Pinus devoniana LIKELY AVOIDS DROUGHT STRESS BY DELAYING SHOOT ELONGATION

Abstract

Understanding the growth rate and the timing of conifer seedling bud elongation can be useful in selecting tree species for commercial plantations and ecological restoration, either under the current climate or to adapt to climatic change. Shoot growth dynamics of three dominant Pinus species of the pine-oak forest of the Nuevo San Juan Parangaricutiro indigenous community in Western Mexico were inspected. Using a common garden trial of three species and seven provenances, growth was related to contemporary (1961-1990 period averages) and future (rcp6.0 ensemble and decade centered on year 2060) climate. Significant differences between species
were found in two-year-old plants, P. pseudostrobus and P. leiophylla showed greater shoot elongation and plant height, larger elongation period and plant height, and later growth cessation than P. devoniana, P. pseudostrobus and P. leiophylla, which begin their growth and elongate their shoots during the warm, dry season (March to May). Pinus devoniana delays the start of growth until the end of the dry season (end of May). This suggests that P. devoniana, at least for the second year of growth, probably avoids drought stress by delaying shoot elongation, which could partly explain why this species grows at lower altitude than the other pines. Climate change projections for Mexico indicate an increase in aridity conditions by the year 2060, particularly for the lower altitudinal limit of the populations of P. pseudostrobus and P. leiophylla. Reforestation with P. devoniana might be required at the lower altitud limits of these pines if forest decline continues.