Composition of tree species can mediate spatial variability of C and N cycles in mixed beech forests
2017
Kooch, Yahya | Bayranvand, Mohammad
The process of establishing a mixed canopy composition by intermingling individuals of beech, hornbeam, and maple is an ongoing trend in adaptive forest management strategies. However, our understanding of the potential of these strategies to promote forest floor and soil quality remains limited.Beech (Fagus) is one of the most valuable industrial species in Iran, which is present in combination with other tree species with different effects on soil fertility. This study measures the role of different canopy compositions of beech trees, including mixed beech (beech-maple-hornbeam), beech-hornbeam, beech-maple and pure beech on forest floor quality, soil features and C and N cycles of the Hyrcanian forest in Iran.Five replicates are regarded for each canopy composition and a total of 20 permanent plots were considered in the forest. Four forest floor and soil samples, with an area of 25cm×25cm, were taken from 0 to 15cm depth under each canopy cover and a composite sample for each plot (for forest floor and soil separately) was transferred to the laboratory. Forest floor (C, N and thickness) and soil physico-chemical (water content, bulk density, aggregate stability, pH, EC, organic C, total N, available P, K, Ca and Mg), biological (earthworm biomass/density, nematode density, fine root biomass, N mineralization and basal respiration or BR), biochemical (NH4+ and NO3− concentrations, substrate induced respiration or SIR, particulate organic matter C - N or POM-C and POM-N, dissolved organic C - N or DOC and DON), soil aggregate size (macro and micro) features and soil enzyme activity (urease, acid phosphatase, arylsulphatase and invertase) were measured.Mixed composition of canopy cover had the highest forest floor quality, with the greatest amount of N and the lowest of C. The highest amounts of soil aggregate stability, pH, total N and available nutrients were found in the mixed composition and the highest amounts of water content, organic C and C/N ratio, with the least of soil bulk density, were observed under pure beech. In general, higher values of earthworm density/biomass, nematode density, fine root biomass, N sequestration and mineralization, NH4+, NO3−, BR, SIR, POM-N, DON, macro aggregate, N in macro- and micro-aggregates and enzyme activity were observed in the mixed beech compared to the other canopy composition. The highest values of POM-C, DOC, C in macro- and micro-aggregates were found under pure beech canopy than in mixed beech composition. The lowest value of the C availability index (CAI) was found under pure beech canopy cover. C sequestration of different tree compositions did not show any statistically significant difference.The influence of trees on forest floor and soil features is detectable even in a mixed stand and the soil landscape experience a mosaic of changes, reflecting the chemical characteristics of the various tree species present in the stand. Our results suggest that the composition of tree species can change the forest floor quality, soil fertility and microbial activities related to C and N in mixed forests. As a conclusion, increasing the soil quality by tree species composition – employing hornbeam and maple for amending the forest soils with accompanying beech can be suggested in pure beech stand.
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