Wind erosion and associated dust emissions play a fundamental role in many ecological processes, yet most ecological studies do not explicitly consider dust-driven processes despite the growing body of evidence suggesting that wind erosion is a key driver of land surface dynamics and many other environmentally relevant processes such as desertification. This study provides explicit support for a pervasive underlying but untested desertification hypothesis by showing that at the vegetation patch scale shrubs are significantly more efficient at capturing wind-blown sediment and other resources such as nutrients than grasses and that this difference is amplified following disturbance. At the landscape scale, the spacing and shape of woody plants were found to be a major determinant of dryland aeolian sediment transport processes in grasslands, shrublands, woodlands and forests, particularly following disturbance. This study also found that disturbance such as fire can have a significant influence on background dust emissions, which can have important consequences for many basic ecological and hydrological processes. Potential interactions between aeolian and fluvial processes were also evaluated in this study, and a new conceptual framework was developed that highlights important differences and similarities between the two processes as a function of scale-dependencies, mean annual precipitation, and disturbance. This study also explicitly evaluates the effect of climatic extremes and alternate land management practices on the absolute and relative magnitudes of wind and water erosion. Notably, results indicate that wet/dry climatic extremes and grazing can increase the wind-to-water erosion ratio, whereas burning disproportionally increases water erosion relative to wind erosion.

This study focuses on the constraints, adaptations and innovations in the livelihoods of Orma pastoralists. The fieldwork took place with families around Tiltila, Waldena and Kalalani over a period of 9 months in 2007/08. The position of pastoralist peoples in East Africa is characterised by social, political and economic marginalisation, weak land tenure, and declining per capita livestock holdings, while their shrinking grazing lands are widely regarded to be on the front line of climate change, both in terms of climate impacts and biofuel/agribusiness land pressure. The dearth of good quality data on pastoralist populations and livelihoods is widely cited as one of the fundamental barriers to improving the effectiveness of development support in the drylands. This study seeks to address these knowledge gaps for Orma pastoralists, while contributing to the body of theory on pastoralist livelihood dynamics. Data on the effects of wealth, education and food aid on household mobility were analysed using a theory of asset threshold dynamics. An adapted typology of livelihood strategies was developed to interpret and structure the data. Using child mortality as a proxy for respondent health, the impacts of wealth and mobility status on families’ health were explored. In the context of an almost total lack of data on community redistribution of food aid, both for the Orma and for East African pastoralists more generally, the study provides empirical data on de facto community food aid allocation patterns. The study also examines a controversial large-scale expropriation of land in Tana River (subsidised under the Kyoto Protocol’s Clean Development Mechanism) which will undermine the capacity of Orma pastoralists and other minority groups, to adapt to increased and more extreme environmental variability. In an environment in which enrolment in formal education is very low (particularly for girls), the study found that community nursery schools represent a relatively recent (and thus far undocumented) innovation organised and funded by groups of parents. The data demonstrates unprecedented levels of female enrolment despite cost constraints faced by least wealthy families. It is therefore suggested that incorporation of the community nursery model into the basic literacy element of the proposed national distance learning strategy, offers significant potential for addressing ‘Education For All’ in Kenya’s drylands.

A historiografia contemporânea aponta que a escravidão foi um fato inegável nos sertões da América Portuguesa e do Brasil desde o estabelecimento desta instituição. A presente dissertação questiona quais foram os mecanismos que permitiram a existência e a possibilidade de permanência de escravos nas regiões, que tiveram por base econômica, a atividade pecuária. Advoga-se, em geral, que a manutenção por meio do cerceamento da mobilidade e recurso à violência permitia que a escravidão fosse mantida. No entanto, no que concerne ao controle dos escravos, houve mais do que a pura violência física. Um conjunto de práticas e saberes, que envolveu também complexas relações entre senhores e escravos, imbricadas teias de arranjos e negociações assimétricas estiveram presentes nos processos que permitiram sua manutenção. Neste trabalho, que visita a historiografia sobre o tema, defende-se a hipótese de que, no caso da pecuária, um fator de manutenção do escravismo teria sido a possibilidade de constituição de famílias cativas, na conformação de um protocampesinato escravo, nos interstícios do Sistema Colonial. / The Contemporary Historiography about Dryland Slavery and the undeniable fact of its establishment over the Portuguese America and Brazil. This research questions which mecanisms allowed the existence and the possibility that slaves could remain over the regions, that had Cattle activity, as main economy. In general, the argument is that slavery was maintenned through the restriction of mobility and use of violence. However, regarding the control of slaves, was more than pure physical violence. A set of practices and knowledge, which also involves complex relationships between masters and slaves, overlapping webs of asymmetric relations and arrangements were present in the processes that allowed the continuation of slavery. This thesis deals with the debate of this historiography and the hypothesis that in the case of cattle, a factor maintaining the slavery system would have been the possibility to form slave families in the formation of a slave proto-peasantry in the interstices of the Colonial System.

A historiografia contemporânea aponta que a escravidão foi um fato inegável nos sertões da América Portuguesa e do Brasil desde o estabelecimento desta instituição. A presente dissertação questiona quais foram os mecanismos que permitiram a existência e a possibilidade de permanência de escravos nas regiões, que tiveram por base econômica, a atividade pecuária. Advoga-se, em geral, que a manutenção por meio do cerceamento da mobilidade e recurso à violência permitia que a escravidão fosse mantida. No entanto, no que concerne ao controle dos escravos, houve mais do que a pura violência física. Um conjunto de práticas e saberes, que envolveu também complexas relações entre senhores e escravos, imbricadas teias de arranjos e negociações assimétricas estiveram presentes nos processos que permitiram sua manutenção. Neste trabalho, que visita a historiografia sobre o tema, defende-se a hipótese de que, no caso da pecuária, um fator de manutenção do escravismo teria sido a possibilidade de constituição de famílias cativas, na conformação de um protocampesinato escravo, nos interstícios do Sistema Colonial. / The Contemporary Historiography about Dryland Slavery and the undeniable fact of its establishment over the Portuguese America and Brazil. This research questions which mecanisms allowed the existence and the possibility that slaves could remain over the regions, that had Cattle activity, as main economy. In general, the argument is that slavery was maintenned through the restriction of mobility and use of violence. However, regarding the control of slaves, was more than pure physical violence. A set of practices and knowledge, which also involves complex relationships between masters and slaves, overlapping webs of asymmetric relations and arrangements were present in the processes that allowed the continuation of slavery. This thesis deals with the debate of this historiography and the hypothesis that in the case of cattle, a factor maintaining the slavery system would have been the possibility to form slave families in the formation of a slave proto-peasantry in the interstices of the Colonial System.

abstract: Drylands (arid and semi-arid grassland ecosystems) cover about 40% of the Earth's surface and support over 40% of the human population, most of which is in emerging economies. Human development of drylands leads to topsoil loss, and over the last 160 years, woody plants have encroached on drylands, both of which have implications for maintaining soil viability. Understanding the spatial variability in erosion and soil organic carbon and total nitrogen under varying geomorphic and biotic forcing in drylands is therefore of paramount importance. This study focuses on how two plants, palo verde (Parkinsonia microphylla, nitrogen-fixing) and jojoba (Simmondsia chinensis, non-nitrogen fixing), affect sediment transport and soil organic carbon and total nitrogen pools in a dryland environment north of Phoenix, Arizona. Bulk samples were systematically collected from the top 10 cm of soil in twelve catenae to control for the existence and type of plants, location to canopy (sub- or intercanopy, up- or downslope), aspect, and distance from the divide. Samples were measured for soil organic carbon and total nitrogen and an unmanned aerial system-derived digital elevation map of the field site was created for spatial analysis. A subset of the samples was measured for the short-lived isotopes 137Cs and 210Pbex, which serve as proxy erosion rates. Erosional soils were found to have less organic carbon and total nitrogen than depositional soils. There were clear differences in the data between the two plant types: jojoba catenae had higher short-lived isotope activity, lower carbon and nitrogen, and smaller canopies than those of palo verde, suggesting lower erosion rates and nutrient contributions from jojoba plants. This research quantifies the importance of biota on influencing hillslope and soil dynamics in a semi-arid field site in central AZ and finishes with a discussion on the global implications for soil sustainability. / Dissertation/Thesis / Masters Thesis Geological Sciences 2018

Dans les zones arides, la grande variabilité des eaux de surface a conduit les Hommes à exploiter les eaux souterraines. Cependant, afin de préserver durablement cette ressource, une bonne connaissance des processus de recharge est nécessaire. Ces travaux de thèse ont pour objectifs de caractériser les facteurs de contrôle de la recharge et des écoulements souterrains en zone de piedmont aride et hyper-aride. Dans le Nord du Chili, l’activité minière et les villes nouvelles associées aux déplacements de populations depuis quelques dizaine d’années ont engendré une surexploitation des ressources en eaux souterraines contenues dans l’Aquifère de la Pampa del Tamarugal. Cet aquifère régional est l’une des principales ressources en eau de l’ensemble du Nord du Chili, ce qui en fait une ressource stratégique. Le contexte hyper-aride de cette zone de piedmont (extension nord du Désert d’Atacama) semble suggérer que la recharge actuelle de l’aquifère ne permet pas de soutenir son bilan hydrologique.Afin d’identifier et de caractériser les facteurs de contrôle de la recharge et des écoulements souterrains de l’Aquifère de la Pampa del Tamarugal, une approche multidisciplinaire a été utilisée. Cette approche est basée dans un premier temps sur la caractérisation géologique et géomorphologique de la Dépression Centrale et notamment du Piedmont Andin entre 19,5°S et 20°S. Celle-ci a permis d’identifier le rôle du substratum pré-Oligocène sur l’organisation de la couverture fin-Cénozoïque (i.e. axes de drainages, barrières sédimentaires & paléovallées) et sur les circulations souterraines au niveau du piedmont. Dans un second temps, une approche hydrogéophysique et hydro(géo)logique a été utilisée afin de caractériser et d’identifier les conditions aux limites ainsi que l’évolution spatiale de la piézométrie au sein de la plaine de la Pampa del Tamarugal et du piedmont. De nombreux sondages de résistivité, réalisé par TDEM, ont permis d’identifier un contraste bien défini et corrélé avec le niveau piézométrique de la nappe libre. Des relevés hydro(geo)logiques ont permis de valider les échanges rivière-nappe (zones de recharge) qui ont été déduits à partir de l’étude géophysique. Dans un troisième temps, la caractérisation géochimique et isotopique des eaux souterraines de la zone d’étude a permis d’identifier les origines, les circulations ainsi que les processus de recharge de l’aquifère. La distribution des âges de l’eau de la zone saturée a permis d’identifier les grandes phases de recharge paléoclimatiques de l’Holocène. Dans un quatrième temps, une approche exploratoire par la modélisation des écoulements au sein de la zone non saturée, basée sur un modèle à base physique (Hydrus-1D) et complétée par des relevés de terrain, ont permis d’évaluer la recharge induite par une crue au niveau des cônes alluviaux. L’analyse des chroniques piézométriques a apporté de nombreuses informations sur la quantification de la recharge.Sur la base des résultats de cette étude multidisciplinaire, ces travaux de recherche ont permis de définir, au niveau de l’Aquifère de la Pampa del Tamarugal (Nord Chili), les facteurs de contrôle de la recharge et des écoulements souterrains en zone de piedmont aride et hyper-aride. / In drylands, the scarcity of surface waters has led the population to mainly extract the groundwater resource for water supply. To preserve the groundwater resource of the over-exploitation, the understanding of the groundwater recharge processes is required. The present work aims to assess the factors of control on both the groundwater recharge and the groundwater circulation in dryland piedmonts.In Northern Chile, since a few tens of years, mining activities and the associated population movements have induced an over-exploitation of the Pampa del Tamarugal Aquifer. This regional size aquifer is one of the main groundwater resources of Northern Chile as a whole.In order to assess the controls on the groundwater recharge processes that allow recharging the Pampa del Tamarugal Aquifer as well as the groundwater circulation in the Andean Piedmont, a multidisciplinary approach was carried out in the endorheic catchment of the Pampa del Tamarugal (i.e. lowlands and piedmont) between 19.5°S and 20°S. Firstly, the study is based on a geological and geomorphological assessment of the Central Depression sedimentary basin with a focus on the Andean Piedmont. This work allowed identifying the control of the pre-Oligocene bedrock on both the late-Cenozoic piedmont cover (i.e. alluvial drainage axis, sedimentary barriers, and paleovalleys) and the groundwater circulation. Secondly, a hydrogeophysical (resistivity soundings, via TDEM) and hydrogeological characterization of the vadose zone and the saturated zone of the aquifer was carried out. These measurements allowed identifying a well-defined contrast of resistivity that is correlated with the water-table. This allows to better define the boundary conditions of the aquifer and to shift eastwards (i.e. in the piedmont) the oriental limit of the aquifer. Hydrological surveys allowed to validate the identification of groundwater recharge areas where the rivers fed the aquifer. Thirdly, the study is based on the assessment of the geochemical, isotopic and dissolved gas content of the groundwater. This approach allowed identifying the origin and also the groundwater circulation of the aquifer. The characterization of the groundwater distribution ages allowed to identify the main stages of recharge during Holocene and late-Pleistocene times. Fourthly, an exploratory approach was carried out in order to address the recharge fluxes in the vadose zone. Based on Hydrus-1D model and soil sampling carried out in the field, the recharge fluxes induced by one flood in the alluvial fans were estimated. The behavior analysis of water-table on time series of a few years were also used to estimate the recharge in the lower part of alluvial fans according to the surface geomorphology features.Based on this multidisciplinary approach, these works (performed in Northern Chile) allow defining the controls on the groundwater recharge and circulation in arid and hyperarid piedmont areas.

abstract: Climate change is increasing global surface temperatures, intensifying droughts and increasing rainfall variation, particularly in drylands. Understanding how dryland plant communities respond to climate change-induced rainfall changes is crucial for implementing effective conservation strategies. Concurrent with climate change impacts on drylands is woody encroachment: an increase in abundance of woody plant species in areas formerly dominated by grasslands or savannahs. For example, the woody plant, Prosopis velutina (velvet mesquite), has encroached into grasslands regionally over the past century. From an agricultural perspective, P. velutina is an invasive weed that hinders cattle forage. Understanding how P. velutina will respond to climate change-induced rainfall changes can be useful for management and conservation efforts. Prosopis velutina was used to answer the following question: Is there a significant interactive effect of mean soil water moisture content and pulse frequency on woody seedling survival and growth in dryland ecosystems? There were 256 P. velutina seedlings sourced from the Santa Rita Experimental Range in southern Arizona grown under four watering treatments where mean and pulse frequency were manipulated over two months. Data were collected on mortality, stem height, number of leaves, instantaneous gas exchange, chlorophyll fluorescence, biomass, and the leaf carbon to nitrogen (C:N) ratio. Mortality was low across treatments. Pulse frequency had less impact across response variables than the mean amount of water received. This may indicate that P. velutina seedlings are relatively insensitive to rainfall timing and are more responsive to rainfall amount. Prosopis velutina in the low mean soil moisture treatments lost a majority of their leaves and had greater biomass allocation to roots. Prosopis velutina’s ability to survive in low soil moisture conditions and invest in root biomass can allow it to persist as drylands are further affected by climate change. Prosopis velutina could benefit ecosystems where native plants are at risk due to rainfall variation if P. velutina occupies a similar niche space. Due to conflicting viewpoints of P. velutina as an invasive species, it’s important to examine P. velutina from both agricultural and conservation perspectives. Further analysis on the benefits to P. velutina in these ecosystems is recommended. / Dissertation/Thesis / Masters Thesis Plant Biology and Conservation 2020

abstract: Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C processes. Predictions for future climate include warmer temperatures and altered precipitation regimes, suggesting impacts on future soil C cycling. However, it is uncertain how soil microbial communities and subsequent soil organic carbon pools will respond to these changes, particularly in dryland ecosystems. A knowledge gap exists in soil microbial community responses to short- versus long-term precipitation alteration in dryland systems. Assessing soil C cycle processes and microbial community responses under current and altered precipitation patterns will aid in understanding how C pools and cycling might be altered by climate change. This study investigates how soil microbial communities are influenced by established climate regimes and extreme changes in short-term precipitation patterns across a 1000 m elevation gradient in northern Arizona, where precipitation increases with elevation. Precipitation was manipulated (50% addition and 50% exclusion of ambient rainfall) for two summer rainy seasons at five sites across the elevation gradient. In situ and ex situ soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were measured in precipitation treatments in all sites. Soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were highest at the three highest elevation sites compared to the two lowest elevation sites. Within sites, precipitation treatments did not change microbial biomass C, extracellular enzyme activity, and SOC. Soil CO2 flux was greater under precipitation addition treatments than exclusion treatments at both the highest elevation site and second lowest elevation site. Ex situ respiration differed among the precipitation treatments only at the lowest elevation site, where respiration was enhanced in the precipitation addition plots. These results suggest soil C cycling will respond to long-term changes in precipitation, but pools and fluxes of carbon will likely show site-specific sensitivities to short-term precipitation patterns that are also expected with climate change. / Dissertation/Thesis / Masters Thesis Biology 2019

abstract: Nitrogen is an essential, often limiting, element for biological growth that can act as a pollutant if present in excess. Nitrogen is primarily transported by water from uplands to streams and eventually to recipient lakes, estuaries, and wetlands, but can be modulated by biological uptake and transformation along these flowpaths. As a result, nitrogen can accumulate in aquatic ecosystems if supply is high or if biological retention is low. Dryland and urban ecosystems offer interesting contrasts in water supply, which limits transport and biological activity in drylands, and nitrogen supply that increases with human activity. In my dissertation, I ask: What is the relative balance among nitrogen retention, removal, and transport processes in dryland watersheds, and what is the fate of exported nitrogen? My dissertation research demonstrates that water is a major control on where and when nitrogen is retained and removed versus exported to downstream ecosystems. I used a mass-balance model based on synoptic surveys to study seasonal and spatial patterns in nitrate loading to a dryland stream network. I found that irrigation diversions transport nitrate from agricultural areas to the stream network year-round, even during dry seasons, and are an important driver of nitrate loading. I further explored how seasonal precipitation influences flood nutrient export in an intermittent desert stream by coupling long-term data of flood-water chemistry with stream discharge and precipitation data. I found that higher precipitation prior to a flood fills water storage sites in the catchment, leading to larger floods. In addition, higher antecedent precipitation stimulates biological nitrogen retention in the uplands, leading to lower nitrogen concentration in floods. Finally, I evaluated the consequences of nitrogen export from watersheds on how urban wetlands attenuate nitrate through denitrification that permanently removes nitrogen, and dissimilatory nitrate reduction to ammonium (DNRA) that retains nitrogen in another biologically reactive form. I found that DNRA becomes proportionally more important with low nitrate concentration, thereby retaining nitrogen as ammonium. Collectively, my dissertation research addresses how dryland and urban ecosystems can be integrated into models of watershed nitrogen cycling. / Dissertation/Thesis / Doctoral Dissertation Biology 2019

Regenerative Agriculture (RA) is increasingly promoted as a sustainable agri-food solution. Agronomic studies find that RA practices (e.g. cover crops, reduced tillage, crop rotation, and agroforestry) can regulate soil moisture, sequester atmospheric carbon, enhance biodiversity, and reduce the impacts of droughts and floods. Diverse public, private, and civil society initiatives therefore aim to increase farmer adoption of RA. However, empirical knowledge about the social processes underlying transformation to a regenerative food system is limited. Most research has focused on discourse analyses of RA and farmer experiences employing RA practices. While local institutions are recognized as potentially vital to facilitating RA transformations, there is a lack of empirical research documenting how institutions work to stimulate RA. This thesis presents a case study of Associacion AlVelAl, a grassroots RA movement based in Southeast Spain. Operating since 2015, AlVelAl has more than 500 members, most of whom are almond farmers. Employing concepts of adaptive capacity and bricolage, I examine the social innovations and institutional network that AlVelAl has built to nurture a RA transformation in the region. Specifically, I ask how does AlVelAl navigate sociocultural, ecological, and political-economic contexts at different scales to amplify the transformative potential of its social innovations? I conducted nine weeks of grounded research, involving participation at 7 events and interviews with 16 local actors who included AlVelAl employees, farmer members, and collaborators. My findings suggest that RA transformations depend on enabling farmers while also advancing systemic change. My study answers calls to identify strategies that can amplify adaptive capacity’s potential to generate transformational change. I point to four strategies that AlVelAl relies upon to translate RA practices into contextually-feasible steps for farmers and to mobilize collective action from diverse actors: 1) leveraging synergies among social innovations, 2) social mobilization through a vision for a desired future, 3) employing social-ecological relational thinking, and 4) adopting a systemic cross-scale approach.