DEVONIAN FOREST EXPANSION INCREASED LAND-BASED TROPHIC CAPACITY AND FOOD WEB CONNECTIONS

Size, complexity, and abundance of land plants increased rapidly from Lower to Middle Devonian but surged with the rise of global forests in the Upper Devonian. Woody trees of various types appear in the Middle Devonian as clade-specific innovations produced taller perennial plants. The rise of Middle and Upper Devonian archaeopterid progymnosperms, however, produced the first widespread forests of truly large woody trees. Global forest expansion began in the basal Upper Devonian with the worldwide appearance and rapid spread of Archaeopteris and was complete by upper Frasnian. Archaeopteris was ecologically adaptable and grew in virtually all habitats. Exceptionally deep rooting and shedding of older deciduous leafy branch units enabled Archaeopteris to grow almost year-round. Although of few species, Archaeopteris included small to large trees with variable life spans and habitat specificity that enabled it to dominate Upper Devonian floodplains and form extensive shaded forests and stream-side galleries. The abundance of its leafy branches, logs, wood fragments, and spores in channel, lake, and nearshore deposits attest to its impact on freshwater fluvial and adjacent marine ecosystems. The vastly increased delivery of land-based organic carbon into aquatic ecosystems, via Archaeopteris litter, fed detritus-based food webs that contributed to the increased productivity necessary for the expansion and diversification of fish and tetrapod populations of this time.