Leaf traits variation in silver birch (Betula pendula Roth) across sites, crown positions, and tree social classes in the Western Carpathians

Silver birch (Betula pendula Roth) is a widely distributed, early-successional broadleaved species with ecological and partly also economic significance in Europe. Despite rather extensive research on its ecology and wood production, detailed studies on leaf traits remain limited. This study quantified basic leaf characteristics – leaf area, leaf mass, specific leaf area (SLA), and petiole mass – of young silver birches across ten naturally regenerated stands in Slovakia. A total of 204 trees were sampled, representing four tree social classes (dominant, codominant, intermediate, overtopped), and 3,672 leaves were collected from upper, middle, and lower crown positions. Leaf area and mass were measured after scanning and oven-drying, while SLA was calculated as the ratio of fresh leaf area to dry mass. Results revealed substantial variation in leaf traits among sites, social classes, and crown positions. Leaf area and mass were highest in dominant trees and in upper crown leaves, while overtopped trees produced smaller, lighter leaves. Conversely, SLA increased from dominant to overtopped trees and from upper to lower crown positions, reflecting morphological adaptation to reduced light availability. Analysis of petiole mass indicated that leaf blades accounted for over 93% of total leaf mass, with stalk allocation varying with crown position and tree social status. Significant interactions among sites, crown positions, and social classes highlighted the multifactorial control of leaf morphology. These findings demonstrate the pronounced morphological plasticity of silver birch leaves, enabling flexible resource-use strategies that optimize carbon gain under contrasting light environments. Such plasticity likely contributes to the species’ competitive success, ecological amplitude, and potential role in climate-adaptive forestry. This study provides essential baseline data on leaf traits of silver birch and emphasizes the need for further research linking environmental conditions to variations in leaf morphology and physiology.