بررسی عوامل موثر بر تنوع زیستی با استفاده از رگرسیون خطی چندگانه در جنگل تحقیقاتی واز

This investigation was carried out in the 2^nd district of Vaz research forest, located in Chamestan city (Mazandaran Province). Inventory grid was designed by a random-systematic method with dimension of 150×200 meter and sample circle plots with radius of 17.84 meter. In each sample, some qualitative and quantitative factors of the trees and site were recorded. In order to recognize the type, total surface average equal to trees basal area in sample plot and TWINSPAN (Two Way Indicator Species Analysis) were used. Forests stands were grouped and classified into seven group types as the following: 1-Fagus-Acer velutinum associated with Carpinus betulus, 2-Fagus-Carpinus associated with Acer cappadocicum, 3-Carpinus-Parrotia associated with Acer velutinum and Acer cappadocicum, 4-Carpinus-Parrotia associated with Acer velutinum, 5-Parrotia-Carpinus associated with Acer velutinum, Alnus subcordata and Diospyros lotus, 6-Alnus associated with Carpinus betulus and Diospyros lotus and 7-Zelkova carpinifolia. Biodiversity of forest trees were tested by two species richness indexes (Simpson, Shannon-Vinner) and evenness indexes (Simpson, Smith-Wilson). Then, all of the types grouped in the same ecological categories were analyzed by T-test. In order to test the effective factors on biodiversity index, multiple linear regression model was used. The results showed that biodiversity in the above types of 1 & 3 were more than 2 & 4 types. Moreover, the effect of evenness index on biodiversity was more, because although the types 1 & 3 had less species but high diversity. The relationship between biodiversity index, physiographical factors with qualitative and quantitative stands characteristic in forest types showed that altitude effect had negative trend on the biodiversity indexes. In addition, previous trend was not linear in all cases. The slop factor caused to increase the mentioned indexes, because the stands are damaged in the low land areas and are eliminated in the high land areas. Totally, biodiversity dependes on different factors, but this research considered some of them, and generally biodiversity phenomenon is dynamic and different in the level of ecological succession.