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Forest Structures And Silvicultural Characteristics of Forest-Steppe Transition Zone in Çankırı
The process of changes in the forest structure is determined through the investigation of the forest transition zones. The transition zones clearly reflect the negative effects that emerge when the reduction rate of the forest arising from over-exploitation and destruction, exceeds the rate of regeneration. As a result of recurrent forest destruction, fragmented forest pieces are formed. Determining the dynamics of the transition zone that remain in between the forest and neighbouring sites is of capital importance, in order to clarify whether, the sustainability of these forest areas are secured or the movement of forests progress or regress towards the steppe.
The forests, which take place in the transition zone between Black Sea Region forests and Anatolian steppes, of the region, selected as research area for this thesis study, are replaced by steppe trough south. Thus, cross-sections, initiating from areas where a reduction on the important components of the forest structure (such as density, canopy closure, height, area integrity) to steppe areas where trees disappear and replaced by herbaceous species were taken in northern- southern direction.
The cross-sections were located in Dereçatı, Yakadere and Sarıkaya localities, which take place in the borders of Yapraklı, Sarıkaya and Central forestry enterprises. On each cross section, 3 sample plots as representative for each; forest areas in which the structure started to degraded, transition zone and the contact zones to steppe were sampled. Thus the field studies were conducted on a total of 27 sample plots on 3 cross sections. Stand profiles were prepared via measurements to figure out the stand characteristics at each cross-section. Additionally, to present whether transition zone exhibit differences from forest and steppe areas, plants were sampled during vegetation period. Besides, to expose site conditions, physiographical variables were measured and to determine edaphic variables soil sampling was performed.
According to obtained data, 3 vegetation groups (forest, transition zone and steppe), showing significant differences in the distribution of plant species were determined. The main tree species of forest areas were consist of black pine forests, distributed on elevations between 1250-1400 m with a 0, 70 percentage canopy closure where the canopy stratification is determined as single. In case, the forests located on transition zone, distributed on elevations between 1100-1250 m were consist of degraded black pine forest with a significant shrub layer dominated by Quercus pubescens and Juniperus oxycedrus in which canopy closure degreased up to 0,40 degree. Towards the steppe areas, pines were replaced by bushy species progressively and ended up with steppe vegetation. While, moving on to steppe from the areas that are in contact with forests on the cross section, a decrease in the height of trees, number of trees per hectare, basal area and canopy closure were determined.
The Shannon Wiener diversity index for the areas at the steppes and the transition zones were found to be higher than the forest areas. The diversity index values were negatively correlated with the elevation and coarse fragment content of soil, and otherwise positively correlated with slope, fine soil weight and amounts of carbonate (CaCO₃).
As a result of this research, the current state of the transition zone from forest to steppe have been revealed. Transition zones are ecologically important areas thus, the knowledge of site conditions together with the characteristics of plants that are adopted to this particular areas have a special importance in deciding and determining proper silvicultural methods to practice for protection or restoration of this areas. The stand structure of the areas in question that located in contact with the forests are suitable for both natural regeneration and afforestation practices. However, ecological conditions were not suitable for natural regeneration in the transition zone. It is foreseen that planting the bare areas located in between the oak collectives that are exposed to erosion with native species of the area, would be an appropriate silvicultural treatment.