DISTRIBUCIóN E INVASIóN DE GRAMíNEAS C3 Y C4 (POACEAE) EN UN GRADIENTE ALTITUDINAL DE LOS ANDES DE COLOMBIA

the distribution pattern, species richness, composition, and invasion of c3 and c4 grasses were studied in nine sites located between 300 and 4250 m along an altitudinal gradient in the "transecto sumapaz" (west slope of the cordillera oriental, cundinamarca, colombia). the grasses are represented along the altitudinal gradient by 221 species, 94 genera, and seven subfamilies. one hundred species are c3, while 121 species are c4. the richest subfamilies are panicoideae (40 genera/104 species), pooideae (28 genera/54 species), and chloridoideae (13 genera/39 species). species-rich genera are paspalum (panicoideae, 18 species), eragrostis (chloridoideae, 12 species), panicum (panicoideae, 11 species), calamagrostis (pooideae, 10 species), digitaria (panicoideae, 8 species), agrostis (pooideae, 6 species), festuca (pooideae, 6 species), and sporobolus (chloridoideae, 6 species). among the surveyed species, 180 are native (81%) and 41 are introduced and naturalized (19%), the latter species mostly found in the lowlands. one genus (phleum) and nine species are reported for the first time for colombia. the highest species diversity is found at low and mid altitudes (300-500 m: 102 species, 500-1000 m: 113 species, 1000-1500 m: 68 species). panicoideae are most diverse at low and mid altitudes, while the pooideae are better represented in the highlands. the c4 grasses are more diverse in the lowlands -although with some native species found above 2500 m- whereas the c3 species are more diverse at high altitudes. interestingly, c3 species in lowlands are mainly distributed in aquatic areas and forest understories. the notorious presence of native c4 species at high altitudes (>2500 m) requires further research but they could reflect the inertia of past plant communities widely distributed during the last glaciation, or the importance of other environmental features such as edaphic conditions.