Riparian trees resprout regardless of timing and severity of disturbance by coppicing

Abstract

Human modification of waterways has reduced flooding in many river systems, leading to the decline of riparian forests, which rely on flooding for their regeneration. Coppicing may help to promote the persistence of riparian trees by triggering resprouting and vegetative regeneration. The vigour of resprouting plants can vary with timing and height of coppicing and may depend on stored non-structural carbohydrate reserves like starch, the availability of which can vary seasonally. However, starch storage dynamics and the resprouting potential of broad-leafed evergreen riparian trees is not well understood.We coppiced two riparian tree species, Eucalyptus camphora and Melaleuca squarrosa, at two different times (autumn, spring) and at two different heights (0 cm and 90 cm). Over 52 weeks, we regularly quantified shoot growth and changes in the starch storage pool size, compared to uncoppiced control trees, in different tree organs (root and stem) and estimated the final shoot volume.The final shoot volume did not differ significantly between coppice treatments. Trees coppiced in autumn had a greater reliance on stored starch while they remained leafless (without shoots) over winter. Trees cut at 90 cm had more starch reserves due to remaining stems but also had higher biomass maintenance costs. Starch storage varied seasonally only in E. camphora, with starch concentrations in control trees increasing over winter and decreasing over summer.Although coppice timing and height affected use of stored starch, resprouting in our study species was not limited by starch availability - both species regenerated vegetatively to recover from physical disturbance. Thus, coppicing may be an efficient means to promote rejuvenation and persistence of tree species where site and tree condition are degraded and no longer support recruitment.