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Dead trees, and particularly downed logs, play an important role in the dynamics of forest ecosystems. The contribution of decaying wood to the carbon and nutrient pool of forest soils depends on tree species and the degree of wood decay but the extent to which downed logs affect forest properties in temperate forests has rarely been quantified. In order to investigate the impact of decaying wood on soil properties, we carried out a study in a mixed beech forest of the Liresar district (Mazandaran province, northern Iran). We first investigated if and how the presence of downed logs affects soil quality and function by comparing soils underneath degraded logs and nearby soils of the two dominant forest species, beech and hornbeam. Then, we explored how these effects occur as downed logs decompose by comparing wood with four degrees of decomposition of both tree species. The decay degree of downed logs was classified in four classes (DC1 to DC4). Eight dead trees of each tree species were selected as the center of each sample plot and three composite soil samples under each decaying log and 100 cm near a decaying log (soil around logs) were collected at two soil depths (i.e., 0–15 and 15–30 cm) and then analyzed for main physico-chemical characteristics and microbial activity. Our study showed that downed logs affected physical (5% wetter than control soils), chemical (lower by 2% the pH, increased 100% organic C, and total N in the case of hornbeam and P by 2%) and biological (i.e., soil microbial respiration was enhanced by 10% and , microbial biomass of C 620 mg kg−1, 351.5 mg kg−1 and N 66.47 mg kg−1, 32.18 mg kg−1 by, respectively) characteristics of soils, thus resulting in downed tree soil microsites that strongly differ from those without downed logs. The presence of down logs increased soil microbial activity and soil fertility as wood decayed. Thus, the presence of downed logs should be considered as an important factor influencing forest soils and should be taking into account in forest management practices.

The objective of the study was to examine changes in microbial parameters have been used to monitor changes in soil quality under different land uses in north of Iran. The microbial parameters included microbial respiration (MR), substrate induced respiration (SIR), carbon availability index (CAI), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), ratio of MBC/MBN, metabolic quotient (qCO2) and microbial ratio were determined under different land use/cover, i.e. virgin natural forest (VNF), degraded natural forest (DNF), alder plantation (AP), sequoia plantation (SP), improved fallow (IF) and home garden (HG) areas in northern Iran. Five composed samples per land use/cover were taken from the top 10 cm of the soil. MR and SIR (0.45 and 1.66 mg CO2-C g−1 day−1, respectively) were found to be significantly higher under AP land uses than in the other areas. CAI did not differ for the land uses; MBC (591 and 590 mg kg−1, respectively) had higher significantly under SP and VNF land uses than in the other areas. MBN (64.25 and 62.33, respectively mg kg−1) was significantly higher in AP and VNF land uses, ratio of MBC/MBN (17.02) was higher in SP land use than other areas, HG had significantly higher qCO2 (0.0012 μg CO2-C mg−1 MBC day−1) and finally microbial ratio was significantly higher under IF (599.16) in comparison with HG > AP ≈ DNF > VNF > SP areas. Overall, our results indicate that AP land use (Alnus subcordata C. A. Mey.) increase of soil quality and alder plantation is suitable for rehabilitation of degraded natural forests.

Microbial activity of top soils is directly linked with carbon (C) and nitrogen (N) turnover in terrestrial ecosystems, and thus is an indicator to identify hot spot areas of C and N cycling in forest habitats. The Hyrcanian forests are one of the last remnants of natural deciduous forests in the world and Oriental Beech (Fagus orientalis Lipsky) is one of the most abundant tree species of these forests. It has not been resolved which forest properties of Hyrcanian forests facilitate hotspots with high microbial process rates. We studied those primary causes (i.e. forest properties) of changes on soil characters and processes within old-growth Vaz forests, Northern Iran, and separately sampled different landform positions (i.e. catena, pit-mound and gilgai), single-trees, deadwoods and canopy gaps. Principal component analysis (PCA) of the 31 soil parameters resulted in two principal components that explained more than 60% of the total variance. The first component (PC1) explained the highest variance (48.13%) in the results; while second component (PC2) accounted for 13.68% of the variance. The obtained PCA results indicate a clear differentiation in selected soil properties among forest properties and thus, three groups of drivers for microbial activities were identified. Group 1 (foot and toe slope of V-shape catena, toe slope ofΛ-shape catena, pit structure of hornbeam, decay class 4 of beech deadwoods, small and medium canopy gaps) enhanced soil microbial process and enzyme activities. Group 2 (pit structure of beech, control or non-gilgai position, beech and hornbeam single-trees, decay class 3 and 4 of hornbeam deadwoods and large canopy gap) enhanced soil microbial biomass and greenhouse gas fluxes. Group 1 and 2 drivers were associated with high values of soil water content, organic C, total N, available nutrients, organic matter fractions, earthworm and nematode activities. Group 3 drivers (summit and shoulder slope of V- and Λ-shape catena, back slope of V-and Λ-shape catena, foot slope ofΛ -shape catena, mound of beech and hornbeam, position in a gilgai, decay class 2 and 3 of beech deadwoods, decay class 1 and 2 of hornbeam deadwoods and very large canopy gap) correlated with lowest microbial activities and was associated with high values of soil bulk density, pH, electrical conductivity and C/N ratio. Thus, distribution of microbial hotspot areas in the Hyrcanian forests can be considered as mosaic of pedons characterized by specific sets of key parameters, which depend on landform, especially the toe slope of V-shape catena, and stand characteristics (e.g. tree species or canopy gap).

Microbial and enzyme activities are increasingly being recognized as sensitive indicators of soil quality. This study aims to determine the impacts of different kinds of land use/cover, i.e. virgin natural forest (VNF), degraded natural forest (DNF), alder plantation (AP), sequoia plantation (SP), improved fallow (IF) and home garden (HG) areas on soil properties in northern Iran. Five composed samples per land use/cover were taken from the top 10 cm of the soil. Soil microbial respiration was found to be in the ranked order of AP > VNF > HG > DNF > IF ≈ SP areas, being more than one-and-a-half-fold under AP compared with SP. The values of microbial biomass carbon were almost two times higher under SP ≈ VNF than under IF ≈ HG areas. Microbial biomass nitrogen was found to be significantly higher under AP ≈ VNF than in the other kinds of land covers. AP ≈ VNF significantly increased the activities of urease and acid phosphatase, whereas greater activities of invertase occurred in AP ≈ VNF ≈ SP sites. Arylsulphatase activity was significantly higher to be significantly higher under AP in comparison with VNF > HG > DNF > SP > IF areas. As a conclusion, alder (Alnus subcordata C. A. Mey.) plantation improved the soil quality to levels similar to natural forest ecosystems. This research recommends the preservation of natural forests to increase soil quality and a plantation with suitable native broad-leaved species and forestation plan management to rehabilitate degraded natural forests.

Native to Eurasia, Eastern Europe, and Western Asia, Oriental beech (Fagus orientalis Lipsky) stands extend from the north-western part of Turkey, the eastern part of the Caucasus Mountains in Georgia and Russia to the Alborz Mountains in Iran. The effect of different development stages of beech stands on the forest floor and soil characteristics are so far almost unknown. For this purpose, the Langa forest that is located in northern Iran was investigated to detect the effect of forest development on major traits of soil biology and related soil characteristics. For this aim, 45 forest floors and soil samples (15 samples per each development stage i.e. initial, optimal, and decay stage) were analysed. In addition, the water content, temperature, and biological dynamics were monitored over the different development stages in summer and fall. Among the considered independent factors, the development stage of beech had the largest explanatory power for the variations of the soil water content (34.7%), total earthworm density and biomass (29.6% and 32.3%, respectively), Acarina (30.3%), nematode (64.3%), protozoa (57.7%), bacteria, (62.8%), fungi (59.5%), basal respiration (53.0%), substrate-induced respiration (53.8%), microbial biomass carbon (30.4%), microbial biomass nitrogen (36.0%), microbial biomass phosphorous (59.1%) and net nitrification rate (19.1%). Soil temperature (42.5%), collembola density (18.2%), net ammonification rate (29.9%), and net N mineralization rate (2.1%) were predominantly determined by the seasons. With the ageing of the forest stands, soil fertility, biota abundance, and soil function were enhanced. To figure out the most vital soil features affecting C and N sequestrations, a stepwise regression model was applied. Carbon sequestration correlated positively to N, the C/N ratio, and negatively to porosity, and the nematode abundance. In addition, nitrogen sequestration correlated positively to C, the sand content, and fine root biomass and negatively to the C/N ratio, soil porosity, and aggregate stability. Although all forest stages of the Oriental beech have an important ecological role and their place in the evolutionary process, the old-growth (i.e. decay) stage is especially important for the soil functions exhibiting the highest fertility and biological relevance. The understanding of ecological changes within different development stages can be helpful in forest management and the evaluation of silvicultural methods.

Foresters always emphasize the understanding of soil properties in evaluating site capacity to support productive forests. In order to conserve and improve soil quality and functions, sophisticated forest management systems are of particular importance. Hyrcanian forests of Iran have been harvested under different silvicultural operations such as shelterwood and selective cutting systems. So far, no studies have been conducted to explore the effects of forest management systems on soil properties in this ecosystem. Consequently, the present study aimed to investigate the impact of shelterwood and single-tree cutting systems on soil quality and functions (i.e. organic matter fractions, biota and microbial/enzyme activities), 10 and 20 years after employing these systems in Hyrcanian beech stands, compared to intact forests (control areas). A total of 60 soil samples (30 × 30 × 10 cm) including 30 samples in August 2008 and 30 samples in August 2018 from each site (i.e. control areas, shelterwood and single-tree systems) were transferred to the laboratory. In addition, topsoil water content, temperature and biological dynamics (August 2008, November 2008, August 2013, November 2013, August 2018 and November 2018) were monitored across the different forest management systems. Based on our data, the studied forest sites and soil properties could be separated by PCA output. The first and second axes, respectively, accounted for 38.59 and 10.95% of the explained variance. The control areas enhanced soil organic matter fractions, biota and microbial/enzyme activities. Between different silvicultural operations, the single-tree system, which is considered as a close-to-nature system, has provided better conditions for soil quality and functions as compared to the shelterwood management system. The understanding of ecological changes within widespread forest management systems can be helpful in forest management and plays a significant role in evaluating silvicultural systems.

The effects of rangeland management on biogeochemical processes that control the exchange of C and nutrients between the soil and plant are not well understood. For this purpose, aboveground litter properties and decomposition of three dominant species (Artemisia aucheri, Astragalus podolobus, and Eurotia lanata) were studied in four rangeland management systems of northern Iran including continuous grazing, intermittent grazing, and two non-grazing sites (i.e. woody and non-woody rangelands). We tested the following hypotheses: (i) woody rangeland improves litter quality, with a higher rate of decomposition, soil fertility and biochemical functions compared to non-woody rangeland and grazed sites, and (ii) continuous grazing reduces microbial C and N turnover. Plant residues from all rangeland species in the grazing and non-grazing areas were collected and soil samples were taken and analyzed for chemical properties and microbial activities. Based on the obtained data, litter decomposition was faster under woody rangeland ecosystem (Artemisia aucheri > Astragalus podolobus > Eurotia lanata) compared with the other study sites. The results revealed improved litter quality and increased soil available nutrients, as well as C and N mineralization for the woody rangeland, whereas under intermittent grazing the soil C/N ratio, microbial basal respiration (BR), substrate induced respiration (SIR) and microbial biomass C (MBC) increased. Soil pH, EC, qCO2 (BR: MBC) were significantly higher under continuous grazing, but with lower contents of soil organic C, total N, and available Mg. Furthermore, C and N stocks, microbial entropy (MBC: organic C), C availability index (BR: SIR), particulate organic matter C, dissolved organic C, mineral N (i.e., NH4 and NO3), microbial biomass N, particulate organic matter N and dissolved organic N were decreased in the continuous grazing site. Thus, we concluded that continuous grazing might depress soil C and N microbial activity, but woody rangeland could improve soil quality.