Abundance of pests and diseases in Arabica coffee production systems in Uganda - ecological mechanisms and spatial analysis in the face of climate change.

Coffee production worldwide is threatened by a range of coffee pests and diseases (CPaD). Integrated management options require an understanding of the bioecology of CPaD and the prevalent interdependencies within the agroecological context. The comparison of different shading systems (e.g. shade-grown vs. sun-grown coffee) and the identification of tradeoffs for ecosystem services is still a matter of ongoing debates. There is little quantitative knowledge of field-level investigation on shade effects and its ecological mechanisms across environmental and shading system gradients. Considering the increasingly evident effects of progressive climate change on CPaD, the need to examine the balance of shade effects under different environmental conditions becomes apparent. With the example of the coffee growing region of Mt Elgon, Uganda, this project aimed at addressing the complexity of shading effects on economically relevant CPaD using environmental and production system gradients. The approach was designed in an interdisciplinary manner, to involve the broader context of coffee agroforestry systems. The first two chapters of this thesis dealt with general aspects of coffee smallholder farming. The diversity of existing coffee production systems was characterized along an altitudinal gradient. A typology of production systems based on indicators related to the vegetation structure was generated and classified as coffee open canopy, coffeebanana inter-cropping, and densely shaded coffee systems. The typology served as the basis for comparison across the environmental and production system gradients. In the second chapter, farmers’ knowledge on CPaD and the role of shade trees was contrasted with expert knowledge and field observations. Discrepancies regarding CPaD symptomatology, management and response to shade were revealed. Tackling institutional obstacles and disentangling shading effects are therefore a priority for the improvement of plant health management. The last two chapters focused more specifically on biophysical aspects of Coffee Leaf Rust (CLR, Hemileia vastatrix) and White Coffee Stem Borer (WCSB, Monochamus leuconotus). The effects of environment and production system on CLR abundance were spatio-temporally variable and either directly, interactive or indirectly mediated by microclimate. The development of white coffee stem borer was controlled by the bimodal rainfall, and by altitude and shade through their effect on minimum temperature. The findings emphasize the enormous importance of micro-environments for the ecology of CPaD, not least because of its implications in the context of climate change

Revisiting the “thin months” – a follow-up study on the livelihoods of Mesoamerican coffee farmers

Smallholder coffee farmers in Mesoamerica face formidable challenges, including highly variable coffee prices, increasing climate change impacts, and worsening outbreaks of pests and diseases, which contribute to chronic debt and food insecurity. Despite these difficulties, the results of a recent follow-up or longitudinal survey show improvement in key aspects of farmers’ livelihoods, though there is an urgent need to continue working with farmers on these issues. The findings point to promising strategies for enhancing livelihoods, including carefully selected crop diversification practices to improve food security; site-specific instead of blanket recommendations for improved agricultural management and livelihood diversification; access to affordable financing and training in financial literacy; and other education and training programs for farmers

Opportunities for sustainable intensification of coffee agro-ecosystems along an altitudinal gradient on Mt. Elgon, Uganda

The viability of coffee farming in East Africa is endangered by multiple factors including climate change, population pressure, low yields, and coffee price volatility. Sustainable intensification (SI) through intercropping and/or agroforestry has been suggested to improve farmers' livelihoods, facilitate adaptation of coffee production to climate change and contribute to biodiversity conservation. In order to understand how sustainable intensification through an ecosystem-based approach might offer opportunities to respond to changes in temperature and rainfall, we analyzed a variety of existing coffee agro-ecosystems that differ in vegetation structure, shade tree diversity, and socio-economic characteristics on Mt. Elgon, Uganda along an altitudinal gradient (1100–2100 m.a.s.l.). We (i) compared the performance of the agro-ecosystems regarding coffee yield and shade tree diversity, and (ii) analyzed determinants of adoption of each system. Three different coffee agro-ecosystems were identified: open canopy coffee system, coffee-banana intercropping, and coffee-tree systems, based on the vegetation structure of 144 coffee plots. The vegetation structure of the analyzed coffee systems varied along the altitudinal gradient. Banana density increased with increasing altitude, while shade tree density and diversity increased with decreasing altitude. Coffee yield also increased with increasing altitude, but this relationship varied with shade level. Coffee yields benefited from shade trees at low altitudes, while no yield differences among systems were observed at mid and high altitudes. Increasing water availability and reliance on on-farm food crops with increasing altitude were identified as the main determinants of the increasing intercropped banana densities. High temperatures and longer dry season in combination with reduced access to forest products at lower altitudes, appeared to be the main driver for increased adoption of coffee-tree systems. Furthermore, socio-economic status of farmers influenced the type of coffee system adopted; poor farmers preferred high intercropping (either with bananas and/or shade trees) to diversify income and reduce risks related to open systems, while wealthier farmers mainly owned open canopy coffee systems. Climate, farm and household size, and access to forests and markets, play a crucial role in determining what constellation of plot-level provisioning ecosystem services benefit farmers' livelihoods on Mt. Elgon. Our findings reveal inherent trade-offs in socio-ecological conditions. Minimizing these is required for achieving the multiple objectives of livelihood improvement, sustainable intensification of coffee production, and biodiversity conservation

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements