Biomechanical Properties and Resistance to Uprooting of Laboratory‐Scale Wood Logs

Abstract

Wood dynamics affects riparian ecosystem functioning and river morphology. The spatial and temporal dynamics of wood pieces in river corridors, in particular of deposited rejuvenated wood logs, depend on their biomechanical properties and resistance to uprooting. The ability of stranded wood logs to withstand drag forces depends on how efficiently their roots have sprouted and on the interarrival time, magnitude, and duration of the moderate floods to which they are subjected. We performed static pullout tests on small-scale wood logs (Salix species) of four different sizes, growth stages, and sediment moisture content. Statistics of root biomass growth rate and related spatial distribution along the trunk reveal important insights for upscaling dynamics. Similarly, force-displacement curves indicate the maximum resistance and related energy for uprooting. Autocorrelation analysis of the sequence of force drops in the force-displacement signal reveals the statistical nature of the mechanism of load redistribution among roots. These results are then used to advance a physically based mathematical model of the resistance of wood log roots to flow-induced drag forces. Given that the magnitude, duration, and return period of hydrologic events are typically correlated, our model implies the existence of windows of opportunity for wood logs to either survive or remobilize.

Allometric equations for estimating peak uprooting force of riparian vegetation

“…Finally, in the third stage, the uprooting force diminishes over time due to the gradual breakage and slippage of roots from the soil ( Bailey et al., 2002 ). The three phases are consistent with what has been observed in previous studies ( Edmaier et al., 2014 ; Bau and Perona, 2020 ). We also observed multiple force drops subsequent to the peak uprooting force.…”

“…In turn, riparian vegetation is influenced by river-driven disturbances (e.g., flooding, droughts, groundwater fluctuations, etc. ), which may cause the death of vegetation by scouring ( Chen et al., 2012 ; Bywater-Reyes et al., 2015 ), uprooting ( Bywater-Reyes et al., 2015 ; Bau and Perona, 2020 ; Piqué et al., 2020 ), burying ( Kui and Stella, 2016 ), and desiccation ( Barnes et al., 2013 ; Coughlan et al., 2018 ). Among these, uprooting is a major mechanism of riparian vegetation mortality that occurs when the hydraulic drag force exerted on the plant exceeds the resisting force provided by its roots ( Bau and Perona, 2020 ).…”

Effects of Root Architecture on Uprooting Properties between Deciduous and Evergreen Species with Different Growth Habits

“…The above findings are particularly important in regard to better understanding how roots affect the triggering of shallow landslides and how they contribute to soil stabilization. Furthermore, uprooting forces may not be established by the individual and simultaneous contributions of all the roots [40,41]. Because the results of the uprooting force−displacement relationship curve analysis show that there was a progressive failure between the roots during the vertical uprooting process (i.e., when some roots were pulled out or broken), their loads were redistributed to other roots that are not or will be stressed.…”