Tree resilience after successive low-growth episodes in ponderosa pine old forests.

Lloret F, Keeling E, Sala A (2011) Tree resilience after successive low-growth episodes in ponderosa pine old forests. Oikos doi: 10.1111/j.1600-0706.2011.19372.x.

Carbon reserves and canopy defoliation determine the recovery of Scots pine 4yr after a drought episode

Galiano L., Martínez-Vilalta J., Lloret F. (2011) Carbon reserves and canopy defoliation determine the recovery of Scots pine 4yr after a drought episode. New Phytologist. 190: 750-759.
Enllaç
Doi: 10.1111/j.1469-8137.2010.03628.x

Resum:

Severe drought may increase physiological stress on long-lived woody vegetation, occasionally leading to mortality of overstory trees. Little is known about the factors determining tree survival and subsequent recovery after drought. We used structural equation modeling to analyse the recovery of Scots pine (Pinus sylvestris) trees 4yr after an extreme drought episode occurred in 2004-2005 in north-east Spain. Measured variables included the amount of green foliage, carbon reserves in the stem, mistletoe (Viscum album) infection, needle physiological performance and stem radial growth before, during and after the drought event. The amount of green leaves and the levels of carbon reserves were related to the impact of drought on radial growth, and mutually correlated. However, our most likely path model indicated that current depletion of carbon reserves was a result of reduced photosynthetic tissue. This relationship potentially constitutes a feedback limiting tree recovery. In addition, mistletoe infection reduced leaf nitrogen content, negatively affecting growth. Finally, successive surveys in 2009-2010 showed a direct association between carbon reserves depletion and drought-induced mortality. Severe drought events may induce long-term physiological disorders associated with canopy defoliation and depletion of carbon reserves, leading to prolonged recovery of surviving individuals and, eventually, to delayed tree death. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.

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Llebot E. (ed). Impactes, vulnerabilitat i retroalimentacions climàtiques als ecosistemes terrestres catalans. Segon informe sobre el canvi climàtic a Catalunya.

Peñuelas J, Filella I, Estiarte M, Ogaya R, Llusià J, Sardans J, Jump A, Curiel J, Carnicer J, Rutishauser T, Rico L, Keenan T, Garbulsky M, Coll M, Diaz de Quijano M, Seco R, Rivas-Ubach A, Silva J, Boada M, Stefanescu C, Lloret F, Terradas J (2011) Llebot E. (ed). Impactes, vulnerabilitat i retroalimentacions climàtiques als ecosistemes terrestres catalans. Segon informe sobre el canvi climàtic a Catalunya. Institut d'Estudis Catalans i Generalitat de Catalunya. Barcelona, pp. 373-407.

Predicting the future of forests in the Mediterranean under climate change, with niche- and process-based models: CO2 matters!

Keenan T., Maria Serra J., Lloret F., Ninyerola M., Sabate S. (2011) Predicting the future of forests in the Mediterranean under climate change, with niche- and process-based models: CO2 matters!. Global Change Biology. 17: 565-579.
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Doi: 10.1111/j.1365-2486.2010.02254.x

Resum:

Assessing the potential future of current forest stands is a key to design conservation strategies and understanding potential future impacts to ecosystem service supplies. This is particularly true in the Mediterranean basin, where important future climatic changes are expected. Here, we assess and compare two commonly used modeling approaches (niche- and process-based models) to project the future of current stands of three forest species with contrasting distributions, using regionalized climate for continental Spain. Results highlight variability in model ability to estimate current distributions, and the inherent large uncertainty involved in making projections into the future. CO2 fertilization through projected increased atmospheric CO2 concentrations is shown to increase forest productivity in the mechanistic process-based model (despite increased drought stress) by up to three times that of the non-CO2 fertilization scenario by the period 2050-2080, which is in stark contrast to projections of reduced habitat suitability from the niche-based models by the same period. This highlights the importance of introducing aspects of plant biogeochemistry into current niche-based models for a realistic projection of future species distributions. We conclude that the future of current Mediterranean forest stands is highly uncertain and suggest that a new synergy between niche- and process-based models is urgently needed in order to improve our predictive ability. © 2010 Blackwell Publishing Ltd.

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Altitudinal distribution patterns of bryophytes in the Canary Islands and vulnerability to climate change

Lloret F., González-Mancebo J.M. (2011) Altitudinal distribution patterns of bryophytes in the Canary Islands and vulnerability to climate change. Flora: Morphology, Distribution, Functional Ecology of Plants. 206: 769-781.
Enllaç
Doi: 10.1016/j.flora.2011.04.007

Resum:

We report the pattern of bryophyte distribution through the elevation gradient of three Canary Islands (Fuerteventura, Tenerife and Gomera) assessing their vulnerability risk to climate change. We considered a conservative scenario of upslope climatic shift of 200-400. m and a drop in the upper limit of the cloud belt from 1500 to 1000. m. Climate change vulnerability was analyzed from the overlap between the predicted shift in isotherms or cloud-belt edges and the current species range, following the Colwell and colleagues's model.Liverworts show narrower ranges and tend to live at lower elevations than mosses. Perennials and long-lived shuttle species establish in the upper localities. Many perennials and most of the long-lived shuttle species grow in cloud forests. Many annual shuttle species and colonists establish in the lowest localities. Colonists also occupy the harsh summit in the highest islands.In accordance with the Colwell model, most elements of this bryoflora appears vulnerable to rapid climatic change. Upland extinction and contraction challenges the bryoflora on the driest, lowest island Fuerteventura; range-shift gaps do this on the highest island Tenerife. Liverworts tend to be more vulnerable to range-shift gaps; mosses are more vulnerable to upland extinction. On the lowest island, perennials and long-lived shuttle species are more vulnerable to upland extinction; perennials are also vulnerable to range-shift gaps. Colonists are most vulnerable to upland contraction or extinction on the high islands Gomera and Tenerife. Annual shuttle species tend to be more vulnerable to lowland attrition on these high, most humid islands. Many elements of the bryoflora of the upper limit of the cloud forests appear to be vulnerable, while most of the flora of other cloud forest areas presumably will not be so affected, with the exception of the most restricted species.A simple model illustrates the feasibility of preliminary assessments of climate change on organisms which show a lack of published detailed information on their distribution and biology. This assessment gains by incorporating estimates of biological attributes. © 2011 Elsevier GmbH.

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Components of tree resilience: Effects of successive low-growth episodes in old ponderosa pine forests

Lloret F., Keeling E.G., Sala A. (2011) Components of tree resilience: Effects of successive low-growth episodes in old ponderosa pine forests. Oikos. 120: 1909-1920.
Enllaç
Doi: 10.1111/j.1600-0706.2011.19372.x

Resum:

Recent world-wide episodes of tree dieback have been attributed to increasing temperatures and associated drought. Because these events are likely to become more common, improved knowledge of their cumulative effects on resilience and the ability to recover pre-disturbance conditions is important for forest management. Here we propose several indices to examine components of individual tree resilience based on tree ring growth: resistance (inverse of growth reduction during the episode), recovery (growth increase relative to the minimum growth during the episode), resilience (capacity to reach pre-episode growth levels) and relative resilience (resilience weighted by the damage incurred during the episode). Based on tree ring analyses, we analyzed historical patterns of tree resilience to successive drought-induced low growth periods in ponderosa pine trees growing in unmanaged, remote forests of the Rocky Mountains. Low-growth periods registered in tree rings were related to anomalies in the Palmer drought severity index (PDSI) and were attributed to drought. Independently of the impact of a specific event, subsequent growth after a single low-growth episode was related to the growth prior to the event. Growth performance differed with tree age: young trees were overall more resistant to low-growth periods, but older trees recovered better from more recent events. Regardless of tree age, recently burned sites exhibited lower post-episode growth and lower resistance and resilience than unburned ones. We found mixed evidence for the cumulative effect of past low-growth episodes: overall, greater impacts of a prior event and greater cumulative effects of past low-growth periods caused a decrease in resistance. However, we did not find a progressive decrease in resilience over time in old trees. Our results highlight the value of using a combination of estimators to evaluate the different components of resilience. Specifically, while tree responses to disturbance depend on past disturbance episodes, the response is context-specific and depends on the impact the capacity to recover after disturbance. This suggests that recent increases in forest mortality under current climate trends could relate to thresholds on specific components of resilience (resistance, recovery, resilience itself) rather than to an overall loss of resilience over time. Identifying such thresholds and their underlying mechanisms is a promising area of research with important implications for forest management. © 2011 The Authors.

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Solving the conundrum of plant species coexistence: Water in space and time matters most

Peñuelas J., Terradas J., Lloret F. (2011) Solving the conundrum of plant species coexistence: Water in space and time matters most. New Phytologist. 189: 5-8.
Enllaç
Doi: 10.1111/j.1469-8137.2010.03570.x

Resum:

[No abstract available]

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