Degradation of biodiversity and ecosystem functioning in subtropical grasslands, and thresholds for restoration

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Ecological restoration aims at maximizing biodiversity and restoring ecosystem functions. Current theory assumes that human-impacted ecosystems show distinct degradation stages that are characterized by (1) deviation in both abiotic conditions and biotic composition from reference ecosystems, (2) deterioration of ecosystem functions, and (3) resilience and restoration thresholds that define if degraded ecosystems can return to a particular stage. While this theory provides a useful conceptual framework, it has rarely been tested. In the proposed project we will apply, test and further develop this framework for the case of South American grasslands. South American grasslands are rich in biodiversity and they are under pressure due to changing land use. In Rio Grande do Sul, Brazil, about 50% of the grasslands have been converted to agriculture, forestry or lost due to urban expansion. Only about 2% are within nature reserves where, on cessation of human action natural succession with woody species takes place. The grasslands exist in various degradation and restoration stages that might differ in their ability to support specific ecosystem functions, but the relative stability of these stages and potential transition thresholds are largely unknown. This is particularly true for hybrid ecosystems and novel ecosystems which feature species combinations that have not occurred previously within the study region and result of unsustainable land use and biological invasions. The proposed project is a close cooperation of researchers at Technische Universität München, with expertise in restoration and terrestrial ecology, and researchers at the Universidade Federal do Rio Grande do Sul in Brazil with excellent knowledge on biodiversity and ecology of Brazilian grasslands. The project includes large-scale surveys of degraded grasslands, rapid assessments of ecosystem functions and restoration field experiments in the highlands of Rio Grande do Sul. The project will investigate management practices that shift grasslands across resilience thresholds beyond which they are unable to return to the reference state without human assistance. The applied outcome of the project will be recommendations for grassland restoration and for management of hybrid and novel ecosystems.