The role of the peat seed bank in plant community dynamics of a fire‐prone New Zealand restiad bog

Abstract

New Zealand restiad bogs have histories of natural fire, which is reflected in the presence of plant species with adaptations such as serotiny and fire-stimulated flowering. The possibility of fire-cued germination has not been investigated in restiad bogs, despite its widespread occurrence in other fire-prone environments, globally. We performed a glasshouse experiment to assess the role of peat seed banks in post-fire regeneration at Kopuatai Bog in northern New Zealand. Peat samples collected were either (a) heated until they reached 70 °C, (b) exposed to wood smoke for 30 min, (c) heated and smoked consecutively, or (d) left untreated. The emergence of vascular plants was then monitored for 105 days in a glasshouse. Mean seedling density was highest in the control treatment (7228 ± SE 1040 m−2); it was lowest in the heated samples, suggesting that the heat treatment may have been excessive. Smoke did not significantly increase emergence. Epacris pauciflora accounted for 76.7% of total seedlings, consistent with our hypothesis based on vegetation surveys that this species relies on synchronous post-fire seed bank germination. E. pauciflora was most abundant in the control, suggesting that emergence is in response to some disturbance-related cue other than heat or smoke. The restiad Sporadanthus ferrugineus was abundant in the control and smoke treatments. Its emergence following heating was reduced, but still considerable enough to cast doubt on its classification as a fire-sensitive species. In contrast, the dominant peat-forming restiad Empodisma robustum showed low levels of emergence. Our overall findings demonstrate that substantial quantities of viable seed are stored in the upper peat layers of a restiad bog and are capable of germinating in response to disturbance-related environmental changes. These findings contribute to our understanding of restiad peatland plant community dynamics, particularly explaining the mechanism behind increased E. pauciflora dominance post-fire.