Coal forest
Encyclopedia
Coal forests were the vast swathes of wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....

s that extended over much of the tropical land areas during late Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 (Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...

) and Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 times. These forests got their name because they accumulated enormous deposits of peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...

 which later changed into coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

. As much of the carbon in this enormous amount of peat came from photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

 splitting existing carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, it is thought that the accompanying split-off oxygen went into the atmosphere, greatly increasing its ppO2
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

: one estimate says to about 35%, making it easier for animals to breathe air as a source of oxygen, as seen in the size of Meganeura
Meganeura
Meganeura is a genus of extinct insects from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of more than 75 cm , M. monyi is one of the largest known flying insect species; the Permian Meganeuropsis...

 compared to modern dragonflies.

Coal Forests covered tropical Euramerica
Euramerica
Euramerica was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica, and Avalonia cratons .300 million years ago in the Late Carboniferous tropical rainforests lay over the equator of Euramerica...

 (Europe, eastern North America, northwesternmost Africa) and Cathaysia (mainly China). Climate change devastated these tropical rainforests during the Carboniferous Period. The Carboniferous Rainforest Collapse
Carboniferous Rainforest Collapse
The Carboniferous Rainforest Collapse was an extinction event that occurred around 305 million years ago in the Carboniferous period). Vast coal forests covered the equatorial region of Euramerica...

 was caused by a cooler, drier climate that initially fragmented, then collapsed the rainforest ecosystem. During most of the rest of Carboniferous times, the Coal Forests were mainly restricted to refugia
Refugia
In biology a refugium , sometimes termed simply a refuge, is a location of an isolated or relict population of a once more widespread species. This isolation can be due to climatic changes, geography, or human activities such as deforestation and over-hunting...

 in North America (such as the Appalachian and Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

 coal basins) and central Europe. At the very end of the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 period, however, the Coal Forests underwent a resurgence, expanding mainly in eastern Asia, notably China; they never recovered fully in Euramerica. The Chinese Coal Forests continued to flourish well into Permian times. This resurgence of the Coal Forests in very late Carboniferous times seems to have coincided with a lowering of global temperatures and a return of extensive polar ice in southern Gondwana, perhaps due to lessening of greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

 due to massive coal deposition abstracting much carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 from the atmosphere.

Environment

The coal forests seem to have been areas of flat low-lying swampy land with rivers flowing through from higher drier land. The rivers, when they flooded, dropped most of their silt near the river, gradually building up natural levee
Levee
A levee, levée, dike , embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels...

s. Sometimes areas subsided and became lakes; sometimes lakes silted up and became land. Sometimes a high flood would break a levee and bury an area in new silt. Sometimes a river would change its course. Sometimes the forest dried enough to be set on fire by lightning; the fusain
Fusain
Fusain is a fossilised carbon deposit, which - after some controversy - has been identified as fossilised charcoal.It is fibrous, black and opaque, and often preserves details of cell wall architecture...

 component of coal is derived from charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...

 left by forest fires.

Plant Life

There seems to have been a rich and varied flora, with sets of species for each type of growing condition. The most varied flora seems to have been levee vegetation, with many species of trees, bushes, creepers, etc. Calamites thickets seem to have favored the edges of lakes and waterways. There seem to have been genera of lycopsids specialized for various roles: Paralycopodites as a pioneer on lakes newly silted shallow enough for land vegetation to start; Diaphorodendron later when the ground had become peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...

y. Other species specialized in re-settling land which had been briefly deforested by flooding: Synchysidendron and Lepidodendron in mineral-soil areas and Lepidophloios in peat areas. Cordaites may have favored drier areas of the swamp. One author thinks that Sigillaria
Sigillaria
Sigillaria is a genus of extinct, spore-bearing, arborescent plants which flourished in the Late Carboniferous period but dwindled to extinction in the early Permian period. It was a lycopodiophyte, and is related to the lycopsids, or club-mosses, but even more closely to quillworts, as was its...

 favored the intermediate areas between levee habitat and swamp habitat. In the later part of this period tree ferns tended to take over from lycopsid trees.

Animal life

Animal life was invertebrates (particularly insects), fish, labyrinthodont amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s, and early reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s. One evidence for plant-eating is tree lycopsid tracheid
Tracheid
Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast...

s found in an Arthropleura
Arthropleura
Arthropleura was a 0.3–2.6 metre long relative of centipedes and millipedes, native to the Upper Carboniferous of what is now northeastern North America and Scotland...

's gut. Amphibians were widespread but once the coal forests fragmented, the new environment was better suited to reptiles, which became more diverse and even varied their diet in the rapidly changing environment.

Species list

Some of the characteristic plants of the Coal Forests were:
  • Sigillaria
    Sigillaria
    Sigillaria is a genus of extinct, spore-bearing, arborescent plants which flourished in the Late Carboniferous period but dwindled to extinction in the early Permian period. It was a lycopodiophyte, and is related to the lycopsids, or club-mosses, but even more closely to quillworts, as was its...

  • Lepidodendron
    Lepidodendron
    Lepidodendron is an extinct genus of primitive, vascular, arborescent plant related to the Lycopsids . It was part of the coal forest flora. They sometimes reached heights of over , and the trunks were often over in diameter, and thrived during the Carboniferous period...

  • Calamites
    Calamites
    Calamites is a genus of extinct arborescent horsetails to which the modern horsetails are closely related. Unlike their herbaceous modern cousins, these plants were medium-sized trees, growing to heights of more than 30 meters...

  • pteridosperms


Genera recorded in Great Britain include:
  • Pteridosperm leaves: Alethopteris
    Alethopteris
    Alethopteris is an genus of fossil seed ferns that existed in the Carboniferous period ....

    , Callipteridium, Cyclopteris (leaf bases), ?Desmopteris, Dicksonites, Eusphenopteris, Fortopteris, Hymenophyllites, Karinopteris, Laveinopteris, Linopteris, Lonchopteris, Lyginopteris, Macroneuropteris, Margaritopteris, Mariopteris, Neuralethopteris, Neuropteris
    Neuropteris
    Neuropteris is an extinct seed fern that existed in the Carboniferous period, known only from fossils.Major species include Neuropteris loschi....

    , Odontopteris, Palmatopteris, Paropteris, Reticulopteris
  • Pteridosperm spore organs: Aulacotheca (male), Boulaya, Potoniea (male), Whittleseya (male)
  • Pteridosperm seeds: Gnetopsis, Hexagonocarpus, Holcospermum, Lagenospermum, ?Polypterocarpus, Rhabdocarpus, Trigonocarpus
  • Fern fronds: Aphlebia, Bertrandia, Corynepteris, Crossotheca, Cyathocarpus, Lobatopheris, Oligocarpia, Pecopteris
    Pecopteris
    Pecopteris was a form genus of leaves from several unrelated plant groups that flourished the early Carboniferous period and on to c. 250 Ma. Pecopteris first appeared in the Devonian period, but flourished in the Carboniferous, especially the Pennsylvanian...

    , Polymorphopteris, Renaultia, Sphyropteris, Sturia, Zeilleria
  • Tree-fern leaves: Caulopteris
  • Tree-fern stems: Artisophyton, Megaphyton
  • Lycopsid tree stems and leafy shoots: Cyperites, Lepidodendron
    Lepidodendron
    Lepidodendron is an extinct genus of primitive, vascular, arborescent plant related to the Lycopsids . It was part of the coal forest flora. They sometimes reached heights of over , and the trunks were often over in diameter, and thrived during the Carboniferous period...

    , Ulodendron
  • Lycopsid tree stems: Asolanus, Bothrodendron, Cyclostigma, Lepidophloios, Sigillaria
    Sigillaria
    Sigillaria is a genus of extinct, spore-bearing, arborescent plants which flourished in the Late Carboniferous period but dwindled to extinction in the early Permian period. It was a lycopodiophyte, and is related to the lycopsids, or club-mosses, but even more closely to quillworts, as was its...

    , Sublepidophloios, Syringodendron (de-barked)
  • Lycopsid reproductive parts: Flemingites, Lepidodostrobus, Lepidodostrobophyllum (sporophylls), Sigillariostrobus
  • Lycopsid (herbaceous) stems: Lycopodites, Selaginellites
  • Sphenopsid leaves: Annularia
    Annularia
    Annularia is a plant fossil from the Carboniferous . It is a form taxon. Its radiating structures are most likely the leaves of Calamites....

    , Asterophyllites
  • Sphenopsid stems: Calamites
    Calamites
    Calamites is a genus of extinct arborescent horsetails to which the modern horsetails are closely related. Unlike their herbaceous modern cousins, these plants were medium-sized trees, growing to heights of more than 30 meters...

  • Sphenopsid reproductive parts: Bowmanites, Calamostachys, Macrostachya, Palaeostachya
  • Cordaite leaves: Cordaites
    Cordaites
    Cordaites is an important genus of extinct gymnosperms which grew on wet ground similar to the Everglades in Florida. Brackish water mussels and crustacea are found frequently between the roots of these trees. The fossils are found in rock sections from the Upper Carboniferous of the Dutch -...

  • Cordaite stem pith case: Artisia (pith cast)
  • Cordaite seeds: Cordaicarpus
  • Cordaite cones and seeds: Cordaitanthus
  • May be progymnosperm
    Progymnosperm
    The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the "trimerophytes", and eventually gave rise to the gymnosperms. They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida...

    : leaves: Noeggerathia
  • Conifer leaves: Walchia
  • Seeds: Carpolithus, Cornucarpus, Samaropsis


Palaeontologists have described many species for some of these genera, e.g. (in Britain): Sigillaria 33, Lepidodendron 19, Alethopteris (pteridosperm leaves) 11, Calamites
Calamites
Calamites is a genus of extinct arborescent horsetails to which the modern horsetails are closely related. Unlike their herbaceous modern cousins, these plants were medium-sized trees, growing to heights of more than 30 meters...

 8.

Some easily identified species occur over a wide area but only for a small part of the coal-forming period, and are thus useful as zone fossils.

Further reading

  • Prehistoric Park#Episode 5: The Bug House and Walking with Monsters#Episode Two are set partly in coal forest.

Links to reconstruction images of coal forest

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