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

生态修复的目标是最大限度地利用生物多样性，恢复生态系统功能。目前的理论假设人类影响的生态系统具有不同的退化阶段，其特征是：(1)非生物条件和生物组成与参考生态系统的偏离，(2)生态系统功能的恶化，以及(3)确定退化的生态系统是否可以恢复到特定阶段的恢复力和恢复阈值。虽然这一理论提供了一个有用的概念框架，但很少被检验。在拟议的项目中，我们将针对南美草原的情况应用、测试并进一步开发这一框架。南美草原拥有丰富的生物多样性，由于土地利用的变化，它们面临着压力。在巴西南里奥格兰德州，约50%的草原已被退耕还林或因城市扩张而丧失。只有大约2%在自然保护区内，在那里，当人类活动停止时，木本物种的自然演替发生。草原处于不同的退化和恢复阶段，其支持特定生态系统功能的能力可能不同，但这些阶段的相对稳定性和潜在的过渡阈值在很大程度上是未知的。混合生态系统和新型生态系统尤其如此，它们的特点是研究区域内以前没有发生过的物种组合，是不可持续的土地利用和生物入侵的结果。拟议的项目是由在恢复和陆地生态学方面具有专业知识的明兴理工学院的研究人员和巴西南里奥格兰德联邦大学的研究人员密切合作的，他们对巴西草原的生物多样性和生态具有丰富的知识。该项目包括对退化草原的大规模调查，对生态系统功能的快速评估，以及南里奥格兰德州高地的恢复实地试验。该项目将调查将草原跨越弹性阈值的管理做法，超过这些阈值，草原在没有人工帮助的情况下无法恢复到参考状态。该项目的应用成果将是草原恢复和混合生态系统和新型生态系统管理的建议。

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.