But entail costs in harnessing them as usable energy resources
Renewable stock resources
living organisms fish cattle and forests with a natural capacity for growth
inanimate systems (such as water and atmospheric systems) reproduced through time by physical or chemical processes
arable and grazing lands as renewable resources reproduction by biological processes (such as the recycling of organic nutrients) and physical processes (irrigation exposure to wind etc.).
Are capable of being fully exhausted.
4 Biological growth processes G G(S) An example (simple) logistic growth Where g is the intrinsic growth rate (birth rate minus mortality rate) of the population. 5 Figure 17.2 Steady-state harvests. 6 Commercial fisheries Open access vs Restricted access fisheries What is an open access fishery Consequences of open access entry continues until all rents are dissipated (profit per boat zero). Stock sizes will tend to be lower and harvest rates will tend to be higher (but may not always be) compared with a restricted access (private property or common property) fishery. Exhaustion or even extinction is more likely but will not necessarily happen. 7 Switch now to Model Equations document 8 Figure 17.3 Steady state equilibrium fish harvests and stocks at various effort levels. 9 Figure 17.4 Steady state equilibrium yield-effort relationship. 10 Figure 17.5 Stock and effort dynamic paths for the illustrative model. 11 Figure 17.6 Phase-plane analysis of stock and effort dynamic paths for the illustrative model. 12 (No Transcript) 13 (No Transcript) 14 Figure 17.7 Present value maximising fish stocks with and without dependence of costs on stock size and for zero and positive interest rates. 15
OPEN ACCESS AND SPECIES EXTINCTION
The extinction of renewable resource stocks is a possibility in conditions of open access but open access does not necessarily result in extinction of species.
Open access enhances the likelihood of catastrophic outcomes because
Incentives to conserve stocks for the future are very weak.
Free riding once a bargain has been struck
Crowding diseconomy effects
EXCESSIVE HARVESTING AND SPECIES EXTINCTION
There are many reasons why human behaviour may cause population levels to fall dramatically or in extreme cases cause species extinction. These include
Even under restricted private ownership it may be optimal to the owner to harvest a resource to extinction. Clark (1990) demonstrates however that this is highly improbable.
Ignorance of or uncertainty about current and/or future conditions results in unintended collapse or extinction of the population.
Shocks or disturbances to the system push populations below minimum threshold population survival levels.
WHATEVER THE REGIME SPECIES EXTINCTION IS MORE LIKELY
the higher is the market (gross) resource price of the resource
the lower is the cost of harvesting a given quantity of the resource
the more that market price rises as the catch costs rise or as harvest quantities fall
the lower the natural growth rate of the stock and the lower the extent to which marginal extraction costs rise as the stock size diminishes
the higher is the discount rate
the larger is the critical minimum threshold population size relative to the maximum population size.
Renewable resources policy
Quantity restrictions on catches (EU Total Allowable Catches)
Fishing season regulations
Technical restrictions on the equipment used - for example restrictions on fishing gear mesh or net size or boat size.
19 Forestry As far as forests as sources of timber are concerned much of the previous analysis applies. But a new issue arises the average length of a rotation. What is also important here is the multiple service functions of much forestry. This can often extend optimal rotation lengths.
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