Dasylirion cedrosanum Trelease (Nolinaceae) Density Varies Depending on Elevation and Slope in the Northeast of Zacatecas, Mexico

There is little or no specific and concise information on the ecological conditions which constrain distribution, abundance, and density of Dasylirion cedrosanum Trelease keeping in mind that such knowledge is indispensable to promote and support plantations and reforestation programs in order to confront the consequences of a possible depletion of natural populations. Therefore, the aim of this study was to evaluate D. cedrosanum density as related to ecological factors such as latitude, longitude, altitude, slope, soil texture fractions, pH, electric conductivity, available nitrogen and phosphorus contents, and organic matter content on a xerophytic scrub in the northeast of the Mexico’s state of Zacatecas. Data from 41 square–shaped sampling units of 1.000 m 2 each from an area of 2.422.2 ha where altitude varies from 2.000 to 2.356 masl, and slope inclination changes from moderate (5.5%) to steep (44.2%) was analyzed through linear relationships, quadratic functions, and principal components analysis. Results provide compelling evidence about D. cedrosanum density depends on elevation, inclination, and soil silt and sand contents. A triangularshaped dispersion of observations when density is plotted against each soil, silt or sand, contents was appreciated. A significant humped trend suggest that sites having slopes around 20%, although it could be in the 10 to 30% slope range, provides a better habitat for this species. D. cedrosanum plants are scarcer, that is, present at low and minimum densities (< 259 plants ha-1) in the sampled units characterized by high