Modeling the Evolution of Riparian Woodlands Facing Climate Change in Three European Rivers with Contrasting Flow Regimes

Abstract

Global circulation models forecasts indicate a future temperature and rainfall pattern modification worldwide. Such phenomena will become particularly evident in Europe where climate modifications could be more severe than the average change at the global level. As such, river flow regimes are expected to change, with resultant impacts on aquatic and riparian ecosystems. Riparian woodlands are among the most endangered ecosystems on earth and provide vital services to interconnected ecosystems and human societies. However, they have not been the object of many studies designed to spatially and temporally quantify how these ecosystems will react to climate change-induced flow regimes. Our goal was to assess the effects of climate-changed flow regimes on the existing riparian vegetation of three different European flow regimes. Cases studies were selected in the light of the most common watershed alimentation modes occurring across European regions, with the objective of appraising expected alterations in the riparian elements of fluvial systems due to climate change. Riparian vegetation modeling was performed using the CASiMiR-vegetation model, which bases its computation on the fluvial disturbance of the riparian patch mosaic. Modeling results show that riparian woodlands may undergo not only at least moderate changes for all flow regimes, but also some dramatic adjustments in specific areas of particular vegetation development stages. There are circumstances in which complete annihilation is feasible. Pluvial flow regimes, like the ones in southern European rivers, are those likely to experience more pronounced changes. Furthermore, regardless of the flow regime, younger and more water-dependent individuals are expected to be the most affected by climate change.

Riparian responses to extreme climate and land-use change scenarios

“…Specifically, the expected reduction of 15% in mean annual discharges (Average Flow) was shown to result in the prediction of an overall riparian shrinkage for the 2046-2065 time slice, and a consequent decrease in the lateral and longitudinal connectivity of the riparian galleries. Our results are corroborated by previous studies that identified changes in flow regimes as the main causes of riparian modifications under global warming scenarios (Poff and Zimmerman, 2010;Rivaes et al, 2014). Studies assessing the effect of fluvial disturbance on riparian vegetation dynamics reported a decrease in both the mean patch size and the total area occupied by riparian woodlands, as a consequence of the reduction in natural streamflows caused by water scarcity scenarios (Kominoski et al, 2013;Rivaes et al, 2014).…”

“…More recent research used dynamic hydro-vegetation models to describe the evolution of riparian woodlands and flow relationships with vegetation stages facing climate change (e.g. Rivaes et al, 2013Rivaes et al, , 2014, and to explore the future distribution of species' functional traits in different climate change scenarios (Catford et al, 2012;Rocha et al, 2015). Nevertheless, most studies rely on the single-hydrological perspective, and particularly lack the well documented influence of landuse change on the establishment of riparian structural and compositional patterns (Allan, 2004;Aguiar and Ferreira, 2005;Burton et al, 2005;Hooke, 2006;Fernandes et al, 2011).…”

Can riparian vegetation shade mitigate the expected rise in stream temperatures due to climate change during heat waves in a human-impacted pre-alpine river?

“…Changes in vegetation height and density in floodplain forests in natural systems are mainly due to succession (Primack, 2000;Garssen et al, 2014;Rivaes et al, 2014). The present potential natural floodplain forest is in many areas reduced to narrow fringes accompanying the river, which are flooded at least annually.…”

“…Community changes which might affect vegetation height and density are possible within the next century, though changes in vegetation height and density in floodplain forests in natural systems are mainly due to succession. Primack (2000), Garssen et al (2014) and Rivaes et al (2014) studied the effect of climate change on natural riparian vegetation cover via changes in the hydrological regime including inundation periods and intensity, days since rain and the decline of water table. As the Pinka is anthropogenically influenced and will be regulated for the foreseeable future, no dynamical changes and no natural succession dynamics are expected which could cause an extreme change in vegetation cover.…”

Ecological modeling of riparian vegetation under disturbances: A review

“…Disturbances on riparian vegetation can be classified into two categories suggested in this research: natural and anthropogenic ones. Many studies classify climate changes as the primary natural disturbance on riparian vegetation (Martin, 1993;Politti et al, 2014;Rivaes et al, 2014;Witte et al, 2014), which affect riparian vegetation primarily through climate-driven hydrologic changes. Climate change in the Alpine floodplain is an example of a natural disturbance: as a relatively discrete event, climate change scenarios create regression or succession processes .…”