dominant weed is well recognized in many vegetation types throughout the world (see Braid, 1959, for a review). It has been demonstrated that this dominance is a consequence of the fern's rapid extension of underground stems and abundant vegetative reproduction (Watt, 1943, 1947), its strong allelopathic potential (Gliessman & Muller, 1972), and its resistance to fire (Vogl, 1964). Very little attention has been directed to spore germination, gametophyte formation, and sporeling establishment in relation to the dominance of Bracken. Bracken is capable of producing large numbers of spores on each frond, and the time of spore release can extend through much of the growing season (Conway, 1957). In temperate regions, however, most spore dispersal takes place during the drier part of the year or just before the winter begins, times of the year that do not particularly favor sporeling establishment. This would explain, at least in part, reports of the small number of Bracken sporelings which become established under natural field conditions (Conway, 1953). In the tropics, where conditions of temperature and humidity are much more equable, such climatic control of spore germination and early growth presumably is less important. I have observed continual growth of new Bracken fronds throughout the year in several locations in Costa Rica (Gliessman, 1976). It is possible, then, that spore release is not restricted to a certain period, as it is in temperate regions (Conway, 1957), but may be much more haphazard over the entire year. Thus, a constant source of spores could be available for any potentially habitable area. Observations were made in the field in Costa Rica to determine the conditions under which Bracken sporelings become established, which has possible implications for Bracken control. In Costa Rica, Bracken is encountered frequently from just above sea level on well-drained soils up to more than 3000 m elevation. As in other areas of the tropics (Richards, 1966, pp. 391-399), Bracken most often forms a type of deflected succession in regions formerly covered with dense, tropical forest. These are areas that have an annual rainfall in excess of 2500 mm, the majority of which is concentrated in the wet season that extends from mid-May to late December. Due to frequent cloud cover (especially at higher elevations) and the occurrence of sporadic rainfall even in the dry season, humidity at the soil level is quite favorable for sporeling establishment all year around. The pattern of land use in this part of the tropics appears to lend itself quite well to the establishment of Bracken. Most forest clearing, using the well known system of and burn, takes place towards the end of the wet season (December) until late in the dry season (late April). The felled material is allowed to dry as much as possible. Before the more frequent rainfall begins in early May, the slash is burned. As a consequence, when the wet season rains begin in earnest,