مجله جنگل ایران
سال سیزدهم شماره 2 (تابستان 1400)

The structure of forest stands changes over time and under the influence of local disturbances, these changes are referred as the dynamics of forest stands. Changes in the structure of forest stands result in the formation of development phases. The purpose of this study was to identify the structural characteristics of natural beech forests during the stage of growing up volume in the Kheyroud forest. For this purpose, three one-hectare sample plots with structural features of growing up volume stage were selected and the location, diameter and height of all trees within each sample plot with DBH N 7.5 cm were measured. The structural properties of this stage were investigated using a set of indices based on the nearest neighbors. Based on the results, the mean values of uniform angles and Clark and Evans indices were 0.49 and 0.96, respectively, which indicated a random clumped spatial pattern of trees at this stage. The results of the mingling index showed that the tendency of beech trees to mix with other species was low. The results of diameter differentiation index indicated a clear difference and height differentiation index showed a moderate difference in dimensions of trees with each other. In general, using the nearest neighbor indices showed that these indices have a high ability to detect the differentiation of forest stands in the growing up volume stage and thus are useful tools for forest management.

In order to study the effect of fire on some physical, chemical and biological characteristics of soil, 36 sample plots with three low, medium and high fire intensities and control treatments were set up in the Namkhaneh district of University of Tehran Forest. Soil samples were then taken from 0-10 cm layer in three phases (one day, 6 and 12 months after the fire) and some soil properties were studied. Data analysis was done by repeated measures ANOVA in SPSS software. The results showed that fire intensity had no significant effect on soil physical properties including bulk density, moisture content and soil texture. The results of soil chemical properties analysis showed that fire intensity had a significant effect on electrical conductivity, organic carbon, total nitrogen, carbon to nitrogen, phosphorus, calcium, potassium and magnesium ratios but had no significant effect on pH. In terms of biological characteristics, fire intensity had no significant effect on carbon microbial biomass but on microbial respiration and nitrogen microbial biomass. Time after fire had significant effect on moisture content, microbial respiration, microbial carbon and nitrogen, available phosphorus and potassium but had no significant effect on other physical, chemical properties. Since fire causes long-term depletion of soil nutrients, some post-fire preventive and rehabilitative measures in areas with moderate and high fire severities are required to restore soil functions more quickly.

The aim of this study was to analyze the annual, monthly, and seasonal rainfall changes over a thirty-year period as well as before and after the emergence of declining oak. (Quercus brantii var. persica) trees (2000) in Ilam and Lorestan provinces. For this purpose, the authors used long-term data of daily rainfall in 1987–2017 period recorded by four synoptic meteorological stations; Ilam, Dehloran, Khoramabad, and Aligudarz. The Mann-Kendall non-parametric test was used to determine the rainfall trends. The decreasing trends of annual rainfall as well as mean differences in annual precipitation before and after emerging oak decline were not statistically significant at all meteorological stations. The average rainfall of four stations was 502 mm in the first decade (1987-1997), while it decreased to 422 and 371 mm in the second (1998-2007) and third decades (2008- 2017), respectively. The difference in the amount of annual rainfall before and after the emerging oak decline (442 against 401 mm) did not alter the mean rainfall event (̴7 mm). Although the thirty-year trends of seasonal rainfall were not significant, winter rainfall was decreased after emerging oak decline by 11% and spring, autumn, and summer rainfalls were increased by 5, 4, and 2%, respectively. Rainfall fluctuations in the Zagros vegetation region may act an accelerating factor for the emergence and extension of oak trees declining in the Zagros forests of Lorestan and Ilam provinces.

Knowing the effects of anthropogenic disturbances on the natural spatial pattern of trees can provide good information about the response of nature to human intervention. This study aimed to reveal the effects of human interventions on the spatial pattern of Caucasian oak stands in the Arasbaran region, located on Hatam Mashe Si, Meshgin-Shahr. For better distribution of study locations, three areas with different disturbance intensities were selected and the nearest tree to the transect as a reference tree with the four nearest neighbors was measured. To analyze the spatial pattern of trees, two groups of indicators based on the nearest neighbor’s distance index were used, including distance-dependent indices (distance from the nearest neighbor, Clark-Evans, and Pielou), and angle-dependent indices (mean directional, mean of angles, and uniform angle). The results showed that the average distance to the neighborhood in areas with high intensity of disturbance is significantly more than the other two areas. As the disturbance index increases, the distance between the trees and the numerical value of the Clark-Evans and Pielou indexes increases. The mean angle index showed a moderate and positive relationship and the uniform angle index showed a negative relationship with the anthropogenic disturbance index, and the mean directional index did not show a relationship with the anthropogenic disturbance index. Anthropogenic disturbances (such as cutting trees, livestock grazing, and fires) in the long term have led to changes in the spatial pattern of trees, as a result, their distribution is relatively regular. In conclusion, it can be concluded that minimizing the effects of anthropogenic disturbances in forests can partially maintain the heterogeneity of the forest structure.

Forests as one of the important ecosystems plays a noticeable role in reducing the carbon dioxide by the  annual atmospheric carbon sequestration into the biomass of woody plants and soil. The three determining factors for estimating the carbon storage in a forest ecosystem are soil, vegetation, and litters. This study was carried out to investigate the carbon storage and its sequestration in four 1 ha square sample plots in forests of Boyer-Ahmad and Dena counties, Kohgiluyeh and Boyer-Ahmad province. Relevant allometric equations were used to estimate the biomass and carbon storage of the tree species in two vegetative form of coppice and high forests. For the measurement of soil carbon storage, five soil samples were taken from depths of 0- 30 cm, and percentage of organic matter and bulk density were measured in the laboratory. Analysis of variance showed that the total carbon storage in the trees, soil and litter had no significant difference amongst different sites, but the total carbon storage among the trees showed a significant difference (Parikadon site with 31 and Vezg site with 17 tons/ha, respectively). According to the results, the enclosed area (Vezg) had the highest carbon storage and the Sarabtaveh (northern aspect) had the lowest carbon storage. The average carbon storage of the studied areas was more than 159 tons/ha. The average of carbon storage in litters was about 730 kg/ha and the mean economic value of total carbon storage per ha was estimated 188 million Tomans.

In this study, a habitat of wild cherry (111 ha) in Mamji-Darasii in the province of East Azerbaijan, the city of Kalibar, was fully inventoried and all wild cherry trees were then counted and measured. Frequency of cherry regenerations was also calculated by establishing 23 0.1 ha ample plots. The results showed that 86.6% of the cherry trees were healthy and vital and their mean height, diameter at breast height and volume were 9.3 m, 12.6 cm and 0.08 m3, respectively. The highest and lowest frequencies were 10 and 25 cm DBH classes, respectively . Density, basal area and volume of cherry trees in stand level were calculated as 2.14 individual.ha-1, 0.032 m2.ha-1 and 0.17 m3.ha-1, respectively. There was no significant correlation between the quantitative characteristics of trees and slope but diameter, height and basal area of the cherry trees decreased with increasing the altitude. Most of the trees (62%) were found on the northeast-facing slopes. The trees were taller in the northeast directions and in terms of diameter, basal area and volume, trees in the eastern aspects had higher dimensions. A total of 53 dead trees were counted, of which 43 were standing and 10 fallen. They constituted 18.2% of total cherry trees. The regeneration rate of cherries was 36.1 individual.ha-1. The highest abundance of trees belonged to the hornbeam followed by oak Wild cherry with 3% abundance was in fourth place. To enhance and increase the density of wild cherries, slight opening of the canopy is necessary using appropriate silvicultural operations.

Trees are one of the most important carbon reservoirs on the earth and carbon sequestration into plant biomass is an easiest and economically most practical way for mitigating the CO2 from atmosphere. This study aims at determining the biomass and carbon storage in stump and roots of Populus deltoides in Tanian poplar plantations of Guilan province. For this purpose, 15 poplar trees were selected based on selection sampling method 15. After the cutting and moving the logs from the stump to somewhere outside the plantation, excavator machinery (KOMATSU PC 200) was used to remove the stumps and roots from the soil. After separating the stumps and roots, mentioned parts were weighed using a digital scale. In order to estimate the amount of biomass and carbon storage, some samples of various components of poplar trees were then fallen down and weighed. After drying the samples in oven (80 ̊C), the dry weight of the samples was determined. After burning an enough amount of dried samples in the electric kiln, the weight of organic matter and carbon of the stump and root samples were obtained. Results showed that the mean of stump biomass, root biomass, stump and root carbon sequestration for each tree were 2.15, 22.18, 1.05 and 10.94 kg per tree, respectively. Results indicated there was a positive and significant correlation between the biomass and carbon sequestration of stump and root with collar diameter. The amount of carbon storage in the root and stump parts was 3.836 tons per hectare and the economic value of carbon storage was calculated as 46723015.68 Rials per hectare.

Evaluation of management practices in forests is necessary to determine the appropriate method of sustainable management. Therefore, some quantitative parameters of beech forests, harvested sequentially as shelterwood system and single-selection method were evaluated and compared to a controle compatrment. The control and harvested compartments were selected in Muzisay forest plan in Neka. The measurement was done within 0.1 ha sampe plots in 150×200m gridin 2019. Some quantitative characteristics were measured including the species type, DBH of all trees greater  than 12.5 cm, and the height of eight trees in each sample plot. The results showed that from 2001 to 2019, the frequency of beech in exploited plots increased from 81.51% to 96.2%. The abundance of hornbeam decreased from 14.41% to 2.9%. In control compartment, the beech frequency increased from 89.9 to 93.7% too. The average number of trees in the control plot was gradually declined from 275.5 to 245.83.  In contrast, it increased from 259.23 to 315.81 in managed plots. The opposite was seen regarding to the stand volume. In the managed compartments, the stand volume was declined from 481.47 silves to 426.31 silves. In contrast, it raised from 454.4 to 528.27 silves in control compartment. Both areas had an nearly regular age structure and near to normal volume structure. There were no significant differences between control and harvested compartments in light of total height, average number tree, and volume h-1. The exploitation of these forests by the shelterwood and the single selection method did not cause any destruction.