Differences in germination response to smoke and temperature cues in ‘pyrophyte’ and ‘pyrofuge’ forms of Erica coccinea (Ericaceae)

Abstract

Many plants in fire-prone ecosystems produce seeds that are cued to germinate after fire. However, fire is not uniform in the landscape, and there are often refugia where fire does not reach, like rocky outcrops or moist valleys. Erica coccinea, a heath shrub from the South African fynbos, has two distinct pyrophyte forms (a resprouter and a seeder) as well as a ‘pyrofuge’ form that only occurs in fire refugia. We measured germination response to smoke and incubation temperature in seeds from pyrophyte (resprouter and seeder) and pyrofuge populations to determine whether these forms responded differently to a fire-cue (smoke) and a general germination cue (temperature). We found that seeds from pyrofuge plants had high germination success (80.9–92.0%) at the lowest incubation temperature (15/8°C 12h day/night cycle) regardless of smoke exposure. In contrast, seeds from pyrophytes (resprouters and seeders) responded strongly to the smoke cue (71.2–95.0%) and were not as limited by temperature. These results show that fire presence and absence is driving divergence of the primary germination cue in Erica coccinea. Given the patchiness of many natural fire regimes worldwide, we expect there may be pyrofuge populations exhibiting a similar divergence of traits in other species and other fire-prone ecosystems.