Growth Forms of Opuntia compressa (Cactaceae) in Florida Sandridge Habitats

2003

Ecology

Self Cite

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.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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

2003

Ecology

Self Cite

“…Scrubby flatwoods is the most open canopied of the three associations studied (Abrahamson and Rubinstein, 1976;Abrahamson et al, 1984;Abrahamson and Hartnett, 1990;Myers, 1990;Abrahamson, 1995Abrahamson, , 1999. Acorn production levels for oaks growing in sand pine scrub were consistently lower than levels in southern ridge sandhill or scrubby flatwoods.…”

Section: Influence Of Ramet Size and Vegetation Association Onmentioning

confidence: 94%

Relation of ramet size to acorn production in five oak species of xeric upland habitats in south‐central Florida

2002

American J of Botany

This study examined variation in two components of acorn production. Percentage of bearing ramets (stems) and number of acorns per bearing ramet were examined in five clonal oaks in three xeric habitats of south-central peninsular Florida in relation to ramet size within and between species and vegetative associations. Counts of acorns on two white oaks (Quercus chapmanii and Q. geminata) and three red oaks (Q. inopina, Q. laevis, and Q. myrtifolia) were conducted annually from 1969 to 1996 (except in 1991) on permanent grids in southern ridge sandhill, sand pine scrub, and scrubby flatwoods associations at the Archbold Biological Station, Florida, USA. Percentage of bearing individuals and mean number of acorns per bearing individual increased with increasing ramet size for all species across all vegetation associations. However, in Q. geminata and Q. myrtifolia, acorn production declined in the largest size class (>3.2 m), implying that larger individuals of these clonal species may become senescent. All oak species in sand pine scrub, which had a nearly closed overstory, had lower frequencies of bearing oaks and mean numbers of acorns compared with similar-sized individuals of the same species in the more open-canopied southern ridge sandhill and scrubby flatwoods associations, suggesting light limitation. The annual production of acorns by a given oak species was correlated across vegetative associations and annual acorn production of oak species was correlated for species within the same section. Intermediate-size class oaks contributed the most acorns per unit area, suggesting that stands managed with short fire-return times will provide fewer acorns to wildlife than stands managed to produce more variable distributions of oak size classes. However, our study suggests that long-unburned stands, such as those studied here, will maintain relatively constant levels of acorn production as a consequence of ramet replacement within the clones of these shrubby oaks to create a variable distribution of size classes. Of the oak species studied, Q. myrtifolia had the highest acorn production and the smallest acorns, while Q. laevis had the lowest acorn production and the largest acorns, suggesting an allocation trade-off between acorn numbers and size.

“…The lower level of nut production by scrub hickory in scrub compared to sandhill or scrubby flatwoods is likely a consequence of the reduced light availability in scrub. Canopy coverage is nearly complete in scrub as a consequence of the dense sand pine overstory, which translates into scrub having the lowest available PAR of the associations studied (Abrahamson and Rubinstein, 1976;Abrahamson, 1999). This pattern of production across associations was parallel to that of acorn production by the oaks of these three associations (Abrahamson and Layne, 2002a).…”

Section: Nut Production In Relation To Ramet Size and Vegetation Assomentioning

confidence: 80%

“…The scrubby flatwoods site at the lowest elevation had the lowest minimum air and soil temperatures. Measurements of overstory canopy cover and photosynthethically active radiation (PAR) in these associations showed that available PAR is lowest in scrub (with the highest canopy cover), intermediate in sandhill (intermediate canopy cover), and highest in scrubby flatwoods (least canopy cover) (Abrahamson and Rubinstein, 1976;Abrahamson, 1999).…”

Section: Description Of Study Area-mentioning

confidence: 99%

Long‐term trends in annual reproductive output of the scrub hickory: factors influencing variation in size of nut crop

2004

American J of Botany

Reproductive output by the Florida-endemic scrub hickory (Carya floridana Sargent) was studied over a 28-yr period in three south-central Florida vegetation associations: southern ridge sandhill, sand pine scrub, and scrubby flatwoods. The objectives were to describe multi-annual patterns of variation in nut production, identify factors involved in this variation, and investigate differences in patterns among associations. Peaks (higher values bracketed by lower values) in nut production occurred in 7 yr in sandhill and scrub and 8 yr in scrubby flatwoods during the 22-yr period for which we had continuous data. Of the total of 22 peaks in the three associations combined, 17 occurred at intervals of 2 or 3 yr, and peaks occurred in the same years in 18 of the 22 cases. Periodicities of nut production generated by spectral analyses (Fourier transforms) generally agreed with the observed peaks. Numbers of nuts per bearing ramet, proportion of ramets bearing nuts, ramet height, and light availability were positively correlated with nut production. Weather variables, specifically winter rainfall and minimum spring temperatures, accounted for a total of about one-quarter to one-half of the variance in nut production depending on the vegetation association. Following a prescribed fire in a sandhill plot, scrub hickory quickly regained fruit production, but over a 5-yr period following the fire nut production by ramets in the largest size class was reduced compared with the unburned control plot.