Because of the altitude that vary right from sea level to summits that touch the skies ,the flora and fauna naturally covers a wide spectrum. Nowhere in the world in such a small area can one find flora and fauna of all varieties - Tropical to the Alpines. Sikkim's botanical and zoological richness is awe- inspiring, boasting of more than 4000 species of plants and 30% of all the birds found in the Indian sub-continent . No wonder Sikkim has been a dream of naturalists. Dr. J. Hooker during the middle of the last century surveyed in the detail the botanical wealth in Sikkim and his findings were embodied in the publication 'Himalayan Journal' that is still considered as an authoritative document. Dr. Salim Ali an ornithologist has given a detailed account on birds in his book 'The birds of Sikkim'. Besides these there are many books available on the flora & fauna of sikkim.
Plants:

The lowlands in the south, 800'to 5000', experience a tropical climate; lush vegetation such as figs, laurel, Sal trees and bamboos have been cleared in some areas for farming. The temperate forest of oak, chestnut, maple, birch, alder, magnolia and silver fir dominates between 5000; and 13000. Above 13000, is the alpine zone where juniper, cypresses and rhododendrons grow. The perpetual snowline lies at 16000'. Luxuriant forests cover 36% of the land, more than 4000 species of plant have been recorded in Sikkim. Over 600 species of orchids grow in Sikkim, Epiphytal and terresterial types, in the tropical and temperate zones. 35 species of rhododendrons grow in temperate and alpine regions, their flowering from May to August colours hillsides.

Animals
Amongst the mammals of Sikkim are the rare Snow Leopard, Himalayan Black Bear, Red panda, Musk Deer and Blue Sheep.

Birdlife is abundant with Giant Lammergeier, Vultures, Eagles, Whistling Thursh, Minivets, Bulbuls and Pheasants among the 550 species to be seen in Sikkim.