![]() The message that the undisturbed cryptogam layer facilitates C. For germinated seedlings, mortality through the dry season (June–August) was not significantly different among surface treatments, nor did survivorship depend on density, with the result that initial differences in germination among the treatments persisted. Within the burned plots, fire scarification appeared to increase germination but this effect was not significant. scoparius establishment undisturbed plots produced more seedlings than burned or scraped plots. Both seed number and surface treatment showed significant effects on seedling density, along with a significant interaction between the two factors. Seed treatments ranged from 20 to 1000 seeds per m 2. ![]() scoparius seed dormancy, by adding seeds either before or after the burn. ![]() The effect of fire was partitioned into two factors: burning of the background vegetation/substrate versus breaking C. I used disturbance treatments to investigate the role of the thick cryptogamic layer in these prairies, disturbing cryptogams by scraping or by fire. Do invaded sites become ‘saturated’ with seeds? How rapidly does this occur, and how does the process depend on the availability of safe sites? Are safe sites, and consequently invasion, promoted by disturbance? I quantified the response of seedling establishment to seed input and disturbance in Cytisus scoparius (Scotch broom), an exotic shrub invading glacial outwash prairie remnants in western Washington, USA. ![]() An infestation of invading pest plants results in a seed-production gradient, from the edge where seeds are limiting, to the center where seeds may be in excess. In all plant populations, establishment is controlled by two factors: the supply of propagules and their access to ‘safe sites’ for growth. ![]()
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