Individual variation in acorn production by five species of southern Appalachian oaks

Acorns are an important wildlife food resource and seed source for oak rege neration. Most acorn production studies note wide and consistent difference s in acorn productivity among individuals, but none clearly demonstrate det erminants of productivity. Acorn production by black, northern red, scarlet , chestnut and white oak was measured from 1993 to 1997 in the southern App alachians was measured and compared among species and individuals. To stand ardize comparisons among different sized trees and simplify for use by fore st managers, the number of acorns per tree were converted to the number/m(2 ) BA (basal area). On average, white oak produced the most acorns and chest nut oak the fewest. Northern red and white oak produced higher green weight and dry biomass than the other three species. There was a significant posi tive relationship between tree basal area and the number of acorns produced per crown for all species (r(2) between 0.10 and 0.27). However, this is b ecause larger trees have greater crown areas for producing acorns, and not because they produce more acorns per unit area of crown. Alone, BA was sign ificantly, positively correlated with the number of acorns/m(2) BA only in black, northern red (p < 0.06) and white oak (not in scarlet or chestnut oa k) but explained little of the variation in acorn production among individu als. Trees less than or equal to 25 cm DBH of most species produced signifi cantly fewer acorns/m(2) BA than their larger counterparts. However, many s mall (<23 cm DBH) scarlet oaks originating from a 1967 clear-cut were proli fic producers, whereas white oaks (<25 cm DBH) in the same stand were not. Frequency of acorn production ranged from never to yearly among individuals . Good producers (trees producing greater than or equal to 5-year species m ean) composed 20% (chestnut oak) to 46% (northern red oak) of sample popula tions but contributed disproportionately to the acorn crop in moderate and good crop years. Good producers produced acorns more frequently and had mor e acorns/m(2) BA on fruiting trees than did poor producers. However, in any given year good and poor producers were similarly represented in the fruit ing population. Hence, good producers could not be easily identified by the presence of acorns during poor crop years, nor could poor producers be ide ntified by an absence of acorns in good crop years. (C) 2000 Elsevier Scien ce B.V. All rights reserved.