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  • Publication
    Restriction temporaire
    Towards a multi-dimensional assessment of plant diversity in an enriched oil palm plantation
    (Neuchâtel : Université de Neuchâtel, 2025)
    Montoya-Sánchez, Vannesa 
    ;
    Zemp, Clara 
    La biodiversité comprend de multiples dimensions qui reflètent des propriétés et des processus écologiques uniques à travers les espèces, les communautés et les écosystèmes. Au-delà de la diversité spécifique, la biodiversité s’exprime à travers des dimensions fonctionnelles, structurelles, phylogénétiques, phytochimiques et spectrales, chacune apportant un éclairage complémentaire sur la complexité, le fonctionnement et la résilience des écosystèmes. Capturer cette multidimensionnalité est essentiel pour comprendre la dynamique des écosystèmes et faire face à l’érosion mondiale de la biodiversité. Les forêts tropicales de plaine, qui abritent une biodiversité terrestre exceptionnelle, sont gravement menacées par l’expansion et l’intensification agricoles. En Asie du Sud-Est, la conversion des forêts en plantations industrielles de palmier à huile et d’hévéa a entraîné une perte considérable d’habitats, une diminution de la richesse spécifique et une perturbation de la stabilité des écosystèmes. Les initiatives de restauration, telles que l’enrichissement en biodiversité par des plantations multi-espèces, constituent une stratégie prometteuse pour atténuer ces impacts en augmentant l’hétérogénéité des habitats et la biodiversité. Cependant, l’évaluation du succès de ces initiatives nécessite des approches innovantes et multidimensionnelles intégrant des perspectives complémentaires sur la biodiversité. Cette thèse doctorale contribue à la recherche sur la biodiversité en explorant la diversité végétale selon des dimensions structurelles, phytochimiques et spectrales dans une plantation de palmier à huile enrichie en biodiversité à Sumatra, en Indonésie. En combinant des mesures au sol, des données et techniques de télédétection, ainsi que la métabolomique non ciblée, j’ai caractérisé la diversité végétale au sein de 52 îlots expérimentaux d’arbres intégrés dans une plantation de 140 hectares. Cette approche multidimensionnelle apporte un éclairage sur les mécanismes écologiques façonnant la biodiversité et fait progresser les cadres méthodologiques pour l’évaluation et le suivi exhaustifs de la biodiversité en contexte de restauration. Dans le Chapitre 2, j’ai évalué la diversité structurelle de la végétation en utilisant la télédétection laser terrestre et aéroportée ainsi que des inventaires au sol, mettant en évidence la complémentarité de ces méthodes pour capturer la complexité tridimensionnelle des écosystèmes en régénération. Dans le Chapitre 3, j’ai analysé la diversité spectrale à l’aide de la spectroscopie d’imagerie et souligné son potentiel et ses limites pour la caractérisation de la biodiversité du sous-bois dans des écosystèmes verticalement stratifiés dominés par les canopées de palmier à huile. Enfin, dans le Chapitre 4, j’ai exploré la diversité phytochimique grâce à une analyse métabolomique non ciblée, révélant une forte variabilité chimique parmi les espèces ligneuses naturellement régénérées. Les résultats de cette thèse doctorale soulignent l’importance d’adopter des approches multidimensionnelles pour évaluer la biodiversité en contexte de restauration. En intégrant les dimensions structurelle, phytochimique et spectrale, cette recherche améliore la compréhension des mécanismes écologiques à l’oeuvre lors du rétablissement de la biodiversité et fournit des éléments essentiels pour améliorer les méthodologies d’évaluation et de suivi de la biodiversité. ABSTRACT Biodiversity encompasses multiple dimensions that reflect unique ecological properties and processes across species, communities, and ecosystems. Beyond species-level diversity, biodiversity is expressed through functional, structural, phylogenetic, phytochemical, and spectral dimensions, each offering complementary insights into ecosystem complexity, functioning, and resilience. Capturing this multidimensionality is essential for understanding the dynamics of ecosystems and addressing global biodiversity loss. Tropical lowland forests, which harbour high terrestrial biodiversity, face severe threats from agricultural expansion and intensification. In Southeast Asia, forest conversion to large-scale oil palm and rubber plantations has led to significant habitat loss, reduced species richness, and disrupted ecosystem stability. Restoration initiatives, such as biodiversity enrichment through mixed-species plantations, offer a promising strategy to mitigate these impacts by enhancing habitat heterogeneity and biodiversity. However, evaluating the success of these initiatives requires innovative, multidimensional approaches that integrate complementary perspectives on biodiversity. This doctoral dissertation contributes to biodiversity research by exploring plant diversity across structural, phytochemical, and spectral dimensions in a biodiversityenriched oil palm plantation in Sumatra, Indonesia. Using ground-based measurements, remote sensing data and techniques, and untargeted metabolomics, I characterised plant diversity within 52 experimental tree islands embedded in a 140-oil palm plantation. This multidimensional approach provides insights into the ecological mechanisms shaping biodiversity and advances methodological frameworks for comprehensive biodiversity assessment and monitoring in restoration contexts. In Chapter 2, I evaluated vegetation structural diversity using terrestrial and airborne laser scanning and ground-based inventories, demonstrating the complementary strength of these methods in capturing the three-dimensional complexity of multilayer recovering ecosystems. In Chapter 3, I assessed spectral diversity using imaging spectroscopy and highlighted its potential and limitations in capturing understorey biodiversity within vertically stratified ecosystems dominated by oil palm canopies. Finally, in Chapter 4, I explored phytochemical diversity through untargeted metabolomic analysis, uncovering high chemical variability among naturally regenerated woody species. The findings of my doctoral dissertation underscore the importance of adopting multidimensional approaches for assessing biodiversity in restoration contexts. By integrating structural, phytochemical, and spectral dimensions, this research advances the understanding of ecological mechanisms during biodiversity recovery and offers critical insights for improving methodologies for biodiversity assessment and monitoring.
  • Publication
    Accès libre
    Amphibian occupancy and abundance in beaver ponds in Switzerland
    (Neuchâtel : Université de Neuchâtel, 2024)
    Bolle, Patricia 
    ;
    Zemp, Clara 
    ;
    Schmidt, Benedikt
    ;
    Angst, Christof
    As ecosystem engineers, beavers are capable of creating heterogeneous environments that have a positive impact on many species. They increase habitat availability that can be colonised by species (endangered or not) and reduce fragmentation. Amphibians, one of the most threatened groups of vertebrates, are part of the species that could use and colonise the beaver ponds. The aim of this study is to analyse the occupancy and abundance of amphibians in beaver ponds in Switzerland. This analysis addressed the following questions: 1) What is amphibian abundance and occupancy at beaver ponds, 2) Does Rana temporaria use beaver ponds as ovipositional sites, 3) What are the factors (e.g., dam age) that drive amphibian occupancy and abundance in beaver ponds, and 4) if beaver ponds increaseconnectivity. Results of the occupancy analysis revealed that there were some preferences for the type of beaver pond occupied, most of them being flooded forests. Then, results from both abundance and occupancy showed that the strongest predictor that always came up was the dam age. Indicating that the older the dam is, the better, with more individuals in middle aged dams. Results from the connectivity revealed that beaver ponds had higher diversity if there were at least two amphibian breeding ponds nearby (less than one kilometre). Meaning that beavers could extend the already existing amphibian network by creating new ponds. Consequently, they have a good potential for conservation goals by maintaining stable and increasing amphibian populations.
  • Publication
    Accès libre
    Exploring Stand Structural Complexity’s Drivers: A Cerrado (São Paulo State, Brazil) Case Using Stand Structural Complexity Index (SSCI)
    (Neuchâtel : Université de Neuchâtel, 2023)
    Fontaine, Louis 
    ;
    Zemp, Clara 
    Developing and understanding full potential of new tools for large scale reforestation programs has become essential nowadays. In this framework, stand structural complexity (SSC) has been identified as essential driver for multiple ecosystem services. Using terrestrial laser scanner (TLS) with light detection and ranging (LiDAR), I measured stand structural complexity index (SSCI) among four experimental reforestation sites in early development stage (three to eighteen years old) to identify impact of five potential SSC drivers: (1) water availability, (2) species diversity, (3) functional diversity, (4) tree density and (5) treatment applied on reforested sites. I find that (1) increased water availability enhances SSC as well as species diversity on lower level (up to six species) and (3) functional diversity. Contrastingly, no effect on SSC was observed for (2) high species diversity (twenty to one hundred fourteen species), (4) tree density and (5) treatment. SSC is likely to be enhanced by (1) water availability by promoting shade tolerant species abundance, and niche complementarity can explain positive impact on SSC by both (2) species and (3) functional diversity. On the other hand, competition for resources is likely to explain the limited impact on SSC by (4) increased tree density and (5) treatment. Finally, niche complementarity saturation is likely to explain saturating SSC on high species diversity plots. I conclude that (1) water availability plays a crucial role for improving stand structural complexity, being its main driver, (2) species diversity and (3) functional diversity (on lower level) improves it, but high tree density and species diversity as well as increased treatment play a neglectable role for enhancing stand structural complexity on forest’s early stage. Those results put forward the importance of species mixtures with various functional traits in reforestation programs, and the unnecessity of increasing tree density and treatments (resulting in additional costs) for enhancing stand structural complexity.