Hydrologic thresholds for riparian forest conservation in a regulated large Mediterranean river

Abstract

Most riparian trees are phreatophytic, water table-dependent plants which broadly differ in their tolerance to drought and permanent flooding. In semi-arid settings, as water is limiting, inundations may be regarded as inputs rather than stresses for the survival of phreatophytes. In this study, the mortality rates and abundances of Populus alba, P. nigra, Salix alba and local Tamarix spp. were examined in 43 plots with different hydrologic conditions distributed across the floodplain of a large semi-arid and Mediterranean river, the Ebro River (Spain). The objectives were to determine hydrologic thresholds for the maintenance of declining populations of those species, while providing novel information on their phreatophytic nature, and to examine shifts in the species composition along hydrologic gradients. All species exhibited significant relationships between mortality rates and hydrologic variables (deepest water table-WT, flood duration-FD and flood frequency-FF). S. alba was found to be the species with lowest tolerance to drier conditions (hydrologic thresholds for maintaining a mortality rate <50%: WT > À1.22 m; FD: out of observation range; FF > 5.4 events y ). Only a significant reduction in S. alba relative abundance was observed as conditions got drier. The results provided quantitative information useful to guide management plans for the protection of Mediterranean phreatophytic tree species from further degradation and suggested that eventual natural or regulation-induced droughts and groundwater declines would accelerate the loss of all phreatophytic species, especially S. alba.

Six decades of changes in the riparian corridor of a Mediterranean river: a synthetic analysis based on historical data sources

“…This constrained our reconstructed time series to a monthly resolution. This rather coarse temporal resolution is not ideal when investigating impacts on riparian systems because riparian vegetation is highly dependent on and responsive to shorter events, particularly droughts González et al, 2012) and floods (Blondel and Aronson, 1999;Naiman et al, 2008), which often form crucial elements in the definition of environmental flow regimes for riparian conservation Paredes-Arquiola et al, 2011). However, only monthly data are available for many rivers and regions (Richter et al, 2012), and in the present case, this was the highest resolution to which we felt able to construct an internally consistent flow series.…”

“…Numerous references about this decline in semi-arid North American rivers have been reported since the 1980s (e.g. Groeneveld and Griepentrog, 1985;Howe and Knopf, 1991;Busch and Smith, 1995;Stromberg et al, 1996;Patten, 1998;Williams and Cooper, 2005) and also more recently in the context of Mediterranean basins (Muller et al, 2002;González et al, 2010;González et al, 2012). In many cases, this decline is preceded by a significant increment in riparian biomass (Johnson, 1994), although this new vegetation may be composed of exotic woody species (Johnson et al, 1995;Dixon and Johnson, 1999).…”

Gravel bar inundation frequency: an important parameter for understanding riparian corridor dynamics

“…On the other hand, riparian vegetation dynamics are strongly affected by river processes. Rivers provide water, thereby enhancing soil moisture and nutrients for plant growth and facilitating hydrochoric seed dispersal (Pezeshki and Shields 2006;Gonzalez et al 2012;Bertoldi et al 2014). Mass processes such as the transport of river sediments not only create new depositional zones for vegetation Abstract Riparian zones are some of the most valuable and at the same time endangered ecosystems in the world.…”

Riparian vegetation patterns according to hydrogeomorphological factors at different spatial and temporal scales in Mediterranean rivers.

“…This fact constrained our reconstructed time series to a monthly resolution. This rather coarse temporal resolution is not ideal when investigating impacts on riparian systems because riparian vegetation is highly dependent on and responsive to shorter events, particularly droughts (Mahoney and Rood, 1998a;González et al, 2012) and floods (Blondel and Aronson, 1999;Naiman et al, 2008), which often form crucial elements in the definition of environmental flow regimes for riparian conservation Paredes-Arquiola et al, 2011). However, only monthly data are available for many rivers and regions (Richter et al, 2012), and in the present case, this was the highest resolution to which we felt able to construct an internally consistent flow series.…”

“…Numerous references about this decline in semi-arid North American rivers have been reported since the 1980s (e.g. Groeneveld and Griepentrog, 1985;Howe and Knopf, 1991;Busch and Smith, 1995;Patten, 1998;Williams and Cooper, 2005) and also more recently in the context of Mediterranean basins (Muller et al, 2002;González et al, 2010;González et al, 2012). In many cases, this decline is preceded by a significant increment in riparian biomass (Johnson, 1994), although this new vegetation may be composed of exotic woody species (Johnson et al, 1995;Dixon and Johnson, 1999).…”