Terrestrial Palaeoecology and Global Change

Chapter 7. Climate change
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- Foliage wind-roughness associating with deciduousness,
- Taphonomic evidence of reproductive structures developing before leaves,
- Alpha and beta diversities, both higher in the evergreen zone,
- Dominance types, grading from prevailingly mono- and oligodominant in deciduous
zone to polydominant in evergreen zone,
- Plant-animal interactions, with specialized entomophily more typical of evergreen
zone,
- Plant litter accumulation types, with leaf mats and leaf coals confined to deciduous
zone,
- Sedimentological evidence of seasonal input of plant dead mass, such as distribution
of organic debris over lacustrine varvites.
The zonation was distinct over most of the Phanerozoic except for the relatively brief
azonal episodes in the Early Carboniferous, Early Triassic and Early-Middle Eocene.
VII.4.1. Deciduous/evergreen zonal boundary through time
Since temperate deciduousness is reflected by both palaeoecological and taphonomic
criteria ( the distinctness of growing season increments, wind roughness of foliage, shoot
dropping, low diversity, mono- to oligodominance, pollination before leaves, leaf mats),
the boundaries of deciduous and evergreen biomes are most reliably documented by the
fossil record, even in case of extinct vegetation types.
The Middle to Late Devonian archaeopterids shed lateral branch systems (homologous
to macrophylls of the later appearing gymnosperms) preserved as the leaf mat-type
bedding plane accumulations (Krassilov et al., 1987b). They are dominant over northern
North America and Eurasia, with their southern boundary marked by the relatively rare
occurrences in Belgium, Bohemia, Donetsk Basin and Minusinsk, about 50°N (modern
latitudes). Cuticle coals formed by the thalloid Orestovia-Shuguria type plants are confined
to this zone.
Over the Late Carboniferous and Permian, the deciduous zone is represented by the
Angara-type assemblages, the leaf-mats of Rufloria (“Cordaites”)–Zamiopteris morphotypes
and their associated Vojnovskya–Gaussia ovulate heads (IV.3.1). A warmtemperate
ecotone extends over northern Kazakhstan, Central Asia, Junggar-Hinggan
zone of northern China to southern Primorye, bordering on evergreen vegetation of the
Cathaysian realm. The gigantopterid records mark a western outlier of this zone into
Asia Minor and Middle East.
Over the Late Mesozoic, the boundary is marked by the dominance of heteroblastic
taeniophyllous, spur-shoot dropping Phoenicopsis to the north – the pachycaul macrophyllous
cauliflorous Cycadeoidea to the south (Krassilov, 1972b). Ginkgophytes are
more diverse and numerically prominent in the Phoenicopsis zone while brachyphyllous
coniferoids prevail south of it. The Cycadeoidea zone assemblages are more diverse