Population dynamics of the perennial Plantago media in semi-natural grasslands

In this study we investigated population dynamics of a perennial forb, Plantago media, in semi-natural grasslands in southeastern Sweden. Plantago media is a rather common inhabitant of grasslands in this region, but it has been shown to experience dispersal limitations both among managed grassland sites and at potential dispersal routes along road verges. The demography of P. media was studied in 22 permanent plots at two sites over five years. A seed sowing experiment was also performed at each site. The Life-cycle of P. media includes seedlings, juveniles, small vegetative rosettes, large vegetative rosettes and flowering rosettes. The population growth rates (lambda-values) were negative for both populations, with one exception: the first year transition matrix at one site. The projected life span for individuals surviving from seedlings to flowering rosettes varied between 19.6 yr and 227.8 yr. Elasticity analysis showed that remaining in the large rosette stages, both vegetative and flowering, was the most important factor influencing population growth rate. LTRE analysis gave similar results, indicating that spatial and temporal variation have similar effects on the population growth rate. The expected time to extinction in populations with an initial size of between 100 and 1000 individuals varied between 60 and 200 yr. The seed sowing experiment showed that seedling emergence was enhanced by both seed addition and disturbance, suggesting that recruitment is limited by seed and microsite availability. Recruitment was not found to have much impact on population growth rate. However, long-term population maintenance may depend on occasional small-scale disturbances that enhance pulses of recruitment. Fragmented landscape is likely to effect plant populations including rare and endangered species as well as more common species which have limited dispersal mechanisms.