Intraspecific variation in the relationship between weather and masting behavior in valley oak, Quercus lobata

Masting behavior--variable and synchronized reproduction by a population of plants--has long been recognized as correlating with weather. How and why weather conditions influence seed production is, however, poorly understood. We investigated the relationships between acorn production and both local weather and long-term climate in 10 populations across the geographic range of the valley oak (Quercus lobata Nee), a California endemic that matures acorns in a single season. Acorn production was larger following a cold spring in the prior year and dry conditions in the winter and spring immediately preceding acorn maturation; similar patterns were also found, with minor differences, at all 10 individual sites. The strength of the relationships varied geographically in the case of the correlation between winter rainfall and annual acorn production, which was stronger (more negative) at wetter sites. Thus, in contrast to a recent study in Quercus petraea (Matt.) Liebl., weather had generally similar effects on acorn production throughout the range of Q. lobata. Similar to Q. petraea, however, the strength of the relationship between site-level annual acorn production and one of the weather factors affecting acorn production (winter rainfall in the case of Q. lobata) varied geographically in ways that may be related to differences among sites in the degree of pollen limitation. Understanding the mechanisms by which weather affects seed production is challenging but critical if we are to understand how climate change will affect masting behavior in the future. Key words: acorn production, masting, Quercus lobata, valley oak, variable reproduction. Il est depuis longtemps reconnu que la reproduction synchronisee et variable dans une population de plantes (<>) est correlee avec les conditions meteorologiques. Cependant, on comprend mal comment et pourquoi les conditions meteorologiques influencent la production de semences. Nous avons etudie les relations entre la production de glands et les conditions meteorologiques locales ainsi que le climat a long terme chez 10 populations dans l'aire de repartition du chene lobe (Quercus lobata Nee), un chene endemique de la Californie dont les glands arrivent a maturite en une seule saison. La production de gland etait plus abondante a la suite d'un printemps froid l'annee precedente et des conditions seches durant l'hiver et le printemps precedant immediatement la maturation des glands. Des patrons similaires ont ete observes, avec des differences mineures, dans l'ensemble des 10 stations individuelles. La force de la relation variait geographiquement dans le cas de la correlation entre la chute de pluie hivernale et la production annuelle de glands; la correlation etait plus forte (plus negative) dans les stations plus humides. Par consequent, contrairement a une etude recente qui portait sur Quercus petraea (Matt.) Liebl., les conditions meteorologiques avaient generalement des effets similaires sur la production de glands partout dans l'aire de repartition de Q. lobata. Comme avec Q. petraea cependant, la force de la relation entre la production annuelle de glands a l'echelle de la station et un des facteurs meteorologiques qui influencent la production de glands (chute de pluie hivernale dans le cas de Q. lobata) variait d'un endroit a l'autre. Cette variation pouvait etre reliee a des differences entre les stations concernant la disponibilite du pollen. Il est difficile mais essentiel de comprendre les mecanismes par lesquels les conditions meteorologiques influencent la production de semences si nous voulons comprendre de quelle facon le changement climatique affectera la reproduction synchronisee dans le futur. [Traduit par la Redaction] Mots-cles: production de glands, masting, Quercus lobata, vallee du chene, reproduction variable.
Introduction Variable, synchronized seed production, known as mast-fruiting or masting behavior, is commonly observed in many taxa of plants and is particularly widespread among temperate and boreal trees. The evolutionary [...]