Riparian forest structure, vegetation cover and flood events in the Piave River

Abstract

Until very recently, rivers have been considered as the result of the interaction between water and sediments, thus simplifying this very complex system. In doing so, one important component was missed. This is vegetation, namely trees growing on banks, floodplains, and bars/islands. The pattern of riparian vegetation in gravel bed rivers depends on the climate, hydrological regime, floods, sediment transport and the morphological settings of the river. Also, the marked spatial variability of density, height, species diversity, age, and rates of growth reflects the very complex nature of bed colonization, the strong influence of sequences and magnitude of floods, and the feedbacks between morphology, vegetation and hydraulics. Furthermore, a wide array of human impacts acting at either the basin or river network scales can influence substantially the morphodynamics and thus the characteristics, types and distribution of vegetation within the river corridor. The aim of the work is to analyze the relationship between the vegetation structure and the morphological characteristics of two sub-reaches of the Piave river which suffered both floods and intense and multiple human impacts especially due to dam building and inchannel gravel mining. Six cross sections were surveyed and vegetation, soil variables and sediment deposited were measured on 214 plots, (4 x 4 m each one and 10 m spaced). Each vegetation plot were recognized on a recent aerial photo (2009) and its ages were calculated performing both a multi-temporal analysis of older photos (1960, 70, 80, 91, 99, 2006 and 2009) analysis. The Piave River shows a complex pattern of vegetation distribution along the cross-sections with no clear relationship between the elevation and the plant communities. However later successional plant communities cover older surfaces and the thickness of the sand layer helps explaining differences in areas dominated by different species (e.g. Salix alba and Salix eleagnos).

Characteristics of fluvial islands along three gravel bed-rivers of North-Eastern Italy

“…The median grain size varies between 20 and 50 mm. The Piave River features a complex pattern of vegetation distribution along the analysed study reach (Picco et al 2012a(Picco et al , 2012b(Picco et al , 2014, which is far more composite than those identified in less disturbed river systems (Hupp and Osterkamp, 1996;Gurnell and Petts, 2002;Tabacchi et al, 1998;Bendix and Hupp, 2000). …”

“…Kellerhals et al (1976) further discriminated between occasional, frequent, split and braided island patterns. The various aspects and characteristics of fluvial islands can also help to describe the river processes that happend in the past, some plant species require specific growth conditions, such as inundation duration, gradient, and particle size (Picco et al, 2012b) and that can help to determine the flow conditions in the area.…”

Bank erosion and large wood recruitment along a gravel bed river

“…The analyzed study site presents a complex pattern of vegetation (Picco et al, 2012a). The narrowing and incision phase during the 20 th century (Comiti et al, 2011) has allowed the colonization of large areas by riparian forests (Picco et al, 2012a). Furthermore, the widening tendency shown during the last 20 years has led to the creation of pioneer islands through LW recruitment from bank erosions (Picco et al, 2012a).…”

“…There are no tributaries within the study reach. The analyzed study site presents a complex pattern of vegetation (Picco et al, 2012a). The narrowing and incision phase during the 20 th century (Comiti et al, 2011) has allowed the colonization of large areas by riparian forests (Picco et al, 2012a).…”

Relationships between woody vegetation and geomorphological patterns in three gravel-bed rivers with different intensities of anthropogenic disturbance

“…1) of the basin area disconnected from the lower river channel in terms of bedload transport, and between the 1960s and 1980s, there was intense sediment mining along the main channel [49]. As a result, the Piave River underwent narrowing and incision (see Table 1), and a progressive change from braided to a wandering/single-thread morphology, with the encroachment of riparian vegetation on the former active channel [7,44,47,55,59]. Widespread channel narrowing occurred in the range of 60-70% in the reach studied in this work [7].…”