The Himalaya is not only the tallest mountain range in the world, but also perhaps one of the youngest. This is an important reason for encountering the diversity of species that we find here. Although fossil records from across the Himalaya  suggest that several million years ago, the land was situated below the ocean, the Himalaya have never experienced inundation after their creation unlike most other  areas on the earth. Apart from glaciation on a smaller scale on the snow peaks themselves, there is no evidence of the mass-scale influence of continental glaciation on the entire range, at least not in the last several million years. The lack of disturbance has enabled speciation to occur, while at the same time allowing the older species to survive. This has furthered the species diversity found here, not only of plant forms, but also of birds, animals and insects.

The extreme diversity in the number of species of Himalayan flora may be attributed to several other factors, such as altitude which is by far one of the most influential in terms of the composition of Himalayan flora and a basic reason for its diversity. In no other place on earth, though perhaps on a slightly smaller scale in the Andes of South America, does one experience such a range in altitudes, often within relatively short distances, as in the Himalaya. In several places, the snow peaks rise more than 10,000 vertical feet from the bottom of the valley floor. Such a drastic altitudinal range supports numerous levels of distinct (and on a smaller scale less distinct) biological microhabitats as a result of the changes in vegetation brought about by the altitudinal difference.

There can be a wide variation in the micro-climates found within any one valley, as one ascends to higher altitudes. It is also possible to experience climatic changes between two locations at the same altitude and within the same valley,  just a short distance apart and varying only in aspect (the direction that the slope faces). This could be caused by the effects of mountain breezes coming down from the snows that are capable of heavily influencing the vegetation on slopes that are prone to these breezes.

On the other hand, sheltered caves and some south facing locations could be completely devoid of the influence of mountain breezes and harbour an entirely different selection of plant species. Yet another contributing factor could   be   that   north-facing   slopes  are snowed-over for a longer period each year as they are exposed to less sunshine each day. This would enable only the more hardy species to frequent these faces, while the south-facing slopes are exposed to greater lengths of sunshine and can harbour  less hardy plant forms or plants from lower altitudes. Hence, it is possible within a few hours' trek to cross over from one side of a mountain to the other side, and in the process encounter a vastly different vegetation cover.

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