جستجوی مقالات مرتبط با کلیدواژه « species richness » در نشریات گروه « جنگلداری »

The importance of canopy gaps in the natural forests as a part of the development processes of the stand is not hidden for ecologists. According to the gap size, different changes will be made in the microclimate of the region, which will ultimately cause the preservation and dynamics of the structure of these stands. In close to nature silviculture, while recognizing natural disturbance regimes, efforts are made to use them as a model in sustainable forest management. The purpose of applying management based on imitation is to preserve, sustain and promote species diversity. Mimicking natural disturbances has shown different effects in managed forests. In some cases, more suitable conditions have been created for the growth of seedlings and the increase of species diversity. But in some cases, management actions were either ineffective or caused negative effects. Therefore, optimal management strategies should be based on a deep assessment of forest stands, which will provide useful data in this research.

In this research, in order to determine the possible changes due to the implementation of management, the indices of diversity of herbaceous species in the gaps of a single-selection managed and a control (non-managed) beech forest were compared in district one of Livan and Banafshtape forestry projects in Golestan province. For this purpose, after identifying and measuring the surface of all gaps, in each forest, they were classified into three groups: small (less than 200 m2), medium (200 to 500 m2) and large (more than 500 m2) and Three replicates from each group were randomly analyzed. The type and percentage of cover of all herbaceous plant species were recorded in five sample plots (one in the center and the others in the four main geographical directions of each gap). Harvesting of herbaceous species of the forest floor was done using the modified Braun-Blanquet scale. To evaluate the richness of plant species in the studied habitats, the number of plant species in each sample plot was used. Biodiversity was investigated and compared in the surveyed plots using Simpson and Shannon-Weiner diversity indices and for uniformity, Paylo's evenness index was used. The comparison of the average indices between the two compartments was done using independent t and Mann-Whitney tests, and in the gaps with different sizes, Tukey and Kruskal-Wallis tests were performed. The cluster analysis method was used to group the gaps with different sizes.

In this research, 25 herbaceous species were identified in the two investigated areas. 17 and 21 herbaceous species were identified in the gaps of the managed and unmanaged plots, respectively. Some herbaceous species were present in only one of the gap size classes, but others were identified in all three gap size classes. The results showed that there is not a significant difference between the indicators of richness (7.2±0.7 vs. 8.3±0.6), evenness (0.6±0.05 vs. 0.5±0.04), Shannon (1.1±0.1 vs. 1.1±0.09) and Simpson (0.5±0.06 vs. 0.5±0.05) between the managed and unmanaged compartments, respectively. Also, the cluster analysis showed that in terms of herbaceous cover, the gaps of the managed area cannot be separated from the unmanaged area. It is interesting to note that the species richness in the managed stand with small gap size (less than 500 m2) was significantly lower than other gaps in this stand. There was no significant difference between the other investigated indicators between the different sizes of the gaps in the managed and unmanaged compartments.

The harvesting of forest trees in the form of management can change the environmental conditions such as light and temperature in the created microclimate by creating gaps that are larger or smaller than the natural size and thus cause a change in the diversity of plant species. Although the results of some researchers showed that forest management can increase the diversity of tree species compared to unmanaged forests, but in the upcoming research, the management based on the single selection method after a period of 10 years had a significant effect on the composition and there was no diversity of herbaceous cover in the created gaps. Of course, it is necessary to remember that the type of forest management can affect biodiversity on a regional scale without causing a change on a local scale. Also, the effect of forest management on plant diversity depends on biotic and abiotic conditions and forest management approaches. The results of some studies have shown that the abundance of herbaceous species in the forest floor depends on the abundance of tree species. Therefore, in a pure forest where the number of tree species is less than in a mixed forest, the low abundance of floor covering species is not far from expected. In any case, the accurate evaluation of the effects of applied management requires more studies of the floristic and soil characteristics of the gaps in different periods of time after the implementation of cuttings.

In order to achieve the goals of sustainable forest management, single tree selection method was implemented in Hyrcanian forests. But it is not clear what effect the implementation of this method has on the reproductive characteristics of trees in forest stands. For this purpose, we compared the quantitative and qualitative characteristics of beech seedlings and saplings in the gaps of two managed and unmanaged compartments. Expanded gaps with an area > 100 m2 were identified in the two compartments. Except of density and richness of tree species, the average of other quantitative characteristics of saplings was significantly (ρ<0.05) in the unmanaged than the managed compartment. While the highest frequency of healthy and unforked seedlings was observed in the managed compartment (ρ<0.05). Species richness in both compartments showed a low value. Considering that one of the goals of sustainable forest management is to increase the diversity of trees and adapt to the ecosystem, it is necessary to pay attention to the promotion of the diversity and richness of tree species in the future management plans in the studied areas.

The symbiosis of mycorrhizal fungi with plant roots is one of the most important symbiotic relationships in soil. In this study, biodiversity and symbiosis of arbuscular mycorrhizal fungi (AMF) with Amygdalus arabica Olivier, A. lycioides Spach, A. elaeagnifolia Spach and A. orientalis Mill. were investigated in three sites in Ilam province. After extracting soil samples from a depth of 0-30 cm, spores of mycorrhizal fungi were separated by the wet sieving method and the fungi were identified based on the morphological characteristics of the spores. The results revealed 34 different species of AMF belonging to 10 different genera. The highest biodiversity of fungi (28 species) was observed in A. arabica. In addition, 19 AMF species in A. elaeagnifolia, 25 in A. orientalis and 26 in A. Lycioides were identified. Moreover, the lomus with 49% and G. nanolumen with 21% were of the highest relative frequency of AMF genus and species among all the tree species, respectively. Significant differences were observed between Amygdalus species in terms of spore density, species richness and Shannon–Wiener diversity index of AMF. So that most of the three indices were observed in A. arabica. Also, spore density showed a negative correlation with soil sand percentage and phosphorus amount, as well as a positive correlation with soil clay percentage.

The uprooting of large trees leads to the formation of depressions in the root area and plate-like features next to it, which are referred to as pit and mound microtopography. For studying the plant species diversity in these positions, Deldareh forests, Nowshahr was selected. For this purpose, all pits and mounds were identified in 70 ha of the study area. The presence and frequency of plant species were recorded on these positions and each pit and mound was compared with a plot 2×4m located 25m far from these positions. Firs, to analyze the plant species, biodiversity indices were computed. Then, to study SIV in each position, relative frequency, relative density, and relative dominance were also calculated. The results indicated all indices of diversity and richness had significant difference between positions, except the Simpson one. Accordingly, in the comparison between the pit and control positions, the control position, and between the control and mound positions, the mound position had higher values of the indices. Also, neither of both evenness indices showed a significant difference between different positions. The study of the SIV also showed that in all positions, there is a normal logarithmic curve. The findings of the present study show the high ability of pit and mound effects on increasing the species richness in forest stands. Therefore, the design of silviculture methods should be such that by maintaining and increasing the thickn trees, a certain number of pit and mound microtopography remains per unit area.

In order to investigate the effect of traditional utilization on the diversity and composition of woody species diversity in the western oak forest, two disturbed and less disturbed stands were selected with similar physiographic and floristic conditions. Therefore, 30 circularly shape plots with 1000 m2 surface area were established based on random-systematic sampling with 50×50 m network dimensions. In each sample plot, the frequency and type of woody species were recorded in the prepared sheets of inventory. The average Margalaf species richness indices, Pielo evenness, Shannon-Weiner and Simpson species diversity were calculated in each plot and normalized by Kolmogorov-Smirnov test. To test the significance of the difference between the mean of indices, t-student test was used for normal data and Mann-Whitney U test for abnormal data. Detrended Correspondence Analysis (DCA) was used for ordination of the woody species samples. The results of the study showed that the means of richness and diversity indices in the disturbed stand were significantly lower than in the less disturbed stand; however, the mean of evenness index did not show any statistically significant differences between two stands. High correlation of first axis of DCA proves the importance of destructive factors, such as cutting, branching, frequency of copping, grazing, and qualitative factors, such as basal area and number of trees. These factors plays an important role in differentiation of the forest stands.

After over five decades of establishing plantations in Chitgar Forest Park in Tehran, no study has yet been carried out on the soil seed bank in this region. This study aimed to investigate the composition of above-ground vegetation and soil seed bank. Therefore, 30 releves were established with 450m2 area each. For sampling soil seed bank within each releve, two samples were randomly collected by hammering a 400 cm2 into the soil to a depth of 5-10. Following this, the soil seed bank was estimated using the seedling emergence method. All in all there were 22 families and 62 species in above-ground vegetation and 29 species from 13 families were identified in the seed bank. All species in the soil seed bank were present in the above-ground vegetation. The results also showed that the above-ground vegetation included a higher species richness than the soil seed bank. High similarity of the soil seed bank and above-ground vegetation showed that the soil seed bank has the potential for reclamation of above-ground vegetation, but the lack of tree species in the soil seed bank hampers the practicability of the reforestation with an emphasis on seed germination of the soil seed bank. Furthermore, because of the structure and the type of the previous above-ground vegetation across the test site, the natural tendency of the area is towards the non-forest species.

In this research, regeneration diversity of species in protected and non-protected areas of Arasbaran forests were compared in species richness, evenness and diversity indices. First, two forest stands with similar floristic and physiognomic characteristics were selected using aerial photographs acquired in 1986 (1:20000 scale). Regeneration of tree species were recorded in 77 0.01 ha circle plots using 250 × 250 m grid size in the both protected and non protected areas. The mean of diversity indices were computed in both areas and t-test was used to show significant differences. The results indicated that the computed species diversity indices are as follows: mean species richness index: 6.69 and 5.39, Shannon evenness index: 0.87 and 0.76,Shannondiversity index: 1.64 and 1.23, simpson index: 0.76 and 0.61 in protected and non protected areas, respectively. So the protection increase regeneration diversity in Arasbaran forest stands. Therefore, prevention of livestock grazing and irregular tree cutting in the degraded forest stands can be suggested as a suitable approach for natural restoration and increasing plant diversity.

Using species richness, Shannon-Wiener diversity and Simpson indices, diversity of woody species in protected and non protected areas of Arasbaran forests were studied and compared in this research. Two forest stands with similar floristic and physiognomic situation were selected by using of aerial photographs of 1968 with 1:20000 scale. Then tree species were recorded in 92 transects, each with 30 meter lengths, which was established in 150×300 m grid in the forest stands of the protected area and in a similar way in the non protected area. For data analysis, the means of different diversity indices were calculated and t-test was used to test all indices means differences in the studied areas. Results showed that species richness, evenness and plant diversity indices were significantly increased in the protected area. One can conclude that preservation-based management caused increasing of the woody plant diversity in Arasbaran forests. Therefore, preventing against livestock grazing in the forest stands and uncontrolled tree cutting in the destroyed forest stands could be introduced as a suitable approach for natural restoration and increasing of plant diversity.