Fontes L, Bontemps JD, Bugmann H, Van Oijen M, Gracia C, KramerK, Lindner M, Rötzer T, Skovsgaard JP (2010) Models for supporting forest management in a changing environment. Forest Systems 19: 8-29.
Gracia C (2010) Biocombustibles: Energia o aliment. Omniscellula 25: 21-27.
Vicente-Serrano SM, Lasanta T, Gracia C (2010) Aridification determines changes in forest growth in Pinus halepensis forests under semiarid Mediterranean climate conditions. Agricultural and Forest Meteorology 150: 614-628.
Requardt A, Siwe R, Riedel T, Köhl M, Tröltzsch K, Varis S, Travaglini D, Corona P, Sanchez A, Vayreda J, Gracia C, Camia A, San Miguel J (2010) Pilot study on harmonising national forest inventories in Europe. European Commission. Joint Research Centre 136 pp.
Peñuelas J, Gracia C, Filella I, Jump A, Carnicer J, Coll M, Lloret F, Curiel J, Estiarte M, Rutishauser T, Ogaya R, LLusiá J, Sardans J (2010) Intégration des effets du changement climatique sur les forêts méditerranéennes : observation, expérimentation, modélisation et gestion p. 351. Introducing the climate change effects on Mediterranean forest ecosystems: observation, experimentation, simul ation and management . Forêt Méditerranéenne XXXI, nº 4 pp. 357. ISSN 0245-484X.
Keenan T., Sabate S., Gracia C. (2010) Soil water stress and coupled photosynthesis-conductance models: Bridging the gap between conflicting reports on the relative roles of stomatal, mesophyll conductance and biochemical limitations to photosynthesis. Agricultural and Forest Meteorology. 150: 443-453.EnllaçDoi: 10.1016/j.agrformet.2010.01.008
Various plant responses to water stress have been reported, but conflicting reports as to which limiting process is the most important and ecophysiologicaly relevant during water stressed periods make it difficult to confidently model terrestrial CO2 and water flux responses. It has become increasingly accepted that mesophyll conductance could play a role in regulating photosynthesis during periods of water stress. We adapt the Farquhar-BB-type canopy photosynthesis-conductance model coupling to incorporate mesophyll conductance, embed it in an ecophysiological forest model and use it to simulate the effects of seasonal soil water stress on canopy CO2 and water fluxes at a Mediterranean Quercus ilex forest. Tests of various hypotheses regarding the relative roles of stomatal conductance limitations (SCL), mesophyll conductance limitations (MCL) and biochemical limitations (BL) confirmed that during water stressed periods, applying only BL allows for the accurate simulation of CO2 and water fluxes. Neither SCL nor MCL alone could accurately reproduce the observed CO2 and water fluxes. However, a combination of both MCL and SCL was successful at reproducing water stress induced reductions in CO2 and water fluxes, suggesting that mesophyll conductance could bridge the gap between conflicting reports on the processes behind responses to water stress in the field. © 2010 Elsevier B.V.
Keenan T., Sabate S., Gracia C. (2010) The importance of mesophyll conductance in regulating forest ecosystem productivity during drought periods. Global Change Biology. 16: 1019-1034.EnllaçDoi: 10.1111/j.1365-2486.2009.02017.x
Water availability is the most limiting factor to global plant productivity, yet photosynthetic responses to seasonal drought cycles are poorly understood, with conflicting reports on which limiting process is the most important during drought. We address the problem using a model-data synthesis approach to look at canopy level fluxes, integrating twenty years of half hour data gathered by the FLUXNET network across six Mediterranean sites. The measured canopy level, water and carbon fluxes were used, together with an inverse canopy ecophysiological model, to estimate the bulk canopy conductance, bulk mesophyll conductance, and the canopy scale carbon pools in both the intercellular spaces and at the site of carboxylation in the chloroplasts. Thus the roles of stomatal and mesophyll conductance in the regulation of internal carbon pools and photosynthesis could be separated. A quantitative limitation analysis allowed for the relative seasonal responses of stomatal, mesophyll, and biochemical limitations to be gauged. The concentration of carbon in the chloroplast was shown to be a potentially more reliable estimator of assimilation rates than the intercellular carbon concentration. Both stomatal conductance limitations and mesophyll conductance limitations were observed to regulate the response of photosynthesis to water stress in each of the six species studied. The results suggest that mesophyll conductance could bridge the gap between conflicting reports on plant responses to soil water stress, and that the inclusion of mesophyll conductance in biosphere-atmosphere transfer models may improve their performance, in particular their ability to accurately capture the response of terrestrial vegetation productivity to drought. © 2009 Blackwell Publishing Ltd.
Keenan T, Garcia R, Friend AD, Zaehle S, Gracia C, Sabate S (2009) Improved understanding of drought controls on seasonal variation in Mediterranean forest canopy CO2 and water fluxes through combined in situ measurements and ecosystem modelling. Biogeosciences 6: 1423-1444.
Cotillas M., Sabaté S., Gracia C., Espelta J.M. (2009) Growth response of mixed mediterranean oak coppices to rainfall reduction. Could selective thinning have any influence on it?. Forest Ecology and Management. 258: 1677-1683.EnllaçDoi: 10.1016/j.foreco.2009.07.033
Climate change is one of the major challenges for ecosystem conservation. One of the most vulnerable areas to climate change is the Mediterranean Basin which is expected to suffer important changes in temperature and precipitation in the next few decades, leading to a warmer and dryer climate. Therefore, it is necessary to determine species-specific responses to increased drought to predict possible future changes in the structure and composition of Mediterranean forests, as well as to identify appropriate management strategies to mitigate these effects. The main aim of this study has been to experimentally simulate the effects of a 15% reduction in annual rainfall on the survival and growth of two co-occurring Mediterranean oaks with contrasting leaf-habit (the evergreen Quercus ilex spp. ilex and the winter-deciduous Quercus cerrioides) and, to assess whether traditional selective thinning carried out in these mixed oak coppices (i.e. selection of one to few stems per stump) can modify the consequences of rainfall reduction. Soil moisture decreased under the rainfall reduction level while it increased in the thinned plots. Reduced rainfall did not influence tree mortality, but did lead to species-specific effects on height growth: no changes were observed in Q. ilex while height growth rate of Q. cerrioides decreased (c.a. 20%). Selective thinning improved tree growth (c.a. 50%) in stands both under natural and, and to a lesser extent, under reduced rainfall conditions. Nevertheless, the positive effects of thinning rapidly declined during our three years experiment, probably because the vigorous resprouting of thinned stumps. Our results show that the forecasted reduction in annual rainfall for the Western Mediterranean Basin can constrain the growth of some deciduous oaks in mixed oak coppices. Traditional selective thinning can increase soil moisture and encourage tree growth, thus partially mitigating this effect. However, the transient results observed in this experiment suggest the need to reconsider the intensity and the frequency of this traditional management practice in light of new climatic scenarios. © 2009 Elsevier B.V. All rights reserved.
Keenan T., Ülo N., Sabate S., Gracia C., Pẽuelas J. (2009) Seasonality of monoterpene emission potentials in quercus ilex and pinus pinea: Implications for regional VOC emissions modeling. Journal of Geophysical Research Atmospheres. 114: 0-0.EnllaçDoi: 10.1029/2009JDO11904
VOC emissions from terrestrial ecosystems provide one of the principal controls over oxidative photochemistry in the lower atmosphere and the resulting air pollution. Such atmospheric processes have strong seasonal cycles. Although similar seasonal cycles in VOC emissions from terrestrial ecosystems have been reported, regional emissions inventories generally omit the effect of seasonality on emissions. We compiled measurement data on seasonal variations in monoterpene emissions potentials for two evergreen species (Quercus ilex and Pinus pinea) and used these data to construct two contrasting seasonal response functions for the inclusion in monoterpene emission models. We included these responses in the Niinemets et al. model and compared simulation results to those of the MEGAN model, both with and without its predicted seasonality. The effect of seasonality on regional monoterpene emissions inventories for European Mediterranean forests dominated by these species was tested for both models, using the GOTILWA+ biosphere model platform. The consideration of seasonality in the Niinemets et al. model reduced total estimated annual monoterpene emissions by up to 65% in some regions, with largest reductions at lower latitudes. The MEGAN model demonstrated a much weaker seasonal response than that in the Niinemets et al. model, and did not capture the between species seasonality differences found in this study. Results suggest that previous regional model inventories based on one fixed emission factor likely overestimate regional emissions, and species-specific expressions of seasonality may be necessary. The consideration of seasonality both largely reduces monoterpene emissions estimates, and changes their expected seasonal distribution. Copyright 2009 by the American Geophysical Union.
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