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

Plant Species Richness (PSR) plays an important role in forest ecosystem functions and services. Despite the fact that Fine Woody Debris (FWD) occupy a large volume of the temperate forest ecosystem in the north of Iran, they have received less attention than Coarse Woody Debries (CWD). FWD is a component of natural forests, in addition to increasing the productivity of forest trees, helping to trees regeneration, maintaining and increasing soil moisture and nutrients, and long-term carbon storage, contribute the enhanced function of newly developing microhabitats with an important function in plant understory richness. Therefore, not paying attention to FWD leads to wrong estimation of the total volume of woody debries and its key role on the performance of forest ecosystems. Therefore, it was considered for current study that Boosted Regression Tree (BRT) machine learning technique used to model the PSR in unmanaged forest stands. For this aim, Oak - hornbeam stand in Loveh forest in the east of Golestan province, Iran was selected for sampling.

For this purpose, 30 sample plots 400 m2 (20 m × 20 m) were set in the study area, and the type and percentage of plant cover was recorded based on the Braun-Blanquet index. In the following, the number of plant species recorded in each sample plot was the basis for calculating species richness. In order to measure the volume of FWD, the alignment of the sides of the sample plot of 400 square meters was used as the basis of calculation. Therefore, in line with the sides of each sample plot and in the form of a linear transect with a total length of 80 meters (equal to the perimeter of each sample plot), FWD intersected with the transect were identified. The names of tree species of each of the FWD is specified, and according to the cross diameter with the transect, the FWD were placed in one of three diameter classes: 1 to 2.5 cm, 2.5 to 4.5 cm, and 4.5 to 7.5 cm. To measure the percentage of soil moisture and organic matter, the soil was taken from the center of each sample to a depth of 15 cm. Soil moisture percentage was obtained by using the difference between wet and dry weight of soil and also the amount of soil organic matter by Walkley-Black method in the laboratory. The gmb package in R programming language was used to fit the boosted regression tree model. This model is one of the methods that helps to improve the performance of a single model by using the combination of multiple models. Therefore, in this method, the combination of two algorithms "regression tree and classification" and "boosting" is used. It should be noted that in this research, in order to reach the optimal number of trees, the number of 1000 was used as the starting point. In this study, the amount of species richness in each plot as the response variable, and the variables of slope percentage, slope aspect, altitude, soil moisture percentage, soil organic matter percentage, average of total volume of fwd, average volume of fwd in decay class 1, average volume of fwd in decay class 2 and the type of fwd were considered as predictor variables.

Based on the results, the initial model fitted in the number of trees 7700 showed the highest accuracy. However, due to the lack of influence of some variables in the model, the variables of slope, slope aspect, altitude, the type of fwd and the average volume of fwd in decay class 1, these variables were excluded from the model based on the deviation changes. And the model was refitted in the optimal number of trees of 7800. Based on the final model of the BRT, the highest amount of species richness was recorded with the increase of soil organic matter to > 2.15% and in a soil moisture percentage >30%. Furthermore, a high amount of FWD from the first diameter class and with the decay class 2 (rotten) led to an increase in plant richness in the studied area. In the present study, the adjusted R squared > 0.99 with the Root Mean Square Error (RMSE) < 0.039 shows the high accuracy of the BRT model.

Although fwd comprise a large part of woody debries in the forests of the north of Iran, no specific place has been considered for it in any of the statistical protocols. This matter has led to the fact that there is no specific estimate of the volume of fwd and its role on the forest ecosystem is neglected. Therefore, this study was conducted with the aim of modeling the effect of this important component on the richness of plant species in a broadleaf stand in Loveh forests of Golestan province. The findings of the research showed that by creating favorable habitat conditions, the fwd increase the abundance of plant species and maintaining this component is important in increasing the organic matter of the forest soil. The high rate of decomposition in fwd compared to cwd causes that while maintaining and increasing the soil moisture, the organic materials in the wood are available to the soil layer in a short period of time. In recent years, some experts in the field of natural resources have emphasized the collection of fwd and their use in cellulose industries. A large part of these opinions has also found a scientific basis in the shadow of the minimization of the volume and role of the fwd and the lack of sufficient information about this very important component. If the findings of this research clearly show that the collection and removal of fwd will have a negative impact on soil moisture and organic matter and thus on the richness of plant species. Conducting similar and additional studies by including soil nutritional variables as well as other plant indicators can significantly help in confirming or rejecting this result

 Biodiversity is one of the most important indicators of the sustainability of forest ecosystems, which is affected by stand mixture. Vegetation composition and diversity data are the most important basic information for recognizing the natural capacity and targeting for the principled management of forest habitats. On the other hand, the correct understanding of the regeneration status in the forest is the most important The components in predicting the future of the forest are in terms of structure and composition of tree elements. The aim of this study was to compare the diversity of herbaceous cover and regeneration in pure beech, pure hornbeam and mixed stands in Darbakola educational and research forest of Sari.

 For this purpose, the inventory was performed by randomized systematic method with grid dimensions of 75 × 100 meters and in each stand, 25 sample plots with an area of 400 square meters were implemented and the diameter and height characteristics of the trees were collected. To study biodiversity, names of herbaceous species and the type and number of regenerations were collected in 2×2 meter micro sample plots in four quarters and the center of the sample plots in two stages (May and September). Diversity indices of Shannon and Simpson richness indices of Margalf and Manhenick and evenness Owens and Burger Parker diversity indices were used to study the biodiversity of regenerations and grass cover. One-way analysis of variance was used to compare quantitative characteristics of biomass and biodiversity between habitats and to compare the means by SNK test in SAS software environment and to draw graphs using Excel-2010 software. Past software was used to study biodiversity.

 The results of the present study showed a higher density of beech regeneration in all three studied stands. The highest total number of regeneration was observed in mixed habitat (4040). The highest indices of diversity, richness and regeneration evenness were observed in pure hornbeam and the lowest in pure beech. Regarding herbaceous cover, no significant difference was observed between diversity indices among different stands, while the average of these indices was higher at the beginning of the growing season than at the end of the growing season. Therefore, stand mixture has more tangible effects on regeneration diversity than herbaceous cover, and herbaceous cover diversity is more affected by the during the growing season than type of stand mixture.

 Based on the results of the present study, the future composition of the studied populations will be affected by the dominant species of beech. Also, due to the species diversity in the mixed habitat, the highest total number of regeneration and forest density will be related to this stand. Regarding the grass cover, the higher average of diversity indices at the beginning of the growing season than at the end of the growth season, indicates that the environmental conditions are better in terms of temperature and soil moisture in this season. Therefore, mixing has more noticeable effects on regenerative diversity than grass cover and the difference in grass cover diversity is more affected by the time period of the growing season.

The aim of this study was to investigate the woody and herbal frequency and species diversity in the mountain forests of northern Iran, Poudeh village of Roodsar, over time and as a result of traditional exclosure of these forests.

The study area is located in the forests of Poudeh village, Roodsar, Guilan province. According to the traditions of the region, people protected the spots of the destroyed forest areas near their hazelnut gardens for flood prevention and personal exploitation. They do this by using stones and placing shrubs on it, or using wooden stems and barbed wires. In this area, there are many of exclosure forest spots that have been protected and enclosed by the native people. Three exclosure forest spots were selected for this study. For this purpose, plots with different conservation history including low-term enclosed forest area (Less than 40 years), middle-term enclosed forest area (More than 40 years) and reference forest area were selected and the indicators of relative frequency, relative ecological importance value and species diversity were calculated.

The results showed that with increasing the duration of forest protection, the relative abundance of beech in both strata levels increased the relative abundance of hornbeam and the amount of species diversity also decreased. The highest and lowest differences in relative abundance of beech between the two strata were observed in reference forest area and low-term enclosed forest area respectively. The ratio between the abundance of beech in the upper story to the understory for low-term enclosed forest area and middle-term enclosed forest area was 1.18 and 1.24, respectively. In the control area where the highest relative abundance of beech species (80%) was recorded in the upper floor (tree), there is a moderate relationship between the two floors (r = 0.61, p <0.001) and in short-term protection, this relationship is significant (r = 0.72, p <0.001). In the middle-term enclosed forest area (more than 40 years) with increasing the relative abundance of beech in the upper story, its relative abundance in the understory also increased significantly (r = 0.88, p<0.001).

The process of species change is a complex and time-consuming process. The results show in the evolution of the stand structure in the affected areas, medium-term protection can facilitate the formation of understory. It is recommended that middle-term enclosed forest area along with silvicultural treatment be applied to formation of understory.