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ŠUMARSKI LIST 9-10/2022 str. 47     <-- 47 -->        PDF

richness in older stands. Also, Behera and Misra (2006) did not find a significant difference among the stands in terms of the Shannon diversity index in their study on the analysis of herbaceous vegetation in four different stands consisting of broad-leaved species. On the other hand, Pitkanen (1997) reported that species richness is higher in young stands and in the fertile areas, and also, albeit at a lesser level, the basal area, crown cover and species mixing ratio in trees are also influential on this. Contrary to this, Zhu et al. (2009) indicated that species diversity was greatest in the mid-successional stage, which appears similar to our results. This can be interpreted as a peaked (n-shaped) diversity - age (or diameter) class relationship, while Gosper et al. (2013) found a U-shaped relationship between diversity and time since fire. In this study, based on the gamma diversity level, relatively young stands (GB) have the poorest diversity in terms of the Simpson and Shannon indices. They peak in GC stands and then decrease in GA stands, which represent the older (thicker) areas.
In the statistical analyses based on the diversity indices calculated at the alpha diversity level, there were no significant differences in terms of the Simpson diversity index in fir stands according to stand type, aspect and observation period. However, stand type-aspect interaction had a significant effect on diversity. Since the fir stands have a vertically layered structure, it is assumed that the more stable and similar microclimatic conditions in the stand are responsible for this. On the other hand, while there were no significant differences in terms of stand type and aspect among the diversity values found according to the Shannon index, it was seen that observation period was effective and that the diversity decreased periodically from June to September. It is thought that with the beginning of the vegetation period, a large number of plants began to appear, but that later on, due to both the climatic conditions and the life span of the plants, they disappeared from the area. The Shannon diversity indices in fir stands (except GB) on the southern aspects had higher values than the northern aspects. Graae and Heskjaer (1997) stated that soil moisture is influential on vegetation. Although no soil moisture measurements were carried out in this study, it is thought that favorable site conditions for diversified species under the vertical and thick crown layer of fir stands can be formed on south aspects with more sunlight. Since the study area is adjacent to the steppe transition zone and the partial drought seen in the summer months affects the distribution of plants in terms of species and quantity, the decrease in diversity from June to September can be explained by the fact that some species disappear due to summer drought or their short vegetation period.
Periodic differences in vegetative diversity indices or plant richness may also have resulted from the sampling method used. As a matter of fact, the quadrate (frame) samples taken from the stands were not at the same place in every period of observation, and conscious systematic shifts were made in order to better represent the stands. For this reason, since the plants are not homogeneously distributed in the forest stand area, the plants observed in one place in the stand might not be seen in other areas around. So, some plants may not have coincided with the quadrates and may have not been evaluated as to whether they exist in the area. Although this type of sampling is advantageous in terms of revealing the plant richness of the stands, it may lead to the fact that sparse plants in the area cannot be sampled every time, and that therefore, they are considered as dried out and lost from the environment.
CONCLUSION
ZAKLJUČAK
Only the developmental stages of stand types change under normal conditions while forests are being managed. Therefore, knowing the plant diversity in terms of stand types will help to predict the future vegetative diversity depending on the change of stand types over time. With the present study, the vegetative diversity values of the stands for fir were revealed. From this, diversity can be calculated for different forest areas and for the entire forest. In this way, vegetative diversity can be determined numerically and steps can be taken towards its integration into forest planning and management.
Since fully stocked stands (having a closure of more than 70%) will be formed under successful forest management conditions, this study has been limited to this type of stand. It is necessary to present the vegetative diversity numerically for different closure situations, even for different site and elevation situations and in different tree species. In this way, comparisons can be made in terms of tree species and stand types by using vegetative diversity indices such as site class, which expresses the wood yield strength of a habitat.
ACKNOWLEDGEMENTS: This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK), with Project ID: TOVAG-115O958. We also thank to Ahmet Ayteğin and Yusuf Ercan for their collaboration on field.
DECLARATIONS: We confirm that the manuscript is the authors’ original work and it has not received prior publication and is not under consideration for publication elsewhere.
FUNDING: This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK, Project ID: TOVAG-115O958).
CONFLICTS OF INTEREST/COMPETING INTERESTS: The authors declare that they have no known competing or conflicts of interests.