Floodplain downed wood volumes: a comparison across three biomes

Abstract

Downed large wood (LW) in floodplains provides habitat and nutrients for diverse organisms, influences hydraulics and sedimentation during overbank flows, and affects channel form and lateral migration. Very few studies, however, have quantified LW volumes in floodplains that are unaltered by human disturbance. We compare LW volumes in relatively unaltered floodplains of semiarid boreal lowland, subtropical lowland, and semiarid temperate mountain rivers in the United States. Average volumes of downed LW are 42.3 m3 ha−1, 50.4 m3 ha−1, and 116.3 m3 ha−1 in the semiarid boreal, subtropical, and semiarid temperate sites, respectively. Observed patterns support the hypothesis that the largest downed LW volumes occur in the semiarid temperate mountain sites, which is likely linked to a combination of moderate‐to‐high net primary productivity, temperature‐limited decomposition rates, and resulting slow wood turnover time. Floodplain LW volumes differ among vegetation types within the semiarid boreal and semiarid temperate mountain regions, reflecting differences in species composition. Lateral channel migration and flooding influence vegetation communities in the semiarid boreal sites, which in turn influences floodplain LW loads. Other forms of disturbance such as fires, insect infestations, and blowdowns can increase LW volumes in the semiarid boreal and semiarid temperate mountain sites, where rates of wood decay are relatively slow compared with the subtropical lowland sites. Although sediment is the largest floodplain carbon reservoir, floodplain LW stores substantial amounts of organic carbon and can influence floodplain sediment storage. In our study sites, floodplain LW volumes are lower than those in adjacent channels, but are higher than those in upland (i.e. non‐floodplain) forests. Given the important ecological and physical effects of floodplain LW, efforts to add LW to river corridors as part of restoration activities, and the need to quantify carbon stocks within river corridors, we urge others to quantify floodplain and instream LW volumes in diverse environments. Copyright © 2016 John Wiley & Sons, Ltd.

Large wood recruitment and mobility in steep mountain streams of contrast European landscapes

“…The majority of LW is recruited here directly from the active valley floor by tree throws, which most likely happens only during high-magnitude flood events similar to the 2000 event. Although some previous studies suggested slow decay rates of wood in semi-arid conditions [17,18], we observed relatively fast decay processes in the Sfakiano most likely due to biotic agents (wood-destroying insects). Therefore we were not able to successfully apply cross-dating methods to estimate residence time or the year of LW recruitment in this ephemeral stream.…”

Long-Term Effect of Prescribed Burning Regimes and Logging on Coarse Woody Debris in South-Eastern Australia

“…However, a similar experiment presented by Aponte et al [8] had an almost identical mean volume of 68 m 3 ha −1 in its experimental plots, while the long unburnt plots presented were much higher at 96 m 3 ha −1 . Northern American boreal (42.3 m 3 ha −1 ) and subtropical (50.4 m 3 ha −1 ) floodplains are lower than our presented value, while temperate floodplains are considerably higher (116.3 m 3 ha −1 ) [41].…”

Drivers of Low Instream Large Wood Retention and Imprints of Wood Mobility in Mountain Nonperennial Streams of a Mediterranean Semiarid Environment

“…In summary, low wood abundance in the studied reaches were dictated mainly by the presence of sparse riparian corridors as recruitment areas of LW, as well as by the specifics of the decay of local coniferous trees and the flashy hydrological regime of the streams draining this semiarid Mediterranean environment. The limited production of biomass in semiarid climatic zones is perceived to be imprinted in low‐frequency recruitment of wood pieces rather than small sizes, which leads to low LW volumes in these channels (Galia, Škarpich, et al, ; Lininger et al, ; Wohl et al, ). Our quantification of living tree biomass along the stream courses confirmed this assumption, as the mean basal area of all trees in the riparian corridor was equal to 17.4 m 2 /ha.…”