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Global Carbon Cycle (global + carbon_cycle)
Selected AbstractsUsing Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weatheringEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2006Yoann Copard Abstract This work relates to the debate on the fossil organic carbon (FOC) input in modern environments and its possible implication for the carbon cycle, and suggests the use of Rock-Eval 6 pyrolysis as a relevant tool for tracking FOC in such environments. Considering that such a delivery is mainly due to supergene processes affecting the continental surface, we studied organic matter in different reservoirs such as bedrocks, alterites, soils and rivers in two experimental catchments at Draix (Alpes de Haute Provence, France). Samples were subjected to geochemical (Rock-Eval 6 pyrolysis) investigations and artificial bacterial degradations. After comparing the geochemical fingerprint of samples, geochemical markers of FOC were defined and tracked in the different reservoirs. Our results confirm the contribution of FOC in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of FOC during its exchange between these pools. In addition, the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter (FOM). Bedrock to river fluxes, controlled by gully erosion, are characterized by a qualitative and quantitative preservation of FOM. Bedrock to alterite fluxes, governed by chemical weathering, are characterized by FOC mineralization without qualitative changes in deeper alterites. Alterite to soils fluxes, controlled by (bio)chemical weathering, are characterized by strong FOC mineralization and qualitative changes of FOM. Thus weathering and erosional processes induce different FOM evolution and affect the fate of FOC towards the global carbon cycle. In this study, gully erosion would involve maintenance of an ancient sink for the global carbon cycle, while (bio)chemical processes provide a source of CO2. Finally, this study suggests that Rock-Eval 6 pyrolysis can be considered as a relevant tool for tracking FOC in modern environments. Copyright © 2006 John Wiley & Sons, Ltd. [source] Plant functional traits and soil carbon sequestration in contrasting biomesECOLOGY LETTERS, Issue 5 2008Gerlinde B. De Deyn Abstract Plant functional traits control a variety of terrestrial ecosystem processes, including soil carbon storage which is a key component of the global carbon cycle. Plant traits regulate net soil carbon storage by controlling carbon assimilation, its transfer and storage in belowground biomass, and its release from soil through respiration, fire and leaching. However, our mechanistic understanding of these processes is incomplete. Here, we present a mechanistic framework, based on the plant traits that drive soil carbon inputs and outputs, for understanding how alteration of vegetation composition will affect soil carbon sequestration under global changes. First, we show direct and indirect plant trait effects on soil carbon input and output through autotrophs and heterotrophs, and through modification of abiotic conditions, which need to be considered to determine the local carbon sequestration potential. Second, we explore how the composition of key plant traits and soil biota related to carbon input, release and storage prevail in different biomes across the globe, and address the biome-specific mechanisms by which plant trait composition may impact on soil carbon sequestration. We propose that a trait-based approach will help to develop strategies to preserve and promote carbon sequestration. [source] Genome sequence of Desulfobacterium autotrophicum HRM2, a marine sulfate reducer oxidizing organic carbon completely to carbon dioxideENVIRONMENTAL MICROBIOLOGY, Issue 5 2009Axel W. Strittmatter Summary Sulfate-reducing bacteria (SRB) belonging to the metabolically versatile Desulfobacteriaceae are abundant in marine sediments and contribute to the global carbon cycle by complete oxidation of organic compounds. Desulfobacterium autotrophicum HRM2 is the first member of this ecophysiologically important group with a now available genome sequence. With 5.6 megabasepairs (Mbp) the genome of Db. autotrophicum HRM2 is about 2 Mbp larger than the sequenced genomes of other sulfate reducers (SRB). A high number of genome plasticity elements (> 100 transposon-related genes), several regions of GC discontinuity and a high number of repetitive elements (132 paralogous genes Mbp,1) point to a different genome evolution when comparing with Desulfovibrio spp. The metabolic versatility of Db. autotrophicum HRM2 is reflected in the presence of genes for the degradation of a variety of organic compounds including long-chain fatty acids and for the Wood,Ljungdahl pathway, which enables the organism to completely oxidize acetyl-CoA to CO2 but also to grow chemolithoautotrophically. The presence of more than 250 proteins of the sensory/regulatory protein families should enable Db. autotrophicum HRM2 to efficiently adapt to changing environmental conditions. Genes encoding periplasmic or cytoplasmic hydrogenases and formate dehydrogenases have been detected as well as genes for the transmembrane TpII- c3, Hme and Rnf complexes. Genes for subunits A, B, C and D as well as for the proposed novel subunits L and F of the heterodisulfide reductases are present. This enzyme is involved in energy conservation in methanoarchaea and it is speculated that it exhibits a similar function in the process of dissimilatory sulfate reduction in Db. autotrophicum HRM2. [source] Linking the global carbon cycle to individual metabolismFUNCTIONAL ECOLOGY, Issue 2 2005A. P. ALLEN Summary 1We present a model that yields ecosystem-level predictions of the flux, storage and turnover of carbon in three important pools (autotrophs, decomposers, labile soil C) based on the constraints of body size and temperature on individual metabolic rate. 2The model predicts a 10 000-fold increase in C turnover rates moving from tree- to phytoplankton-dominated ecosystems due to the size dependence of photosynthetic rates. 3The model predicts a 16-fold increase in rates controlled by respiration (e.g. decomposition, turnover of labile soil C and microbial biomass) over the temperature range 0,30 °C due to the temperature dependence of ATP synthesis in respiratory complexes. 4The model predicts only a fourfold increase in rates controlled by photosynthesis (e.g. net primary production, litter fall, fine root turnover) over the temperature range 0,30 °C due to the temperature dependence of Rubisco carboxylation in chloroplasts. 5The difference between the temperature dependence of respiration and photosynthesis yields quantitative predictions for distinct phenomena that include acclimation of plant respiration, geographic gradients in labile C storage, and differences between the short- and long-term temperature dependence of whole-ecosystem CO2 flux. 6These four sets of model predictions were tested using global compilations of data on C flux, storage and turnover in ecosystems. 7Results support the hypothesis that the combined effects of body size and temperature on individual metabolic rate impose important constraints on the global C cycle. The model thus provides a synthetic, mechanistic framework for linking global biogeochemical cycles to cellular-, individual- and community-level processes. [source] Quantifying carbon sequestration as a result of soil erosion and deposition: retrospective assessment using caesium-137 and carbon inventoriesGLOBAL CHANGE BIOLOGY, Issue 12 2007TIMOTHY ANDREW QUINE Abstract The role of soil erosion in the global carbon cycle remains a contested subject. A new approach to the retrospective derivation of erosion-induced quantitative fluxes of carbon between soil and atmosphere is presented and applied. The approach is based on the premise that soil redistribution perturbs the carbon cycle by driving disequilibrium between soil carbon content and input. This perturbation is examined by establishing the difference between measured carbon inventories and the inventories that would be found if input and content were in dynamic equilibrium. The carbon inventory of a profile in dynamic equilibrium is simulated by allowing lateral and vertical redistribution of carbon but treating all other profile inputs as equal to outputs. Caesium-137 is used to derive rates of vertical and lateral soil redistribution. Both point and field-scale estimates of carbon exchange with the atmosphere are derived using the approach for a field subject to mechanized agricultural in the United Kingdom. Sensitivity analysis is undertaken and demonstrates that the approach is robust. The results indicate that, despite a 15% decline in the carbon content of the cultivation layer of the eroded part of the field, this area has acted as a net sink of 11 ± 2 g C m,2 yr,1 over the last half century and that in the field as a whole, soil redistribution has driven a sink of 7 ± 2 g C m,2 yr,1 (6 ± 2 g C m,2 yr,1 if all eroded carbon transported beyond the field boundary is lost to the atmosphere) over the same period. This is the first empirical evidence for, and quantification of, dynamic replacement of eroded carbon. The relatively modest field-scale net sink is more consistent with the identification of erosion and deposition as a carbon sink than a carbon source. There is a clear need to assemble larger databases with which to evaluate critically the carbon sequestration potential of erosion and deposition in a variety of conditions of agricultural management, climate, relief, and soil type. In any case, this study demonstrated that the operation of erosion and deposition processes within the boundaries of agricultural fields must be understood as a key driver of the net carbon cycle consequences of cultivating land. [source] The regional variation of aboveground live biomass in old-growth Amazonian forestsGLOBAL CHANGE BIOLOGY, Issue 7 2006YADVINDER MALHI Abstract The biomass of tropical forests plays an important role in the global carbon cycle, both as a dynamic reservoir of carbon, and as a source of carbon dioxide to the atmosphere in areas undergoing deforestation. However, the absolute magnitude and environmental determinants of tropical forest biomass are still poorly understood. Here, we present a new synthesis and interpolation of the basal area and aboveground live biomass of old-growth lowland tropical forests across South America, based on data from 227 forest plots, many previously unpublished. Forest biomass was analyzed in terms of two uncorrelated factors: basal area and mean wood density. Basal area is strongly affected by local landscape factors, but is relatively invariant at regional scale in moist tropical forests, and declines significantly at the dry periphery of the forest zone. Mean wood density is inversely correlated with forest dynamics, being lower in the dynamic forests of western Amazonia and high in the slow-growing forests of eastern Amazonia. The combination of these two factors results in biomass being highest in the moderately seasonal, slow growing forests of central Amazonia and the Guyanas (up to 350 Mg dry weight ha,1) and declining to 200,250 Mg dry weight ha,1 at the western, southern and eastern margins. Overall, we estimate the total aboveground live biomass of intact Amazonian rainforests (area 5.76 × 106 km2 in 2000) to be 93±23 Pg C, taking into account lianas and small trees. Including dead biomass and belowground biomass would increase this value by approximately 10% and 21%, respectively, but the spatial variation of these additional terms still needs to be quantified. [source] Inversion of terrestrial ecosystem model parameter values against eddy covariance measurements by Monte Carlo samplingGLOBAL CHANGE BIOLOGY, Issue 8 2005Wolfgang Knorr Abstract Effective measures to counter the rising levels of carbon dioxide in the Earth's atmosphere require that we better understand the functioning of the global carbon cycle. Uncertainties about, in particular, the terrestrial carbon cycle's response to climate change remain high. We use a well-known stochastic inversion technique originally developed in nuclear physics, the Metropolis algorithm, to determine the full probability density functions (PDFs) of parameters of a terrestrial ecosystem model. By thus assimilating half-hourly eddy covariance measurements of CO2 and water fluxes, we can substantially reduce the uncertainty of approximately five model parameters, depending on prior uncertainties. Further analysis of the posterior PDF shows that almost all parameters are nearly Gaussian distributed, and reveals some distinct groups of parameters that are constrained together. We show that after assimilating only 7 days of measurements, uncertainties for net carbon uptake over 2 years for the forest site can be substantially reduced, with the median estimate in excellent agreement with measurements. [source] Estimating soil carbon fluxes following land-cover change: a test of some critical assumptions for a region in Costa RicaGLOBAL CHANGE BIOLOGY, Issue 2 2004Jennifer S. Powers Abstract Changes in soil carbon storage that accompany land-cover change may have significant effects on the global carbon cycle. The objective of this work was to examine how assumptions about preconversion soil C storage and the effects of land-cover change influence estimates of regional soil C storage. We applied three models of land-cover change effects to two maps of preconversion soil C in a 140 000 ha area of northeastern Costa Rica. One preconversion soil C map was generated using values assigned to tropical wet forest from the literature, the second used values obtained from extensive field sampling. The first model of land-cover change effects used values that are typically applied in global assessments, the second and third models used field data but differed in how the data were aggregated (one was based on land-cover transitions and one was based on terrain attributes). Changes in regional soil C storage were estimated for each combination of model and preconversion soil C for three time periods defined by geo-referenced land-cover maps. The estimated regional soil C under forest vegetation (to 0.3 m) was higher in the map based on field data (10.03 Tg C) than in the map based on literature data (8.90 Tg C), although the range of values derived from propagating estimation errors was large (7.67,12.40 Tg C). Regional soil C storage declined through time due to forest clearing for pasture and crops. Estimated CO2 fluxes depended more on the model of land-cover change effects than on preconversion soil C. Cumulative soil C losses (1950,1996) under the literature model of land-cover effects exceeded estimates based on field data by factors of 3.8,8.0. In order to better constrain regional and global-scale assessments of carbon fluxes from soils in the tropics, future research should focus on methods for extrapolating regional-scale constraints on soil C dynamics to larger spatial and temporal scales. [source] Introductory perspective on the COREF ProjectISLAND ARC, Issue 4 2006Yasufumi Iryu Abstract Coral reefs are tropic to subtropic, coastal ecosystems comprising very diverse organisms. Late Quaternary reef deposits are fossil archives of environmental, tectonic and eustatic variations that can be used to reconstruct the paleoclimatic and paleoceanographic history of the tropic surface oceans. Reefs located at the latitudinal limits of coral-reef ecosystems (i.e. those at coral-reef fronts) are particularly sensitive to environmental changes , especially those associated with glacial,interglacial changes in climate and sealevel. We propose a land and ocean scientific drilling campaign in the Ryukyu Islands (the Ryukyus) in the northwestern Pacific Ocean to investigate the dynamic response of the corals and coral-reef ecosystems in this region to Late Quaternary climate and sealevel change. Such a drilling campaign, which we call the COREF (coral-reef front) Project, will allow the following three major questions to be evaluated: (i) What are the nature, magnitude and driving mechanisms of coral-reef front migration in the Ryukyus? (ii) What is the ecosystem response of coral reefs in the Ryukyus to Quaternary climate changes? (iii) What is the role of coral reefs in the global carbon cycle? Subsidiary objectives include (i) the timing of coral-reef initiation in the Ryukyus and its causes; (ii) the position of the Kuroshio current during glacial periods and its effects on coral-reef formation; and (iii) early carbonate diagenetic responses as a function of compounded variations in climate, eustacy and depositional mineralogies (subtropic aragonitic to warm-temperate calcitic). The geographic, climatic and oceanographic settings of the Ryukyu Islands provide an ideal natural laboratory to address each of these research questions. [source] Darkness visible: reflections on underground ecologyJOURNAL OF ECOLOGY, Issue 2 2005A. H. FITTER Summary 1Soil science and ecology have developed independently, making it difficult for ecologists to contribute to urgent current debates on the destruction of the global soil resource and its key role in the global carbon cycle. Soils are believed to be exceptionally biodiverse parts of ecosystems, a view confirmed by recent data from the UK Soil Biodiversity Programme at Sourhope, Scotland, where high diversity was a characteristic of small organisms, but not of larger ones. Explaining this difference requires knowledge that we currently lack about the basic biology and biogeography of micro-organisms. 2It seems inherently plausible that the high levels of biological diversity in soil play some part in determining the ability of soils to undertake ecosystem-level processes, such as carbon and mineral cycling. However, we lack conceptual models to address this issue, and debate about the role of biodiversity in ecosystem processes has centred around the concept of functional redundancy, and has consequently been largely semantic. More precise construction of our experimental questions is needed to advance understanding. 3These issues are well illustrated by the fungi that form arbuscular mycorrhizas, the Glomeromycota. This ancient symbiosis of plants and fungi is responsible for phosphate uptake in most land plants, and the phylum is generally held to be species-poor and non-specific, with most members readily colonizing any plant species. Molecular techniques have shown both those assumptions to be unsafe, raising questions about what factors have promoted diversification in these fungi. One source of this genetic diversity may be functional diversity. 4Specificity of the mycorrhizal interaction between plants and fungi would have important ecosystem consequences. One example would be in the control of invasiveness in introduced plant species: surprisingly, naturalized plant species in Britain are disproportionately from mycorrhizal families, suggesting that these fungi may play a role in assisting invasion. 5What emerges from an attempt to relate biodiversity and ecosystem processes in soil is our extraordinary ignorance about the organisms involved. There are fundamental questions that are now answerable with new techniques and sufficient will, such as how biodiverse are natural soils? Do microbes have biogeography? Are there rare or even endangered microbes? [source] Soil restorative effects of mulching on aggregation and carbon sequestration in a Miamian soil in central OhioLAND DEGRADATION AND DEVELOPMENT, Issue 5 2003G. S. Saroa Abstract Soils play a key role in the global carbon cycle, and can be a source or a sink of atmospheric carbon (C). Thus, the effect of land use and management on soil C dynamics needs to be quantified. This study was conducted to assess: (1) the role of aggregation in enhancing soil organic carbon (SOC) and total soil nitrogen (TSN) concentrations for different mulch rates, (2) the association of SOC and TSN with different particle size fractions, and (3) the temporal changes in the SOC concentration within aggregate and particle size fractions with duration of mulching. Two experiments were initiated, one each in 1989 and 1996, on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) in central Ohio. Mulch treatments were 0, 8, and 16,Mg,ha,1,yr,1 without crop cultivation. Soil samples from 0,5,cm and 5,10,cm depths were obtained in November 2000; 4 and 11 years after initiating the experiments. Mulch rate significantly increased SOC and TSN concentrations in the 0,5,cm soil layer only. The variation in the SOC concentration attributed to the mulch rate was 41 per,cent after 4 years of mulching and 52 per,cent after 11 years of mulching. There were also differences in SOC and TSN concentrations among large aggregate size fractions, up to 2,mm size after 4 years and up to 0,5,mm after 11 years of mulching. There were also differences in SOC and TSN concentrations among particle size fractions. Variation in the SOC concentration in relation to particle size was attributed to clay by 45,51 per,cent, silt by 34,36 per,cent, and to sand fraction by 15,19 per,cent. Bulk of the TSN (62,67 per,cent) was associated with clay fraction and the rest was equally distributed between silt and sand fractions. The enrichment of SOC and TSN concentrations in the clay fraction increased with depth. The C:N ratio was not affected by the mulch rate, but differed significantly among particle size fractions; being in the order of sand >silt >clay. Copyright © 2003 John Wiley & Sons, Ltd. [source] Improved temperature response functions for models of Rubisco-limited photosynthesisPLANT CELL & ENVIRONMENT, Issue 2 2001C. J. Bernacchi ABSTRACT Predicting the environmental responses of leaf photosynthesis is central to many models of changes in the future global carbon cycle and terrestrial biosphere. The steady-state biochemical model of C3 photosynthesis of Farquhar et al. (Planta 149, 78,90, 1980) provides a basis for these larger scale predictions; but a weakness in the application of the model as currently parameterized is the inability to accurately predict carbon assimilation at the range of temperatures over which significant photosynthesis occurs in the natural environment. The temperature functions used in this model have been based on in vitro measurements made over a limited temperature range and require several assumptions of in vivo conditions. Since photosynthetic rates are often Rubisco-limited (ribulose, 1-5 bisphosphate carboxylase/oxygenase) under natural steady-state conditions, inaccuracies in the functions predicting Rubisco kinetic properties at different temperatures may cause significant error. In this study, transgenic tobacco containing only 10% normal levels of Rubisco were used to measure Rubisco-limited photosynthesis over a large range of CO2 concentrations. From the responses of the rate of CO2 assimilation at a wide range of temperatures, and CO2 and O2 concentrations, the temperature functions of Rubisco kinetic properties were estimated in vivo. These differed substantially from previously published functions. These new functions were then used to predict photosynthesis in lemon and found to faithfully mimic the observed pattern of temperature response. There was also a close correspondence with published C3 photosynthesis temperature responses. The results represent an improved ability to model leaf photosynthesis over a wide range of temperatures (10,40 °C) necessary for predicting carbon uptake by terrestrial C3 systems. [source] Forest Conversion and Degradation in Papua New Guinea 1972,2002BIOTROPICA, Issue 3 2009Phil L. Shearman ABSTRACT Quantifying forest change in the tropics is important because of the role these forests play in the conservation of biodiversity and the global carbon cycle. One of the world's largest remaining areas of tropical forest is located in Papua New Guinea. Here we show that change in its extent and condition has occurred to a greater extent than previously recorded. We assessed deforestation and forest degradation in Papua New Guinea by comparing a land-cover map from 1972 with a land-cover map created from nationwide high-resolution satellite imagery recorded since 2002. In 2002 there were 28,251,967 ha of tropical rain forest. Between 1972 and 2002, a net 15 percent of Papua New Guinea's tropical forests were cleared and 8.8 percent were degraded through logging. The drivers of forest change have been concentrated within the accessible forest estate where a net 36 percent were degraded or deforested through both forestry and nonforestry processes. Since 1972, 13 percent of upper montane forests have also been lost. We estimate that over the period 1990,2002, overall rates of change generally increased and varied between 0.8 and 1.8 percent/yr, while rates in commercially accessible forest have been far higher,having varied between 1.1 and 3.4 percent/yr. These rates are far higher than those reported by the FAO over the same period. We conclude that rapid and substantial forest change has occurred in Papua New Guinea, with the major drivers being logging in the lowland forests and subsistence agriculture throughout the country with comparatively minor contributions from forest fires, plantation establishment, and mining. RESUMEN Sopos long kisim gutpela save long senis i kamak long tropics em i wanpela bik pela samting long wanem, bikpela bus em wanpela hap we wok konsevason na carbon cycle bai inap kirapim gutpela wok. Insait long olgeta hap long world, PNG em wanpela hap we bikpela bus em i stap yet. Insait long dispela wok mipela soim olsem bikpela senis em i kamap long insait long bikpela bus na long hamas bikpela bus yumi gat. Nogat wanpela kain wok painimaut emi painim dispela senis bipo. Mipela lukluk gut long we olgeta bikpela bus i raus na we bus i kisim bagarap insait long, yia 1972 i kamap inap long yia 2002. Long yia 1972 mipela i usim map ol i kolim land cover map na long yia 2002 mipela lukluk long olgeta PNG high-resolution satellite imagery. Long yia 2002, 28,251,967 hectares bikpela bus i stap insait long Papua New Guinea. Long namel long 1972 igo inap long 2002, Papua New Guinea i lusim 15 percent long algeta bipela bus belong en. Insait long dispela 15 percent, 8.8 percent em i kamap bikos ol lain i katim diwai long salim. As bilong senisim bikela bus emi stap long ples we igat bikpela diwai long katim. Insait long dispela hap yumi lusim 36 percent, sampela we yumi inap long salim, tasol narapela emi bikos yumi rausim bus long wokim gaden or narapela kainkain pasin yumi wokim. Long 1972 i kamap inap long yia 2002, yumi lusim 13 percent long bikpela bus raonim ol bikpela maunten. Mipela painim olsem, long yia 1990 igo inap long yia 2002, long algeta kantri kain senis i wok long kamap bikpla. Senis istap insait long 0.8 igo inap long 1.8 percent long wan wan yia, tasol insait long wan wan liklik hap some pela i kisim bikpela senis, na ol narapela ino tumas. Long ol hap igat gutpela diwai long katim, senis i stat long 1.1 percent igo inap 3.4 percent. Dispela senis em i winim estimates we ol lain FAO i bin tokaut long em bipo. Long dispela wok painimaut, mipela iken tok olsem, as bilong dispela bikpela senis emi kamap long wanem ol i rausim na bagarapim bikpela bus. Dispela asua i kamap taim yumi rausim planti diwai tumas long salim na sampela taim yumi katim bus long wokim garden. Sampela taim bikpela paia tu i save kukim bikpela bus. [source] Estimating Fine Root Turnover in Tropical Forests along an Elevational Transect using MinirhizotronsBIOTROPICA, Issue 5 2008Sophie Graefe ABSTRACT Growth and death of fine roots represent an important carbon sink in forests. Our understanding of the patterns of fine root turnover is limited, in particular in tropical forests, despite its acknowledged importance in the global carbon cycle. We used the minirhizotron technique for studying the changes in fine root longevity and turnover along a 2000-m-elevational transect in the tropical mountain forests of South Ecuador. Fine root growth and loss rates were monitored during a 5-mo period at intervals of four weeks with each 10 minirhizotron tubes in three stands at 1050, 1890, and 3060 m asl. Average root loss rate decreased from 1.07 to 0.72 g/g/yr from 1050 to 1890 m, indicating an increase in mean root longevity with increasing elevation. However average root loss rate increased again toward the uppermost stand at 3060 m (1.30 g/g/yr). Thus, root longevity increased from lower montane to mid-montane elevation as would be expected from an effect of low temperature on root turnover, but it decreased further upslope despite colder temperatures. We suggest that adverse soil conditions may reduce root longevity at high elevations in South Ecuador, and are thus additional factors besides temperature that control root dynamics in tropical mountain forests. [source] Detecting Tropical Forests' Responses to Global Climatic and Atmospheric Change: Current Challenges and a Way ForwardBIOTROPICA, Issue 1 2007Deborah A. ClarkArticle first published online: 21 DEC 200 ABSTRACT Because of tropical forests' disproportionate importance for world biodiversity and for the global carbon cycle, we urgently need to understand any effects on these ecosystems from the ongoing changes in climate and atmosphere. This review, intended to complement existing data reviews on this topic, focuses on three major classes of challenges that we currently face when trying to detect and interpret directional changes in tropical forests. One is the very limited existing information on the historical context of study sites. Lasting effects from past climate, natural disturbances, and/or human activities could be significantly affecting current-day processes in tropical forests and need to be investigated for all active field sites. Second, while progress has been made in recent years on standardizing and refining research approaches, a number of methods- and data-limitations continue to affect efforts both to detect within-forest changes and to relate them to ongoing environmental change. Important outstanding needs are improved sampling designs, longer time-series of observations, filling key data gaps, and data access. Finally, forest responses to ongoing environmental change are complex. The effects of many simultaneously changing environmental factors are integrated by the plants, and their responses can involve significant lags, carryovers, and non-linearities. Specifying effects of individual environmental changes, however, is required for accurate ecosystem-process models and thus for projecting future impacts on these forests. After discussing these several types of challenges and ways to address them, I conclude with a priority agenda for this critical area of research. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp. RESUMEN Debido a la importancia desproporcionada de los bosques tropicales para la biodiversidad mundial y para el ciclo global del carbono, es urgente identificar los impactos sobre estos ecosistemas provocados por los cambios actuales en el clima y en la atmósfera. Este artículo de revisión, escrito con el propósito de complementar otras revisiones recientes, se enfoca en tres principales clases de retos que enfrentamos actualmente en la detección e interpretación de cambios direccionales en los bosques tropicales. Primero es la gran escasez de información histórica acerca de los sitios de estudio. Los procesos actuales en los bosques tropicales pueden reflejar los efectos prolongados del pasado climático, las perturbaciones naturales y/o las actividades humanas, por lo que deben de ser investigados en todos los sitios actuales de estudio. Segundo, a pesar de avances recientes en la estandarización y el refinamiento de los métodos de investigación, nuestra habilidad para detectar cambios en los bosques y ligarlos a los grandes cambios ambientales sigue siendo limitada. Para garantizar avances en el área se requiere mejorar los diseños de muestreo, extender las series de observación en el tiempo a plazos mayores, llenar ciertos vacíos claves en el conocimiento, y facilitar el acceso a los datos existentes. Por último, se requiere de enfoques que tomen en cuenta la complejidad de las respuestas de los bosques a los cambios ambientales. Las plantas integran los efectos de cambios simultáneos en múltiples factores ambientales, y sus respuestas pueden ser no lineales e incluir efectos de retraso y acarreo. No obstante, es importante también especificar los efectos individuales de los diferentes cambios ambientales para afinar los modelos de procesos a nivel del ecosistema, y así poder proyectar los impactos futuros sobre estos bosques. Después de discutir dichos retos y estrategias para enfrentarlos, concluyo con una agenda de prioridades para esta área crítica de investigación. [source] | |||||||||||||