Population structure and environmental relationships of the tropical tree Nectandra rudis (Lauraceae), a rare species in western Mexico

The tree N. rudis is a rare species from western Mexico of which community and population features are unknown. We studied a population in an altitudinal gradient, from 550-1 850 to above sea level in the Sierra de Manantlan, Jalisco, Mexico. We established four 60x48 m sample sites at vertical distances of 100 m along this altitudinal gradient. Within each plot, ten 100 m(2) circular sub-sampling units were randomly located. At each unit, we recorded diameter at breast height (dbh) and tree height for all woody vegetation >= 2.5 cm dbh. Basal area, tree density, frequency, species richness and importance values per species and plot. We estimated the vertical structure (total tree height) and diameter( as M=5log(10)N) for all N. rudis individuals. A direct ordination through Canonical Correspondence Analysis was done, involving amongst other species, edaphic and environmental data matrices. The record of 44 N. rudis individuals, in seven out the 56 plots sampled, represents the most septentrional record for the species and the first in Western Mexico. Its density and basal area represented 4.5 % and 8.7 % respectively of the total estimated for the community. The greatest importance values were observed at 1650 to above sea level. The population structure off. rudis is structured into five diameter categories in an inverse "J" shaped distribution. This is a typical behavior observed to occur in the Lauraccae, which produces big seeds of short viability that germinate when there is high soil moisture content. The species tend to form dense seedling banks although only a reduced number of them are able to survive. Species richness varies from 27 to 39 at plot level; the greatest importance values for the plots on which N. rudis was found, corresponds to Urera verrucosa (Liebm.) VW. Steinm., N. rudis, Ficus sp., Belischmiedia manantlanensis Cuevas y Cochrane, amongst others. Canonical Correspondence Analysis suggests that environmental variables such as rooted trees, crown cover, litter depth and soluble magnesium are the more significant explanatory variables for the distribution and abundance of N. rudis.