Diversidad de plantas vasculares en bosques continuos y relictuales de Nothofagus antarctica (Nothofagaceae) en Patagonia Austral

Abstract

La historia de los bosques de Nothofagus antarctica (ñire, ñirre) de Santa Cruz está asociada a profundos disturbios geológicos y climáticos. A estos se le suman los disturbios antrópicos más recientes que debido a los usos de la tierra contribuyen a la fragmentación del hábitat. En este trabajo se comparó la diversidad de plantas vasculares en bosques de Nothofagus antarctica relictuales (R) y bosques continuos aledaños (A) distribuidos en un amplio gradiente latitudinal. Para ello se relevaron las plantas vasculares de cinco localidades ubicadas en el ecotono bosque-estepa y se analizaron los componentes alfa y beta de la diversidad. Se registró un total de 152 especies. La diversidad alfa se evaluó mediante el Índice Shannon-Wiener (H) y no hubo diferencias significativas (p = 0,580) entre los ambientes A y R. Sin embargo, el índice H varió significativamente entre localidades (p <0,001). Los mayores valores de H se registraron en la localidad ubicada en el extremo latitudinal norte, mientras que los menores valores H se registraron en la localidad ubicada en el extremo latitudinal sur. El análisis de los componentes de la diversidad beta global (βsor) muestra menores valores en las localidades de los extremos norte y sur. Además en las otras localidades predomina el componente de recambio de especies (βsim), mientras que en la localidad más austral predomina el componente de diferenciación de especies por anidamiento (βnes). Se concluye que el gradiente latitudinal tiene fuertes influencias en la diversidad de la comunidad del sotobosque de N. antarctica. Además la intensidad del uso histórico de los bosques estaría relacionada a una mayor disminución en la riqueza de plantas vasculares de relictos, con respecto a los bosques continuos aledaños. Esto último denota una mayor sensibilidad de relictos a los disturbios antrópicos y la necesidad de implementar medidas adecuadas de conservación de los ambientes naturales.

in Santa Cruz is associated with significant geological and climatic disturbances. More recently, anthropic disturbances contributed to habitat fragmentation process. In the forest-steppe ecotone N. antarctica forms small forests inserted in a steppe matrix and separated from the Andean forests that are found towards the West forming continuous forest mass. Five localities of Santa Cruz were surveyed in order to study the patterns of diversity of vascular plants comparatively between relictual forests (R) and their surrounding continuous forests (A). The localities are located in a wide latitudinal gradient (47º 4’- 51º 5’ S) and experience different histories of use. The alpha and beta components of the diversity were linked to other environmental variables through a multivariate redundancy analysis (RDA). A total of 152 species were registered. The alpha diversity was evaluated using the Shannon-Wiener Index (H’). There was no significant differences (p = 0.585) between environments A and R. However, when comparing the sites the differences were significant (p <0.0001). The highest H’ values were recorded in the northern site, while the lowest H’ values occurred in southern site. The components analysis of global beta diversity (βsor) showed lower values in the northern and southern extreme locations. In addition, while in the most austral site the component of species differentiation by nesting (βnes) was more relevant, in the other evaluated sites the turnover component (βsim) was predominant. The RDA shows that there is a close relationship between environmental characteristics (soil and climate) and species composition. It also shows that mean temperature is the main factor that relates localities of low similarity to each other (1 and 5). While the higher nutrient content in the soil is related to the intermediate localities (2, 3 and 4). We concluded that the latitudinal gradient had strong influences on the diversity of the understory community of N. antarctica forests. Furthermore, the intensity of the historical use of the forests can be related to a greater decrease in the vascular plant richness in relicts compared to the surrounding continuous forests. This denotes a greater sensitivity of relicts to anthropogenic disturbances and the need of an adequate conservation action.