Population Structure and Habitat Characteristics of Dicksonia sellowiana Hook. in the Sierra Madre Oriental, Mexico

The American tree fern Dicksonia sellowiana reaches its northern distribution limit in Mexico. This species grows only in the highly fragmented remnants of the montane cloud forest (MCF). Given the lack of data on ecological aspects of this endangered tree fern species, considered under special protection by Mexican legislation, the objectives of the present research were to investigate the structure of D. sellowiana populations and to characterize its habitats. The study was carried out in seven populations located at different elevations and latitudes in the MCF of the Sierra Madre Oriental in Mexico. In each locality, three sampling plots were established to characterize the habitat and to record density, height, stem diameter, number of leaves, and individual fertility. The resulting values were analyzed with univariate and multivariate statistics. In four of the D. sellowiana populations, individuals of low height predominated; these were classified as dynamic populations. However, the density of individuals by unit area was low compared with some South American populations, probably because of the high degree of fragmentation of the MCF. The variation in population density was mainly explained by the vegetation cover. Environmental factors such as elevation and slope orientation, however, explained better the variation of the basal area of tree fern populations. These results constitute the first reference on the current state of Mexican D. sellowiana populations, which is important for the management and conservation of this endangered species, and for monitoring changes in the environmental conditions of its natural habitat, the MCF of Mexico.