THE BRACKEN FERN (PTERIDIUM ARACHNOIDEUM (KAULF.) MAXON) DILEMMA IN THE ANDES OF SOUTHERN ECUADOR

Resumen

Bracken fern (Pteridium aquilinum (L.) Kuhn) is one of the world's most powerful weeds, especially in agricul- tural areas. Its vigor and resistance to any kind of non-polluting pest control result from its extensive rhizome system. Gro- wth of this rhizome system is strongly promoted by fire. As elsewhere in the tropics, farmers in the Andes of southern Ecuador make extensive use of fire to convert primary forest into arable land and to maintain their pastures. This com- munication addresses, from a phytosociological viewpoint, the ecological problems arising from the use of fire as an agri- cultural tool in the presence of the extremely aggressive and fire-tolerant bracken fern Pteridium arachnoideum. Repeated burning of the pastureland weakens the competitive strength of the most important pasture grass Setaria sphacelata, whi- le the competitive strength of bracken increases. Pastures are finally abandoned when Pteridium has become completely predominant. Wind-dispersed seeds of several weedy Asteraceae and Melastomataceae species germinate under the canopy of the bracken leaves and, due to the steepness of the slopes, the seedlings receive sufficient light for further growth. The majority of these species are bushes that finally overtop the bracken leaves and can successfully compete with the shade intolerant fern. A vegetation composed of dense patches of Pteridium interspersed with individual bushes develops, which, because of the immense seed production of the bushes and the vigor of the bracken, is very stable and appears to be a long- lasting and even at times the final successional stage. Since natural regeneration of the indigenous forest is very unlikely in these areas, reforestation may be the only way out of the dilemma caused by the extensive use of fire and the fire-tolerance of bracken. Accepted 28 January 2003.