Changing patterns of vegetation through Siwalik succession

Abstract

The palaeobotanical record from the Neogene of Himalaya has been examined and an attempt has been made to reconstruct the vegetation patterns and throw light on palaeoclimate of the region during Siwalik time. Though the flora of the Pre-Siwalik Neogene from which the Siwalik flora evolved is poorly documented, a few palynofossils from the Kasauli and Dagshai formations indicate the existence of subtropical to temperate vegetation in the Upper reaches of the newly built Himalaya. On the contrary, a fairly rich assemblage of megafossils from the Siwalik indicates widespread tropical evergreen to moist deciduous mixed forest in the lowland sub-Himalayan zone during Middle Miocene-Pliocene The assemblage is dominated by wet evergreen dipterocarps and associated taxa, most of which are known to have entered the Indian subcontinent from southeast Asia during Miocene and subsequently spread all over and finally reached the lower slopes of sub-Himalaya. This has resulted increase in the diversity of tropical vegetation.
 The post-Pliocene orogeny of Himalaya brought great changes in the topography and climate which adversely affected the vegetation patterns of the region. The Early and Middle Siwalik tropical evergreen forest whose chief component are Anisoptera, Dipterocarpus, Hopea, Shorea (other than Shorea robusta), Polyalthia, Calophyllum, Aphanamixis, Dysoxylum, Gluta, Dracontomelum, Mangifera, Swintonia, Cynometra, Koompassia, Ormosia, Pongamia, Sindora, Duabanga, Diospyros spp., Myristica, etc. started dwindling towards the end of Middle Siwalik and subsequently disappeared from western and central sectors, though a few taxa like Mangifera, Litsea, Cinnamomum, Bauhinia, Dalbergia, Ficus, etc. continued to adjust to the new climatic conditions. Extinction of tropical evergreen taxa and further rise of Himalaya gave way to proliferation and diversification of tropical and subtropical moist deciduous to dry deciduous temperate vegetation in the lower and higher slopes respectively, as is also evidenced from the palynological record.

Antiquity and migratory paths of angiosperms in India

“…The dicot forms became richer during the Oligocene (Awasthi & Mehrotra, 1995) but the palms are represented by Nypa only (Mehrotra et al, 2003). The new forms are Saccopetalum, Kayea, Pterygota, Santiria, Parishia, Entada, Rhizophora, Vernonia, Memecylon, Avicennia, Alstonia, Myristica, Apollonias, Bridelia, etc. After the Oligocene, an influx of Southeast Asian elements has been observed in the fossil records as Dipterocarpaceae, a typical Southeast Asian family, could be seen in the fossil records at the beginning of the Neogene (Awasthi, 1992;Guleria, 1992). The other forms, such as, Gluta and Swintonia of Anacardiaceae, Sindora, Koompassia, Afzelia-Intsia, etc.…”

A brief account of Cenozoic (Tertiary) flora of India: its development, significance and future considerations

“…More and more fossil plants were studied with a point of view of their taxonomy so that the antiquity of the taxon could be traced which may throw light on the evolution of particular taxon. A large amount of data was accumulated and synthesized for the proper evaluation of the Cenozoic (Tertiary) flora (Awasthi, 1974(Awasthi, , 1982(Awasthi, , 1992Bande, 1992;Bande et al, 1988;Bonde, 2008;Bonde & Kumaran, 2002a, b;Bera & Banerjee, 2001;*Chitaley, *1950*Chitaley, * , 1974Guleria, 1992Guleria, , 2005Guleria & Srivastava, 2001;Guleria et al, 2002;Gupta et al, 2002;*Mahabale, 1950a*Mahabale, , b, 1959*Mahabale, , 1963*Mahabale, , 1965*Mahabale, , 1968Prakash, 1974;Lakhanpal, 1970Lakhanpal, , 1988Lakhanpal, , 1991Lakhanpal, , 1998Mehrotra, 2003;Roy & Mukhopadhyay, 2005;Prasad, 2008;Prasad & Pandey, 2008;Puri, 1957;*Sahni, 1953*Sahni, , 1964Trivedi, 1974;Vishnu Mittre, 1965;Kar et al, 2004;Banerjee et al, 2005) and many more. For further references and details readers may consult Srivastava 1990;Srivastava and Guleria 2006.…”

Investigation on plant fossils from Seria Naka in the Himalayan foot-hills of Uttar Pradesh, India

“…Alarge number of plant fossils including woods, leaves, fruits, seeds and flowers have been reported from the Siwalik sediments at different places, viz., Mohand, Hardwar, Kalagarh, Kathgodam, Tanakpur and Koilabas (at Indo-Nepal border) in Uttar Pradesh (Awasthi, 1992;Prasad, 1994aPrasad, , 1994bPrasad, , 1994cPrasad, , 1994d. Unfortunately, the fossiliferous area Seria Naka remained untouched and there is no report of plant fossils from this area, although this area is very rich in plant fossils especially leaf-impressions and fruit and seed-impressions.…”