The effect of refforestation on some soil properties and understory vegetation in Kolt forests of Mazandaran province

Reforestation stands can effect on diversity of plant species and soil characteristics of an area. In this study, the effects of 25-year-old reforestation stands with Acer velutinum Bioss., Alnus subcordata C. A. M. and Cupressus sempervirens species on plant biodiversity, understory vegetation and some physico-chemical of soil properties were studied compared with natural forest (Carpinus betulus and Fagus orientalis) in the Kolet forests of Mazandaran province.

In each reforested stands and natural forest, ten plots (2020 meters) were selectively sampled in transects which were 100-m stretches systematically. Then, the list of all herbaceous species and their abundance (cover percentage) was recorded. Also, in each sample plot, a soil sample was taken from the four corners and its center at a depth of 0-15 cm, then these samples were mixed together and a composite sample were taken to study the physic-chemical characteristics of the soil (bulk density, soil texture, acidity, electrical conductivity, organic carbon, total nitrogen, absorbable phosphorus and potassium). The indices of richness (Margalf and Menhenic), evenness (Shannon-Wiener) and diversity (Simpson and Shannon-Wiener) were also studied.

The results showed that reforested stands were significantly different from natural forest (control) in terms of soil reaction rate (P <0.05), potassium, clay and relative soil moisture (P <0.01). Also, the amount of acidity and absorbable potassium reaction in Acer velutinum Bioss mass (6.99, 904.51 mg kg-1) was the highest and lowest in natural mass (6.18, 557.57 mg / kg). It was observed that the highest percentage of clay in natural mass (43.57%) and the lowest percentage in Alnus subcordata mass (39.32%) and the relative moisture in Acer velutinum Bioss mass (40.78%) was the highest and It has the lowest value in Cupressus sempervirens mass (20.12%). But other soil variables did not show significant differences with natural forest. Margalf and Manhenic richness in the four reforestation stands was significantly different (P <0.05). The diversity indices (Simpson, 0.58 and Shannon-Wiener, 1.26) and the richness (Margalf, 2.00 and Mannick, 1.57) were higher in the natural forest than four reforestation stands and the evenness index (Shannon-Wiener, 0.82) showed the highest value in the Cupressus sempervirens stand. Multiple regression of soil variables with the first and second axes of DCA analysis indicates that only potassium has been effective in the separation and differentiation of vegetation in the area and the four studied stands can be distinguished in terms of understory vegetation.

In general, the results of the present study showed that the richness indices of understory vegetation species as well as the characteristics of moisture, soil reaction and adsorbable potassium changed under the influence of reforestation and according to DCA analysis is the most important component in mass segregation. Potassium is an absorbable plant. Also, the study of biodiversity indices showed that the diversity and richness indices were higher due to the fusion of species in the natural massif (Carpinus betulus and Fagus orientalis) compared to the reforested massifs of conifers (Cupressus sempervirens). In other words, the results show a greater protective role of broadleaf stands (Acer velutinum Bioss and Alnus subcordata C.A.M) and natural stands (Carpinus betulus and Fagus orientalis) than needle stands (Cupressus sempervirens) for richness and diversity of understory vegetation species and sustainable maintenance of communities the underside is in the Kolet area.