EGU21-4354, updated on 01 Dec 2021
https://doi.org/10.5194/egusphere-egu21-4354
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Is there an environmental crisis in Madagascar’s highlands? Insights from the spatio-temporal evolution and demographic modelling of lavaka (large gullies)

Liesa Brosens1,2, Benjamin Campforts3, Liesbet Jacobs2, Vao Fenotiana Razanamahandry2, Quinten Van Moerbeke2, Nils Broothaerts2, Tantely Razafimbelo4, Tovonarivo Rafolisy4, Steven Bouillon2, and Gerard Govers2
Liesa Brosens et al.
  • 1Research Foundation Flanders (FWO), Brussels, Belgium.
  • 2Department of Earth and Environmental Sciences, KU Leuven, Leuven, Belgium
  • 3Institute for Arctic and Alpine Research, University of Colorado at Boulder, Boulder, CO
  • 4Laboratoire des Radio Isotopes, Université d’Antananarivo, Antananarivo, Madagascar

The Malagasy highlands are scattered with large inverse teardrop-shaped gullies called lavaka, which are by many considered as the prime indication of a currently ongoing human-induced environmental crisis. Yet, these gullies are known to have existed long before human arrival on the island, resulting in the highly debated role of anthropogenic disturbances on their formation. Here, we assess the dynamics of 700 lavaka in the lake Alaotra region from 1949 to the 2010s by using historical aerial pictures and present day satellite imagery. An overall birth to stabilization ratio of 6.1 indicates a currently rapid growing lavaka population. Observed growth-, birth- and stabilization rates allowed us to calculate a mean lavaka population age of 410 ± 40 years, and estimate that the current crisis started at 943 ± 430 cal. yr BP. This timeframe corresponds well with the “subsistence-shift”, where people move from hunting and foraging to farming and herding practices upon the introduction of cattle in the region. These findings were integrated into a novel, temporally explicit lavaka population model - building upon the observed lavaka growth-, birth- and stabilization rates and lavaka size distributions - where different environmental pressure scenarios were tested. Modelling outcomes show that the currently observed lavaka crisis largely results from a rapid increase in environmental pressure over the last centuries, likely caused by the combined effects of deforestation and overgrazing related to human population growth and the introduction of cattle. With this study we show the potential of an integrated data-modeling approach, where demographic concepts are applied to geomorphological features, allowing to link their evolution with past anthropogenically driven environmental changes.

How to cite: Brosens, L., Campforts, B., Jacobs, L., Razanamahandry, V. F., Van Moerbeke, Q., Broothaerts, N., Razafimbelo, T., Rafolisy, T., Bouillon, S., and Govers, G.: Is there an environmental crisis in Madagascar’s highlands? Insights from the spatio-temporal evolution and demographic modelling of lavaka (large gullies), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4354, https://doi.org/10.5194/egusphere-egu21-4354, 2021.

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