tree structure

The wood quality in forest trees largely depends on their self-pruning and forest management pays attention to the pruning factor to achieve high quality of wood products. Therefore, this study aimed to determine the relationship between self-pruning index in Oriental beech trees and some of their structural attributes. For this purpose, 186 beech trees were randomly selected in Alandan, Sari and the self-pruning index along with other structural features were measured. The correlation results showed that there is a significant positive correlation between self-pruning index with DBH, crown length, area and crown volume and also a significant negative correlation with symmetry and crown ratios. No significant difference was observed in the height classes of beech trees in terms of self-pruning index (Sig.=0.164). The highest mean value of the pruning index belongs to the class of 75-46 cm in diameter (Sig.=0.002). The analysis of variance results showed that the highest mean value of the index was present in the groups of three trees. With increasing the stubbiness ratio, the self-pruning index increased (p=0.009). A significant interaction was observed between stubbiness ratio with crown length, crown area and volume, DBH and height of beech trees in site. In general, the results showed that self-pruning in large-sized beech trees was performed according to forest conditions and this important index was related to the structural attributes of trees such as height, DBH, surface area and volume of the crown and it is also necessary to consider the pruning of forest trees in intermediate-cutting operations to increase the wood quality.

Rainfall-runoff simulation is one of the most important challenges in the management of water resources in each basin, considering the climatic changes and the increase of extreme values in recent years, especially in different regions of Iran. In this study, the rainfall and runoff values in the statistical period of 1993-2019 were used regarding the rainfall-runoff simulation in the Qale Shahrokh sub-basin in the Zayandeh-Rood Dam basin. In this study, the Vine copula-based simulation approach was used to simulate and joint frequency analysis the flow discharge in Qale Shahrokh station given by the rainfall in Chelgerd, Meyheh and Marghmalek stations. By analyzing the tree sequence of vine copulas and using internal rotated copulas, D-vine copula was selected as the best copula based on the studied statistics. By using the best copula and the conditional relationship c(u4|u1,u2,u3), the flow discharge simulation was done given by rainfall of the upstream stations. The simulation results showed an error rate equal to 18.57 (m3/s) based on the RMSE statistic and the efficiency of the model was 86% based on the NSE statistic. The results of the simulation of flow discharge values given by rainfall in the upstream stations showed that the proposed approach has simulated the average of observed values with high accuracy. By considering the condition of rainfall occurrence in the frequency analysis of flow discharge in Qale Shahrokh station, the joint return period curve and the conditional probability of occurrence in this sub-basin were obtained. Using this curve, it is possible to estimate the flow discharge values of the studied station with high accuracy along with different return periods and different probability of occurrence. Considering the fact that the proposed method is based on the condition of rainfall in the region as well as the marginal distribution according to the data, it has no implementation limitations and is somehow specific to the studied region.

The growth of forest trees is controlled by various components. One of the main factors determining the structure and composition of the forest is the competition between the trees and competition involves complex relationships that depend on the pattern of tree distribution, the availability of resources, and the efficiency of resource utilization. Therefore, knowledge of tree competition mechanisms is ecologically and economically important. The purpose of this study was to determine the correlation between competition index and some characteristics of Persian oak (Quercus brantii Lindl var.persica) in Hashtad-Pahlu, Khorramabad.

A total of 30 Oak trees were selected randomly in different aspects. Height, DBH and crown diameter were measured. Beneath their crown in two aspects (north-south) at a distance of one meter from trunk, fine roots sampling (60 samples) was performed at 0-30 cm depth.

The result of analysis of variance showed that there was a significant difference between the value of competition index for Iranian oak species in different ranges (Sig = 0.000) so that the highest average value of this index was related to the northern exposition. Significant difference was observed for competition index in diameter class but no difference in height class. With increasing crown diameter, DBH and decreasing height/DBH ratio as well as crown diameter / DBH, competition index values ​​increased and decreased respectively. Correlation showed that with increasing crown diameter and DBH, competition index value increased and with decreasing height / DBH ratio as well as crown diameter / DBH index value decreased. Results revealed the significant differences for trees in terms of crown diameter, DBH, height / DBH ratio and crown diameter/DBH ratio in aspects. Pearson correlation coefficients showed that there was a significant negative correlation between competition index and carbon biomass of Persian oak fine roots.

The difference between the competition index in the height and diameter classes of Persian oak trees indicates the importance and role of these two important characteristics in estimating it and also the difference in the competitiveness of trees in different stages of forest stand development. The results showed that light-demanding Oak trees based on various site conditions differ in terms of competitiveness and some characteristics in different positions.

Canopy gaps in different sizes have been created by the implementation of different silvicultural practices such as single-tree selection in beech forest stands in Hyrcanian forests. Investigating the effects of forest gaps on the characteristics of trees and soil in the forest ecosystem can be very helpful in planning silvicultural operations. Shade-tolerant beech trees in this ecosystem are of ecological and economic importance and knowing the reaction of such a valuable tree can be effective for forest management and selection of forestry methods.Therefore, the purpose of the present study was to determine the correlation between structure, fine roots properties of beech trees and soil biology(MBC,MBN and MBP) in different gaps (n = 15) created by single-tree selection system with competition index in beech forest stands in Mazandaran-Sari province.

In the beech forest stand, 15 forest gaps were identified including three classes of small (80-130), medium (175-131) and large (176-300m2) size and five replicates were selected for each level. In four cardinal positions of each gap, beech trees were selected and their height, diameter at breast height, crown diameter, area, volume and fine roots as well as competition index were measured.

Pearson correlation coefficients showed a significant positive correlation between competition index with height, DBH, crown diameter, crown area and length of Bole and also negative correlation with height to diameter ratio (H/D) of beech trees. There was a significant negative correlation between competition index and microbial biomass nitrogen and a significant positive correlation with microbial biomass carbon to microbial biomass nitrogen ratio (MBC/MBN). With increasing density, specific root length and specific area of fine roots, the values of competition index increased. There was a significant correlation between some structural characteristics of beech trees with fine root characteristics at the edge of gaps. Correlation coefficients between fine root characteristics of beech trees show significant correlation between some variables.

In general, the results of the study showed that forest management through the application of single-tree selection system and the formation of canopy gaps in beech stand has influenced the structural characteristics and fine roots of beech trees six years after the creation of gaps.

Competition between trees has an impact on their structural features and it is very important to measure the competition index and determine the correlation with some of the characteristics of the trees. To conduct the research, circular sample plots (n = 24) with an area of ​​400 m 2 were established in a 150 × 100 m grid in the forest, Savadkoh-Mazandaran. Within each sample plot, frequency, height, crown diameter and diameter at breast height (dbh) for each tree were measured in the overstorey. The richness and diversity index of trees and competition index for each plot were calculated. The results showed that there was a significant difference between the values ​​of competition index for the three tree species. Competition index with height, dbh and crown diameter had significant positive correlation for all tree species, but negative significant correlation with height and H/D for beech and alder and also positive correlation for hornbeam. There was a negative significant correlation between beech competition index and tree richness index and a positive correlation between alder competition index and tree diversity index. With increasing altitude, competition index values ​​decreased only for hornbeam species. Significant differences were observed among the three tree species in terms of crown diameter, dbh, height and H/D ratio in stand. In general, regarding the relationship between some tree variables and the index of competition in the stand, this information can be used in the selection and application of silvicultural operations such as thinning and remarking in temperate Hyrcanian broadleaf forest.