Determining the harvest age (economic) of even- aged stands of paulownia plantation in Dr. Bahramnia's Forestry Plan

Abstract
Background
Increasing need for wood and wood resource depletion caused and exacerbated by the fast-growing plantation species. One way to avoid excessive harvesting of these forests could be growing plantation species series. harvest age Economic is the age that the maximum value of the current or the current economic value is today in terms of reach. One of the trees in recent decades for afforestation with short harvest period, especially in South East Asia is considered different species paulownia. Under normal circumstances a ten-year paulownia tree size 40-30 cm diameter at breast height and volume choebdeh between .0.3-0.5 cubic meters per year and the best environmental conditions for the operation of timber trees produce 5-6 years. The development of paulownia planted by farmers in Sri Lanka indicated that the net present value at an interest rate of 7.5 percent paulownia planted 4627721 rupees and 3.28 benefit to cost ratio and internal rate of return is 28.34 percent. The aim of this study was to determine the most appropriate age paulownia planting harvest biomass forestry projects in the province according to the Dr Bahram-nia maximum economic value in each in each of the spacing is studied.

Materials and methods
For this study, a 18- year-old Paulownia fortunei plantation was selected which was located in compartment two of series one of Dr. Bahram- nia Forestry Plan (Shastkalateh Gorgan). Three spacing of 3*6, 5*8 and 6*10 meter were examined. Five sample trees were chosen from the list of dominant trees of each spacing plantation. After felling of the selected trees, sample discs were cut from trunk height of .4 and 1.3 meter and 2 meter interval to tree top. Also, stand volume were calculated at different stand ages using form factor. In the next stage, the optimum harvest age (economic criteria) was determined on the basis of the stumpage values. Also, revenue and costs and net present value of the project were estimated at the optimum harvest age. Also, revenue and costs and net present value of the project were estimated at the optimum harvest age.
Results
Results showed that Optimum harvesting age (economic criteria) were distinguished 8, 9 and 10 years for 3*6, 5*8 and 6*10 meter plantation spacing considering 12 percent interest rate and 750 Rials per kilogram price of stumpage wood. Result also showed that changes in wood prices do not affect on optimum harvesting ages of stands while increasing or decreasing interest rates will change optimum harvesting age, indirectly
Key words: Paulownia, Optimum harvest age (Economic), Spacing,Shastkalateh Gorgan