Individual variation in acorn production by ®ve species of southern Appalachian oaks

Acorns are an important wildlife food resource and seed source for oak regeneration. Most acorn production studies note wide and consistent differences in acorn productivity among individuals, but none clearly demonstrate determinants of productivity. Acorn production by black, northern red, scarlet, chestnut and white oak was measured from 1993 to 1997 in the southern Appalachians was measured and compared among species and individuals. To standardize comparisons among different sized trees and simplify for use by forest managers, the number of acorns per tree were converted to the number/m BA (basal area). On average, white oak produced the most acorns and chestnut oak the fewest. Northern red and white oak produced higher green weight and dry biomass than the other three species. There was a signi®cant positive relationship between tree basal area and the number of acorns produced per crown for all species (r between 0.10 and 0.27). However, this is because larger trees have greater crown areas for producing acorns, and not because they produce more acorns per unit area of crown. Alone, BA was signi®cantly, positively correlated with the number of acorns/m BA only in black, northern red (p < 0.06) and white oak (not in scarlet or chestnut oak) but explained little of the variation in acorn production among individuals. Trees 25 cm DBH of most species produced signi®cantly fewer acorns/m BA than their larger counterparts. However, many small (<23 cm DBH) scarlet oaks originating from a 1967 clear-cut were proli®c 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 5-year species mean) composed 20% (chestnut oak) to 46% (northern red oak) of sample populations but contributed disproportionately to the acorn crop in moderate and good crop years. Good producers produced acorns more frequently and had more acorns/m BA on fruiting trees than did poor producers. However, in any given year good and poor producers were similarly represented in the fruiting population. Hence, good producers could not be easily identi®ed by the presence of acorns during poor crop years, nor could poor producers be identi®ed by an absence of acorns in good crop years. # 2000 Elsevier Science B.V. All rights reserved.