Hari, Chantal (2025). Combined impacts of climate and land use change on future biodiversity at global and regional scales. (Thesis). Universität Bern, Bern
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Abstract
Biodiversity is declining at an unprecedented rate due to human activities, with climate and land use change being recognized as direct drivers. However, a lack of understanding remains regarding their combined impacts on future biodiversity. This thesis addresses research questions related to these knowledge gaps, focusing on the impacts of climate and land use change on future biodiversity from global to regional scales. It examines these drivers' separate and combined importance across different combinations of Shared Socioeconomic Pathways (SSPs) and Representative Concentration Pathways (RCPs) scenarios. Additionally, it assesses the effectiveness of protected area (PA) expansion strategies in mitigating biodiversity loss and explores how regional climate and land use change impact vegetation dynamics in arid and semi-arid lands (ASALs). To investigate these questions, this thesis employs one modeling approach at a global scale and another at a regional scale. At the global scale, we combine climate-driven species distribution models (SDMs) with land use change projections to assess the impact of climate and land use change on terrestrial vertebrate diversity under two differing future scenarios. Additionally, we evaluate how different PA expansion strategies impact biodiversity outcomes under these projected changes. Global analyses highlight African ASALs as particularly vulnerable to biodiversity loss, motivating a regional study. At a regional scale, we analyze simulations of the adaptive dynamic global vegetation model (aDGVM) designed explicitly for African savanna ecosystems. We investigate how climate-driven vegetation changes in Kenya's ASALs, which are increasingly threatened by woody encroachment. We further compare the findings from the aDGVM simulations to land use change projections from integrated assessment models (IAMs). By integrating these two modeling approaches across scales, this thesis provides new insights into biodiversity impact assessments under future climate and land use change. Our results indicate that climate and land use changes drive biodiversity loss equally, with climateinduced biodiversity loss scaling with the climate scenario. While land use change exacerbates these losses under an "inequality" (SSP2-RCP6.0) scenario, it can alleviate them under a "sustainability" (SSP1-RCP2.6) scenario. Low and mid-latitude regions were found to be particularly affected, with sub-Saharan Africa emerging as a high-risk area where land use change is the dominant driver of biodiversity loss. Building on this first global analysis, we further assess the effectiveness of PA expansion strategies under different PA and SSP-RCP scenarios. While PA expansion to 30% (in line with the Global Biodiversity Framework (GBF) target of reaching 30% of PAs globally by 2030) of land reduces species richness loss compared to the current 17% of PAs, its effectiveness in reducing biodiversity loss depends on adequate management and sustainable land use policies. Notably, we find II that climate mitigation and sustainable land use have a stronger leverage on reducing biodiversity loss than PA expansion alone. After establishing the broader global patterns of biodiversity change and identifying high-risk regions for biodiversity loss, the thesis focuses on a particularly vulnerable biodiversity hotspot—sub-Saharan Africa—to investigate climate-driven vegetation shifts and land use change projections at a regional scale. Our results indicate a projected increase in woody encroachment, reducing savanna and grassland ecosystems, especially under a high-emission scenario. These vegetation changes have profound implications for biodiversity conservation, as many species depend on savanna ecosystems that are projected to decline. However, when comparing these climate-driven projections to land use change projections, we find that the projected rise in woody aboveground biomass (AGB) may be constrained by land use change, especially agricultural expansion under SSP2-RCP4.5. Overall, this thesis provides key advancement in our understanding of future biodiversity change under climate and land use change at global and regional scales. It provides novel insights into the scenario- and region-dependent importance of these drivers and additionally provides necessary methodological advancements in developing a modeling framework that integrates land use change projections into climate-driven SDM projections. From the learnings at a global scale, the thesis zooms into a region identified where biodiversity is most at risk. With this, the thesis offers a second scale and employs a second modeling approach (DGVM) to provide a more holistic perspective on projections of future biodiversity change. The findings highlight the urgent need for immediate action on both climate and land use change to curb biodiversity loss. While PA expansion offers some buffering capacity, following a more sustainable, low-emission development pathway remains the most effective strategy. Delayed action risks severe biodiversity loss, with cascading consequences for nature and people.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 16 April 2025 |
| Subjects: | 500 Science > 530 Physics |
| Institute / Center: | 08 Faculty of Science > Physics Institute |
| Depositing User: | Hammer Igor |
| Date Deposited: | 13 Nov 2025 11:27 |
| Last Modified: | 13 Nov 2025 11:27 |
| URI: | https://boristheses.unibe.ch/id/eprint/6874 |
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