Natural vegetation expresses the whole environment (climate, topography, geology and soil) and hence studies of vegetation composition leading to production of flora can form a basis for land use. In contrast to the area, Pakistan has a very diverse flora including roughly 6,000 plant species of flowering plants.

Climate and Topography

The type of the flora of Pakistan as a rule depends on the climate, soil and topography which incessantly varies as one travels from sea level to the Northern Pakistan. On the basis of temperature, Pakistan is roughly divided into following four zones:
1. Tropical very hot and winterless.
2. Subtropical hot with a cool winter.
3. Temperate with a warm summer and a
pronounced winter.
4. Arctic with a short summer and long
severe winter.
The mean annual temperature of Pakistan exceeds 25°C over the whole country with the exception of hilly areas.

The diurnal range of temperature does not appear to have a significant effect on vegetation provided tolerable limits are not over-stepped. High diurnal ranges of temperature are found in the central Indus plains and parts of Quetta and Kalat Divisions. The highest mean annual diurnal range of 4°C has been recorded for Kalat. The annual diurnal range is usually below —9.5°C in the Himalayan areas.

Rainfall

The mean annual rainfall ranges from less than 50 mm to 125 mm in Pakistan. The variation in annual rainfall from year to year is an important factor for plant growth. It is apparent over most of Pakistan that the length of dry season determines the type of vegetation found.

Except for a small area which is humid and perhumid (1.5%) and a little larger area (8.5%) in the submontane region which is dry, subhumid and wet, the rest of Pakistan is arid (72%) and semi-arid (18%).

Topography

Few countries have such a diversity of the terrain as found in Pakistan. It stretches from the Arabian Sea on the west to the wild of Tibet in Central Asia. Beginning at the sea level the country rises to 8,611 m. at K-2 in the Karakoram mountains, the second highest peak in the world. Large alluvial plains are the creation of the river Indus. A large area of Pakistan was desert and this untamed land came under cultivation by a well-established canal system, but as a result some of the land has become waterlogged. The waterlogging accompanied by alkalinity and salinity poses a serious problem in those areas.

Floristic Regions

As a result of diversity in the climate and the terrain a number of distinct floristic elements are found in Pakistan. However, Pakistan can be divided into four floristic regions: the first floristic region is called as Saharo-Sindian or Sudanian region. The flora of this region is predominantly tropical or subtropical type and, in fact, an extension of North African desert, Sahara. In

Pakistan this Saharo-Sindian flora stretches from the desert of Sind, Punjab deserts in the coastal plains and southern Baluchistan, foothills in NWFP and even penetrates the Himalayan range along the river Indus. Floristically this region is of great interest. The most distinctive is the flora of the tidal swamps found along the coast of Sind and Baluchistan. This is dominated by various species of mangroves viz. Avicennia marina, Aegiceras corniculata and Rhizophora and Ceriops species.

Pakistan this Saharo-Sindian flora stretches from the desert of Sind, Punjab deserts in the coastal plains and southern Baluchistan, foothills in NWFP and even penetrates the Himalayan range along the river Indus. Floristically this region is of great interest. The most distinctive is the flora of the tidal swamps found along the coast of Sind and Baluchistan. This is dominated by various species of mangroves viz. Avicennia marina, Aegiceras corniculata and Rhizophora and Ceriops species.

The second floral region in Pakistan is usually called as Irano-Turanian region. It includes northern Baluchistan and upper Waziristan, on one side, and the portion of upper Hazara, Chitral, Gilgit, portion of Baltistan in the northern regions of Pakistan, on the other.

The most interesting and distinctive flora in Baluchistan of Irano-Turanian region is called the “juniper tracts”. Under this head may be included the vegetation from 2,000 to 3,000 m. and embraces the country around Ziarat, the Pu range and the Zarghun range near Quetta.

The flora of Gilgit, upper Hazara, upper Chitral, Astor and Skardu in the eastern Irano-Turanian subregion is very interesting. The areas are drier and less tropical. Due to the diversity in local topography and climate, particularly of rainfall, the flora varies from place to place.

The third and perhaps the most interesting region is called as Sino-Japanese region. The territory of this region in Pakistan is narrow and lies between 33° -35°NL. Part of Kashmir, upper Murree hills, parts of Hazara and Chitral are included in it.

The last and the smallest region of our flora is known as the South Asian region. In Pakistan, the territory of this region lies in the extreme southeast part and lies between 27° —28° NL and includes Nagar Parker and the area of Rann of Kuch. The flora of Nagar Parker is quite different from its adjoining areas due to its higher rainfall. The average annual rainfall is as high as 24”. Flora is dominated by mostly Saharo-Sindian elements.