Genetic variation and spatial structure in sugar maple (Acer saccharum Marsh.) and implications for predicted global-scale environmental change

Current ecosystem model predictions concerning the effects of global temper ature increase on forest responses do not account for factors influencing l ong-term evolutionary dynamics of natural populations. Population structure and genetic variability may represent important factors in a species' abil ity to adapt to global-scale environmental change without experiencing majo r alterations in current range limits. Genetic variation and structure in s ugar maple (Acer saccharum Marsh.) were examined across three regions, betw een two stands within regions, and among four to five open-pollinated famil ies within stands (total N = 547 genotypes) using 58 randomly amplified pol ymorphic DNA (RAPD) markers. Differences within open-pollinated families ac count for the largest portion of the total variation (29%), while differenc es among regions represent less than 2% of the total variation. Genetic div ersity, as indicated by estimates of percent polymorphic loci, expected het erozygosity, fixation coefficients, and genetic distance, is greatest in th e southern region, which consists of populations with the maximum potential risk due to climate change effects. The high level of genetic similarity ( greater than 90%) among some genotypes suggests that gene flow is occurring among regions, stands, and families. High levels of genetic variation amon g families indicate that vegetational models designed to predict species' r esponse to global-scale environmental change may need to consider the degre e and hierarchical structure of genetic variation when making large-scale i nferences.