Abies religiosa habitat prediction in climatic change scenarios and implications for monarch butterfly conservation in Mexico

Abstract

Abies religiosa (HBK) Schl. & Cham. (oyamel fir) is distributed in conifer-dominated mountain forests at high altitudes along the Trans-Mexican Volcanic Belt. This fir is the preferred host for overwintering monarch butterfly (Danaus plexippus) migratory populations which habitually congregate within a few stands now located inside a Monarch Butterfly Biosphere Reserve. Our objectives were to predict and map the climatic niche for A. religiosa for contemporary and future (2030, 2060 and 2090) climates, suggest management strategies to accommodate climate changes, and discuss implications for conservation of monarch butterfly overwintering sites in Mexico. A bioclimate model predicting the presence or absence of A. religiosa was developed by using the Random Forests classification tree on forest inventory data. The model used six predictor variables and was driven primarily by the mean temperature of the warmest month, an interaction between summer precipitation to and winter temperatures, and the ratio of summer to annual precipitation. Projecting the contemporary climate niche into future climates provided by three General Circulation Models and two scenarios suggested that the area occupied by the niche should diminish rapidly over the course of the century: a decrease of 69.2% by the decade surrounding 2030, 87.6% for that surrounding 2060, and 96.5% for 2090. We discuss assisted migration of A. religiosa upwards in altitude by 275m so that populations of 2030 would occupy the same climates as today. The projections also show that by the end of the century, suitable habitat for the monarch butterfly may no longer occur inside the Biosphere Reserve. We therefore discuss management options and associated research programs necessary for assuring perpetuation of future butterfly habitat.