The ecology of the Himalayas changes based on climate, rainfall, altitude, and soil types. The climate changes from tropical near the bottom of the mountains to permanent ice and snow at the highest points. Yearly rainfall increases from west to east on the southern side of the range. These different types of climate, altitude, rainfall, and soil help many different plant and animal species live there, such as the Nepal gray langur (Semnopithecus schistaceus).

Lowland forests

The Indo-Gangetic Plain, located at the foot of mountains and fed by the Indus and Ganges-Brahmaputra river systems, has different types of vegetation depending on rainfall. In the dry northwest, thorn scrub forests grow in the plains of Pakistan and the Indian Punjab. To the east, moist deciduous forests cover the Upper Gangetic Plains in Uttarakhand and Uttar Pradesh, and the Lower Gangetic Plains in Bihar and West Bengal. These forests are monsoon forests, with trees that lose their leaves during the dry season. In the wetter Brahmaputra Valley, semi-evergreen forests are found in Assam. Additionally, subtropical moist forests grow in the lower valleys of the Margalla Hills.

The Terai belt

Above the floodplain is the Terai strip, a wet area with sandy and clay soils that become moist seasonally. The Terai receives more rainfall than the floodplain, and rivers flowing down from the Himalayas slow and spread out in the flatter Terai region. During the monsoon season, these rivers deposit rich silt, which then disappears during the dry season. The Terai has a high water table because groundwater seeps down from nearby areas. The center of the Terai belt includes the Terai-Duar savanna and grasslands, a mix of grasslands, savannas, deciduous and evergreen forests, and some of the world's tallest grasslands. The grasslands of the Terai belt are home to the Indian rhinoceros (Rhinoceros unicornis).

Bhabhar belt

Above the Terai belt is a higher area called the Bhabhar. This region has soils that are full of holes and rocks, formed from material carried down by water from the mountains. The area is located at the base of the Himalayas, where streams from the mountains flow down to the flatlands. The Bhabhar and the lower Shiwalik ranges have a subtropical climate. In the western part of this climate zone, there are forests with many pine trees, mainly Chir Pine (Pinus roxburghii). In the middle part of the range, there are subtropical forests with broad leaves. One type of forest in this area is mainly made up of sal trees (Shorea robusta).

Siwalik Hills

The Sivalik Hills, also known as Churia or Margalla Hills, are the outermost range of foothills in the Himalayan region. They stretch across Pakistan, India, Nepal, and Bhutan. This area includes many smaller mountain ranges. The highest points in the Sivalik Hills are usually between 1,500 and 2,000 meters (4,900 to 6,600 feet). The southern slopes are steeper and form along a fault zone called the Himalayan Frontal Thrust (HFT), while the northern slopes are gentler. Rocks that allow water to pass through let rainwater soak into the ground, flowing downslope into the Bhabhar and Terai regions. This supports only sparse scrub forests on higher ground. The Himalayan subtropical moist broadleaf forests extend into this area.

Inner Terai or Dun Valleys

The Inner Terai valleys are open areas located north of the Shiwalik Hills or found between smaller mountain ranges of the Shiwalik. Examples of these valleys include Dehra Dun in India and Chitwan in Nepal. These regions are home to Himalayan subtropical moist broadleaf forests, which are forests with moist, broad-leafed trees that grow in subtropical areas of the Himalayas.

Lesser Himalaya

Also known as the Mahabharat Range, the Lesser Himalayas is a mountain range that rises 2,000 to 3,000 meters (6,600 to 9,800 feet) above sea level. It was formed along a fault zone called the Main Boundary Thrust, with a steep southern side and gentler slopes on the north. The range is mostly continuous, except in places where rivers from the north cut through the mountains, creating deep gorges that look like candelabra.

At these heights and above, the plant and animal life of the Himalayas is often divided by the Kali Gandaki Gorge in central Nepal, one of the deepest canyons in the world.

At middle elevations, subtropical forests give way to temperate broadleaf and mixed forests that grow between 1,500 and 3,000 meters (4,900 and 9,800 feet). These forests are split by the Gandaki River into two groups: the western Himalayan broadleaf forests and the eastern Himalayan broadleaf forests. The western forests extend from the Kashmir Valley, through Himachal Pradesh and Uttarakhand, and into western Nepal. The eastern forests stretch across eastern Nepal, through Sikkim and Bhutan, and into much of Arunachal Pradesh.

Midlands

This "hilly" region, called Pahad, is usually about 1,000 meters (3,300 feet) high, located just north of the Mahabharat Range. It rises to around 4,000 meters (13,000 feet) over a distance of 100 kilometers (62 miles) near the Main Central Thrust fault zone, where the Greater Himalaya begin.

Above the broadleaf forests, between 3,000 and 4,000 meters (9,800 and 13,100 feet), are temperate coniferous forests. These forests are also divided by the Gandaki River. The western Himalayan subalpine conifer forests are found below the tree line in northern Pakistan, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, and western Nepal. The eastern Himalayan subalpine conifer forests are found in eastern Nepal, Sikkim, Bhutan, and Arunachal Pradesh. Along the border between Arunachal Pradesh and Tibet, the eastern subalpine conifer forests mix with the northeastern Himalayan subalpine conifer forests. Important trees in these forests include East Himalayan Fir, West Himalayan Spruce, and Himalayan Hemlock. Rhododendrons are very diverse here, with more than 60 species found in the northeastern Himalayan subalpine conifer forests.

Greater Himalaya

North of the Main Central Thrust, the highest mountain ranges rise sharply up to 4,000 meters (13,000 ft) into areas covered by snow and ice all year. As the Himalayan system stretches wider from east to west, more parallel high ranges appear. For example, the Kagmara and Kanjiroba ranges reach more than 6,000 meters (20,000 ft) north of the Dhaulagiri Himalaya in central Nepal.

Alpine tundra is found above the natural tree line. These areas are mainly made up of plants that live for only one year, divided into alpine grasslands and meadows. Steep slopes are mostly covered by grasses, while meadows are dominated by plants with soft stems and leaves. The northwestern Himalayan alpine shrub and meadows are located in high elevations of northern Pakistan, Jammu and Kashmir, and Himachal Pradesh. To the east, the western Himalayan alpine shrub and meadows cover large areas along the Tibetan border with Uttarakhand and western Nepal. The eastern Himalayan alpine shrub and meadows grow above subalpine conifer forests along the Tibetan border with eastern Nepal, Sikkim, Bhutan, and Arunachal Pradesh. These shrublands include juniper trees and many types of rhododendrons. They also have a wide variety of wildflowers, such as the Valley of Flowers National Park in the western Himalayan alpine shrub and meadows, which has over 520 plant species, with 498 being flowering plants. The upper limit of grasslands increases from west to east, rising from 3,500 meters (11,500 ft) to 5,500 meters (18,000 ft). Grasslands serve as summer habitats for the endangered snow leopard (Panthera uncia).

Trans-Himalaya

The line that separates rivers flowing south into the Ganges or Indus from rivers flowing north into the Brahmaputra or mainstem Indus often runs along lower, less steep mountains located many kilometers north of the highest mountain ranges. Rivers that flow south create valleys in this area, which are often dry because the mountains block rainfall. These valleys contain some of the highest villages in the world, built on the slopes of the mountains.

Ecoregions

These are the ecoregions of the Himalayas and nearby areas:

• Karakoram–West Tibetan Plateau high mountain grasslands
• Southeast Tibet shrubland and grasslands
• Northwestern Himalayan high mountain shrubland and grasslands
• Western Himalayan high mountain shrubland and grasslands
• Eastern Himalayan high mountain shrubland and grasslands
• Western Himalayan lower mountain conifer forests
• Eastern Himalayan lower mountain conifer forests
• Western Himalayan broadleaf forests
• Eastern Himalayan broadleaf forests
• Himalayan subtropical pine forests
• Himalayan subtropical broadleaf forests
• Margalla Hills subtropical broadleaf forests
• Brahmaputra Valley semi-evergreen forests
• Terai–Duar savanna and grasslands
• Balochistan dry forest areas