Abstract
High elevation warming is one of the major consequences of global change and generates concerns for the integrity of montane ecosystems and livelihoods of smallholder communities thriving at higher elevations across Latin America. As a global hotspot for biodiversity, environmental degradation throughout the Andean region is of great ecological concern and threatens soil health, biodiversity, and a range of important ecosystem services. Steep topography and often extreme climates in the Andes accentuate these threats and underscore the urgent need to understand how land uses and possible adaptation strategies to global change can influence ecosystem services and biodiversity in montane ecosystems across Latin America. In this dissertation, I aim to address this need by evaluating the potential of agroforestry in mountain areas of Latin America as a land use component to mitigate the impact of global change. Additionally, I sought to understand the role of climate change on the performance of important traditional Andean crops and problematic weedy species. Our goals were to: i) synthesize current related literature (max 30 years old) into a comprehensive structured-review by means of a meta-analysis (chapter 1), ii) study woody land use interaction on the landscape scale in a representative Andean montane landscape (chapter 2), iii) investigate the impact of direct environmental drivers on the establishment and productivity weedy vegetation during the fallow phase of crop rotations in the high Andean region (chapter 3), and iv) use the Andean mountain landscape as a natural laboratory to global change impacts on traditional crop production (chapter 4). Mountain agroecosystems in Latin America provide multiple ecosystem functions (MEFs) and products from global to local scales, particularly for the rural communities who depend on them. Agroforestry has been proposed as a climate-smart farming strategy throughout much of the region to help conserve biodiversity and enhance MEFs, especially in mountainous regions. However, large-scale synthesis on the potential of agroforestry across Latin America is lacking. To understand the potential impacts of agroforestry at the continental scale, we conducted a meta-analysis examining the effects of agroforestry on biodiversity and MEFs across mountain agroecosystems of Latin America. A total of 78 studies were selected for the meta-analysis based on a formalized literature search in the Web of Science. We analyzed differences between i) silvoarabale systems vs cropland, ii) silvopastoral systems vs pastureland, and iii) agroforestry vs forest systems, based on response ratios. Response ratios were further used to understand how climate zones, precipitation, and soil properties (texture) influence key MEFs and biodiversity in agroforestry systems. Our results revealed that MEFs related to carbon sequestration, soil fertility, nutrient cycling, biodiversity, and erosion control were generally higher in agroforestry systems (silvopastoral and silvoarable) compared to nearby croplands and pasturelands without trees. However, the impacts of agroforestry systems on crop yields varied depending on the system considered (i.e., coffee vs cereals), while forest systems generally provided greater levels of biodiversity and MEFs than agroforestry systems. Further analysis demonstrated that the impacts of agroforestry systems on biodiversity and MEFs depends greatly on climate, soil, and precipitation. For example, silvoarable systems appear to generate the greatest benefits in arid or tropical climates, on sandier soils, and under lower precipitation regimes. Hence, the ecological context should always be considered when promoting agroforestry systems. Overall, our findings highlight the widespread potential of agroforestry systems to support biodiversity and multiple MEFs, compared to pasture and crop lands, across montane regions of Latin America. Trees can have important impacts on multiple ecosystem services and biodiversity in agricultural landscapes. The influence of trees can extend beyond forested areas and into adjacent land uses, however, this is rarely accounted for in the ecological literature. To better understand the influence of trees in Andean agroecosystems, we examined alternative landscape scenarios in the community of Quilcas (JunÃn, Peru), where we explored the potential impact of replacing tree-based land uses (with crops and pasture) on landscape carbon (C) storage and soil biodiversity (soil macrofauna and ground vegetation). Additionally, we estimated the influence of tree-based land uses on soil C storage (0-20 cm depth) and macrofauna diversity in adjacent croplands and pastures. Tree-based land uses were dispersed across landscape and occupied 26% of the area, including a mix of forest patches, plantations, and hedgerows. Given that above- and belowground C stocks were generally higher in land uses with trees versus those without, the inclusion of trees in this landscape is estimated to increase the total landscape C storage by 153%. Macrofauna diversity also varied across different land uses, being highest in alder (Alnus acuminata) forests and hedgerows, such that the inclusion of trees enhances overall macrofauna diversity (Shannon Index) by 25% but appears to have a slightly negative effect (-6%) on ground vegetation diversity. When accounting for the influence of trees on adjacent land uses, estimates for overall soil C storage at the landscape scale increased by 1.4%, while macrofauna diversity increased by approximately 5%. Our findings indicate that the addition of trees can greatly enhance overall C stocks and soil macrofauna diversity in agricultural landscapes, and that it is important to consider spatial interactions between land uses to fully quantify and optimize these interactions. Intensification of crop rotations and associated agricultural practices are reducing the capacity of traditional fallows to restore soil fertility and provide forage in Andean cropping systems. While the implementation of improved fallows offers great promise to enhance forage provision and maintain soil productivity, effects of these practices on the establishment of problematic weeds, including non-native plant species, remain poorly understood. To address this knowledge gap, we studied: i) how biotic and abiotic environmental factors influence the establishment and productivity of weeds in traditional fallows; and ii) to what extent improved fallows can help control weedy vegetation in smallholder rotations of the high Andes. Specifically, in this research, we focused on the invasive plant species Rumex acetosella L., which is a common concern of farmers throughout the central Peruvian Andes. We leveraged a multi-site, participatory research trial established in 2017 across eight communities in the region to understand the main drivers of R. acetosella presence and productivity. We used a total of 82 sites, each with paired treatments of traditional fallow (control with natural revegetation) and improved fallow (seeded with Vicia sativa L. and Avena sativa L.). Prior to treatment establishment we measured soil texture, pH, soil organic matter content as well as exchangeable micro- and macro-nutrients. Vegetation data was recorded in each treatment and divided into four categories: i) A. sativa, ii) V. sativa, iii) R. acetosella, and iv) other weeds, and weighed to determine the relative biomass contribution of each. From these data, we calculated an index for R. acetosella pressure, weed pressure and forage productivity. Our findings indicate that improved fallows greatly suppress weedy vegetation relative to unmanaged controls, including the invasive R. acetosella. Multivariate analyses suggested that R. acetosella abundance was associated with the presence of other non-planted weeds and predictors of soil fertility. The mean R. acetosella index in improved fallows was significantly lower compared to traditional fallows. We found R. acetosella biomass to be greater at lower productivity sites, i.e., those at higher elevations with cooler climates and sites with less fertile soils. Our findings indicate that if the fallow portion of a rotation is kept productive via adequate soil fertility inputs, the biomass of weeds, including the alien R. acetosella, is dramatically reduced. Food security for traditional smallholder mountain communities around the globe is being jeopardized by global change. Rising temperatures are projected to impact the suitability of cultivation areas for crops. To maintain yields under warming conditions, smallholders tend to alter the nutrient management, the timing of cultivation, or even the crops currently cultivated. In the Andean region, farmers typically grow crops across a range of altitudes and environmental conditions as means to diversifying their faring systems and crops they grow. To cope with warming climates, farmers relocated crops to higher and cooler elevations. However, failure to relocate crops could result in increased susceptibility to warmer temperatures and a higher incidence of pests. To date, limited research has examined the impact of global change on locally significant crops. It is my belief that adopting traditional crop management practices and cultivating orphan crops are viable, sustainable solutions for coping with rapid climate warming in the Andean region and securing food security for local communities. To test this hypothesis two side-by-side experiments were established with traditional Andean crops (Oxalis tuberosa and Lupinus mutabilis) at three elevations, each with two fertility treatments (organic and synthetic). Soil and climate data (i.e., temperature and precipitation) were collected throughout the growing season, and crop performance was evaluated through various indicators, including yield and plant phenotypic characterization to understand the influence of site (climate), nutrient management, and their interaction on crop performance. Results showed that a warmer climate negatively impact the production and performance of O. tuberosa, but that organic fertilization can help reduce impacts on crop yield and biomass production of O. tuberosa. In contrast, L. mutabilis showed an accelerated growth cycle with increasing temperature, but grain yield and biomass production were not significantly affected. Our findings highlight that climate warming is a serious threat to small-scale agriculture in the Peruvian Andes and could cause severe declines in production of locally important crops. Continued use of organic inputs rather than shifting to synthetic fertilizers may help support crop growth and improve agroecosystem resilience. The results of this dissertation provide evidence that agroforestry systems, tree-based land uses, improved fallow systems, and traditional farming practices can help mitigate the impacts of global change, preserve biodiversity, and enhance the resilience of ecosystems. this research also underscores the vulnerability of orphan crops in addressing global change challenges and highlights the importance of sustainable farming practices, such as the use of organic fertilizers. By examining the complex interactions among crop types, environmental factors, and landscape characteristics, this dissertation emphasizes the need for designing adaptive and sustainable agricultural systems. The findings demonstrate the interdependence of agricultural sustainability, climate change mitigation, and biodiversity conservation in the context of agroforestry systems and traditional agriculture practices. Finally, this dissertation suggests that promoting resilient crops, particularly orphan crops, may offer a promising solution for enhancing food security and conserving agrobiodiversity in mountain regions worldwide.