Palynological studies and Holocene ecosystem dynamics in north western Khyber Pakhtunkhwa Province of Pakistan in the Hindu Kush Himalayan region

Abstract

Khyber Pakhtunkhwa (31°49´N, 70°55´E to 35°50´N, 71°47´E) is located in north western Pakistan in south Asia. The Hindu Kush mountains of Afghanistan lies to its west, Indian Himalayas to the northeast and Karakorum Mountains south of Tibetan Plateau of China, lying to its north. This PhD-project comprises of three separate studies conducted along a 200 km elevational gradient in Khyber Pakhtunkhwa starting from the sedimentary basin plains of Peshawar valley (275 m a.s.l.) reaching high up to Malam Jabba Hills in Swat (2600 m a.s.l.). The first study based on a specific dataset of 160 Poaceae species reveal trends showing that C3 and C4 polyploid Poaceae species have larger grain sizes than their respective diploid species. C4 species have larger grain size than C3 species in our specific dataset. Grasslands dominated by C3 or C4 Poaceae species from different regions and habitats can be separated by studying the pattern of trend in their increasing or decreasing pollen grain sizes. Polyploidy is more common in C4 than in C3 Poaceae species in our dataset. The method used can be applied on Poaceae pollen grains deposited in environmental archives to reconstruct past climate and to assess the dynamics of past grassland ecosystems. This study will not only help the ongoing palaeo-ecological studies in unravelling aspects such as changes in vegetation composition and shifts in biomes of past grassland ecosystems but also provide useful insights for future predictions. The second study deals with modern pollen spectra from surface samples and their relationship with the surrounding vegetation which provide useful data for the interpretation of future Holocene pollen records. Along the 200 km gradient four distinct elevational zones are defined by dominating plant families, which are reflected in the pollen assemblages by different proportions, indicating a significant correlation between pollen rain and vegetation in families like Poaceae, Asteraceae, Cyperaceae, Verbenaceae, Acanthaceae and Euphorbiaceae. Pollen assemblages also vary considerably from the associated vegetation composition and major discrepancies are caused by large differences in pollen and vegetation proportions in Boraginaceae, Saxifragaceae, Apiaceae, Balsaminaceae and Rubiaceae families. The establishment of a modern pollen rain – vegetation relationship, at least on family level, is necessary for calibration and interpretation of fossil pollen record from such sites. The third study deals with fossil pollen record from Kabal Swat area, providing a detailed history of the vegetation and climate of the Hindu Kush Mountains since the last 3300 years of the late Holocene. From 3300 to 2400 cal yrs BP, the subtropical semiarid herbaceous vegetation represented by Cyperaceae and Poaceae species was dominant in the valley. They were replaced by mixed coniferous forests of Taxus, Pinus, Juglans, Poaceae and Cyperaceae from 2400 to 900 cal yrs BP, suggesting a comparatively moderate climatic variability during the late Holocene. herbaceous vegetation from 2400 to 1500 cal yr BP and again its increase from 1500 to 1200 cal yr BP, points to the respective shrinkage and spread of grassland boundaries in Kabal Swat valley, and also suggest that the area went through respective wet-cool and dry-warm periods. Herbs were mostly abundant in most samples from 900-300 cal yr BP. This change can be attributed to a more pronounced impact of widespread deforestation, agricultural activities and to a drier summer climate. Evergreen trees and shrubs such as Oleaceae, Myrtaceae, Moraceae species, Juglans and Dodonaea dominated and were consistently present from 2400 cal yr BP to the present. Conifers like Pinus, Taxus, Picea, Abies and Cedrus were frequent in the study area from 300 cal yr BP to the present. These conifers mostly occur in the mixed coniferous forests at higher elevation in the alpine area today. Further high resolution Holocene pollen records of the Hindu Kush are needed, to allow a more elaborate comparison with other South and Central Asian palaeo-archives, providing more detailed and applicable knowledge for management and conservation issues.