Investigations on the ecology and production-biology of the "floating meadows" (Paspalo-Echinochloetum) on the Middle Amazon. Part 1: The floating vegetation and its ecology

Investigations on the "floating meadows" (Paspalo-Echinochloetum) of the vârzea- region of central Amazonia in the surroundings of Manaus were made from May 1967 until October 1968. The ecology of the dominating species Pasþalum reþens BERG, Pasþalum fasciculatum WILLD., Echinocltloa þoþstaclqta (H. B. K.) HITCCHKOCK, Leersia ltexandra Swart (Fam. Gramineae) and diverse subsidiary species (Oryza þerennis Moench, Hymeachne amþlexicaalis (Rudge) Nens, Panicum chloroticum Nens (.Fam. Gramineae), Scirþus cubensis Poepp Kunth. (Fam. Cyperaceae) etc., was studied in details. Regarding Pasþalum reþens Berg, various floating and one terrestrial forms of growth were observed. Further, quantitative investigations on primary production and the development of populations of this species were made. As shown by 4 Pasþalum reþens- populations which were growing under different environmental conditions, conclusions on age and rapidity of growth of the population could be drawn from the relation between quantity of stems and number of shoots. The preliminary conditions for a "secondary colonization" of floating populations by non-floating plants and the repercussions of such sort of colonization on the primary populations are discussed. The vârzea-waters are subdivided into 3 biotopes with regard to the floating vegetation, and the factors responsible for them are discussed: l) Bank- and sedimentation-zones in the Solimões-Amazon. Dominating species: Pasþalumfasciculatum, Pasþalum reþens, Echinocltloa poþstaclgta, 2) Vârzea lakes with high fluctuations of water level. Dominating species: Pasþalum fasciculatum, Pasþalum. reþens, Echinocltloa þoþstachya. Sometimes, however, as well all other mentioned species occur in masses. Biotope richest in species. 3) Várzea lakes with relatively little fluçtuations of water level. Dominating species: Leersia hexandra, Scirþus cubensis, Pasþalum reþens. Both the current-region of the Solimões-Amazon as a biotope of its own and the influence of black-water on the vegetation are discussed