EFFECTS OF SITE QUALITY AND GENETICS ON BEAR OAK MAST PRODUCTION

From a total sample of 1,350 bear oak (Quercus ilicifolia) trees on which all acorns had been counted, the 10 highest, 10 lowest and 10 intermediate acorn producers were selected. No significant differences in site quality were found to exist beneath these trees. Fifty-four additional trees were transplanted onto a common site. One-third of these were high acorn producers, one-third were medium and one-third were poor acorn producers. These trees failed to converge in productivity, indicating that genetics plays a major role in determining acorn yields in bear oak. STUDIES of acorn yields in several species of oaks have indicated that certain individual trees are inherently better acorn producers than other trees of the same species (Wood, 1934; Cypert and Webster, 1948; Downs, 1949; Burns et al., 1954; Christisen, 1955; Collins, 1959; Tryon and Carvell, 1962; Goodrum, Reid, and Boyd, 1971). Most of these studies were descriptive rather than experimental in approach. Similar differences in acorn production of individual bear oak (Quercus ilicifolia) trees were observed in the Pine Barrens of southern New Jersey. Bear oak is found on dry sandy barrens along the coast, on rocky hillsides, and on the dry, infertile soils of plateaus and mountain tops. This species, which is intolerant of shade, covers extensive tracts where the forest has been opened up by lumbering or fire (Brown, 1938). Bear oak is found in all of the states which border the Atlantic Ocean from North Carolina north through Maine as well as in Pennsylvania and West Virginia (Brown, 1938; Worley, Bramble, and Byrnes, 1957). Wolgast and Stout (1977) indicate that high humidity at the time of flowering adversely affected fruit set in bear oak, but little else is known or even hypothesized concerning the factors which influence acorn production in this species, although some theories of acorn production in general have been formulated (Sharp and Chisman, 1961; Sharp and Sprague, 1967). The purpose of this paper is to report on the results of a designed experiment that tested the relative influence of site quality and genetics on bear oak acorn production. PROCEDURES-Counts of mature acorns were conducted on approximately 1,350 bear oak trees 1 Received for publication 12 August 1977; revision accepted 10 January 1978. during the fall of 1971 on the Manchester Wildlife Management Area in Ocean County, New Jersey. These nine-year-old trees were growing in full sunlight with no overtopping vegetation present. From these 1,350, a sample of the ten highest, ten lowest and ten in the middle in terms of acorn production were chosen. The following site characteristics were measured immediately beneath each sample tree selected: depth to the water table, nitrate nitrogen, ammonium nitrogen, iron, magnesium, phosphorus, potassium, organic matter, pH, and soil texture (Table 1). There were no detectable differences in depth to the water table beneath the selected trees, but there were differences in all other factors measured. Step-wise multiple linear regression analysis was performed on these data and an equation was developed to predict the relative influence of these site characteristics on acorn productivity. An additional study was located on the Greenwood Forest wildlife management area in Ocean County, New Jersey. Eighteen of the highest acorn producing trees, 18 of the lowest, and 18 in the middle were selected from a stand of nineyear-old trees which were growing in full sunlight. These trees were transplanted onto a common site during March of 1971, in a randomized block design as described in Zar (1974). The number of immature acorns produced in 1971 and the number of immature and mature acorns produced in 1972, 1973, and 1974 were counted on each tree and the data subjected to analyses of variance (Table 2). RESULTS AND DISCUSSION-Table 1 presents the information on acorn counts and site characteristics. The equation which best describes the relative effects of each of these site factors is as follows: