جستجوی مقالات مرتبط با کلیدواژه « تاج درخت » در نشریات گروه « جنگلداری »

One of the environmental problems of Zagros forests is oak decline, which is less intense in northern Zagros than in middle and southern Zagros. The purpose of this study was to investigate the oak decline in Baneh County (Kurdistan Province) in 2019, 2020, 2021, and 2022. In order to carry out this research, two plots (with 100 trees) were considered in Belveh (tree dieback–southern slope) and Saraki (tree dieback–northern slope) sites in Baneh County in the northwest of Kurdistan Province. In 2019, oak trees were numbered at the desired sites, and in October 2019, 2020, 2021, and 2022, oak decline classes (five classes) were recorded for each tree. The results showed that the number of healthy trees in the Saraki and Belveh sites decreased by 25 and 28 trees, respectively, from 2019 to 2022; in contrast, the number of dieback trees increased by 14 and 19 trees, respectively, and the intensity of oak decline was greater in the Belveh site (southern dieback stands) than in Saraki (northern dieback stands). In general, the decline rate in the southern stands was higher than that in the northern stands, and the highest oak decline was observed in the southern slope. To optimally manage these forests, it is necessary to manage the factors that exacerbate oak decline and to control human interference and forest destruction so that the current situation is fixed and the seeds of healthy stands on the northern slopes are used for the regeneration and development of the forest.

In this study, the rate of seedling emergence from direct seeding of Brant`s oak (Quercus brantii Lindl.) and wild pistachio (Pistacia atlantica Desf.) in Dalab forests of Ilam in two altitude and five regeneration establishment positions during two years 2018-2019 was examined. For this, six sites were selected at an altitude of 1400 and 1550 m above sea level with the same aspects. In each site, a transect was implemented perpendicular to the slope, and on it regeneration establishment positions including “under tree crown”, “under shrub”, ‘under bushes”, “next to the rock” and bare spaces, observing three replicates were established. At each regeneration establishment position 12 holes were dug. In the dug holes, the seeds of the mentioned species were planted in the winter of 2017. The number of green holes and the number of emerged seedlings were counted during the spring and summer of 2018 and 2019 years. The results showed that the effect of sampling year, sampling season, altitude, regeneration establishment position and interaction effect of altitude and regeneration establishment position on the percentage of green holes is significant. The percentage of green holes decreased in the second year compared to the first year and in summer compared to spring. The highest percentage of seedling emergence was at lower altitudes and under tree crowns. The performance of Stones and bushes was better than shrubs which ranked after tree crowns. It was concluded that if seed sowing is done according to the natural pattern of regeneration, successful results can be hoped for.

Since the long-term sustainability of the natural ecosystem depends on soil quality protection, knowledge about soil conditions in natural lands is effective for their correct management. The aim of this study was to investigate the impact of Christ's thorn (Ziziphus spina-christi L.) crown on soil physicochemical and biological characteristics in the Izeh region of Khuzestan province. Soil sampling was carried out from the soil surface (0-20 cm) under the crown and open area (control) by using random transects. In addition, several numbers of soil physical (bulk density, and saturation moisture), chemical (acidity, organic carbon, potassium, and phosphorous) and biological (carbon microbial biomass, basal respiration, and microbial quotient) properties were measured. According to the result, the organic carbon content under the crown was 1.90 percent, which was 23.5% higher than that of the soil outside the crown. The available soil potassium content (233.35 mg kg-1) under Christ's thorn crown was higher than that of open area. However, pH was not shown to be affected by trees, with no significant difference between measured values in free space and under the crown. The highest amounts of carbon and nitrogen microbial biomass (547 and 60.1 mg kg-1, respectively) were found under the canopy. In addition, the highest basal respiration rate was 19.29 mg of carbon dioxide per kg of soil under the tree crown. The microbial quotient of 1.68% was highest under the crown. Based on the results, the metabolic rate showed an inverse trend, with the highest amount was observed outside the tree shadow. Furthermore, the presence of Christ's thorn trees in the study area has resulted in increasing soil fertility and the improvement of soil microbial activities.

In arid and semi-arid ecosystems, isolated trees have an important effect on soil properties and could determine the structure of the soil fauna communities and herbaceous species under the tree which could influence these types of ecosystems. The aim of this study was to find out the effect of tree canopy on the spatial distribution of soil nutrients (OC, N, P, K, Na and Li) with varied chemical characteristics. In this research, soil samples were taken under and around a pistachio (Pistacia atlantica Desf.var.Kurdica) tree in Sarvabad region, West of Iran. The samples were taken every 2 m and then at 50 cm intervals in a regular grid of 20 m × 20 m around the tree for analyzing the spatial properties using geostatistical techniques. Total nitrogen (N) content similarly to soil organic carbon (OC) was higher under the tree. Phosphorus (P) content also was higher under the tree canopy. Potassium (K) decreased with distance from the tree base. Sodium (Na) had a medium spatial distribution related to tree canopy, while Lithium (Li) showed a sparse spatial pattern and its distribution seems to be independent of the tree position. These results support the hypothesis that the presence of a tree affects differently the spatial distribution of the various nutrients depending on their chemical characteristics.