| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Ecology |
2Archbold Biological Station, Lake Placid, Florida 33862 USA; 3Department of Biology, Bucknell University, Lewisburg, Pennsylvania 17837 USA
Received for publication November 21, 2003. Accepted for publication May 11, 2004.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Key Words: Carya floridana • climate • fire • multi-annual nut production • nut consumers • relation of nut production to ramet size • scrub hickory • xeric vegetation associations
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
; Kelly and Sork, 2002
). The number of seeds produced can be influenced by a number of intrinsic and external factors such as genotype, plant size, site conditions, and climate (e.g., Klinkhamer et al., 1992
; Koenig and Knops, 2000
; Kelly and Sork, 2002
). Annual seed production is often correlated with plant size because reproduction is dependent on accumulated resources (Schmid et al., 1995
; Reekie, 1998
). Furthermore, site conditions including nutrient and light availability can influence the rate of resource accumulation by long-lived plants and hence can alter their patterns of reproductive output (Harper and White, 1974
). Consequently, we would expect that larger individuals of a given species or individuals growing in resource-rich sites would produce greater numbers of seeds than smaller individuals or individuals living in resource-limited sites.
Within a site, annual crop size also can be affected by disturbance and climate (Sork et al., 1993
; Houle, 1999
; Abrahamson and Layne, 2002a
, b
, 2003
). Favorable precipitation and/or temperatures in certain seasons can promote above-average seed production in that year or in subsequent years (Norton and Kelly, 1988
; Smith et al., 1990
). Conversely, adverse temperature, humidity, or wind at the time of pollination or seed development can reduce flowering or seed set in one year and thus conserve resources that could positively influence flowering or fruiting levels in a subsequent year. For species of fire-prone sites, fire events can markedly impact both short- and long-term fruit-production levels. Because the length of time from fire to seed production directly affects recruitment, we expect plants of fire-prone sites to have adaptations that enable rapid regeneration and minimal delay until reproduction following burning.
External influences such as climate and fire are likely to have an impact on any endogenous reproductive patterns that long-lived plants may express (Sork et al., 1993
; Houle, 1999
). The interactions of endogenous reproductive rhythms with climatic factors or disturbance events could generate years of no reproduction or small seed crops interspersed with the periodic production of large seed crops that may be synchronous over large areas (Janzen, 1971
, 1976
, 1978
; Waller, 1979
; Silvertown, 1980
; Sork et al., 1993
; McKone et al., 1998
; Keeley and Bond, 1999
; Abrahamson and Layne, 2003
).
The study reported here describes patterns of variation in nut production for scrub hickory, Carya floridana Sargent, an endemic to peninsular Florida whose sizeable fruit is an important wildlife food source. We examined nut production over a 28-yr period in three major xeric upland vegetation associations for cyclic patterns of reproductive effort, influences by climatic factors, differences among associations, the relation of plant size to reproductive output, and the effect of prescribed fire on nut crops in one of the associations. The variability of seasonal and annual temperature and precipitation on the Florida peninsula provided an opportunity to examine the relationships between variation in annual fruit production and these climatic variables. Specifically, we investigated (1) long-term trends in annual crops to see if scrub hickory has regular cycles of nut production and if climatic variables correlate with production; (2) differences in crop size across associations differing in soil, microclimate, and light availability reflecting canopy coverage; (3) the relation of nut production to ramet (= stem) height; and (4) the effects of fire on nut production.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
; Wunderlin and Hansen, 2003
). It is particularly characteristic of xeric vegetation associations of the Lake Wales Ridge (Abrahamson et al., 1984
). Scrub hickory is typically a shrub 3–5 m high or a small tree (Sargent, 1922
) but may reach 25 m with a diameter at breast height (dbh) of about 50 cm (Elias, 1980
). It is a clonal species, which is evidenced even in larger individuals by the often distinct clustering of several trunks, termed the "multi-trunk" condition by Grauke (2004)
. Despite its endemic status and xeric-habitat specialization, little is known of the details of the demography of scrub hickory or of its role in the biotic community.
The high energy and nutrient content of the scrub hickory nut (Abrahamson and Abrahamson, 1989
) make it a potentially important wildlife food species. In our study area, gray squirrels (Sciurus carolinensis) and flying squirrels (Glaucomys volans) appear to be the principal mammalian predators on the nuts. In periodic checks of nest boxes used by gray squirrels and flying squirrels, scrub hickory nuts were the most frequently encountered food item, occurring in 87.3% of boxes containing food items. Black bear (Ursus americanus) scats in the study area and stomachs of individuals killed on nearby highways contained remains of scrub hickory nuts. Bears also occasionally raided squirrel nest boxes to obtain stored nuts. Other mammals known or suspected to utilize scrub hickory nuts in the study area include the Florida mouse (Podomys floridanus), cotton mouse (Peromyscus gossypinus), oldfield mouse (Peromyscus polionotus), golden mouse (Ochrotomys nuttalli), and feral hog (Sus scrofa). Grauke (2004)
cited black bears, foxes, raccoons, and rodents as mammalian predators on scrub hickory nuts. Birds known to consume the nuts include Florida scrub jays (Aphelocoma coerulescens), blue jays (Cyanocitta cristata), red-bellied woodpeckers (Melanerpes carolinus), and red-headed woodpeckers (Melanerpes erythrocephalus) (Woolfenden and Fitzpatrick, 1984
; R. Bowman, Archbold Biological Station, personal communication; G. E. Woolfenden, Archbold Biological Station, personal communication). The infrequent occurrence of isolated scrub hickories well removed from the nearest population presumably reflects a low incidence of transport of the large nuts by birds. In an intensive study of caching behavior of blue jays in the vicinity of our study plots, C. A. Adkisson (Virginia Polytechnic Institute and State University, personal communication) has never recorded a jay transporting a scrub hickory nut in the thousands of caching trips observed. Furthermore, although he has found numerous oak seedlings and saplings in citrus groves where blue jays frequently cache acorns, he has never observed a seedling or sapling of scrub hickory in such a site. Insects are also important predators on scrub hickory nuts in our study plots, with infestation rates of nut-consuming weevil larvae (Curculio caryae Horn) ranging from 23 to 53% (Abrahamson and Abrahamson, 1989
).
Description of study area
The study was conducted on the Archbold Biological Station (27°12' N, 81°21' W) 12 km south of the town of Lake Placid, Highlands County, in the southern Lake Wales Ridge region of peninsular Florida. Hot, wet summers and mild, dry winters characterize the climate of the study area (Abrahamson et al., 1984
). Mean annual daily temperature over a 49-yr (1952–2000) period was 22.3°C. Average monthly daily temperatures range from 16.0°C in January to 27.5°C in August. Long-term mean annual rainfall is 1335 mm, of which 796 mm (60%) is received from July to September.
Sampling was conducted on permanent 2.7-ha grids located in three of the major vegetation associations of Archbold Biological Station: southern ridge sandhill–turkey oak phase, sand pine scrub–oak phase, and scrubby flatwoods–inopina oak phase (Abrahamson et al., 1984
), hereafter referred to as sandhill, scrub, and scrubby flatwoods, respectively. Sandhills occupy the highest portions of the study area, while scrub occurs at intermediate elevations, and scrubby flatwoods are in the lowest portions of the study area that host scrub hickory. The soils of these associations are acidic sands, which are excessively well drained in sandhill and scrub but only moderately well drained in scrubby flatwoods (Table 1). The soil of the sandhill study area differs from that of scrub or scrubby flatwoods in that it is characterized by deep red subsoil that is classified by Alt and Brooks (1965)
as a paleosoil, which reflects a long period of emergence above sea level.
|
), and one sandhill subtype (southern ridge sandhill–scrub hickory phase) is characterized by dominance of scrub hickory instead of turkey oak (Abrahamson et al., 1984
). Scrub has a nearly closed canopy of sand pines and a small tree–shrub understory of most of the same species as in sandhill. Ground cover consists mainly of sprouts of the shrub-layer components, with few herbaceous species. Mature scrub has a generally well-developed litter layer and fewer openings with sparse litter or bare sand than sandhill sites.
Scrubby flatwoods have a widely open tree layer of slash pines and sand pines; a generally dense, low (1–2 m) shrub layer, with scattered openings with wiregrass, forbs, and lichens. Archbold oak (Q. inopina) is a characteristic component of the shrub layer, and fetterbush (Lyonia lucida) and staggerbush (Lyonia ferruginea) are also more frequent in this association than in sandhill or scrub. Scrub hickory is not a characteristic species of scrubby flatwoods in the southern ridge region, and it was less abundant and more restricted in distribution in the scrubby flatwoods study area compared with the sandhill and scrub.
The three study sites were last burned in a major wildfire in 1927. The more than 70-yr fire-free interval greatly exceeds the normal range for sandhill but is within that for scrub, which under natural conditions is typically subject to infrequent but high intensity fires (Myers, 1990
). Abrahamson et al. (1984)
ranked scrubby flatwoods above sandhill in terms of flammability, although as a result of the low biomass and prevalence of sandy patches, this association probably has a natural fire frequency more similar to that of scrub than sandhill.
The rank order of the three associations in terms of stability of microclimate is scrub > sandhill > scrubby flatwoods (Abrahamson et al., 1984
) based on variation in air temperatures, soil temperatures, soil moisture, and air movement (Table 1). 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
).
Mean density of scrub hickory ramets based on combined data from vegetation surveys in 1969, 1979, and 1989 (Givens et al., 1984
; Menges et al., 1993
) was highest in sandhill (684 ramets/ha, range = 61–1265), intermediate in scrub (407 ramets/ha, range = 114–581), and lowest in scrubby flatwoods (141 ramets/ha, range = 2–223). Ramet density was greatest in the ground layer in all three associations, with scrub having the highest proportion of shrub- and tree-sized individuals and scrubby flatwoods the lowest. The size distribution of ramets in each association varied considerably between censuses, with a reduction of ramets in the ground layer as a result of thinning (Givens et al., 1984
; Menges et al., 1993
) and a shift to larger size classes with an associated sharp decrease in overall density in all associations in 1979 compared with 1969 and a return in 1989 to a size distribution more like that of 1969. Mean ± SE and maximum scrub hickory heights in the tree stratum (>3.2 m) in the combined 1969, 1979, 1989 vegetation surveys were 4.3 ± 0.1 m, 7.6 m in sandhill; 4.1 ± 0.1 m, 6.1 m in scrub; and 4.1 ± 0.1 m, 4.4 m in scrubby flatwoods. Maximum heights of trees sampled in mast counts were 9.1 m in sandhill, 7.6 m in scrub, and 7.6 m in scrubby flatwoods.
Sampling of nut production
Nut production was measured annually from 1969 through 1996, with the exception of 1991, on the three 2.7-ha grids in sandhill, scrub, and scrubby flatwoods. Sixty specimens in sandhill and scrub and 30 in scrubby flatwoods were sampled during the fall each year to obtain estimates of the proportion of ramets bearing nuts and mean numbers of nuts per bearing ramet. The time of sampling ranged from early August to early October, depending upon the timing of development of the nuts in a given year. In the case of the sandhill and scrub associations, the basic sampling procedure involved selecting the nearest individual in each quarter centered on a permanent marker at each of 15 stations evenly distributed over the grid. This procedure was modified as necessary to (1) eliminate stems located along paths that might have been subject to damage by foot traffic or clearing, (2) minimize the possibility of sampling ramets from the same clone by selecting stems from well-separated clusters, and (3) to insure adequate samples of all height classes. Because of the restricted distribution and low density of scrub hickory on the scrubby flatwoods grid, counts in that association were made on individuals selected without reference to station markers and spaced widely enough to minimize the possibility of including ramets from the same clone as reflected by obvious clustering of ramets. Because of the small size of scrub hickory, we were able to count all nuts on bearing ramets. In the case of specimens taller than about 2.5 m on which it was difficult to see nuts on the upper branches, a slender bamboo pole was used to brush through the edge of the canopy, which allowed detection of unseen nuts by contact. Further details of the sampling protocol are given in Abrahamson and Layne (2002a
, b
, 2003
).
In May 1993, a second 2.7-ha sandhill grid separated from the primary sandhill grid by a wide fire lane was prescribed burned and the regrowth and nut production of scrub hickory ramets was monitored each fall through 1998, with the unburned grid serving as the control.
Two components of nut production, number of nuts on bearing ramets and proportion of bearing ramets, were considered in the analyses of the relation between ramet size and nut production and the effects of prescribed fire on reproduction. For analysis of annual trends in nut production, mean number of nuts on all ramets for combined size classes was used. This value was calculated from the means of individual size classes to avoid the bias of unequal sample sizes between size classes (height classes used were 0.3–0.8, 0.9–1.4, 1.5–2.0, 2.1–2.6, 2.7–3.2, and >3.2 m).
Statistical analyses
Statistical analyses were performed using Statistica (StatSoft, 1994
), except for the Mann-Whitney U test based on Siegel (1956)
. To explore the possibility that cyclical variation was present in nut production over time, we performed a spectral (Fourier) analysis on annual nut production. Such an analysis will identify the number of cycles in a time series if the data have periodicity. Hamming weights with a data window of five were used for our spectral analysis, and the overall mean was substituted for the missing value for 1991. Substituting the minimum and maximum values of production over all years for the missing 1991 data did not significantly alter the results of the analysis. Significance was tested with Bartlett's Kolomogorov–Smirnov D (one-sample). In addition, to explore the relationship of climatic variation and nut production, a stepwise multiple regression analysis was performed between mean number of nuts per ramet and eight weather parameters: mean minimum daily temperature in winter (December–February), spring (March–May), summer (June–August), and fall (September–November) and rainfall in winter, spring, summer, and fall.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
|
A spectral analysis confirmed the existence of cyclic patterns of nut production by scrub hickory. The two highest periodogram peaks of annual crop size produced by spectral analysis were (periodogram values in parentheses) 2.2 (224.9) and 3.7 (240.3) yr for sandhill; 2.5 (214.0) and 4.7 (112.7) yr for scrub; and 2.5 (411.4) and 9.3 (196.6) yr for scrubby flatwoods. There was no significant autocorrelation in annual mean numbers of nuts per ramet with lags of 1–15 yr within any association.
A stepwise multiple regression analysis found that weather variables significantly (P < 0.05) associated with size of the nut crop were mean winter rainfall (r = 0.52) and mean minimum spring temperature (r = 0.44) in sandhill and mean winter rainfall (r = 0.40) in scrub. No single weather variable was significantly correlated with nut production in scrubby flatwoods, although the correlation with mean minimum spring temperature (r = 0.52) approached significance (P = 0.07).
Nut production in relation to ramet size
The proportion of bearing ramets and number of nuts per bearing ramet increased with ramet size in all vegetation associations (Fig. 2), the differences among size classes being significant for all associations (
2 = 938–1374, df = 5, P < 0.001). The proportions of bearing ramets within size classes did not differ significantly among associations (2 = 12.98, df = 10, P = 0.22), although the percentage of bearing ramets in sandhill and scrubby flatwoods leveled off by size class 2.7–3.2 m in contrast to a continued increase in the proportion of bearing ramets in the larger size classes in scrub. Correlations between number of nuts per bearing ramet and ramet height were also significant (P < 0.001) for all associations (sandhill: r = 0.29; scrub: r = 0.25; scrubby flatwoods: r = 0.24), with no significant differences between associations in r values (P = 0.34–0.84).
|
|
|
Effect of prescribed fire on nut production
Pre-fire parameters of nut production in the sandhill grid burned in 1993 and the unburned control were generally similar for comparable ramet size classes, although the unburned control tended to have a higher proportion of bearing ramets and mean number of nuts in all size classes except the smallest (Fig. 4). Post-fire ramets produced no nuts in the fall of 1993 following the burn in May, and only two nuts occurred on one of three ramets >0.3 m sampled in fall 1994. The data for subsequent years indicate comparable proportions of bearing ramets and mean number of acorns per ramet in the smaller size classes and a relatively consistent tendency for ramets in the largest size class to be more productive on the control than burned grid (Fig. 4).
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
). Mean (maximum in parentheses) production by bearing trees of three species in Ohio over a 6-yr period was C. glabra, 482.2 nuts (2350); C. ovata, 219.6 nuts (1498); and C. tomentosa, 367.7 nuts (3134) (Nixon et al., 1980
). Carya sp. >25.4 cm dbh in Missouri produced an estimated mean of 57 nuts/tree (Dalke, 1953
), as compared with 10.8 nuts/total ramets for the largest (>3.2 m) size class of scrub hickory. Given the relationship between stem size and nut production, extrapolation of scrub hickory ramet size to that of the hickory species with larger sized trees would give a comparable level of production in spite of scrub hickory growing in sandy soils with very low nutrient availability.
There was no year among the 27 yr of monitoring that scrub hickory nut production failed in all three of the associations studied. Even though the high degree of variation in seasonal and annual precipitation on the Florida peninsula would suggest that scrub hickory should have highly variable annual crops, a comparison of the CVs of nuts per bearing individual for scrub hickory with other hickories showed that scrub hickory has similar variability. The CVs of nuts per bearing individual reported for other hickory species were 121.0% for C. glabra (Sork, 1983
), 117.3% for C. glabra, 168.1% for C. tomentosa (Nixon et al., 1980
), compared with 139.4% for C. floridana for combined habitats in the present study. Furthermore, there was no indication of a correlation between relative variability in nut production and mean number of nuts on bearing trees.
Climatic factors had a substantial effect on scrub hickory nut production, with winter rainfall in sandhill and scrub and minimum spring temperature in sandhill and scrubby flatwoods having the strongest effects of the eight weather variables. The significant correlation between minimum spring temperature and nut production in sandhill and scrubby flatwoods but not in scrub may reflect the moderating effect on air temperature provided by the better developed canopy and shrub layer of the scrub association, which might in turn benefit flower development. Over a 13-yr period, mean and lowest minimum (in parentheses) air temperatures in March, the peak month of flowering, were 7.7°C (5.2°C) in scrub, 7.0°C (3.5°C) in sandhill, and 2.7°C (–0.6°C) in scrubby flatwoods. Limited rainfall during the winter dry season creates periodic drought stress in the xeric associations of this study (Menges and Gallo, 1991
; Menges, 1994
), and such drought stress may impact scrub hickory flowering or fruit development. The combination of highly variable annual and seasonal precipitation with the excessively well-drained, nutrient-poor sandy soils of sandhill and scrub associations may result in rainfall events having profound effects on the reproduction of scrub hickory. The lack of a significant correlation between production and winter rainfall in scrubby flatwoods may reflect the relatively high water table in scrubby flatwoods compared to sandhill and scrub. Although soil-moisture values in scrubby flatwoods during the dry season do not appear to support this interpretation (Table 1), the soil-moisture measurements made at a 5-cm depth likely do not accurately reflect soil-moisture conditions in the deeper root zone.
In general, the evidence for effects of weather variables on annual production of scrub hickory was more clearcut than in the case of oaks in the same associations (Abrahamson and Layne, 2003
), probably reflecting the greater complexity of climatic effects on co-occurring oak species with both 1- and 2-yr reproductive cycles (not including initiation of catkins in spring of the previous year) compared with the 1-yr cycle of scrub hickory. Support for this interpretation is the closer correlations of mast crops of scrub hickory and species of the white oak than red oak groups. In a study of effects of various precipitation and air-temperature variables on reproduction in C. glabra, C. ovata, and C. tomentosa in Ohio, only mean temperature in early May, corresponding to the usual flowering period, was significantly correlated (positively) with nut production (Nixon et al., 1980
).
The substantial residual variance in annual production of scrub hickory remaining after removal of the effects of weather variables suggests that, as a result of the relatively sterile soils and xeric conditions of the species' habitats combined with the large nut size, several years are required to accumulate the necessary resources between one large crop and the next, with weather conditions affecting the rate and degree of accumulation of resources, as suggested for acorn production by species of oaks (Sork et al., 1993
). Spectral analysis identified cycles of peak crops at 2.2 and 3.7 yr in sandhill, 2.5 and 4.7 yr in scrub, and 2.5 and 9.3 yr in scrubby flatwoods. Peak years of nut production in sandhill and scrub coincided in all (seven) cases, while four of eight peaks in scrubby flatwoods differed by 1–3 yr from those in the other associations. Across all vegetation associations, 17 of 22 peaks in mean number of nuts per ramet during the 22 yr of continuous monitoring occurred at intervals of 2 or 3 yr, an interval similar to that of many larger Carya species. Larger seed crops in other Carya are produced almost yearly in C. aquatica or at usual intervals of 2 yr in C. glabra and C. laciniosa, 1–3 yr in C. ovata, 2–3 yr in C. illinoensis, C. tomentosa, and C. myristicaeformis, or 3–5 yr in C. cordiformis (Boisen and Newlin, 1910
; Bowers, 1960
; Fowells, 1965
; Chesemore, 1975
; Nixon et al., 1980
). Although McCarthy and Quinn (1989)
concluded that for C. ovata and C. tomentosa genetic differences had a greater influence on nut production than environmental effects, they recognized that yearly weather patterns and depletion and accretion of resources in combination with geography, site quality, and other factors also played a role in annual variation in flowering and fruiting.
Of the three vegetation associations represented in this study, only scrubby flatwoods had a significant trend in annual total crop size during 1969–1996, with a modest, though significant, increase during 1983–1996. This trend may reflect an increase in shrub-sized ramets during this interval, as suggested by the increase of ramets in the 0.4–0.8 m size class from 0% in 1969 and 1979 to 14% in 1989.
Over the 1969–1996 interval during which annual nut production was monitored, cumulative departure of annual rainfall from the 49-yr (1952–2000) mean went from a surplus of 1317 mm in 1969 to a deficit of –313 mm by 1996. However, this long-term trend appeared not to be reflected in that of annual scrub hickory crop size in any vegetation association.
Nut production in relation to ramet size and vegetation association
The proportion of bearing ramets and nuts per bearing scrub hickory ramet were strongly associated with ramet height in all three associations, results that parallel findings from other plant species (Harper and White, 1974
; Schmid et al., 1995
; Reekie, 1998
). A similar trend was exhibited by the five oak species that co-occur with scrub hickory (Abrahamson and Layne, 2002a
), as well as in other oak species (e.g., Moody, 1953
; Greenberg, 2000
). A high correlation (r = 0.84, P < 0.001) between ramet height and crown width in a random sample (N = 269) of stems ranging from sprouts to mature scrub hickories from all associations suggests that the increase in nut production with size is due to increased canopy coverage rather than an increased number of nuts per unit area of canopy. Greenburg (2000)
showed a similar relationship for five southern Appalachian oak species. Significantly (P = 0.001) weaker correlations between ramet height and canopy width in scrub (r = 0.71) compared with sandhill (r = 0.95) and scrubby flatwoods (r = 0.93) may reflect an effect on the ramet height to crown ratio of lower light level in scrub as a result of scrub's more closed canopy. Among the three vegetation associations, scrub had the lowest percentage of bearing ramets and mean number of nuts per bearing ramet among the larger size classes. The proportion of bearing ramets in scrub also continued to increase in larger size classes rather than leveling off as in sandhill and scrubby flatwoods. In contrast, mean number of nuts per bearing ramets continued to increase in scrub as in the other associations, although at a lower rate. 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
). Coblentz (1980)
also reported a similar trend of lower acorn production by Quercus garryana in closed canopy vs. open savannah.
Compared with the five species of oaks co-occurring in the same three study sites (Abrahamson and Layne, 2002a
), scrub hickory had a slightly higher proportion of bearing ramets than the oaks (48.8% for scrub hickory vs. 43.7% for oaks) and a lower mean number of nuts per bearing ramet (11.0 vs. 15.4). The mean number of scrub hickory nuts per bearing ramet was considerably greater than that of Quercus laevis (7.3), which is also a small, deciduous tree with the largest acorns (65% of the fresh mass of the nut of scrub hickory) of the five oak species (Abrahamson and Abrahamson, 1989
). Relative variability (CV) of nuts per bearing ramet for scrub hickory within habitats was less than that for acorns of oaks (sandhill, hickory = 137.1%, mean for oaks = 186.7%; scrub, hickory = 135.1%, mean for oaks = 154.3%; scrubby flatwoods, hickory = 146.0%, mean for oaks = 187.3%). Of the two components of fruit production, the percentage of bearing ramets had the strongest correlations between scrub hickory and the five species of oaks in the same associations over the period of continuous monitoring (1969–1990). The correlations, although significant (P < 0.05) only in the case of white oaks (Q. chapmanii in scrub, r = 0.63; Q. geminata in scrub and scrubby flatwoods, r = 0.45 and 0.48, respectively), were higher between scrub hickory and white oak species than red oak species in six of seven other comparisons. The tendency for annual scrub hickory crop size to correlate with species of the white oak group, but not with the red, presumably reflects the similarity of the reproductive schedule (flowering and fruiting within 1 yr vs. 2 yr, with initiation of flower buds in the preceding year) of the scrub hickory and white oak species, resulting in both groups being subjected to the same weather conditions during the interval from pollination to maturation of the nuts.
Response to fire
Scrub hickory quickly produces new ramets following fire (Abrahamson and Abrahamson, 1996
), and the present study documents that many ramets soon initiate flower development. A few nuts were produced by new ramets in the year following the May burn in sandhill, and by the third year, production in the two smaller size classes on the burned and unburned study grids were comparable. Whereas both the percentage bearing and the mean nuts per ramet of the largest size class were consistently higher in the unburned grid, the difference was more pronounced in the post-burn years. The results indicate, therefore, that scrub hickory quickly begins fruit production following fire; however, full recovery of nut production by larger ramets requires more than 5 yr. The timing of post-burn recovery of production by scrub hickory as reflected in percentage of bearing ramets and mean number of nuts per bearing ramet was generally comparable to that of oaks in the white oak group on the same sandhill study grid, with some nuts being produced the first year following the burn (Abrahamson and Layne, 2002b
). However, in contrast to the larger size classes of oaks, particularly the two species of the white oak group, scrub hickory tended to have higher production in the unburned, rather than burned grid, during the 5 yr following burning.
|
FOOTNOTES |
|---|
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Abrahamson W. G. C. R. Abrahamson 1989 Nutritional quality of biotically dispersed fruits in Florida sandridge habitats. Bulletin of the Torrey Botanical Club 116: 215-228[CrossRef][ISI]
Abrahamson W. G. J. R. Abrahamson 1996 Effects of a low-intensity, winter burn on long-unburned sand pine scrub. Natural Areas Journal 16: 171-183
Abrahamson W. G. A. F. Johnson J. N. Layne P. A. Peroni 1984 Vegetation of the Archbold Biological Station, Florida: an example of the southern Lake Wales Ridge. Florida Scientist 47: 209-250
Abrahamson W. G. J. N. Layne 2002a Relation of ramet size to acorn production in five oak species of xeric upland habitats in south-central Florida. American Journal of Botany 89: 124-131
Abrahamson W. G. J. N. Layne 2002b Post-fire recovery of acorn production by four oak species in southern ridge sandhill association in south-central Florida. American Journal of Botany 89: 119-123
Abrahamson W. G. J. N. Layne 2003 Long-term patterns of acorn production for five oak species in xeric Florida uplands. Ecology 84: 2476-2492[CrossRef][ISI]
Abrahamson W. G. J. Rubinstein 1976 Growth forms of Opuntia compressa (Cactaceae) in Florida sandridge habitats. Bulletin of the Torrey Botanical Club 103: 77-79[CrossRef][ISI]
Alt D. H. K. Brooks 1965 Age of the Florida marine terraces. Journal of Geology 73: 406-411
Boisen A. T. J. A. Newlin 1910 The commercial hickories. USDA Forest Service Bulletin 80
Bowers R. R. 1960 The tree that pays the taxes. West Virginia Conservation 24: 12-15
Carter L. J. D. Lewis L. Crockett J. Vega 1989 Soil survey of Highlands County, Florida. USDA Soil Conservation Service, Washington, D.C., USA
Chesemore D. L. 1975 Ecology of fox and gray squirrels (Sciurus niger and Sciurus carolinensis) in Oklahoma. Ph.D. dissertation, Oklahoma State University, Stillwater, Oklahoma, USA
Coblentz B. E. 1980 Production of Oregon white oak acorns in the Willamette Valley, Oregon. Wildlife Society Bulletin 8: 348-350
Dalke P. D. 1953 Yields of seeds and mast in second growth hardwood forest, southcentral Missouri. Journal of Wildlife Management 17: 378-380[CrossRef][ISI]
Elias T. S. 1980 The complete trees of North America. Van Nostrand & Reinhold, New York, New York, USA
Fowells H. A. 1965 Silvics of forest trees of the United States. USDA Handbook 271. Washington, D.C., USA
Givens K. T. J. N. Layne W. G. Abrahmson S. C. White 1984 Structural changes and successional relationships of five Florida Lake Wales Ridge plant communities. Bulletin of the Torrey Botanical Club 111: 8-18[CrossRef][ISI]
Grauke L. J. 2004 An introduction to the genus Carya. United States Department of Agriculture—Agricultural Research Service, Pecan Breeding & Genetics, Southern Crops Research Laboratory, Crop Germplasm Research Unit, website: http://extension-horticulture.tamu.edu/Carya (accessed 29 April 2004)
Greenberg C. H. 2000 Individual variation in acorn production by five species of southern Appalachian oaks. Forest Ecology and Management 132: 199-210[CrossRef][ISI]
Harper J. L. J. White 1974 The demography of plants. Annual Review of Ecology and Systematics 5: 419-463
Houle G. 1999 Mast seeding in Abies balsamea, Acer saccharum, and Betula alleghaniensis in an old growth, cold temperate forest of north-eastern North America. Journal of Ecology 87: 413-422[CrossRef][ISI]
Janzen D. H. 1971 Seed predation by animals. Annual Review of Ecology and Systematics 2: 465-492
Janzen D. H. 1976 Why bamboos wait so long to flower. Annual Review of Ecology and Systematics 7: 347-391
Janzen D. H. 1978 Seeding patterns of tropical trees. In P. B. Tomlinson and M. H. Zimmerman [eds.], Tropical trees as living systems, 83–128. Cambridge University Press, Cambridge, UK
Keeley J. E. W. J. Bond 1999 Mast flowering and semelparity in bamboos: the bamboo fire cycle hypothesis. American Naturalist 154: 383-391[CrossRef][ISI][Medline]
Kelly D. V. L. Sork 2002 Mast seeding in perennial plants: why, how, where?. Annual Review of Ecology and Systematics 33: 427-447[CrossRef][ISI]
Klinkhamer P. G. L. E. Meelis T. J. deJong J. Weiner 1992 On the analysis of size-dependent reproductive output in plants. Functional Ecology 6: 308-316[CrossRef][ISI]
Koenig W. D. J. M. H. Knops 2000 Patterns of annual seed production by northern hemisphere trees: a global perspective. American Naturalist 155: 59-69[CrossRef][ISI][Medline]
Little E. L. Jr. 1977 Minor eastern hardwoods, vol. 4. Atlas of United States trees. USDA Forest Service Miscellaneous Publication 1342
McCarthy B. C. J. A. Quinn 1989 Within- and among-tree variation in flower and fruit production in two species of Carya (Juglandaceae). American Journal of Botany 76: 1015-1023[CrossRef][ISI]
McKone M. J. D. Kelly W. G. Lee 1998 Effect of climate change on mast-seeding species: frequency of mass flowering and escape from specialist insect seed predators. Global Change Biology 4: 591-596[CrossRef][ISI]
Menges E. S. 1994 Fog temporarily increases water potential in Florida scrub oaks. Florida Scientist 57: 65-74
Menges E. S. W. G. Abrahamson K. T. Givens N. P. Gallo J. N. Layne 1993 Twenty years of vegetation change in five long-unburned Florida plant communities. Journal of Vegetation Science 4: 375-386[CrossRef][ISI]
Menges E. S. N. P. Gallo 1991 Water relations of scrub oaks on the Lake Wales Ridge. Florida Scientist 54: 69-79
Moody R. D. 1953 Mast production of certain oak species in Louisiana. Proceedings of the Annual Conferences Southeastern Association of Game & Fish Commissioners 7: 1-19
Myers R. L. 1990 Scrub and high pine. In R. L. Myers and J. J. Ewel [eds.], Ecosystems of Florida, 150–193. University of Central Florida Press, Orlando, Florida, USA
Myers R. L. D. L. White 1987 Landscape history and changes in sandhill vegetation in north-central and south-central Florida. Bulletin of the Torrey Botanical Club 114: 21-32[CrossRef][ISI]
Nixon C. M. M. W. McClain L. P. Hansen 1980 Six years of hickory seed yields in southeastern Ohio. Journal of Wildlife Management 44: 534-539[CrossRef][ISI]
Norton D. A. D. Kelly 1988 Mast seeding over 33 years by Dacyrdium cupressinum Lamb. (rimu) (Podocarpaceae) in New Zealand: the importance of the economies of scale. Functional Ecology 2: 399-408
Reekie E. G. 1998 An explanation for size-dependent reproductive allocation in Plantago major. Canadian Journal of Botany 76: 45-60
Sargent C. S. 1922 Manual of the trees of North America (exclusive of Mexico), vol. 1. Dover Publications, New York, New York, USA
Schmidt B. F. A. Bazzaz J. Weiner 1995 Size dependency of sexual reproduction and of clonal growth in two perennial plants. Canadian Journal of Botany 73: 1831-1837
Siegel S. 1956 Nonparametric statistics for the behavioral sciences. McGraw-Hill, New York, New York, USA
Silvertown J. W. 1980 The evolutionary ecology of mast seeding in trees. Biological Journal of the Linnaean Society 14: 235-250[CrossRef]
Smith C. C. J. L. Hamrick C. L. Kramer 1990 The advantage of mast years for wind pollination. American Naturalist 136: 154-166[CrossRef][ISI]
Sork V. L. 1983 Mammalian seed dispersal of pignut hickory during three fruiting seasons. Ecology 64: 1049-1056[CrossRef][ISI]
Sork V. L. J. Bramble O. Sexton 1993 Ecology of mast-fruiting in three species of North American deciduous oaks. Ecology 74: 528-541[CrossRef][ISI]
StatSoft. 1994 Statistica for Windows. StatSoft, Tulsa, Oklahoma, USA
Waller D. M. 1979 Models of mast fruiting in trees. Journal of Theoretical Biology 80: 223-232[CrossRef][ISI][Medline]
Woolfenden G. E. J. Fitzpatrick 1984 The Florida scrub jay: demography of a cooperative-breeding bird. Princeton University Press, Princeton, New Jersey, USA
Wunderlin R. P. B. F. Hansen 2003 Atlas of Florida vascular plants. Institute of Systematic Botany, University of South Florida, Tampa, website: http://www.plantatlas.usf.edu (accessed 29 April 2004)
This article has been cited by other articles:
|
|
 |
|
  W. G. Abrahamson Leaf traits and leaf life spans of two xeric-adapted palmettos Am. J. Botany, August 1, 2007; 94(8): 1297 - 1308. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
5 in burned and unburned sites