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

Abstract

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.

NTFP harvesters as citizen scientists: Validating traditional and crowdsourced knowledge on seed production of Brazil nut trees in the Peruvian Amazon

“…For example, both Brazil nut harvesters and research scholars [7,21] have argued that seed production is positively influenced by natural forest cover which is the preferred habitat of the Brazil nut pollinator bees [41], as well as by the presence of other plant species that are visited by these bees [22,42]. The smoke produced by vegetation burning has been cited by harvesters as negatively affecting pollinator presence and Brazil nut seed production, in line with findings elsewhere [43]. The fact that the flowering of the Brazil nut in Madre de Dios (December to February [44]) overlaps with the wettest period of the year when vegetation burning is minimal, might suggest that smoke and fire produced during other periods of the year may influence the bees’ presence, and possibly abundance, in the flowering season.…”

Explaining variation in Brazil nut fruit production

“…Disease, herbivory, or adverse weather such as high winds or storms, particularly during key phenological events such as pollination or fruit development, can reduce flowering or seed set (Stephenson, 1981). Liana presence has been shown to reduce fruit production of trees (Stevens, 1987;Kainer et al, 2006), and proximate disturbances such as fire also have been implicated (Layne and Abrahamson, 2004). Controlled experiments in monoculture orchards (Ponder and Jones, 2001), agroforestry systems (Jones et al, 1995), and natural forests (Vaughton, 1991) clearly demonstrate the importance of nutrient and light availability as explanatory variables of production variation.…”

“…Reproduction is a function of accumulated resources, and is positively correlated to total tree height (Layne and Abrahamson, 2004) and diameter (Ares and Brauer, 2004). Successful reproduction in 1 year, however, is often followed (or ''switched'') at the expense of vegetative growth (Harper and White, 1974;Kelly and Sork, 2002).…”

Differences in life‐cycle stage components between native and introduced ranges of five woody Fabaceae species

“…Unfortunately, due to logistical constraints, our study only provides a snapshot of one season of reproduction. Second, environmental and biogeographic factors, including rainfall, soil nutrients and light availability, are likely to affect plant size, seed weight, seed quantity and quality (Auld & Myerscough ; Kelly & Sork ; Layne & Abrahamson ). In this study, we did not measure site‐specific environmental characteristics; however, we did find significant variation among sites within ranges for all variables except crown projection and time to germination.…”