçi basalt

Using the Ar–Ar technique, we have obtained the first numerical dates for the Pleistocene volcanism along the valley of the River Ceyhan in the Düziçi area of southern Turkey, in the western foothills of the Amanos Mountains. Our six dates indicate a single abrupt episode of volcanism at  270 ka. We have identified a staircase of 7 fluvial terraces, at altitudes of up to  230 m above the present level of the Ceyhan. Using the disposition of the basalt as an age constraint, we assign these terraces to cold-climate stages between marine oxygen isotope stages 16 and 2, indicating rates of fluvial incision, equated to surface uplift, that increase upstream through the western foothills of this mountain range at between 0.25 and 0.4 mm a^− 1. Extrapolation of these uplift rates into the axis of the range suggests that the entire  2300 m of present-day relief has developed since the Mid-Pliocene, a view that we confirm using numerical modelling. Since  3.7 Ma the Amanos Mountains have formed a transpressive stepover along the northern part of the Dead Sea Fault Zone, where crustal shortening is required by the geometry. Using a physics-based technique, we have modelled the overall isostatic response to the combination of processes occurring, including crustal thickening caused by the shortening, erosion caused by orographic precipitation, and the resulting outward flow of mobile lower-crustal material, in order to predict the resulting history of surface uplift. This modelling suggests that the effective viscosity of the lower crust in this region is in the range  1–2 × 10¹⁹ Pa s, consistent with a Moho temperature of  590 ± 10 °C, the latter value being in agreement with heat flow data. This modelling shows that the nature of the active crustal deformation is now understood, to first order at least, in this key locality within the boundary zone between the African and Arabian plates, the structure and geomorphology of which have been fundamentally misunderstood in the past.     

Development and setting of the Alcudia Bay beach–dune system (Mallorca, Spain)

The beach–dune system of Alcudia Bay is located in the north of the island of Mallorca. The system includes both simple and compound parabolic dunes formed by N to NNE winds and is made up of two dune areas with different dynamics: 1) the northern area, where, despite the fact that the source of beach sediment is from the south, dunes are formed by northerly winds and develop a narrow and linear barrier which separates a marsh from the bay; and 2) the southern area, where complex parabolic dunes formed by north-northeasterly winds, prograde south-southwest landward extending several kilometers inland. The broad pattern of the dunefield size is limited to the southeast by a mountain range and to the west by the effects of a topographic corridor, oriented north–south, which channels the prevailing northerly wind, causing a southward dune progression and limiting the westward extension of the dunefield.