Vegetation composition and altitudinal distribution of Andean rain forests in El Angel and Guandera reserves, northern Ecuador

Patterns of vascular plant species composition and structure of the remaining rain forest of the Andean Cordillera in northern Ecuador were studied in two reserves: Guandera and El Angel. Thirty three plots located between 3300 and 3700 in were examined along two altitudinal transects crossing the Upper Forest Line (UFL). The phytosociological subdivision using TWINSPAN revealed two communities for Guandera and five communities for El Angel on the basis of both floristic composition and percentage of cover. The distribution pattern of these forest communities clearly corresponds to a humidity gradient declining East to West from Guandera to El Angel. The high Andean and the Andean rain forest zones of Guandera were not floristically discernable by our analysis at the community level. The Guandera forest patches in paramo (3550-3700 m) are in terms of structure and floristic coinposition similar to the high Andean forest below the UFL (3600-3620 m), differing only at the level of variants. This indicates that the separation of the forest patch is relatively recent or that the forest patch was easily colonized by direct input from the high Andean forest located at ca. 50 m from the patch. No direct floristic affinity was detected between the forest types identified in our study area and 14 other forest sites of Colombia and Ecuador. The sharp and abrupt present-day UFL in Guandera (at 3640 m) is probably a consequence of frequent and extensive fires. All this suggests that the natural UFL was at slightly higher altitude in the undisturbed setting. In El Angel, the natural UFL as well as the high Andean forest have disappeared by clear cutting leading to a process of "paramizacion". Thus the isolated asteraceous forest patches at 3740 m could not be Compared to the high Andean forest stands in El Angel. The Andean forest patches in El Angel currently suffer from continuous wood extraction and are becoming depleted