Size and spatial pattern of Festuca rubra genets in a mountain grassland: its relevance to genet establishment and dynamics

Authors


*Correspondence: J. Suzuki (fax + 81-11-706-7142, e-mail jsuzuki@orange.lowtem.hokudai.ac.jp).

Summary

1 For many clonal plant species, the density of shoot populations makes it almost impossible to determine genet natality directly. We identified genets by a randomly amplified polymorphic DNA (RAPD) method and used their size and spatial pattern, together with demographic parameters (genet spreading rate and mortality rate of shoots) determined in the field to estimate natality rates for Festuca rubra (red fescue).

2 In each of two sites (a species-rich and a species-poor site in a mountain grassland) three plots were established. Each plot contained two 1 m × 3.3 cm transects, composed of 3.3 × 3.3 cm square cells. Estimates of genet number per plot (18–49 and 27–33, respectively, in the two sites) were based on a randomization test. Mean genet size (1.2–1.6 cells) was not significantly different between the sites, nor was the spatial pattern of genets significantly different from random at either site. Interactions between genets therefore appeared to be negligible.

3 A spatial simulation model was developed for the genet population. Values estimated from the growth and demographic data over several years for the genet spreading rate (0.2–0.3) and for the mortality rate of shoots per cell (0.2–0.3) were among those used in the simulation. When a constant genet natality rate of 3–7 genets m–2 year–1 was included in the model, the simulation generated numbers and size frequency distributions of genets that were similar to those found in the field.

4 In this mountain grassland, F. rubra appeared to show repeated seedling recruitment, instead of the initial seedling recruitment following disturbance that is thought to be typical of many grasses. Founder effects were immaterial at the rates of seedling recruitment apparent in these populations. A stable population was achieved with the values of genet spreading rate and mortality rate of shoots per cell observed in the field, and repeated seedling recruitment. However, genet natality rates may vary if environmental conditions fluctuate.

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