Distribution and morphology of columnar cacti in tropical deciduous woodland, Jalisco, Mexico

Abstract

The distribution and branching morphologies of four species of columnar cactus species in tropical deciduous woodland in Jalisco, western Mexico, are examined. Two species, Stenocereus marginatus and especially Pachycereus pecten-aboriginum, are taller and extend through the woodland canopy, and only these two species occupy habitats where the woodland vegetation is taller, on N- and NE-facing aspects where incident radiation levels are lowest. Two species, Stenocereus standleyi and Cephalocereus purpusii, are shorter, subcanopy species, and are more restricted to low-angle slopes and slopes with S- to W-aspects, where the woodland vegetation is shorter and more open, with a greater penetration of radiation into the vegetation. Branching morphology is affected by the vegetation cover in all species, but in different ways between the two taller and the two shorter species. Ecological segregation in these four species is achieved apparently by differences among the light regimes of subhabitats correlated to the morphology of the cacti. This contrasts to segregation in Sonoran Desert columnar cactus species, which segregate by different strategies of water uptake and utilization, and in columnar cacti in woodlands in Oaxaca further south in Mexico, where adult individuals are very similar in branching morphology, but the younger individuals differ in this respect and presumably become established in different sorts of light gaps.