The water level influence on biomass of Echinochloa polystachya (Poaceae) in the Jurumirim Reservoir (São Paulo, Brazil).

In the Paranapanema River mouth, Jurumirim Reservoir (23 degrees 27'-23 degrees 29'S and 48 degrees 39'-48 degrees 36'W, SP, Brazil), the biomass of E. polystachya was monthly determined with eight quadrats of 0.25 m2 from August 1993 to July 1994. The seasonal variation in biomass was unimodal, with greater biomass from November 1993 to April 1994. The average biomass was 1,933.7 +/- 479.5 gDW.m-2, with a variation along the year from 1,149.0 to 2,755.9 gDW.m-2. The annual variation of aerial green biomass, aerial and aquatic detritus suggest that the main growth period of E. polystachya was from December 1993 to May 1994, with peak between February to March 1994. The data indicate that this macrophyte is adapted to water level variation.