Long-Term Patterns of Acorn Production for Five Oak Species in Xeric Florida Uplands

Abstract

The number of seeds produced by a population of woody plants can vary markedly from year to year. Unfortunately, knowledge of the patterns and causes of crop‐size variation is limited, and most studies have examined only single species in a single mesic environment. We examined long‐term patterns of acorn crop sizes for five species of shrubby oaks in three xeric upland vegetative associations of south‐central peninsular Florida for evidence of regular fruiting cycles and in relation to winter temperature and precipitation. Counts of acorns on two white oak species (Quercus chapmanii and Q. geminata) and three red oak species (Q. inopina, Q. laevis, and Q. myrtifolia) were conducted annually from 1969 to 1996 (except in 1991) on grids in southern ridge sandhill, sand pine scrub, and scrubby flatwoods associations. As the result of the dissimilar timing of reproductive events in species of red and white oaks and individual species responses to climatic variables, annual acorn production of red and white oak species in a given vegetation association were not synchronized, which dampened the variability of combined annual acorn production. Consequently, acorns were produced with reasonable abundance every year by at least one species. Oaks of nearly closed‐canopy scrub produced fewer acorns than similar‐sized oaks of the same species in the more open‐canopied sandhill and scrubby flatwoods, suggesting light limitation. We identified regular cycles of acorn production that ranged from 2 to 2.4 yr for white oak species and from 3.6 to 5.5 yr for red oak species and found evidence that annual acorn production is affected by the interactions of precipitation, which is highly variable seasonally and annually in peninsular Florida, with endogenous reproductive patterns. Multiple regression models using precipitation variables accounted for as much as 74% of crop‐size variation in Q. inopina, 65% in Q. laevis, 60% in Q. chapmanii, and 44% in Q. geminata, but only 29% for Q. myrtifolia. In contrast, acorn production showed no significant association with minimum winter temperatures. Of the various hypotheses offered to explain supra‐annual variation in seed crops, our data are most compatible with the nonadaptive resource‐matching hypothesis.

Do ecological and silvicultural factors influence acorn mass in Holm Oak (southwestern Spain)?

“…The tradeoff between offspring weight and number has been a foundation of much of the theoretical work on life history patterns (Smith and Fretwell 1974;Wilbur 1977). Many authors have observed an inverse relationship between offspring size and number in diverse plant species (Jakobsson and Eriksson 2000;Leishman et al 2000;Abrahamson and Layne 2003). In contrast, in a study of Q. lobata, Koenig et al (2009) found no such tradeoff between seed number and size, and suggested that factors other than resources available to individual trees determined the relationship between seed size and number.…”

Influence of pruning and the climatic conditions on acorn production in holm oak (Quercus ilex L.) dehesas in SW Spain

“…Climatic conditions during the reproductive stages from bud initiation to acorn ripening have been shown to account partly for the variability in acorn production by some oak species [1,11,19,31]. Precipitation in 2002 and 2003 exceeded that in 2004 and, especially, 2005, which was a very dry year (Tab.…”

Acorn production in Spanish holm oak woodlands

“…Two main explanations have been proposed: i) mast seeding is a direct response to environmental variability («resource matching»); ii) it is an evolved reproductive strategy, related to some economy of scale such as wind pollination or predator satiation. These two hypotheses are compatible; masting might be a result of their interaction (Herrera et al, 1998;Kelly and Sork, 2002;Abrahamson and Layne, 2003). Masting seems to be more patent in dominant wind pollinated species and higher in mid-latitudes, paired to the variability of rainfall (Kelly and Sork, 2002;Koenig and Knops, 2000).…”

“…Particularly in the Mediterranean Region acorns play a basic role in domestic and wildlife feeding and most forests and woodlands are threatened by lack of regeneration. It has been demonstrated for some oak species that climatic conditions during the reproductive stages, from bud initiation to acorn maturation, account for some of the variability in acorn production Masaka and Sato, 2002;Abrahamson and Layne, 2003). Some oak species' fruiting patterns can be approached to species specific cycles, meaning either positive or negative annual autocorrelations (synchrony) in annual acorn production.…”

“…The cycles are partly explained by the acorn maturation pattern, either 1-year or 2-year (Koenig and Knops, 2000;Kelly and Sork, 2002;Liebhold et al, 2004), and are influenced by resource limitations, either light, nutrients or rainfall. So, like mast seeding patterns in other genera, oak acorn production is likely to result from resources interacting with plant endogenous reproductive patterns Koenig and Knops, 2000;Kelly and Sork, 2002;Abrahamson and Layne 2003).…”