Foliar resorption of beech and maple along an elevation gradient in a northern hardwood forest

Foliar resorption is a principal nutrient conservation mechanism in terrestrial vegetation that could be sensitive to ongoing changes in climate and atmospheric nitrogen (N) deposition. We quantified N resorption in northern hardwood forests along an elevation gradient of decreasing temperature and increasing soil N availability to evaluate how this critical nutrient cycling process can be expected to respond to global and regional environmental changes. Foliar N resorption proficiency (NRP) increased significantly at lower elevations for both sugar maple and American beech, the dominant species in these forests. Foliar N resorption efficiency (NRE) also decreased with increasing elevation, but only in one year. Both species exhibited strong negative relationships between NRP and soil N availability. Thus, we anticipate that with climate warming and decreasing N inputs, northern hardwood forests can be expected to exhibit stronger N conservation via foliar resorption. Both species also exhibited strong correlations between resorption efficiency of N and C, but resorption of both elements was much greater for beech than sugar maple, suggesting contrasting mechanisms of nutrient conservation between these two widespread species.