r. akhavan

Forest volume stock is one of the most important quantitative characteristics of forests, which is estimated and monitored in national forest inventories to study the current situation and changes in forest resources. Therefore, its results can be used in forest management policies and plans. The purpose of this study was to estimate the volume stock of the Hyrcanian forests of Iran using permanent sample plots and a two-stage sampling method, which is specific for inventory in large areas. This forest inventory was conducted in the Hyrcanian vegetation region in northern  Iran including 104 watersheds, using a two-stage sampling method. Based on this sampling method, 42 watersheds were randomly selected and sampling was carried out in  randomly selected parcels of them using a regular grid with dimensions of 150×200 meters with circular permanent sample plots of 1000 m2 area. Inside each sample plot, the diameter at breast height (DBH) of all tree species greater than 7.5 cm, their distance and angle to the center of the  plot, the height of the closest tree to the center,  and  the diameter of the thickest tree in each sample plot were measured and recorded. At the end of inventory, a total of 1195 circular sample plots (each 10 Ares) were established and 33517 trees were measured. Results showed that the mean quadratic mean diameter (QMD), basal area, standing volume and forest density in these forests, considering a minimum DBH of 7.5 cm, are 38 cm (arithmetic mean: 29.5 cm), 29 m2/ha, 359 m3/ha and 340 trees/hectare, respectively (The mean standing volume and tree density, considering a minimum DBH of 12.5 cm, are 355 m3/ha and 254 trees/ha, respectively). The highest and lowest standing volumes were observed in the middle land and lowland areas of these forests, respectively. In terms of volume distribution across diameter classes, the majority of volume stock was observed in the large and extra-large diameter classes, i.e., in the diameter range of 50 to 80 cm accounting for approximately 46% of the total volume stock. Furthermore, the highest forest density was found in the lowland and highland and the lowest in the middle land areas of these forests. Based on the obtained results, beech (Fagus orientalis Lipsky) and hornbeam (Carpinus betulus L.) together constitute  56.5% of total tree  abundance and 71.2% of the total volume stock in the Hyrcanian forests of Iran. By calculating the stock (density, basal area and standing volume) of these forests, in addition to obtaining important biometric information from this valuable vegetation region, the necessary data for  resource management,  biodiversity assessment,  carbon storage estimation, stand quality improvement and planning  silvicultural interventions  to control both the quantity and  quality of these forests are provided.

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.

Due to the weakness of the ecosystem in the Zagros forests, which is due to human and livestock pressure over the past decades and the occurrence of recent droughts, most of the forest areas have declined. In this situation, it is necessary to study the effects of various management activities in order to design strategic plans. To do this, the current study was conducted in Dinarkuh forest area of Ilam province to investigate the impact of different management activities on tree, soil and biodiversity variables of tree species, taken during the last decade. Experimental treatments included exclosure, exclosure + pruning, exclosure + pruning + afforestation, exclosure + pruning + afforestation + catchment system and control which considering aspect in the form of factorial statistical plan, 19 treatments with four replications were considered for each treatment. In total, 76 sample plots with area of 1500m2 were established in the field. The interested variables were measured and calculated in each sample plot and then compared between different treatments using two- way ANOVA with two factors: management activities and aspect. The results showed that among the biometric variables of trees; DBH, height, crown diameter, sprout diameter and tree density, among physical and chemical properties of soil; percentage of organic matter, silt, sand, bulk density, lime, carbon, phosphorus, potassium, soil depth, erosion and among biodiversity indices; Shannon-Wiener, Pielou and Heip indices were significantly different under management activities' areas compared to the control area. Even though, all management treatments had effective and positive effects on tree biometric variables and soil physico-chemical characteristics, as well as on biodiversity indices and in most cases made improved the current situation, considering the required costs for management treatments and their destruction in the field, exclosure can be introduced as the best management treatment in the region.

Spatial distribution and size of canopy gaps have important implications for light regime and regeneration, and affect species diversity. In this regard, the present study was conducted with the aim of investigating the spatial pattern and structure of harvesting canopy gaps and comparing with natural canopy gaps in mixed beech forests in the Sordar-Anarestan forestry plan located in Chamestan-Noor, Mazandaran. All natural and harvesting canopy gaps were surveyed by a full inventory and gaps area were measured by using of triangles method. In order to spatial analysis, O-ring statistics, variogram analysis and mark correlation function (MCF) were used. The results showed that the most frequency of gaps was related to canopy gaps with area less than 200 m2. The spatial pattern of natural and harvesting gaps was similar and up to a maximum distance of 35 m was clustered and then random. Only the harvesting gaps indicated a spatial structure up to a distance of 168 m. Natural canopy gaps did not have spatial structure and revealed that the gaps are independent of each other in terms of area. Thus, in silvicultural management, disturbance should be created with different areas that unfortunately have been less considered in the study area.

In order to investigate the effect of environmental factors, including slope gradient, aspect and elevation on regeneration of Juniperus excelsa subsp. polycarpus, some Juniper stands were selected at Hezar Masjed Mountains, north of Khorasan Razavi province, north-east of Iran. Maps of slope gradient, aspect, elevation and landform were used and combined together to develop homogenious polygons of land units. The sampling was made, using stratification method and three sample plots, each 1000 m2. The plots were then laid out on the land units. To study the physico-chemical properties, one soil sample was made from subsoil, at each plot. The soil data were analyzed, using the Principle Component Analysis (PCA). Some parameters, including number of Juniper seedlings and their total height, collar diameter, health and vitality status were measured. The results showed that the elevation has significant effect on number of the seedlings, collar diameter and total height of the seedlings and proportion of health classes. Slope gradient showed significant effect on number of the seedlings per plot. The geographic aspect showed significant relation only with the proportion of moderate healthy seedlings. The impact of land form on Juniper seedlings was not significant. The Principle Component Analysis (PCA) output showed that phosphorus, clay, silt, EC and CaCo3 are the most important factors influencing regeneration of Juniperus excelsa subsp. polycarpus.