Strategies to Mitigate Pressures on Terrestrial Ecosystems from Multiple Stressors

Terrestrial ecosystems in Norway and the Tibetan plateau are under increasing stress, especially as a result of ongoing temperature rise and human activities. However, a detailed understanding of the main past and future challenges, and how multiple stressors interact at a landscape level, was missing. MITISTRESS has addressed this gap and mapped changes in climatic conditions and land uses, and assessed ecosystem stress levels by focusing on the cumulative effects. The major stressors covered are climate change, land use, population pressure, and wild herbivore browsing, and the ecosystem services include both provisioning and regulating services. The project processed satellite data, field measurements, and calibrated and run regional climate and ecosystem models. The datasets are publicly available together with the scientific articles that present the results. In the Tibetan Plateau, we analyzed the sensitivity and future exposure of ecosystem services to climate change, showing that carbon sequestration generally increased, but there are interconnections among multiple landscape services that vary across the region. Soil retention, water yields, and habitat quality typically decreased, but there are synergies between regulating and supporting services. A new research has identified potential climate refugia, i.e., buffer regions for species against exposure to changes in climate that mitigate the impacts on biodiversity. They have been identified using multiple environmental diversity indicators (vegetation and topography) and local sensitivity to climate change, revealing that the existing network of protected areas (PAs) has critical conservation gaps. We argue for the urgency of incorporating climate refugia into the future planning of PAs to increase conservation effectiveness. We also found evidence of negative effects from increased human activities (only 30% of existing PAs were free from any measurable pressure), showing the need to promote better protection measures. Upgrading the PA status (e.g., from provincial to national level) rapidly increased conservation effectiveness. A key ecological role is found in protected area edges, which are effective options to secure vegetation greenness, cover, and productivity. In Norway, we used a new method that unraveled co-benefits and trade-offs among ecosystem services at a grid-specific level, and produced a novel land cover dataset that includes annual forest harvest disturbances. We found i) declines in habitat quality within landscapes affected by agriculture and forest management, ii) increases in water yield and soil erosion primarily due to increased precipitation, and iii) increased carbon sequestration and provisioning services mainly caused by higher temperatures and management. The analysis of remotely sensed observations in the past two decades shows a widespread greening as a response to temperature rise (with the strongest positive effect in May). Livestock mainly had a negative effect on vegetation greenness above 69º N, while the negative effect of wildlife is mainly located in the southeast forestlands (below 61º N). We investigated how forest management influences local surface temperature (LST) in Fennoscandia through a set of machine learning algorithms. More developed forests are typically associated with higher LST than young forests, except for the summer. We generated a novel, simple yet reliable statistical model based on high resolution maps that can link individual forest management practices to LST. Its application shows a weak annual mean cooling of -0.01 °C due to forest harvest from 2015 to 2018, with an increased daytime temperature in the summer of about 0.04 °C. This open-source model achieves higher accuracy and precision than regional climate models, it can be used by non-experts and it ultimately supports the design of climate-smarter forest management strategies. For the first time, we also investigated how climate change and moose browsing alter aboveground tree biomass and albedo using a new empirical dataset from herbivore exclosures within clear-cut forests. We find a higher total aboveground tree biomass (mainly deciduous species) in unbrowsed forest plots. Moose browsing limited the growth of birch, thereby favoring the growth of coniferous species (especially spruce). At the same time, moose increased forest albedo, driving biophysical cooling. When averaged at regional levels, climate effects due to changes in biomass and albedo are of similar magnitude, but contributions can diverge in specific locations. Given its influence on tree growth rates and climate impacts, management of moose browsing density should be integrated into optimal forest management plans. The project shows the status of land use and ecosystem services in two critical ecosystems such as Norway and the Tibet, and provide a wide empirical basis of measurements and datasets for future studies and improved management strategies.

Our results offer an overview on the status of land use and ecosystem services in two critical ecosystems such as Norway and the Tibetan Plateau, provide a wide empirical basis of measurements and datasets for future studies, and make available to scientific peers and national stakeholders the opportunities to understand existing threats to ecosystems and possible sustainable management strategies to secure a long-term delivery of ecosystem services. More specifically, one of the main significant aspects of the results for the Tibetan Plateau concerns the status and effectiveness of protected areas. This information is useful to the local managers as they can identify the protected areas where conservation is less effective, and the main drivers of the detrimental effect (i.e., climate change, increased pressure from human activities or declines in ecosystem services). We also propose and assess the effectiveness of solutions that can strengthen conservation benefits, for example by actively considering in the planning of protected areas the establishment of climate refugia, and/or maximizing the beneficial role played by protected area edges (which can be expanded and secured). For Norway, examples of practical relevance of the results include the elaboration of high-resolution maps of annual forest harvest disturbances, which inform about annual area harvested and outtake volumes per main tree species (spruce, pine, and birch). These maps are integrated with other land cover datasets, providing a consistent basis of land cover distribution for the entire country (with the forest and harvest characteristics). They have been produced by reproducing the latest advances in remote sensing approaches for Norway, and they can be regularly updated. This new dataset offers useful insights to both research peers, which can use it as input for climate and environmental impact models, and to private and public stakeholders, which can monitor and visualize the trends and locations of harvest disturbances. We also generated an open-source model that can estimate effects of forest management on local surface temperature, and it can be applied to both historical data or used to quantify effects of alternative management scenarios. Given its inherent simplicity and the possibility to be used across different scales, it can be applied by non-experts and it ultimately supports the design of climate-smarter forest management strategies. The project also created new knowledge on how moose browsing in productive forests affects timber value and climate change. Because of the influence on tree growth rates and climate impacts, we argue that management of moose browsing density should be integrated into forest management plans to optimize climate change mitigation and forest productivity.

Terrestrial ecosystems are sensitive to multiple stressors. The IPBES assessment recently concluded that biodiversity in Europe and central Asia has been continuously declining because of both land use change and intensification of agriculture and forestry. Many future scenarios of the IPCC envisage a future that is more heavily reliant on terrestrial ecosystems to supply renewable energy and materials. Stressors from land use changes and management are thus expected to be the dominant driver of ecosystem damage in low-fossil carbon scenarios. Stressors from pollution and climate change can additionally challenge the adaptation of ecosystems. The effects on ecosystem services associated with multiple stressors remain largely unexplored, especially when it comes to the response at an ecosystem level where multiple stressors can interact in complex ways. Terrestrial ecosystem stress is already manifesting in several parts of Norway and the Tibetan plateau. MITISTRESS plans to map land uses and ecosystem stress levels in Norway and the Tibetan Plateau to quantify the cumulative effects on ecosystem services. The ultimate ambition is to better understand ecosystem-stressor interactions to guide the design of future sustainable land management strategies. The major stressors covered in the project are land uses, driven by multiple societal demands, climate and pollution. MITISTRESS will: - Provide historical maps of land uses, drivers, and key attributes of ecosystem status - Carry out fieldwork to test and calibrate model algorithms and parameterizations - Develop novel approaches to assess environmental impacts and cumulative effects of multiple stressors on terrestrial ecosystems - Quantify the ecosystem response to multiple stressors and perform scenario analysis under different societal development pathways MITISTRESS will generate new robust scientific knowledge in this field, thereby assisting the design of future land management policies in Norway and China