Terrestrial Palaeoecology and Global Change

76 Valentin A. Krassilov. Terrestrial Palaeoecology
graphic origins, as the “Malaysian” lowland – “Australian” upland belts of New Guinea
(Schuster, 1972), an evolutionary perspective interface.
In a stable vegetation system, both seral and catenic sequences tend to get longer by
an interstitial build-in, such an expansion of the Jurassic brachyphyllous belt upslope and
its differentiation into several catenic communities over the Cretaceous (above). With a
major environmental change, new belts are added by a terminal build-up. Rising mountain
ranges drive the catenas upslope, while a hammada-type community can be added
on a rocky ground of the piedmonts. The opposite tendency is manifested by truncation
of a sere or by marginal cut-off of catenic belts. Certain members of vegetation sequences,
most often end-members, are periodically reduced and then repaired. Where
evolutionary innovations arise during the cutoff/repair cycles, they are confined to the
end-members. In most cases studied, new plant communities develop either from an
early stage of a seral system or from understorey (that can also be seral to the overstorey),
or else from marginal catenic variants.
Early land plants formed an essentially single-storey vegetation of a small aboveground
biomass and a relatively large underground biomass. With the build-up of a multistratal
canopy and reallocation of biomass to aboveground organs the slightly modified
early communities survived as the marginal/early seral stages. Evolution of the plant
body – secondary growth, elaboration of vascular system, planation of photosynthetic
organs – was primarily related to elevation of overstorey, with modest reproductive
innovations. The overstorey trees of the mid-Devonian–Tournassian forests were freesporing
(including the so-called progymnosperms that resemble gymnosperms in their
wood anatomy alone), while the precursors of seed-plants (e.g Lenlogia: Krassilov &
Zakharova, 1995) appeared in the relatively primitive telomic understorey seral to these
forests.
The Early Carboniferous evolution of gymnosperms was still confined to the edaphic
periphery and/or early seral stages of the free-sporing wetlands (pteridosperms in the
roof shales of lepidophytic coals: Scott, 1977). During the Pennsylvanian and Early Permian,
gymnosperms gradually invaded all recognizable catenic belts. In the Late Permian
regressive sequences, gigantopterids replaced the pecopterid–calamite marshes as a
successional phase (III.3.3).
Adaptive radiation of Mesozoic gymnosperms was related to differentiation of new
catenic systems, such as the scale-leaved Brachyphyllion with cycadophytic helophytes,
riparian Phoenicopsion, upland Ginkgoion and the seral/edaphic Czekanowskietum,
Pityophylletum, Pseudotorellietum, etc. (III.3.1). Free-sporing dominance was retained
in the fern–horsetail marshes, a widespread wetland type, occasionally seral to gymnosperm
wetlands. With a decline of fern-marsh communities the belt was invaded by the
pioneer elements of the bennettite- gnetophyte wetlands that gave rise to proangiosperm
communities (Krassilov, 1997). A mid-Cretaceous wave of catenic/seral replacements
brought their descendent early angiosperm communities to the understorey of conifer
forests and downslope to hydrophilous vegetation downslope.