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Serge Rambal - One of the best experts on this subject based on the ideXlab platform.
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growth duration is a better predictor of stem increment than carbon supply in a mediterranean oak forest implications for assessing forest productivity under climate change
New Phytologist, 2015Co-Authors: Morine Lempereur, Serge Rambal, Jeanmarc Ourcival, Nicolas K Martinstpaul, Alain Rocheteau, Claire Damesin, R JoffreAbstract:Understanding whether tree growth is limited by carbon gain (source limitation) or by the direct effect of environmental factors such as water deficit or temperature (sink limitation) is crucial for improving projections of the effects of climate change on forest productivity. We studied the relationships between tree basal area (BA) variations, eddy covariance carbon fluxes, predawn water potential (Ψpd ) and temperature at different timescales using an 8-yr dataset and a rainfall Exclusion Experiment in a Quercus ilex Mediterranean coppice. At the daily timescale, during periods of low temperature (< 5°C) and high water deficit (< -1.1 MPa), gross primary productivity and net ecosystem productivity remained positive whereas the stem increment was nil. Thus, stem increment appeared limited by drought and temperature rather than by carbon input. Annual growth was accurately predicted by the duration of BA increment during spring (Δtt0-t1 ). The onset of growth (t0 ) was related to winter temperatures and the summer interruption of growth (t1 ) to a threshold Ψpd value of -1.1 MPa. We suggest that using environmental drivers (i.e. drought and temperature) to predict stem growth phenology can contribute to an improvement in vegetation models and may change the current projections of Mediterranean forest productivity under climate change scenarios.
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the temporal response to drought in a mediterranean evergreen tree comparing a regional precipitation gradient and a throughfall Exclusion Experiment
Global Change Biology, 2013Co-Authors: Nicolas K Martinstpaul, Jeanmarc Limousin, Serge Rambal, Helene Vogtschilb, Jesus Rodriguezcalcerrada, Damien Longepierre, Laurent MissonAbstract:Like many midlatitude ecosystems, Mediterranean forests will suffer longer and more intense droughts with the ongoing climate change. The responses to drought in long-lived trees differ depending on the time scale considered, and short-term responses are currently better understood than longer term acclimation. We assessed the temporal changes in trees facing a chronic reduction in water availability by comparing leaf-scale physiological traits, branch-scale hydraulic traits, and stand-scale biomass partitioning in the evergreen Quercus ilex across a regional precipitation gradient (long-term changes) and in a partial throughfall Exclusion Experiment (TEE, medium term changes). At the leaf scale, gas exchange, mass per unit area and nitrogen concentration showed homeostatic responses to drought as they did not change among the sites of the precipitation gradient or in the Experimental treatments of the TEE. A similar homeostatic response was observed for the xylem vulnerability to cavitation at the branch scale. In contrast, the ratio of leaf area over sapwood area (LA/SA) in young branches exhibited a transient response to drought because it decreased in response to the TEE the first 4 years of treatment, but did not change among the sites of the gradient. At the stand scale, leaf area index (LAI) decreased, and the ratios of stem SA to LAI and of fine root area to LAI both increased in trees subjected to throughfall Exclusion and from the wettest to the driest site of the gradient. Taken together, these results suggest that acclimation to chronic drought in long-lived Q. ilex is mediated by changes in hydraulic allometry that shift progressively from low (branch) to high (stand) organizational levels, and act to maintain the leaf water potential within the range of xylem hydraulic function and leaf photosynthetic assimilation.
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mast seeding and flowering in mediterranean oak woodlands under increasing drought results from a long term dataset and from a rainfall Exclusion Experiment
2010Co-Authors: Ignacio Manuel Perezramos, Jeanmarc Limousin, Jeanmarc Ourcival, Serge RambalAbstract:12 pages, 4 figures, 3 tables. I. M. Perez-Ramos was supported by a postdoctoral fellowship from the Spanish Ministry of Science and Innovation. We are grateful to R. Rodriguez-Cortina for assistance in the field. El titulo que figura en el Repositorio Digital CSIC, corresponde a la version pre-print autorizada. En Ecology 91(10) aparece titulado: Mast seeding under increasing drought: results from a long-term data set and from a rainfall Exclusion Experiment.
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mast seeding under increasing drought results from a long term data set and from a rainfall Exclusion Experiment
Ecology, 2010Co-Authors: Ignacio Manuel Perezramos, Jeanmarc Limousin, Jeanmarc Ourcival, Serge RambalAbstract:Mast seeding, the synchronous, highly variable seed production among years, is very common in tree species, but there is no consensus about its main causes and the main environmental factors affecting it. In this study, we first analyze a long-term data set on reproductive and vegetative growth of Quercus ilex in a mediterranean woodland in order to identify the main environmental drivers of interannual variation in flower and seed production and contrast the impact of climate vs. adaptive factors as main causes of masting. Second, we conducted an Experiment of rainfall Exclusion to evaluate the effects of an increasing drought (simulating predictions of global change models) on both reproductive processes. The annual seed crop was always affected by environmental factors related to the precipitation pattern, these abiotic factors disrupting the fruiting process at different periods of time. Seed production was strongly dependent upon water availability for the plant at initial (spring) and advanced (summer) stages of the acorn maturation cycle, whereas the final step of seed development was negatively affected by the frequency of torrential-rain events. We also found clear evidence that seed masting in the study species is not only regulated by selective endogenous rhythms, but is mainly a physiological response to the variable environment. Our results from the rainfall Exclusion Experiment corroborated the conclusions obtained from the 26-year fruiting record and demonstrated that the high interannual variation in seed crop was mainly determined by the success in seed development rather than by the flowering effort. Under a global change scenario, it could be expected that the drier conditions predicted by climate models reinforce the negative effects of summer drought on seed production, leading to negative consequences for tree recruitment and forest dynamics.
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functional changes in the control of carbon fluxes after 3 years of increased drought in a mediterranean evergreen forest
Global Change Biology, 2009Co-Authors: Laurent Misson, Jeanmarc Limousin, Serge Rambal, Jeanmarc Ourcival, Alain Rocheteau, Raquel RodriguezAbstract:Our objective was to test how a long-term increased water limitation affects structural and functional properties of a Mediterranean ecosystem, and how these changes modify the response of the main carbon fluxes to climatic controls. In 2003, a 27% throughfall Exclusion Experiment was installed in a Quercus ilex L. forest in France. Gross primary production (GPP), ecosystem respiration (R ECO ) and net ecosystem exchange (NEE) were estimated in a control and a dry treatment. Decreasing throughfall decreased GPP by 14% and had a smaller effect on R ECO (-12%), especially soil respiration R S (—11%). Interannual variability of GPP (29%) was higher than for R ECO (12%). Error propagation was used to estimates uncertainties in the NEE fluxes, which ranged from 3% to 10% in the control treatment but up to 167% for NEE in the dry treatment because more steps and data types were involved in the scaling. After 3 years of throughfall Exclusion, we found no acclimation of R s to climatic drivers. Functional properties of the response of R s to soil water, temperature and rain pulse remained similar in the control and the dry treatments. A diurnal clockwise hysteresis in R s was probably controlled by canopy photosynthesis with a 3h lag. The proportion of diurnal variation of respiration due to photosynthesis was similar in all treatments (4-5%). Because of the characteristic of rain in Mediterranean climates, a continuous decrease of water input in these environments have an effect on topsoil water and consequently on R S only during short periods when rainfall is characterized by infrequent and small events that does not allow the topsoil to reach field capacity and does not allow to dry completely. However, in the longer term, we expect a stronger decrease in R S in the dry treatment driven by the decrease in GPP.
Jeanmarc Limousin - One of the best experts on this subject based on the ideXlab platform.
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the temporal response to drought in a mediterranean evergreen tree comparing a regional precipitation gradient and a throughfall Exclusion Experiment
Global Change Biology, 2013Co-Authors: Nicolas K Martinstpaul, Jeanmarc Limousin, Serge Rambal, Helene Vogtschilb, Jesus Rodriguezcalcerrada, Damien Longepierre, Laurent MissonAbstract:Like many midlatitude ecosystems, Mediterranean forests will suffer longer and more intense droughts with the ongoing climate change. The responses to drought in long-lived trees differ depending on the time scale considered, and short-term responses are currently better understood than longer term acclimation. We assessed the temporal changes in trees facing a chronic reduction in water availability by comparing leaf-scale physiological traits, branch-scale hydraulic traits, and stand-scale biomass partitioning in the evergreen Quercus ilex across a regional precipitation gradient (long-term changes) and in a partial throughfall Exclusion Experiment (TEE, medium term changes). At the leaf scale, gas exchange, mass per unit area and nitrogen concentration showed homeostatic responses to drought as they did not change among the sites of the precipitation gradient or in the Experimental treatments of the TEE. A similar homeostatic response was observed for the xylem vulnerability to cavitation at the branch scale. In contrast, the ratio of leaf area over sapwood area (LA/SA) in young branches exhibited a transient response to drought because it decreased in response to the TEE the first 4 years of treatment, but did not change among the sites of the gradient. At the stand scale, leaf area index (LAI) decreased, and the ratios of stem SA to LAI and of fine root area to LAI both increased in trees subjected to throughfall Exclusion and from the wettest to the driest site of the gradient. Taken together, these results suggest that acclimation to chronic drought in long-lived Q. ilex is mediated by changes in hydraulic allometry that shift progressively from low (branch) to high (stand) organizational levels, and act to maintain the leaf water potential within the range of xylem hydraulic function and leaf photosynthetic assimilation.
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mast seeding and flowering in mediterranean oak woodlands under increasing drought results from a long term dataset and from a rainfall Exclusion Experiment
2010Co-Authors: Ignacio Manuel Perezramos, Jeanmarc Limousin, Jeanmarc Ourcival, Serge RambalAbstract:12 pages, 4 figures, 3 tables. I. M. Perez-Ramos was supported by a postdoctoral fellowship from the Spanish Ministry of Science and Innovation. We are grateful to R. Rodriguez-Cortina for assistance in the field. El titulo que figura en el Repositorio Digital CSIC, corresponde a la version pre-print autorizada. En Ecology 91(10) aparece titulado: Mast seeding under increasing drought: results from a long-term data set and from a rainfall Exclusion Experiment.
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mast seeding under increasing drought results from a long term data set and from a rainfall Exclusion Experiment
Ecology, 2010Co-Authors: Ignacio Manuel Perezramos, Jeanmarc Limousin, Jeanmarc Ourcival, Serge RambalAbstract:Mast seeding, the synchronous, highly variable seed production among years, is very common in tree species, but there is no consensus about its main causes and the main environmental factors affecting it. In this study, we first analyze a long-term data set on reproductive and vegetative growth of Quercus ilex in a mediterranean woodland in order to identify the main environmental drivers of interannual variation in flower and seed production and contrast the impact of climate vs. adaptive factors as main causes of masting. Second, we conducted an Experiment of rainfall Exclusion to evaluate the effects of an increasing drought (simulating predictions of global change models) on both reproductive processes. The annual seed crop was always affected by environmental factors related to the precipitation pattern, these abiotic factors disrupting the fruiting process at different periods of time. Seed production was strongly dependent upon water availability for the plant at initial (spring) and advanced (summer) stages of the acorn maturation cycle, whereas the final step of seed development was negatively affected by the frequency of torrential-rain events. We also found clear evidence that seed masting in the study species is not only regulated by selective endogenous rhythms, but is mainly a physiological response to the variable environment. Our results from the rainfall Exclusion Experiment corroborated the conclusions obtained from the 26-year fruiting record and demonstrated that the high interannual variation in seed crop was mainly determined by the success in seed development rather than by the flowering effort. Under a global change scenario, it could be expected that the drier conditions predicted by climate models reinforce the negative effects of summer drought on seed production, leading to negative consequences for tree recruitment and forest dynamics.
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functional changes in the control of carbon fluxes after 3 years of increased drought in a mediterranean evergreen forest
Global Change Biology, 2009Co-Authors: Laurent Misson, Jeanmarc Limousin, Serge Rambal, Jeanmarc Ourcival, Alain Rocheteau, Raquel RodriguezAbstract:Our objective was to test how a long-term increased water limitation affects structural and functional properties of a Mediterranean ecosystem, and how these changes modify the response of the main carbon fluxes to climatic controls. In 2003, a 27% throughfall Exclusion Experiment was installed in a Quercus ilex L. forest in France. Gross primary production (GPP), ecosystem respiration (R ECO ) and net ecosystem exchange (NEE) were estimated in a control and a dry treatment. Decreasing throughfall decreased GPP by 14% and had a smaller effect on R ECO (-12%), especially soil respiration R S (—11%). Interannual variability of GPP (29%) was higher than for R ECO (12%). Error propagation was used to estimates uncertainties in the NEE fluxes, which ranged from 3% to 10% in the control treatment but up to 167% for NEE in the dry treatment because more steps and data types were involved in the scaling. After 3 years of throughfall Exclusion, we found no acclimation of R s to climatic drivers. Functional properties of the response of R s to soil water, temperature and rain pulse remained similar in the control and the dry treatments. A diurnal clockwise hysteresis in R s was probably controlled by canopy photosynthesis with a 3h lag. The proportion of diurnal variation of respiration due to photosynthesis was similar in all treatments (4-5%). Because of the characteristic of rain in Mediterranean climates, a continuous decrease of water input in these environments have an effect on topsoil water and consequently on R S only during short periods when rainfall is characterized by infrequent and small events that does not allow the topsoil to reach field capacity and does not allow to dry completely. However, in the longer term, we expect a stronger decrease in R S in the dry treatment driven by the decrease in GPP.
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long term transpiration change with rainfall decline in a mediterranean quercus ilex forest
Global Change Biology, 2009Co-Authors: Jeanmarc Limousin, Serge Rambal, Jeanmarc Ourcival, Richard Joffre, Alain Rocheteau, R RodriguezcortinaAbstract:In the Mediterranean basin, precipitation is expected to decline as a consequence of climate change. The response of a Quercus ilex forest in southern France to such a decline in water availability was studied using a 4-year throughfall Exclusion Experiment. Seasonal courses of sap flow and leaf water potential were obtained from 2004 to 2007 and used to characterize tree water relations in a control and a dry treatment. The Experiment reduced the average precipitation input to the soil by 29%, and resulted in a 23% reduction in annual transpiration. Soil water potential was significantly lower in the dry treatment only during summer drought, but transpiration was reduced all year round even during well-watered periods. Despite a tight stomatal control over transpiration, whole-tree hydraulic conductance was found to be lower in the trees growing in the driest conditions. This reduction in water transport capacity was observed jointly with a reduction in leaf transpiring area. Canopy leaf area decreased by 18% in the dry treatment as a consequence of the throughfall Exclusion, which was found to validate the ecohydrological equilibrium theory.
Jeanmarc Ourcival - One of the best experts on this subject based on the ideXlab platform.
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growth duration is a better predictor of stem increment than carbon supply in a mediterranean oak forest implications for assessing forest productivity under climate change
New Phytologist, 2015Co-Authors: Morine Lempereur, Serge Rambal, Jeanmarc Ourcival, Nicolas K Martinstpaul, Alain Rocheteau, Claire Damesin, R JoffreAbstract:Understanding whether tree growth is limited by carbon gain (source limitation) or by the direct effect of environmental factors such as water deficit or temperature (sink limitation) is crucial for improving projections of the effects of climate change on forest productivity. We studied the relationships between tree basal area (BA) variations, eddy covariance carbon fluxes, predawn water potential (Ψpd ) and temperature at different timescales using an 8-yr dataset and a rainfall Exclusion Experiment in a Quercus ilex Mediterranean coppice. At the daily timescale, during periods of low temperature (< 5°C) and high water deficit (< -1.1 MPa), gross primary productivity and net ecosystem productivity remained positive whereas the stem increment was nil. Thus, stem increment appeared limited by drought and temperature rather than by carbon input. Annual growth was accurately predicted by the duration of BA increment during spring (Δtt0-t1 ). The onset of growth (t0 ) was related to winter temperatures and the summer interruption of growth (t1 ) to a threshold Ψpd value of -1.1 MPa. We suggest that using environmental drivers (i.e. drought and temperature) to predict stem growth phenology can contribute to an improvement in vegetation models and may change the current projections of Mediterranean forest productivity under climate change scenarios.
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mast seeding and flowering in mediterranean oak woodlands under increasing drought results from a long term dataset and from a rainfall Exclusion Experiment
2010Co-Authors: Ignacio Manuel Perezramos, Jeanmarc Limousin, Jeanmarc Ourcival, Serge RambalAbstract:12 pages, 4 figures, 3 tables. I. M. Perez-Ramos was supported by a postdoctoral fellowship from the Spanish Ministry of Science and Innovation. We are grateful to R. Rodriguez-Cortina for assistance in the field. El titulo que figura en el Repositorio Digital CSIC, corresponde a la version pre-print autorizada. En Ecology 91(10) aparece titulado: Mast seeding under increasing drought: results from a long-term data set and from a rainfall Exclusion Experiment.
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mast seeding under increasing drought results from a long term data set and from a rainfall Exclusion Experiment
Ecology, 2010Co-Authors: Ignacio Manuel Perezramos, Jeanmarc Limousin, Jeanmarc Ourcival, Serge RambalAbstract:Mast seeding, the synchronous, highly variable seed production among years, is very common in tree species, but there is no consensus about its main causes and the main environmental factors affecting it. In this study, we first analyze a long-term data set on reproductive and vegetative growth of Quercus ilex in a mediterranean woodland in order to identify the main environmental drivers of interannual variation in flower and seed production and contrast the impact of climate vs. adaptive factors as main causes of masting. Second, we conducted an Experiment of rainfall Exclusion to evaluate the effects of an increasing drought (simulating predictions of global change models) on both reproductive processes. The annual seed crop was always affected by environmental factors related to the precipitation pattern, these abiotic factors disrupting the fruiting process at different periods of time. Seed production was strongly dependent upon water availability for the plant at initial (spring) and advanced (summer) stages of the acorn maturation cycle, whereas the final step of seed development was negatively affected by the frequency of torrential-rain events. We also found clear evidence that seed masting in the study species is not only regulated by selective endogenous rhythms, but is mainly a physiological response to the variable environment. Our results from the rainfall Exclusion Experiment corroborated the conclusions obtained from the 26-year fruiting record and demonstrated that the high interannual variation in seed crop was mainly determined by the success in seed development rather than by the flowering effort. Under a global change scenario, it could be expected that the drier conditions predicted by climate models reinforce the negative effects of summer drought on seed production, leading to negative consequences for tree recruitment and forest dynamics.
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functional changes in the control of carbon fluxes after 3 years of increased drought in a mediterranean evergreen forest
Global Change Biology, 2009Co-Authors: Laurent Misson, Jeanmarc Limousin, Serge Rambal, Jeanmarc Ourcival, Alain Rocheteau, Raquel RodriguezAbstract:Our objective was to test how a long-term increased water limitation affects structural and functional properties of a Mediterranean ecosystem, and how these changes modify the response of the main carbon fluxes to climatic controls. In 2003, a 27% throughfall Exclusion Experiment was installed in a Quercus ilex L. forest in France. Gross primary production (GPP), ecosystem respiration (R ECO ) and net ecosystem exchange (NEE) were estimated in a control and a dry treatment. Decreasing throughfall decreased GPP by 14% and had a smaller effect on R ECO (-12%), especially soil respiration R S (—11%). Interannual variability of GPP (29%) was higher than for R ECO (12%). Error propagation was used to estimates uncertainties in the NEE fluxes, which ranged from 3% to 10% in the control treatment but up to 167% for NEE in the dry treatment because more steps and data types were involved in the scaling. After 3 years of throughfall Exclusion, we found no acclimation of R s to climatic drivers. Functional properties of the response of R s to soil water, temperature and rain pulse remained similar in the control and the dry treatments. A diurnal clockwise hysteresis in R s was probably controlled by canopy photosynthesis with a 3h lag. The proportion of diurnal variation of respiration due to photosynthesis was similar in all treatments (4-5%). Because of the characteristic of rain in Mediterranean climates, a continuous decrease of water input in these environments have an effect on topsoil water and consequently on R S only during short periods when rainfall is characterized by infrequent and small events that does not allow the topsoil to reach field capacity and does not allow to dry completely. However, in the longer term, we expect a stronger decrease in R S in the dry treatment driven by the decrease in GPP.
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long term transpiration change with rainfall decline in a mediterranean quercus ilex forest
Global Change Biology, 2009Co-Authors: Jeanmarc Limousin, Serge Rambal, Jeanmarc Ourcival, Richard Joffre, Alain Rocheteau, R RodriguezcortinaAbstract:In the Mediterranean basin, precipitation is expected to decline as a consequence of climate change. The response of a Quercus ilex forest in southern France to such a decline in water availability was studied using a 4-year throughfall Exclusion Experiment. Seasonal courses of sap flow and leaf water potential were obtained from 2004 to 2007 and used to characterize tree water relations in a control and a dry treatment. The Experiment reduced the average precipitation input to the soil by 29%, and resulted in a 23% reduction in annual transpiration. Soil water potential was significantly lower in the dry treatment only during summer drought, but transpiration was reduced all year round even during well-watered periods. Despite a tight stomatal control over transpiration, whole-tree hydraulic conductance was found to be lower in the trees growing in the driest conditions. This reduction in water transport capacity was observed jointly with a reduction in leaf transpiring area. Canopy leaf area decreased by 18% in the dry treatment as a consequence of the throughfall Exclusion, which was found to validate the ecohydrological equilibrium theory.
Karlheinz Haberle - One of the best experts on this subject based on the ideXlab platform.
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growth and mortality of norway spruce and european beech in monospecific and mixed species stands under natural episodic and Experimentally extended drought results of the kroof throughfall Exclusion Experiment
Trees-structure and Function, 2020Co-Authors: Hans Pretzsch, Karlheinz Haberle, Thorsten E E Grams, Karin Pritsch, Taryn L Bauerle, Thomas RotzerAbstract:Under severe drought, growth of Norway spruce suffered much more than European beech. Norway spruce benefited from growing in the environment of beech, and both species acclimated slightly to 5 years of Experimentally extended drought. Recent studies show that the detrimental effects of drought on stand growth are mitigated when the stand contains mixed tree species. We analysed the growth responses of Norway spruce and European beech to episodic and Experimentally extended drought in intra- and inter-specific mature stands. We used annual diameter growth records dating back to 1998 to determine the impact of the natural episodic drought in 2003 and 2015. To analyse extended drought, spruce and beech trees were exposed to extreme drought under automatic throughfall Exclusion roofs from 2014 to 2018. The growth of spruce in an inter-specific environment with beech was 20–50% less affected by natural episodic drought compared with an intra-specific constellation. When beech grew in an inter-specific environment, it was by 23% more affected by drought compared to intra-specific conditions, but seemed to recover faster. The induced drought from 2014 to 2018 resulted in a strong growth reduction in the first year particularly for spruce, followed by a slight acclimation to the dry conditions. Beech acclimated and recovered faster than spruce across all growing conditions, while spruce only acclimatized faster in the environment of beech. Both species showed a higher mortality under induced drought compared with the controls; for spruce, the mortality rate was fivefold higher compared to the long-term mortality. The long-term moderate-growth stabilization and the growth increase after the 5-year exposure to drought suggest a gradual acclimation to drought by beech. The resistance and acclimation to drought of spruce when growing in mixture should be considered when designing resource efficient and productive mixed conifer-broadleaved stands for future climates.
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acclimation of branch and leaf hydraulics in adult fagus sylvatica and picea abies in a forest through fall Exclusion Experiment
Tree Physiology, 2018Co-Authors: Martina Tomasella, Barbara Beikircher, Karlheinz Haberle, Benjamin D Hesse, Christian Kallenbach, Rainer Matyssek, Stefan MayrAbstract:Decreasing water availability due to climate change poses the question of whether and to what extent tree species are able to hydraulically acclimate and how hydraulic traits of stems and leaves are coordinated under drought. In a through-fall Exclusion Experiment, hydraulic acclimation was analyzed in a mixed forest stand of Fagus sylvatica L. and Picea abies (L.) Karst. In drought-stressed (TE, through-fall Exclusion over 2 years) and control (CO) trees, hydraulic vulnerability was studied in branches as well as in leaves (F. sylvatica) and end-twigs (P. abies, entirely formed during the drought period) sampled at the same height in sun-exposed portions of the tree crown. In addition, relevant xylem anatomical traits and leaf pressure-volume relations were analyzed. The TE trees reached pre-dawn water potentials down to -1.6 MPa. In both species, water potentials at 50% loss of xylem hydraulic conductivity were ~0.4 MPa more negative in TE than in CO branches. Foliage hydraulic vulnerability (expressed as water potential at 50% loss of leaf/end-twig hydraulic conductance) and water potential at turgor loss point were also, respectively, 0.4 and 0.5 MPa lower in TE trees. Minor differences were observed in conduit mean hydraulic diameter and cell wall reinforcement. Our findings indicate significant and fast hydraulic acclimation under relatively mild drought in both tree species. Acclimation was well coordinated between branches and foliage, which might be essential for survival and productivity of mature trees under future drought periods.
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mixed norway spruce picea abies l karst and european beech fagus sylvatica l stands under drought from reaction pattern to mechanism
Trees-structure and Function, 2014Co-Authors: Hans Pretzsch, Karlheinz Haberle, Rainer Matyssek, Thomas Rotzer, Thorsten E E Grams, K Pritsch, R Kerner, Jean Charles MunchAbstract:Key message We review causes of synergies in mixed-species stands, develop guiding hypotheses for revealing their mechanisms and present a rainfall Exclusion Experiment along with a transect (KROOF) for exploring drought effects.
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mixed norway spruce picea abies l karst and european beech fagus sylvatica l stands under drought from reaction pattern to mechanism
Trees-structure and Function, 2014Co-Authors: Hans Pretzsch, Karlheinz Haberle, Rainer Matyssek, Thomas Rotzer, Thorsten E E Grams, K Pritsch, R Kerner, Jean Charles MunchAbstract:We review causes of synergies in mixed-species stands, develop guiding hypotheses for revealing their mechanisms and present a rainfall Exclusion Experiment along with a transect (KROOF) for exploring drought effects. While monocultures have dominated forest research and practice in the past, in face of growing resource scarcity and climate change, mixed-species stands are on the advance. Long-term observations show that mixed-species stands frequently over-yield monocultures, and they further suggest that the over-yielding is often higher on poor than on fertile sites and in low-growth than in high-growth years. However, the underlying causes have not yet been clarified. We start with a review of, among others, hydraulic redistribution, complementary eco-physiological traits, and ectomycorrhizal networks as possible causes behind the observed productivity gains in mixed-species stands. Then, we develop guiding hypotheses for further exploration of synergies in mixed-species stands. Finally, we introduce into the concept and model approach of the rainfall Exclusion Experiment for examining the role of water supply in mixed versus pure forest stands of spruce and beech. At the Kranzberg site, six plots are equipped with water retention roofs, which only close during rain events. The remaining six plots serve as non-roofed control. Together with the rainfall Exclusion Experiment, an ecological gradient with five sites extending through SE-Germany forms the “Kranzberg Roof Experiment” (in short KROOF). Kranzberg Forest is a part of this gradient from moist to dry conditions, with each site providing mixed and pure associations each of spruce and beech. The ecophysiological approach will be complemented by tree ring analysis and modelling of productivity of the tree associations under intense drought.
K Dhileepan - One of the best experts on this subject based on the ideXlab platform.
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seasonal variation in the effectiveness of the leaf feeding beetle zygogramma bicolorata coleoptera chrysomelidae and stem galling moth epiblema strenuana lepidoptera tortricidae as biocontrol agents on the weed parthenium hysterophorus asteraceae
Bulletin of Entomological Research, 2003Co-Authors: K DhileepanAbstract:Variation in the effectiveness of biocontrol agents on the weed Parthenium hysterophorus L. was evaluated at two properties (Mount Panorama and Plain Creek) in Queensland, Australia for four years (1996-2000) using a pesticide Exclusion Experiment. At Mount Panorama, higher levels of defoliation by the leaf-feeding beetle Zygogramma bicolorata Pallister and galling by the moth Epiblema strenuana Walker in 1996-97 coincided with an above average summer rainfall, but in the following three years with below average summer rainfall the defoliation and galling levels were significantly lower. Biocontrol had significant negative impact on the weed only in 1996-97 with no major impact in the following three years. At Plain Creek, galling by E. strenuana was evident in all the four years, but varied significantly between years due to non-synchrony between P. hysterophorus germination and E. strenuana emergence. At Plain Creek biocontrol had limited impact on the weed in 1996-97 and 1997-98, with no significant impact in the following two years. Over the 4-year period, defoliation and galling resulted in 70% reduction in the soil seed bank at Mount Panorama, but the reduction in the soil seed bank at Plain Creek due to galling was not significant. Effectiveness of Z. bicolorata and E. strenuana was dependent on weather conditions and as a result had only limited impact on the weed in three out of four years.
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effectiveness of introduced biocontrol insects on the weed parthenium hysterophorus asteraceae in australia
Bulletin of Entomological Research, 2001Co-Authors: K DhileepanAbstract:Six species of insects and a rust fungus have been successfully established for biocontrol of the weed Parthenium hysterophorus L. in Queensland, Australia. Effectiveness of biocontrol insects was evaluated at two properties in Queensland during 1996‐97 based on an Exclusion Experiment using insecticides. Partheniuminfested plots with and without biocontrol insects were sampled at monthly intervals and the impact of biocontrol insects on parthenium at individual plant and whole population levels monitored. Biocontrol insects were more effective at Mt Panorama (central Queensland) than at Plain Creek (north Queensland). At Mt Panorama, the leaf-feeding beetle Zygogramma bicolorata Pallister caused 96% defoliation and the stem-galling moth Epiblema strenuana Walker affected 100% of the plants, resulting in reductions of 90% in weed density, 40% in plant height, and 82% in flower production. Exclusion of biocontrol insects resulted in a 52% increase in seedling emergence and a seven-fold increase in the soil seed bank in the following season. At Plain Creek, E. strenuana was the only prominent agent. It affected 92% of the plants and prevented 32% of plants from producing any flowers, reduced plant height by 40% and flower production by 49%, but did not reduce the plant biomass, weed density or soil seed bank. However, Exclusion of biocontrol insects resulted in an eight-fold increase in the soil seed bank in the following season.