Tiering on Land – Trees and Forests (Late Palaeozoic)

Abstract

Trees with woody trunks first appeared in Middle Devonian times (390 MYA). However, a number of other types of Palaeozoic plants also achieved large sizes, most notably the arborescent lycopsids. The tropical wetlands of late Carboniferous and early Permian age (320–280 MYA), often referred to as the coal swamps or coal forests, were dominated by the arborescent lycopsids. Because of the unusual growth and reproductive strategies of these plants, and the water‐logged and low pH substrates, the ecological structure of these forests was quite different from most modern‐day forests. Rather than there being a vertical stratification of the vegetation controlled by light availability, there was a lateral ecological partitioning of the habitats controlled mainly by substrate conditions.

Key Concepts:

  • The late Palaeozoic coal forests were relatively open habitats, and therefore, light levels were not significant in controlling their ecological partitioning.

  • Substrate conditions were most important for controlling plant distribution in the coal forests, resulting in a lateral ecological partitioning, rather than a vertical tiering as is typical in most modern‐day forests.

  • The rapid determinate growth of the arborescent lycopsids that dominated the coal forests meant that huge amounts of peat were generated, which are now preserved as coal.

  • The coal forests were a major carbon sink during the late Palaeozoic times and had a significant impact on levels of atmospheric carbon dioxide and global climates.

Keywords: forests; Palaeozoic; Palaeobotany; trees

Figure 1.

Arborescent lycopsids growing in the wettest parts of the late Carboniferous coal forests. In the centre is a fully mature plant with a large crown of branching shoots bearing cones. On either side are younger plants at various stages of development, each consisting of an upright stem covered with leaves for much of its length. Illustration by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 2.

Model of part of the trunk of an arborescent lycopsid (Lepidodendron). Far left segment shows leaves still attached. Centre left shows the trunk after leaves have been removed, leaving photosynthetic leaf bases. Centre and far right show the trunk after different levels of bark have been shed. Modelled in wax by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 3.

Fossil of part of the bark from an arborescent lycopsid trunk (Lepidodendron), showing the leaf bases left after the leaves were shed. The specimen originated from the Pennant Formation, South Wales (late Moscovian in age), and is now in the collections of the National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 4.

Model of terminal leafy branches of a mature arborescent lycopsid. Modelled in wax by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 5.

Model of the female cone of an arborescent lycopsid (Lepidocarpon). Also shown are some isolated sporophylls from such a cone, each of which bore a single functional spore. The sporophylls would have detached themselves from the cone on maturity and aided the wind dispersal of the spore. Modelled in wax by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 6.

View of the vegetation growing on a raised levee in the late Carboniferous coal forests. In the background can be seen the large stems of arborescent lycopsids growing in the wetter parts of forest. In the foreground are marattialean tree ferns with an upright trunk and a crown of fronds. The undergrowth consisted of a combination of shrubby and herbaceous ferns, pteridosperms and cordaites. Artwork by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 7.

Reconstruction of a typical late Carboniferous horsetail (Calamites). These were characteristic of the banks of lakes and rivers of the tropical coal forests and were capable of regenerative growth if the plants were flooded by mud. Drawing by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 8.

Reconstruction of a typical late Carboniferous cordaite tree. Drawing by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 9.

View of part of the coal forests, showing the backswamp vegetation dominated by arborescent lycopsids on the left and centre. To the right is a river bounded by levees, growing on which were ferns, pteridosperms, cordaites and some sphenophytes. Artwork by Annette Townsend (Cardiff) and now stored in the Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff. Copyright of National Museum Wales.

Figure 10.

Palaeogeograhical map showing distribution of coal forests (green) during middle Moscovian times. Land areas shown in light brown, upland areas in dark brown. Redrawn from Cleal and Thomas using a base map by C Scotese, with modifications after Laveine et al.. Copyright of National Museum Wales.

Figure 11.

Correlation of the geographical size of the coal forests (centre) with evidence of global temperatures, determined from the size of the polar ice sheet (left) and vegetation patterns observed in the northern temperate and high latitudes. Modified from Cleal and Thomas .

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Further Reading

Cleal CJ (ed.) (1991) Plant Fossils in Geological Investigation: The Palaeozoic. Chichester, UK: Ellis Horwood.

Cleal CJ and Thomas BA (1994) Plant Fossils of the British Coal Measures. London: The Palaeontological Association.

Cleal CJ and Thomas BA (1995) Palaeozoic Palaeobotany of Great Britain. London: Chapman and Hall.

Cleal CJ and Thomas BA (2009) Introduction to Plant Fossils. Cambridge: Cambridge University Press.

Meyen SV (1987) Fundamentals of Palaeobotany. London: Chapman and Hall.

Stewart WN and Rothwell GW (1993) Paleobotany and the Evolution of Plants, 2nd edn. Cambridge, UK: Cambridge University Press.

Taylor TN, Taylor EL and Krings M (2009) Palaeobotany. The Biology and Evolution of Fossil Plants (Second Edition). Burlington, MA: Academic Press.

Thomas BA and Spicer RA (1986) The Evolution and Palaeobiology of Land Plants. London: Croom Helm.

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Cleal, Christopher Jonathan(Sep 2010) Tiering on Land – Trees and Forests (Late Palaeozoic). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001642.pub2]