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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    • "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.
    New Phytologist 04/2015; 207(3). DOI:10.1111/nph.13400 · 7.67 Impact Factor
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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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    International Journal of Environmental Research 07/2014; 8(3):577-582. · 1.10 Impact Factor
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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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    ABSTRACT: An increase in temperature and water deficits caused by the ongoing climate change might lead to a decline growth rates and threaten the persistence of tree species in drought-prone areas within the Mediterranean Basin. Developmental instability (the error in development caused by stress) may provide an index of the adaptability of woody plants to withstand climatic stressors such as water shortage. This study evaluated the effects of drought stress on growth variables in three stands of a Mediterranean oak (Quercus faginea) exposed to differing climatic conditions (xeric, mesic and cooler) along an altitudinal gradient in northeastern Spain, in two climatically contrasting years (wet and dry years). Two indices of developmental instability, fluctuating and translational asymmetries, which reflect environmental stress, were measured in leaves and current-year shoots, respectively. We also measured branch biomass and fractal complexity of branches as indicators of the species’ performance. After a period of drought the individuals’ at the most xeric site presented lower developmental instability and less branch biomass than did the individuals from the mesic and cooler sites. We interpret that difference as an adaptive response to drought which reflects a trade-off between maintenance of homeostasis and growth when water is scarce. The study demonstrated that developmental instability constitutes a useful index to assess the degree of adaptation to stressful environmental conditions. The assessment of developmental instability in sites and years with contrasting climatic conditions provides a means of quantifying the capacity of plants to develop plastic adaptive responses to climatic stress.
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