Study

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.

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 vegetation removal (simulating that experienced by a passing shrubland fire) on seedling germination was assessed.

Study areas: The study was undertaken at two sites in the national forest of La Gardiole, 15 km southwest of Montpellier, Languedoc-Roussillon, southern France. Site 1 was a mixed stand of Cistus monspeliensis and C.albidus burnt in the summer of 1984. Site 2 was a mixed stand of Cistus monspeliensis and oak Kermes oak Quercus coccifera which established after a fire in 1973 or 1974.

Experimental design: In February 1984, vegetation in a 5 x 2.5 m plot at Site 1 and in a 2.5 x 2.5 m plot in Site 2 were removed. Plots were positioned to be about representative of the average physiognomies of each stand. The woody stem bases of the two Cistus study species were collected for ring number (i.e. age) determination. Stem samples of resprounting Kermes oak were also taken.

Light quality: Light quality (red to far-red ratio) outside and below the canopy was measured and canopy light transmission calculated.

Seedling counts: At the end of April 1984, seedlings were counted a long five pairs of 0.25 x 4 m transects in Site 1, five below the Cistus canopy and five in full light. Site 2 was not suitable for counts as the stand border was a frequently tilled fire break.

Longevity and seed production: In August 1989, about 40 Cistus plants of each species were collected from each site and also nearby to determine plant longevity and any seed production-age relationship. Seed production was estimated by multiplying the number of fruits by the average number of seeds per fruit measured on 15 fruits per plant.

Light quality: Germination of both Cistus monspeliensis and C.albidus was enhanced by a change in light quality bought about by vegetation removal in the plots, similar to that which occurs when fire removes the light-filtering green leaves.

Plant recruitment: In the two study stands, one (12 years old) composed of the two Cistus species and the second (9 years old) composed of C.monspeliensis and Q. coccifera, Cistus, it was evident that recruitment occurred steadily during the 5 post-fire years and then stopped.

Longevity and seed production: For both Cistus species, age at first seed production was 2 years, with seed production levelling off at 5 years; maximum plant longevity was around 14 years.
Pronounced stand decline was observed at 15 years old. This was due to a combination of old plants dying off combined with restriction on seedling recruitment caused by unfavourable (high canopy density) germination conditions.

Conclusions: The time for Cistus stands to decline is correlated with the frequency of fire which affect their habitats. Periodic burning would help regeneration of stands of both Cistus monspeliensis and C.albidus through promotion of more open conditions suitable for seed germination.


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:

http://links.jstor.org/sici?sici=0021-8901%281992%2929%3A3%3C647%3AGAPDOC%3E2.0.CO%3B2-U

 

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