Dynamic relationships between gross primary production and energy partitioning in three different ecosystems based on eddy covariance time series analysis

Ecosystems are responsible for strong feedback processes that affect climate. The mechanisms and consequences of this feedback are uncertain and must be studied to evaluate their influence on global climate change. The main objective of this study is to assess the gross primary production (GPP) dynamics and the energy partitioning patterns in three different European forest ecosystems through time series analysis. The forest types are an Evergreen Needleleaf Forest in Finland (ENF_FI), a Deciduous Broadleaf Forest in Denmark (DBF_DK), and a Mediterranean Savanna Forest in Spain (SAV_SP). Buys-Ballot tables were used to study the intra-annual variability of meteorological data, energy fluxes, and GPP, whereas the autocorrelation function was used to assess the inter-annual dynamics. Finally, the causality of GPP and energy fluxes was studied with Granger causality tests. The autocorrelation function of the GPP, meteorological variables, and energy fluxes revealed that the Mediterranean ecosystem is more irregular and shows lower memory in the long term than in the short term. On the other hand, the Granger causality tests showed that the vegetation feedback to the atmosphere was more noticeable in the ENF_FI and the DBF_DK in the short term, influencing latent and sensible heat fluxes. In conclusion, the impact of the vegetation on the atmosphere influences the energy partitioning in a different way depending on the vegetation type, which makes the study of the vegetation dynamics essential at the local scale to parameterize these processes with more detail and build improved global models

Economics of Land Degradation and Improvement – A Global Assessment for Sustainable Development

environmental economics; biodiversity; sustainable developmen

IRRIGATION IN THE WESTERN UNITED STATES: OCCURRENCE, IMPACTS, AND SUSTAINABILITY

Irrigation represents our greatest intervention in the hydrological cycle, accounting for over 80% of extracted freshwater in the Western U.S. Despite its economic and ecological importance, irrigation’s spatial and temporal occurrence, magnitude, impacts on streamflow, and response during water shortages has not been characterized in our region. The major objective of this dissertation was to systematically assess irrigation over the Western US to answer the following questions: 1) Where and when does irrigation occur within the study region? 2) How has the intensity, area, and distribution of irrigation changed over the course of the past 35 years? 3) What impact is irrigation having on surface water (i.e., rivers) in the region, how do impacts differ across basins, and what is driving them? 4) Finally, how do irrigators respond to drought and what can be expected of the irrigated system during water scarce times? To answer these questions, we developed a 35-year dataset covering the western U.S. consisting of high resolution satellite-derived irrigation and evapotranspiration data alongside streamflow, field-scale agricultural boundaries, and detailed climate information. We used a combination of data-driven methods to infer the behavior of irrigation in time and space, Bayesian regression modeling to define relationships between climate, irrigation and streamflow, and detailed geospatial and economic data analysis to explore drivers of the behavior of irrigated systems. We show that both climate change and irrigation are impacting streamflows, and that contrary to government statistics, irrigation is expanding in intensity, area, and water use. We show evidence for the large-scale operation of the ‘paradox of irrigation efficiency’, where despite increasing on-farm irrigation efficiency enabled by advances in irrigation infrastructure, basin-scale crop water use increases. We show how streamflow is changing and where the changes are driven by changes in climate and irrigation. Finally, we show that crop prices appear to drive crop planting decisions (and thus irrigated water use) to a greater degree than seasonal climate conditions and that intensely irrigated regions are unresponsive to drought. This dissertation contributes to our understanding of the systems-level impact of irrigation and provides opportunities for basin-specific management actions to mitigate irrigation and climate impacts on streamflow

The Dagara farmer at home and away : migration, environment and development in Ghana

Will people in drylands be forced to migrate due to climate change and environmental degradation? And what impact does migration have on the environment and development in the migrants' home and destination areas? These are some of the questions this study tries to answer. Based on local case study material among the Dagara people of Northwest Ghana and regional analyses of migration propensities and environmental scarcity, this study shows that structural differences in agro-ecological conditions - rather than degradation and disaster - are a principal cause of Dagara migration. The study further challenges alarming findings about deforestation and land degradation as a result of Dagara migration into the Brong Ahafo Region. Lastly, it shows that in the short term out-migration contributes to food and livelihood security in the home area, but in the long run it seems to thwart a transition to more sustainable land use and livelihoods and hamper rural development

Adventices et érosion du sol dans un agroécosystème montagneux du Nord de la Thaïlande : une étude multidisciplinaire

In Mountainous South-East Asia, rapid agricultural intensification and the expansion of rubber tree plantations in the past decades led to drastic biodiversity losses and intense soil degradation. Weeds provide diverse ecosystem services, including soil protection and support for biodiversity at higher levels. However, the determinants of weed communities in mountainous areas of Southeast Asia, and the interactions of these communities with soil characteristics and erosion processes, are still largely unknown. We conducted soil characterisation and botanical inventories in Huai Lang, Northern Thailand, in 20 fields from different land uses along the transition from annual crops to mature rubber tree plantations twice a year from 2016 to 2018. Using 1m2 erosion microplots, we also measured runoff and soil erosion in different land uses, and in rubber tree plantations under different weeding practices. We show that weed communities composition was mostly determined by land use and landscape characteristics, while crop temporal variability was an important determinant of plant diversity. Rubber tree plantations had specific weed communities and had exceptionally high soil detachment rates compared to maize or young plantations, but weed cover was effective in decreasing these erosion rates. Altogether, our results suggest that soil and plant biodiversity conservation in mountainous Southeast Asia should involve both on-field adaptations (e.g. less intense weeding practices, especially under rubber tree plantations) and landscape-scale management programs, with a focus on maintaining landscape diversity.L’intensification et l’expansion rapide des plantations d’Hevea brasiliensis dans les régions montagneuses d’Asie du sud-est ont conduit à d’importantes dégradations de la biodiversité et des sols. Les adventices remplissent de nombreux services écosystémiques, par exemple en favorisant la protection du sol. Toutefois, les facteurs déterminants les communautés adventices et les interactions entre ces communautés et les processus d’érosion du sol sont mal connus. Deux fois par an entre 2016 et 2018, nous avons réalisé des inventaires botaniques et des caractérisations de sol à Huai Lang, au nord de la Thaïlande, dans 20 champs appartenant à plusieurs types d’usage du sol correspondant à la transition entre les cultures annuelles et les plantations d’hévéa. Nous avons également mesuré l’effet du type d’usage du sol et des pratiques de désherbage sur le ruissellement et le détachement de sol dans des plots d’érosion de 1m2. Les résultats montrent que la composition des communautés végétales est principalement déterminée par le type d’usage du sol et les caractéristiques paysagères, tandis que la variabilité temporelle des cultures dans un champ favorise la diversité végétale. Les plantations d’hévéa matures supportent des communautés végétales très spécifiques et favorisent des ruissellements et détachements de sol très élevés, qui peuvent être atténués par la présence d’un couvert végétal. Cette étude suggère que la conservation du sol et de la biodiversité en Asie du sud-est devrait être fondée à la fois sur une évolution des pratiques à l’échelle du champ (par ex. désherbage moins intense) et sur un maintien de la diversité spatiale des agroécosystèmes