Davies, Neil

Gibling, Martin

Ghent University Academic Bibliography

Geophysical Research AbstractsVol. 14, EGU2012-6429, 2012EGU General Assembly 2012© Author(s) 2012Deep Time Ecosystem Engineers: The Correlation between PalaeozoicVegetation, Evolution of Physical Riverine Habitats, and Plant andAnimal TerrestrializationN.S. Davies (1) and M.R. Gibling (2)(1) Department of Geology & Soil Science, Ghent University, Ghent, Belgium (neil.davies@ugent.be), (2) Department ofEarth Sciences, Dalhousie University, Halifax, Canada (martin.gibling@dal.ca)Evidence from the deep time geological record attests to the fundamental importance of plant life to the con-struction of physical habitats within fluvial environments. Data from an extensive literature review and originalfieldwork has demonstrated that many landforms and geomorphic features present in modern river systems donot appear in the deep time stratigraphic record until terrestrial vegetation had adopted certain evolutionary ad-vances that enabled them: for example, stable point bars are associated with the development of deep rooting inthe Siluro-Devonian and avulsive anabranching fluvial systems appear at the same time as extensive arborescentvegetation in the Carboniferous. In this presentation, we demonstrate a correlation between the diversification ofphysical fluvial sedimentary environments and the expansion of terrestrial fauna and flora throughout the Cambrianto Carboniferous, and offer an explanation for this observation that considers plants as ecosystem engineers on anevolutionary timescale. Many extrinsic factors have been considered when attempting to identify controls on theevolutionary timelines of terrestrialization for various different organisms. Factors such as O2 and CO2 levels inthe atmosphere, climatic events, global tectonic organisation, sea-level changes, extinction events, weathering ratesand nutrient supply are all known to have played a role. However, another factor is likely to have been a fundamen-tal prerequisite for achieving terrestrial biodiversity: the variety of physical habitats available for newly evolvedorganisms. In fluvial environments, this is a function of the diversity of hydrodynamic regimes (both temporal andspatial) within the world’s river systems. In a world where only sheet-like ephemeral braided rivers existed, suchas appears to be the case in pre-vegetation settings, both the geographic extent of riparian margins and the diversityof hydrodynamic regimes would be minimal. However, as fluvial corridors narrowed throughout the Ordovicianand Silurian, the potential importance of riparian zones as a global biome would have increased as they becamemore extensive in continental environments. Furthermore, the move towards climatic controls on the ephemeralor perennial nature of streams would have boosted the diversity of temporally diverse hydrodynamic regimes. Assingle-thread meandering channels and extensive muddy floodplains, stabilised by vegetation, became significantcomponents of the global suite of alluvial geomorphic components throughout the Siluro-Devonian, further di-versification of the extent and diversity of physical habitats within the global riparian biome occurred. Into theCarboniferous, the evolution of the anabranching habit within alluvial systems created further new physical land-forms for colonization and would have promoted increasingly complex hyporheic flow regimes. Furthermore theassociated advent of arborescent vegetation and, specifically, the large woody debris supplied by this, would havecreated a wealth of new microhabitats for continental organisms. The expanding extent and diversity of physicalalluvial niches during the Palaeozoic can be argued to be an underappreciated driver of the terrestrialization ofearly continental life. The study of the deep time fossil and stratigraphic record also illustrates that vegetation isa fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and micro-habitats.

Deep time ecosystem engineers: the correlation between Palaeozoic vegetation, evolution of physical riverine habitats, and plant and animal terrestrialization

https://biblio.ugent.be/publication/2124543/file/2152957

Deep time ecosystem engineers: the correlation between Palaeozoic vegetation, evolution of physical riverine habitats, and plant and animal terrestrialization

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