High altitude zones constitute a special world, with their own complex of semi-alternated harsh atmosphere, low air temperature, high atmosphere aridity marking a sharp contrast between the microclimate and macroclimate.

The Himalayan high-altitude physical features are remarkable in influencing and modifying the climate and vegetation not any in Nepal and India, but also the entire middle Asia. With a steady increase in altitude, the environment also changes gradually and finally modifies directly or indirectly several other factors and their interaction with man and animals. The average conditions of life above the timber line in the Alps are perhaps magnified tenfold in the Himalaya (Mani, 1962).

The snowline limits of the Himalaya vary on different slopes primarily due to differences in latitudes. The snowline is lower in Eastern Himalaya (e.g. Thimpu 27 degree N). In western Himalaya in summer it is between 4500 and 5500m, but in winter it comes down to 2450m and 2750m.

The following factors are of focal interest in the environment above the timber line:

Low Air Pressure: With the increase in altitude, the atmospheric pressure falls and the density of the air is also reduced. However, the pressure fall is not uniform in all levels. The atmospheric pressure above the timber line in NW Himalaya are less than two thirds that at sea level, only half that at sea level at an altitude of above 6000m and at higher altitude the rarefaction of air is higher (Mani, 1962).

The oxygen tension at the timber line is about 68% that of the air at sea level and at 6000m altitude in NW Himalaya only about 45%. The tensions commonly produced in warm-blooded animals are not only due to oxygen deficiency, but also in great part to escape of bubbles of Nitrogen in the blood stream (Mani, 1962).

Cold temperature: At higher altitudes, the cold is intense due to low density of air and its high transparency. These factors are readily permits the sun’s rays to pass through without the air itself being warmed up as denser air near sea level. Due to thinner air the solar radiation is intense causing sunstroke during the day and frostbite at night. For every 1000m rise in altitude the temperature falls about 6.2 degrees centigrade, but at 4000m the lapse rate becomes abrupt.

Atmospheric Aridity: the air high altitude is relatively dry and pronounced aridity occurs in spite of thick ice and snow cover. This is mainly due to the fact that with an increase in altitude the air pressure decreases resulting in lowering of water vapor tension in the atmosphere. Air contains 55% more water vapor at an elevation of 4500m than it would at sea level at the same temperature (Mani, 1962).

High Wind Velocity: With a rise in altitude, the wind velocity increases for which reason region above altitude of 5000m generally regions of strong wind. It has been observed that at high altitudes the constant violent wind contributes for more misery to human beings than the low oxygen tension at the great atmospheric cold (Mani, 1962).

High wind velocity: Since the air at high altitude is semi-rarefied and dry it can offer no protection for which the intensity of solar radiation with UV ray increases with altitude. According to Mani (1962), rough estimations have shown that mean total radiation falling above timber line con not in any case be less than 20 or 30 times as great as in Taiga zone.

In NW Himalaya, despite the general aridity of atmosphere, snow cover is not considerable. Zone above 3000m and below permanent snowline is generally under winter cover for 8-9 months in the year. On the while, average snow cover is proportionately heavier in Eastern and Kumoan Himalaya than in NW Himalaya. With increase in latitude above 4500m there is opaque snow (cover) and ice (transparent snow).

Snow cover is of great ecological importance to wildlife, especially nival insects. It provides favorable conditions for wildlife exposed to semi rarefied air and filtered solar radiation. Insect life possible at higher biotopes because of snow cores that serves as effective protective blanket for nival insects during hibernation (Mani, 1962). Another significant fact is that enormous quantities of solar heat are absorbed as latent heat by melting snow. Thus, snow cover contributes to high aridity of the atmosphere, especially during winter.

Local condition and Microclimate: This factor is primary very essential for only small elements of wildlife especially particular insects. The climate of immediate surroundings of insects is really a micro climate or the climate of square and cubic centimeter and still smaller spaces on or in soil, under stones, rocks crevices, in ground cavities, under snow, under vegetation mats and other similar situations. This factor of microclimate is more or less greatly influenced by complex interactions of reduced atmospheric pressure, cold and aridity and by local condition.

Ecological Condition in High Altitude Valleys: The specialized high altitude climatic complex in the Himalayas is governed by a major longitudinal valley above the timber line running parallel to mountain ranges on either side of them.

Biotic Factors: Environment in general and the microclimate in particular above timber line are greatly influenced by a number of biotic factors. The main specialized biotic features of the high altitude biotopes are the absence of trees and restriction of growth period of even the scanty, characteristically low-matted dwarf vegetation through the all-too-short summer.