Do All Oaks Mast

Acorn production patterns are often characterized as masting, a term that implies synchronous acorn production that results in boom or bust

Figure 10.2. Mean (1993-1997) (±SE) number of acorns/m2 BA produced by four diameter classes of black oak (BO) (F = 5.8; p = 0.0012), northern red oak (NRO) (F = 11.8, p = 0.0001), scarlet oak (SCO) (F = 3.85; p = 0.0013), chestnut oak (CO) (F = 1.1; p = 0.3509), and white oak (WO) (F = 6.71; p = 0.0003) in the southern Appalachians. Letters A-C denote significant differences in mean acorn production among diameter classes. Acorn data were natural log transformed for ANOVA but are presented as actual means.

Figure 10.2. Mean (1993-1997) (±SE) number of acorns/m2 BA produced by four diameter classes of black oak (BO) (F = 5.8; p = 0.0012), northern red oak (NRO) (F = 11.8, p = 0.0001), scarlet oak (SCO) (F = 3.85; p = 0.0013), chestnut oak (CO) (F = 1.1; p = 0.3509), and white oak (WO) (F = 6.71; p = 0.0003) in the southern Appalachians. Letters A-C denote significant differences in mean acorn production among diameter classes. Acorn data were natural log transformed for ANOVA but are presented as actual means.

crop years. Most studies of eastern oaks report large fluctuations in acorn crop size (e.g., Downs and McQuilken 1944, Burns et al. 1954, Beck 1977). However, despite the large year-to-year fluctuations exhibited by most oak species, moderate crop sizes also are common. The degree of synchronized fruiting within a population of conspecifics is not directly addressed in most studies. Koenig, Mumme, et al. (1994) found evidence of species-specific masting intervals at the individual level but not at the population level. Conversely, Sork et al. (1993) found that most northern red and white oak conspecifics (and to a lesser degree black oak) produced acorns in the same years.

Between 1993 and 1997 annual acorn production by individual trees within a population was not synchronous for any species in our study. Within a species the proportion of trees bearing acorns ranged from 70% (chestnut oak, 1996) to 90% (white oak, 1996) during the maximum crop year and from 3% (white oak) to 29% (black oak) during the poorest crop year (1996 for scarlet oak, 1997 for all other species). At least 29% of individuals of all species produced acorns every year except the poorest crop year for that species. At least one year of the five-year study was characterized by approximately one-third to two-thirds of sample trees producing acorns for each species (Greenberg and Parresol 2000). Koenig and Knops (Chapter 9) report some evidence for "normal" masting in California oaks and other temperate-zone oaks, tempered by environmental variables. Indeed, high year-to-year variability in the degree of fruiting synchrony and crop size within a population suggests that "normal" rather than "strict" masting (sensu Kelly 1994) better characterizes the fruiting patterns of southern Appalachian oaks.

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