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Disentangling the effects of climate and people on Sahel vegetation dynamics
J. W. Seaquist1, T. Hickler1, L. Eklundh1, J. Ardö1, and B. W. Heumann2
1Department of Physical Geography and Ecosystems Analysis, Geobiosphere Science Centre, Lund University, Sölvegatan 12, 223 62, Lund, Sweden
2Department of Geography, University of North Carolina at Chapel Hill, Saunders Hall, Campus Box 3220, Chapel Hill, NC 27599-3220, USA
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Abstract. The Sahel belt of Africa has been the focus of intensive scientific research
since the 1960s, spurred on by the chronic vulnerability of its population
to recurring drought and the threat of long-term land degradation. But
satellite sensors have recently shown that much of the region has
experienced significant increases in photosynthetic activity since the early
1980s, thus re-energizing long-standing debates about the role that people
play in shaping land surface status, and thus climate at regional scales. In
this paper, we test the hypothesis that people have had a measurable impact
on vegetation dynamics in the Sahel for the period 1982–2002. We compare
potential natural vegetation dynamics predicted by a process-based ecosystem
model with satellite-derived greenness observations, and map the agreement
between the two across a geographic grid at a spatial resolution of
0.5°. As aggregated data-model agreement is very good, any local
differences between the two could be due to human impact. We then relate
this agreement metric to state-of-the-art data sets on demographics,
pasture, and cropping. Our findings suggest that demographic and
agricultural pressures in the Sahel are unable to account for differences
between simulated and observed vegetation dynamics, even for the most
densely populated areas. But we do identify a weak, positive correlation
between data-model agreement and pasture intensity at the Sahel-wide level.
This indicates that herding or grazing does not appreciably affect
vegetation dynamics in the region. Either people have not had a significant
impact on vegetation dynamics in the Sahel or the identification of a human
"footprint" is precluded by inconsistent or subtle vegetation response to
complex socio-environmental interactions, and/or limitations in the data
used for this study.
Discussion Paper (PDF, 1723 KB) Interactive Discussion (Final Response, 2 Comments)
Citation: Seaquist, J. W., Hickler, T., Eklundh, L., Ardö, J., and Heumann, B. W.: Disentangling the effects of climate and people on Sahel vegetation dynamics, Biogeosciences Discuss., 5, 3045-3067, 2008. Bibtex EndNote Reference Manager
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