Seed germination characteristics are known to influence population and community dynamics, especially in variable environments. Southern California coastal sage scrub (CSS) is primarily made up of dominant perennial shrub canopies and annual forb understories, which co-occur. Exploring germination patterns amongst species in this system may help elucidate strategies that support species persistence in the landscape, and inform our understanding of seed bank dynamics.
Temperature and water influence seed germination. Therefore, we explored germination patterns of three Southern (CSS) plant species: Salvia columbariae (annual forb), Encelia californica (perennial shrub), and Eriogonum fasciculatum (perennial shrub) under a range of temperatures (8°C, 14°C, 22°C, 28°C) and water potentials (-0.025, -0.125, -0.325, -0.5 mPa) through a series of growth chamber experiments. We compared germination fraction, germination rate, and germination timing amongst the three species. We hypothesized that annual forbs would exhibit a more conservative germination niche, and perennial shrubs would germinate over a wider set of conditions, because in CSS, forbs are thought to rely on long-term seed banks, while shrubs are thought to depend on consistent year-to-year seedling recruitment.
We generated time-course curves for each species, and compared data amongst species. Germination patterns varied amongst species, with clear differences observed between functional groups. Maximum germination percentage for the annual forb S. columbariae was lower than both shrub species, and occurred at 14°C and -.025 mPa. Maximum germination percentage for E. fasciculatum was highest of the three species, and occurred at 14°C and -.325 mPa. In S. columbariae, maximum germination percentage decreased as water potential became more negative, while in E. fasciculatum, germination percentage increased as water potential became more negative, specifically under the 14°C and 22°C treatments. Germination rate was highest for S. columbariae at 14°C and -.025 mPa, and highest for E. californica at 22°C and -.025 mPa. Germination rate was highest for E. fasciculatumat 22°C, but equal across water potential treatments. Timing of first germination was latest in the 8°C treatment and earliest in the 22°C treatment, across species.
Comparing germination behavior across members of this plant community provides insight into CSS seed ecology. Our findings may not only inform the selection of plant species suitable for restoring specific environments, but may also improve our predictions about how these vegetation communities may respond to global change.