Estructura y sucesión en bosques montanos del Noroeste de Argentina

Abstract

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 dé San Javier, Argentina. Quadrats (20 x 20 m) wete sampled in 12 sites. Sites were ordered using correspondence analysis. Ttie first ordinatioh axis was clearly associated to a gradient in complexity IIÍId diversity. The less complex forests were d6minated by Alnusacuminata,' . Podocarpus pdrlatorei, and Crinodendron tucUmanum. Richest and most com.plex fotests were domiDat'ed.by Myrtaceae species such aS Bleplu;¡rocalyx salicifolius, Myrcianthes mato and Myrcianthes pseudomato, acct>mpánied bY ' Cedrela, lillpi, Ilex argentiTUl, P1'fPIus tucumanensis, and pthers. Intermediate values of diversity and cOplplelPty were found in mature forests of "', acuminata and P. parlatorei; and in forests dominated by the treetets I),unalia lorentzii, Sambucus peruviana and Solanum grossum. Sites were grouped using the Twinspan software package. Within eachcluster, diameter distribution of the most important species was used to describe tegeneration trends. Myrtaceae species showed an "inverted-f' distribution of díarneter, suggesting a continous regeneration mode. On the other hand,specíes which dominate símple 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 densities. The results suggest tlu;¡t 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 eveIlts of recruitment fóllowed by forest succession.