Phenological responses to extreme droughts in a Mediterranean forest

Abstract

Mediterranean regions are projected to experience more frequent, prolonged and severe drought as a consequence of climate change. We used a retractable rainfall shelter, to investigate the impact of extreme droughts on the development of Quercus ilex leaves, flowers and fruit. In 2008, 97% of rainfall was excluded from a forest plot during the autumn, representing 50% of the 1127mm of rain that fell during the year. In 2009, 87% of rainfall was excluded during the spring, representing 58% of the 749mm that fell during the year. The rainfall shelter did not impact neither incident radiation nor air temperature. Autumn rainfall exclusion did not significantly affect leaf, flowers or fruit development. Spring rainfall exclusion resulted in larger and more sustained depression of leaf water potential during the key phases of foliar and floral development. Consequently, only half of the sampled trees (6) reached the shoot lengthening stage which leads to functionally mature leaves (phenophase 4), with one abandoning leaf development at budburst (phenophase 3) and the other two at the bud swelling stage (phenophase 2). All trees of the control plot passed phenophase 4, with most reaching complete leaf development. The impact of extreme droughts on flower development differed between the sexes. The spring exclusion had no effect on male flower, but only one of six trees completed female fruit maturation, compared with four in the control plot. The difference between the male and female drought impacts is likely attributable to the occurrence of male floral development before the period of lowest leaf water potential, and to the lower resource allocation requirements of male flowers. The information provided by our experimental approach may constitute a crucial step to evaluate the impact of increasing drought due to climate change on the most dominant Mediterranean tree species and to help drawing a full picture of the ecological consequences of the decline in water resource on forest dynamics under changing conditions

Prior height, growth, and wood anatomy differently predispose to drought-induced dieback in two Mediterranean oak speciesk

“…Holm oak trees showing lower growth rates and producing vessels with smaller areas were more prone to drought-induced leaf shedding and dieback. Our findings partially coincide with results obtained from rainfall exclusions showing how drought precludes shoot extension and reduces leaf production in this species (Ogaya and Peñuelas 2006;Limousin et al 2010;Misson et al 2011). However, these exclusions did not usually alter xylem vessel area.…”

Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

“…In particular, the environmental conditions during summer and early autumn have been demonstrated to impact the timing of budburst and flowering the following spring (Sanz-Pérez and Castro-Díez 2010;Misson et al 2011). However, scarce effort has been directed at modeling the induction of dormancy, which is tightly linked to leaf senescence and cold acclimation and, further, impacts spring phenophases.…”

Impacts of extreme precipitation and seasonal changes in precipitation on plants

“…While the effects of individual droughts have been extensively studied (Breshears et al, 2009;Allen et al, 2010), the effects of altered timing of precipitation on plants remain largely unknown (Misson et al, 2011;Volder et al, 2013).…”

“…Further, changes in the seasonality of precipitation are expected to exhibit substantial regional and temporal variation (Christensen et al, 2007). Projections for future climate scenarios are that many regions will experience more intense, extreme precipitation (Christensen et al, 2007;Smith, 2011), whereas some regions are projected to receive seasonal shifts, including Africa (Hely et al, 2006), oak savannas (Volder et al, 2013) and prairies in the United States (Chimner et al, 2010), southern Australia (CSIRO, 2011) and Mediterranean regions (Misson et al, 2011), including semi-arid Spain (Miranda et al, 2009a). Southern France and south-east Australia may experience decreased precipitation in spring and increases in autumn (CSIRO, 2011;Misson et al, 2011).…”

“…Projections for future climate scenarios are that many regions will experience more intense, extreme precipitation (Christensen et al, 2007;Smith, 2011), whereas some regions are projected to receive seasonal shifts, including Africa (Hely et al, 2006), oak savannas (Volder et al, 2013) and prairies in the United States (Chimner et al, 2010), southern Australia (CSIRO, 2011) and Mediterranean regions (Misson et al, 2011), including semi-arid Spain (Miranda et al, 2009a). Southern France and south-east Australia may experience decreased precipitation in spring and increases in autumn (CSIRO, 2011;Misson et al, 2011). Mixed-grass prairies in the United States are projected to receive wetter winters and drier summers (Chimner et al, 2010), whereas oak savannas are projected to experience drier summers and wetter spring and autumn (Volder et al, 2013).…”