Germination and population dynamics of Cistus species in relation to fire

Published source details Roy J. & Sonie L. (1992) Germination and population dynamics of Cistus species in relation to fire. Journal of Applied Ecology, 29, 647-655.
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Summary

The shrubs narrow-leaved cistus Cistus monspeliensis and grey-leaved cistus C.albidus often dominant in Mediterranean habitats degraded by recurrent fires. To determine the role of fire in the regulation of the population dynamics of these two species, the germination requirements and population age-structure were examined for populations in southern France. In this particular experiment the effect of heat pre-treatment (simulating a passing shrubland fire) on germination was investigated in the laboratory.

Study area: The study was undertaken in the national forest of La Gardiole, 15 km southwest of Montpellier, Languedoc-Roussillon, southern France. The site was an established mixed stand of Cistus monspeliensis and C.albidus burnt in the summer of 1984.

Germination experiments: Germination experiments were conducted form September 1983 to November 1984 using seed collected from Site 1 (stored at room temperature or 5 ºC) in June 1983.

Seed heat treatments (30, 60, 90, 120 and 150ºC) lasting 10 min (the heat wave in a Mediterranean shrubland fire typically lasts no longer than 10 min) were conducted in an oven.

Germination experiments were then conducted in a germination chamber with seeds placed on Petri dishes (200/dish, three replicates of each) on filter paper disks placed on a layer of 6 mm glass beads with 20 cm³ distilled water added to each at the beginning of the experiment and 2 weeks later. 17ºC is known to be the optimum germination temperature for these two Cistus species.

Experiments were conducted either in the dark or with a 10h day/14 h night period (10 h at 20ºC and 14 h at 15º C). Germination was considered to have occurred when the radicle emerged from the seed testa, with seeds checked regularly for up to 6 weeks.

Heat treatment at 90ºC for 10 min was by far the optimum for seed germination of both Cistus species (see Table 1, attached).

For Cistus monspeliensis at 90ºC germination success was around 33-42% and for C.albidus 63-68%.

For Cistus monspeliensis at 60ºC germination success was around 4-9% and for C.albidus 23-34%.

For Cistus monspeliensis at 30ºC germination success was around 4-9% and for C.albidus 24-31%.

At temperatures of 120 and 150ºC all seeds were killed.

Conclusions: The seed pre-treatments designed to simulate fire temperatures in Mediterranean shrubland enhanced germination of both Cistus monspeliensis and C.albidus up to 90ºC, whilst at temperatures of 120 and 150ºC all seeds were killed.

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