ABSTRACT The seasonally dry subtropical forest, especially the Espinal forest in central Argentina (one of the most fragmented ecoregions), is affected by intensive agricultural activity. These activities are the main anthropogenic sources of atmospheric nitrogen compounds and their effects on lichens have been extensively studied, making them excellent ecological indicators. However, in the Espinal forest, the agricultural emissions are not monitored therefore analysis of the response of lichen diversity to these activities has a fundamental role in providing baseline data for monitoring. We analyzed changes in the frequency of families and genera of epiphytic lichen communities in 39 circular buffer areas at different scales comprising crop production, stock farming (feedlots), grazing and forest. Significant correlations at different taxonomic levels were detected in relation to land use. Frequency of Physciaceae increased with an increasing area of cropland to a distance of 600 m. Likewise a positive correlation was observed between the frequency of Collemataceae and the forest area. At genus level, Physcia presented a different response to livestock according to the intensity of production, since the frequency of these species increased in forest patches surrounded by grazing but decreased in areas with livestock farming where the stocking density is higher. This result could indicate an eutrophication process in the Espinal ecosystem, even for Physcia species. Our results can be used to start a list of indicator species to impact of agricultural in forest ecosystems.

Four species of lichenized Ascomycetes are mentioned for the first time from Argentina: Endocarpon pallidulum, Placidium arboreum, Pyxine astridiana and Usnea michauxii. A brief description of each one is presented considering morphological, anatomical and chemical characteristics. The distribution of 68 lichen species in Argentina is also extended.

Se mencionan por primera vez para el país cuatro especies de Ascomycetes liquenizados: Endocarpon pallidulum, Placidium arboreum, Pyxine astridiana y Usnea michauxii. Se presenta una breve descripción de cada una considerando características morfológicas, anatómicas y químicas. A su vez se amplía la distribución de 68 especies de líquenes en el centro de Argentina.