فصلنامه پژوهشهای علوم و فناوری چوب و جنگل
سال سی و یکم شماره 2 (تابستان 1403)

In the last two decades, sustainable biological nanomaterials such as nanocellulose (bacterial nanofibers cellulose and wood cellulose nanofiber) have received much attention from researchers to produce products in various fields. Biocompatibility, biodegradability, renewability, cheap and plentiful raw material availability, appropriate mechanical properties, and safety are among the most important properties of biological nanomaterials. Based on these properties, many applications have been created for it. One of these products is nanofilm, which is formed by creating hydrogen bonds between cellulose nanofibers, and no additives or adhesives are used in its production. When bacterial cellulose nanofibrils (BCNF) and wood cellulose nanofibers (WCNF) are used as a film as reinforcement in the construction of layered nanocomposites, due to the presence of cellulose network structure show excellent reinforcement ability. In recent years, the focus on nanocomposite production, optimizing its properties, and using high-tech products is increasing. Considering the technical and practical importance of nanofibrocellulose, cellulose nanofilm (layer), and nanocomposite prepared them, as well as the need for investigation and evaluation of these products as much as possible for future applied research, this study, is intended to determine the physical and mechanical properties of cellulose layered wood nanocomposite and bacteria be examined and compared. wood cellulose nanofiber gel and bacterial cellulose nanofiber film were used for this study. Tomake wood cellulose nanofiber layered nanocomposites, first, wood cellulose nanolayer was made using wood cellulose nanofiber and vacuum-filtration method .In the next step, the solvent displacement of nanolayers was done with ethanol and acetone several times. Then, epoxy resin, hardener, and acetone were mixed with a ratio of 20:10:70 and placed on a magnetic stirrer to remove bubbles. In the next step, the cellulose nanolayer was coated with epoxy resin, and 4 layers were placed on top of each other, and then layered nanocomposite with a heat press machine. They were dried for 3 hours at 60°C. The manufacturing steps of bacterial cellulose layered nanocomposite are similar to wood cellulose layered nanocomposites, with the difference that to prepare bacterial cellulose nanolayer, the bacterial cellulose nanofiber film was dried in a hot press at 70°C for 3 hours, and in the next step, the related layered nanocomposite was made. To investigate the properties of the resulting nanocomposites, various tests such as scanning electron microscopy (FESEM), X-ray diffraction (XRD), infrared spectroscopy (ATR-FTIR), static tension and water absorption were used. The results showed that the average diameter of bacterial nanocellulose and wood nanocellulose was 45±15 and 38±16 nm, respectively. The water absorption of layered nanocomposite was lower than the nanolayer prepared both nanostructures. The XRD peaks of bacterial nanocellulose and wood nanocellulose are different , and their crystallinity was calculated as 87% and 69%, respectively. Elastic strength, Young's modulus, and strain of the layered nanocomposite prepared of bacterial nanocellulose were higher than the related values of the layered nanocomposite prepared of wood nanocellulose. layered nanocomposites prepared of cellulose nanofibers have shown suitable physical and mechanical properties such as low water absorption and high resistance. Therefore, based on these properties and the growing trend of related research, it is expected that shortly find wider applications in the fields of aerospace, automobile, medicine, medical engineering, food industry, filmmaking, electronics and magnetism, etc.Keywords: epoxy, bacterial cellulose nanofiber, wood cellulose nanofiber, nanofilm, layered nanocomposite.

Competition between trees is a key factor affecting the development, structure, and dynamics of forests. Therefore, many ecologists have sought to quantify competition and related factors in the forest. The forests of Lorestan province with area 1,112,475 ha are part of the important ecosystems of the Middle Zagros, the main type of which is the Iranian oak. One of the important wood species of these forests is Hawthorn, which is often present as an accompanying species and in some areas as a pure forest. This research was conducted with the aim of comparing the crown competition and the spatial distribution pattern of Hawthorn in two forest type formation and companion species.

In this study, two forest habitats Khoshkeroud (with a dominant type of hawthorn) and Perk (with a dominant type of oak) were studied in Khorramabad. After the Search in the forest and determining the areas where the density of Hawthorn species existed and the necessary conditions for calculating crown competition, areas with an area of about 45 ha were determined. In each of these forests with a relatively uniform distribution, the number of 45 Hawthorn stems that had crown overlap with at least one neighbor were identified as central trees. To identify competing trees, the crown overlap method was used, and to quantify the level of competition, the ratio of the crown size of the central tree to the neighbors was used, and to calculate the spatial patterns, the uniform angle index was used. Then information including the distance and azimuth of the neighbors, the height of the central trees, and the size of the diameters of the crowns of the reference trees and competitors were measured. Due to the non-normal distribution of the data based on the Kolmogorov-Smirnov test, the non-parametric Mann-Whitney test was used to compare the means.

Due to the different conditions of the two habitats of Khoshkeroud and Perk, there is an obvious difference in the types and diversity of species in these habitats. In addition, the average distance to effective neighbors in the competition shows a big difference, if other characteristics do not have a big difference. The number of influential neighbors in the BDC index for the Khoshkeroud habitat reaches four neighbors, while in the Perk habitat; there are at most three neighbors with overlapping crowns for the central trees. Meanwhile, more than 80% of the neighbors in the Perk habitat are species other than Hawthorn, while in the Khoshkeroud habitat, other species have allocated a small percentage. In addition to the different admixture, the results of the uniform angle index also indicate the different spatial distribution pattern of Hawthorn species in the two investigated habitats. Despite the difference in admixture and spatial distribution, there is no significant difference between the results of the competition index on the reference trees.

Considering that the Hawthorn genus has been suggested for afforestation of degraded areas in Zagros due to its features such as edible fruit and its ability to be used as a precursor and nurse species, the results of this research can be useful in the field of afforestation and forest cultivation.

Structure of forest ecosystems undergoes changes in the temporal and spatial scale that this changes cause development. Development process is very slow and takes place in long term in this unites. For evaluation of this changes are used density, canopy and mixing amount. Structural attributes, show the ecological diversity and sustainability of forest ecosystems well. We conducted this study to compare changes in the structural attributes of density and canopy with diversity of tree species between different stories, as well the relationship these variables with diversity indices, between two periods of inventory in fixed location and natural environment where external factors have the least proportion in stand development.

Permanent sample plot with an area of 16 ha is located at 770-920 elevation and Northwest and west directions in 32 compartment, district one Shast Kalateh forest. Inventory was carried out using 100 % sampling method with 1 ha sample plot. Differences from 2003 to 2023 quantitative attributes of density, canopy and biodiversity indices were measured with standard method and compared through ANOVA in different stories.

The density of trees in the investigated plot reduced from 306.31 to 275.44 trees per hectare in 2003 and 2023. Only, Beech (Fagus orientalis Lipsky) species increased in density during this period. The highest frequency of tree individual belonged to under story in 2003, but in 2023, it was transferred to middle story. The average crown coverage percentage reduced from 86% to 70%. The highest amount of canopy percentage assigned to middle and upper stories. The average of Shannon's heterogeneity in 2003 in three story was (1.32, 1.29, 0.72) and in 2023 (0.49, 0.53, 0.58) respectively. The Shannon Wiener diversity index provided a better judgment of the species diversity in the investigated plot than other indices.

The investigated plot is a Mixed beech stand in which Beech shade tolerance species is dominant. Mixing more tree species while increasing diversity at different levels will bring stability of forest ecosystems. The results of this research showed that the indices of species diversity are only one of the methods of interpretation and evaluation of forest ecosystems and other characteristics should also be paid attention to. The periodic monitoring of this indices correctly shows changes trend of forest ecosystem. The results of used indices can be basis of evaluation and comparison with similar forest. Keywords: Structure dynamics, Diversity, Tree strata, Mixed beech stand

The majority of fires in Iran's natural areas are anthropogenic, frequently initiated deliberately prior to the rainy season or during periods of peak heat to diminish above-ground biomass and alter land use. Different ecosystems exhibit varying responses to surface fires based on their plant structures. The present study investigates the ecological resistance and resilience behavior against surface fire in four plant communities of shrubland and forest, which are located along an elevational gradient. Furthermore, this research aims to elucidate how grazing, as a disturbance factor, impacts the response of these communities to surface fire.

Focusing on four plant communities with the type species of: Calligonum crinitum, Rhamnus pallasii, Prunus lycioides, and Juniperus excelsa, the study was conducted from 2009 to 2022 in the east of Little Ararat Mountains foothills. These communities were situated along an elevation gradient ranging from 800 to 1900 meters. Each community was divided into two zones, designated as grazed and grazing excluded. Two categories of surface fire occurrences were identified: sites experiencing a single fire event and those with at least two fire events during the study period. Ecological resistance was quantified by comparing vegetation cover before and after the fire, while ecological resilience was assessed by evaluating the rate of recovery towards pre-fire vegetation cover in subsequent years. A general linear model was used to assess the effects of community, disturbances (fire and grazing), and fire frequency. Principal component analysis (PCA) was employed to analyze the relationships among vegetation cover, resistance, resilience, and precipitation.

Calligonum stood out as the community with the lowest resistance but the highest resilience compared to the other study areas. The communities exhibited a distinct gradient in both resistance and resilience that closely aligned with their respective elevations, with the high-altitude Juniperus community at one end of the spectrum and the low-lying Calligonum at the other. The protection status of the lands did not emerge as a significant factor influencing the ecological resistance. However, it did play a key role in determining their resilience levels, with protected areas generally exhibiting greater resilience than their unprotected counterparts, except in the case of the Rhamnus community. The analysis further reveals subtle responses to the frequency of surface fire events: Ecological resistance did not differ significantly between communities that experienced a single fire versus those that were impacted twice, with the notable exceptions of Juniperus and Prunus, which displayed reduced resistance following the second fire. In terms of resilience, a significant decline was observed in the Rhamnus and Prunus communities after the second fire, while the other two communities were able to maintain their resilience levels. Spatial mapping of the fire-affected locations showed a concerning result, with the majority of sampled points situated far from the full recovery isoline, indicating a general lack of ecological sustainability across the study area. Some points within the Prunus and Juniperus communities were found to be closer to this benchmark, suggesting enhanced ecological stability within these communities. In PCA Calligonum emerged as closely associated with resilience, Juniperus with resistance, Rhamnus with vegetation cover, and Prunus with a combination of cover and resistance.

Resilience-enhancing practices like moderate grazing exclusion can improve stability in most communities, but a comprehensive fire management strategy is needed accounting for the distinct fire response patterns across this elevation/vegetation gradient. The Prunus community exhibited the highest overall sustainability, suggesting its suitability for fire-prone environments. Allowing repeated fires can seriously impair long-term resistance and resilience, emphasizing the need for carefully planned fire management.

An accurate estimate of trees height is essential for evaluation of the forest stands volume and above-ground biomass. Also, nonlinear mixed-effects models using random effects with accounting variation between plots, in addition to maintaining the diameter-height relationship, improve the accuracy of the models, and these mixed effects models account for intergroup variation and intragroup variation. Therefore, this study aimed to develop a Height-Diameter relationship Oak (Quercus Castanefolia C.A.M) using nonlinear models and nonlinear mixed-effect models in uneven-aged broad-leaved stands in Golestan province (Shast-kalateh, Jafar-abad and Loveh forestry plan).

We applied a systematic sampling method to collect field data within a 150×200 m network (71 circular plots), and in each plot, tree species, height and diameter at breast height (DBH) of all trees were measured. In the first stage, we used 20 non-linear diameter-height models to select candidate models, then refitted in the second stage using mixed-effect model using dominant height, mean quadratic DBH, Basal area, BAL, stand volume and tree density.

The results of fitting non-linear models for Oak showed that RMSE and R2 are ranged 3-4 meters and 0.4-0.62, respectively. By adding dominant height, mean quadratic DBH, Basal area, BAL, stand volume, and tree density as random effects in the nonlinear mixed-effect method, R2 improved by about 10 to 16%, and the RMSE improved about 0.2- 1 m. By adding

The results showed that using the nonlinear mixed-effect method in comparison with nonlinear regression models improved the accuracy of estimating the height, especially in uneven-aged broadleaved stands. These models can show variability height in stands. Therefore, this approach can be a suitable alternative to estimate tree height, despite few studies conducted in this field. Also, additional research on the use of nonlinear mixed-effect models for all important species of the Hyrcanian forests and other vegetation regions of Iran is necessary. Also, accurate information can be used in forest sustainable management and conservation programs. These models can be used in forest planning.The results showed that using the nonlinear mixed-effect method in comparison with nonlinear regression models improved the accuracy of estimating the height, especially in uneven-aged broadleaved stands. These models can show variability height in stands. Therefore, this approach can be a suitable alternative to estimate tree height, despite few studies conducted in this field. Also, additional research on the use of nonlinear mixed-effect models for all important species of the Hyrcanian forests and other vegetation regions of Iran is necessary. Also, accurate information can be used in forest sustainable management and conservation programs. These models can be used in forest planning.

In Hirkan forests, fine-grained clayey soils have created many problems in construction projects, especially road construction, due to their swelling, and have caused the instability of the road surface and as a result, the pavement has been damaged. Fine-grained soils are problematic due to unfavorable technical properties, especially plastic properties, low permeability, low strength, changes in pore water pressure, changes in volume, texture, chemical properties, and grain structure, and may present complex engineering problems for construction. One of the ways to improve the swelling characteristics of the soil is soil stabilization. Soil stabilization is the use of natural or synthetic additives to improve the mechanical properties of soil. Lime and plant waste are cheap, available and easy to use materials.

In this research, a fixed amount of three percent hydrated lime along with reed plant ash from Phragmites australis with a mixing ratio of three, six, nine and twelve percent to the road bed soil of the study area located in the educational and research forest of Sari University of Agricultural Sciences and Natural Resources - Darabkala was added and then soil mechanics tests including: Atterberg limit, standard compaction test, California bear ratio(CBR) test and uniaxial compressive strength(UCS) test were performed in three repetitions after the processing period. In this research, a constant amount of three percent hydrated lime along with reed ash with a mixing ratio of three, six, nine, and twelve percent was added to the road bed soil of the study area.

The results show that the liquid limit and plasticity index decreased and placticity limit of the soil increased. The maximum dry weight of the samples decreased with the increase of reed ash, and the highest value of 14.52 KN/m3 was recorded and the lowest value of 11.97 KN/m3 was recorded in the soil sample with 3% lime and 12% reed ash. In CBR test, an increasing trend was recorded from 4.9% to 9.7% in the soil sample containing 3% lime and 12% reed ash. The result of the uniaxial compressive strength test in three time periods of 7, 14 and 28 days on the samples shows that the highest value of uniaxial compressive strength is 2.6 Kg/cm2 in the sample containing 3% lime and 6% reed ash after 28 days.

Based on the findings of this research, it was concluded that reed ash can be used as a suitable pozzolanic material to stabilize the bed soil of the forest roads in the study area, and the ratio of three percent lime and six percent ash can be used for 28 days to stabilize the bed clay.

In order to reduce water consumption and producing suitable seedlings, we need have a perfect knowledge of grey mangrove habitat condition in two vegetative periods and their growth replies in the nursery. So, the aim of this study was to investigate the germination percentage and grey mangrove replies to the different levels of light, irrigation and contracted effects of them in two 3-month growth periods in the nursery.

Propagules were collected from 30 healthy mother trees in the summer of 2022 and cultivated in five groups (3 pots in every group) of plastic pots in the coastal nursery (Factorial statistical design). We carried out irrigation regimes (2 times a day, once a day, every other day and every second day) and light treatments in five levels of 0%, 25%, 50%, 75% and 100% on propagules. In order to investigate vegetative replies of seedling to light and irrigation in the two 3-month periods (measurements), collar diameter, height and leaf number (after becoming bi-foliate), were measured using digital caliper and ruler. Growth amounts were calculated from the differences of collar diameter and height in two 3-month periods. Germination percentage was recorded at the initial growth and also leaf area of 6-month seedlings were measured in all treatments and were analyzed using GLM at the level of 95%.

According to the results, germination percentage was higher in two times and daily irrigation as well as 50% and 75% light treatments than that of in the others (P≤0.05). In two times irrigation, leaf area with amount of 22.83 cm2 had a significant difference than the other treatments (P≥0.05). leaf area had the highest amounts in 50%, 0 and 75% light treatments (P≤0.05). All vegetative characteristics in the first 3- month and second 3-month measurement had a different reply to the light and irrigation significantly. Also, all the growth properties of seedling, except for leaf number, were higher in the first 3-month measurement that those of in the second 3-month measurement. In the second 3-month measurement, there were lower differences among treatments. According to the results, in the first 3-month measurement, diameter growth had the highest amount in the irrigation regime of two times a day (0.41 mm), once a day (0.36 mm) and light level of 50% (0.32 mm) while in the second 3-month measurement, diameter growth differences decreased in 50, 25 and 75% light treatment and were in the same groups. Also, in the first 3-month measurement, height growth had the highest amount in the twice a day irrigation treatment with the value of 4.75 cm decreased in the second 3-month measurement (2.41 cm) that was at the same group along with once-a-day irrigation regime (2.21 cm). Height growth in the first 3-monthe measurement had the highest amount at 50% light (4.48cm) and 75% (4.34 cm) light treatment changed in the second 3-month measurement. Unlike the other vegetative characteristics, leaf number was lower in the first 3-month than that of in the second 3-month.

According to the results, grey mangrove seedlings are more sensitive to the light and irrigation at the first 3-month growth and exhibit stronger replies to them. So, providing the suitable irrigation and shade is so important in the initial growth of grey mangrove seedling in the nursery. We must provide 50% light and twice a day irrigation at the first 3-month for grey mangrove seedling in order to grow suitable while we can increase light intensity and also irrigation cycle.