Trends in Woody Species Diversity Across Different Age Classes of Pinus brutia and Cupressus horizontalis Plantations in Ghapan Region, East of Golestan

Forest degradation influences ecosystem sustainability and reduces plant species diversity. Plantations with coniferous trees in degraded ecosystems help the native species to become established and play a major role in preserving and improving plant diversity. This study aims at measuring and comparing the woody species diversity across different age classes of Pinus brutia and Cupressus horizontalis in Ghapan region, East of Golestan. Plantations were classified in the following age classes: <10, 10-20, and 20-30 years old. Then an area of about 5 ha were chosen for every age class and a number of 30 plots (400 m2) were systematic randomly selected. List of woody species and their density in each sample plot were recorded. Number of woody species was calculated using species richness, expected richness, and Margalef indices; diversity was calculated using Simpson and Shannon-Wiener indices; and evenness was calculated using Camargo and Simpson indices. Analysis of variance showed that the effects of species, age classes, and their interaction were significant. Slicing of interaction effect indicated an outstanding difference of richness, diversity, and evenness indices across the different age classes of Pinus brutia plantations. The difference of expected richness and Margalef, Simpson, and Shannon-Wiener indices were not significant across the different age classes of Cupressus horizontalis plantations. But, the increasing of species richness and evenness of Camargo and Simpson indices were significant across the age classes of <10 and 10–20 years old. Also, it was showed that Pinus brutia plantation is more suitable for establishment and development of woody species than Cupressus horizontalis and therefore it is recommended for future plantations at the study region.