Title: Modeling human impact in the past: a dynamic soil model as a step towards quantifying agricultural carrying capacity
Authors: Van Loo, Maarten
Verstraeten, Gert
Issue Date: 2015
Host Document: Geophysical Research Abstracts vol:17
Conference: EGU General Assembly location:Vienna date:13-17 April 2015
Article number: EGU2015-10316
Abstract: Humans have impacted their environment throughout history, especially since the introduction of widespread agriculture
and the associated forest logging activities. For the Mediterranean region the idea existed that the soil
erosion following the cultivation of land degraded the landscape to such an extent it caused crisis in ancient societies.
In order to quantify the impact of ancient societies on the landscape a simple water balance driven crop
yield model is coupled to a soil erosion model. The soil erosion model was validated based on a detailed 4000
year long chronology of sediment deposition in a small mountainous catchment (1250 m a.s.l.) in the territory of
the ancient city of Sagalassos (SW Turkey). The historic sediment dynamics are modeled reasonably well, with
a model efficiency of 0.75 and a relative root mean squared error of 0.23, based on 250 yr averages. The model
is capable of simulating the soil erosion phase after major deforestation from the Iron Age onwards, as well as
the depletion of soil reservoirs on limestone lithologies on the hillslopes and the resulting decrease in sediment
delivery towards the central valley around the Roman period. Although the spatial pattern of crop yield changes
drastically throughout time, following the changes in soil thickness, the simulations show that the average yields
in the catchment stay relatively constant, and certainly not collapse completely. Average barley yield at 4000 BP is
estimated around 400 kg/ha, whereas during Roman times this even increases to around 500 kg/ha. These estimates
however assume optimal conditions with no limitations from soil nutrients and land availability in the central valley
bottoms. The latter could have been an issue, since results show that during winter water losses under a highly
degraded landscape could have increased significantly, potentially resulting in an expansion of the lake occupying
the lowest parts of the catchment. These stresses would have forced farmers to come up with adaptive water management
techniques, or relocate their agricultural activities in order to reach the same level of crop yields as before
land degradation. In order to validate this human-environment coupling however, a more detailed archaeobotanical
analysis is required. Nevertheless, these novel methods of quantifying agricultural carrying capacity should allow
to nuance traditional views of direct links between landscape degradation and societal crisis, and open the debate
on the higher resilience of these societies in the past.
Publication status: published
KU Leuven publication type: IMa
Appears in Collections:Division of Geography & Tourism

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