Structure and dynamics of southern Chilean natural forests with special reference to the relation of evergreen versus deciduous elements

Abstract

This contribution aims to improve our knowledge of the structural peculiarities of natural forest communities in southern Chile, paying special attention to leaf lifespan and morphology. Species are classified into 17 life-form categories. Using information contained in Braun-Blanquet releves, the relative frequency of the life-form categories, based on quantitative importance such as cover degree (not mere species numbers), is calculated for 26 natural forests. Communities are categorized as belonging to six different types: (A) evergreen forests; (B) forests with mixed laurophyll-deciduous canopy; (C) forests with mixed canopy of sclerophyllous or small / needle-leaved evergreens and deciduous species (specifically C.1 with dwarf-shrub or grass field layer, and C.2 with laurophyll and mesophyll shrubs and a relatively sparse field layer); and (D) deciduous forests (specifically D.1 with laurophyll undergrowth, and D.2 with a herbaceous ground cover). In the gradient from warm and dry to cool and wet, the characteristic composition of the structural elements reflects climatic site properties, revealed by the distribution of the vegetation units. This gradient represents a gradual retreat of evergreen elements from top (upper tree layer) to bottom (undergrowth), which always follows the order from laurophyllous to sclerophyllous elements, and from small or needle-leaved to deciduous elements. Finally, this retreat terminates in the rare structural type characterized by purely herbaceous ground cover beneath a deciduous canopy. Shifts between structural types do not necessarily involve variation in species composition. These units, reacting rapidly even to slight changes in site conditions, seem to be especially well-suited to monitor changing climatic effects. Human impact on forests, resulting in community shifts towards vegetation of warmer and drier habitats, causes structural changes, as does natural disturbance.