اسحاق عطایی

Altitudinal gradient is effective on biodiversity indices. Tiremrud Basin (Watershed 32) were investigated to find the relationship of plant biodiversity indices. Data were collected by transect method with at least one sample plot per align lines with 50 m interval and 44 plots in total. In each sample plot the total number of tree species was recorded. Micro plots (5*2 m2) in four corners and center of each plot were determined and recorded based on the Brown-Blanket cover percentage and frequency of vegetative elements for sampling of herbs. Bilateral index species analysis was used to introduce the communities of the region. The results showed that the four ecological groups of the region had an average altitude of 2070, 1236, 924 and 375 meters above sea level and an average slope of 43, 50, 40 and 59 percent (no significant difference). Comparison of ecological groups showed that these groups have significant differences in terms of plant biodiversity indicators. Examination of Shannon-Wiener and Simpson-Pilo species diversity index values ​​showed that the first, fourth and two second and third ecological groups have maximum, minimum and average values ​​of species diversity indices, respectively. Meanwhile, in terms of Pilo uniformity index, the first and third groups, along with the second and fourth groups, have the maximum, minimum and average uniformity index values, respectively. In terms of species richness index, the first, third, second and fourth groups are ranked respectively.   Altitudinal gradient is effective on biodiversity indices. Tiremrud Basin (Watershed 32) were investigated to find the relationship of plant biodiversity indices. Data were collected by transect method with at least one sample plot per align lines with 50 m interval and 44 plots in total. In each sample plot the total number of tree species was recorded. Micro plots (5*2 m2) in four corners and center of each plot were determined and recorded based on the Brown-Blanket cover percentage and frequency of vegetative elements for sampling of herbs. Bilateral index species analysis was used to introduce the communities of the region. The results showed that the four ecological groups of the region had an average altitude of 2070, 1236, 924 and 375 meters above sea level and an average slope of 43, 50, 40 and 59 percent (no significant difference). Comparison of ecological groups showed that these groups have significant differences in terms of plant biodiversity indicators. Examination of Shannon-Wiener and Simpson-Pilo species diversity index values ​​showed that the first, fourth and two second and third ecological groups have maximum, minimum and average values ​​of species diversity indices, respectively. Meanwhile, in terms of Pilo uniformity index, the first and third groups, along with the second and fourth groups, have the maximum, minimum and average uniformity index values, respectively. In terms of species richness index, the first, third, second and fourth groups are ranked respectively.

A comprehensive understanding of plant associations, especially in transition areas can be achieved by identification of vegetation and study of relationships between plant species and environment. Borders of ecotones and forest communities (Tiremrud basin in the southern part of Tonekabon, Iran) were found based on environmental factors such as elevation, slope and changes in floristic patterns. Totally, 44 plots (20 × 20 m) were collected by the transect method with at least one sample plot per contour line and 50 m interval. A total number of tree species was recorded separately in each sample plot. Herbaceous species were sampled based on the Brown-Blanket cover percentage and frequency of vegetative elements by 5 × 2 m2</sup> micro plots in four corners and centre of each main plot. Four ecological groups were identified on altitudes 2070, 1236, 924, and 375 m above sea level with mean slopes of 43, 50, 40, and 59%, respectively. The first and fourth ecological groups were at the highest and the lowest elevations, respectively, while the second and third ones in the middle of the two groups. A comparison of ecological groups in terms of plant biodiversity indicated significant differences altogether. In terms of species diversity indices, Shannon-Wiener and Simpson-Pilo ​​revealed that the first, fourth, and second ecological groups had maximum, minimum, and average values, respectively. According to findings of this study, ecological groups had significant differences in terms of altitude factor.