مجله جنگل ایران
سال چهاردهم شماره 4 (زمستان 1401)

The interaction between forest vegetation and soil can highly affect the soil water balance. In a holistic approach, forest managers are expected to have a better understanding of these interactions and the importance of soil water conservation. This will certainly lead to a required hydrologic balance in the forests. This research aims at studying the amount of soil water storage at different depths and its connection with changes in vegetation types and their root distribution. To this aim, soil volumetric water content and root distribution data collected under Picea abies and Fraxinus excelsior plantations were used to determine the soil water storage for different soil layers including 20, 40, 60, and 100 cm. A cumulative water storage for the whole soil profile (1-meter profile) was also calculated. Afterwards, the number of roots and the Root Area Ratio (RAR) were determined for different layers of soil with a 10 cm interval. Ultimately, the connections between soil water storage at given layers of soils with their corresponding root numbers and RAR values were investigated for each forest plantation. Friedman and Mann-Whitney non-parametric tests were used to compare the means of soil water storage, number of roots, and RAR values at different layers of soils and plantations studied. According to the results, an increasing trend in soil water storage and a decreasing trend in root numbers (and RAR) can be observed with soil depths. However, both root distribution and soil water storage experience a rapid increase and decrease to a depth of 40 cm, and then the trends remain relatively constant. In most cases, soil water storage at different soil depths and for the 1-meter soil profile under Picea abies was significantly lower than that under Fraxinus excelsior.

Various measures are considered to stabilize the erodible beds such as planting. Environmental variables in the canopy cover of plants, including soil temperature and moisture, are readily indicators of planting projects success evaluation. Therefore, this study was planned to evaluate the success of Tamarix (Tamarix ramosissima Ledeb.) plantation in modulating modifying soil temperature and moisture indices in the dried-up beds of Lake Urmia. To this endFor this purpose, 15 stands of seven-year-old Tamarix shrubs were randomly systematically selected and their heights and canopy area were measured. Additionally, in four cardinal directions, the top-soil temperature and humidity were also measured in the inside and outside of the under of canopy zones (120 points in total) following the prevailing erosive winds. Afterward, tThe results were then statistically analyzed. Two-way analysis of variance showed significant differences (p<0.01) for soil temperature and humidity among the sampling points (inside and outside of the microclimate zones) and significant differences (p<0.01) for soil temperature among the cardinal directions of sampling. The mean temperature and moisture content of the soil surface in the inside and outside of the Tamarix shrubs canopy were 23.77 and 34.78 °C, and 2.95 and 1.82%, respectively. So that, a significant decrease (p<0.01; 45%) in the soil temperature and a significant increase (p<0.01; 62%) in the soil moisture content were recorded in the inside of the canopy zones in comparison to the outside zones. The findings showed that the selection of Tamarix shrubs with larger canopy and planting with higher density should be considered to improve the environmental conditions in erosion-prone deserts management programs.

The structural complexity of forest stands is one of the most important characteristics of natural forests. Changes in the forest stand structure through the development of stands cause complexity in the stand structure. We conducted this research to quantitative analysis of structural complexity in the three stages of stand development in the Hyrcanian forests. Three one-hectare study areas were selected within developmental stages (Totally 12 hectares) and after forest inventory, the structure complexity index was calculated for each stage. We employed ten variables including stem per hectare, mean of diameter at breast height (DBH), coefficient of variation of DBH, diameter Gini coefficient, number of trees with a diameter larger than 100 cm at breast height, the ratio of the number of trees in different stories, the faction of canopy gaps, amount and volume of dead woods and tree size variation to calculate this index. The mean and median complexity index was 65.46 and 66.15. the highest value obtained in the terminal (transition) stage was equal to 84.17 and the lowest was 49.3 in the initial stage. The structure complexity significantly was higher in the terminal stage, meanwhile based on the Tukey test, the difference between the initial (58.85±3.33) and optimal stage (61.39±4.23) was not significant. Considering the role of diversity and complexity of forests structure on forest ecological functions like maintaining biological diversity, it is necessary to consider complexity in all interventions and forest tending operations. Also, we proposed the forest complexity enhancement besides maintaining biodiversity should consider as the most important goal of forest management plans.

Cultivation of the summer truffle, Tuber aestivum Vittad., has become as a new agricultural activity that for rural economies is often considerably more beneficial than conventional agriculture and also promotes reforestation, as well as land use sustainability. Considering examples from Italy, Hungary, Spain and France, truffle cultivation induces the economic and social development of small and rural communities. Because there is no tradition of creating truffle gardens in Iran, knowledge of environmental factors regulating the formation of T. aestivum fruiting bodies is limited. Since the establishment of truffle plantations in the world, several studies have been conducted to improve their productivity and stability. Success in the continuation of truffle plantations depends clearly on the mycorrhizal status of the host trees over the years, from inoculated seedlings to truffle producing trees. Therefore, monitoring the status of ectomycorrhizal fungi in the natural habitats of truffles and increasing knowledge about ectomycorrhizal communities of T. aestivum host species is crucial to ensure the successful production of summer truffles in truffle orchards. In this study, the presence of T. aestivum ectomycorrhizae on roots of oak (Quercus castaneifolia) and its abundance in natural habitats of truffle fungi in three selected sites in Golestan province was investigated and the diversity and structure of other ectomycorrhizal fungi were evaluated. In selecting the studied sites, differences in altitude, dominant geographical direction and plant species in the regions were considered. The results showed that although the species composition was up to 70% similar between sites, but the number of fungal species, diversity and species richness of fungi were different among sites with different host plants and the site with only oak.

In this study, we investigated the effects of forest operation on runoff and sediment using small-scale plots. The runoff and sediment samples were collected from 36 sample plots with dimensions of one by two meters in different areas of the operation. We used the Multi-Layer Perceptron (MLP) for modeling, with 65% of the data for training, 10% for validation, and 25% for testing. We evaluated the accuracy of the model using the coefficient of determination (R²), root mean square error (RMSE), and mean absolute error (MAE), and compared our results with optimized models obtained through trial and error. We collected information and produced runoff and sediment maps using GIS. Our results showed that the most important factors affecting runoff production were soil bulk density, rainfall intensity, slope, rainfall values, percentage of grass cover, and canopy cover percentage. For sediment, the most important factors were rainfall intensity, soil bulk density, slope percentage, and surface cover percentage. The MSE and R values for runoff modeling were 0.009 and 0.9 in the training stage and 0.01 and 0.82 in the test stage, respectively. For sediment modeling, the MSE and R values were 0.01 and 0.86 in the training stage and 4.3 and 0.8 in the test stage, respectively. Our results showed that neural networks have high capability in modeling runoff and sediment in forest lands. We also conducted an overlap analysis to measure the accuracy, precision, and efficiency of the results and methods presented in our study. Therefore, the proposed model can be used to combine ANN and GIS in the simulation and modeling of runoff and sediment in forest areas."

Comprehensive description and quantification of stand structure are needed for managing or maintaining forests as complex systems. The Structural Complexity Index (SCI) is a suitable criterion for quantifying the structural heterogeneity of forest stands, which can be used to compare the structural heterogeneity of stands. In this study, we used this index to quantify the structural heterogeneity of three pure beech stands in the Hyrcanian forests of Iran. Forest inventory was performed using a fixed grid of 150×200 m dimension and sample plots of 1000 m2 in watersheds of 46, 49, and 66a in Mazandaran province, where two stands were managed, and one was unmanaged. Using the spatial coordinates and diameters of trees in 90 measured sample plots in the three stands, we calculated the SCI index for each sample plot as well as its average for each stand. The results showed that the rate of this index in these three stands fluctuated between 2.7 to 11.7. However, its average in each region is approximately 6, without any statistically significant difference between them. The results also showed that the amount of this index was positively correlated with the variables of basal area and standing volume of the stands. The SCI index in protected forests with high ecological quality can be used as a reference or baseline for assessing the suitability of management techniques to maintain or enhance the structural heterogeneity of stands.

Fire is one of the most important natural disturbances in forest ecosystems, and it has significant effects on soil properties depending on its severity and duration. The aim of this study was to compare the properties of forest soil beneath Iranian oak (Quercus brantii Lindl.) on northern and southern slopes that were heated under laboratory conditions. To collect soil samples, northern and southern slopes were selected in the forest area of Baneh. A transect was established on the counter lines of both slopes. On each transect, the closest tree to the transect was selected, and the next seven trees were chosen at 30-meter intervals. In total, sixteen soil samples were taken from a depth of 0-5 cm. The soil samples were divided into four parts in the laboratory (unburned soil and three treatments heated at 200, 400, and 600°C). The amount of organic carbon did not change at 200°C but decreased after that. The amount of nitrogen increased at a temperature of 200°C and then decreased to 0.05 and 0.02 at 600°C in the soil of the northern and southern slopes, respectively. The pH and phosphorus levels decreased initially and then increased. The electrical conductivity was 1093 and 838 μS/cm at 600°C in the soil of the northern and southern slopes, respectively. The amount of magnesium increased in treatments of 200 and 400°C but decreased in treatments of 600°C. The amount of phosphorus, potassium, calcium, and electrical conductivity in the soil of the southern slope was 75%, 32%, 32%, and 100% higher than that of the northern slope at 600°C treatment, respectively. In conclusion, it can be inferred that the soil properties of southern aspects can be more affected than those of northern aspects by heat of fire with moderate to high severity.

The aim of this study was to develop a mixed-effects model and compare it with nonlinear models for estimating the heights of velvet maple and ironwood trees in the uneven-aged, mixed Shast-kalateh forests of Gorgan. We applied a systematic sampling method to collect field data within a 150×200 m network, comprising of 308 circular sample plots, and measured the height, diameter at breast height (DBH), and tree species in each plot. Model fitting was done in two stages: In the first stage, we used a fixed-effect approach to select candidate models, where height was the dependent variable and DBH was the independent variable. In the second stage, the dominant height, mean DBH, basal area, basal area of trees larger than the desired tree, tree density, and volume of trees were refitted using a mixed-effect approach. We used adjusted coefficient of determination and root mean square error to assess the models. The results of fitting nonlinear models for velvet maple species showed that the Curtis and Michailief models with R2 values of 0.74 and the lowest RMSE values of 3.43 and 3.24, respectively, were the best models. For ironwood trees, the Nassland and Michailoff models with R2 values of 0.42 and the RMSE values of 2.92 and 2.91 m were selected as the best models. The results of fitting the nonlinear mixed-effect model showed that compared to the nonlinear models, the R2 values for velvet maple and ironwood species increased by 20% and 23%, respectively, and the RMSE improved to 1.75 m for velvet maple and 0.45 m for ironwood.