جستجوی مقالات مرتبط با کلیدواژه « age » در نشریات گروه « جنگلداری »

The mechanical characteristics of roots can serve as a significant factor for selecting trees in the plantation of arid regions for soil bioengineering. This research aims to evaluate the mechanical characteristics of Tehran pine roots at various vegetative ages (one-year-old, three-year-old, and five-year-old seedlings) and under different water stress levels (light, medium, and severe) in Robat Karim. The mechanical properties of the roots were studied after estimating the water requirement of the studied seedlings at different ages for one year and based on the water stress levels. Then, five seedlings from each treatment (equal to 9 treatments) were selected and coded completely randomly to evaluate the water stress on the mechanical characteristics of the roots of Tehran pine. Initially, some root parameters such as root diameter, length of the whole root, length of thin roots, and length of the longest root were measured. Then the tensile force, tensile strength, and Young's modulus of the roots were measured and recorded using a standard Centam device. The results showed that with the increase in root diameter, the tensile force of the root changes based on the positive power relationship, and the tensile strength and Young's modulus of the root changes based on the negative power relationship. Furthermore, laboratory examinations showed that at any age, the length of the whole root and the root length densities are higher with the increase in water stress. The use of covariance analysis showed that the results of the average comparison between one-year-old age and mild drought stress, three-year-old age and moderate stress, and five-year-old age and severe stress are significant with a probability of 95%. The results of this research show that the mechanical characteristics of the root can be used as an important factor for the selection of pine seedlings in the afforestation of arid areas for soil bioengineering purposes. Therefore, it is recommended that these properties be considered in soil reinforcement modeling.

This study was conducted to study the environmental literacy of students in Urmia University. In this study, the sample size was determined using the Krejcy-Morgan table. From the 7810 students of Faculty of Natural Resources, Engineering, Agriculture and Economics, 466 students of them responded to the questionnaire by random sampling. The questionnaire used in this research is a researcher-made questionnaire, which includes questions in two sections: general environmental questions and regional environmental questions and is set in quintuple Spectrum Pattern. The validity of the questionnaire was confirmed by the experts and the Cronbach's alpha coefficient was used to assess the reliability of the questionnaires. To compare the level of environmental knowledge of college students, one-way analysis of variance and Duncan's comparison test were used. Spearman correlation test was used to determine the relationship between the level of environmental knowledge and parameters such as age, number of family members, father's education, mother's education and monthly income level of the family. There was no significant difference between the studied faculties (5% = α) regarding to level of general knowledge. However, in the case of regional environmental knowledge, the level of this knowledge is the highest in students of the Faculty of Natural Resources and the least amount was in the students of the Faculty of Science and Engineering.

One of the most important disturbance occurred in beech stand is tree uprooting that creates pit and mound microsite where caused serious change in soil physical and chemical properties. Pit and mounds have different ages in forest. So this research was carried out to investigate the relation of pit and mound dynamics with some physical and chemical properties of soil in a mixed beech forest in Shastkolate forest، Golestan Province. Soil samples were collected from 4 microsites: pit، mound، around the dead woods and closed canopy، in 4 different decay stages. Then soil Organic matter، bulk density and pH were compared in different age and 4 sections using one way ANOVA. Results showed that the amount of soil organic matter، bulk density and pH in 4 sections were significantly different (P<0. 05). The most amounts of soil organic matter were found in pit while the most amounts of soil bulk density and pH were found in mound. Also the amount of soil organic matter and bulk density in different ages were significantly different among decay stages except for pH. The greatest amount of soil organic matter and bulk density were found respectively in 10-15 and less than 5 years. It can be concluded that soil organic matter increase while bulk density decreases when time following up and pit become older. However، older pit has richness and fertile soil because litter decomposition well done and microorganisms activities increases. Microsites created by the beginning of change، forest stand development and soil fertility.

Oriental Beech forests have economic and ecological importances in Hyrcanian zone in the north of Iran. Therefore qualitative and quantitative controls of the stands are essential in management of these forests. This study was aimed for determining the effect of age on growing variables of beech trees in Lomir forest in Asalem, Guilan Province. In this study, 179 Beech trees were selected based on diameter classes (5 cm). The relationships between tree age and growing variables of beech trees were tested by regression analysis. The results of this study indicated that tree age-diameter (=0.93) and tree age-height (=0.77) relationships were described using Power model. Volume growth was fitted by power model with the adjusted coefficient of determination of 0.92 (=0.92). The S-curve model gave the best result for relationship between age-crown diameter (=0.78) and age-bark thickness (=0.80). But the tree artificial form factor is not affected with increasing tree age. These results indicated that diameter and height trends of annuall increment are negative in final periods of tree life. But volume trend of annual increment always is positive. The results of this research could be a guideline for foresters to manage forest economically.

Yew is one of 4 conifer species which is distributed and endangered in the northern forest of Iran. In order to study the effect of cutting and bed soil in nursery on success of vegetative propagation of Yew, two different kinds of cuttings (one and two years twigs) and four different soils (loam, sand, sandy loam and mixed soil) were used. A total of 540 cuttings, containing 15 cuttings in each treatment were studied. Results showed that there was a significant difference between treatments at level of 5%. The highest rate of rooted cuttings (82.2%) was observed within one year old woody cuttings in pure sand bed, while the lowest rate (13.3%) was observed within older cutting in loam bed.

In 2000, fourty seed trees which were located at Sanghdeh Forest of Caspian Region with altitude ranged between 1700 to 2300 m-above sea level, were selected. 200 seeds were collected from each tree, subsequently. The seeds were sown in 2000 and in 2001 repeatedly, in plastic bage containg forest soil and kept in a forest nursery located at the same forest at 1550 m. above sea level altitude. Seed germination and seedling survival was measured in 2000 and 2001. According to T-Test data analysis, there were significant differences between seed germinatin and seedling survival of the treatments in both years. Total seed germination (TSG) in 2000 was 9.22% more than TSG in 2001. Seed germination was correlated significantly and negatively with the seed trees age and diameter. Seed trees with moderate age and at diameter class of 30 cm, performed the highest percentage of seed germination in 2000 (without seed storage). There was minimum reduction in seed germination for seeds collected from trees at moderate diameter class and stored for one year.