Size and position matter: riparian plant establishment from fluvially deposited trees

Abstract

The sprouting of fluvially deposited trees is an important process for floodplain woodland regeneration along dynamic rivers. This paper investigates how tree size and relative elevation of the location of fluvially deposited trees affects their survival. The survival of newly deposited trees along the River Tagliamento, Italy, was monitored over three field campaigns (2001, 2003 and 2005). A significant negative correlation was found between relative elevation and tree survival, while tree length was significantly positively correlated to survival. Consequently, larger trees deposited at lower elevations have a greater likelihood of regeneration, although the influence of these factors varied according to genera.survivorship were analysed using point-biserial correlation, and differences between genera were investigated using Kruskal-Wallis and Mann-Whitney analyses. ResultsThe three surveys included samples of 170, 92 and 39 trees in 2001, 2003 and 2005, respectively, of which 66 (39%), 33 (36%), and 22 (56%) were found to be sprouting in July/August following deposition in the previous spring. Increasing relative elevation is detrimental to survivorshipThere was no differentiation between genera according to relative elevations (Kruskal-Wallis; H = 5·098, p = 0·078), indicating that all genera are deposited across the range of elevations found within the active zone. Most trees were deposited between 0·5 and 1·5 m below the elevation of the floodplain woodland, with mean relative elevation being −1·00 m (Figure 2(A)). Surviving trees were found at almost all elevations, but the mean relative elevation of surviving Figure 2. (A) Histogram of relative elevations of deposited trees within the study site from combined survey data. Elevation is expressed in metres below the level of floodplain woodland. (B) Histogram of relative elevations of surviving trees within the study site from combined survey data. Elevation is expressed in metres below the level of floodplain woodland. (C) Histogram of deposited tree lengths (m) within the study site from combined survey data. (D) Histogram of tree lengths (m) of surviving trees within the study site from combined survey data.

Understanding reference processes: linkages between river flows, sediment dynamics and vegetated landforms along the Tagliamento River, Italy

“…Francis (2007) noted from several surveys in the Flagogna reach that sprouting deposited trees were distributed widely across the active tract but reached a peak frequency at approximately 1 m below floodplain surface level (corresponding approximately to 200 cm stage at Villuzza). The elevations and frequencies of sprouting trees and the vegetated patches into which they can develop reflect a balance between water availability to support growth (maximized at lower elevations) and flow disturbance (minimized at higher elevations).…”

“…Since the largest uprooted, deposited trees are the most likely to sprout successfully (Francis, 2007), a supply of large uprooted trees is crucial to seeding the next generation of pioneer and larger islands within the active tract. Established islands, which support the largest trees are usually aggraded to floodplain level and so, although withinbank river stages may erode island edges, delivering some sizeable trees for fluvial transport, bankfull river stages (300 cm), capable of strongly modifying island configurations, are required to disperse large numbers of uprooted trees into the active tract.…”

Control of sediment dynamics by vegetation as a key function driving biogeomorphic succession within fluvial corridors

“…and Populus spp. recruitment is intimately controlled by hydrogeomorphic constraints (Mahoney and Rood, 1998;Cooper et al, 1999;Johnson, 2000;Guilloy et al, 2002), a rapid sequence of large fl oods, which can occur on the River Tech, could strongly modify the spatial pattern of ligneous species recruitment, favouring species capable of re-sprouting from vegetative fragments at relatively higher levels on alluvial bar surfaces (Francis, 2007).…”

Lower Scotts Creek Floodplain and Habitat Enhancement Project

“…and Salix spp. are capable of regenerating from pieces or whole fallen trees (Francis 2007). Recruitment of live wood occurs typically when trees fall into the channel as a result of bank erosion (Opperman et al 2008).…”

“…The plan is experimental and we are building a literature by Dr. Jeff Opperman of TNC and others (2005, 2007, and 2009) looking at longevity of wood in small coast streams in Ca. Data by Opperman (who sat next to me from much of grad school...) suggests high levels of longevity for hardwoods-especially willows and alders IF the trees stay alive.…”