Relación clima-vegetación: adaptaciones de la comunidad del jarillal al clima semiárido, Parque Nacional Lihué Calel, provincia de La Pampa, Argentina

Abstract

El estudio de la vegetación desde la Geografía se centra en el análisis de su distribución espacial y los factores que inciden en la misma. Uno de ellos es el clima que determina las características de las formaciones vegetales y, en una escala más grande, a las comunidades. El objetivo de este trabajo es analizar la relación clima-vegetación mediante el estudio de las adaptaciones de la comunidad del jarillal con respecto al clima semiárido en el Parque Nacional Lihué Calel, Argentina. Para ello se realiza el balance hídrico de Thornthwaite y Mather utilizando datos de la estación meteorológica del parque pertenecientes al periodo 1995-2010. Se aplican índices bioclimáticos y se realizan estands para conocer la composición florística y fisonomía de la vegetación. Se analizan las respuestas adaptativas identificadas en los individuos vegetales relevados y se comprueba que el clima semiárido condiciona la morfología y fisonomía del parque. Se demuestra la presencia de vegetación xerófila con predominio de arbustos y de cobertura abierta. Entre las adaptaciones observadas se distinguen la pérdida de hojas en la estación desfavorable, el reemplazo de hojas por espinas, hojas pequeñas y resinosas, inclinación de la hoja y raíces extensas.

The study of vegetation from the Geography perspective focuses on the analysis of the spatial distribution and on the factors affecting it. One of these factors is the climate, which determines the characteristics of the vegetation and, on a larger scale, of the communities. The aim of this paper is to analyze the climate-vegetation relationship by studying adaptations of the jarillal community regarding the semiarid climate in the Lihué Calel National Park, Argentina. Therefore, this contribution is concerned with the knowledge of the characteristics of the environment in order to understand how vegetation responds to certain phenomena, so management of protected areas will be more suitable. Lihué Calel National Park is a national protected area located in the south-center of La Pampa province, Argentina. According to Cabrera (1976) the area belongs to the floristic province of “monte” and the climate is warm and dry. In the interest to achieve the goals of this paper, Thornthwaite and Mather´s water balance was done. The data was collected from a weather station that belongs to the national park, for the period 1995-2010. Emberger›s pluviothermic coefficient, Lang´s rainfall index, De Martonne´s aridity index and Currey´s continentality index were analyzed. In addition, ten stands or plots of vegetation were placed to determine the floristic composition and the vegetation physiognomy. Then, plants species were identified as individuals and their adaptive responses were also analyzed. In conclusion, the survey verified that semi-arid climate conditions determine the morphology and the appearance of jarillal. Climate analysis shows that for the period 1995-2010 the average annual temperature is 16.2° C and reveals that thermal summers and winters are well differentiated. Large water deficit is defined, because water balance indicates that the evapotranspiration exceeds precipitation during every month of the year. According to Thornthwaite’s criteria, the area is a semiarid climate type. With the analysis of other bioclimatic indices, more information is obtained: Lang´s index value is 25.7 (arid), Emberger’s index is 41.8 (semiarid), De Martonne’s index is 15.9 (that refers to a semi-arid climate) and, at last, Currey’s index certified the existence of a continental climate because the result was 1.16. Vegetation was surveyed and the result was quite interesting: 1 508 individuals that belong to 33 species. The percentage is: shrubs 57.6%, grasses 36.4% and trees 6.1%. Most of them were evergreen and only some deciduous. The distribution of vegetation in Lihué Calel responds to the semi-arid conditions. Some adaptations were observed like the development of the deep root system with an horizontal pattern in order to absorb the water from the soil, the loss of leafs in the unfavorable season, the replacement of leaves by thorns, small resinous leaves, leaf tilting and extensive roots, among others. The dominant plant of the jarillal is Larrea divaricata and it is considered as a xerofite plant. The process indicates that when stomata are open, transpiration rates increase; when they are closed, transpiration rates decrease. The Cactaceae family is represented by two species: Opuntia puelchana and Cereus aethiop. They are considered succulent plants that keep humidity inside. During rainy periods they absorb large amounts of water that they then use during the dry periods. These types of studies are relevant to understand how plants adapt to different environmental events, whether they are natural and/or anthropogenic. As a reference, in 2003, major fires occurred inside the National Park and they affected 7 000 hectares. The resinous leaves of the jarilla helped to propagate the fire all around the place. The next phase of the investigation process will be related to the physiological and morphological properties, through chemical analysis, so the adaptation of vegetation can be tested. With these new studies, the final purpose will be reached: good practice for plant conservation.