RESUMO
Resumen En el noreste de México existe un incremento en el establecimiento de pastizales para la ganadería, lo cual ha ocasionado cambios en la estructura y diversidad florística. El objetivo de la presente investigación fue determinar algunos parámetros dasométricos y de diversidad de los elementos leñosos presentes en un área de matorral espinoso tamaulipeco (MET), con actividad pecuaria, en el estado de Nuevo León, México, para establecer si las modificaciones realizadas contribuyen o no a la conservación de la diversidad vegetal. La actividad pecuaria que se realizaba en el área de estudio era un aprovechamiento mixto de moderada intensidad, con aclareos por lo bajo (d ˂ 5 cm). Se seleccionaron cuatro sitios de muestreo de 1 600 m2 cada uno. Se recolectaron datos sobre variables dasométricas y se obtuvieron índices ecológicos. Los resultados permitieron un registro de 8 familias, 16 géneros y 17 especies arbóreas y arbustivas. La densidad absoluta reportada fue de 309 individuos/ha, mientras que el área de copa estimada fue de 9 521.83 m2/ha. La riqueza (Da = 3.03) y diversidad (H´ = 2.31) específicas, resultaron en valores similares a matorrales sin actividad productiva. Las especies con mayor importancia dentro del área de estudio fueron características del MET: Prosopis laevigata (IVI = 28.59), Havardia pallens (IVI = 13.41) y Cordia boissieri (IVI = 8.89), de las cuales, Prosopis laevigata tiene antecedentes de uso forrajero. Se concluye que la composición de especies arbóreas y arbustivas en este sistema pecuario conserva atributos deseables de las comunidades vegetales nativas, como la riqueza de especies, diversidad, densidad y área de copa.
Abstract In the northeastern region of Mexico, there is an increase in the establishment of grasslands for livestock, which has created changes in the structure and floristic diversity of ecosystem. The aim of this study was to determine the structure and diversity of the woody species vegetation of an area of Tamaulipas thorn-scrub (MET) which was modified for livestock rising in Nuevo Leon, Mexico, to establish whether or not the changes have contributed to the conservation of plant diversity. The livestock activity practiced in the researched area is mixed purpose use at a moderate intensity, with a thinning treatment at the lower vegetation layer (d ˂ 5 cm) to create open areas for cattle grazing in the study area. Four sampling plots of 1 600 m2 each were selected. Dasometric measures were recorded and ecological indexes were estimated. The results are a record of 8 families, 16 genus and 17 species of trees and shrubs. The absolute density was 309/ha, while the estimated canopy area was 9 521.83 m2/ha. Richness (Da = 3.03) and species diversity (H' = 2.31) resulted in similar values to scrubs with nonproductive activity. Species with the greatest IVI are characteristic of the MET: Prosopis laevigata (IVI = 28.59), Havardia pallens (IVI = 13.41) and Cordia boissieri (IVI = 8.89), from which, Prosopis laevigata is considered as a species for forage use. We conclude that the composition of the tree and shrub species in this livestock rising system contributes to preserving the desirable attributes of the native vegetation communities, such as richness and species diversity, density and canopy area.
RESUMO
Livestock-caused rangeland degradation remains a major policy concern globally and the subject of widespread scientific study. This concern persists in part because it is difficult to isolate the effects of livestock from climate and other factors that influence ecosystem conditions. Further, degradation studies seldom use multiple plant and soil indicators linked to a clear definition of and ecologically grounded framework for degradation assessment that distinguishes different levels of degradation. Here, we integrate two globally applicable rangeland degradation frameworks and apply them to a broad-scale empirical data set for the country of Mongolia. We compare our assessment results with two other recent national rangeland degradation assessments in Mongolia to gauge consistency of findings across assessments and evaluate the utility of our framework. We measured livestock-use impacts across Mongolia's major ecological zones: mountain and forest steppe, eastern steppe, steppe, and desert steppe. At 143 sites in 36 counties, we measured livestock-use and degradation indicators at increasing distances from livestock corrals in winter-grazed pastures. At each site, we measured multiple indicators linked to our degradation framework, including plant cover, standing biomass, palatability, species richness, forage quality, vegetation gaps, and soil surface characteristics. Livestock use had no effect on soils, plant species richness, or standing crop biomass in any ecological zone, but subtly affected plant cover and palatable plant abundance. Livestock effects were strongest in the steppe zone, moderate in the desert steppe, and limited in the mountain/forest and eastern steppes. Our results aligned closely with those of two other recent country-wide assessments, suggesting that our framework may have widespread application. All three assessments found that very severe and irreversible degradation is rare in Mongolia (1-18% of land area), with most rangelands slightly (33-53%) or moderately (25-40%) degraded. We conclude that very severe livestock-induced rangeland degradation is overstated in Mongolia. However, targeted rangeland restoration coupled with monitoring, adaptive management and stronger rangeland governance are needed to prevent further degradation where heavy grazing could cause irreversible change. Given the broad applicability of our degradation framework for Mongolia, we suggest it be tested for application in other temperate grasslands throughout Central Asia and North America.
