Geostatistically estimation and mapping of forest stock in a natural unmanaged forest in the Caspian region of Iran (Case study: Keyroud forest, Nowshahr)

Estimation and mapping of forest resources is a prerequisite for research, management, and planning. In this study, we applied kriging geostatistical interpolation for estimation and mapping of forest stock attributes in a natural, uneven-aged and unmanaged forest in the Caspian region of northern Iran. The elevation across the 516-ha study area ranged from 1100 to 1450 m a.s.l. Field sampling was performed using 1000 m2 circular sample plots in a 75 m × 200 m systematic grid. Total numbers of 309 plots were sampled. Experimental variograms were fitted for stem basal area (BA), volume stock (V) and stem density (N) using geo-referenced plots. The variograms of BA and V exhibited no spatial autocorrelation, except for the stratified data based on diameter classes and tree species. The N showed yet a medium spatial structure which was fitted by a spherical model. The stem density was estimated by ordinary block kriging. The cross-validated results showed high estimation accuracy. The applied geostatistical methods were concluded to be advantageous for accurately capture the spatial variability of stem density which was reflected in the stem density maps. The methods can be applied to similar unmanaged, uneven-aged stands in the north of Iran, and thereby support the estimation of forest growing stock.