Spatial growth and population dynamics of a perennial tussock grass (Achnatherum calamagrostis) in a badland area

Guardia, R Raventos, J Caswell, H

R. Guardia et al., Spatial growth and population dynamics of a perennial tussock grass (Achnatherum calamagrostis) in a badland area, J ECOLOGY, 88(6), 2000, pp. 950-963

49

INGLESE

Article

Environment/Ecology

JOURNAL OF ECOLOGY

0022-0477 → ACNP

88

6

2000

950 - 963

ISI

0022-0477(200012)88:6<950:SGAPDO>2.0.ZU;2-4

1 Achnatherum calamagrostis (L.) Beauv. is a perennial, tussock forming gra ss which is conspicuously successful as a pioneer in badlands in submediter ranean areas. We analysed its population dynamics using a matrix population model that is intermediate between traditional demographic models and full y spatially explicit models. 2 Tussocks are considered as a set of spatial units, each classified accord ing to the number and state (seedling, juvenile or adults) of the tillers i t contains. The growth rate (lambda (i)) determined from the model estimate s the spatial spread of A. calamagrostis as a rate of increase in the numbe r of occupied quadrats. 3 We constructed six projection matrices from data for populations on two s ubstrate types, in 2 years with differing climatic conditions and consideri ng the whole life cycle or eliminating sexual reproduction or vegetative mu ltiplication. 4 All the matrices predicted growth rates greater than one. Sexual reproduc tion was an important process for spatial spread in A. calamagrostis, unlik e many other perennial grasses. In contrast, new colonization by vegetative reproduction contributed little to spatial growth of populations, although some expansion may still be possible in the absence of sexual reproduction . 5 A. calamagrostis, like other tussock-forming plants, exhibits a conservat ive tactic of slow spread. Tiller dynamics serve mainly for consolidation a nd maintenance of the plant in already occupied space and sexual reproducti on is the main way to ensure colonization of new safe-sites. Climatic condi tions influenced growth rates which increased during non-drought years abov e the near maintenance value seen in drought years.