Research Article
Benchmark of Plant Communities of Cholistan Desert
Cholistan Institute of Desert Studies, Islamia University, Bahawalpur, Pakistan
Ghulam Akbar
World Wide Fund for Nature (WWF), Islamabad, Pakistan
The vegetation of Cholistan desert is typical of arid regions and represents xerophytic species adapted to extremes of salinity, temperature, moisture fluctuations and wide variety of endemic factors. Compared with the hyper arid southern region, vegetation cover is comparatively better in Greater Cholistan. A wide variety of nutritious and multiple stress tolerant species of grasses, shrubs and trees grow there. These plant species, though slow growing, respond very well to the favourable climatic conditions particularly, the timely rains and produce ample fodder. Important genera of grasses include Lasiurus, Cenchrus, Sporobolus, Cymbopogon and Panicum; shrubs include Suaeda, Capparis, Calligonum, Leptadenia, Salsola & Haloxylon. Prosopis, Tamarix, Zizyphus and Acacia are notable indigenous trees. Each site depicts a typical plant community with xeric genetic adaptations (Akbar et al., 1996; Akbar & Arshad, 2000).
Communities, in fact are the mirrors of landmass or indicators of lands biological resources. Based upon this information, the plant communities are reliable indicators of environments and economic potentialities of the area. Update benchmark about plant communities in Cholistan desert being presented in this paper will be the basis of future planning particularly with regard to conservation strategies of biological resources, management of ranges and other developmental activities. No concrete information is available about the plant communities of Cholistan desert however, Dasti and Agnew (1994) recognized six of them. Apparently they scanned a very small area of the desert. Arshad and Rao (1995) studied the vegetation pattern in Cholistan desert in relation to the phytogeographic states. Rao et al. (1989) explored the vegetation of Cholistan desert and identified eleven distinct phytosociological categories. Arshad et al. (2002) identified plant communities in fenced and unfenced desert reserve areas of National Park Lalsuhanra. Investigations on phytosociologcial distribution of plants have been conducted by Hoare et al. (2000); Qain (1999) and Qain et al. (1999). To study the vegetation of Cholistan desert, much stress has been paid to the plant communities.
The vegetation of Cholistan desert has not so far been studied properly. The present study is the first rational approach to explore the plant communities of Cholistan desert. Besides this it is a matter of significance that several plant species collected during this study and incorporated in this manuscript are new record from this desert as these plant species have never been reported previously from Cholistan desert. The main objectives of this study were:
* | To explore the benchmark of plant communities of Cholistan desert. |
** | To study the vegetation of Cholistan desert. |
Study area: Cholistan desert located in southern Punjab, Pakistan occupies about 26000 km2 area having a length of about 480 km and the width varying from 32 to 192 km. This desert can be divided into two geomorphic regions; the northern region or Lesser Cholistan, bordering canal irrigated areas and the southern region or the Greater Cholistan. The Lesser Cholistan consists of large saline alluvial flats locally called dahars alternating with low sandy ridges/sand dunes. The Greater Cholistan is a wind eroded sandy terraced desert having large sand dunes and less depressions with dune heights of 100 m or so (Akbar et al., 1996; Akbar & Arshad, 2000).
Climate: Cholistan is a hot arid sandy desert. The mean annual rainfall varies from less than 100 mm in the west to 250 mm in the east. Rain usually falls during monsoon with a few showers in winter and spring. Cholistan is one of the hottest deserts in Pakistan. Mean minimum temperature is 20°C. The mean maximum summer temperature (May-June) is 34°C with the highest reaching above 51°C (Arshad et al., 2002). Prolonged aridity/droughts are the most striking features of this desert. Low rainfall, high rate of water infiltration coupled with high evaporation prevents the accumulation of surface water. Fresh rainwater is collected in dug out playas (water ponds locally called tobas) for subsequent use. Underground brackish water is at a depth of 30-40 m with an E.C. level ranging from 620-29800 mg/hectare (Anonymous, 1993).
To assess the plant communities in the representative habitats of Cholistan desert, several plant collecting trips were undertaken from 1990 to 2000. The representative habitats (collecting study sites) were selected on the basis of differing species composition, their density, overgrazing, texture and structure of soil, dune height and other related factors. To record the vegetation parameters like plant cover, frequency and density line intercept method was used (Canfield, 1940; Mueller-Dumbois and Ellenberg 1974).
In Cholistan desert, sixteen plant communities were identified in different land forms. Out of these sixteen plant communities, ten were identified in Smaller (south western) Cholistan and six in Greater (south eastern) Cholistan. The composition and structure of these plant communities are being described along with their habitats.
I - Smaller Cholistan
Calligonum polygonoides-Haloxylon salicornicum community
Habitat: Deep hummocky aeolian soil with clayey substratum. Supposedly originated around individual clumps of plants apparently because of grazing activity of animals loosening the fragile soil layers and making it erodible.
Composition and Structure: The top plant layer is composed of Calligonum polygonoides followed by Haloxylon salicornicum. Other plant species found in the area were: Prosopis cineraria, Capparis decidua, Leptadenia pyrotechnica, Calotropis procera (seedlings), Crotalaria burhia, Heliotropium strigosum, Dipterygium glaucum, Indigofera argentea, Tribulus longipetalus, Limeum indicum, Aerva persica, Fagonia cretica, Corchorus depressus, Polygala erioptera, Boerhaavia diffusa, Haloxylon recurvum, sesuvium sesuvioides, tribulus longipetalus, Euphorbia prostrata and Mollugo cerviana. Among the grasses and sedges Lasiurus scindicus, Cenchrus biflorus, Cenchrus ciliaris, Aristida mutabilis, Aristida adscensionis, Eragrostis barrelieri, Stipagrostis plumosa, Leptothrium senegalense, Cenchrus ciliaris, Cyperus conglomeratus, Ochthochloa compressa and Cymbopogon jwarancusa were prominent.
Aristida spp. and Cenchrus biflorus density is very high because this area had been subjected to heavy grazing pressure in the past. Palatable grasses like Stipagrostis plumosa, Lasiurus scindicus and Cenchrus ciliaris are making a come back but slowly. Aristida species and Cenchrus biflorus may decrease with the increase in vegetation cover by other species.
Tamarix aphylla-Suaeda fruticosa community
Habitat: Leveled habitat shaping up by the flow of water into or through the area or after the erosion of upper deposits of fine silt. The soil is clayey and highly saline.
Composition and structure: The community consist of Tamarix aphylla as the first storey, followed by Suaeda fruticosa as the second dominant. Other associated plants are: Prosopis cineraria, Cleome brachycarpa, Cressa cretica, Fagonia cretica, Farsetia hemiltonii, Euphorbia prostrata, Trianthema crystallin and, Sesuvium sesuvioides. The grass species at this community area are: Aeluropus lagopoides, Sporobolus iocladus, Cymbopogon jwarancusa and Ochthochloa compressa. This community is a typical of saline soils, moisture remains available to the plants for longer period.
Haloxylon recurvum community
Habitat: Flat piece of land with silty clay loam or clay loam but alkaline in nature.
Composition and structure: Haloxylon recurvum bushes are interspaced with some Haloxylon salicornicum and Salsola baryosma shrubs. Other plant species found are: Acacia nilotica (seedling), Aerva persica, Fagonia cretica, Corchorus depressus, Euphorbia prostrata, Sesuvium sesuvioides, Trianthema crystallina and Anticharis linearis. Among the grasses and sedges Aristida mutabilis, Aristida hystricula, Ochthochloa compressa, Cymbopogon jwarancusa and Eragrostis barreler are the prominent species of this community. Obviously a halophytic community consisting of only Haloxylon recurvum and some of the highly salt tolerant species, low salinity tolerants are present on the accumulated patches of soil.
Calligonum polygonoides-Lasiurus scindicus-Cyperus conglomeratus community
Habitat: A large and tall dune with sandy composition showing some fine soil in deeper layers.
Composition and structure: This differs from the Calligonum polygonoides-Haloxylon salicornicum community in that Haloxylon salicornicum is occasionally present but not as a dominant component because of greater depth of soil. Lasiurus scindicus and Cyperus conglomeratus appear to be the distinct and dominant component of this community. The species present here are: Haloxylon salicornicum, Aerva persica, Dipterygium glaucum, Farsetia hamiltonii, Calotropis procera (seedlings), Limeum indicum, Gisekia pharnaceoides, Tribulus longipetalus, Boerhavia diffusa, Mollugo cerviana, Polygala erioptera, Mukia madraspatana, Antichoris lineari and Convolvulus microphyllus. Grasses and sedges found at this community are: Cenchrus biflorus, Cenchrus ciliaris, Aristida mutabilis, Aristida adscensionis, Cenchrus prieurii, Panicum turgidum, Cyperus conglomeratus, Lasiurus scindicus, Cymbopogon jwarancusa and Leptothrium senegalense.
Prosopis cineraria-Haloxylon salicornicum community
Habitat: Old bed of the dried up "Hakra" river, mostly flat terrain with small sandy hummocks of sandy loam soil.
Composition and structure: Strikingly this community is having two storeys of the old and young trees of Prosopis cineraria over and above the Haloxylon salicornicum layer forming the third storey with some bushes of Suaeda fruticosa and Aerva persica. A very characteristic feature of this community is the abundance of dwarf annual Aristida hystricula forming small tussocks in the landscape and the other species are: Aerva persica, Suaeda fruticosa, Dipterygium glaucum, Antichoris linearis, Tribulus terresteris, Tribulus longipetalus, Cleome scaposa, Trianthema crystallina, Corchorus depressus, Euphorbia prostrat and, Citrulus colocynthis. Cymbopogon jwarancusa, Cenchrus biflorus, Ochthochloa compressa, Aristida hystricula, Tragus racemosu and, Eragrostis barreleri are the important grasses and sedges of the area.
Capparis decidua-Aerva persica-Haloxylon recurvum-Haloxylon salicornicum community
Habitat: An old and stable 4-5 m high dune partially eroded and covered with small concretions.
Composition and structure: An interesting dunned community with a combination of Capparis decidua, Haloxylon recurvum and Haloxylon salicornicum. The top storey is formed by Capparis while the two Haloxylon spp. form the second layer. The third layer is composed of Aerva persica, Chrozophora plicata. The other species present are: Crotalaria burhia, Dipterygium glaucum, Calotropis procera (seedling), Tribulus longipetalus, Citrulus colocynthis, Cucumis melo ssp. figarii, Sesuvium sesuvioides, Gisekia pharnaceoides, Euphorbia prostrata, Limeum indicu and, Mollugo cerviana. Among the grasses and sedges Cymbopogon jwarancusa, Lasiurus scindicus, Cenchrus biflorus, Ochthochloa compressa, Aristida adscensionis, Eragrostis barrelieri and Eragrostis ciliaris.
Capparis decidua-Cymbopogon jwarancusa community
Habitat: A compact plain dahar buried under the eroded sand.
Composition and structure: A community having first layer of Capparis decidua and second layer of stubbles of Cymbopogon jwarancusa. Some plants of Octhochloa compressa, Tragus racemosus, Aristida hystricula, Corchorus depressus and Euphorbia prostrata were sparsely seen.
Prosopis cineraria-Haloxylon recurvum-Haloxylon salicornicum community
Habitat: A disturbed sloppy habitat extending to a "Toba" receiving runoff water after rains. Its overuse resulted in the loss of old deposits of soils, leaving some patches of thin soil-cover or bare areas with clayey substrate. The terrain obviously traces the human activity for water harvesting and may have been the site of encampment of travelers in the older days.
Composition and structure: The tree layer in this community is of Prosopis cineraria which, generally had been looped heavily. Calligonum polygonoides is present where the sand cover was deep or was once deeper. Haloxylon recurvum and Haloxylon salicornicum occupy areas of shallow sand cover above the clayey lower substrate. Haloxylon recurvum and Haloxylon salicornicum being better salt tolerants, were seen colonizing brackish standing water having higher concentration of salts. Other plant species of this community are: Aerva persica,Suaeda fruticosa, Fagonia cretica, Cleome scaposa, Calotropis procera (seedlings), Dipterygium glaucum, Sesuvium sesuvioides, Limeum indicum, Euphorbia prostrata, Boerhavia diffusa, Trianthema crystallina, Polygala erioptera, Launia nudicaulis, Tribulus longipetalus, Mollugo cerviana and Corchorus depressus. Lasiurus scindicus, Cymbopogon jwarancusa, Cenchrus ciliaris, Cenchrus prieurii, Tragus racemosus, Eragrostis barrelieri, Aristida adscensionis and Ochthochloa compressa are the grass species found at this community.
Prosopis cineraria-Capparis decidua-Calligonum polygonoides community
Habitat: Irregular high sand dune with loose top crust. Dominant spp. Capparis decidua had been harvested.
Composition and structure: Tree and tall shrub layer was constituted by Prosopis cineraria and Calligonum polygonoides. Rare Capparis decidua had been felled. Calligonum is surviving patchily but in relatively poor stand. Other plants noted are: Aerva persica, Haloxylon salicornicum, Dipterygium glaucum, Calotropis procera (seedling), Tribulus longipetalus, Limeum indicum, Citrulus colocynthi and Mollugo cerviana. Among the grasses Lasiurus scindicus, Cenchrus ciliaris, Cenchrus biflorus, Aristida mutabilis, Cymbopogon jwarancusa and Stipagrostis plumosa. were prominent.
Haloxylon recurvum-Haloxylon salicornicum community
Habitat: Flat, compact clayey Dahar with a few small hummocks of trapped sand, partially impervious to rain water.
Composition and structure: Haloxylon recurvum present with Haloxylon salicornicum on the small hummocks. The entity remains plantless until flying sand settles down forming top layer for colonization The composition of other plant species is: Suaeda fruticosa, Cleome brachycharpa, Cleome scapos and Trianthema crystallina. Grasses are: Lasiurus scindicus, Aristida mutabilis, Eragrostis barrelier and Ochthochloa compressa.
II - Greater Cholistan
Calligonum polygonoides-Haloxylon salicornicum-Dipterygium glaucum community
Habitat: Low to high dunes generally unstabilized with moving sand. Vegetation cover rather high going up to 30% or so.
Composition and structure: First layer of this community is Calligonum polygonoides and Haloxylon salicornicum. Others plants are Dipterygium glaucum, Tribulus longipetalus, Polygala erioptera, Limeum indicum, Boerhavia diffusa, Neurada procumben, Lasiurus scindicus, Aristida mutabilis, Aristida adscensionis, Cenchrus biflorus, Cenchrus ciliaris, Cenchrus prieurii and Stipagrostis plumosa.
Calligonum polygonoides-Aerva pseudotomentosa community
Habitat: Large dunes and highly sandy.
Composition and structure: The dominant layer at this community are Calligonum polygonoide and Aerva pseudotomentosa. Other plants recorded at this community are Dipterygium glaucum, Euphorbia prostrata, Tribulus longipetalus, Mollugo cerviana, Indigofera argentea, Mukia madraspatana, Lasiurus scindicus, Cenchrus prieurii, Aristida mutabilis, Aristida adscensioni and Stipagrostis plumosa.
Haloxylon salicornicum community
Habitat: Flat, eroded, duneless, degraded site, with lot of dead stubbles of Cymbopogon jwarancusa due to over grazing and denuded root system caused by wind erosion.
Composition and structure: The leading dominant at this community is Haloxylon salicornicum associated with Prosopis cineraria, Capparis deciduas, Aerva persica, Dipterygium glaucum, Crotalaria burhia, Anticharis linearis, Limeum indicum, Arnebia hispidissima, Euphorbia prostrata, Corchorus depressus, Corchorus tridens, Tribulus longipetalus, Citrulus colocynthis, Boerhavia diffusa, Gisekia pharnaceoides, Cocumis melo ssp. agrestis, Convolvulus microphyllus, Convolvulus desertii, Cleome scaposa. Among the grasses Aristida adscensionis, Ochthochloa compressa, Eragrostis barrelieri, Cynodon dactylon, Cenchrus biflorus, Cenchrus prieurii, Cymbopogon jwarancusa, Tragus racemosus and Aristida mutabilis are prominent.
Calligonum polygonoides-Aerva pseudotomentosa-Panicum turgidum community
Habitat: Badly disturbed and sloping habitat of very high and large dunes. Vegetation cover 40%. Lot of dead stubbles of Cyperus conglomeratus. Locust on solitary phase.
Composition and structure: Calligonum polygonoides, Aerva pseudotomentosa, Leptadenia pyrotechnica and Aerva persica appeared as first layer at this community. Other plants are Crotalaria burhia, Indigofera sessiliflora, Indigofera argentea, Tribulus longipetalus, Limeum indicum, Mollugo cerviana, Panicum turgidum, Lasiurus scindicus, Cenchrus biflorus, Cenchrus prieurii, Aristida mutabilis, Aristida adscensionis, Ochthochloa compressa and Cyperus conglomeratus.
Calligonum polygonoides community
Habitat: Very large and high unstable mass of shifting sand dunes.
Composition and structure: This community differs from other communities because of fast moving sand dominated by Calligonum polygonoides interspaced with the Aerva persica, Haloxylon salicornicum, Farsetia hamiltonii, Dipterygium glaucum, Euphorbia prostrata, Limeum indicum, Mollugo cerviana, Aristida adscensionis, Cymbopogon jwarancusa, Lasiurus scindicus and Cyperus conglomeratus..
Ochthochloa compressa community
Habitat: Interdunal sandy areas lying in between very high sand dunes. Vegetation cover about 60%. A lot of dry plants of Haloxylon salicornicum. A dominant community near Fort Bijnot.
Composition and structure: First layer at this community are Haloxylon salicornicum, Aerva persic and, Calligonum polygonoides. Other plants recorded are Capparis decidua, Prosopis cineraria, Leptadenia pyrotechnica, Crotalaria burhia, Citrulus colocynthis, Tribulus longepetalus, Cleome scaposa, Heliotropium strigosum, Indigofera sessiliflora. Among grasses and sedges Lasiurus scindicus, Cenchrus biflorus, Cymbopogon jwarancusa, Stipagrostis plumosa, Panicum turgidum, Ochthochloa compressa and Cyperus conglomeratus were prominent plants.
Floral records of Cholistan desert remain awfully deficient due to lack of interest, inaccessibility, inadequacy of rainfall and over exploitation. Besides vegetation, the flora differed in composition of species (climatic forms) very much, thus the dynamic rhythm of plant life was seen varying in magnitude as one passed through the desert, however, the sharp changes were there in relation to topographic features, heterogeneity of soil and distance among the habitats. At places, particularly close to rain water collecting ponds (tobas) over exploitation and heavy grazing pressure marred the plant community structure and failed to maintain its optimal posture. Prolonged droughts of many years also affected the growth patterns and distribution of vegetation in the desert.