Effect of Temperature on Germination and Distribution of Pinus ayacahuite Ehrenb. ex Schltdl. Under Climate Change Scenarios in Mexico

Pinus ayacahuite is an important species for reforestation in Mexico, as it is a pioneer species in open areas. Its regeneration could be threatened by rising temperatures. The effect of a temperature gradient on germination was analyzed, and potential distribution projections of climate change scenarios were modeled at various time scales. Seeds were collected in Huayacocotla, Veracruz; these were germinated under nine constant temperatures (5–45 °C). Germination parameters, cardinal temperatures, and thermal time were estimated using a Gaussian model. Germination occurred between 10 and 40 °C, with optimal, base, and ceiling temperatures of 27 °C, 10 °C, and 42 °C, respectively, and a thermal time (Tt50) of 118.5 °C d−1. Based on climate change projections (SSP1-2.6 and SSP5-8.5), NASA’s GISS-E2-1-G model predicts temperature increases from 1.1 to 2.3 °C by 2050 and from 1.7 to 3.6 °C by 2090, which would accelerate germination by 12.9–25 days. However, the species’ potential distribution is projected to decline by 15%–22%, primarily in southern states such as Chiapas, Oaxaca, and Puebla, although it could shift to new suitable areas in Tamaulipas and Nuevo León. These results suggest that while higher temperatures may favor earlier germination, water availability will remain the main limiting factor for successful establishment. Integrating physiological parameters into distribution models offers a stronger foundation for seed storage, conservation, and reforestation strategies in the face of changing climatic conditions.