Adaptation to climate and correlated evolution in pines
To understand what drives distributions of plants across the landscape, we need to determine how species adapt to contrasting environments. Functional variation across resource gradients may be caused by individual traits responding to different environmental selection pressures and by correlated evolution among functionally linked traits. To test for adaptation to climate and correlated evolution among functional traits, I used physiological data from 26 pine species grown in a common garden. Adaptive relationships were evaluated using standard correlations and phylogenetically independent contrasts. Key trade-offs among functional traits support a division of pines into more competitive versus retentive functional types. Warmer southern climates were associated with fast plant growth, water transport, high leaf biomass and low photosynthetic efficiency, whereas northern pines exhibited slower growth, water transport, reduced leaf tissue and higher photosynthetic efficiency. Results suggest that pine distribution is largely influenced by adaptation to temperature and correlated evolution among functional traits.