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Selected AbstractsEnvironmental signals for seed germination reflect habitat adaptations in four temperate CaryophyllaceaeFUNCTIONAL ECOLOGY, Issue 3 2008F. Vandelook Summary 1Requirements for dormancy break and seed germination are specific for all species and depend chiefly on phylogeny, geographical distribution, habitat preference and life cycle. Studying germination requirements of closely related species with a similar geographic distribution allows one to attribute variation in germination requirements to differences in habitat preference between the species. 2We investigated requirements for dormancy break and the effect of environmental signals on induction of germination in seeds of four closely related Caryophyllaceae species growing in a variety of habitats (Moehringia trinervia, Stellaria holostea, S. nemorum and S. graminea). The species studied depend on disturbances in the vegetation for seed germination and subsequent seedling establishment. 3Seedlings of all four species emerged both in summer and spring. Stellaria nemorum and M. trinervia, both growing in temperate forests, emerged mainly in summer under a closed forest canopy. Seeds of S. graminea, occurring in grasslands, did germinate in summer at an open site, but could not germinate under a closed forest canopy. Seedlings of S. holostea were observed in late summer when buried at an open site or in early spring when sown in a forest patch. 4Seeds of S. holostea and M. trinervia were completely dormant at dispersal in early summer, while germination was low in fresh seeds of S. graminea and S. nemorum. Dormancy was broken, to a certain extent, during all three after-ripening treatments applied (dry storage, cold and warm stratification). 5The effect of three gap-detection signals (light, fluctuating temperatures, nitrates) on germination of fresh and dry stored seeds was tested. Seeds of S. holostea only germinated in response to daily fluctuating temperatures. Although light was the most important signal affecting germination of S. graminea and M. trinervia, we also observed a positive effect of fluctuating temperatures and nitrates on germination. The effect of fluctuating temperatures on germination of S. nemorum was small in both light and dark incubated seeds. Seed germination in this species generally occurred in response to addition of light and nitrates. 6This study on dormancy breaking and germination requirements of the four species enabled us to expose, sometimes subtle, differences in germination requirements. These contrasting germination patterns were related to differences in the species' habitat preferences. [source] Seasonal snowpack dynamics and runoff in a cool temperate forest: lysimeter experiment in Niigata, JapanHYDROLOGICAL PROCESSES, Issue 20 2005Andrew C. Whitaker Abstract Seasonal snowpack dynamics are described through field measurements under contrasting canopy conditions for a mountainous catchment in the Japan Sea region. Microclimatic data, snow accumulation, albedo and lysimeter runoff are given through the complete winter season 2002,03 in (1) a mature cedar stand, (2) a larch stand, and (3) a regenerating cedar stand or opening. The accumulation and melt of seasonal snowpack strongly influences streamflow runoff during December to May, including winter baseflow, mid-winter melt, rain on snow, and diurnal peaks driven by radiation melt in spring. Lysimeter runoff at all sites is characterized by constant ground melt of 0·8,1·0 mm day,1. Rapid response to mid-winter melt or rainfall shows that the snowpack remains in a ripe or near-ripe condition throughout the snow-cover season. Hourly and daily lysimeter discharge was greatest during rain on snow (e.g. 7 mm h,1 and 53 mm day,1 on 17 December) with the majority of runoff due to rainfall passing through the snowpack as opposed to snowmelt. For both rain-on-snow and radiation melt events lysimeter discharge was generally greatest at the open site, although there were exceptions such as during interception melt events. During radiation melt instantaneous discharge was up to 4·0 times greater in the opening compared with the mature cedar, and 48 h discharge was up to 2·5 times greater. Perhaps characteristic of maritime climates, forest interception melt is shown to be important in addition to sublimation in reducing snow accumulation beneath dense canopies. While sublimation represents a loss from the catchment water balance, interception melt percolates through the snowpack and contributes to soil moisture during the winter season. Strong differences in microclimate and snowpack albedo persisted between cedar, larch and open sites, and it is suggested further work is needed to account for this in hydrological simulation models. Copyright © 2005 John Wiley & Sons, Ltd. [source] Contributions of diffusional limitation, photoinhibition and photorespiration to midday depression of photosynthesis in Arisaema heterophyllum in natural high lightPLANT CELL & ENVIRONMENT, Issue 3 2000Hiroyuki Muraoka ABSTRACT Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non-diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1,A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 ,mol mol,1. A350 was estimated from the electron transport rate (JT), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ,peak' of diurnal assimilation was 70% greater than that obtained before the ,peak', but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II (,F/Fm,) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ,peak'. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 ,mol m,2 s,1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation (JO) of RuBP were estimated from A and JT. In sun leaves, the JO/JT ratio was significantly higher after the ,peak', but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non-photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration. [source] The Use of Gasoline: Value, Oil, and the "American way of life"ANTIPODE, Issue 3 2009Matthew T. Huber Abstract:, While the critical literature has focused on the geography of oil production, the politics of "outrageous" gasoline prices in the United States provide a fertile path toward understanding the wider geography of petro-capitalism. Despite the deepening contradictions of US oil consumption, "pain at the pump" discourse projects a political sense of entitlement to low priced gasoline. I use a value-theoretical perspective to examine this politics as not only about the quantitative spectrum of price, but also the historical sedimentation of qualitative use-values inscribed in the commodity gasoline. Gasoline is analyzed both as a use-value among many within the postwar value of labor power and as a singular use-value fueling broader imaginaries of a national "American way of life." While use-value still represents an open site of cultural and political struggle infused within value itself, the case of gasoline illustrates how use-values are not automatically mobilized toward politically savory ends. [source] Effect of a postfire environment on the establishment of Prosopis caldenia seedlings in central semiarid ArgentinaAUSTRAL ECOLOGY, Issue 5 2007ANA E. De VILLALOBOS Abstract The objective of this work was to evaluate postfire environmental effects on the emergence, survival and growth of Prosopis caldenia seedlings in relation to different controlled fire frequencies, seed scarification methods, and planting site. Seedling emergence was significantly higher in experimental units exposed twice and three times to controlled fire than in unburned experimental units. The highest average seedling survival was recorded with triple exposure to controlled fires. Emergence, survival and growth of seedlings from seeds exposed to acid scarification and 600°C for 5 min were higher in the burned experimental units than in the unburned ones. In the former, seedling survival was higher beneath a P. caldenia canopy than in an adjacent open site, though seedling emergence was similar in both planting sites. Our results suggest that postfire conditions characterized by a reduction in the vegetative cover and competition interference and an increase in soil temperatures and nutrients levels (e.g. nitrogen and phosphorus) may facilitate the establishment of P. caldenia seedlings in the Caldenal. [source] Standsicherheitsuntersuchung für ein räumliches Böschungssystem , Berechnung mit einem zusammengesetzten dreidimensionalen Bruchmechanismus und Modellversuch im Gelände , Teil 2: Durchführung der Berechnung und ErgebnisseBAUTECHNIK, Issue 1 2004Michael Goldscheider Dr.-Ing. Für die Berechnung der Sicherheit gegen einen räumlichen Grabenbruch an einer hohen Randböschung eines Braunkohletagebaus wird ein räumlicher zusammengesetzter Starrkörperbruchmechanismus entwickelt und berechnet. Die Grundlagen und Grundgleichungen wurden in Teil 1 behandelt. Der Teil 2 beschreibt die Durchführung der Berechnung, die Optimierung des Bruchmechanismus und typische Berechnungsergebnisse. Stability analysis for a three-dimensional slope system , calculation with a composed rigid body failure mechanism and model test in an open site. Part2: Execution of the calculation and results. To determine the safety factor against a three-dimensional graben rupture on a high rim slope of an open-cast lignite mine a three-dimensional composed rigid body failure mechanism is outlined and calculated. The basic relations and equations are presented in part 1 of this paper. In the part 2 the execution of calculation, the optimization of the failure mechanism and typical results are described. [source] Recreational Portage Trails as Corridors Facilitating Non-Native Plant Invasions of the Boundary Waters Canoe Area Wilderness (U.S.A.)CONSERVATION BIOLOGY, Issue 5 2005SARA JO M. DICKENS corredores; invasiones; perturbación humana; recreación; senderos Abstract:,Wilderness areas are protected and valued in part for recreation; recreational use, however, can negatively impact these areas. In particular, recreational use can facilitate transport of non-native propagules and create open sites for establishment of non-native species. We examined the role of recreational portage trails in the introduction and establishment of non-native plants into the Boundary Waters Canoe Area Wilderness of northern Minnesota (U.S.A.). On 20 portages, we sampled non-native plant richness and cover at four distances (0, 10, 25, and 50 m) from trails. Non-native richness and cover were not related to distance from wilderness entry point. Non-native richness and cover were, however, negatively related to distance from trails. All six non-native species we observed were either directly on or within 1 m of trails. These results suggest that recreational trails act as corridors facilitating invasions of non-native plants into wilderness areas. It remains unclear, however, whether these effects are caused by dispersal of propagules, creation of bare ground, or changes in the native plant community. Resumen:,En parte, las áreas silvestres son protegidas y valoradas para recreación; sin embargo, el uso recreativo puede impactar a estas áreas negativamente. En particular, el uso recreativo puede facilitar el transporte de propágulos no nativos y crear áreas abiertas para el establecimiento de especies no nativas. Examinamos el papel de senderos recreativos en la introducción y establecimiento de plantas no nativas en el Boundary Waters Canoe Area Wilderness en el norte de Minnesota (E.U.A.). En 20 senderos, muestreamos la riqueza y cobertura de plantas no nativas a cuatro distancias (0, 10, 25 y 50 m) de los senderos. La riqueza y cobertura de no nativas no se relacionaron con la distancia al punto de entrada al área silvestre. Sin embargo, la riqueza y cobertura de no nativas se relacionaron negativamente con la distancia a los senderos. Las seis especies no nativas fueron observadas directamente sobre o a 1 m de los senderos. Estos resultados sugieren que los senderos recreativos fungen como corredores que facilitan la invasión de plantas no nativas a las áreas silvestres. Sin embargo, aún no es claro si estos efectos son causados por la dispersión de propágulos, la creación de suelo desnudo o por cambios en la comunidad de plantas nativas. [source] Locomotion and Escape Modes in Rodents of the Monte Desert (Argentina)ETHOLOGY, Issue 6 2003Paula Taraborelli Modes of locomotion and escape tactics are attributes that affect the structure of animal communities, promoting exploitation of different microhabitats and the coexistence of different species. Bipedal locomotion is considered to be more effective than a quadrupedal gait in escaping attacks by predators because it allows for higher speed, a faster response to attack, sudden changes of direction and better detection of aerial raptors. The aim of this study was to determine the type of locomotion used at the moment of escape by three rodent species of the Monte desert ,Eligmodontia typus, Akodon molinae and Graomys griseoflavus. The study was carried out in three plant communities of the Ñacuñán Reserve (Mendoza). All three species showed differences in both mode of escape and locomotory pattern. Graomys griseoflavus exhibited the highest proportion of escapes using quadrupedal saltation. The mode of locomotion employed by E. typus varied according to the type of plant communities it inhabited. Those occurring at open sites (Medanal community) exhibited a greater propensity to jump during escapes than those from more sheltered habitats (Algarrobal community). Akodon molinae relied primarily on a quadrupedal gait when fleeing from predators, which would explain its greater dependence on plant cover. Therefore, the morphological and behavioural characteristics of these species are related to their mode of locomotion and the strategies they employ to diminish the risk of predation. [source] The effects of stream canopy management on macroinvertebrate communities and juvenile salmonid production in a chalk streamFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2009W. D. RILEY Abstract, The effects of changes in shading (through riparian canopy removal and re-growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in-stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels. [source] Seasonal snowpack dynamics and runoff in a cool temperate forest: lysimeter experiment in Niigata, JapanHYDROLOGICAL PROCESSES, Issue 20 2005Andrew C. Whitaker Abstract Seasonal snowpack dynamics are described through field measurements under contrasting canopy conditions for a mountainous catchment in the Japan Sea region. Microclimatic data, snow accumulation, albedo and lysimeter runoff are given through the complete winter season 2002,03 in (1) a mature cedar stand, (2) a larch stand, and (3) a regenerating cedar stand or opening. The accumulation and melt of seasonal snowpack strongly influences streamflow runoff during December to May, including winter baseflow, mid-winter melt, rain on snow, and diurnal peaks driven by radiation melt in spring. Lysimeter runoff at all sites is characterized by constant ground melt of 0·8,1·0 mm day,1. Rapid response to mid-winter melt or rainfall shows that the snowpack remains in a ripe or near-ripe condition throughout the snow-cover season. Hourly and daily lysimeter discharge was greatest during rain on snow (e.g. 7 mm h,1 and 53 mm day,1 on 17 December) with the majority of runoff due to rainfall passing through the snowpack as opposed to snowmelt. For both rain-on-snow and radiation melt events lysimeter discharge was generally greatest at the open site, although there were exceptions such as during interception melt events. During radiation melt instantaneous discharge was up to 4·0 times greater in the opening compared with the mature cedar, and 48 h discharge was up to 2·5 times greater. Perhaps characteristic of maritime climates, forest interception melt is shown to be important in addition to sublimation in reducing snow accumulation beneath dense canopies. While sublimation represents a loss from the catchment water balance, interception melt percolates through the snowpack and contributes to soil moisture during the winter season. Strong differences in microclimate and snowpack albedo persisted between cedar, larch and open sites, and it is suggested further work is needed to account for this in hydrological simulation models. Copyright © 2005 John Wiley & Sons, Ltd. [source] Desert shrubs have negative or neutral effects on annuals at two levels of water availability in arid lands of South AustraliaJOURNAL OF ECOLOGY, Issue 6 2008James T. Weedon Abstract 1Perennial plants have been shown to facilitate understorey annual plant species in arid lands through the modification of spatial patterns of resources and conditions. This effect can result from a balance between simultaneously positive and negative interactions, both direct and indirect. This balance may shift with temporal variability in water availability. 2We conducted a field experiment in a chenopod shrubland in South Australia to separate the effects of shade, below-ground competition, and soil modification by shrubs on the performance of annual plants, and to determine if the strength and direction of the interaction shifted with changes in water availability. 3Annual plant diversity and seedling density was highest in plots established in open sites away from the dominant shrubs (Maireana sedifolia). Experimental removal of M. sedifolia increased seedling density compared to plots under undisturbed shrubs and plots where the removed shrub was replaced with artificial shade. Shading of open plots also reduced seedling density. Annual plant biomass was highest in areas where shrubs had been removed and was reduced by artificial shading. Biomass was higher in open plots than under intact shrubs. Experimental water addition did not alter plant density, but increased biomass across all treatments, particularly in artificially shaded bush plots. 4Synthesis. Our results show that the overall effect of shrubs on the annual plant community in the system is negative under the range of water availabilities experienced during the experiment. This negative net-effect results from a combination of simultaneous facilitation via soil modification, and above- and below-ground competition. Assessment in different systems of different combinations of mechanisms that have simultaneously positive and negative effects will allow us to refine hypotheses seeking to explain the relative importance of facilitation across spatial and temporal gradients. [source] Strategies providing success in a variable habitat: III.PLANT CELL & ENVIRONMENT, Issue 8 2001Dynamic control of photosynthesis in Cladophora glomerata Abstract Diurnal patterns of photosynthesis were studied in July and April populations of Cladophora glomerata (L.) Kütz. from open and from shaded sites. Summer samples exposed to full sunlight showed decreased efficiency of open photosystem II at noon, and only slight differences were found between samples that had grown at open or at shaded sites. Electron transport rate was limited at highest fluence rates in shade plants, and non-photochemical quenching (NPQ) revealed faster regulation in samples from open sites. Daily course of de-epoxidation was not linearly correlated with the course of NPQ. The comparison of samples from open and from shaded sites revealed a higher capacity of thermal energy dissipation and an increase in the total amount of xanthophyll-cycle pigments (21%) in samples from open sites. In April, down-regulation of the efficiency of open photosystem II was related to lower water temperature, and hence, increased excitation pressure. In April the pool size of xanthophyll-cycle pigments was increased by 21% in comparison with summer and suggested higher levels of thermal energy dissipation via de-epoxidized xanthophylls. In both, summer and spring the amount of xanthophyll-cycle pigments was 20% higher in samples from open sites. Acclimation of C. glomerata to growth light conditions was further shown by experimental induction of NPQ, indicating NPQ increases of 23%, and increases of 77% in the reversible component of NPQ in open site samples. The effect of temperature on photosynthetic rate was non-linear, and different optimum temperatures of electron transport rate and oxygen evolution were exhibited. [source] Strategies providing success in a variable habitat: II.PLANT CELL & ENVIRONMENT, Issue 10 2000Ecophysiology of photosynthesis of Cladophora glomerata ABSTRACT Cladophora glomerata (L.) Kütz. is the dominant filamentous algae of the river Ilm, Thuringia, Germany. For most of the year it can be found at open as well as at shaded sites. Photosynthetic acclimation of C. glomerata to different light intensities was detected by chlorophyll fluorescence measurements and pigment analysis. Cladophora glomerata from highlight sites showed decreased values of efficiency of open photosystem II (Fv/Fm) as compared with C. glomerata from low-light sites. Winter populations revealed higher Fv/Fm values than summer populations. A light-induced decrease in efficiency of the closed photosystem II was observed at increasing irradiance intensities. The decrease was higher in C. glomerata from shaded sites compared with plants from open sites. Differences in the photosynthetic electron transport rate of different populations of C. glomerata were shown by photosynthesis,irradiance curves. Summer populations from high-light sites yielded higher maximum electron transport rates than plants from low-light sites, whereas winter populations exhibited significantly decreased values compared with the summer populations. Results of the analysis of photosynthetic pigments corresponded with data from chlorophyll fluorescence measurements. In addition to these long-term acclimation effects, C. glomerata expressed its ability to cope with rapid changes in the light environment by the de-epoxidation of violaxanthin during exposure to high light intensities. [source] Dionaea muscipula (Venus Flytrap) Establishment, Release, and Response of Associated Species in Mowed Patches on the Rims of Carolina BaysRESTORATION ECOLOGY, Issue 4 2005James O Luken Abstract Carolina bays are depression wetlands of high conservation value that occur across the Southeastern Coastal Plain of the United States. Venus flytrap (Dionaea muscipula) is one rare carnivorous plant that grows in open habitats on the rims of Carolina bays. Without frequent burning, vegetation on bay rims becomes dominated by evergreen shrubs and Venus flytrap populations decline. This project examined the utility of mechanical mowing, soil clearing, transplanting, and seeding as an approach to restoring populations of Venus flytraps when fire is precluded. Mowing of patches on bay rims produced open sites with little ground-layer vegetation. After two growing seasons, adult Venus flytraps transplanted to mowed patches showed high survivorship and relatively high leaf number/plant. Suppressed Venus flytraps existing on-site quickly initiated growth in response to mowing. These volunteers and the transplants had higher flowering percentages than plants in reference populations. Seeds of Venus flytraps were scattered in mowed and cleared plots. Seedling establishment was low, but seedlings persisted into the second growing season. Mowing created suitable habitat for growth and flowering of adult Venus flytraps and facilitated establishment of two other carnivorous species, Sundew (Drosera capillaris) and Bladderwort (Utricularia subulata). But, mowing and clearing also facilitated invasion by four species of grasses and rushes; evergreen shrubs resprouted quickly after mowing. Maintaining persistent openings by mowing the rims of Carolina bays will be an ongoing challenge due to availability of potential invaders and rapid regrowth of shrubs. [source] What helps Opuntia stricta invade Kruger National Park, South Africa: Baboons or elephants?APPLIED VEGETATION SCIENCE, Issue 2 2007L.C. Foxcroft Germishuizen & Meyer (2003) for plant species Abstract Question: Is Opuntia stricta more frequent, and its patches larger, under trees suitable for baboon roosting? If so, does it mean that baboons are major dispersal agents and that plants established under these trees are important foci of Opuntia stricta spread? Location: Skukuza, Kruger National Park, South Africa. Method: We surveyed an area invaded by Opuntia stricta in the Skukuza region of KNP. The survey included plots under potential baboon roosting trees,plots under trees unlikely to support baboons,and paired randomly located open sites. Results: The null hypothesis -tree- Opuntia spatial independence , can be rejected for Acacia nilotica, but not for Spirostachys africana. Opuntia plants are positively associated with Acacia trees suitable for baboon roosting. However, there is no significant difference between frequency of Opuntia under Acacia trees suitable and unsuitable for baboon roosting. It appears that all Acacia trees can serve as nurse trees for Opuntia. Compared to plots under Acacia trees, frequencies of old and robust Opuntia plants are significantly higher in open areas and under dead trees. Conclusions: While baboons may be responsible for long distance Opuntia dispersal (over km),their role is not detectable at a local scale. On the other hand, elephants seem to contribute substantially to the local vegetative propagation of this species. Opuntia establishment and growth are more influenced by micro-habitat than previously thought. [source] The ecological value of Eryngium horridum in maintaining biodiversity in subtropical grasslandsAUSTRAL ECOLOGY, Issue 5 2009ALESSANDRA FIDELIS Abstract The role of facilitation in the structuring of plant communities has been often demonstrated in environments under high abiotic stress, especially in semi-arid and arid ecosystems and high elevations. Few studies, however, analysed facilitation in systems that are highly productive and rich in species, which are thought to be theoretically unlikely to demonstrate strong effects of facilitation. Here, we investigate the importance of Eryngium horridum, a rosette species, on the maintenance of plant diversity in subtropical grasslands in southern Brazil. We evaluated facilitation in areas under two different types of management: abandonment and grazing. Plots were established in areas with and without individuals of E. horridum and all species were identified and had their cover estimated. The Relative Neighbour Effect index was calculated in order to verify the presence of competition or facilitation. Our results indicated facilitation in both abandoned and in grazed grasslands, but apparently through different mechanisms. In the first case, the plant's architecture opens the canopy and allows more light to reach small forbs in the grass matrix. In the second case, E. horridum appears to protect more palatable species from herbivores. Otherwise considered an obnoxious species, E. horridum plays an important ecological role in subtropical grasslands in southern Brazil by facilitating other species and consequently, increasing local richness. Areas with this rosette species are important sources of diaspores, which are able to colonize new open sites and thus, maintain biodiversity. [source] | ||||||||||||||||