资源描述
Chapter 11 Storable,Renewable Resources:Forests11.1 IntroductionMain contents:Explore how economics can be combined with forest ecology to assist in efficiently managing this important resource.11.1 IntroductionCharacterizing what is meant by an efficient allocation of the forest resource when the value of the harvested timber is the only concern.Model the efficient decision to cut a single stand or cluster of trees with a common age by superimposing economic considerations on a biological model of tree growth.Refine the model to demonstrate how the multiple values of the forest resource should influence the harvesting decision and how the problem is altered if planning takes place over an infinite horizon,with forests being harvested and replanted in a continual sequence,Examine the inefficiencies that have resulted or can be expected to result from both public and private management decisions and strategies for restoring efficiency.11.2 Defining Efficient Management 12.2.1 Special Attributes of the Timber Resource12.2.2 The Biological Dimension12.2.3 The Economics of Forest Harvesting12.2.4 Extending the Basic Model11.2.1 Special Attributes of the Timber ResourceTimber shares with many other animate resources the characteristic that it is both an output and a capital good.In contrast to many other living resources,however,the time period between initial investment(planting)and recovery of that investment(harvesting)is especially long.Finally,forestry is subject to an unusually largy variety of externalities,which are associated with either the standing timber or the act of harvesting timber.11.2.2 The Biological DimensionA biological model of the growth of a stand of trees(see figure 12.1)11.2.2 The Biological DimensionThe mathematical function relating volume to age stand in Figure 12.1 is the third degree polynomial of the form v=a+bt+ct2+dt3,where v=volume in cubic feet,t=the age of the stand in years,and a,b,c,d,are parameters which take on the values 0,40,3.1 and 0.016,respectively.11.2.2 The Biological DimensionWhen should this stand be harvested?Foresters have come up with a calculation called the Mean Annual Increment(MAI).The MAI is calculated by dividing the cumulative volume of the stand at the end of each decade by the cumulative number of years the stand has been growing up to that decade.For tree growth patterns,the MAI rises during the early ages and then falls during the later ages.According to the biological decision rule,the forest should be harvested at the age when the MAI is maximized.Table 12.111.2.3 The Economics of Forest HarvestingTo an economist,the biological criterion fails to consider any of the factors such as the value of the timber,the time value of money,or costs associated with planting and harvesting which would play a central role in an efficient harvesting decision.11.2.3 The Economics of Forest HarvestingFrom the definition of efficiency,the optimal time to harvest this stand would be that time which maximizes the present value of the net benefits from the wood.11.2.3 The Economics of Forest HarvestingSome interesting conclusions can be gleaned from Table 12.2:First,discounting shortens the time until the stand is harvested.Second,changing the magnitude of the planting and harvesting costs does not change the optimal harvesting point.Third,with high enough discount rates,replanting may not be efficient.11.2.4 Extending the Basic ModelOur basic model is somewhat unrealistic in several respects.It considers the harvest as a single event rather than a part of an infinite sequence of harvesting and replanting.The single-period model we developed would be appropriate for an infinite planting period if and only if all period were independent.But interdependencies do exist among time periods.11.2.4 Extending the Basic ModelThe more complicated model also yields some rather different conclusions from our original model.If the planting costs rise,the marginal opportunity cost of delaying the cycle would be reduced.As a result,the optimal rotation would increase as planting costs increase.A similar result would be obtained when harvesting costs are increased.11.2.4 Extending the Basic ModelAnother limitation of our basic model lies in its assumption of a constant relative price for the wood over time.Introducing relative prices for timber that rise at a constant rate in the infinite-horizon model causes the optimal rotation period to increase.11.2.4 Extending the Basic ModelA final concern with the models as elaborated so far is that they all are concerned solely with the sale of timber as a product.In fact,forests serve several other purposes as well.For these uses,additional benefits accrue to the standing timber which are lost or diminished when the stand is harvested.11.3 Sources of InefficiencyGlobal inefficienciesBiodiversityGlobal warmingPoverty and debtPerverse incentives11.4 Implementing Efficient ManagementMost of the changes could be implemented by individual nations to protect their own forests.And to do so would be in their interests.11.4 Implementing Efficient ManagementBut what about the global inefficiencies?How can those be resolved?Several economic strategies exist.Debt-nature swapsExtractive reservesEstablishing conservation easementsObjectives&Requirements:Understand the definition of efficient management of forest Knowing the sources of forest management inefficiency and how to implement an efficient management Discussion:Suppose there are two forest plots which are identical except that one will be harvested and left while the second will be cleared after the harvest and turned into a housing development.In terms of efficiency,which should have the oldest harvest age?Why?
展开阅读全文