Growth of foxtail pine seedlings at treeline in the southeastern Sierra Nevada, California, USA

I examined elevational trends in growth and nutrient use of foxtail pine (Pinus balfouriana) seedlings in the south-eastern Sierra Nevada, U.S.A., in areas where seedlings have established above the current treeline. I measured growth, foliar nitrogen concentration, and nitrogen relative accumulation rates of seedlings at three elevations: (i) forest interior sites (3435 m), (ii) treeline (3460 m), and (iii) above treeline (3485 m). As elevation increased, the basal area of adult trees and density of seedlings declined, nutrient inputs from aboveground litter declined, and litter C:N ratio declined. Annual height growth; of seedlings increased significantly with elevation in 7 of 8 years measured (1985-1992). There was no significant change in annual lateral twig growth with, elevation. There was a positive trend in relative: growth rates and nitrogen relative accumulation rates with elevation. Variance among years in height and twig growth was higher at and above treeline than in forested sites. Significant correlations ber seen annual growth and climate were few and inconsistent among variables and elevations. The concentration of nitrogen in needles declined with needle age, but neither nitrogen concentration nor nitrogen relative accumulation rare in seedlings differed significantly among elevations. Based an patterns of seedling growth, I conclude that, relative to forest interior sites, conditions above the treeline were favorable for seedling growth during the last 12 years.