Cretaceous and Tertiary climate change and the past distribution of megathermal rainforests

Abstract

"It was in Mid Cretaceous mid-latitudes, which were in part characterized by perhumid, frost-free climates, that mesic forests first became an important setting for angiosperms in both hemispheres, and by the Cenomanian most of the physiognomic leaf types characteristic of megathermal forests—including simple entire leaves with drip tips, compound and palmate leaves—were already in place." p.6 "Within the equatorial zone, mesic angiosperm-dominated forests did not appear until some time after their appearance in mid-latitudes (Morley, 2000a)." Angiosperm Venation and transpiration - affecting regional climate and micro-climates, diversification of angiosperms and of pteridophytes. K-T boundary: The K–T meteorite impact probably had a major effect on rainforests globally (Figure 1.3) but did not substantially affect the main angiosperm lineages that characterized each area. Gymnosperms, however, fared particularly poorly in the low latitudes following the K–T event. In the earliest Tertiary gymnosperms were virtually absent from each of the equatorial rainforest blocks. Recovery of rainforest diversity after the K–T event is generally acknowledged to have taken some 10 Myr (Fredriksen, 1994), but a recently discovered leaf fossil flora from the Paleocene of Colorado (Johnson and Ellis, 2002) suggests much more rapid recovery, perhaps within 1.4Myr, suggesting that much more work needs to be done to determine just how long it takes for rainforests to re-establish their diversity after a cataclysmic event. Diversity: conclusions p. 26 The scene for evolution of rainforest species is thus of gradual differentiation over a long time period with different forcing mechanisms inhibiting dispersal and isolating populations. The high diversities seen in rainforest refugia—or hot spots—are likely to relate to areas of long-term continuity of moist climates within those areas rather than to allopatric speciation driven by habitat fragmentation. The highest diversities, however, are seen where climatic stability coincides with areas which have experienced phases of orogeny and especially of plate collision, as seen from pollen data for Java following the Middle/Early Eocene collision of the Indian and Asian Plates, and for the Middle Miocene of the Sunda region following the collision of the Australian and Asian Plates. From the neotropics, molecular and biogeographical data suggest that high diversities may relate to the uplift of the Andes in the Miocene and the formation of the Panamanian Isthmus in the Pliocene. Low equatorial floristic diversities may follow periods of cool, and particularly dry climates, as was the case following the end Eocene cooling event, when in Southeast Asia cool climate oscillations brought freezing temperatures to tropical mountains with corresponding seasonally dry lowland climates. Similarly, for equatorial Africa increased seasonality of climate from the Early Miocene onward accounts for the current depauperate nature of African rainforest flora. _____________ Note: refers to similarity of ecological succession and phasic communities on peat forests in Borneo in studies of Middle Miocene coals in Brunei (Anderson and Muller, 1975), and current-day succession (Morley in press) Morley, R. J. (in press) Ecology of Tertiary coals in SE Asia. In: T. A. Moore (Ed.), Coal Geology of Indonesia: From Peat Formation to Oil Generation (Advances in Sedimentology Series). Elsevier, North-Holland, The Netherlands. 1.1 Introduction 1.2 Differences between Quaternary and Tertiary megathermal forests 1.3 Late Cretaceous expansion of megathermal forests 1.4 Megathermal rainforests during the Early Tertiary period of greenhouse climate 1.5 Middle Eocene to Oligocene climates 1.5.1 General trends 1.5.2 Climate change in low latitudes 1.6 Early Miocene and earliest Middle Miocene, return of greenhouse climates 1.6.1 General trends 1.6.2 Climate change in low latitudes . 1.7 Later Middle Miocene to Pliocene, global cooling, and retraction of megathermal rainforests to the tropics 1.8 Trends in rainforest diversity based on the palynological record 1.9 Scenario for rainforest evolution and diversification 1.10 References