Modeling tree diversity, stand structure and productivity of northern temperate coniferous forests of Mexico.

There is increasing evidence complex forest structure and tree diversity correlates positively with the productivity of forest ecosystems. However, there is little quantitative information regarding the effect of these factors on stand productivity of northern temperate coniferous forests of Mexico. This study aimed to test the hypothesis tree diversity and canopy structure positively associates with forest productivity. Parameterization of tree diversity, stand structure and productivity were carried out on dasometric data from 36 permanent sampling plots re-measured in 1982, 1993, and 2004. Statistical analysis of stand parameters tested the null hypothesis. Statistical relationships revealed well-balanced canopy strata and imbalanced diameter structures positively correlated with stand productivity. Tree diversity was also positively linked with stand productivity, but the effect appeared to be most important in the early to intermediate stages of succession. Further research is required to understand the long-term effects of tree diversity and canopy structure on stand productivity. These preliminary observations stress the importance of prescribing silvicultural practices that maintain the three-dimensional structure of stands and diversity of forest canopies that aim to preserve ecosystem function, diversity, and productivity.

Biomass estimation equations for mesquite trees in the Americas.

Mesquite trees are the preferred dendroenergy sources in arid and semi-arid forests. In spite of their relative importance, regional aboveground biomass (AGB) equations for mesquite trees are scarce in the scientific literature. For that reason, the aims of this study were to: (a) harvest trees and develop regional biomass equations; (b) contrast measured data with equations developed previously; and (c) test the applicability of the fitted equation for mesquite trees in the arid and semi-arid forests of the Americas. We harvested 206 new mesquite trees from arid and semi-arid forests in northern Mexico (Coahuila, Nuevo Leon, and Tamaulipas) in addition to using two other previously compiled data sets from Mexico (N = 304) to develop a regional equation. To test the validity of this equation, for biomass equations reported for the rest of the country, as well as for North and South American mesquite trees, we contrasted AGB measurements with predictions of fitted equations. Statistical analysis revealed the need for a single, regional, semi-empirical equation as together the three data sets represented the variability of the aboveground biomass of mesquite trees across northern Mexico, as well as mesquite trees in America's arid and semiarid regions. Due to the large quantity of mesquite trees harvested for sampling and their variability, the regional biomass equation developed encompasses all other North and South American equations, and is representative of mesquite trees throughout the arid and semi-arid forests of the Americas.

An assessment of stream water quality of the Rio San Juan, Nuevo Leon, Mexico, 1995-1996.

Good water quality of the Rio San Juan is critical for economic development of northeastern Mexico. However, water quality of the river has rapidly degraded during the last few decades. Societal concerns include indications of contamination problems and increased water diversions for agriculture, residential, and industrial water supplies. Eight sampling sites were selected along the river where water samples were collected monthly for 10 mo (October 1995-July 1996). The concentration of heavy metals and chemical constituents and measurements of bacteriological and physical parameters were determined on water samples. In addition, river discharge was recorded. Constituent concentrations in 18.7% of all samples exceeded at least one water quality standard. In particular, concentrations of fecal and total coliform bacteria, sulfate, detergent, dissolved solids, Al, Ba, Cr, Fe, and Cd, exceeded several water quality standards. Pollution showed spatial and temporal variations and trends. These variations were statistically explained by spatial and temporal changes of constituent inputs and discharge. Samples collected from the site upstream of El Cuchillo reservoir had large constituent concentrations when discharge was small; this reservoir supplies domestic and industrial water to the city of Monterrey.