Responses of hardwood regeneration to fire in mesic forest openings. III. Whole-plant growth, biomass distribution, and nitrogen and carbohydrate relations

The effects of fire on the carbon and nitrogen balance of northern red oak (Quercus rubra L.), white ash (Fraxinus americana L.), and sugar maple (Acer saccharum Marsh.) regeneration were studied in mesic openings in a hardwood forest. A plot in each of four openings was burned in the spring of both 1989 and 1990. Relative growth rate, leaf weight ratio, and concentrations of nonstructural carbohydrate and N were monitored on planted and extant regeneration in burned and nonburned plots. In the absence of fire, extant oak grew as rapidly as ash and maple, but the relative growth rate of planted oak was the lowest of any species or regeneration type. Repeated burning had little effect on the net growth of oak, but it decreased that of ash and maple by 24-85%. Fire effects on relative growth rate were mediated primarily by changes in leaf weight ratio, but the causes underlying these changes were not fully elucidated. They were not consistent with trends in plant nonstructural carbohydrate or N concentration, which increased or remained unaffected after fire in all species. In general, oak possessed a number of characteristics, such as a high root starch concentration and an abundance of belowground dormant buds, which appeared to contribute to its post-fire vigor.