Accumulation trend of fine woody debris volume stock in the altitudinal range of Kheiroud research forest, Iran

Given the significance of fine woody debris (FWDs) in the context of the carbon cycle, climate change, and its implications for renewable energy and economic development, it is imperative to obtain accurate information on the dispersion of FWDs volume stock for effective management of Hyrcanian forests in Iran.

This study was conducted in the Kheiroud forest in Nowshahr county, Iran, employing cluster sample plots distributed along the altitude range of 100-1815 meters above sea level (m.a.s.l.). Circular sample plots were established within each cluster, employing a line transect with a constant azimuth of 150 degrees and a radius length of 7.32 meters. Three diameter classes (1-2.5 cm, 2.5-4.5 cm, and 4.5-7.5 cm) were measured based on line-intersected fallen woods. The coordinates of the samples were recorded, and kriging and inverse distance weighted (IDW) methods were utilized to elucidate the autocorrelation of FWDs volume stock. Stand type, aspect variations, and altitudinal range were considered as main factors in the multiple-way ANOVA.

The findings revealed that the mean FWDs volume stock for each diameter class was 2.14, 6.01, and 16.23 m3/ha in the studied forest. Notably, fluctuations in the FWDs at the third diameter class were less pronounced than in other diameter classes. The goodness of fit data between observations and estimations indicated that both Kriging and IDW techniques estimated responses with low accuracy (R2 = 0.16; RMSE = 6.32) and no accuracy (R2 = 0.04; RMSE = 21.17; R2 = 0.03; RMSE = 37.11). Geostatistical techniques demonstrated that FWDs volume stock cannot be considered a regional variable, lacking autocorrelation and spatial correlation. Consequently, ANOVA results, based on observed power and partial eta squared, revealed that the interaction of altitude, stand type, and aspect did not significantly influence variations in FWDs volume stock (P > 0.05). Pairwise comparisons based on the LSD test indicated that the marginal mean of FWDs in the first diameter class was significantly different only along the altitude (P < 0.05).

In conclusion, the observed variation in FWDs volume stock at different diameter classes appears to be random and independent of the considered interactions. However, complex ecological and biological factors likely contribute to the dispersion of FWDs volume stock in the studied forest.