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  • 1.
    Ayalew Nurihun, Biruk
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The relationship between climate, disease and coffee yield: optimizing management for smallholder farmers2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Climate change and diseases are threatening global crop production. Agroforestry systems, which are characterized by complex multispecies interactions, are considered to provide nature-based solutions for climate change mitigation and pest and disease regulation. Understanding the role of the abiotic environment and species interactions in shaping diseases and yield in agroforestry systems would enable us to develop effective ecologically-informed pest and disease management under a changing climate, support sustainable agricultural practices, and maximize the benefits gained from agroforestry systems. To gain such a comprehensive understanding of what shapes pest and disease levels and yield in agroforestry systems, we need to investigate how the interactions between agroforestry system components, such as trees, crops and their associated organisms, vary in space and time, and how they are influenced by abiotic factors in terms of pests and diseases and yield. 

    In this thesis, my overarching goal was to understand how microclimate and management impact major coffee pests and diseases, their natural enemies, and coffee yield, as well as farmers’ perceptions of climate change and climate-mediated changes in disease dynamics and yield, with the aim of using these insights to optimize management decisions for smallholder farmers in southwestern Ethiopia. With this aim, I selected 58 sites along a gradient of management intensity, ranging from minimal management in the natural forest to moderate management in smallholder farms and intensive management in commercial plantations. As an approach, I combined observational and interview studies to examine i) the impact of shade tree species identity and canopy cover on coffee pests and diseases, ii) the effect of climate and management on coffee berry disease and yield, iii) the impact of climate on a host-hyperparasite interaction, and iv) farmers’ perceptions of climate change and climate-mediated changes in disease dynamics and yield. 

    I found that tree identity affected the incidence and severity of coffee diseases, whereas insect pests were strongly affected by canopy cover, but in a species-specific way (I).  Both climate and management affected coffee berry disease and yield. Importantly, the effect of climatic variables on disease and yield differed strongly between the developmental stages from flowering to ripening (II). In chapter (III), I found that the climatic niches of coffee leaf rust and its hyperparasite differed, with coffee leaf rust severity preferring high maximum temperatures, whereas the hyperparasite preferred cold nights. The interviews revealed that the majority of farmers perceived long-term changes in one or more aspects of the climate, and the majority of farmers perceived an increase in coffee leaf rust and a decrease in coffee berry disease. Climate data also supported farmers’ knowledge on climate-disease-yield relationships (IV). 

    Taken together, my thesis advances our understanding of the relationship between climate and management of coffee pests, diseases and yield, and this may contribute to the development of ecologically-informed pest and disease management strategies for coffee production and other agroforestry crops.

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  • 2.
    Burger, Hannah F.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Lund University, Sweden.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ayalew, Biruk
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    van Dam, N. M.
    Mendesil, E.
    Schedl, A.
    Shimales, T.
    Zewdie, Beyene
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bottom-up and top-down drivers of herbivory on Arabica coffee along an environmental and management gradient2022In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 59, p. 21-32Article in journal (Refereed)
    Abstract [en]

    While sustainable agriculture relies on natural pest control, we lack insights into the relative importance of bottom-up and top-down factors on pest levels, especially along broad environmental and management gradients. To this aim, we focused on bottom-up and top-down control of herbivore damage in sixty sites in the centre of origin of Arabica coffee in southwestern Ethiopia, where coffee grows along a management gradient ranging from little or no management in the natural forest to commercial plantations. More specifically, we examined how canopy cover, percentage of surrounding forest and management intensity affected caffeine and chlorogenic acid concentration (bottom-up process) and attack of dummy caterpillars by ants and birds (top-down process), and how these in turn affected pest levels. Caffeine and chlorogenic acid concentrations were negatively related to canopy cover, while ant attack rate was positively related to canopy cover. Both ant and bird attack rate increased with the percentage of surrounding forest. Yet, secondary chemistry and caterpillar attack rates were unrelated to herbivory, and herbivory was only directly and positively affected by management intensity. Our study highlights that canopy cover can have contrasting effects on plant defence and predation, and that changes in bottom-up and top-down factors do – unlike often assumed – not necessarily translate into reduced pest levels. Instead, direct effects of management on pest levels may be more important than bottom-up or top-down mediated effects.

  • 3. Getachew, Merkebu
    et al.
    Tolassa, Kassaye
    De Frenne, Pieter
    Verheyen, Kris
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ayalew, Biruk
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Boeckx, Pascal
    The relationship between elevation, soil temperatures, soil chemical characteristics, and green coffee bean quality and biochemistry in southwest Ethiopia2022In: Agronomy for Sustainable Development, ISSN 1774-0746, E-ISSN 1773-0155, Vol. 42, no 4, article id 61Article in journal (Refereed)
    Abstract [en]

    Green coffee bean quality and biochemistry are influenced by environmental variables. The present study was designed to study the influence of soil temperatures and soil chemistry on bean physical attributes, bean quality (assessed by three internationally trained, experienced, and certified Q-grade cuppers licensed by the Specialty Coffee Association (SCA) Coffee Quality Institute (CQI) and biochemistry of green coffee beans). The study was performed in 53 farms in southwest Ethiopia distributed along an elevational gradients (1500–2160 m a.s.l.) and with varying shade canopy cover (open to dense shade). A total of 159 individual coffee trees were sampled. Shade tree canopy cover, soil temperature, and soil chemistry, as well as coffee management intensity, were quantified as explanatory variables. Green bean quality was negatively correlated to soil temperatures. On the other hand, hundred bean mass and green bean biochemistry (caffeine, trigonelline, and chlorogenic acid contents) were negatively correlated to soil temperatures but positively to soil chemistry. During the coffee fruit development period (flowering to fruit maturity), temperature appeared to be a driving factor influencing coffee bean quality and biochemistry. Total specialty quality was significantly associated with soil chemistry, in which 84% of the variation could be explained by soil chemical variables. This study is the first to demonstrate the relationship between soil temperatures and chemistry in coffee bean quality and green bean biochemical compositions. Although the relative importance of factors such as air temperatures and humidity and soil moisture are missing from this study, we find that soil temperatures and soil chemistry have a strong effect on coffee bean quality and biochemistry. Overall, climate change, which generally involves a substantial increase in mean temperatures of tropical regions, could be expected to have a negative impact on coffee bean quality and biochemistry.

  • 4. Getachew, Merkebu
    et al.
    Verheyen, Kris
    Tolassa, Kassaye
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ayalew, Biruk
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Boeckx, Pascal
    Landuyt, Dries
    De Frenne, Pieter
    Effects of shade tree species on soil biogeochemistry and coffee bean quality in plantation coffee2023In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 347, article id 108354Article in journal (Refereed)
    Abstract [en]

    Shade trees are used in many coffee production systems across the globe. Beyond the benefits on biodiversity conservation, climate buffering, carbon sequestration and pathogen regulation, shade trees can impact the soil nutrient status via, for instance, litter inputs and nitrogen fixation. Since soil nutrients affect coffee quality and taste, there is also a potential indirect effect of shade tree species on coffee quality. Yet, in spite of the potentially large impact of shade tree species, quantitative data on the effects of shade trees on (i) soil biogeochemistry and (ii) the associated coffee bean quality remain scarce. To what extent four widely used shade trees species (Acacia abyssinica L., Albizia gummifera L., Cordia africana L. and Croton macrostachyus L.) in a plantation coffee agroforestry system impact soil biogeochemistry, and how this in turn affects coffee quality, measured as cupping scores and bean size. A significant negative impact of N-fixing shade tree species on soil pH and base cation concentrations was found. Plant-available and total phosphorus was enhanced by the presence of Albizia gummifera L. Thus, the present findings demonstrate that careful selection and integration of shade tree species such as Acacia abyssinica L. and Albizia gummifera L. into coffee production systems is a good practice for sustaining soil chemical properties in coffee agroecosystem. Despite the impacts on soil chemical characteristics, the shade tree species had no effect on coffee cup quality but did affect the bean mass. In this particular study, an attempt was made to quantify the impacts of widely used shade tree species on soil biogeochemistry and the subsequent effect on coffee bean quality in a plantation agroforestry system over the course of one season in southwest Ethiopia. However, it might be feasible to accommodate both relatively sparse time-series experimental data consisting of coffee farms from plantations and smallholders, which needs to be the goal of future research to accurately examine the impacts on the outcome variables.

  • 5. Kemppinen, Julia
    et al.
    Nurihun, Biruk Ayalew
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Greiser, Caroline
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    von Schmalensee, Loke
    Stockholm University, Faculty of Science, Department of Zoology.
    De Frenne, Pieter
    Microclimate, an important part of ecology and biogeography2024In: Global Ecology and Biogeography, ISSN 1466-822X, E-ISSN 1466-8238Article in journal (Refereed)
    Abstract [en]

    Brief introduction: What are microclimates and why are they important? Microclimate science has developed into a global discipline. Microclimate science is increasingly used to understand and mitigate climate and biodiversity shifts. Here, we provide an overview of the current status of microclimate ecology and biogeography in terrestrial ecosystems, and where this field is heading next.

    Microclimate investigations in ecology and biogeography: We highlight the latest research on interactions between microclimates and organisms, including how microclimates influence individuals, and through them populations, communities and entire ecosystems and their processes. We also briefly discuss recent research on how organisms shape microclimates from the tropics to the poles.

    Microclimate applications in ecosystem management: Microclimates are also important in ecosystem management under climate change. We showcase new research in microclimate management with examples from biodiversity conservation, forestry and urban ecology. We discuss the importance of microrefugia in conservation and how to promote microclimate heterogeneity.

    Methods for microclimate science: We showcase the recent advances in data acquisition, such as novel field sensors and remote sensing methods. We discuss microclimate modelling, mapping and data processing, including accessibility of modelling tools, advantages of mechanistic and statistical modelling and solutions for computational challenges that have pushed the state-of-the-art of the field.

    What's next? We identify major knowledge gaps that need to be filled for further advancing microclimate investigations, applications and methods. These gaps include spatiotemporal scaling of microclimate data, mismatches between macroclimate and microclimate in predicting responses of organisms to climate change, and the need for more evidence on the outcomes of microclimate management.

  • 6.
    Nurihun, Biruk Ayalew
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Adugna, Girma
    Zewdie, Beyene
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Impact of climate on a host-hyperparasite interaction on Arabica coffee in its native rangeManuscript (preprint) (Other academic)
    Abstract [en]
    1. Natural enemies of plant pathogens might play an important role in suppressing plant disease levels in natural and agricultural systems. Yet, plant pathogen-natural enemy interactions might be sensitive to changes in the climate. Understanding the relationship between climate, plant pathogens, and their natural enemies is thus important for developing climate-resilient, sustainable agriculture.
    2. To this aim, we recorded shade cover, daily minimum and maximum temperature, relative humidity, coffee leaf rust, and its hyperparasite at 58 sites in southwestern Ethiopia during the dry and wet season for two years
    3. Coffee leaf rust severity was positively related to maximum temperature and hyperparasite severity was higher when the minimum temperature was low (i.e. in places with cold night temperatures) during three of the four surveying periods. While canopy cover did not have a direct effect on rust severity, it reduced rust severity indirectly by lowering the maximum temperature. Canopy cover had a direct positive effect on hyperparasite severity.
    4. Synthesis and applications. Our findings highlight that coffee leaf rust and its hyperparasite are both affected by shade cover and temperature, but in different ways. On the one hand, these niche differences between coffee leaf rust and its hyperparasite provide opportunities to develop strategies to manage the environment (such as shade cover and microclimate) in such a way that the rust is disfavored and the hyperparasite is favored. On the other hand, these niche differences lead to the worrying prediction that levels of coffee leaf rust will increase, and its hyperparasite will decrease, with climate change.
  • 7.
    Nurihun, Biruk Ayalew
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Adugna, Girma
    Zewdie, Beyene
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Impact of climate on a host-hyperparasite interaction on Arabica coffee in its native range2024In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 61, no 3, p. 538-550Article in journal (Refereed)
    Abstract [en]
    1. Natural enemies of plant pathogens might play an important role in controlling plant disease levels in natural and agricultural systems. Yet, plant pathogen–natural enemy interactions might be sensitive to climatic changes. Understanding the relationship between climate, plant pathogens and their natural enemies is thus important for developing climate-resilient, sustainable agriculture.
    2. To this aim, we recorded shade cover, daily minimum and maximum temperature, relative humidity, coffee leaf rust and its hyperparasite at 58 sites in southwestern Ethiopia during the dry and wet season for 2 years.
    3. Coffee leaf rust severity was positively related to the maximum temperature. Hyperparasite severity was higher when the minimum temperature was low (i.e. in places with cold night temperatures). While canopy cover did not have a direct effect on rust severity, it reduced rust severity indirectly by lowering the maximum temperature. Canopy cover had a direct positive effect on the hyperparasite severity during one surveying period.
    4. Synthesis and applications. Our findings highlight that coffee leaf rust and its hyperparasite are both affected by shade cover and temperature, but in different ways. On the one hand, these niche differences lead to the worrying prediction that levels of coffee leaf rust will increase, and its hyperparasite will decrease, with climate change. On the other hand, these niche differences between coffee leaf rust and its hyperparasite provide opportunities to develop strategies to manage the environment (such as shade cover and microclimate) in such a way that the rust is disfavoured and the hyperparasite is favoured.
  • 8.
    Nurihun, Biruk Ayalew
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Adugna, Girma
    Zewdie, Beyene
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Zignol, Francesco
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Impact of climate and management on coffee berry disease and yield in Arabica coffee’s native rangeManuscript (preprint) (Other academic)
    Abstract [en]

    Climate change might increase plant diseases, reduce crop yields and threaten the livelihoods of millions of smallholder farmers globally. It is thus important to understand the relationships between climate, disease levels and yield to improve management strategies for sustainable agroforestry in a changing climate. One of the major threats to coffee production in Africa is coffee berry disease, caused by the fungal pathogen Colletotrichum kahawae. To investigate the effects of climatic and management variables on coffee berry disease and yield, we recorded daily minimum and maximum temperature and relative humidity, as well as incidence of coffee berry disease and yield in 58 sites along a broad environmental and management gradient in southwestern Ethiopia in both 2018 and 2019. Coffee berry disease was affected by several climatic and management variables, with relatively high consistency between years. For example, coffee berry disease incidence was higher in sites with high minimum temperatures during the fruit expansion stage from March to April, and was lower in sites with high minimum temperatures during the endosperm filling stage from May to June. Coffee berry disease incidence was negatively affected by the proportion of resistant cultivars, whereas management intensity had no effect on disease incidence. Coffee yield decreased with increasing minimum and maximum temperatures during the flowering period in 2018 and the fruit developmental period in 2019, respectively. Coffee yield was negatively affected by canopy cover, and positively affected by management intensity, in both years. Our findings highlight that coffee berry disease and yield were affected by different climatic and management variables. Yet, managing for low disease-high yield is practically difficult, as the effect of several climatic variables was season-dependent, and at the same time climatic variables were highly correlated between seasons. One way to break the correlation of climatic variables between seasons might be to take advantage of differences among shade trees in the presence or timing of leaf drop. To reduce levels of coffee berry disease, an effective strategy is to use resistant cultivars, but this might threaten the wild coffee genetic reservoir.

  • 9.
    Nurihun, Biruk Ayalew
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Adugna, Girma
    Zewdie, Beyene
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Zignol, Francesco
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden.
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Impact of climate and management on coffee berry disease and yield in coffee's native range2024In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 76, p. 25-34Article in journal (Refereed)
    Abstract [en]

    Climate change might increase plant diseases, reduce crop yields and threaten the livelihoods of millions of smallholder farmers globally. It is thus important to understand the relationships between climate, disease levels and yield to improve management strategies for sustainable agroforestry in a changing climate. One of the major threats to coffee production in Africa is the coffee berry disease (Colletotrichum kahawae). To investigate the effects of climatic and management variables on coffee berry disease (CBD) incidence and yield, we recorded minimum and maximum temperature and relative humidity, as well as CBD and yield, along a broad environmental and management gradient in southwestern Ethiopia during two consecutive years. CBD was affected by several climatic and management variables. For example, CBD incidence increased with minimum temperature during the fruit expansion stage, and decreased with minimum temperature during the endosperm filling stage. CBD incidence was negatively affected by the proportion of resistant cultivars, whereas the coffee structure index (pruning) had no effect on disease incidence. Coffee yield decreased with increasing minimum temperature during the flowering period in 2018 and maximum temperature during the fruit developmental period in 2019. Coffee yield was negatively affected by canopy cover and positively affected by the coffee structure index in both years. Our findings highlight that CBD and yield were affected by different climatic and management variables. Yet, managing for low disease levels and high yield is practically difficult due to season -dependent effects of several climatic variables. One way to break the correlation of climatic variables between seasons might be to take advantage of differences among shade trees in the presence or timing of leaf drop. To reduce CBD incidence, using resistant cultivars is an effective strategy, but this might threaten the wild coffee genetic reservoir.

  • 10.
    Nurihun, Biruk Ayalew
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Börjeson, Lowe
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Adugna, Girma
    Beche, Dinkissa
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Using local knowledge to reconstruct climate-mediated changes in disease dynamics and yield – a case study on Arabica coffee in its area of originManuscript (preprint) (Other academic)
    Abstract [en]
    • While some countries have monitored major crop diseases for several decades or centuries, other countries have very limited historical time series. In such areas, we lack data on long-term patterns and drivers of disease dynamics, which is important for developing climate-resilient disease management strategies. 
    • We adopted a novel approach, combining local knowledge, climate data, and spatial field surveys to understand long-term climate-mediated changes in disease dynamics in coffee agroforestry systems. For this, we worked with 58 smallholder farmers in southwestern Ethiopia, the area of origin of Arabica coffee.
    • The majority of farmers perceived an increase in coffee leaf rust and a decrease in coffee berry disease, whereas perceptions of changes in coffee wilt disease and Armillaria root rot were highly variable among farmers. Climate data supported farmers’ understanding on the climatic drivers (increased temperature, less rainy days) of these changes. Temporal disease-climate relationships were matched by spatial disease-climate relationships, as expected with space-for-time substitution.
    • Understanding long-term disease dynamics and yield is crucial to adapt disease management to climate change. Our study demonstrates how to combine local knowledge, climate data and spatial field surveys to reconstruct disease time series and postulate hypotheses for disease-climate relationships in areas where few long-term time-series exist.
  • 11.
    Nurihun, Biruk Ayalew
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Börjeson, Lowe
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Adugna, Girma
    Beche, Dinkissa
    Zignol, Francesco
    Swedish University of Agricultural Sciences, Sweden.
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Using local knowledge to reconstruct climate-mediated changes in disease dynamics and yield-A case study on Arabica coffee in its native range2024In: Plants, People, Planet, E-ISSN 2572-2611Article in journal (Refereed)
    Abstract [en]

    Societal Impact Statement

    Adapting agriculture to climate change requires an understanding of the long-term relationship between climate, disease dynamics, and yield. While some countries have monitored major crop diseases for decades or centuries, comparable data is scarce or non-existent for many countries that are most vulnerable to climate change. For this, a novel approach was developed to reconstruct climate-mediated changes in disease dynamics and yield. Here, a case study on Arabica coffee in its area of origin demonstrates how to combine local knowledge, climate data, and spatial field surveys to reconstruct disease and yield time series and to postulate and test hypotheses for climate-disease-yield relationships.

    Summary

    While some countries have monitored crop diseases for several decades or centuries, other countries have very limited historical time series. In such areas, we lack data on long-term patterns and drivers of disease dynamics, which is important for developing climate-resilient disease management strategies.

    We adopted a novel approach, combining local knowledge, climate data, and spatial field surveys to understand long-term climate-mediated changes in disease dynamics in coffee agroforestry systems. For this, we worked with 58 smallholder farmers in southwestern Ethiopia, the area of origin of Arabica coffee.

    The majority of farmers perceived an increase in coffee leaf rust and a decrease in coffee berry disease, whereas perceptions of changes in coffee wilt disease and Armillaria root rot were highly variable among farmers. Climate data supported farmers' understanding of the climatic drivers (increased temperature, less rainy days) of these changes. Temporal disease-climate relationships were matched by spatial disease-climate relationships, as expected with space-for-time substitution.

    Understanding long-term disease dynamics and yield is crucial to adapt disease management to climate change. Our study demonstrates how to combine local knowledge, climate data and spatial field surveys to reconstruct disease time series and postulate hypotheses for disease-climate relationships in areas where few long-term time series exist.

  • 12.
    Nurihun, Biruk Ayalew
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Zewdie, Beyene
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Shimales, Tamiru
    Adugna, Girma
    Mendesil, Esayas
    Nemomissa, Sileshi
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The impact of shade tree species identity on coffee pests and diseases2022In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 340, article id 108152Article in journal (Refereed)
    Abstract [en]

    The multifunctional role of shade trees for conservation of biodiversity and ecosystem services in natural forests and agroforests is well documented, yet we lack insights into the impact of shade tree species identity on pest and disease dynamics on agroforestry crops such as coffee and cacao, and its implications for management. We conducted two surveys on the impact of shade tree species identity and canopy cover on pests, diseases and a fungal hyperparasite on Arabica coffee in southwestern Ethiopia, which is one of the areas of origin of Arabica coffee. One survey was in a commercial plantation, and the other along a management gradient from only little managed coffee growing in the natural forest to intensively managed commercial plantations. To link these findings to current shade tree selection criteria, we complemented these surveys by interviews with farmers and managers. Shade tree species identity left a weak imprint on insect pest levels, and insect pests levels differed strongly in the strength and direction of their response to canopy cover. In contrast to the insect pests, the incidence of coffee leaf rust and its hyperparasite, as well as coffee berry disease, differed among shade tree species, with particularly high levels of coffee leaf rust and the hyperparasite underneath the canopy of the shade trees Acacia abyssinica and Croton macrostachyus, and coffee berry disease underneath the canopy of Acacia abyssinica and Polyscias fulva. Smallholder farmers used many criteria for selecting shade trees, such as leaf traits and competition for soil moisture, but low priority is given to the effect of shade tree species identity on pests and diseases. Our findings help to understand spatial variation in pest and disease dynamics in natural forests and agroforests, and may inform the selection of shade tree species by coffee producers and thereby contribute to ecologically-informed pest and disease management. Importantly, our finding highlight the potential for using tree identity for the sustainable management of pests and diseases, with relevance for global agroforestry systems.

  • 13. Shimales, Tamiru
    et al.
    Mendesil, Esayas
    Zewdie, Beyene
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Department of Horticulture & Plant Sciences, Ethiopia.
    Ayalew, Biruk
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Management intensity affects insect pests and natural pest control on Arabica coffee in its native range2023In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 60, no 5, p. 911-922Article in journal (Refereed)
    Abstract [en]

    1. Agroforestry systems provide opportunities to reduce the trade -off between agricultural production and biodiversity, for example by enhancing a diverse community of species potentially acting as natural pest control agents. While management of agroforestry systems is intensifying across the globe, we lack insights into the impact of management intensity on pest levels and natural pest control, especially along broad management gradients and as compared with nat- ural forests.

    2. We assessed the impact of management intensity on major insect pests (the coffee blotch miner, the serpentine leaf miner, the coffee leaf skeletonizer and damage by other free-feeding herbivores) and natural pest control by parasitoid wasps across sixty sites in the centre of origin of Arabica coffee in southwestern Ethiopia. Within this region, coffee is growing along a broad management gradi- ent ranging from little or no management in the natural forest to intensively man- aged commercial plantations.

    3. In the wet season, pest levels were largely similar in the natural forest, semi-forest and semi-plantation systems, whereas pests reached outbreak densities in the most intensively managed plantation system. In contrast, management intensity did not significantly affect pest levels in the dry season. The insect pests differed in their seasonal dynamics, consistently declined with elevation and were largely unaffected by shade levels. Parasitism rate of the coffee blotch miner was lower, and the parasitoid community was distinct, in the most intensively managed plan- tation system.

    4. Synthesis and applications : Our findings support the hypothesis that the weaker top -down control by parasitoids in the intensively managed plantation sites leads to higher pest levels, and that - at least for some pest species - there is a threshold in the effect of management intensity on pest levels and natural pest control. It is important to consider such non-linear relationships to maintain or enhance the sustainability of agroforestry systems during management intensification. Overall, our findings highlight that ecological knowledge of natural pest control can be used to intensify production to improve the livelihood of smallholder farmers without jeopardizing natural pest control but only up to a certain point where it starts to deteriorate.

  • 14.
    Zewdie, Beyene
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ayalew, Biruk
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Wondafrash, Melaku
    Nemomissa, Sileshi
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Plant biodiversity declines with increasing coffee yield in Ethiopia's coffee agroforests2022In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 59, no 5, p. 1198-1208Article in journal (Refereed)
    Abstract [en]
    1. Tropical agroforestry systems provide farmers with resources for their livelihoods, but are also well-recognized as refuges for biodiversity. However, the relationship between yield and biodiversity might be negative in these systems, reflecting a potential trade-off between managing for increased yield or biodiversity. The potential for synergies will depend partly on the shape of the biodiversity–yield relationship, where a concave relationship suggests a faster decline in biodiversity with increasing yields than a linear or convex shape.
    2. We studied the relationship between biodiversity (plant species richness and composition) and coffee yield along a gradient of management in south-western Ethiopia, coffee's native range. We inventoried species richness and community compoasition of woody plants, herbaceous plants and bryophytes at 60 sites. We also measured coffee management-related variables and assessed coffee yield for 3 consecutive years at each site.
    3. Species richness of woody plants had a concave relationship with coffee yield, that is, tree richness declined fast initially before levelling out at higher yields, whereas there was no relationship between coffee yield and species richness of herbaceous plants or bryophytes. Species composition of woody plants, herbaceous plants and bryophytes all had a concave relationship with coffee yield.
    4. From a methodological perspective, we found that multi-year data on yield were necessary to reliably assess the relationship between biodiversity and yield, and that the number of coffee shrubs or coffee dominance were poor proxies for yield when trying to capture the biodiversity–yield relationship.
    5. Synthesis and applications. The concave relationship between biodiversity components (species richness and composition) and yield suggests that there is a strong conflict between the goals of increasing production and conserving biodiversity. However, it is important to recognize that this pattern is largely driven by the very low-yielding sites in natural forests. Here, even minor intensification of coffee management seems to rapidly erode biodiversity. Along the rest of the productivity gradient, there was generally no negative relationship between yield and biodiversity, implying opportunities for developing strategies for increasing yields without biodiversity loss.
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