Relationships between needle traits, needle age and site and stand parameters in Pinus pinaster

Needle age class explains most of the variability in maritime pine leaf traits. Needle size and area are related to climate and foliar nutrients. Specific leaf area is highest in stands with high site index and nutrient concentrations. Needle size, leaf traits and site parameters were studied in 31 Pinus pinaster plots (93 trees) located in Galicia (NW Spain). All needles were classified according to age class, and foliar nutrients were analyzed for each tree and age class. Needle age significantly affected the needle length (NLength), needle width (NWidth), needle thickness (NThickness), leaf area (projected A (p) and total A (t)), specific leaf area (SLA(p) and SLA(t)), needle tissue density (N (d)), N per unit leaf area (NN), average dry weight (D (w)) and moisture content (M (u)). The age class effect was the most important factor for assessing the variability in leaf dimensions. A regression model developed to predict the NLength in age class 1 indicated the importance of climate and nutritional conditions. An important proportion of the variation (25.2 %) in NLength for age classes 1 and 2 can be predicted only with spring precipitation. The SLA(p) was positively affected by concentrations of foliar nutrients, particularly K (FK), and showed a rather high level of plasticity considering that maritime pine is a light demanding species. The SLA(p) in the stands under study was higher than that of provenances from drier areas. SLA(p) was higher in plots located at low elevations, with good site index and nutritional status of K and Mg (FMg). Boosted regression tree analysis showed that FN contributed most to explaining needle traits. FN concentration was negatively correlated with N (d), SLA(p) and site index.