Effect of beech (Fagus orientalis Lipsky) and hornbeam (Carpinus betulus L.) canopy compositions on soil biological characteristics in Hyrcanian region

Forest stands have an important role in the ecosystem function, quantity and quality of produced organic matter, nutrients and finally soil biological characteristics. In pure and mixed stands, effects of deciduous tree species on soil processes have been received less attention. Therefore, this study aimed to investigate the variability of some soil biological characteristics in beech and hornbeam forest stands with a certain composition ratio, which has not been reported so far.

In this study, 5 combinations of forest stands (1. pure beech, 2. pure hornbeam, 3. beech and hornbeam, 4. beech-hornbeam, 5. hornbeam-beech) were considered by 5 sample plots replications in each stand in 3 parts (east, center and west) of Hyrcanian region (total of samples were 75). Sampling as a selected sample plots are considered circle form (1000 m2) in the center of each stands, with same conditions for aspect (northeast), slope (30-60%), altitude (average 1200 m) and the stands with middle-aged trees (diameter 40-60 cm) to each sample (for establishment the same conditions). Sampling of organic layers and mineral soil from 25 × 25 area and 0-10 cm depth was performed in the center of each sample plot and four main directions. Statistical analyzes were performed using ANOVA analysis of variance and Duncan multiple comparisons in SPSS 20 software, also using principal component analysis or PCA by PC-Ord V. 5. 0 software.

The results showed that the organic layer carbon in pure beech (49.73%) and organic layer nitrogen in pure hornbeam (2.57%) stands had significant difference and had the highest measured value. Soil organic carbon (5.17%) and C/N (28.17%) had significant difference in pure beech and showed the highest measured amount, while soil pH (7.10) and N (0.50%) had significant difference and showed the highest values in pure hornbeam stands. Fine root biomass (93.36 g m-2), density and biomass of total earthworm ecological groups (respectively 2.47 n m-2 and 32.08 mg m-2) and microbial respiration (0.53 mg CO2 g-1 day-1) were significantly different in pure hornbeam stands and showed the highest values compared to other studied stands. In this study, the analysis of all the characteristics studied on the first and second axes of PCA analysis justifies 47.62 and 14.22 percent of variance, respectively, which shows the highest soil biological activity in pure hornbeam and dominant hornbeam stands compared to pure beech and dominant beech.

In general, the results of this study indicated that the composition of hornbeam tree species in beech stands caused significant differences in the improvement of soil biological indicators, so it was verified for mixing regulation and afforestation on the presence of hornbeam species in pure beech stands. The findings of this study can be used to prioritize the selection of stands consisting of beech and hornbeam tree species to regulate mixture in breeding operations and rehabilitate degraded areas in the north of Iran. Therefore, it is suggested that during marking operations, management planning and afforestation in the habitats of these two species, maintaining their mixture should be a priority.