1. Many leaf traits strongly vary with tree size and environmental factors, but the importance of these factors to intraspecific variations of leaf traits in forest trees have rarely been simultaneously evaluated.
2. We measured needle longevity and specific leaf area (SLA) and nitrogen (N) content of every needle age (0 to 4 year old) for 65 individuals with 0.3-100 cm diameter at breast height (DBH) for an evergreen coniferous species, Pinus koraiensis Sieb. et Zucc., in Northeast China. We simultaneously evaluated effects of tree size (DBH or tree height) and environment factors (light intensity, soil N content and water availability) on the needle longevity, SLA, foliage N content as well as the slopes of regressions of SLA and foliage N content against needle age.
3. All of the studied leaf traits and slopes of regressions of SLA and foliage N content against needle age were significantly related to tree size. Tree height had a greater impact on SLA and area-based leaf N content (N_area), whereas DBH was more important for needle longevity and mass-based leaf N content (N_mass). The environment variables, light intensity, soil N content and water availability, were rather minor factors for trait variations compared with tree size. Significant influences of light intensity were found only on needle longevity, and soil N and water availability had no effects on the leaf traits.
4. Our study clearly showed that tree size is an important driver of intraspecific variations in the key leaf traits of Pinus koraiensis in a natural forest. We also emphasize the importance of DBH or tree height varies depending on leaf traits, suggesting various mechanisms of size effects on the intraspecific variations in leaf traits. We suggest that ecological significance of leaf trait variations needs reconsideration incorporating tree size effect.

The original data on functional traits, environment factors (light, soil nutrient and soil water) were collected at individual scale for an evergreen coniferous species within a wide size range (0.3-100 cm DBH) in northeast China. 

Someon interested in exploring the effects of tree size on variations of leaf traits and relationships between leaf trait and needle age maybe interest in these data.