Effects of disturbance on the reproductive potential of Lavandula stoechas, a Mediterranean sclerophyllous shrub

Studies on the effects of perturbations on Mediterranean shrub vegetation have most often emphasized the role of disturbance by fire Here I report on the effects of a relatively mild (as opposed to burning) disturbance on Lavandula stoechas The study was carried out in two adjacent plots, one in which all shrub aboveground biomass had been eliminated mechanically two years before, the other with an intact layer of shrub Although the study species lacks developed underground organs, root sprouting ensued clearing and average interplant distance at the treated site was indistinguishable from that in the control area Average percent plant mass accounted for by living branches with leaves was significantly higher for rejuvenated, cleared-plot individuals, which also produced about twice as many flowering heads and seeds per head as their control-plot counterparts, along with heavier individual seeds Naturally occurring seedlings survived relatively better at the cleared plot, probably as a result of the joint effects of decreased litter cover, increased water availability, and higher growth rates The average fresh mass of one-year-old seedlings at the Open was 243 mg, vs 10 mg of shrub-plot seedlings No seedling survived the first summer drought out of ca 1000 seedlings that emerged from seed sown in a nearby, intact shrub stand It is hypothesized that mild, relatively local disturbance elicits competitive release, which has a major effect on both the fecundity of individuals and the demography of this species