Effect of pine harvesting on leaf nutrient dynamics in young oak trees at NW Spain

Abstract

The recovering of the native oak forest from pine plantations in unproductive areas is one of the scientific and politic challenges faced in NW Spain. We studied the effect of Pinus pinaster clearcutting on nutrient dynamics and availability for the late-successional species Quercus robur that dominates the understory of the pine canopy. Variations in leaf nutrient content (nitrogen, phosphorus, potassium and sodium) expressed on a leaf mass and area basis, were studied during a growing season, and changes in resorption efficiency, resorption proficiency, nutrient-use efficiency and nutrient-response efficiency were studied in oak leaves of harvested and undisturbed sites. Soil available nitrogen was 30% lower on the harvested sites, but no differences in the inorganic and organic soil phosphorus fractions were detected. Leaf specific mass was significantly higher in trees of the harvested sites, due to the lower leaf area found on these site. Leaf N concentration was 20% higher at the undisturbed sites, but pine harvesting did not modify the leaf P concentration. Consequently, nutrient content in plants seemed to reflect soil nutrient availability. The leaf N-to-P (between 18 and 20) ratio suggested that P was more limiting for growth than N for the young oaks. Pine harvesting increased the resorption rate and resorption efficiency of the young oaks for N, P and K. Pine harvesting decreased by 25% the minimum amount of N and K in the oak leaves (resorption proficiency), but no differences were found in the P resorption proficiency between sites. For P, the resorption proficiency values were nearer to those considered as complete resorption on both sites. Pine harvesting increased the leaf-level nutrient-use efficiency for all nutrients, but decreased the P uptake efficiency on the deforested sites. Our results suggested that changes in nutrient-use efficiency and nutrient resorption of young oaks after pine harvest may be influenced by changes in soil nutrient and light availability caused by pine harvest.