PhD Candidate: Ronny Rotbarth

Defence date: 23-09-2024
Time: 15:30
Institute: Wageningen University & Research
Location: Omnia, Hoge Steeg 2, Building number 105, Wageningen
Online: Livestream

PhD supervisors:
dr. Milena Holmgren
prof.dr. Marten Scheffer

Title thesis: The future face of the last frontier – boreal forest resilience to global change

Abstract:

This thesis explores the response of boreal forests to climate change, focusing on whether the biome is shifting northward in response to warming temperatures and increasing disturbances. Boreal forests, critical for global carbon storage, climate regulation, biodiversity, and human livelihoods, are experiencing significant environmental changes. The central aim of this research is to determine if these forests are moving poleward and to assess the consequences of such shifts for their ecological functions.

Using a combination of satellite data, field observations, statistical analyses, and simulation models, I investigate the spatial dynamics of boreal forests across North America and globally. The analysis reveals a complex pattern of change. While tree cover has increased in the core regions of the boreal zone, there is little evidence of a northward expansion. Instead, the southern boundary of the biome has shown notable declines due to increased wildfire activity and logging, suggesting that boreal forests may be contracting rather than simply shifting. This contraction poses risks to carbon storage and forest resilience.

Globally, my projections indicate that boreal forests are transitioning toward a more open forest structure, driven by rising temperatures and more frequent disturbances such as fires and insect outbreaks. Simulations suggest that in the future, these forests may predominantly consist of open-canopy forests, increasing the likelihood of wildfires and contributing to further carbon emissions. This shift away from dense forest cover could have profound implications for the forests’ role in mitigating climate change.

Further examination of specific mechanisms, such as the impact of insect outbreaks on tree mortality and recovery, highlights the complexity of forest dynamics under climate change. My findings suggest that forest recovery from disturbances may become slower or fail altogether, which could exacerbate the vulnerability of boreal forests to future climatic shifts.

The results of this thesis underscore the growing sensitivity of boreal forests to climate change and its associated disturbances, with potential consequences for global carbon cycles, biodiversity, and the people who rely on these ecosystems. This thesis emphasises the need for proactive management strategies to protect and adapt boreal forests in the face of ongoing environmental changes, while also providing insights for safeguarding other natural biomes under similar pressures.