Índices de calidad de sitio de Populus nigra ‘Italica’ en plantaciones lineales en el noroeste de Chubut

En el noroeste del Chubut, los álamos se encuentran establecidos en cortinas de protección en predios de pastoreo o donde se cultivan pasturas y forrajes en secano. El Populus nigra ‘Italica’ es el clon más difundido en plantaciones lineales, ubicadas en diferentes calidades de sitio. No existen antecedentes sobre crecimiento en altura e Índice de Sitio en la zona. Se seleccionaron ocho sitios de muestreo, donde fueron apeados 24 árboles dominantes, a los que se les realizó análisis fustal. Con los pares de datos de edad-altura, resultantes del análisis de fuste de los árboles muestra, se ajustó el modelo de Chapman-Richards mediante técnicas de regresión no lineal. Se construyó una familia de curvas de crecimiento en altura, según la metodología de curva guía. Las curvas de Índice de Sitio, basadas en altura y edad, se construyeron mediante deducción matemática a partir de la función de crecimiento en altura, tomándose como edad de referencia 25 años a la altura del pecho. Se definieron cinco calidades de sitio, con un rango de 4 metros, con Índices de Sitio comprendidos entre 19 y 35 m.

Effect of Prosopis flexuosa on understory species and its importance to pastoral management in woodlands of the Central Monte Desert

In the Monte Biogeographic Province, located in the arid region of Argentina, the presence of Prosopis flexuosa DC. produces spatial heterogeneity through edaphic modifications and microclimate changes. This results in vegetation patches differing in species composition and abundance. However, this interaction can be modified by the occurrence of gradients of biotic stress or disturbance intensity. In particular, grazing has been observed to enhance or reduce vegetation heterogeneity. Such complex of interactions could determine forage availability for cattle in one of the driest areas of the Monte Desert. We assessed the effect of Prosopis on understory species and analyzed whether the outcomes of this interaction differed with distance to watering points, as a proxy of grazing intensity, in the Northeast of Mendoza Province, Argentina. We used a two-way factorial design including the following factors: 1) microsite (under the cover of P. flexuosa trees and in intercanopy microsites) and 2) distance to watering points ("near the watering point", 500-700 m away, and "far from the watering point", 3-4 km away). Cover of each species, total cover, bare soil, and litter were recorded, and plant diversity, richness, and evenness were estimated with the modified Point Quadrat method. Results showed that P. flexuosa cover, distance from watering points, and the interaction between them determined species composition, abundance and spatial distribution of understory species, and were, consequently, a determining factor for forage availability. The presence of P. flexuosa enhances carrying capacity by supporting higher abundance of grasses under its canopy. Near watering points, high grazing intensity appears to disrupt the patches formed under P. flexuosa canopies, reducing the differences between microsites.