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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 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.

Beech and hornbeam are two of the most common species in old-growth temperate forests. However, how these two species affect soil carbon (C), soil nitrogen (N) and soil microbial and enzymatic activities is still not well understood. Thus, the aim of the present study was to quantify the effects of beech and hornbeam on soil chemical, biochemical and biological features at Makarod forest, Northern Iran, by sampling either forest floor or mineral soil (30 × 30 × 15 cm) under individual trees of both species. Based on our data, hornbeam showed higher concentrations of N, phosphorous (P), potassium (K), calcium (Ca) and magnesium (Mg), but lower total thickness, C and C: N ratio in the forest floor. Top mineral soil under hornbeam had alkaline condition (pH > 7), higher electrical conductivity (EC), total N, N in micro- and macro-aggregates, N sequestration, available P, K, Ca, Mg, humic acid, fine root biomass, total earthworm (i.e. epigeic, anecic and endogeic) density and biomass, total nematode, acarina and protozoa densities. Hornbeam trees increased soil basal respiration and substrate induced respiration (0.50 and 1.47 mg CO2 g−1) compared to beech. The two studied species did not show any significant difference in soil microbial biomass C, metabolic quotient, microbial ratio, C availability index, particulate organic C and dissolved organic C, whereas, higher values of soil microbial biomass N, particulate organic N and dissolved organic N (66.97 mg kg−1, 0.52 g kg−1 and 38.53 mg kg−1, respectively) were again found under hornbeam. Except for arylsulfatase, all the other soil enzyme activities (i.e. urease, acid phosphatase and invertase) were almost two-fold higher under hornbeam (24.55 μg NH4+–Ng−1 2 h−1, 498.30 μg PNP g−1h−1 and 296.2 μg Glucose g−1 3 h−1, respectively). As well, higher values of ammonification rate were measured under hornbeam (0.38 mg kg−1 d−1), whereas beech significantly increased the nitrification rate (−0.16 mg kg−1 d−1). Net N mineralization rate was about three-fold higher under hornbeam (0.14 mg kg−1 d−1) than under beech. Our results indicate that differences in functional traits between beech and hornbeam caused changes in microbial community and in its activity, underlying a higher forest floor quality, higher soil fertility and more active microbial populations under the latter.

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.

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.

Conversions of land use/cover are associated with changes in soil properties and biogeochemical cycling, with implications for carbon (C), nitrogen (N), and trace gas fluxes. In an attempt to provide a comprehensive evaluation of the significance of different land uses (Alnus subcordata plantation, Taxodium distichum plantation, agriculture, and deforested areas) on soil features and on the dynamics of greenhouse gas (GHG) fluxes at local scale, this study was carried out in Mazandaran province, northern Iran. Sixteen samples per land use, from the top 10 cm of soil, were taken, from which bulk density, texture, water content, pH, organic C, total N, microbial biomass of C and N, and earthworm density/biomass were determined. In addition, the seasonal changes in the fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were monitored over a year. Our results indicated that the different land uses were different in terms of soil properties and GHG fluxes. Even though the amount of the GHG varied widely during the year, the highest CO2 and CH4 fluxes (0.32 mg CO2 m(-2) day(-1) and 0.11 mg CH4 m(-2) day(-1), respectively) were recorded in the deforested areas. N2O flux was higher in Alnus plantation (0.18 mg N2O m(-2) day(-1)) and deforested areas (0.17 mg N2O m(-2) day(-1)) than at agriculture site (0.05 mg N2O m(-2) day(-1)) and Taxodium plantation (0.03 mg N2O m(-2) day(-1)). This study demonstrated strong impacts of land use change on soil-atmosphere trace gas exchanges and provides useful observational constraints for top-down and bottom-up biogeochemistry models.