Annu. Rev. Earth Planet. Sci. 2001. 29:461-87 
RESPONSE OF LATE CARBONIFEROUS AND 
EARLY PERMIAN PLANT COMMUNITIES 
TO CLIMATE CHANGE ^ 
William A DiMichele^, Hermann W Pfefferkorn^, and 
Robert A Gastaldo^ 
Department of Paleobiology, National Museum of Natural History, Smithsonian 
Institution, Washington, D.C. 20560; e-mail: dimichele.bill@nmnh.si.edu 
Department of Earth and Environmental Sciences, University of Pennsylvania, 
Philadelphia, Pennsylvania 19104; e-mail: hpfeffer?sas.upenn.edu 
Department of Geology, Colby College, Waterville, Maine 04901; 
e-mail: ragastal@colby.edu 
Key Words    ecosystem stability, glaciation, biome, coal, extinction 
I Abstract Late Carboniferous and Early Permian strata record the transition from 
a cold interval in Earth history, characterized by the repeated periods of glaciation 
and deglaciation of the southern pole, to a warm-climate interval. Consequently, this 
time period is the best available analogue to the Recent in which to study patterns of 
vegetational response, both to glacial-interglacial oscillation and to the appearance of 
warm climate. Carboniferous wetland ecosystems were dominated by spore-producing 
plants and early gymnospermous seed plants. Global climate changes, largely drying, 
forced vegetational changes, resulting in a change to a seed plant-dominated world, 
beginning first at high latitudes during the Carboniferous, reaching the tropics near the 
Permo-Carboniferous boundary. For most of this time plant assemblages were very 
conservative in their composition. Change in the dominant vegetation was generally a 
rapid process, which suggests that environmental thresholds were crossed, and involved 
little mixing of elements from the wet and dry floras. 
INTRODUCTION 
When the Carboniferous or "Coal Age" is popularly envisioned, steaming trop- 
ical jungles, giant insects, and bizarre plants take center stage. Although coal 
swamps were prominent in tropical lowland-wetland areas, distinct vegetation oc- 
cupied tropical extrabasinal areas and the northern and southern temperate zones 
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461 
462 DIMICHELE ? PFEFFERKORN ? GASTALDO 
PERMIAN 
UPPER 
PERMIAN 
MIDDLE 
LOWER 
Artinskian 
Sakmarian 
Asselian 
UPPER 
CARBONIFEROUS 
STEPHANIAN 
Stephanian C 
UPPER 
PENNSYLVANIAN 
Stephanian B 
Barrulelian 
Cantabrian 
WESTPHALIAN 
Westphalian D MIDDLE 
PENNSYLVANIAN Bolsovian 
Duckmanttan 
LOWER 
PENNSYLVANIAN 
Langsettian 
NAMURIAN 
Yeadonian (G1) 
Marsdenian (R2) 
Kinderscoutian (R1) 
Alportian (H2) 
LOWER 
CARBONIFEROUS 
Chokierian (HI) 
MISSISSIPPIAN 
Arnsbergian (E2) 
Pendleian (E1) 
VISEAN 
TOURNAISIAN 
Figure 1    General stratigraphic nomenclature for the late Paleozoic. 
(DiMichele & Aronson 1992, Chaloner & Lacey 1973, Chaloner & Meyen 1973, 
Meyen 1982, Cuneo 1996). The Late Carboniferous was a cold interval in geolo- 
gical history. The expansion and contraction of glaciers, primarily in the Southern 
Hemisphere (Martini 1997), affected global climate and vegetational patterns in 
ways similar to those of the Pleistocene. Consequently, the Late Carboniferous 
serves as an excellent model system and the only point of comparison from the 
deep past to the Recent from which to examine the response of vegetation to global 
warming and cooling (Gastaldo et al 1996). 
In this review, we concentrate on vegetational patterns in the Late Carbonifer- 
ous and Early Permian, particularly in the tropics, which have received the most 
intensive study. Figure 1 shows the relevant stratigraphic nomenclature. 
CARBONIFEROUS AND PERMIAN VEGETATION 
Carboniferous vegetation can be divided into three broad paleogeographic pro- 
vinces (Chaloner & Lacey 1973): the tropical or Euramerican Province, the north- 
temperate or Angaran Province, and the south-temperate or Gondwanan Province. 
CARBONIFEROUS ECOLOGY AND CLIMATE 463 
These broad regions were characterized by distinctly different floras, and each 
contained multiple biomes reflective of climatic and edaphic differences within 
the province. Overlap among the provinces has been documented in several geo- 
graphical areas (Broutin et al 1995, Chandra & Sun 1997). These provinces may 
have changed compositionally over time within the Carboniferous as indicated 
by mid-Carboniferous floras on Gondwana that were referred to as the Paracas 
flora (AUeman & Pfefferkorn 1988, Pfefferkorn & Alleman 1989, lannuzzi et al 
1998). The tropical coal belt appears to have developed during the Namurian A 
(Pendleian), during the late Early Carboniferous (Raymond 1996), probably in 
response to the onset of glaciation (Roberts et al 1995). 
Raymond (1996) argued that glaciation increased global biogeographic dif- 
ferentiation by establishing and maintaining an ever-wet, ever-warm equatorial 
climate and by steepening the equator-to-pole temperature and rainfall gradient. 
This kind of climate persisted into the Permian, and an analysis of Permian vegeta- 
tional zonation (Ziegler 1990) suggests strong parallels to that of the modern world 
(Walter 1985). Because of the similarity of climate in the Late Carboniferous and 
Early Permian, it is likely that Late Carboniferous vegetation was more complex 
in its biogeographic distribution than is currently understood. 
Euramerica 
The tropical Euramerican Province consisted of at least two major biomes: 
that of wetlands and that of seasonally dry environments (Cridland & Morris 
1963; Havlena 1971, 1975; Broutin et al 1990; DiMichele & Aronson 1992; 
Falcon-Lang & Scott 2000). There is evidence of an even drier biome by the 
latest Early Permian and probably well before that time (DiMichele et al 2001). 
The ambiguity with which such vegetational zonation must be described reflects a 
significant taphonomic megabias (factors related to the formation and preservation 
of the fossil record that introduce large, systematic biases) in the terrestrial record 
(Gastaldo et al 1995, Behrensmeyer et al 2000), namely that the biota of uplands 
or extrabasinal areas (Pfefferkorn 1980) was rarely preserved in the older fossil 
record. Consequently, our knowledge of it depends on (a) fortuitous preservation 
of specimens transported into the depositional lowlands or into the marine realm, 
(b) rare occurrences of marginal assemblages in basinal areas during brief periods 
when climate was conducive to growth of the flora there (Havlena 1961, 1982, 
Cunningham et al 1993), (c) the preservation of an extrabasinal flora at the base of 
a basin fill when sedimentation had started but conditions had not yet changed, or 
(d) the close juxtaposition of elevated limestone terrain and a karst valley (Leary 
& Pfefferkorn 1977; Leary 1975, 1981). 
Wetlands The wetland biome is by far the best known and can be broadly subdi- 
vided into (a) the coal swamp flora of peat-forming mires and organic-rich swamps 
and (b) the flood basin flora of mineral or clastic substrate wetlands (Gastaldo 
464 DIMICHELE ? PFEFFERKORN ? GASTALDO 
1987, Gastaldo et al 1996). These floras overlapped considerably in composition, 
although largely at the generic level, and there were intermediate environments 
such as clastic swamps. 
Peat swamps have been botanically analyzed for more than 150 years because 
of the preservation of plants as permineralizations, which are generally composed 
of calcium carbonate and known as coal balls (Phillips et al 1976). Vegetational 
studies based on coal balls (Phillips et al 1985) complement extensive studies of 
coal-forming vegetation based on palynology (Smith 1962, Hacquebard et al 1965, 
Kosanke 1988, Eble & Grady 1990). The dominant plants of peat-forming swamps 
and mires were the arborescent lycopsids, or giant club mosses, particularly during 
the Namurian and Westphalian, or in American terminology, the Early and Middle 
Pennsylvanian. Lycopsid trees were differentiated ecologically within swamps and 
mires (Phillips & Peppers 1984, DiMichele & Phillips 1985), although all appear 
to have been short-lived, rapidly growing, and physiologically distinct from other 
trees (Phillips & DiMichele 1992). Their bark accounts for the vast bulk of tissue 
in coals of Westphalian age (Phillips et al 1985). 
During the Stephanian, roughly the Late Pennsylvanian, marattialean tree ferns 
dominated peat-forming habitats except in China, where lycopsid dominance con- 
tinued in wetlands (Guo 1990). Tree ferns were largely opportunistic weeds in the 
Westphalian and large trees in the Stephanian, cheaply constructed with massive 
reproductive output (Lesnikowska 1989). Both lycopsids and ferns reproduced 
strictly by spores freely released into the ambient environment. Other impor- 
tant tree groups were the seed-producing cordaites, which were close relatives of 
the conifers, and which dominated in some mid-Westphalian swamps (Costanza 
1985, Rothwell & Warner 1984), and medullosan pteridosperms or seed ferns, and 
the spore-producing calamites, close relatives of modern horsetails and scouring 
rushes and the only clonal trees in the wetland biome (Gastaldo 1992). 
Flood basin habitats were far more environmentally heterogeneous than peat 
swamps (Gastaldo et al 1995). The same basic plant groups characterized clastic 
and peat soils; the relative dominance-diversity patterns, however, were distinct. 
Flood basin floras, except for swamps, were dominated by pteridosperms, ferns, 
and calamites in proportions depending on the time and environment under consid- 
eration (Scott 1977, 1978; Pfefferkorn & Thomson 1982; Gastaldo 1987). Clastic 
swamps were dominated by lycopsids and pteridosperms in the Westphalian and 
by ferns and pteridosperms in the Stephanian, with some lycopsid dominance 
remaining. 
Seasonally Dry Environments Evidence for a seasonally dry biome in the Car- 
boniferous tropics appears in rocks of Westphalian age near the beginning of the 
Middle Pennsylvanian (Scott 1984) with the advent of conifer remains. Through- 
out the Westphalian, conifers occurred as fusain, or fossil charcoal, in areas 
adjacent to contemporaneously rising uplands (Lyons & Darrah 1989). Such flo- 
ras did not make their full appearance, however, until the Stephanian, in which 
they occurred as well-developed, strongly seed-plant-dominated assemblages 
CARBONIFEROUS ECOLOGY AND CLIMATE 465 
(Cridland & Morris 1963, McComas 1988, Winston 1983, DiMichele & Aronson 
1992) containing many genera and species unknown in typical wetland habitats. 
Groups such as conifers, peltasperms, ginkgophytes, pteridosperms, and cordaites 
were complemented by minor amounts of ferns and sphenopsids and virtually no 
club moss trees. In general, the plants of this flora were more advanced evolu- 
tionarily than those of the wetland biome, reflecting an evolutionary bias, namely 
that of new body plans surviving preferentially in marginal areas under reduced 
competition for resources. 
Angara 
Meyen (1982) provided the only English synopsis of the north-temperate Angara 
flora, the study of which has focused mainly on biogeographic and stratigraphic 
patterns in the distribution of species rather than on the paleoecological structure 
of the plant assemblages. Studies by Oshurkova (1985,1996), however, addressed 
paleoecological patterns. 
Early Carboniferous vegetation was dominated by a variety of lycopsids mostly 
of a subtree stature. Four stratigraphically successive phases have been recognized, 
each of low diversity with various pteridosperms and sphenopsids complementing 
the dominant lycopsid taxa. 
The lycopsid flora was rapidly replaced throughout Angaraland by a pterido- 
sperm-dominated assemblage beginning in the late Early Carboniferous or the 
earliest Late Carboniferous. Pteridosperm dominance was relatively short-lived, 
but it signified major, widespread environmental changes, probably climatic cool- 
ing and a decrease in the seasonality of rainfall. Recently, Falcon-Lang (1999a) 
inferred such a climatic shift in the Early Carboniferous of Great Britain on the 
basis of growth ring patterns. With the appearance of the pteridosperm flora, the 
first traces of coal appeared in the Angaran Province. The accumulation of peat 
in the Late Carboniferous at these high latitudes indicates likely floristic segrega- 
tion along environmental lines within the Angaran region beginning at this time, 
paralleling that development in Euramerica. 
Pteridosperm dominance was followed by three successive floras characterized 
by cordaitean gymnosperms. Although related to the cordaites of the Euramerican 
Province, Angaran cordaites belonged to distinct families and are described collec- 
tively as Ruflorians. Rufloria floras 1 and 2, the latter of which is the most diverse 
Angaran flora recorded, characterized the Late Carboniferous. These floras, de- 
spite their diversity of approximately 120 species, were almost entirely distinct tax- 
onomically from the tropical Euramerican flora. Overlap occurred at the generic 
level only in common genera such as Sphenophyllum, Annularia, Neuropteris, 
and Pecopteris, in addition to some less common genera such as Dicranophyl- 
lum. Actual diversity in these assemblages may have been higher than presently 
believed and may require considerable taxonomic revision in light of recent inves- 
tigations of the Carboniferous form genera to which these latter taxa belong. Cu- 
ticular analyses of pteridosperms (Zodrow & Cleal 1993, Krings & Kerp 1997) and 
466 DIMICHELE ? PFEFFERKORN ? GASTALDO 
cordaites (Zodrow et al 2000) demonstrate much higher diversity than is recogniz- 
able by gross morphology alone. These floras showed some regional variation 
in taxonomic composition but represented common species pools throughout 
Angaraland. Dominant elements in most collections were mainly cordaites and 
the pteridosperms, especially Angaropteridium, and in places, sphenopsids. 
Rufloria flora 3 was characteristic of the Early Permian and continued to be dom- 
inated by Ruflorian cordaites, the pteridosperm Angaropteridium, and sphenop- 
sids. Coexisting with Rufloria 3 was a flora that Meyen (1982) characterized as the 
first of four Rufloria-Cordaite floras. Such floras were dominated by Ruflorians, 
more typically Euramerican cordaites, sphenopsids, and minor amounts of ferns. 
As with the Carboniferous floras, there were regional differences in dominance 
and diversity patterns that reflected variation of a common species pool. 
Rufloria-Cordaite floras 3 and 4 were typical of the Late Permian. These floras 
included a number of genera that appeared earlier during the Early Permian in the 
Euramerican Province, such as the genera Comia and Compsopteris and the cal- 
lipterids. Also in this species pool were Euramerican genera such as Neuropteris, 
Annularia, and Pecopteris. In Euramerica, floras with these taxa represented the 
later development of the seasonally dry tropical flora. 
Gondwana 
Late Paleozoic floras of Gondwanaland were sharply divided into two types: 
those of Late Carboniferous character and those of Permian character. These 
floras were strikingly different. The Late Carboniferous flora was described by 
Archangelsky (1986, 1990) as being of low diversity but uniformly developed 
across the Gondwanan continent between 30?S and 60?S. The flora consisted 
of the likely pteridosperms Nothorhacopteris, Botrychiopsis, and Triphyllopteris, 
among others (Vega & Archangelsky 1997), and the lycopsids Bumbudendron, 
Malanzania, and Lepidodendropsis. Other leaves were assigned to Cordaites, 
although they were not clearly aligned to the Euramerican species of that form 
genus, and the ginkgophytes (Archangelsky & Cuneo 1990). 
Permian floras of Gondwanaland were significantly more diversified biogeo- 
graphically than those of the Late Carboniferous (Ciineo 1996), and the floristic 
provinciality changed during the course of the Permian. The characteristic plant 
of this flora was Glossopteris, a genus with many species, probably highly dif- 
ferentiated ecologically. Conifers and ferns were also important and dominated 
vegetation in some regions. Sphenopsids and lycopsids remained important com- 
ponents locally. In general, however, the Permian flora was nearly entirely distinct 
from that of the Late Carboniferous, suggesting a major environmental shift be- 
tween these two periods. 
Gondwanan climate was cool-temperate to periglacial as well as monsoonal 
over long time intervals throughout the Late Carboniferous and Early Permian 
(Parrish 1990). This view is certainly suggested by the plants (Archangelsky 1983, 
Retallack 1980) and sedimentological features (Krull 1999). Retallack (1980) 
CARBONIFEROUS ECOLOGY AND CLIMATE 467 
presented a detailed picture of the vegetation throughout this interval in the Sydney 
Basin of Australia, where the Late Carboniferous flora grew in floodplain settings 
and was dominated by several different pteridosperms. Isoetoid lycopsids may 
have been mangroves in protected coastal areas, paralleling other cormose lycop- 
sids in Euramerica (Blanton-Hooks & Gastaldo 1997). With the onset of glaciation 
in the Permian (Lopez-Gamundi 1997), the flora changed dramatically with the 
appearance of Glossopteris and the disappearance of most of the Late Carbonif- 
erous elements. The Permian flora appears to have been differentiated environ- 
mentally, although any given environment supported vegetation of low diversity. 
For the Early Permian, Retallack (1980) identified tundra vegetation dominated by 
the pteridosperm Botrychiopsis (Retallack 1999), taiga vegetation dominated by 
the glossopterid Gangamopteris, which marked the tree line, and swamp forests 
rich in Glossopteris species, many accumulating peat (which later became coal). 
The first of these coals was thin and accumulated in narrow mires with charac- 
teristic features of permafrost, including a Gangamopteris-dovmn&icA flora. Later 
coals were thicker, apparently accumulating under more cold-temperate condi- 
tions, and were dominated by Glossopteris (Krull 1999). The petrography of 
such coals was described by Diessel (1986, 1992), who developed a method of 
inferring vegetational structure and composition from the petrographic character 
of the coal. Bustin (1997) summarized these studies and compared Gondwanan 
Permian coal formation to that of modern cold-temperate environments. For the 
Late Permian, Retallack (1980) described the appearance of new kinds of vege- 
tation in alluvial plain environments associated with local uplift and tectonically 
induced drying of the Sydney Basin. This vegetation included a wider variety of 
conifers (Archangelsky & Ciineo 1987, Stockey 1990) in families that appeared 
to be restricted regionally. 
In Antarctica, at least three phases of vegetational change have been reported, 
primarily on the basis of the palynological record (Playford 1990). Certain 
early palynological reports have come under suspicion of contamination dur- 
ing processing (Schopf 1983), resulting in discounting of reports of Euramerican 
taxa in otherwise regionally distinct Gondwanan assemblages. The microfloral 
zones recognized by Kyle & Schopf (1982) encompassed the latest Carboniferous 
and Early Permian in which there was an interpreted increase in the abundance 
of cordaitean and pteridosperm taxa (Schopf & Askin 1980). The Parasaccites 
Zone, which may cross the systemic boundary, was interpreted to preserve not 
only cordaites and pteridosperms but also early glossopterids, cycadophytes, and 
ginkgophytes. Still greater palynological diversity was reported from the Pro- 
tohaloxpinus Zone, in which there was an increase in presumably glossopterid 
disaccate pollen. At least in the Weller coal measures there was an expansion of 
pteridophyte spores, which has been attributed to a warming trend in the region 
(Playford 1990). Kyle & Schopf (1982) correlated the palynoflora in the Weller 
coal as Artinskian or "Aktastinian-Baigendzhinian" (Early Permian) in age. Flu- 
vial and paludal environments in the Amery Group of the Prince Charles Mountains 
yielded a palynoflora that was somewhat younger, although the exact stratigraphic 
468 DIMICHELE ? PFEFFERKORN ? GASTALDO 
position is debatable. The Praecolpatites Zone originated from a reasonably di- 
verse flora that was dominated by glossopterids but comprised a variety of other 
groups. 
Mixed Gondwanan-Euramerican floras have been reported in many areas along 
the border of the two regions. Wagner (1962) documented a mixed Cathaysian- 
Gondwanan flora from Turkey, and El-Khayal & Wagner (1985) reported a mixed 
flora of Late Permian age from Saudi Arabia. The overlap of floral provinces 
is manifested by Zechstein-type conifers (e.g. Pseudovoltzia, Ullmannia) and 
Cathaysian plants (e.g. gigantopterids, Lobatannularia). In addition, El-Khayal 
& Wagner (1985) reported several species that are identical to those found in 
Turkey, including a Glossopteris (Archangelsky & Wagner 1983), which unites 
these assemblages on a climatic basis. 
LATE CARBONIFEROUS CLIMATE 
The Late Carboniferous was a globally cold interval, in the sense of Fischer (1982). 
Glaciation in the Southern Hemisphere may have involved large continental ice 
sheets (Visser 1993, 1997), although smaller glaciers in dispersed centers may 
have been more common than ice sheets, both near the pole and in high-altitude 
parts of the temperate zone (Dickens 1996). During this time, atmospheric CO2 
levels appear to have been low, contributing to the cold conditions (Berner 1998), 
and oxygen levels may have been high (Berner et al 2000). Glaciation began in 
the Early Carboniferous, possibly as early as the Tournaisian (Roberts et al 1995, 
Saltzman et al 2000), albeit long-term glacial-interglacial oscillations apparently 
did not develop fully until near the end of the Early Carboniferous (Frakes et al 
1992, Lopez-Gamundi 1997, Smith & Read 2000). Glacial-interglacial oscilla- 
tions likely had major effects on patterns of atmospheric circulation affecting the 
tropics by causing changes in the width and degree of oscillation of the Intertropical 
Convergence Zone. 
Once entrained, the pattern of deposition on the cratonic margins suggests 
repeated rises and falls of sea level (Ross & Ross 1988), probably paralleling 
those seen in the current ice age that result from the expansion and contraction of 
large facies (DiMichele et al 1996). Such changes in sea level were likely major 
contributors to perceived periodicity of depositional cycles in Late Carboniferous 
rocks, particularly on the craton. "Cyclothems" (Heckel 1986) record the repetition 
of marine and terrestrial environments and likely represent the compound effects 
of eustacy, tectonics, and climate (Klein & Willard 1989, Cecil 1990, Gastaldo 
et al 1991, Demko & Gastaldo 1996, Greb & Chesnut 1996). It is most likely 
that changes in the base level (in most cases, sea level), especially when caused in 
significant part by glacial-interglacial oscillations, were strongly correlated with 
climatic changes in the tropics. Such changes were recorded in terrestrial rocks, 
which vary from coals, indicative of high levels of available moisture, to palesols 
with features indicative of seasonality in moisture delivery (Cecil 1990). 
CARBONIFEROUS ECOLOGY AND CLIMATE 469 
Models of Late Carboniferous climate (Crowley & Baum 1992, Crowley et al 
1996) suggest cool climates in the tropics during intervals of peat formation. 
Climates also may have changed from one state to another over periods shorter 
than 100,000 years (Crowley & North 1988). Such geologically rapid changes are 
indicated in the geological record (Frakes et al 1992) by equally rapid changes in 
floras (Phillips & Peppers 1984). 
The continents of this period were beginning to coalesce into Pangaea, creating 
a large land mass on the equator (Scotese et al 1999). Consequently, strongly 
monsoonal patterns of atmospheric circulation posited for the tropics would have 
strongly affected patterns of rainfall and vegetational development across the trop- 
ical regions (Parrish 1982). 
Studies of coal quality and paleobotanical patterns suggest a directional trend 
from tropical rainfall toward more seasonal and perhaps generally drier conditions 
throughout the Pennsylvanian, a trend that became particularly prominent at the 
Westphalian-Stephanian boundary. Climates appear to have become markedly 
more seasonal in the Stephanian (Phillips & Peppers 1984, Schutter & Heckel 
1985, Cecil 1990, Winston 1990, Donaldson & Eble 1991). Strong evidence 
suggests that in the early and middle Westphalian time domed mires were the 
source of major coal beds, whereas evidence from coal palynology and petrography 
suggests that planar peats predominated during the late Westphalian (Cecil et al 
1985, Winston & Stanton 1989, Cecil 1990). In climate-sensitive characteristics 
of fossil floras, changes similarly reflect changing climatic conditions in the late 
Westphalian (Pfefferkorn & Thomson 1982). For the Stephanian, the evidence 
from paleofloras suggests distinct oscillations in wetter and drier climatic intervals 
(DiMichele & Aronson 1992). 
VEGETATIONAL RESPONSE TO CHANGING CLIMATE 
Climatic changes affect vegetation on many spatial and temporal scales. Paleon- 
tology traditionally has been assigned analysis of those dynamics that leave their 
imprint on scales of hundreds of thousands to millions of years when, in fact, 
much shorter-term responses can be resolved. One of the major challenges faced 
by ecologists and paleoecologists alike is understanding how processes operating 
on different spatiotemporal scales affect patterns and constrain or enhance pro- 
cesses on larger or smaller scales. At this time, such understanding is elusive, 
even though patterns on different scales can be described. 
Short-Term Responses 
Vegetational responses to disturbances such as fires, floods, river avulsions, and 
changes in canopy structure can be considered short term. It is clear that climatic 
change may bring about directional changes in the frequencies and magnitudes of 
such events, so that such effects may be manifested on longer time scales. 
470 DIMICHELE ? PFEFFERKORN ? GASTALDO 
Disturbance Late Carboniferous and Permian terrestrial ecosystems were sub- 
ject to the same kinds of disturbances as modern systems. Consequently, it can 
be assumed that the relative importance and magnitude of disturbance agents var- 
ied both geographically and temporally. Fire is perhaps the best documented 
through the preservation of fusain and its petrographic equivalent, fusinite (Scott 
1989, Teichmiiller 1989, Scott & Jones 1994). In coal swamps, certain vegetation 
types have been found to be preferentially associated with charcoal and mineral 
matter, especially those enriched in medullosan pteridosperms and the lycopsid 
Paralycopodites (DiMichele & Phillips 1988, 1994), transitional between peat 
and clastic substrates (Pryor & Gastaldo 2000). The consequences of fires in 
peat swamps were highly variable, including termination of peat accumulation, 
changes in dominance patterns, or no detectable effects on vegetational compo- 
sition (Scott & Jones 1994). Fires also have been documented in better-drained 
environments including floodplains (Scott 1978, Falcon-Lang 1999b) and possibly 
uplands (Falcon-Lang & Scott 2000). Models of the oxygen content of the Late 
Carboniferous atmosphere suggest very high levels (Berner et al 2000), possibly 
causing higher fire frequencies than those of today (Beerling et al 1998). This 
conclusion has been disputed (Falcon-Lang & Scott 2000) on the basis of analysis 
of fossil wood in upland ecosystems. The effects of canopy disturbance, such as 
that caused by wind, can be seen only under peculiar preservational circumstances, 
although they may be inferred from spatial variation in assemblages representing 
rapid burial of a single forest. Such uprooting of trees (blowdown) was described 
by Wnuk & Pfefferkorn (1987) in organic shales preserved beneath a late Middle 
Pennsylvanian coal seam. In this deposit, whole trees, both canopy and understory, 
were preserved and demonstrated preferential directions of fall. Unfortunately, a 
deposit of this type does not record the nature of ecological recovery after such a 
catastrophic, short-term event. 
When contemporaneous vegetation can be evaluated over a wide geographic 
area, it may be possible to determine which associations of plants represent op- 
portunists specialized to disturbed environments. In a single Early Carboniferous 
autochthonous forest. Ware & Gastaldo (2000) identified discrete associations of 
canopy, subcanopy, and groundcover taxa in varying ratios. These data demon- 
strate variation in the pteridosperm biomass that accumulated on the forest floor 
in proportion to the amount of canopy biomass. These studies were supported 
by others that found differences in the cuticular thickness of pteridosperm leaves, 
reflecting growth in sun versus shade (Schabilion & Reihman 1985, Arens 1997). 
Determination of the light regimes under which plants grew permits separation of 
taxa that preferred open growth habitats, possibly resulting from canopy distur- 
bances, from those that preferred closed canopies. 
The consequences of flooding for vegetation must be inferred indirectly. Studies 
of coal swamp assemblages preserved in coal balls (Phillips & DiMichele 1981, 
DiMichele & Phillips, 1988, DiMichele & Phillips, 1996a) suggest the existence 
of specialized, low-diversity assemblages lacking ground cover and adapted to 
standing-water conditions. Such assemblages were dominated by the lycopsid tree 
CARBONIFEROUS ECOLOGY AND CLIMATE 471 
Lepidophloios and have been found in clastic swamps as well (Gastaldo 1987). 
On the basis of reproductive morphology and patterns of occurrence, few Late 
Carboniferous plants, other than arborescent lycopsids and calamites, appear to 
have been tolerant of long-duration flooding or partial burial by sediment (Gastaldo 
1992), a disturbance mode that would have dramatically altered local landscapes. 
Succession Succession has been documented in tropical coal swamps, both with 
megafossils and microfossils. Analysis of this process examined dynamics similar 
to those studied by both neoecologists and paleoecologists evaluating Quaternary 
vegetation. A Late Carboniferous peat-forming mire may have taken up to 10,000 
or more years to accumulate (White et al 1995, DiMichele et al 1996). Over 
such a long period, successional patterns may be seen both as repeated transitions 
between one vegetation type and another or as a directional pattern of vegetational 
change through the period of accumulation of the peat body (DiMichele & Phillips 
1994). In the latter case, vegetational change was likely driven by changes in 
climate during peat accumulation or by changes in edaphic conditions brought on 
by thickening of the peat substrate. 
Transition frequency analysis of data from coal-ball macrofossils, especially 
data on patterns of root penetration, have revealed patterns of succession in peat- 
forming mires. Raymond (1988) identified three plant communities in a Middle 
Pennsylvanian coal from Iowa: those dominated by cordaitean gymnosperms, 
those dominated by medullosan pteridosperms and marattialean tree ferns, and 
those dominated by arborescent lycopsids, in that order of temporal succession. 
Studies of peat preservation suggest that the three assemblages grew under different 
environmental conditions and followed one another as peat accumulated, showing 
only minor intercalations. The pattern suggests a strong environmental control on 
vegetational change during peat accumulation. 
Pryor (1993) similarly found a directional trend in dominance patterns in a 
Late Pennsylvanian coal bed in Ohio. In this instance, subtree lycopsids were 
succeeded by pteridosperm and marattialean tree fern vegetation with extensive 
shrubs and a fern ground cover, which were then succeeded by a canopy of marat- 
tialean tree ferns. Although there were minor reversals of this pattern during peat 
accumulation, there was a clear overall temporal trend in patterns of dominance. 
DiMichele & Phillips (1988) did not find such patterns of successional change 
in a profile analysis of a thick, late Middle Pennsylvanian coal seam from Illinois. 
Rather, they recorded a shifting pattern of recurrence among three major plant 
assemblages representing a very wet to less wet gradient. The different kinds 
of successional patterns in peat-forming environments depend on the particular 
geographic site sampled within the ancient swamp. Spatial variability in edaphic 
conditions, including proximity to clastic influx, variations in nutrient availability, 
and variation in topography exerted by subsurface geology, would have played a 
major role in vegetational recurrence patterns. 
Palynological studies, combined with analyses of coal petrography and sed- 
imentology, provide a powerful means of analyzing vegetational changes in 
472 DIMICHELE ? PFEFFERKORN ? GASTALDO 
peat-forming mires and of correlating such changes with environmental con- 
trols. Such combined analyses were pioneered by Eble and colleagues and fo- 
cused mainly on coal beds of the Appalachian Basin of the eastern United States 
(e.g. Eble & Grady 1993, Eble & Greb 1997, Eble et al 1999, Greb et al 1999b). 
Two broad patterns in peat accumulation, relative to environmental controls, were 
detected from these analyses. Many peat bodies appear to have accumulated under 
planar, or rheotrophic (nutrients come from groundwater sources), conditions in 
which water chemistry and depth were the major controlling factors on plant dis- 
tribution (Cecil et al 1985). In such environments, vegetation was heterogeneous, 
and distinct patterns of vertical succession are not detectable. Vegetational dynam- 
ics in planar mires were described palynologically for numerous coals in tropical 
Euramerica (Mahaffy 1985, 1988; Bartram 1987; Grady & Eble 1990; Eble & 
Grady 1993; Willard 1993; Eble et al 1994; Hower et al 1994; Eble & Greb 1997, 
Eble et al 1999; Greb et al 1999b). Other peats showed patterns of vertical succes- 
sion attributable to progressive doming of peats, in which hydrology was controlled 
almost entirely by rainfall. Such mires are described as ombrotrophic and find ana- 
logues among modem peats in the Indonesian archipelago (Anderson 1964). 
Potonie & Koorders (1909), Leclercq (1926), and Teichmiiller (1955) suggested 
that modern tropical peat accumulations could serve as models for Carboniferous 
coals. Smith (1962, 1964), however, was among the first to argue on the basis 
of palynological and petrographic profiles for domed mires during the Late Car- 
boniferous. Patterns of directional, if sometimes oscillating, succession have been 
described that generally record a trend from lycopsid trees and pteridosperms to 
tree ferns and small lycopsids in upper layers of the peat (Eble & Grady 1990, 
Pierce et al 1991, Pierce et al 1993, Greb et al 1999a). As with coal ball macro- 
fossil analyses, distinct assemblages have been recognized in association with the 
base of the coal, with mineral partings, and with different degrees of peat de- 
cay, suggesting relationships with nutrient availability, standing water, and even 
seasonality of rainfall. 
In summary, vegetational analyses of tropical coal beds record the effects of 
climate during the period of peat accumulation. Both palynological and macro- 
fossil analyses indicate that some peats accumulated under strong influences of 
ground water, masking the effects of directional climatic trends as long as water 
levels were sufficiently consistently high to support swamp vegetation. In such en- 
vironments, sedimentological analysis may reveal climatic changes that separated 
benches of coal, recording an end to peat accumulation followed by reinitiation; 
such changes were often rapid and repeated. Other peats appear to have accu- 
mulated under conditions of consistently high rainfall and recorded directional 
successional trends related largely to the self-regulatory process of peat doming 
and progressive restriction of available nutrients. 
Such fine resolution of long-term vegetational trends is not possible in most 
clastic depositional systems because of the considerable hiatuses in sediment ac- 
cumulation and the taphonomic consequences of very short-term accumulation of 
plant debris (Gastaldo et al 1995, Wing & DiMichele 1995) in most floodplain 
CARBONIFEROUS ECOLOGY AND CLIMATE 473 
settings. It is possible, however, to evaluate these assemblages over longer time 
scales when the same (isotaphonomic) depositional settings have been preserved 
within fifth- and fourth-order cycles, particularly in coastal-deltaic regimes. Scott 
(1978) and Pryor & Gastaldo (2000), using finely split, layer-by-layer analysis, 
quantitatively examined patterns of vegetational change on floodplains and in clas- 
tic swamp habitats. They generally found compositional stability within a given 
setting, representing periods of accumulation of tens to hundreds of years, sug- 
gesting long-lived mature forests as the source vegetation. 
Patterns of Persistence and Change During 
Glacial-Interglacial Fluctuations 
The environmental signature of the Late Carboniferous and Early Permian, like 
that of the Holocene, was one of change. Glacial-interglacial fluctuations and their 
attendant climatic and sea level fluctuations were superimposed on yet longer-term 
climatic trends, reflecting patterns of atmospheric circulation, the slow movement 
of continental regions into different climatic zones, or transitions from globally 
cold to warm conditions. Consequently, from first principles, vegetation might 
be expected to respond by ever changing. This expectation has been confronted 
squarely by Quaternary paleoecology. In the temperate zones, particularly of 
the Northern Hemisphere, there is good evidence that plant species track climate 
individualistically, reflecting their individually evolved tolerances, rather than as 
part of integrated vegetational units (Webb 1988, Overpeck et al 1992). The 
pattern of environmental tracking is not so clear in the modern tropics, however. 
The study of long cores from Amazonia suggests some vertical movements of 
plants superimposed on a pattern of lowland vegetational persistence (Collinvaux 
et al 2000). The alternative hypothesis suggests that tropical vegetation broke up 
into a large number of refugia from which forests reexpanded (Burnham & Graham 
1999). 
As viewed from the Paleozoic, a major concern for all such analyses is what 
constitutes sameness in vegetational composition from temporal point to point. If 
temporally successive assemblages appear to be drawn from the same species pool 
or biome but in different proportions, do they constitute nonanalogue assemblages? 
What is the standard? How different must two assemblages be to be considered 
"different"? Studies of ancient marine communities attempted to answer some of 
these questions (Bennington & Bambach 1996, Bennington & Rutherford, 1999), 
but a solution remains elusive (Ivany 1999). 
In Late Carboniferous terrestrial systems, the concept of sameness was partly 
or perhaps largely defined by contrasts between very different vegetation types 
that succeeded each other temporally. Changes from one vegetation type to the 
other occurred relatively rapidly on all scales of spatiotemporal resolution in all 
paleogeographic provinces, although they were resolved at different levels in each 
province on the basis of the degree of study and the nature of available fossils. 
In the Euramerican tropics, such changes have been identified on several spatial 
474 DIMICHELE ? PFEFFERKORN ? GASTALDO 
scales: within the lowland-wetland species pool or biome at the Westphalian- 
Stephanian boundary (Pfefferkorn & Thomson 1982, Phillips & Peppers 1984), 
between the wetland biome and the seasonally dry biome during the Early Permian 
(Fredericksen 1972, Broutin et al 1990, DiMichele & Aronson 1992), and be- 
tween the seasonally dry and seasonally wet biomes during the late Early Permian 
(Ziegler 1990, DiMichele et al 2001). In the Angaran Province, significant vegeta- 
tional change has been recognized mainly at the biome level during the transition 
from the Early to the Late Carboniferous (Meyen 1982). In Gondwanaland, such 
changes have been described mainly at the level of biomes, particularly at the 
transition from the Carboniferous to the Permian (Retallack 1980, Archangelsky 
1990, Ciineo 1996), although smaller-scale patterns within species pools have 
been discussed (Archangelsky 1990). Alleman et al (1995) described seven dif- 
ferent plant communities from strata in a single section that nevertheless rep- 
resent a single ecological landscape that did not change while these beds were 
deposited. 
Stability and Instability Within a Biome The concept of changing vegetation 
in the face of glacial-interglacial oscillation is most firmly established for the late 
Pleistocene and Holocene temperate zone. Thus, the place to look for such patterns 
in the Late Carboniferous and Permian is in the temperate regions. Archangelsky 
(1990) stated the following: "In Gondwana, Carboniferous and Early Permian 
strata show drastic changes of floral assemblages through successive plant hori- 
zons. This pattern defines Gondwana as a Late Paleozoic floristic unit 
characterized by continuous migrational flows..." He attributed this finding 
to continental mobility and associated paleoclimatic changes. This comment 
suggests a temperate-zone vegetational response not unlike that recorded in the 
Holocene. 
In contrast to this pattern, the tropics of Euramerica recorded patterns of 
long-persistent vegetational associations in peat-forming environments during the 
Westphalian and again in the Stephanian, but on a different compositional theme 
(Phillips et al 1985, DiMichele et al 1996). From one coal bed to the next, each 
separated by climatic and sea level changes (Cecil 1990), similar vegetational gra- 
dients and basic intramire community associations can be identified quantitatively. 
Such persistent associations were not compositionally identical but appear to have 
been drawn repeatedly from the same species pool in roughly the same propor- 
tions, with some notable comings and goings as a consequence of species turnover 
through background extinction. Gradients of taxa by environmental variables were 
conserved. 
During such periods of vegetational stability, species turnover was strongly con- 
fined to ecomorphic themes, such that the loss of a lycopsid tree from low-diversity, 
flooded habitats resulted in replacement by a congener. Similarly, extinction of a 
medullosan pteridosperm or a cordaite species also resulted in replacement within 
the ecological fabric by an ecomorphic congener or close relative within the same 
phylogenetic lineage (DiMichele & Phillips 1996b). Coal ball studies suggest that 
CARBONIFEROUS ECOLOGY AND CLIMATE 475 
ecomorphic replacement and general preservation of ecological structure occur 
with background extinction levels of 10% or less (DiMichele & Phillips 1996b). 
Such low levels of background extinction may permit the fabric of species in- 
teractions to remain intact, thus exerting strong influence on species replacement 
dynamics. 
Similar patterns were found in flood basin environments during this same pe- 
riod at the level of large-scale changes within the tropical wetland species pool 
(Pfefferkorn & Thomson 1982). Data from compression fossils recorded in cores 
through European coal basins revealed a pattern much like that of the coal beds 
themselves, of repeated similar vegetational associations through the early part 
of the Late Carboniferous (Purkynova 1977, Havlena 1982). Analysis of species 
turnover also revealed that vegetation can tolerate about 10% turnover and remain 
structurally intact (Gastaldo et al 1998). 
What happened to vegetation between the coal-forming intervals? Did it mi- 
grate intact to other areas outside of the sampling window of the depositional 
realm? Did it break up into isolated refugia from which it emerged once regional 
climate became favorable again? Presently, such questions cannot be answered. 
A hint may be gained from deposits such as that of the Hamilton Quarry, a Late 
Pennsylvanian deposit from Kansas (Rothwell & Mapes 1988, Cunningham et al 
1993). The Hamilton deposit appears to have formed during a time of regional 
seasonal dryness and lowstand, and it includes conifers and other elements of dry- 
habitat vegetation. It also includes typically Carboniferous wetland plants that 
may have been living along wet stream bottoms in refugia. 
Rapid Changes in Vegetational State Within a Biome Near the boundary be- 
tween the Middle and Upper Pennsylvanian, approximately the boundary between 
the Westphalian and Stephanian, the tropical lowlands experienced a major plant 
extinction and subsequent change in patterns of vegetational dominance and di- 
versity. These changes appear to be a consequence of rapid changes in climate, 
probably caused by a pulse of global warming (Frakes et al 1992) associated with 
strong drying throughout much of the tropics (Phillips & Peppers 1984, Cecil 
1990, Winston 1990). The changes that occurred, although major when exam- 
ined quantitatively in terms of both species extinction and change in ecological 
structure and dynamics, were clearly confined to lowland-wetland vegetation and 
represent a reorganization of that particular species pool within its distinctive set 
of ecological and edaphic tolerances. 
The pattern, first identified by Phillips et al (1974) on the basis of coal pa- 
lynology, involves a major extinction of the dominant lycopsid trees and their 
replacement by marattialean tree ferns. A similar change has been documented in 
compression fossils of North America, although with taxonomic resolution some- 
what lower than that from coal balls (Gillespie & Pfefferkorn 1979). In both 
compression and coal ball assemblages, tree ferns began to rise in quantitative 
importance before the extinction, but they did not reach dominant levels until 
afterward (Pfefferkorn & Thomson 1982, Phillips et al 1985, Willard & Phillips 
476 DIMICHELE ? PFEFFERKORN ? GASTALDO 
1993, Pry or 1993). The dominance-diversity changes occurred in a rapid but time- 
transgressive manner from west to east across the Euramerican tropics (Phillips 
& Peppers 1984), but they never happened in parts of China, where Westphalian- 
type floras persisted into the Late Permian (Guo 1990, Chandra & Sun 1997). 
Macrofossil studies indicate a species loss in coal swamps through this transition 
of approximately 67% (DiMichele & Phillips 1996a), including 87% of the tree 
species. 
Detailed study of the vegetational characteristics of the extinction, on a coal- 
by-coal basis, is limited to coal palynology. Through a sequence of seven coals 
(all lacking coal ball macrofossils). Peppers (1985) documented high variability 
among dominant elements. Dominants varied among the lycopsid tree Sigillaria, 
the marsh-forming lycopsid subtree Chaloneria, and several kinds of tree ferns, 
with locally abundant calamites and pteridosperms. Patterns stabilized later in the 
Stephanian with the rise of marattialean tree ferns of several species and subdo- 
minance of pteridosperms and calamites. 
Several structural ecological changes were brought about by the extinction. 
These included shortening of the wet-dry gradient through extinction of the lycop- 
sid tree Lepidophloios, which colonized standing-water habitats; homogenization 
of lowland landscapes to dominance by tree ferns and pteridosperms in most 
habitats in both flood basins and peat swamps; increased stem diameters and in- 
ferred tree sizes of pteridosperms, trees ferns, and sphenopsids relative to their 
Westphalian ancestors; and a decline of nearly 50% in species diversity in coal 
swamps (DiMichele & Phillips 1996a, 1996b). 
Tree ferns of the Westphalian were largely opportunistic weeds, although larger, 
stand-forming species began appearing in the latest Westphalian (Pfefferkorn & 
Thomson 1982, Lesnikowska 1989). DiMichele & Phillips (1996b) suggested that 
the extinction removed patterns of incumbent advantage and permitted a lottery- 
like period of ecological and evolutionary escalation, much as Vermeij (1987) 
described for marine ecosystems after periods of major extinction. The resulting 
advantage went to opportunistic species capable of rapid exploitation of the dis- 
rupted landscapes and large pools of available nutrients. Marattialean tree ferns 
produced massive quantities of spores, were cheaply constructed, and as a group 
had wide ecological tolerances. Such taxa have the ability to colonize physical 
space and expropriate resources rapidly in ecological time, which may have given 
them an advantage in evolutionary time as well. 
The increase in size among virtually all plant groups that survived the extinction 
is reminiscent of the size changes seen among plants that colonize islands (Carlquist 
1974). It is possible that in a fragmented, postextinction landscape associated with 
considerable release from competitive, stabilizing selection, size increases were 
made possible by relaxation of long-standing constraints. Any explanation of this 
phenomenon must account for its occurrence across clade lines. It is possible that 
changing concentrations of atmospheric gases, particularly CO2 (Berner 1998), 
resulted in higher growth rates and biomass production. 
CARBONIFEROUS ECOLOGY AND CLIMATE 477 
Cold Interval-Warm Interval Transition: Interactions 
Between Biomes 
Beginning in the Stephanian, throughout the Euramerican tropics, floras appeared 
that were clearly distinct in taxonomic composition from those of the wetlands 
and were associated with indicators of seasonally dry climates (Mapes & Gastaldo 
1987, Broutin et al 1990, DiMichele & Aronson 1992). These "extrabasinal" 
floras (see Pfefferkorn 1980) were initially few and were intercalated as distinct 
beds among typically Late Carboniferous floras. This pattern suggests that the 
climatic excursion at the Westphalian-Stephanian boundary was the first in a series 
of oscillations that began to dry and warm the tropics, whereby the pulses of 
warming and drying brought an upland, or extrabasinal, flora into the basins and 
thus into the depositional and preservational window (Cridland & Morris 1963). 
By the middle Early Permian, the trend toward drying and warming was clearly 
established and associated with a marked change in the flora throughout most of 
the tropics except in China (Fredericksen 1972, Knoll 1984). 
The new flora was dominated by seed plants, including conifers, pteridosperms, 
ginkgophytes, and cycads. It was notably poor in ferns, lycopsids, and sphenop- 
sids, which were the framework plants of Late Carboniferous assemblages. The 
seasonally dry biome underwent significant changes through time (Read & 
Mamay 1964) due to gradual species turnover. Thus, this biome had internal 
dynamic properties not unlike those of the tropical wet biome and represented a 
distinct species pool, one having almost nothing in common with the ever-wet 
biome at the species level. The contrast between modern tropical wet and season- 
ally dry biomes is similarly sharp (Ziegler 1990). 
The new flora made its earliest appearances in the early mid-Westphalian 
(Westphahan B or Duckmantian). Scott & Chaloner (1983) and Scott (1984) 
described fusinized remains of conifer foliage from a typical lowland-wetland as- 
semblage. Lyons & Darrah (1989) tabulated the occurrences of all pre-Stephanian 
conifer fossils and found that all are preserved as charcoal and all occur in basins 
proximate to contemporaneously rising upland regions. This finding suggests that 
the charcoal was formed in fires in the highlands and transported into the adjacent 
basins. Conifer remains, because of their robust character and distinctive archi- 
tecture, are more easily recognized than other elements of the flora that might be 
preserved as charcoal and serve as signature plants for this seasonally dry biome. 
The early conifer fossil record indicates that the two biomes existed side by side in 
the tropics much earlier than the first occurrences of well-preserved macrofloras 
would indicate. 
As drying in the tropics continued, the seasonally dry biome was further re- 
placed in the lowlands by a flora adapted to still drier but perhaps seasonally 
wet conditions. DiMichele et al (2001) described a flora from the latest Early 
Permian of Texas that preserved a number of taxa previously known only from the 
Mesozoic, including the conifer Podozamites, the cycad Dioonitocarpidum, and 
478 DIMICHELE ? PFEFFERKORN ? GASTALDO 
Agathis-likc conifer seeds. These were mixed with a number of taxa characteris- 
tic of the Late Permian Zechstein flora (Schweitzer 1986), including the conifers 
Ullmannia and Pseudovoltzia, and the possible cycad Taeniopteris eckhardtii. The 
Zechstein flora, known from the Late Permian of Germany and England, preserved 
other typically Mesozoic elements. 
A significant aspect of this new flora is its implications regarding the Permian- 
Triassic extinction on land. Retallack (1995) presented evidence for major devasta- 
tion of terrestrial environments at this time in Earth's history, and his findings from 
the Southern Hemisphere have been extended to Europe (Looy et al 1999). The 
occurrence of distinctly Mesozoic elements in the Early and Late Permian, how- 
ever, indicates that many lineages survived this devastation, which may have had 
its strongest effect in the basinal lowlands and hence on those sites in which fossil 
assemblages are preserved most commonly (Gastaldo et al 1995). Colonization 
of the lowlands by conifers, cycadophytes, and pteridospermous seed plants in the 
later Triassic and Jurassic obviously did not occur by reevolution of these Paleozoic 
taxa; rather, migrations from extrabasinal refugia must have fueled the recovery. 
FINAL COMMENTS 
In a recent paper, Paine et al (1998) noted that multispecies assemblages have 
evolved in the presence of disturbance and could likely accommodate even very 
large, infrequent disturbances if they were within the typical range of disturbance 
intensity. These authors suggested that major changes in the fundamental state 
of an ecosystem would result from compound perturbations that prevent a system 
from recovering and permanently change its structure. The terrestrial fossil record 
supports their basic conclusions. As reviewed above, species pools, recognized 
largely as biomes, appear to be stable associations for long periods. Biomes re- 
place each other in space as a consequence of major climatic changes. Within such 
species pools there are various degrees of assemblage stability in time and space. 
Changes from one state to another?changes in dominance-diversity pattern and 
taxonomic composition?within a biome appear to correlate with environmental 
changes of great magnitude that bring about extinction levels that exceed back- 
ground levels. 
The fossil record also sheds light on the debate regarding community stability, 
that is, the classic Clementsian-Gleasonian dichotomy: Do multispecies assem- 
blages have emergent group properties, or are they happenstance associations? In 
the temperate zone, species individualism seems to be the rule on virtually all scales 
of time and space, as long as there is significant climatic fluctuation over time to 
act as a forcing mechanism. In the tropics, species assemblages appear to be more 
persistent and may have emergent properties, such as those seen in ecomorphic 
species replacement patterns brought about by incumbency and niche partitioning. 
Only by examining the compositional and quantitative patterns of assemblages over 
intervals of geological time can such patterns be glimpsed, even dimly. 
CARBONIFEROUS ECOLOGY AND CLIMATE 479 
Visit the Annual Reviews Iiome page at www.AnnuaIReviews.org 
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