Revisiting the science and practice of ecosystem restoration in tropical mountains
Keywords: remote sensing
Andes
reforestation
ecological restoration
tropical mountains
satellite data

With an acceleration of restoration initiatives in this UN Decade on Ecosystem Restoration, it is paramount to conduct restoration science and practice in a scalable, long-term and equitable manner and to expand restoration efforts to ecosystems which have so far received less attention.
Tropical mountain ecosystems (TME) such as montane forests and grasslands have been critically destroyed or degraded by human activities. This compromises their habitat functions for threatened biodiversity, their carbon storage and the provision of ecosystem services for human livelihoods in the uplands and lowlands.
Restoration of TME – whether active, passive or mixed interventions – has emerged as an approach to re-create thriving ecosystems. But compared to lowland ecosystems restoration in tropical mountains, particularly in the Andes, remains understudied. My DPhil research looks at how to best inform and implement restoration of mountain ecosystems at three different scales and through three different methodologies. My thesis is framed by the agenda ‘Research Priorities for the Conservation and Sustainable Governance of Andean Forest Landscapes’ by Mathez-Stiefel et al (2017) which serves as a theoretical structure throughout the thesis.
First, I use a systematic review at the pantropical scale to synthesize research on the state of TME restoration science. Second, I use remote sensing analysis at the continental Andean scale to track forest recovery over 15 years and detect restoration priority areas. Last, I interview restoration stakeholder at a local project scale in Peru to understand motivations, preferences and success factors for Andean Forest restoration.
My Chapter 2 (Paper I) is titled ‘A synthesis and future research directions for tropical mountain ecosystem restoration’ (published in Scientific Reports). I review 176 scientific studies focused on ecosystem restoration in mountainous locations across the tropics to identify geographical and thematic research gaps, compare restoration interventions, and consolidate enabling factors and barriers of restoration success. I find that restoration research outside Latin-America, in non-forested ecosystems, and on socio-ecological questions is scarce. For most restoration interventions success is mixed and generally limited by biophysical factors such as dispersal and microhabitat conditions. I propose five directions for future research on tropical mountain restoration in the UN decade of restoration, ranging from scaling up restoration across mountain ranges, investigating restoration in mountain grasslands, to incorporating socio- economic and technological dimensions.
My Chapter 3 (Paper II) is titled ‘Disrupted Forest recovery hinders biodiversity conservation across the Tropical Andes’ (published in Global Ecology & Biogeography). It builds on the knowledge gaps and research priorities identified in the first paper, namely a lack of large spatio- temporal studies using satellite technologies to monitor and inform restoration of mountain ecosystems across the Andes. In this paper, I map forest recovery of Andean tropical montane forests across the continent over a 15-year period using 30m resolution Landsat data. I identify potential recovery sites using tree cover change analysis and develop a method to classify restoration trajectories over a 15-year time frame on a pixel-by-pixel basis using sequences of multi- temporal Normalized-Difference Vegetation Index (NDWI) images. Further, I test the method on well-studied forest restoration landscapes in Peru, Ecuador, and Colombia. I find that the method captures landscape scale dynamics well. However, forest recovery across the Andes is mostly disrupted, arrested or unsuccessful with consequences for biodiversity conservation and provision of ecosystem services. Areas of low recovery identified in this study may be good candidates for active restoration interventions in this UN Decade on Restoration, however, their restoration potential must be determined at a local scale together with mountain communities.
My Chapter 4 (Paper III) is titled ‘Sowing and harvesting water’ – a socio-ecological analysis of forest restoration projects in the Peruvian Andes’ (in review at People & Nature). Andean Forest restoration is a recent endeavour in the megadiverse country of Peru but knowledge about the motivations and socio-economic and governance conditions that determine restoration success is scarce. Through 75 semi-structured interviews with communities, NGOs and government actors in 11 restoration sites this paper synthesizes motivations, enabling and limiting factors, impacts, and local preferences to inform successful future Andean Forest restoration. I find that communities are motivated by an instrumental desire to restore and improve water resources. Enabling factors for restoration success are mostly social and institutional ranging from high communal resource dependence to support from NGOs to creation of communal conservation agreements. All stakeholder groups favour active Andean Forest restoration and highlight a host of desired useful plant species and restoration priorities. While all projects have opportunity costs for farming, there are various models for community involvement and compensation. I identify a ‘payment model’ and a ‘capacity model’ which differ in their project sustainability, social and economic benefits provided and how they create capacity. I conclude by presenting a scaled-up ‘Mountain Landscape Restoration Approach’ suggesting various restoration interventions in line with the social, ecological, and economic priorities identified by the stakeholders.
I conclude the thesis with a synthesis in Chapter 5 which is structured along a 10-point agenda for the science and practice of Andean Forest restoration. Within these agenda points I discuss some of the overarching challenges and solutions to restoration identified across my research and highlight major gaps and recommendations for the science and practice of Andean Forest restoration and for tropical mountain ecosystems more broadly.