Big sagebrush germination patterns: subspecies and population differences.

Abstract

Habitat-correlated differences in laboratory germination response under autumn (15 degrees C) and winter (1 degree C) temperature regimes were examined for 69 big sagebrush (Artemisia tridentata Nutt., Asteraceae) seed collections from a range of habitats in 7 western states. Mountain big sagebrush (ssp. vaseyana) exhibited the widest variation in dormant seed percentage and termination rate at 15 degrees C. Collections from severe winter sites had larger dormant seed fractions and slower germination rates than collections from mild winter sites. Basin big sagebrush (ssp. tridentata) and Wyoming big sagebrush (ssp. wyomingensis) collections were largely non-dormant and germinated quickly at 15 degrees C regardless of collection site winter climate. At 1 degree C, number of days to 50% of total germination was negatively correlated with collections site mean January temperature for all 3 subspecies. Collections from severe winter sites required up to 113 days to germinate to 50% at 1 degree C, while collections from mild winter sites required as few as 6 days. Habitat-correlated variation in germination response appears to be of adaptive significance. Dormancy and slow germination at 15 degrees C may prevent germination during autumn storms in the mountains, while delayed germination at continuous 1 degree C may prevent precocious germination under snowpack. In contrast, at mild winter sites, winter germination is promoted and probably affords the best chance for seedling survival. Between-population variation in germination strategy should be considered when artificially seeding this species.