Assembly and division of the South and South-East Asian flora in relation to tectonics and climate change

Abstract

Abstract:The main phases of plant dispersal into, and out of the South-East Asian region are discussed in relation to plate tectonics and changing climates. The South-East Asian area was a backwater of angiosperm evolution until the collision of the Indian Plate with Asia during the early Cenozoic. The Late Cretaceous remains poorly understood, but the Paleocene topography was mountainous, and the climate was probably seasonally dry, with the result that frost-tolerant conifers were common in upland areas and a low-diversity East Asian aspect flora occurred at low altitudes. India's drift into the perhumid low latitudes during the Eocene brought opportunities for the dispersal into South-East Asia of diverse groups of megathermal angiosperms which originated in West Gondwana. They successfully dispersed and became established across the South-East Asian region, initially carried by wind or birds, beginning at about 49 Ma, and with a terrestrial connection after about 41 Ma. Many Paleocene lineages probably went extinct, but a few dispersed in the opposite direction into India. The Oligocene was a time of seasonally dry climates except along the eastern and southern seaboard of Sundaland, but with the collision of the Australian Plate with Sunda at the end of the Oligocene widespread perhumid conditions became established across the region. The uplift of the Himalaya, coinciding with the middle Miocene thermal maximum, created opportunities for South-East Asian evergreen taxa to disperse into north India, and then with the late Miocene strengthening of the Indian monsoon, seasonally dry conditions expanded across India and Indochina, resulting eventually in the disappearance of closed forest over much of the Indian peninsula. This drying affected Sunda, but it is thought unlikely that a ‘savanna’ corridor was present across Sunda during the Pleistocene. Some dispersals from Australasia occurred following its collision with Sunda and following the uplift of New Guinea and the islands of Wallacea, Gondwanan montane taxa also found their way into the region. Phases of uplift across the Sunda region created opportunities for allopatric speciation and further dispersal opportunities. There is abundant evidence to suggest that the Pleistocene refuge theory applies to the South-East Asian region.

Origins and Assembly of Malesian Rainforests

“…In contrast to the scarce record of plant macrofossils, there are a wealth of Cenozoic palynological data and interpretations available from Malesia (Morley 1982(Morley , 1998(Morley , 2002(Morley , 2003(Morley , 2018aLelono & Morley 2011;Witts et al 2012). Palynological data represent extremely high sample sizes and stratigraphic densities, form the basis of biostratigraphic correlations, and provide evidence of numerous lineages not preserved as macrofossils, although isolated palynomorphs often do not provide sufficient information to allow unambiguous phylogenetic placement on a crown versus a stem lineage (Sauquet et al 2009).…”

“…The aseasonal (perhumid) rainforests of Malesia (Figure 1) may rival or exceed the Amazon forests in tree species richness (Slik et al 2015). They have assembled through time from lineages with remarkably different biogeographic histories (van Steenis 1934;Morley 2003Morley , 2018aSlik et al 2018) while providing habitat for a rich diversity of nonwoody plants, as well as terrestrial, arboreal, flying, gliding, and aquatic animals. Many of the region's lowland and other habitats have been cleared for settlement and agriculture on an industrial scale (Ashton 2014).…”

A molecular phylogeny of Southeast Asian Cyrtandra (Gesneriaceae) supports an emerging paradigm for Malesian plant biogeography

“…In the centre are the numerous smaller terranes and oceanic islands that comprise the Philippines and Wallacea, and in the east is the Sahul shelf and the large island of New Guinea, which is itself of composite origin. Adding a layer of complexity to this is the changing climate of the past 50 ma (Morley 2012(Morley , 2018, most strikingly the fluctuating glacials and interglacials of the Pleistocene (Woodruff 2010, Morley 2012, which impacted sea levels and the extent of vegetation types (Woodruff 2010, Cannon 2012, Morley 2012.…”

Himalayan Cenozoic biotas and climate: an overview of recent advances

“…Studies on phytogeographic aspects have also been undertaken. In an important contribution, Morley (2018) recently discussed the issue of plant dispersal in to and out of India and South-East Asia in relation to plate tectonics and climate change. He suggested that India's drift into the perhumid low latitudes during the Eocene resulted in the dispersal of diverse groups of megathermal angiosperms into South-East Asia.…”