Beech forest site productivity mapping using ordinary kriging and IDW (Case study: research forest of Tarbiat Modares University)

Estimation and mapping of forest resources is a prerequisite for sustainable forest management. Site productivity is a key indicator of forest ecosystem services like wood production, carbon sequestration, etc. It allows foresters to forecast growth and production and hence select the most suitable tree species for a site. Due to the extent of Hyrcanian forests and mountainous areas in these forests that are sometimes difficult to access, it seems necessary to find suitable methods for mapping the quantitative parameters in these forests. In this study, site form index which is the most reliable criterion for evaluating the site productivity of mixed and uneven stands was used. This study aims at mapping beech forest site productivity by using ordinary kriging and inverse distance weighted in research forest of Tarbiat Modares University. For this purpose, 123 0.1 ha circular sample plots were laid out in beech dominated stands. The height and diameter of beechtrees with DBH ≥ 7.5 cm within each plot was recorded. The cross validation results showed that by using criteria such as mean error (OK=-0.036, IDW=-0.192), mean absolute error (OK=1.598, IDW=1.749), root mean square error (OK=2.053, IDW=2.223), relative mean error (OK=0.104, IDW=0.553) and relative root mean square error (OK=5.906, IDW=6.393), Kriging had significant advantage over IDW method and showed high estimation accuracy. Therefore, the methods can be applied to similar uneven-aged beech stands in the north of Iran.