Seed bank, germination and seed longevity of Spanish broom (Spartium junceum, Fabaceae): implications for control

The Spanish broom (Spartium junceum) is an exotic invader of natural grasslands in southern Buenos Aires mountains. We assessed the density of seeds in the soil seed bank and the percentage of germination in botanic garden experiments for samples obtained from three invaded sites. We performed essays outdoors for soil samples, and in germination chamber for seeds collected directly from plants and for seeds obtained from the soil seven years before the experiment. Seeds density in the soil ranged from 600 to 4411 seeds/m(2). Germination percentage for soil samples was 68.33 +/- 26.66%. For chamber experiments, mechanical scarification lead to the germination of all the seeds in the case of those collected from the plants, compared to just 7 +/- 5.7% for the control and figures even smaller for heath shock and combination of heath shock and mechanical scarification. The experiment with seeds form the soil bank resulted in a percentage of germination of 88.73 +/- 11.16% for those seeds previously treated with mechanical scarification, 85.77 +/- 10.50% for heath shock, 40.30 +/- 10.14% for imbibitions and 43.20 +/- 12.01% for the control. Brief exposition to high temperatures, mechanical breakage of the seed cover and soil disturbances significatively favor germination and stimulate invasion.