In the present work we evaluate the effect of parent material and of geomorphological, soil and climatic parameters on the establishment of plant communities and on soil degradation along a toposequence. The study was carried out in the Análisis integral de la toposecuencia y su influencia en la distribución de la vegetación y la degradación del suelo en la Subcuenca de Zapotitlán Salinas, Puebla.

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The inner continental shelf adjacent to the city and port of Veracruz (ICSV) in the southern Gulf of Mexico, which is influenced by the Jamapa River, has been considered to be polluted. Moderate to high Cu and Pb concentrations have previously been reported in the shelf’s terrigenous sediments. These elements are derived from deposition of materials from mainland sources via river transport and may threaten marine life in the coastal area. Because Cu and Pb bioavailability has not been previously assessed in the region, the aim of this study was to determine (i) bioavailability and total concentrations of these elements in the terrigenous sediments of the ICSV, (ii) if concentrations of these elements in sediments are associated with distances from primary sources, and (iii) if concentrations differ during dry and rainy seasons. Bioavailable general average concentrations were 0.21 µg/g for Cu, and 0.24 µg/g for Pb, which accounted for 4.4-4.9 % of the total content. The bioavailable concentrations were higher during the rainy season, and in the fluvial plume of the Jamapa River. The total content of Cu and Pb was significantly associated with fine sediments and exhibited high concentrations in the new port facilities area. Hence, it is concluded that the Jamapa River is a primary source of trace metals to the ICSV. Finally, as concentrations of trace metals are lower than previous records for sediments in the southern Gulf of Mexico and lower than background levels and maximum permissible limits, the ICSV is presently not contaminated by Cu or Pb.

ResumenAntecedentes: La agricultura y ganadería modifican la estructura y funcionamiento del bosque tropical seco. El impacto de estas actividades ha sido evaluado en regiones de Jalisco y Yucatán, en donde la agricultura de roza, tumba y quema, y la ganadería extensiva son los principales tipos de manejo. Sin embargo, existen otras regiones como Guerrero, en donde la agricultura es combinada con la ganadería. No obstante, su impacto sobre el bosque no ha sido evaluado hasta el momento. Pregunta: ¿Cuál es el impacto de la agricultura/ganadería y ganadería sobre el bosque tropical seco de Zirándaro, Guerrero? Sitio y años de estudio: El estudio fue realizado en Zirándaro, Guerrero, en diciembre de 2014 y junio de 2015. Métodos: Se seleccionaron 9 sitios con agricultura/ganadería, ganadería y bosque para muestrear su vegetación y suelo, y calcular 10 indicadores ecológicos. Además, se colectaron 9 muestras de suelo para evaluar sus propiedades físicas y químicas. Resultados: Los suelos de la agricultura/ganadería y ganadería tuvieron mayor densidad aparente, pero menor porosidad y materia orgánica que el suelo del bosque. La agricultura/ganadería y ganadería tuvieron baja riqueza específica y cobertura del dosel. La agricultura/ganadería tuvo menor obstrucción visual y mayor proporción de claros basales que la ganadería. Estas diferencias sugieren que la agricultura/ganadería tiene mayor impacto sobre el bosque que la ganadería. Sin embargo, no se encontraron diferencias significativas en la mayoría de los indicadores ecológicos. Conclusiones: La agricultura/ganadería y ganadería tienen un impacto ecológico relativamente similar sobre el bosque tropical seco de Zirándaro, Guerrero. Palabras clave: Agricultura de temporal, Cuenca del Balsas, degradación de la tierra, ganadería extensiva, selva baja caducifolia. AbstractBackground: Agriculture and cattle raising modify the structure and functioning of tropical dry forest. The impact of these activities has been evaluated in regions of Jalisco and Yucatán, where slash-and-burn agriculture and extensive cattle raising are the main types of management. However, there are other regions such as Guerrero, where agriculture is combined with cattle raising. Yet, its impact on the forest has not been evaluated so far. Question: What is the impact of agriculture/cattle raising and cattle raising on the tropical dry forest in Zirándaro, Guerrero? Study sites and dates: The study was performed in Zirándaro, Guerrero, in December 2014 and June 2015. Methods: We selected 9 sites with agriculture/cattle raising, cattle raising, and forest to sample vegetation and soil, and to calculate 10 ecological indicators. We also collected 9 soil samples to evaluate their physical and chemical properties. Results: The soil of agriculture/cattle raising and cattle raising had higher bulk density, but lower porosity and organic matter content than the forest soil. The agriculture/cattle raising and cattle raising had low plant species richness and canopy cover. The agriculture/cattle raising ha...