Effects of ponderosa pine plantations on steppe microsites of northwestern Patagonia

Abstract

In the steppe of northwestern Patagonian, the vegetation patches, formed by tussocks or bunch grasses and shrubs, generate contrasting microsites, which facilitate the establishment of other species. In this ecosystem, during the last decades, plantation rates of exotic conifers have been increasing as an alternative resource to sheep production. The objectives of this study are to analyze: 1) the effect of pine plantation on the surface soil moisture of the different microsites in a steppe near Bariloche; and 2) the effect of the pine litter on the germination of two bunchgrasses: Festuca pallescens and Stipa speciosa. The soil moisture differed below bunchgrasses and in the interspace (between bunchgrasses) and it varied according to site (pine plantation or steppe). In a young pine plantation the moisture soil conditions tended to be more homogeneous between the different microsites, whereas in the steppe soil humidity below bunchgrasses was significant higher than between bunchgrasses. In an old pine plantation contrasting microsites are not found due to the lack of bunchgrasses. The bunchgrasses biomass was significantly larger in the steppe than in the young pine plantation. The percentage germination of both bunchgrass species was null in the treatment with pine litter and high in the treatments without pine litter. The decrease in bunchgrasses biomass probably determines in the long run the low regeneration and/or local disappearance of other species, due to alteration and/or decrease of the availability of microsites, particularly in old and dense pine plantations.