Abstracts on Global Climate Change

Jun 2007

Storage and release of fossil organic carbon related to weathering of sedimentary rocks

Copard, Y Amiotte-Suchet, P Di-Giovanni, C


The biogeochemical carbon cycle, which plays an undeniable role in global climate change, is defined both by the size of carbon reservoirs (such as the atmosphere, biomass, soil and bedrock) and the exchange between them of various mineral and organic carbon forms. Among these carbon forms, fossil organic carbon (FOC) (i.e., the ancient organic matter stored in sedimentary rocks) is widely observed in modem environments but is not included in the supergene carbon budget. Using a digitized map of the world and an existing model of CO2 consumption associated with rock weathering, we establish the global distribution of FOC stored in the first meter of sedimentary rocks and a first estimation of annual FOC delivery to the modem environment resulting from chemical weathering of these rocks. Results are given for the world’s 40 major river basins and extended to the entire continental surface. With a mean value of I 100 10(9) t, mainly controlled by shale distribution, the global FOC stock is significant and comparable to that of soil organic carbon (1500 10(9) t). The annual chemical delivery of FOC, estimated at 43 10(6) t yr(-1) and controlled by the areal distribution of shales and runoff is of the same order of magnitude as the FOC output flux to oceans. Chemical weathering of bedrock within the Amazon basin produces one-quarter of the total global flux of FOC derived from chemical weathering, and thus is expected to govern FOC release on a global scale. These results raise important questions concerning the role of FOC in the modem carbon cycle as well as the origin and the budget of carbon in soils and rivers. (C) 2007 Elsevier B.V. All rights reserved.

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Strontium isotope tracing of terrigenous sediment dispersal in the Antarctic Circumpolar Current: Implications for constraining frontal positions

Hemming, SR van de Flierdt, T Goldstein, SL Franzese, AM Roy, M Gastineau, G Landrot, G


[1] The vigor of the glacial Antarctic Circumpolar Current (ACC) and the locations of frontal boundaries are important parameters for understanding the role of the Southern Ocean in global climate change. Toward the goal of understanding the locations of currents we present a survey of Sr isotope ratios in terrigenous sediments around the perimeter of Antarctica. The pattern of the variations within the modern ACC is used to suggest that terrigenous sediment from Antarctica is injected into the ACC via the Ross and Weddell gyres in the south. North of the main ACC the Sr isotopes reflect continental contributions from Africa, Australia-New Zealand, and South America. Along a transect northward from the Ross Sea, Sr isotope ratios show a decrease from higher values in the south ( Antarctic provenance) to lower values in the north ( provenance from New Zealand). This otherwise monotonic decrease is interrupted within the ACC by a “zigzag” to lower and then higher values, which accompanies minimum terrigenous flux. This zigzag requires contributions from two additional sediment sources beyond the main Antarctic and New Zealand end-members. The lower Sr isotope ratios are attributable to greater contributions from basaltic sources within the current, a consistent pattern around the ACC. The samples with higher Sr isotope ratios point to an additional contributor, possibly a wind-transported component from Australia. During the LGM there is a systematic geographical variation in the Sr isotope ratios, similar to that of the Holocene. A small offset of the zigzag to the north ( approximately 1 degrees-2 degrees) may indicate a small northward shift of the southern boundary of the ACC. More highly resolved data are required to test whether this northward shift is really significant and whether it applies to other ACC fronts during the LGM.

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May 2007

Decade-centenary resolution records of climate changes in East Siberia from elements in the bottom sediments of lake Baikal for the last 150 kyr

Goldberg, EL Phedorin, MA Chebykin, EP Zolotarev, KB Zhuchenko, NA


High-resolution scanning Synchrotron Radiation X-ray Fluorescence Analysis (SRXFA) was applied to investigate the downcore distribution of elements in the sediments from Lake Baikal (East Siberia). The obtained multi-element time series reveal the presence of abrupt climate shifts in East Siberia which were synchronous with the abrupt warming events in the North Atlantic and Greenland (Dansgaard-Oeschges events (D/O) during the last ice age 24-75 kyr BP. We show here the set of climatic indicators reveals all globally known climate changes from dry and cool or glacial climates to humid and warm ones, which were recorded in Northern Atlantic and East Siberia both on the orbital and millennial time scales during the last 150 kyr. (c) 2007 Elsevier B.V. All rights reserved.

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Peat archives from Siberia: Synchrotron beam scanning with X-ray fluorescence measurements

Phedorin, MA Bobrov, VA Zolotarevd, KV


We used a new approach to measure the downcore distribution of some major and trace elements that record the Holocene history of peat-forming processes in peat from the Elovka mesotrophic swamp (West Siberia). The approach implies continuous non-destructive scanning of natural wet-core fragments under a sharp synchrotron beam combined with measurements of the excited X-ray fluorescence, in attempt to avoid errors due to the loss of volatiles abundant in peat. The obtained data are in good agreement with the results of the certified methods of neutron activation gamma-spectrometry (INAA) and classical SR XRF, though, as we expected, there is some discrepancy in the contents of volatiles (Br, Zn) which are most probably lost in INAA and/or in ignition. The precision of the suggested SR XRF scanning resolved the variability of 18 elements in the peat-core deposited during 0-8 kyr bp at no worse than 30 years in most cases. The distribution of the measured elements provided a clue to the evolution of peat deposition environments that controlled biogenic production, aerosol input, post-depositional processes, and Ca mineralization associated with pore water circulation in soil during the non-mesotrophic stages of the swamp history. (c) 2007 Elsevier B.V. All rights reserved.

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Remote monitoring of spatial and temporal surface soil moisture in fire disturbed boreal forest ecosystems with ERS SAR imagery

Bourgeau-Chavez, LL Kasischke, ES Riordan, K Brunzell, S Nolan, M Hyer, E Slawski, J Medvecz, M Walters, T Ames, S


Due to the large volume of carbon currently stored in boreal regions and the high frequency of wildfire, the prospects of a warming climate would have important implications for the ecology of boreal forests which in turn would have significant feedbacks for carbon cycling, fire frequency, and global climate change. Since ecological studies and climate change models require routine information on surface soil moisture, the ability to remotely sense this variable is highly desirable. Toward this end research was conducted on developing methods for the retrieval of spatially and temporally varying patterns of soil moisture from recently bumed boreal forest ecosystems of Alaska using C-band satellite radar data. To do this we focused on both individual date and temporal SAR datasets to develop techniques and algorithms which indicate how moisture varies across a recently burned boreal forest. For each of the methods developed we focused on reducing errors of SAR-derived soil moisture estimates due to confounding factors of variations in vegetative biomass and surface roughness. For the individual date soil moisture monitoring, we grouped test sites by a measurable biophysical variable, burn severity, and then developed algorithms relating moisture to SAR backscatter for each bum severity group. The algorithms developed had high coefficients of determination (0.56-0.82) and the moisture maps produced had high accuracy (3.61 rms error) based on the minimal validation conducted. For the seasonal soil moisture mapping we used principal component analysis to capture the time-variant feature of soil moisture and minimize the relatively time-invariant features that confound SAR backscatter. This resulted in good agreement between the drainage maps produced and our limited in situ observations and weather data. However, further validation, with larger sample sizes, is needed. While this study focuses on Alaska, research indicates that the techniques developed should be applicable to boreal forests worldwide.

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Modeling data with multiple time dimensions

Breeden, JL


A large class of problems in time series analysis can be represented by a set of overlapping time series with different starting times. These time series may be treated as different probes of the same underlying process. Such probes may follow a characteristic lifecycle as a function of the time since the series began. They may also be subject to environmental shocks according to calendar time. In addition, the calibration of each probe may be unknown such that each series may show a different magnitude of response to the underlying lifecycles and environmental impacts. This paper describes an approach to analyzing these multiple time series as a single set such that the underlying lifecycles and calendar-based shocks may be measured. Simultaneously, the individual calibrations of the time series are also measured. This technique is referred to as dual-time dynamics, and it applies to many important business problems. Applications to tree ring analysis, the SETI@home project, and retail loan portfolio forecasting are provided. Other areas of possible application include digital media services, insurance, human resource management, health care, and biological systems to name a few. (c) 2007 Elsevier B.V. All rights reserved.

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Drought sensitivity shapes species distribution patterns in tropical forests

Engelbrecht, BMJ Comita, LS Condit, R Kursar, TA Tyree, MT Turner, BL Hubbell, SP

NATURE 447:7140 80-U2

Although patterns of tree species distributions along environmental gradients have been amply documented in tropical forests(1-7), mechanisms causing these patterns are seldom known. Efforts to evaluate proposed mechanisms have been hampered by a lack of comparative data on species’ reactions to relevant axes of environmental variation(1). Here we show that differential drought sensitivity shapes plant distributions in tropical forests at both regional and local scales. Our analyses are based on experimental field assessments of drought sensitivity of 48 species of trees and shrubs, and on their local and regional distributions within a network of 122 inventory sites spanning a rainfall gradient across the Isthmus of Panama. Our results suggest that niche differentiation with respect to soil water availability is a direct determinant of both local- and regional-scale distributions of tropical trees. Changes in soil moisture availability caused by global climate change and forest fragmentation are therefore likely to alter tropical species distributions, community composition and diversity.

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Short-rotation forestry of birch, maple, poplar and willow in Flanders (Belgium) I - Biomass production after 4 years of tree growth

Walle, IV Van Camp, N Van de Casteele, L Verheyen, K Lemeur, R

BIOMASS & BIOENERGY 31:5 267-275

During the last three decades, oil crises, agricultural surpluses and global climate change enhanced the interest in short-rotation forestry (SRF). In this study, the biomass production of birch (Betula pendula Roth), maple (Acer pseudoplatanus L.-Tintigny), poplar (Populus trichocarpa x deltoides -Hoogvorst) and willow (Salix viminalis-Orm) growing under a short-rotation (SR) management system were compared after a 4 years period. The plantation was established on former agricultural land. The sandy soil had a mean pH of 4.5 and a mean carbon content of 1.0%. Survival rates after 4 years were 75.8%, 96.8%, 86.3% and 97.6% for birch, maple, poplar and willow, respectively. The mean actual annual biomass production for these four species amounted to 2.6, 1.2, 3.5 and 3.4 t DM ha(-1) yr(-1), respectively. The large variation in biomass production at the different plots of the plantation could not be explained by the measured soil parameters. Biomass production results found here were in the lower range of values reported in literature. However, in contrast to most other studies, no weed control, fertilisation or irrigation was applied in this experiment. As marginal agricultural soils are suboptimal for the growth of poplar and willow, birch can be considered as a very interesting alternative for the establishment of SR plantations in Flanders. (c) 2007 Elsevier Ltd. All rights reserved.

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Reconstruction of solar total irradiance since 1700 from the surface magnetic flux

Krivova, NA Balmaceda, L Solanki, SK


Context. Total solar irradiance changes by about 0.1% between solar activity maximum and minimum. Accurate measurements of this quantity are only available since 1978 and do not provide information on longer-term secular trends. Aims. In order to reliably evaluate the Sun’s role in recent global climate change, longer time series are, however, needed. They can only be assessed with the help of suitable models. Methods. The total solar irradiance is reconstructed from the end of the Maunder minimum to the present based on variations of the surface distribution of the solar magnetic field. The latter is calculated from the historical record of the sunspot number using a simple but consistent physical model. Results. Our model successfully reproduces three independent data sets: total solar irradiance measurements available since 1978, total photospheric magnetic flux since 1974 and the open magnetic flux since 1868 empirically reconstructed using the geomagnetic aa-index. The model predicts an increase in the solar total irradiance since the Maunder minimum of 1.3(-0.4)(+0.2) Wm(-2).

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Depth-mediated reversal of the effects of climate change on long-term growth rates of exploited marine fish

Thresher, RE Koslow, JA Morison, AK Smith, DC


The oceanographic consequences of climate change are increasingly well documented, but the biological impacts of this change on marine species much less so, in large part because of few long-term data sets. Using otolith analysis, we reconstructed historical changes in annual growth rates for the juveniles of eight long-lived fish species in the southwest Pacific, from as early as 1861. Six of the eight species show significant changes in growth rates during the last century, with the pattern differing systematically with depth. Increasing temperatures near the ocean surface correlate with increasing growth rates by species found in depths < 250 m, whereas growth rates of deep-water I(> 1,000 m) species have declined substantially during the last century, which correlates with evidence of long-term cooling at these depths. The observations suggest that global climate change has enhanced some elements of productivity of the shallow-water stocks but also has reduced the productivity, and possibly the resilience, of the already slow-growing deep-water species.

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Spatio-temporal patterns of juvenile marine turtle occurrence in waters of the European continental shelf

Witt, MJ Penrose, R Godley, BJ

MARINE BIOLOGY 151:3 873-885

We present data spanning approximately 100 years regarding the spatial and temporal occurrence of marine turtle sightings and strandings in the northeast Atlantic from two public recording schemes and demonstrate potential signals of changing population status. Records of loggerhead (n = 317) and Kemp’s ridley (n = 44) turtles occurring on the European continental shelf were most prevalent during the autumn and winter, when waters were coolest. In contrast, endothermic leatherback turtles (n = 1,668) were most common during the summer. Analysis of the spatial distribution of hard-shell marine turtle sightings and strandings highlights a pattern of decreasing records with increasing latitude. The spatial distribution of sighting and stranding records indicates that arrival in waters of the European continental shelf is most likely driven by North Atlantic current systems. Future patterns of spatial-temporal distribution, gathered from the periphery of juvenile marine turtles habitat range, may allow for a broader assessment of the future impacts of global climate change on species range and population size.

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Phenological responses of plants to climate change in an urban environment

Luo, ZK Sun, OJ Ge, QS Xu, WT Zheng, JY


Global climate change is likely to alter the phenological patterns of plants due to the controlling effects of climate on plant ontogeny, especially in an urbanized environment. We studied relationships between various phenophases (i.e., seasonal biological events) and interannual variations of air temperature in three woody plant species (Prunus davidiana, Hibiscus syriacus, and Cercis chinensis) in the Beijing Metropolis, China, based on phenological data for the period 1962-2004 and meteorological data for the period 1951-2004. Analysis of phenology and climate data indicated significant changes in spring and autumn phenophases and temperatures. Changes in phenophases were observed for all the three species, consistent with patterns of rising air temperatures in the Beijing Metropolis. The changing phenology in the three plant species was reflected mainly as advances of the spring phenophases and delays in the autumn phenophases, but with strong variations among species and phenophases in response to different temperature indices. Most phenophases (both spring and autumn phenophases) had significant relationships with temperatures of the preceding months. There existed large inter- and intra-specific variations, however, in the responses of phenology to climate change. It is clear that the urban heat island effect from 1978 onwards is a dominant cause of the observed phenological changes. Differences in phenological responses to climate change may cause uncertain ecological consequences, with implications for ecosystem stability and function in urban environments.

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Effects of carbon dioxide, temperature and ultraviolet-B radiation and their interactions on soybean (Glycine max L.) growth and development

Koti, S Reddy, KR Kakani, VG Zhao, D Gao, W


Genetic modifications of agronomic crops will likely be necessary to cope with global climate change. Projected changes in global climate include increasing atmospheric carbon dioxide concentration ([CO2]), temperatures (T) and ultraviolet-B (UV-B) radiation which have significant effects on plants, however, their interactions are not clearly known to date. In this study we tested the hypothesis that soybean genotypes differ in growth and physiology with exposure to treatments of [CO2] [360 and 720 mu mol mol(-1) (+[CO2])], temperature [30/22 and 38/30 degrees C (+T)] and UV-B radiation [0 and 10 kJ m(-2) d(-1) (+UV-B)] and their interactions. Six soybean genotypes (D 88-5320, D 90-9216, Stalwart III, PI 471938, DG 5630 RR, and DP 4933 RR) representing five maturity groups were grown in eight sunlit, controlled environment chambers in which control treatment had 360 mu mol mol(-1) [CO2] at 30/22 degrees C temperatures and 0 kJ UV-B. Results showed that elevated C02 levels compensated the damaging effects caused by negative stressors such as high temperature and high UV-B radiation levels on most of the growth and physiological parameters studied. Total stress response index (TSRI) for each genotype was developed from the cumulative sum of response indices of vegetative and physiological parameters such as plant height, leaf area, total biomass, net photosynthesis, total chlorophyll content, phenolic content, relative injury and wax content. Based on TSRI, the genotypes were classified as tolerant (PI 471938 and D 88-5320), intermediate (DG 5630 RR and D 90-9216) and sensitive (DP 4933 RR and Stalwart 111). The disruption of growth and physiology was significantly reduced in tolerant genotypes compared to sensitive genotypes. Strong correlations between total response of relative injury (RI), an indicator of cell membrane thermo stability and TSRI developed in this study show that RI could be used to predict the overall vegetative performance of the crop. However, the total response of RI did not show any linear correlation with TSRI of our previous study (which was developed with responses of reproductive traits). This suggests that there is a need to develop better screening tools and/or breeding strategies in developing genotypes suitable to cope future climates at both vegetative and reproductive stages. (c) 2006 Elsevier B.V. All rights reserved.

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Groundwater influence on alpine stream ecosystems

Brown, LE Milner, AM Hannah, DM


1. Spatial and temporal variability of relative snow-melt, glacier-melt and groundwater contributions to streams play important roles in shaping alpine freshwater ecosystems. Although meltwater (particularly glacier-fed) streams have received much attention in recent years, the influence of groundwater on alpine freshwater ecosystems remains poorly understood. 2. This study tested the hypotheses that increased groundwater contributions to meltwater-dominated alpine streams would yield increases in water temperature, channel stability, electrical conductivity and particulate organic matter (POM) and decreases in suspended sediment concentration (SSC). These more favourable habitat conditions were hypothesised to result in increased macroinvertebrate abundance and diversity. 3. Groundwater contributions, physicochemical habitat variables and benthic macroinvertebrates were sampled throughout the 2002 and 2003 summer-melt seasons in three streams in the French Pyrenees. 4. Increased groundwater contributions were significantly correlated with higher discharge, water temperature, electrical conductivity, POM and channel stability, but lower SSC. 5. Macroinvertebrate total abundance, taxonomic richness, number of Ephemeroptera, Plecoptera and Trichoptera genera, and per cent Plecoptera all increased significantly with greater groundwater contributions to streamflow. However, beta diversity and Trichoptera relative abundance decreased. 6. Abundance of most macroinvertebrate taxa was highest under groundwater-dominated conditions but a gradient of optimum groundwater preferences was evident across all taxa. Some taxa were found only where groundwater contributions were low (i.e. in predominantly meltwater-fed streams). 7. This study provides evidence that water source, physicochemical habitat and stream biota are strongly linked. Therefore, an interdisciplinary approach is necessary for future studies aiming to develop conservation strategies or predict the response of alpine river ecosystems to global climate change.

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A new chronology for the age of Appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments

Anthony, DM Granger, DE


The relative chronology of landscape evolution across the unglaciated Appalachian plateaus of Kentucky and Tennessee is well documented. For more than a century, geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide-valley straths and smaller terraces. Constraining the timing of river incision into the Appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials. Today, burial dating using the differential decay of cosmogenic Al-26 and Be-10 in clastic cave sediments reveals more than five million years of landscape evolution preserved underground. Multilevel caves linked hydrologically to the incision history of the Cumberland River contain in situ sediments equivalent to fluvial deposits found scattered across the Eastern Highland Rim erosional surface. Cave sediments correlate with: (1) thick Lafayette-type gravels on the Eastern Highland Rim deposited between c. 5 center dot 7 and c. 3 center dot 5 Ma; (2) initial incision of the Cumberland River into the Eastern Highland Rim after c. 3 center dot 5 Ma; (3) formation of the Parker strath between c. 3 center dot 5 Ma and c. 2 center dot 0 Ma; (4) incision into the Parker strath at c. 2 Ma; (5) formation of a major terrace between c. 2 center dot 0 Ma and c. 1 center dot 5 Ma; (6) shorter cycles of accelerated incision and base level stability beginning at c. 1 center dot 5 Ma; and (7) regional aggradation at c. 0 center dot 85 Ma. Initial incision into the Appalachian uplands is interpreted as a response to eustasy at 3 center dot 2-3 center dot 1 Ma. Incision of the Parker strath is interpreted as a response to eustasy at 2 center dot 5-2 center dot 4 Ma. A third incision event at c. 1 center dot 5 Ma corresponds with glacial reorganization of the Ohio River basin. Widespread aggradation of cave passages at c. 0 center dot 85 Ma is interpreted as the beginning of intense glacial-interglacial cycling associated with global climate change. (C) Copyright 2006 John Wiley & Sons, Ltd.

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Impact of predicted climate change on landslide reactivation: case study of Mam Tor, UK

Dixon, N Brook, E

LANDSLIDES 4:2 137-147

Global change is expected to result in worldwide increases in temperature and alteration of rainfall patterns. Such changes have the potential to modify stability of slopes, both natural and constructed. This paper discusses the potential effect of global climate change on reactivation of landslides through examination of predicted changes in rainfall pattern on the active landslide at Mam Tor, Derbyshire, UK. This landslide is of Pleistocene origin and is crossed by a road that is now abandoned. Damaging winter movement is known to occur when precipitation reaches both 1-month triggering and 6-month antecedent thresholds. Return periods for threshold exceedence is modelled statistically, and the climate change data from the UKCIP 2002 report (Hulme et al. 2002) is applied to this model. For the predicted changes in precipitation, it is shown that the instability threshold could decrease from 4 to 3.5 years by the 2080s for the medium-high climate change scenario. However, predicted temperature changes could influence the response of the landslide through increased evapotranspiration leading to a change in the triggering precipitation thresholds, and this will help counter the impact of changes in precipitation. Analysis of sources of uncertainty in the model has been used to establish the factors that contribute to the predicted changes in stability. Assessment of these factors can provide an indication of the potential impact of climate change on landslides in other areas of the UK.

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Vulnerability: A generally applicable conceptual framework for climate change research

Fussel, HM


The term `vulnerability’ is used in many different ways by various scholarly communities. The resulting disagreement about the appropriate definition of vulnerability is a frequent cause for misunderstanding in interdisciplinary research on climate change and a challenge for attempts to develop formal models of vulnerability. Earlier attempts at reconciling the various conceptualizations of vulnerability were, at best, partly successful. This paper presents a generally applicable conceptual framework of vulnerability that combines a nomenclature of vulnerable situations and a terminology of vulnerability concepts based on the distinction of four fundamental groups of vulnerability factors. This conceptual framework is applied to characterize the vulnerability concepts employed by the main schools of vulnerability research and to review earlier attempts at classifying vulnerability concepts. None of these one-dimensional classification schemes reflects the diversity of vulnerability concepts identified in this review. The wide range of policy responses available to address the risks from global climate change suggests that climate impact, vulnerability, and adaptation assessments will continue to apply a variety of vulnerability concepts. The framework presented here provides the much-needed conceptual clarity and facilitates bridging the various approaches to researching vulnerability to climate change. (c) 2006 Elsevier Ltd. All rights reserved.

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Anthropogenic and natural disturbance effects on a macrobenthic estuarine community over a 10-year period

Dolbeth, M Cardoso, PG Ferreira, SM Verdelhos, T Raffaelli, D Pardal, MA


For some decades, the Mondego estuary has been under severe ecological stress, mainly caused by eutrophication. The most visible effect was the occurrence of macroalgal blooms and the concomitant decrease of the area occupied by Zostera noltii beds. Since the end of 1998, mitigation measures were implemented in the estuary to promote the recovery of the seagrass beds and the entire surrounding environment. The present study offers a unique opportunity to evaluate the impact of disturbance and the success of the initial recovery process (before and after implementation of the management measures), over a 10-year period, having secondary production as the descriptor. Before the implementation of the mitigation measures, in parallel with the decrease of the Z. noltii beds, species richness, mean biomass and production also decreased, lowering the carrying capacity of the whole Mondego’s south arm. Yet, after the introduction of management measures, the seagrass bed seemed to recover. Consequently, the biomass and production also increased substantially, for the whole intertidal area. Nevertheless, even after the mitigation measures implementation, natural-induced stressors, such as strong flood events induced a drastic reduction of annual production, not seen before the implementation of those measures. This shows that the resilience of the populations may have been lowered by a prior disturbance history (eutrophication) and consequent interactions of multiple stressors. (C) 2006 Elsevier Ltd. All rights reserved.

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Deforestation affects biogeographical regionalization: a case study contrasting potential and extant distributions of Mexican terrestrial mammals

Escalante, T Sanchez-Cordero, V Morrone, JJ Linaje, M


We used ecological niche modelling projected as species’ potential ( based on the original vegetation map) and extant ( based on the 2000 land use and vegetation map) distributions to analyse changes on patterns of endemism of terrestrial mammals occurring in Mexico. Based on the biogeographic method of Parsimony Analysis of Endemicity, we obtained cladograms under scenarios of species’ potential distribution ( t1) and extant distributions ( t2). We found that the resolution of consensus cladogram in t2 was poorer, while there were more geographic synapomorphies in t1, and more autapomorphies in t2 due to a reduction of species’ distributions as a consequence of deforestation. We defined a hierarchical regionalization with two regions with the cladogram of t1; a transitional zone, two subregions, five dominions, and 15 provinces. Conversely, the consensus cladogram of t2 had a basal trichotomy, and the position of the Sierra Madre Occidental changed compared with t1. In t1 and t2, the Yucatan Peninsula+ Chiapas+ Isthmus of Tehuantepec clade was maintained, although in t2 it was separated from the remaining areas of the country. The impact of deforestation on species distributions strongly affected the biogeographic regionalization of terrestrial mammals in Mexico.

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Potential changes in weed competitiveness in an agroecological system with elevated temperatures

Tungate, KD Israel, DW Watson, DM Rufty, TW


Increases in temperature due to global climate changes could significantly impact weed competitiveness and crop-weed interactions. Factors contributing to the responsiveness of a plant species to increasing temperature include the inherent genetic limitations of the species and the ability to acquire water and nutritional resources. The purpose of this study was to examine the temperature responses of selected species from a model agronomic system in the Southeastern U.S.: soybean (Glycine max), sicklepod (Senna obtusifolia) and prickly sida (Sida spinosa). We also determined temperature effects on mycorrhizal colonization and development of the soybean N-2-fixation system, two below-ground associations critical for resource acquisition. The species were grown at 42/37 (day/night), 36/31, 32/27, 28/23, or 23/18 degrees C for 30 days in a field soil with naturally low fertility. Growth of the weed species was maximized at a higher temperature than that for soybean, 36/31 degrees C versus 32/27 degrees C, probably reflecting different geographical origins. At the optimal temperature, weeds had higher root:shoot mass ratios (1.3-1.5 versus 0.9) than soybean, and greater mycorrhizal colonization. In soybean, nodule weights, numbers, and total nitrogenase activity were highest at the growth temperature optimum but decreased considerably at higher temperatures. The results collectively indicate that increases in aerial temperatures above similar to 32 degrees C would enhance weed competitiveness. Increased interference with soybean growth and yields should be expected. (c) 2006 Elsevier B.V. All rights reserved.

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