The FORager dynamics in Global Ecosystems (FORGE) model simulates dynamic interactions between hunter gatherer populations and their environments, through the hunting of animals and the gathering of edible plants. It is the first realistic global model to directly couple physically-resolved humans with dynamic behaviour to non-human components of ecosystems, within a global grid.

Humans, multiple plant types, and two types of mammals are each carried as a biomass variable. The population biomasses within each grid cell change from one daily timestep to the next according to mechanistic processes. Humans grow, reproduce, metabolize and die, and allocate time to either hunting, gathering or doing something else based on their nutritional status. Plant growth rates are predicted from satellite observations, or taken as an output of the ORCHIDEE global vegetation model, and a small edible fraction of the plants can be consumed by humans within the same grid cell. Mammalian browsers and grazers feed on plants, grow, reproduce, metabolize and die, and are hunted by humans within the same grid cell.

The emergent patterns of time use reflect interactions with ecosystem productivity and the climatic environment, and determine the steady-state biomasses of humans, plants and animals.

One of the surprising results was the degree to which seasonality forces human populations to rely on hunting wherever prolonged periods of cold or drought interrupt the production of edible vegetation. This finding helped to explain discrepancies between the observed population densities of contemporary hunter gatherers and local NPP (Zhu et al., 2021).

FORGE was developed by Dan Zhu. The python code to run FORGE is available on github, as documented by Zhu et al., 2021 (pdf).