Sand dune vegetation of cholistan (pakistan) and
Sand Dune Vegetation of Cholistan (Pakistan) and Some
Control Measures Against Wind Erosion
Dr. Mirza Hakim Khan
Cholistan is a vast sandy desert covering an area of 2407 km2 and is locally known as Rohi.
The area is dominated by sand dunes as high as 12m. There are however, patches of leveled areaslying between the dunes. The Hakra River divide the area into smaller and greater Cholistans. Thesmaller Cholistan lies in the north of Hakra depression and is relatively flat with a few low sanddunes. The greater Cholistan lies in the south and is entirely occupied by large sand dunes. Theencroachment of dunes from the greater Cholistan is a continuous danger for the local people. It isimportant to have a full knowledge of the natural vegetation composition of this area. The presentstudy enlightens this aspect along with suggestions for the stabilization of sand dunes.
Methods of Study
Sand dune sites in the Cholistan area were surveyed for vegetation changes and samples
taken from these sites were analyzed. The pH values were determined by a Beckmann pH meter;whereas the texture was determined by Bouyoucus Hydrometer.
a) Climatic factor:
Cholistan enjoys an arid climate. In summer, temperature is as high
C, and in winter it goes down below freezing point. May and June are the hottest months ofa year. Average annual rainfall is 128mm to 178mm. Most rainfall is during summer but winter rainsare also common. Due to little rainfall and long spells of drought, sometimes ranging between 2-4years, water is scarce in Cholistan. The only water source is that available at 25-90 m depth but thisis too brackish. As such, naturally growing grasses, bushes, shrubs and trees are frequently damagedby drought.
b) Edaphic factor:
There are mainly two types of soils in Cholistan, namely, sandy
soils and clayey soils. The sandy soils are found on stable and unstable dunes. These soils are coarsein texture and show a 8.1 pH. Though the soils lack in carbonates but they are rich in otherexchangeable bases. The clayey soils are of three types and are locally known as hakran wala dahar,chitta dahar and ratta dahar. Soils of hakran wala dahar are rocky in nature and without anyvegetation, whereas chitta dahars are as patches between the dunes. Their texture is heavier and pHis 8.2. These two are devoid of any vegetation. The ratta dahars show a coarse texture with aconsiderable proportion of clay in deeper layers. With pH values ranging from 8.3 to 8.5, the soilsupports a good vegetation the surface layers are free of excessive salts containing fair quantity ofsoluble calcium which balances the effects of excessive sodium.
c) Biotic factor:
Man plays a very important role in the area. The ranges in Cholistan are
subjected to heavy grazing. The seedlings are destroyed before they get established resulting in aconsiderable loss of the seeds. Thus there is a decrease in the forage production. Roots of Lasiurushirsutus are dug out and brushes made for use in the cleaning of earthen wares whereas Calligonumpolygonoides roots are used for making milk churns. Similarly twigs of Leptadenia spartium are usedfor making brushes and ropes. The destruction by man accompanied by grazing of deer, burrowingof hares and rats add to the already deteriorating situation.
The vegetation of Cholistan is mainly xerophytic in nature. The
distribution and diversity of vegetation is mainly controlled by the edaphic and climatic factorsdiscussed above. In all 53 species were observed to grow (Table I).
List of species observed in Cholistan.
Acacia arabica (Lamb.) Willd.
Aerua tomentosa Forssk. (Boil *)
Albizzia lebbeck (L.) Bth.
Aihagi camelorum Fisch (Javan*)
Digitaria pennata (Hochst) T. Cooke.
Haloxylon recurvum Bunge ex. Baiss. (Khar*)
Lasiurus hirsutus (Forsek) Boiss. (Gorkha*)
Dactyloctenium aegyptium (L. )P. BeauvDatura alba Nees
Suaeda fruticosa (L.) Forssk (Lana*).
Withania somnifera (L.) DunalZizyphus nummularia (Burm. f.) W. and A.
e) Vegetational Zonation
: A typical zonation can be observed easily on the sand dunes.
On the top of the dunes (stabilized) Haloxylon salicornicum and Calligonum polygonoides are thedominant species. These species are good soil binders and do not require much moisture, as theirroots can penetrate deeper in search of water. Grasses like Cymbopogan jwarancusa, Panicumantidotale, Digitaria pennata, Dichanthium annulatum and Eragrostis japonica are found to cover themiddle of dunes. These too are good soil binders and have a high fodder value. At the bottom ofdunes the dominant species are Haloxylon recurvum. Aerua tomentosa, Leptadenia spartium,Zizyphus nummularia, and Crotalaria burhia. However, species like AIhagi camelorum, Tribulusterrestris, Euphorbia prostrata, Calotropis procera and C.gigantea were observed to grow abundantlyin shady habitats of the dunes. These plants are neither soil binders nor have they any fodder value.
The eradication of these species will provide a chance for the regeneration of the species would beuseful for the stabilization of the dunes.
: Seeds of Eleusine compressa and Salsola foetida brought by wind are
first to get established on the dahars. With the deposition of more and more sand species like Suaedafruticosa, Haloxylon recurvum, Cymbopogon jwarancusa, Capparis decidua, Prosopis spicigeraget established. After September, sand dunes stop moving. If the climatic conditions becomefavorable and biotic interference is reduced the vegetation starts coming up. Dipterygium glaucumcomes first as colonizer on sand dunes followed by Aristida deprassa. Bushes like Calligonumpolygonoides, Haloxylon recurvum. H.salicornicum and Lasiurus hirsutus appear later. Thus thedunes get established. The bushes like Capparis decidua and Prosopis spicigera grow in shelteredplaces whereas Cenchrus ciliaris is found to grow only on the moist soil where conditions arecomparatively better for its growth. We can, therefore, imagine that during the past when themoisture conditions were better and without heavy grazing these species were growing as climaxspecies. Heavy grazing has resulted in the retrogression of vegetation. A sub-climax species Lasiurushirsutus thus, occupies the area.
: Cholistan is a desert where evaporation far exceeds the precipitation,
even vegetation consumption the latter. Thus following suggestions are deemed to yield good results:
1.Stabilisation of the sand dunes:
Vegetation and moisture are the two factors which
can bind sand dunes. These two factors are interrelated and the best method to bind these would beto utilize the moisture present in dunes for raising vegetation; otherwise this moisture will disappearin no time leaving the sand dunes at the mercy of severe gales. In all the advanced countries of theworld, where such a menace exists various sand binding species have been tried. Usually the grasseshave served this purpose. The tough binding grasses with their harsh tufts check the wind, trap on-coming supplies of sand and continue to grow outwards as the entangled sand accumulates leavingbehind them an intricate network of long roots. Such protective dunes become leveled up and tuftedover. Some tree species have also been tried for this purpose elsewhere. However stress should belaid upon local species than introducing exotic ones. Since dunes have three locations and possessdifferent water content, following species are strongly recommended for plantation at different zonesof dunes. The top of a dune should be planted with Calligonum polygonoides, H.salicornicumSalsola foetida, Dipterygium glaucum, Capparis aphylla, Kochia indica, Salvadora oleoides, Suaedafruticosa, Acacia arabica, Prosopis spicigera and Azadirachta indica. The middle of the dunes withLasiurus hirsutus, Eleusine compressa, panicum antidotale, Cymbopogan jwarancusa, Cenchruspennisetiformis, Dipitaria pennata, Dichanthium annulatum, Aristida depressa, Demostachyabipinnata, Eragrostis japonica and bottom of the dunes with Haloxvlon recurvu, Aerua
Leptadenia spartium, Zizyphus nummularia, Crotalaria burhia, Citrullus colocynthis, Solanumxanthocarpum, Peganum harmala, Fagonia cretica, Tribulus terrestris, Aihagi camelorum, Corchorusdepressus and Cleome brachycarpa. It will be feasible if the seeds, tufts, cuttings or entire plants, asthe case may be, of the above species are planted immediately after the rains in July and August. Thespecies like Datura alba, Withania somnifera, Calotropis procera, C.gigantea, Euphorbia prostrata,Cistanche tubulosa, Solanum nigrum, Chrozophora tinctoria and Orobanche sp. are unpalatable andpossess no economic importance. These species are certainly a drain on the Cholistan habitat. Theintroduction of economically important and palatable species, after the eradication of the latterspecies, will not only increase the potential wealth of the area but also help boost up the economyof the inhabitants of this area.
Proper management of natural resource is necessary for its best utilisation.
Cholistan has a very limited and subnormal vegetation cover. It is, thus, imperative that necessarysteps should be taken not only to restore it to its original level but also to improve it. As such,grazing should be limited by marking areas left for grazing and others should be kept under strictsurveillance or a barbed wire used for demarcation of the areas. Census of the wild lives is alsoimportant since it is dependent on the vegetation of the area. Before any number of livestock isallowed to graze in a particular area the possible number of wild life should also to be taken intoconsideration. Monitoring of the economic plants of the area is needed. These plants should beallowed to be cut in such a manner that they do not jeopardize the existing bad situation. Theparasitic species like Orobanche sp. and Cistanche tubulosa should be eradicated.
3.Development of water points (Tobas):
This step is of paramount importance. The best
time of dig the points is before rains on dahar soils. This would help accumulation of maximumamount which can be used for irrigation and other purposes later on.
4. Plants of economic importance:
Plantation of plants like Zizyphus sp., Albizzia
Iebbek, Tamarix aphylla and Haloxylon recurvum, because of their economic importance, shouldbe encouraged, Haloxylon recurvum is a source of great income for the area. It is a source of nitrateused on large scale in the soda ash factory for the manufacture of soap. This species germinatesprofusely immediately after rains. The seeds of the plant may be broadcast by planes or helicoptersto increase its density and coverage. The species apart from all its qualities is a very good soil binder.
5. Wind barrier species:
Planting for wind breaks of species like Phragmites karka,
Arundo donax and Saccharum spontaneum are useful to check the blowing sands from coming intocrops.
6. Control of poisonous plants:
Some of the following poisonous plants needs attention
because they are unpalatable and poinonous: Ricinus communis, Datura alba, Withania somnifera,Calotropis procera, C.gigantea, Euphorbia prostrata, Cistanche tubulosa, Solanum nigrum,Chrozophora tinctoria, Orobanche sp.
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