Prescribed Burning in the Oak-pine Forest of the New Jersey Pine Barrens: Effects on Growth and Nutrient Dynamics of Two Quercus Species

Abstract

To determine the effect of the transient increase in nutrient availability which follows prescribed burning in the New Jersey Pine Barrens, we monitored growth and foliar nutrient dynamics of white oak (Quercus alba) and chestnut oak (Q. prinus) in neighboring burned and unburned plots. Growth rates of oak trees in the burned plot were significantly higher in 1985 (the postburn year) than in the 4 years prior to the fire. Growth increases in the burned site averaged 55 % for white oak and 38% for chestnut oak. In contrast, relative growth rates of reference site Quercus trees did not differ between preburn and postburn years. Phosphorus resorption and calcium deposition in chestnut oak were greater in the burned site, though growth efficiencies did not differ between chestnut oak trees in the burned and reference sites. Calcium deposition and phosphorus growth efficiency of white oak were greater in the burned site; no differences in white oak N or P resorption were noted. These oaks showed rapid growth responses to the transient increases in nutrient supply produced by prescribed burning. Pinus rigida growth also increased slightly, though the increase was less than those of the oaks. These results contradict earlier assertions of the efficacy of sporadic prescribed burning as a management tool in these oak-pine forests and suggest that sporadic prescribed burning may accelerate, not retard, succession toward oak dominance. INTRODUCTION Since the early 1930s the use of prescribed burning as a forest management tool in the New Jersey Pine Barrens has been justified on the basis of four postulated benefits: (1) improvement of the seedbed for Pinus establishment; (2) preventing the exdusion of Pinus by oaks (Quercus spp.) by slowing or stopping oak growth, and killing oak saplings; (3) reduction of the fuel mass and therefore wildfire probability, and (4) improvement of soil fertility by the release of nutrients bound in the litter and humus (Little and Moore, 1945; Burns, 1952). Though we have demonstrated that prescribed burning on a 3-yr rotation does not mineralize a significantly greater mass of mineral nutrients than occurs through litter decay (Boerner and Lord, 1984), significant transient increases in nutrient availability may occur immediately after a prescribed burn. Current knowledge of the relationship between nutrient availability, nutrient use efficiency, and growth of oaks (Ostman and Weaver, 1982; Boerner, 1984) and the response of stress-tolerating trees to transient increases in nutrient availability (Grime, 1979) suggests that periodic prescribed burning would increase, not decrease, oak growth rate, though possibly at the expense of decreased nutrient use efficiency. If true, the effect of prescribed burning would be to ac'All correspondence should be forwarded to this author.