Arnan X., López B.C., Martínez-Vilalta J., Estorach M., Poyatos R. (2012) The age of monumental olive trees (Olea europaea) in northeastern Spain. Dendrochronologia. 30: 11-14.EnllaçDoi: 10.1016/j.dendro.2011.02.002
Trees can reach ages that in some cases amount to thousands of years. In the Mediterranean region, olive trees (Olea europaea) have traditionally been considered a particularly long-lived species. The main objective of this study was to assess the age of large olive trees considered to be millenarian and classified as monumental trees in northeastern Spain. We extracted cores of 14 individuals and obtained 8 sections of trees which had already been cut in the area where the largest olive trees in the northeastern Iberian Peninsula are found. The age of the sampled olive trees was assessed by counting the number of annual growth rings. Tree rings did not cross-date well, neither within nor between individuals, but boundaries between likely annual rings were clearly distinct. We found a linear relationship between DBH and tree age (in years) (Age=2.11×diameter(cm)+88.93, R2=0.80), which was used to estimate the age of unsampled olive trees. The maximum estimated age (627±110 years) is among the greatest ages reported for olive trees around the world (700 years) and among the oldest trees in Mediterranean ecosystems. © 2011 Istituto Italiano di Dendrocronologia.
Choat B., Jansen S., Brodribb T.J., Cochard H., Delzon S., Bhaskar R., Bucci S.J., Feild T.S., Gleason S.M., Hacke U.G., Jacobsen A.L., Lens F., Maherali H., Martínez-Vilalta J., Mayr S., Mencuccini M., Mitchell P.J., Nardini A., Pittermann J., Pratt R.B., Sperry J.S., Westoby M., Wright I.J., Zanne A.E. (2012) Global convergence in the vulnerability of forests to drought. Nature. 491: 752-755.EnllaçDoi: 10.1038/nature11688
Shifts in rainfall patterns and increasing temperatures associated with climate change are likely to cause widespread forest decline in regions where droughts are predicted to increase in duration and severity. One primary cause of productivity loss and plant mortality during drought is hydraulic failure. Drought stress creates trapped gas emboli in the water transport system, which reduces the ability of plants to supply water to leaves for photosynthetic gas exchange and can ultimately result in desiccation and mortality. At present we lack a clear picture of how thresholds to hydraulic failure vary across a broad range of species and environments, despite many individual experiments. Here we draw together published and unpublished data on the vulnerability of the transport system to drought-induced embolism for a large number of woody species, with a view to examining the likely consequences of climate change for forest biomes. We show that 70% of 226 forest species from 81 sites worldwide operate with narrow (
Galiano L., Martínez-Vilalta J., Sabaté S., Lloret F. (2012) Determinants of drought effects on crown condition and their relationship with depletion of carbon reserves in a Mediterranean holm oak forest. Tree Physiology. 32: 478-489.EnllaçDoi: 10.1093/treephys/tps025
Severe droughts may increase physiological stress on long-lived woody vegetation, occasionally leading to rapid defoliation and progressive increase in mortality of overstorey trees. Over the last few years, episodes of drought-induced tree dieback have been documented in a variety of woodlands and forests around the world. However, the factors determining tree survival and subsequent recovery are still poorly understood, especially in resprouter species. We have studied the effects of a single drought episode on crown condition in a holm oak (Quercus ilex L.) forest located in NE Spain 7 years after the drought event. Generalized linear models were used to study the environmental correlates of forest crown condition 7 years after the drought event. Additionally, we evaluated the association between crown condition and the carbon and nutrient reserves stored in lignotubers 7 years after the drought. Our study reveals the multifactor nature of a drought-driven forest dieback in which soil depth and the characteristics of individual trees, particularly their number of stems, determined a complex spatial pattern of tree-level responses. This dieback was associated with a depletion of the carbon reserves in lignotubers 7 years after the episode, representing a reduction of up to 60 in highly drought-damaged trees. Interestingly, in the absence of new acute droughts, successive surveys in 2007-11 showed a direct association between carbon reserves depletion and further deterioration of crown condition. More frequent droughts, as predicted by climate change projections, may lead to a progressive depletion of carbon reserves and to a loss of resilience in Mediterranean resprouter species. © 2012 The Author.
Hereş A.-M., Martínez-Vilalta J., López B.C. (2012) Growth patterns in relation to drought-induced mortality at two Scots pine (Pinus sylvestris L.) sites in NE Iberian Peninsula. Trees - Structure and Function. 26: 621-630.EnllaçDoi: 10.1007/s00468-011-0628-9
Drought-related tree mortality has become a widespread phenomenon. Scots pine (Pinus sylvestris L.) is a boreal species with high ecological amplitude that reaches its southwestern limit in the Iberian Peninsula. Thus, Iberian Scots pine populations are particularly good models to study the effects of the increase in aridity predicted by climate change models. A total of 78 living and 39 dead Scots pines trees were sampled at two sites located in the NE of the Iberian Peninsula, where recent mortality events have been recorded. Annual tree rings were used to (1) date dead trees; (2) investigate if there was an association between the occurrence of tree death and severe drought periods characterized by exceptionally low ratios of summer precipitation to potential evapotranspiration (P/PET); and (3) to compare the growth patterns of trees that died with those of surviving ones. Mixed models were used to describe the relationships between tree growth (in terms of basal area increment, BAI, and the percentage of latewood, LW%) and climate variables. Our results showed a direct association between Scots pine mortality and severe drought periods characterized by low summer water availability. At the two sites, the growth patterns of dead trees were clearly distinguishable from those of the trees that survived. In particular, the BAI of dead trees was more sensitive to climate dryness (low P/PET summer, high temperatures) and started to decline below the values of surviving neighbors 15-40 years before the time of death, implying a slow process of growth decline preceding mortality. © 2011 Springer-Verlag.
Martínez-Vilalta J (2012) Xylem physiology (and the functional implications of the structure of the xylem network. The significance of xylem hydraulic plasticity for reconstructing past environments. Kippel, Switzerland, 15-17 May 2012. (Comunicació oral convidada).
Martínez-Vilalta J (2012) Envelleixen, els arbres? Omnis Cellula 28: 4.
Martínez-Vilalta J (2012) Drought responses of Scots pine at the dry limit. Research seminar: Disturbance and resilience in Mediterranean forest ecosystems, CTFC, Solsona, 8 June 2012. (Comunicació oral convidada).
Sala A, Martínez-Vilalta J, Lloret F (2012) What do we know about the role and regulation of non-structural carbon compounds stored in trees? AGU Fall Meeting, Francisco, United States of America, 3-7 December 2012. (comunicació oral).
Martinez-Vilalta J, Mencuccini M, Alvarez X, Camacho J, Loepfe J, Pinol J (2012) Spatial distribution and packing of xylem conduits. 7th Plant Biomechanics International Conference, Clermont-Ferrand, France, 20-24 August 2012. (Comunicació oral).
Martínez-Vilalta J, Aguadé D, Banqué M, Barba J, Curiel Yuste J, Galiano L, Garcia N, Gómez M, Heres; AM, López BC, Lloret F, Poyatos R, Retana J, Sus O, Vayreda J, Vilà-Cabrera A (2012) Las poblaciones ibéricas de pino albar ante el cambio climático: con la muerte en los talones. Ecosistemas 21: 15-21.
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