An Economic Assessment Of Uneven-Aged Forestry Based On The Modelling Of Forestry Operations

摘要

In recent years, interest in uneven-aged forestry has been increasing in Britain,udparticularly for sensitive areas such as recreation and amenity forests. Literature on theudeconomics of uneven-aged forestry is scarce and few operational, uneven-aged forestsudare available for study. Therefore, in order to quantify the operating costs associatedudwith uneven-aged forestry, a modelling approach was chosen. The resulting model isudwritten in FORTRAN and uses a series of square two-dimensional arrays to representuda block of forest. The block may then be managed by clearfelling and replanting at audspecified age, or by a system of group management with a choice of four group sizes.udThe resulting model was then used to investigate the effect of the followingudmanagement strategies on operating times:ud1. Varying the scale of working (i.e. the group size and forest size) in the uneven-agedudforest.ud2. Using shortwood or pole-length harvesting systems and a range of machine typesudwithin each harvesting system.ud3. Varying the length of time taken to transform the structure of the forest fromudeven-aged to uneven-aged.ud4. Varying the age of the trees when the transformation from even-aged touduneven-aged structure begins.udThe results obtained from running the model show that the time taken to carry out anudoperation is influenced both by the absolute size of the group within the forest blockudand by the number of groups of that size within the forest block. This fragmentationudeffect explains why it is difficult to determine the absolute costs of working for audspecific group size, because it is the combination of group size, number of groups andudforest block size, which determines costs. Most of the results below are based on audrange of group sizes from 1.000 ha. to 0.0625 ha., with a block size of 16 ha.udForwarders were penalized when the group size was decreased to 0.0625 ha. (-12%udincrease over clearfelling), because very small groups do not contain full forwardingudloads and a large proportion of total forwarding time is spent manoeuvring into and outudof groups. However, the operating times for the three group sizes 1.00 ha., 0.25 ha.udand O. 1 1 ha. were very similar indicating that the group size can be quite small beforeudany extra forwarding costs are incurred. On poor sites, the cost differential between the largest and smallest groups is greater. In contrast to forwarding, skiddersudare most penalized with the decision to adopt an uneven-aged system, and once thatuddecision has been made, there is not a clear increase in costs with decreasing groupudsize.udDuring the transformation period, felling and thinning times in the uneven-aged systemudare significantly higher than those for the even-aged system, because trees are beingudharvested prematurely to create the early groups, but this difference is reduced once theudforest is transformed. Felling and thinning times increase gradually as the group sizeuddecreases, because more care is needed for the felling operation and more time isudneeded for snedding coarse edge trees.udReplanting times for the uneven-aged forest are approximately 8% - 14% higher thanudreplanting times for clearfelling.udThe results from the model were then analysed using the EXCEL spreadsheetudprogramme to examine, among other things, the cost implications of varying groupudsize, and the relative profitability of uneven-aged and even-aged management.udFirst,optimum ages to begin transformation were found, which varied with the YieldudClass and discount rate chosen. Then, the effect of the length of the transformationudperiod was examined and a long transformation period (80-years) was found to beudpreferable to a short transformation period (40-years). The analysis showed that atudhigh discount rates even-aged and uneven-aged management had similar Net PresentudValues, but at lower discount rates the even-aged system was preferred. The greatestudfinancial penalty was incurred with adoption of an uneven-aged system, and reducingudthe group size had relatively little impact on Net Present Values.udOther costs and benefits, such as scenic beauty and recreation potential, could not beudincluded in the model, because research relating these values to forest managementudvariables has not been carried out. Therefore, these mostly non-financial factors wereuddiscussed for even-aged and uneven-aged forestry, based on a review of the literature.