Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

Abstract

Abstract• We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate.• Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth.• High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes.• Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak. Mots-clés :chêne vert / dendroécologie / changement climatique / réchauffement / dehesas / cernes des arbres Résumé -Variabilité des relations climat-croissance chez Quercus ilex L. dans des peuplements forestiers ouverts de différentes densités dans l'ouest de la péninsule Ibérique.• Nous présentons la plus longue chronologie de cernes (141 ans) de Quercus ilex L. (chêne vert) comme et nous discutons les relations climat-croissance chez cette espèce et l'influence de la densité du peuplement sur la sensibilité des arbres au climat.• De façon similaire à Quercus suber L., les variables climatiques les plus influentes sur la croissance du chêne vert ont été les précipitations de la fin du printemps et du début de l'été, qui ont augmenté la croissance, et les températures élevées d'août de l'année précédente et du mois de juillet de l'année, qui ont affecté négativement la croissance.• Les peuplements de densité élevé ont répondu à des facteurs climatiques similaires que les peuplements de faible densité mais leur réponse a été généralement plus faible. La sensibilité du chêne vert au climat a augmentée au cours des dernières décennies, elle pourrait être liée à l'augmentation des températures dans la région. Cette sensibilité est plus élevée dans les peuplements de faible densité. En outre, le effet du stress estival sur la croissance semble avoir augmenté au cours de la même pé-riode, de la même façon que pour d'autres espèces dans la péninsule Ibérique, ce qui suggère que les arbres sont plus vulnérables aux changements climatiques.• La densité du peuplement pourrait amortir la réponse au climat en lissant les extrêmes climatiques. Néanmoins, les effets de la concurrence pourraient inverser cet effet positif au niveau de...

The effects of thinning intensity and tree size on the growth response to annual climate in Cedrus atlantica: a linear mixed modeling approach

“…Using a contrasted approach, Gea-Izquierdo et al (2009) and Piutti and Cescatti (1997) also Thinning affects growth response to climate in cedarhighlighted differences in the correlation between climate variables and annual growth among trees experiencing different competition intensities. Both studies reported a greater effect of water deficit (low precipitation and high temperatures) in denser stands.…”

“…The effect of competition intensity on the climate-growth relationship was often based on experiments that did not reproduce actual silvicultural guidelines: studies were conducted in stands that had not been thinned for decades (Gea-Izquierdo et al 2009;Martínez-Vilalta et al 2012), in stands thinned once (Misson et al 2003) and in stands lightly thinned (Piutti and Cescatti 1997;Timbal 2002;Kohler et al 2010; but see Olivar et al 2013 andSohn et al 2013). As a consequence, several important aspects of management impact on forest functioning were overlooked: (i) the short-and medium-term effects of thinning, (ii) the cumulative effect of successive thinning and (iii) the prospective analysis of the effect of thinning intensities beyond the current guidelines.…”

The role of climate change in the widespread mortality of holm oak in open woodlands of Southwestern Spain

“…ilex has become well-established especially in recent times (Zhang and Romane, 1991;Cherubini et al, 2003;Campelo et al, 2009;Gea-Izquierdo et al, 2009, 2011. These studies have demonstrated that Q. ilex ring formation is very sensitive to climate, indicating the suitability of this species for dendroecological investigations.…”

“…Complete cross-sections are needed for dendrochronological analysis of Q. ilex due to the complex xylem anatomy of this species (narrow rings, missing rings, and intra-annual density fluctuations [Cherubini et al, 2003;Campelo et al, 2007Campelo et al, , 2009Gea-Izquierdo et al 2009]). Previous dendroecological studies on tree mortality in Iberian forests included tree ring data from dead and healthy trees for comparative analyses (e.g.…”

“…1), thus annual growth largely depends on this rainfall. There was also a relationship of growth with temperatures of autumn and winter of the year t-1 in other Q. ilex populations (Zhang and Romane, 1991;Gea Izquierdo et al, 2009, 2011. The positive relationship with minimum temperatures may be explained by photosynthesis, which can take place in these seasons in evergreen species (Baldocchi et al,2010;Gea-Izquierdo et al 2015).…”