Spatial variability of forest growing stock using geostatistics in the Caspian region of Iran

Estimating the amount of variation due to spatial dependence at different scales provides a basis for designing effective experiments. Accurate knowledge of spatial structures is needed to inform silvicultural guidelines and management decisions for long term sustainability of forests. Furthermore, geostatistics is a useful tool to describe and draw map the spatial variability and estimation of forest variables. Therefore, this research was conducted to investigate on spatial variability and to estimate forest stock variables using geostatistical approach in a mixed hardwood forest, located in the Caspian region of Iran. Field sampling was performed based on a ۱۵۰m by ۲۰۰m systematic rectangular grid of ۳ clustered plots (۵۰m away). Each sample plot consisted of two concentric circles. Overall, ۴۳۴ sample plots were measured in ۵۰۲ hectares. Experimental variograms for forest basal area, volume and tree density were calculated and plotted using the geo- referenced inventory plots. All the variograms showed weak spatial auto- correlations between samples, even in short distances. Estimations were made using fitted variogram models and ordinary block kriging. Cross- validation results showed that all the estimations are biased, because of the large variability and weak spatial structure in the forest stock variables. Therefore, kriging could not make accurate estimations because of high spatial variability of forest growing stock related variables in this heterogeneous and uneven-aged forest.   REFERENCES  Biondi, F., Myers, D.E., and avery, C.C., ۱۹۹۴. Geostatistically modeling stem size and increment in an old-growth forest. Can. J. For. Res., ۲۴: ۱۳۵۴-۱۳۶۸. Chiles, J.P. and Delfiner, P., ۱۹۹۹. Geostatistics: modeling spatial uncertainty. Wiley, New York. ۶۹۵ p. Clark, I., ۱۹۷۹. Practical geostatistics. Applied Science Publishers, London. Cressie, N.A.C., ۱۹۹۳. Statistics for spatial data. John Willy and Sons, Inc., New York. ۹۰۰ p. Freeman, E.A. and Moisen, G.G., ۲۰۰۷. Evaluating kriging as a tool to improve moderate resolution maps of forest biomass. Environ. Monit. Assess., ۱۲۸: ۳۹۵-۴۱۰. Goovaerts, P., ۱۹۹۷. Geostatistics for natural resources evaluation. Oxford University Press, New York. ۴۸۳ p. Guibal, D., ۱۹۷۳. L´ estimation des oukoumés du Gabon, note interne ۳۳۳, centre de Morphologie Mathématique, Fontainebleau, France, (In French). Gunnarsson, F., Holm, S., Holmgren, P. and Thuresson, T., ۱۹۹۸. On the potential of kriging for forest management planning. Scan. J. For. Res., ۱۳: ۲۳۷- ۲۴۵. Husch, B., Miller, C. I., and Beers, T. W., ۱۹۸۲. Forest mensuration. ۳rd Edition. John Wiley and Sons, inc., New York. ۴۴۳ p. Isaaks, E.H. and Srivastava, R.M., ۱۹۸۹. An introduction to applied geostatistics. Oxford University Press, New York. ۵۶۱ p. Jost, A., ۱۹۹۳. Geostatistische analyse des Stichprobenfehlers systematischer Stichproben, PhD Dissertation, University of Freiburg, Breisgau, Germany, ۱۱۳ p. (In German). Kint, V., Meirvenne, M.V., Nachtergale, L., Geudens, G. and Lust, N., ۲۰۰۳. Spatial methods for quantifying forest stand structure development: a comparison between nearest neighbour indices and variogram analysis. For. Sci., ۴۹: ۳۶-۴۹. Krige, D. G., ۱۹۵۱. A statistical approach to some mine valuation and allied problems on the Witwatersrand. Master’s thesis, University of Witwatersrand, ۱۹۰ p. Mandallaz, D., ۱۹۹۱. A unified approach to sampling theory for forest inventory based on infinite population model. PhD Dissertation, Academic Press, ETH Zürich, Switzerland, chair of forest inventory and planning. Mandallaz, D., ۱۹۹۳. Geostatistical methods for double sampling schemes: application to combined forest inventory. Technical report, ETH Zürich, chair of forest inventory and planning, ۱۳۳ p. Mandallaz, D., ۲۰۰۰. Estimation of the spatial covariance in universal kriging: Application to forest inventory. Environ. Ecol. Stat., ۷: ۲۶۳-۲۸۴. Montes, F., Hernandez, M.J. and Canellas, I., ۲۰۰۵. A geostatistical approach to cork production sampling in Quercus suber forests. Can. J. For. Res., ۳۵: ۲۷۸۷-۲۷۹۶. Tuominen, S., Fish, S. and Poso, S., ۲۰۰۳. Combining remote sensing, data from earlier inventories and geostatistical interpolation in multi-source forest inventory. Can. J. For. Res., ۳۳: ۶۲۴- ۶۳۴. Webster, R. and Oliver, M.A., ۲۰۰۰. Geostatistics for environmental scientists, Wiley Press, ۲۷۱ p. Zahedi Amiri, Gh., ۱۹۹۱. Determination of tree species increment in Kheiroudkenar forest. MSc. Dissertation,  University of Tehran, Iran, ۱۲۰ p. Zahedi Amiri, Gh., ۱۹۹۸. Relation between ground vegetation and soil characteristic in a mixed hardwood stand, Ph.D. thesis, academic press, University of Gent, Belgium, ۳۱۹ p.

کلیدواژه ها:

Geostatistics ، Growing stock ، Kriging ، Spatial variability ، Variogram