Soil-landscape-vegetation relationships in grassland-forest boundaries, and possible applications in ecological restoration

Abstract

Edaphic influence on plant distribution is essential to community ecology studies, and for vegetation management and restoration in grasslands-forest ecosystems. Pampa biome is a subtropical grassland with high floristic diversity and with an important role in food production in South America, including tree plantations where recent changes in land use soil has been questioned about the impacts on water consumption, soil degradation and potential biodiversity loss. We assessed the relationship of soil physical, chemical and morphological properties with forest and grassland species occurrence, to improve our understanding of soil and landscapes with grasslands-forest mosaics, and contribute to ecological restoration in the biome. Soil physical and chemical properties were determined in different toposequences localized in two forest farms in southern Brazil, both covered with grassland and native forest use. Natural fertility of the studied soils was highest in the lowlands, along with highest moisture and lowest toxic aluminum content. Soil saturated hydraulic conductivity was highest in the summit and backslope soils, influenced by coarser fractions in the granulometry. Soil bulk density, total porosity, microporosity, macroporosity, saturated hydraulic conductivity field capacity, permanent wilting point and available water content, influenced by sand, silt and clay contents, varied among soils and landscape and contributed to vegetation diversity. Some of the plant species occupied specific soils and landscapes. The greatest vegetation frequency was of grassland species (Poaceae and Asteraceae) in both study sites. Grassland-forest area has forest individuals in the middle of the grassland and riparian, while in grassland area the riparian vegetation is composed naturally by grassland. Forest fragments expanded in grassland-forest area during the 15 years prior to our study, but in the grassland area there were no changes in the phyto-physiognomy, demonstrating that the vegetation of grassland occurs naturally in the riparian environment. This study highlights that many of sites covered naturally by grassland, in the Pampa biome, should be protected from disruptive activities and/or recovered with species endemic to the ecosystem, without necessarily by forest enrichment as usually recommended for restoration activities.