Mountains have a diverse array of microclimates arising from their varied topography. Due to the diversity of altitudes, climates and landscapes, they support a high diversity of plants, including many endemic and rare species. The objective of the project was to investigate the impact of climate, altitude and edaphic factors on the floral diversity in Hunza valley (Northern Areas, Pakistan), and further to investigate the changes in endogenous stress hormone (abscisic acid), sugar and proline (as osmoregulant) in plants with respect to variation in altitude.
Five field areas viz. Ultar, Sheshpar, Updegar, Batura and Chupursan were selected for vegetation surveys, measurement of air temperature and humidity during summer, determination of chemical characteristics of the soils and ethnobotanical studies of selected flora. To record the important plants used as curatives by Brusho tribes of Hunza valley an ethnobotanical survey was conducted. Thermo- hygrograph with hair element and bimetal were installed for the measurement of temperature and humidity. Soil moisture determination was made by jet filled tensiometers. High Performance Liquid Chromatography was used for determination of a plant stress hormone abscisic acid whereas, sugars, protein and proline were determined spectrophotometerically. The Ultar pasture was chosen as the area for detailed study, because of its easy access and high plant species diversity. Chemical characteristics of soil were determined using Atomic Absorption Spectrophotometer, as and where applied.
The total number of identified species from the field areas of Sheshpar, Ultar, Batura, Updeger, and Chupursan was 218, belonging to 47 families. The important families were Asteraceae (37 species), Papilionaceae (20 species), Poaceae (14 species), Lamiaceae (11species) and Rosaceae (10 species). The observed species richness pattern in the field areas showed that Sheshpar with 116 species had the highest species richness while Chupursan with 82 species inhabit minimum number of species.
The number of observed species at one to five sites and the number of commonly occurring species differed significantly whereas, the number of rare species showed no significant difference in the five field areas.
Species like Anaphalis nepalensis, Thymus serpyllum and Aristida showed a greater range of altitudinal limits as compared to other plant species observed in the areas of Ultar and Updegar. There was a significant difference in the number of species growing in the range of 0-300 m in the field areas of Ultar and Updegar.
The yearly average maximum and minimum temperatures and humidity recorded from April to September at Ultar and Chupursan showed that 2002 was a relatively warm year than 2001. A decreasing trend of humidity patterns was observed from south (Ultar) to north (Chupursan), showing adequate moisture availability at Ultar as compared to Chupursan.
The observed species richness was higher at Ultar as compared to Chupursan. Data showed that the soils of Ultar and Sheshpar are more acidic as compared to the other field areas. Values for K, Mn, P and N03 - N were observed to be highest at Ultar as compared with other field areas. Chupursan soil showed significantly higher Fe content, lower EC values and lower value of N03 - N content as compared to other areas.
Endogenous sugar, protein, proline and abscisic acid content of leaves were higher in all the species collected at 3,500 m a.s.l. as compared to 3,000 m a.s.l. Higher average soil moisture values were recorded on north facing slope than south facing slope at Ultar.
Over-gazing reduced the diversity of flora, and changed species composition, by depleting species at Ultar pastures. Stocking densities at Ultar pastures for three consecutive years (2000, 2001 and 2002) showed a general trend of increasing number of animal units. The increase in abscisic acid, protein, sugar and proline contents appeared to be correlated with the increase in altitude in all the plant species.