فصلنامه جنگل و فرآورده های چوب
سال هفتاد و هفتم شماره 1 (بهار 1403)

In the present study, we detected the characteristics of precipitation (the amount and the number of events) in the Saharo-Sindian vegetation region located in the south and southeast of Iran over the last three decades. Daily precipitation data during 1987-2019, recorded by eighteen meteorological stations were analyzed. The Mann-Kendall (MK) test was used for trend analysis. Over the past thirty-three years, the mean annual precipitation was 214 mm (SD: 61 mm). Mean maximum and minimum yearly precipitations were recorded in Dogonbadan (439 mm) and Iranshahr (109 mm), respectively. Out of the eighteen stations, only two stations, Ramhormoz and Kish Island, showed significant annual precipitation trends (11% of the total trends). During 33 years, a total of 17275 events (mean event: 7.5 mm; SD: 6.9 mm) were recorded in the stations. The correlation coefficient (r) between the amount of precipitation and the number of events varied from 0.41 to 0.86 (mean: 0.67; SD: 0.13). We found that 83% of the mean annual precipitation occurred during the autumn and winter seasons. The highest and lowest yearly precipitations fell within the 20-40 mm (21%, 45 mm) and over 40 mm (30%, 64 mm) classes, respectively. Over the past three decades, the mean number of dry days per year was 336. Any changes in precipitation characteristics severely impact the vulnerable forest ecosystems in the Saharo-Sindian vegetation region.

Chainsaws, which are widely used in tree felling operations, create vibrations. Long-term and intense exposure to vibration may lead to the development of vascular, neurosensory, and musculoskeletal disorders in the upper limbs of chainsaw workers, known as Hand-arm vibration syndrome. This study investigates the vibration levels during tree bucking operations on poplar trees with the MPTMGS5803 chainsaw model, one of the most widely used chainsaws in forest operations in the western part of Guilan province. Simultaneous vibration measurements in three directions (x, y and z) were carried out using the SVANTEK 106A vibration meter, aiming to determine the total amount of chainsaw vibration and the daily exposure period. The results show that the highest amount of vibration was measured in the x (1.61±0.62), (2.01±0.90) direction and the lowest in the y (1.48±0.17), (0.73±0.09) direction both in the rear handle and front handle of the chainsaw. The rear handle of the chainsaw had a higher overall vibration acceleration (3.05±0.54 m/s2) compared to the front handle (1.94±0.53 m/s2). In terms of the daily exposure period, the level of vibration exposure inflicted on the chainsaw operator during a  three-hour and 70 second working period amounted to 1.19 m/s2 in the front handle and 1.87 m/s2 in the rear handle, with both values falling within the permissible vibration range.

Cytogenetic investigations in plant species, particularly wild and native plants, are crucial for understanding their evolutionary history, establishing species relationships, and determining karyological features. This study delves into chromosome counting and evaluation of karyotypic characteristics of five woody species belonging to three families: Ulmaceae, Cornaceae, and Rhamnaceae within the Hyrcanian Forests. Root tip meristem was used for chromosomal studies by classical methods. The results revealed that all studied species were diploid. The chromosome numbers of three species, Cornus australis (2n=2x=22), Rhamnus sintenisii (2n=2x=26), and Zelkova carpinifolia (2n=2x=28) were documented for the first time in the world. Additionally, two species of Ulmus glabra and U. minor with a chromosomal number (2n=2x=28) were reported for the first time in Iran. Concerning chromosomal length, R. sintenisii displayed the smallest chromosome length (0.9 µm), while U. glabra exhibited the largest (2.34 µm). The chromosomes in three species, R. sintenisii, U. glabra, and Z. carpinifolia were of the metacentric and sub-metacentric types. U. minor presented sub-telocentric chromosomes in addition to the mentioned types, and C. australis displayed metacentric chromosomes in two forms, M and m. Regarding symmetry, chromosomes in three species, R. sintenisii, U. minor, and Z. carpinifolia were classified as 2A, C. australis as 1A, and U. minor as 3A. Given the scarcity of similar studies on forest species, this research significantly contributes to identifying the cytogenetic characteristics of the examined species.

Investigating forest structure is an important and necessary topic, especially in line with the goals of close-to-nature silviculture. This research aimed to quantitatively analyze the complexity of stand structure during the transformational phase of understory formation in the oriental beech (Fagus orientalis Lipsky) forests of Kheyrud, Nowshahr. After field inspections, three one-hectare sample plots in the transformational phase of understory formation were selected, and a full inventory of all stand parameters, including tree diameter at breast height, natural regeneration, size and distribution of gaps, and deadwood, was carried out. To analyze the structural complexity in forest stands, the structure complexity indices, Cox coefficient, coefficient of variation, and Gini coefficient of tree diameter were used. According to the research results, in this evolutionary phase, the highest frequency is in small diameter classes, while the lowest frequency is in large trees. The distribution curve of trees forms a decreasing exponential with a steep slope in small diameter classes. The average deadwood volume was 30 m³, and the average gap factor of crown coverage was 6.4%. Additionally, the mean Gini coefficient and diameter change coefficient were 0.7 and 6, respectively. These values, along with the Cox coefficient, indicate optimal complexity in the stand structure during this phase. In the understory, the average abundance was 306 stems per hectare, with beech being the most abundant species. Based on these results, to maintain heterogeneity in the managed forests while preserving large trees in the stand, it is suggested to implement operations to increase the complexity of the forest stand structure and perform thinning from below.

Chestnut (Castanea sativa Mill.) is one of the native species of Guilan province. Due to fungal diseases and animal grazing, as well as the high amount of unhealthy seeds, native chestnut in vitro culture is one of the effective methods for mass production of this endangered plant. The aim of this research is to determine the optimal culture medium for chestnut tree regeneration through tissue culture. The culture medium used in this research includes GD (Gresshoff & Doy), DKW (Driver and Kuniyuki Walnut) (1 mg/liter BA*) and (Murashige Skoog) MS (half nitrogen concentration) with three different hormone combinations (1 mg/liter + BA 0.1 mg per liter TDZ), (0.5 mg/liter TDZ), and (1 mg/liter + GA3 0.1 mg/liter BA). For in vitro culture of chestnut, lateral buds of one-year-old plants grown in the greenhouse were used. One-way analysis of variance (ANOVA) was performed to investigate the effect of culture media with plant growth regulators on explant length, number of leaves, and stems. The results showed that the length of explants has a significant difference in culture media. No significant difference was observed in the number of stems and leaves. The results of the comparison of means using Tukey's test showed a significant difference between the length of explants in DKW medium and other media. DKW medium with 1 mg/liter BA was found to be the best medium for regeneration and longitudinal growth of chestnut explants. In the present study, in vitro culture of Chestnut is introduced an effective method for mass production of this species.

Different methods have been developed for the heat treatment of wood. Oil heat treatment (OHT), as a unique method, can provide a dry and oxygen-free heating medium. This study used a pilot-scale oil heat treatment to treat poplar wood at different temperatures to enhance its weathering resistance. Poplar timber was subjected to oil heat treatment using a specific heating program at three target temperatures (180, 190, and 200 °C), each held for two hours. The specimens were prepared and subjected to 1000 hours of accelerated weathering with a Gardner wheel. Water absorption and volumetric swelling were also determined during seven days of soaking in water. Contact angle measurements of water droplets, colorimetry, and ATR-FTIR analysis were also conducted before and after weathering. The dimensional stability of treated wood increased with higher processing temperature. Although the water absorption values of treated wood were lower than those of the control specimens, the difference was not significant. The samples exhibited an obvious color difference before weathering due to oil heat treatment, but their color changed to silver-gray tans after weathering. The maximum ∆E value after weathering was observed in the samples treated at 200 °C. Weathering increased the wettability of wood surfaces, but the treated samples still had a higher water droplet contact angle than those of the control sample. ATR-FTIR results determined that oil heat treatment is not an effective method for preventing the degradation of lignin in wood surface exposed to weathering factors.

The paper is a thin, wide sheet formed from the entanglement, flocculation, and bonding of fibers, filaments, and cellulose components. It is produced in various dimensions for numerous applications. Building on a previous study on the fluorescent staining methods of cellulose fibers, the present research investigates the microscopic structure of the sheet and its components in three dimensions (length, width, and depth) using a confocal laser scanning microscope. This study also examines the distribution of cellulose fibers and components within the paper structure's three dimensions using fluorescent properties and confocal microscopy. The cellulosic components of the paper structure exhibited a green fluorescent reflection (420-500 nm) in the visible light region when excited at a wavelength of 405 nm. Beyond the two-dimensional analysis of paper planes, the confocal laser scanning microscope provided a wide array of intriguing images, revealing how fibers or cellulose fiber fractions are distributed within the paper's thickness without the need for layer-by-layer slicing. Depth imaging of paper was successful for samples with basis weights of both 20 and 60 g/m². The resulting images showed increased flocculation and accumulation of fiber elements and segments with depth. Overall, images obtained from the confocal laser scanning microscope demonstrated that the apparatus is suitable for investigating the distribution of labeled fibers and fiber fractions in all three dimensions of the paper structure.

Knowing the forest canopy height is essential for evaluating the health and dynamics of forest ecosystems, as well as for monitoring and modeling the carbon cycle and biodiversity. However, measuring canopy height through ground surveys is costly and time-consuming. Since 2018, the ICESat-2 satellite, equipped with the ATLAS laser sensor, has enabled the direct measurement of tree height. Although ICESat-2 is specifically designed to estimate ice height, it also provides significant data on vegetation height on the Earth's surface. This study aims to investigate the ability of the ATLAS sensor to accurately estimate forest canopy height in northern Iran. For this purpose, the vegetation height data from the ATLAS sensor (ATL08) was evaluated in the Kheyroud experimental forest. To validate the accuracy of the estimated forest canopy height by ATLAS, the forest height data obtained from the satellite were compared with the maximum tree height measured in 121 plots collocated with LiDAR footprints. The estimated forest canopy height by ATLAS and the maximum measured height of trees were compared using a t-test. The RMSE, rRMSE, and R2 values were 0.87 m, 2.7%, and 0.98, respectively, indicating the high accuracy of the ATLAS sensor in forest canopy height estimation. The results of the t-test showed that the mean difference between the measured maximum height of trees in the plots and the corresponding values extracted from ICESat-2 satellite data is not statistically significant (P > 0.05). This study demonstrates that the satellite estimates forest canopy height with very good accuracy in the forests of northern Iran, with a slight overestimation in areas with low-height trees.