Summer-drought constrains the phenology and growth of two coexisting Mediterranean oaks with contrasting leaf habit: Implications for their persistence and reproduction

Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH UK
Trees (Impact Factor: 1.65). 08/2009; 23(4):787-799. DOI: 10.1007/s00468-009-0320-5


This study analyses how coexisting evergreen and deciduous oaks adjust their phenology to cope with the stressful Mediterranean
summer conditions. We test the hypothesis that the vegetative and reproductive growth of the winter deciduous (Quercus faginea Lam.) is more affected by summer drought than that of the evergreen [Quercus ilex L. subsp. ballota (Desf.) Samp.]. First, we assessed the complete aboveground phenology of both species during two consecutive years. Shoot
and litter production and bud, acorn and secondary growth were monitored monthly. Second, we identified several parameters
affected by summer conditions: apical bud size, individual leaf area (LA), leaf mass per area (LMA) and acorn yield in both
species, and leaf-fall in Q. faginea; and analysed their variation over 10years. Q. ilex performed up to 25% of shoot growth and most leaf development during summer, whereas Q. faginea completed most of both phenophases during spring. Secondary growth was arrested in summer under drought conditions. Approximately,
30–40% of bud and 40–50% of acorn growth was undertaken during summer in both species. Summer drought related to differences
in LA, LMA and leaf senescence, but not to acorn yield. Both species had similar year-to-year patterns of acorn production,
though yields were always lower in Q. faginea. Bud size decreased severely in both species during extremely dry years. In Q. ilex, bud size tended to alternate between years of large and small buds, and these patterns were followed by opposite trends in
stem length. In Q. faginea, bud size was more stable through time. Q. ilex was more phenologically active during summer than Q. faginea, indicating a higher tolerance to drought. Furthermore, bud and fruit growth (the only two phenophases that both species
performed during summer) were more severely affected by summer drought in Q. faginea than in the evergreen. The differential effects of summer drought on key phenophases for the persistence (bud growth) and
colonization ability (fruit production) of both species may have consequences for their coexistence.

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Available from: Jesús Julio Camarero
    • "The summer BA increment cessation is frequently reported for Mediterranean trees and is discussed as a period of quiescence of cambial activity induced by water limitation (Campelo et al., 2007; Montserrat-Marti et al., 2009; Camarero et al., 2010; Guti errez et al., 2011). In this study, water deficit played a critical role in the timing of summer increment BA cessation (t 1 ) as evidenced by the positive correlation between the amount of rainfall in spring and t 1 (Table S3). "
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    ABSTRACT: 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. © 2015 CNRS-ADEME New Phytologist © 2015 New Phytologist Trust.
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    • "In the Mediterranean basin, a region characterized by long episodes of droughts, extreme climatic events, a generally low rainfall rate coupled with fragile soils susceptible to degradation processes (e.g. erosion, salinization, pollution, sealing) and human pressure due to the continuous development of both scattered and compact urban settlements, a large set of disturbance factors can be identified threatening nature forests (Juarez- Lopez et al., 2008; Montserrat-Martì et al., 2009; Bobiec et al., 2011). Especially mesophilous oak forests adapted to dry lands constitute an important component of the Mediterranean rural landscape but are progressively threatened by climate change, soil degradation and human pressure due to forest fires and overgrazing (Drunaski and Struve, 2007). "
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    • "Quercus faginea Lam. is a winter-deciduous Mediterranean oak widely distributed in the Iberian Peninsula in relatively humid areas with basic soils (Castro et al., 2005). The climatic conditions that influence shoot and leaf development are those that occur in the previous year (Chauvert-Periera et al., 2009; Montserrat-Martí et al., 2009 "
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