Impact of trees and forests on the Devonian landscape and weathering processes with implications to the global Earth's system properties – A critical review

Abstract

Evolution of terrestrial plants, the first vascular plants, the first trees, and then whole forest ecosystems had far reaching consequences for Earth system dynamics. These innovations are considered important moments in the evolution of the atmosphere, biosphere, and oceans, even if the effects might have lagged by hundreds of thousands or millions of years. These fundamental changes in the Earth's history happened in the Paleozoic: from the Ordovician, the time of the first land plants, to the Carboniferous, dominated by forest ecosystems. The Devonian Plant Hypothesis (DPH) was the first concept to offer a full and logical explanation of the many environmental changes associated with the evolution of trees/forests that took place during this time period. The DPH highlighted the impact of deep-rooted vascular plants, particularly trees on weathering processes, pedogenesis, nutrient transport, CO2 cycling, organic and inorganic carbon deposition, and suggests further possible consequences on the marine realm (oceanic anoxia and extinction during the Late Devonian). Here we attempt to combine the DPH and the related expansion in biodiversity, the Devonian Plant Explosion (DePE), with the Biogeomorphic Ecosystem Engineering (BEE) concept. This idea connects tree growth and activity with initiation and/or alteration of geomorphic processes, and therefore the creation or deterioration of geomorphic landforms. We focus on trees and forest ecosystems, as the assumed dominant driver of plant-initiated change. We find that whereas there is a broad evidence of trees as important biogeomorphic ecosystem engineers, addressing the DPH is difficult due to limited, difficult to interpret, or controversial data. However, we argue the concept of BEE does shed new light on DPH and suggest new data sources that should be able to answer our main question: were Devonian trees Biogeomorphic Ecosystem engineers?