Palaeozoic landscapes shaped by plant evolution

Abstract

Fluvial landscapes diversified markedly over the 250 million years between the Cambrian and Pennsylvanian periods. The diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover. In the absence of widespread vegetation, landscapes during the Cambrian and Ordovican periods were dominated by rivers with wide sand-beds and aeolian tracts. During the late Silurian and Devonian periods, the appearance of vascular plants with root systems was associated with the development of channelled sand-bed rivers, meandering rivers and muddy floodplains. The widespread expansion of trees by the Early Pennsylvanian marks the appearance of narrow fixed channels, some representing anabranching systems, and braided rivers with vegetated islands. We conclude that the development of roots stabilized the banks of rivers and streams. The subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels. Our contention is supported by studies of modern fluvial systems and laboratory experiments. In turn, fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems. We suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms

Belowground rhizomes in paleosols: The hidden half of an Early Devonian vascular plant

“…Although Drepanophycus is characterized by limited xylem and wide cortex tissues (16,32,33), the rhizomatous growth of this plant could produce dense vegetation cover (SI Appendix, Fig. S19), which alone would have protected the substrate against surface erosion while increasing trapping of fine particles (4,39), as has been demonstrated in numerous studies of the erosion-reducing effects of modern plants (5,39). Perhaps more importantly, belowground rhizomes of Drepanophycus formed complex networks as a result of belowground growth as well as sequential burial of aerial stems and rhizomes, which had the potential to bind sediments in a reinforced matrix, thereby increasing soil aggregate stability.…”

“…The Silurian-Devonian periods witnessed a series of secular changes in Earth's atmosphere and surface, including decrease of concentration of atmospheric carbon dioxide, increasing prominence of meandering river facies with stabilized banks and muddy floodplains, and the increase of pedogenic sediments. These changes have been linked to the colonization of terrestrial landscapes by rooted plants (1)(2)(3)(4)(5). Previous studies have emphasized the effects of early trees and forests, which first appeared in the Middle Devonian (6)(7)(8), on enhanced chemical weathering rates and soil development (2,(9)(10)(11).…”

Was the Ediacaran–Cambrian radiation a unique evolutionary event?

“…For example, the spread of vascular plants changed terrestrial weathering patterns and shifted rivers from sheet-braided to meandering channels with abundant mud and clay (Gibling and Davies 2012). Gibling and Davies argue that the development of terrestrial plant ecosystems beginning in the Silurian coupled the evolution of landscapes to evolutionary changes in both plants and animals, with plants acting as "geomorphic engineers," altering fluvial landscapes and thus their own evolution.…”

Rivers through geological time: the fluvial contribution to understanding of our planet

“…The importance of the advent and expansion of terrestrial plants in the parallel evolution of river systems is an important paradigm that researchers have established and reinforced during the past half century (e.g. Schumm, 1968;Went, 2005;Corenblit and Steiger, 2009;Davies and Gibling, 2010a, b;Gibling and Davies, 2012). The most important influences of vegetation during this period of change were on rock weathering, landscape stability and sediment supply to valley-floors, sediment storage, and, acting less directly on river systems, on the composition of the ocean and atmosphere (Algeo and Scheckler, 1998;Davies and Gibling, 2010a).…”