Hawkeye Play · Chapter 3 · Environmental · Social · Legal
The shared pasture
Four herders share one pasture. The grass grows back, but only so fast. Each season, each herder decides how much to take.
The rules
The pasture holds up to 100 units of grass and regrows fastest when it is half full (logistic growth, up to 25% a season when the pasture is nearly bare). Each herder takes either a modest share (1.5 units) or a large share (3 units). Together the four herders can take at most about 6 units a season without running the pasture down. All numbers are made up.
What the model typically shows
Data table
| Season | 4 of 4 modest | 2 of 4 modest | 0 of 4 modest |
|---|---|---|---|
| 0 | 100.0 | 100.0 | 100.0 |
| 5 | 84.3 | 74.8 | 63.9 |
| 10 | 77.6 | 59.7 | 33.0 |
| 15 | 73.8 | 45.4 | 0.0 |
| 20 | 71.5 | 26.1 | 0.0 |
| 25 | 70.0 | 0.0 | 0.0 |
| 30 | 69.0 | 0.0 | 0.0 |
Takeaway
In this model, when each herder weighs only their own gain from taking more, a shared stock that regrows slowly tends to be run down. Field studies find that groups who make, monitor and enforce their own rules often keep such resources in use for long periods, though not in every case.
Sources for the model:
- Hardin, G. (1968). The Tragedy of the Commons. Science 162(3859), 1243–1248 (opens in a new tab)
- Ostrom, E. (1990). Governing the Commons: The Evolution of Institutions for Collective Action. Cambridge University Press.
- Royal Swedish Academy of Sciences (2009). Economic governance: the organization of cooperation (popular information, Prize in Economic Sciences 2009) (opens in a new tab)
What this model leaves out
- Real pastures, fisheries and aquifers have weather, prices and many more users.
- Here the rule is simply “how many herders keep to the modest share”; it does not show how rules are made or enforced.
- Ownership by a state or by individuals is not modelled; the Nobel summary notes each can do better or worse than user management depending on the case.
In the real world
Figures already sourced on the Earth page. The game itself uses made-up numbers.
- In 2015, 33% of marine fish stocks were harvested at unsustainable levels (IPBES Global Assessment, 2019 (opens in a new tab)). See Earth: Land and sea heavily altered.
- Nature managed by Indigenous Peoples and Local Communities is generally declining less rapidly than in other lands (IPBES, 2019 (opens in a new tab)). See Earth: Nature’s stewards.