Tree growth changes with climate and forest type are associated with relative allocation of nutrients, especially phosphorus, to leaves and wood

Aim To test our hypothesis that trees change the allocation and the proportion of different nutrients between leaves and wood to maximize growth along climatic gradients. Location Catalonia, Iberian Peninsula. Methods We tested the relationships of total forest nutrient content, stoichiometry and allocation between leaves and wood in trees with growth along environmental gradients using data from the Catalan Forest Inventory and a suite of multivariate mixed models, ANOVAs and principal components analyses. Results The aboveground growth of trees and the nutrient content of leaves and wood were positively correlated with mean annual precipitation (MAP). The changes in C:nutrient ratios were proportionally higher in leaves than in wood, mainly in deciduous forests. Higher MAP was also related to a lower N:P content ratio in leaves and wood but was not related to a greater allocation of P than N in leaves relative to wood (N:PL/W). Conifers, which presented the highest relative aboveground growth, had the lowest N:PL/W (0.99 ± 0.02), whereas the slow-growing evergreens had the highest N:PL/W (2.26 ± 0.23). Main conclusions In all forest types, growth was related to a higher allocation of nutrients to leaves than to wood, especially of P, coinciding with better climatic conditions for growth (higher MAP in this Mediterranean context). The highest rates of growth were linked to the lowest N:P ratios. The allocation of P relative to N in leaves is higher in conifers than in evergreen and deciduous trees.