Northern hemisphere Holocence land-cover reconstructions from fossil pollen data
Résumé
Terrestrial ecosystems play an important role in Earth systems processes, yet we still do not fully understand the feedbacks between these ecosystems and Earth’s climate. These ecosystem processes operate at multiple timescales; fast processes occur at sub-annual timescales, and slow processes, driven by changes in forest composition and structure, occur over decadal and longer timescales. Slow processes are rarely directly observed from instrumental data, yet are critical to understanding the stability of the terrestrial biosphere over the coming decades. Networks of paleoecological data, particularly sedimentary pollen data, offer our strongest observational constraint on long-term vegetation dynamics and underlying processes and feedbacks.
We reconstruct land-cover for the Holocene for the Northern Hemisphere. To do this, we use: (i) networks of fossil pollen records - the most reliable paleoecological proxy for land-cover; (ii) estimates of pollen productivity and fall speed, and (iii) a model of pollen-vegetation relationships, REVEALS (Sugita, 2007). For the Northern Hemisphere, we estimate the fraction of summergreen trees, evergreen trees, and open land.
To determine the differences between these pollen-based reconstructions and land-use scenarios that are more commonly used land-use models, we compare the fraction of open land with estimates of deforestation from the anthropogenic land-cover change (ALCC) scenarios generated by KK10 (Kaplan et al., 2009). Identifying cause to these differences provides an opportunity for improvement in ALCCs used to inform both global earth system and dynamic vegetation models.
This work results in improved understanding of the history of Holocene land-use change over a large spatial extent and slow ecosystem processes, the biogeochemical and physical forcings from past anthropogenic land-cover change on climate, and the long-term carbon dioxide budget. It is a contribution to PAGES LandCover6k.