The main target of the author in this article is to introduce important influence of forests preservation on the biodiversity. There are a lot of complicated problems that are encountered today with increasing population of urban areas and excessive demand for finding shelters and places of rest and recreations. By increasing the educated population and needs of government and public sectors for preparing enough income to pay unforeseen and foreseen expenditures for these people, forests and rangelands are considered as a gift of god. That is why, over the years, regardless of the value added of forests in preserving water, soil, air, and plant and animal biodiversity, forests have been exploited, and with a set of factors mentioned in this article, conservation and preservation of biodiversity has been lost. In this article, it has been attempted to describe the plant species as the first indices of the forests and their classification in relation to the problems of forest degradation.
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