Estructura y sucesión en bosques montanos del Noroeste de Argentina

Abstract

Se estudió la composición y estructura de tamaños de las especies arbóreas en diferentes fisonomías boscosas de los "Bosques Montanos" de la Sierra de San Javier, en el subtrópico de Argentina entre 1600 y 1800 msnm. En un análisis de correspondencia, los sitios se ordenaron siguiendo un gradiente de riqueza y complejidad. Las especies características de los sitios más diversos como las mirtáceas mostraron distribuciones diamétricas en "J-invertida", lo que sugiere regeneración continua. Por el contrario, las especies características de los bosques simples como A. acuminata, P. parlatorei y C. tucumanum, presesentaron distribuciones diamétricas unimodales con baja proporción de individuos menores. La densidad de individuos menores de 10 cm de DAP muestran que A. acuminata, P. parlatorei y C. tucumanum constituyen especies pioneras que colonizarían áreas no arboladas originando bosques simples. Estas especies son progresivamente reemplazadas por especies tolerantes durante la sucesión originando diversas fisonomías. La diversidad a escala de paisaje de los Bosques Montanos se originaría en eventos' discretos de reclutamiento de las especies pioneras, seguidos de sucesión hacia bosques dominados por especies tolerantes.

Floristic composition and tree size distribution of different forest patches were studied between 1600 and 1800 m altitude in fue Subtropical Montane Forests of Parque Biológico Sierra de San Javier, Argentina. Quadrats (20 x 20 m) were sampled in 12 sites. Sites were ordered using correspondence analysis. The first ordination axis was clearly associated to a gradient in complexity and diversity. The less complex forests were dominated by Alnus acuminata, Podocarpus parlatorei, and Crinodendron tucumanum. Richest and most complex forests were dominated by Myrtaceae species such as Blepharocalyx salicifolius, Myrcianthes mato and Myrcianthes pseudo.mato, accompanied by Cedrela, lilloi, Ilex argentina, Prunus tucumanensis, and others. Intermediare values of diversity and complexity were found in mafure forests of A. acuminata and P. parlatorei, and in forests dominated by the treelets Dunalia lorentzii, Sambucus peruviana and Solanum grossum. Sites were grouped using the Twinspan software package. Within each cluster, diameter distribution of fue most important species was used to describe regeneration trends. Myrtaceae species showed an “inverted-J’ distribution of diameter, suggesting a continous regeneration mode. On the other hand, spacies which dominate simple forests such as A. acuminata, P. parlatorei, and C. tucumanum showed bell-shaped diameter distribution, suggesting lack of regeneration under the canopy. These conclusions were also supported by seedling and sapling den-sities. The results suggest that A. acuminata, P. parlatorei, and C. tucumanum are pioneer species, and that the forests dominated by such species were originated in grasslands or shrublands. These species seems to be gradually replaced by shade tolerant taxa originating patchy heterogeneity and landcape diversity as a result of discrete events of recruitment fóllowed by forest succession.