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FOREST TYPES AND THEIR GEOGRAPHICAL DISTRIBUTION IN PAKISTAN


Distributation of forest in Pakistan is primarily governed by the climate and edaphic factors and it is amply reflected in the diversity of forests types available in the country. While large areas are under natural forests of coniferous and broad leaved species some really productive forests are entirely man made. Starting from the Alpine scrub in the Northern Hamalayes, one come across a variety of types ending up with the Mangroves in the shallow waters of the Arabian Sea in the South. A broad categorization would be as under.
ALPINE SCRUBS: Shrub formation often forming a quite dense cover 0.6 to 1.8 in high composed of a limited number of species, mostly deciduous and with small leaves but including evergreen jumper and sometimes Rhododendron and Ephedra. The stems are generally flexible and adapted to snow pressure. There is a fair degree of segregation of the individual species with the site variations, particularly in water supply. Dwarf prostrate Salix spp. are usually present. There is a good herbaceous flora mainly perennial among the shrubs, including a variety of palatable grasses.
These are generally but not always developed above the birch zone and in patches, sometimes extensive, withnint, probably conditioned by edaphic and biotic factors, in Kashimr, Giligt, Chitral and Hazara. This type ascends normally to 150m, or more above the sub-alpine forests and climate must be similar but more sever than in sub-alpine forests.
The characteristic genera are Salix, Lonicera, Berberis, Contoneaster with Junipers and occasionally Rhodoendorn or Ephedra.
Sub-alpine forests: Coniferous trees limited to Abies (Fir) and Pinus wallichians (blue pine) stand singly and in groups over an irregular, sometimes dense, lower story of broadleaved trees in which Betula typically prominent at the higher elevations and in depressions, with other deciduous trees such as Pyrus and Salix. The cover tends to be completed with tall shrubs, notably Viburnum and Salix, sometimes with the evergreen Rhododendron and Juniper. The conifers rarely exceed 8m in height; the broadleaved trees reach about 9m and the shrub growth about 1 to 3m. the conifers often attain a considerable girth even up to 3m while the birch may reach 2.5m.
This is the topmost tree formation in Hamalayas developed between about 3350m, on northerly aspects and perhaps 150m higher in warmer slopes. It is accordingly met with in Kashmir, Dir, Swat, Chitral, the Gilgit Agency and Hazara. Rainfall range between 660m and 9mm and snowfall is of greater importance for which a depth of 2m and over must be normal.
DRY TEMPERATE FORESTS: These forests are distributed throughout the inner mountain ranges beyond the effective reach of the south-west monsoon, notably in the upper reaches of the Indus and its tributes including the whole of Gilgit and parts of Chitral and the Nilam and Khaghan valleys: also on the higher parts of the Sulwiman Range to the north-west including Takhti-Suleman, Shingarh and Ziarat. The altitudinal range is from about 1525m to 3350m extending to 3650m on southerly aspects. The winters are long and cold; mean annual temperature varying in one to 6 months with the monthly mean below zero. The total annual total precipitation is always less than 750m. Rainfall distribution is of great importance in this zone in which the summer monsoon in weak but western disturbance bring considerable snow and rainfall in the winter and spring.
HIMALAYAN MOIST TEMPERATE FORESTS:  The chief characteristics of this type are the extensive development of coniferous forests. They also extend into the dry temperate regions, and to a small extend into the sub-alpine forests. The number of dominant species is small in fact more or less pure crops or two species mixtures are the commonest form, the species occurring being dependent mainly on altitude and aspects. The conifers generally form a fairly complete forests cover of good height 24 to 46m. All species are capable of attaining considerable girth of 4.5m or more.
The rainfall of the Himalayas between the sub-tropical pine forests and the sub-alpine formation is about 630mm to 1500mm. the altitude range is form about 1375m up to 3050m. The chief coniferous species are Pinus wallichiana, Cedrus deodara, Pecea smithiana and Abies pindrow. Taxus also occurs locally in the lower canopy. Among the broad leaved trees the genus Quercus with several species is prominent in the outer ranges and is prominent in the outer ranges and its commonest associate is Rhododendron arboreum. The temperate deciduous tree genera, Acer, Aesculus, Prunus, Ulmus are met with fairly generally and form local consociations. Litsara and Machilus are found locally in the moister forests. Evergreen Euonymus and Ilex are commonly associated with the oaks. Among the shrubs, Indigogera, Lonicera, Rosa, Desmodium and Vibutum are typical, whilst Strobilanthus spp. May be locally consipicuous.
SUB-TROPICAL PINE FOREST: High forests in which Pinus rocburghii (Chir) forms practically whole of the top canopy which may be upto 37.5 m, high with trees up to 2.0 or 2.5 m in girth. Chir forests are near the western limit of their range in Pakistan and they extend eastward up to Bhutan. They occupy an altitudinal zone between 925m and 1675 m, extending even up to nearly 2150 m on ridges with southern exposure. Main annual temperature lies between 15.6 and 22.2º C. There is definite cold season with frost and some snow. Maximum temperature may go up to 37.8º C. at the lower elevations and only to 32.3º C near the top.
Pinus roxburghii is completely dominant, Quercus incana, with occasional Lyonia ovalifolia and Rhododendron arboreum, occur widely on the cooler mositer sites both along streams and on northerly aspects. Pistacia integerrima, Syzgium cumini, Mallotus philippinenis, Xylosoma longigolium and other broad leaved trees are also there. The shrub growth, when present is commomly of Myrsine africana, Daphne, Lonicera, Rosa, etc ., at the higher altitudes, and Carissa, Dodonaea etc ., at the lower, Berberis and Indigofera, Reinwardtria and Rubus spp.  Occur throughout. Among the grasses, Heteropogon contortus is conspicuous.
DRY SUB-TROPICAL BROAD LEAVED FORESTS: Low forests of branchy trees forming a canopy, varying in density from complete closure under the most favorable conditions to scattered single trees or groups on the driest sites, typically field in with a shrub growth which similarly varies in density. The trees and shrubs are mostly and often thorny small evergreen leaves but sone like the olive and pomegranate are without thorns and have leaves of moderate size through with xerophytic features. During monsoon a fairly complete cover of grass and herbs may develop.
These are distributed in the foothills and lower slopes of the Himalayas, the Salt Range , Kalachitta, the Suleiman Ranges in fact throughout the country at suitable elevations merging downwards with the tropical thorn forests an upwards with the sub-tropical pine and temperate forests.  The temperature varies according to the seasons. Temperature run high in June and July when monthly mean is 29.4 to 33.3º C and its maximum a little above 37.8º C. Grazing and browsing is very heavy.  These forests cover the lower slopes of the hills generally extending from 450m, up to 1525m in the absence of the Chir pine zone.
The characteristics of trees are Olea ferruginea (kau) and Acacia modiesta (phulai) which occur over a wide altitudinal and latitudinal range with pistacia at the higher levels. Punica is often abundant in the Sub-Himalayan occurrences. The shrubs include a many genera and under heavy grazing, to which they are usually submitted, unpalatable species are favored and Dodonaea, Withania and Rhazya become comspicious along with throny Gymnosporia, Monotheca and Carissa.
TROPICAL DRY DECIDUOUS FORESTS: An open rather low forest composed almost entirely of deciduous trees and a few trees of the thorn forests type with a predominantly deciduous shrub layer. A typical feature of this forest is the marked contrast between the dry season condition when it is leafless and the soil bare, and the monsoon period when it takes on an almost luxuriant appearance from the growth of ephemeral herbaceous vegetation coupled with the leafing out of the tees and shrubs. The forests are subjected to repeated ground fires, grazing are heavy as the forests is much close to habitation and cultivation.
It is limited to the Hamalayan foothills and adjoining Siwalik and recent alluvial deposition at the foot of the hills. The forest adjoins the dry sub-tropical and also the sub-tropical pine forests. Mean annual temperature is 21.1 to 26.7º C, with definitely high summer temperature reaching 43.3º C or even more and a marked cold season.
The trees are mostly a limited selection of those of the moist deciduous forests notably Lannea, Salamalia, Flacourtia, Mallotus and Acacia catechu, while common shrubs similarly include Indigofera, Adhatoda, Gymnosporia and Carissa.
TROPICAL THORN FORESTS: Forests in which thorny usually hard wooded species predominate, Acacia spp. being particularly characteristic. The trees usually have short boles and low branch ling crowns which rarely meet except on exceptionally favorable spots. The usual height is 6-9 m.
This is the natural vegetation over the whole of the Indus Plains except for the driest parts and the area covered by the annual inundations. It merges into the subtropical dry evergreen type of the lower hills to the north and West generally. Mean annual temperature is 23.9 to 26.7º C., the hottest month being the June with mean maximum at 40.6º C and the extreme maximum 51.7º C.
Acacia and Prosopis are strongly represented in the tree layer where one is present. Several Shrubs growth notably Suaeda, Salsola, Haloxvlon. Among the grass genera may be mentioned Aristida, Eleusine, Panicum, Cenchrus and Lasiurus.
IRRIGATED FORESTS:  These forests are the outcome of human efforts on sub-marginal lands where irrigation water could be made available. These forests were created after clearing tropical thorn forests.
Commonly known as irrigated plantation, these are spread over the plains of Pakistan converging an area of nearly 103000 hectares out of which almost 50% is stocked. Size of such plantations varies from just 200 hectares to a large as 8000 hectares.
The main species grown in these plantations are Dalbergia sissoo (Shisham) and Morus alba (Mulberry) in the Punjab, and Acacia Arabica (Babul) in Sindh.
RIVERIAN FORESTS: It is an important seral stage of Tropical Thorn Forests type. It forms a complete canopy 12 to 15 m, high in which Acacia Arabica usually strongly predominates with varying amounts of  Populus euphratica and Prosopis cineraria on the drier parts.
These forests occur between the banks of the main stream of the Indus. Main species are Acacia nilotica, Prospis cineraria, populus euphratica, Tamarix spp., Salvadora occur in depressions without over wood.
Tamarix-Poplar Forest is a dense thickest of Tamarix spp., with varying number of poplar trees are distributed on fresh silt alluvium of the rive rain tract of the Indus between Muzaffargarh and Hyderabad with isolated occurrences as far north as Peshawar.
TROPICAL LITTORAL AND SWAMP FORESTS
Tidal Swamp Forests: More or less dense forests of very low average height, often only 3-6 m, further reduced by biotic agencies. Species few and markedly gregarious, all evergreen with entire leathery leaves. Vivipary is usual. The best patches reach 6-7.6 m, high and are found on sites difficult of access on account of soft mud. These occur on the muddy coasts of the Arabian Sea around Karachi. Mean annual rainfall is 152 to 229 mm. rainfall is more important for its effect on the salnity of the soil than for the additional moisture it brings. The main species are Avicenniea officinalis (95%), Ceriops tagal and Bruguiera conjugata (5%).
Littoral Grassland: Grasses predominate on the coastal sand especially with incipient dune formation, with little or no woody growth. Locality factors are a loose sandy soil and full exposure to sea breeze, often with salt spray, depositing more sand whilst blowing some away. The soil is continuously moist below the surface but is not usually saline.
The typical species is Saccharum spp., with Eleusine flagelliefera, Panicum antidotale, Cenchrus sp., and Agrostis sp.
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