Ubiquitous germination among common perennial species in response to facilitated and unfacilitated microhabitats

Abstract

We present results from a study that examines species-specific facilitation of germination in an arid perennial community. This system suffered 64% adult mortality and the local extinction of two common species as a consequence of drought that occurred between 1999 and 2004. Ambrosia dumosa, Larrea tridentata, and Tetracoccus hallii are included as candidate benefactor species based on their high abundance and broad distribution at the study site. Using complementary field and greenhouse experiments, we measured the effects of facilitation, light and nitrogen on germination of four species common to the region, L. tridentata, A. dumosa, Sphaeralcea ambigua and Eriogonum fasciculatum.Our results show that benefactor species do not uniquely influence germination. Species-specific effects among beneficiaries largely explained differences in percent germination in the field, and the interaction between beneficiary species and microhabitat was significant for only one species. E. fasciculatum consistently showed significantly higher germination than more abundant species and showed reduced germination in the interspace. In the greenhouse, germination responses differed at each light level, beneficiaries responding most uniquely at full light. These results refine expectations from previous studies of facilitation at this site by showing that facilitation does not strongly enhance germination.