The effects of grazing and burning on soil and plant nutrient concentrations in Colombian p�ramo grasslands

Abstract

The impact of extensive livestock farming on the physical and chemical characteristics of the volcanic soils and on the nutrient status of green plant tissues of neotropical alpine grasslands (p~amo) is studied. Soil and plant samples were taken over a one-year period at five sites with different agricultural (grazing and burning) management. In the undisturbed pAramo ecosystem, soil moisture (50-250%) and organic matter content are high (7-27%) and decomposition (11-35% yr -1) and element concentrations are low. Low temperatures (max < 10°C) and phosphorus fixation by the soil (5 mg P g-1 soil) determine the low mineralization and turn-over rates.Multivariate analysis of laboratory results indicates that the season of sampling and the agricultural practice are the most important explanatory factors for variation of soil characteristics. After long-term heavy grazing, soils have a higher bulk density and a lower moisture content. The outcome of a litterbag experiment confirms the hypothesis of higher decomposition rates at grazed sites. In the intermediate (wet-dry) season, conditions were somewhat better for plant growth but the system remained nutrient limited. Surprisingly, no relation between soil density, moisture or carbon content and concentrations of available nutrients in the soil is found. This is supported by the rather uniform nutrient concentrations in green plant tissue among the sites. It is concluded therefore that the effect of burning and grazing on p~amo soils is principally restricted to physical characteristics, and that differences in chemical characteristics of the soil do not cause differences in vegetation structure between grazed, burned and undisturbed sites.

Successional dynamics of soil characteristics in a long fallow agricultural system of the high tropical Andes

“…The lack of significant differences in soil water holding capacity between the virgin páramo and the different cropping and fallowing phases indicates that the long fallow agriculture practised in the study area does not modify this parameter that is important for the regional water balance, in which the páramo plays a key role, largely controlling the availability of water in the lowlands (Hofstede, 1995;Sarmiento, 2000).…”

Carbono almacenado en páramo andino

“…La vegetación está integrada mayoritariamente por vastas áreas de gramíneas naturales como Calamagrostis effusa, grandes plantas arrocetadas como el frailejón (Espeletia, sp.) (Hofstede, 1995), mezcladas con matorrales, donde predominan arbustos de los géneros Castilleja, Diplostephium, Hypericum y Pentacalia y parches de bosque que pueden alcanzar hasta los 10 m de altura como el Polylepis Los páramos cubren las partes altas de los Andes, entre los 11° N y 8° latitud S, formando una banda discontinua entre la Cordillera de Mérida, en Venezuela, y la depresión de Huancambaba, en el norte del Perú. Además, existen dos páramos complejos separados.…”

El páramo andino: características territoriales y estado ambiental. Aportes interdisciplinarios para su conocimiento

“…Sin embargo se puede afirmar que el consumo de agua en el páramo es muy bajo porque, a pesar de que los valores de radiación sean elevados, las cubiertas vegetales autóctonas se componen de herbazales y pajonales de marcado carácter xerofítico. La evapotranspiración en esos ambientes se ha estimado entre 1 y 1,5 mm/día (Hofstede, 1995). Este hecho, unido a los altos volúmenes de precipitación, hace que el páramo sea claramente excedentario en agua (De Bièvre, Íñiguez y Buytaert, 2006).…”

“…Un aspecto importante en la regulación hí-drica del páramo son las quemas de pasto. Con el fin de conseguir mejores pastos para el ganado, numerosas superficies de páramo son periódica-mente incendiadas, favoreciendo la aparición de brotes tiernos de fácil acceso a los rumiantes (Hofstede, 1995). Los efectos de estos incendios en la biodiversisad son obviamente notables, pero no así en las propiedades del suelo.…”