Floristic composition and structure of two stands of Senna reticulata differing in age

Senna reliculata ('matapasto') is a woody pioneer which colonizes Amazonian whitewater floodplains. In open areas, especially those which have suffere d a strong anthropogenic impact, Senna reticulata dominates over other wood y and herbaceous species forming large, apparently monospecific stands. In the present study, stands of Senna reticulata which were two and six years old were inventoried in order to describe differences of species dominance and physiognomy. Senna reliculata dominated in the first years after establ ishment, representing 86.4 % of all individuals in the two year old plots a nd forming the canopy at 4-5 m height. In the six year old plots, Senna ret iculata had only 28.4 % of all individuals, and the canopy at 7-8 m height was formed by 12 species. The vitality of Senna reticulata was low in the s ix year old stands. The trees had higher stems but very small crowns with f ew leaves, enabling the co-occurring slow growing, long-lived species to ta ke over dominance. This study shows that Senna reticulata, although conside red a noxious woody weed by the local people, has a restricted period of do minance and represents the initial phase of a successional sequence that le ads to a diversity comparable to that of areas which have not suffered anth ropogenic impact.