Reference conditions for restoration of heterogeneous Mediterranean wetland are best defined by multiple, hydrologically diverse sites

Abstract

In a mediterranean climate, the vegetation of embanked salt marshes can vary considerably in time and space to obscure the definition of reference condition for restoration purposes. The aim of our study was to find a basis for defining reference vegetation for the reinstatement of a wetland hydrological regime on abandoned agricultural land. We investigated five reference sites surrounding a 2,668 ha restoration site in the Doñana National Park (southwest Spain). Environmental conditions were monitored on a sampling grid for seven years: surface elevation and hydroperiod were mapped (using LIDAR -Light Detection and Ranging- and satellite imagery, respectively) and rainfall, soil salinity and soil pH were recorded. The reference sites collectively encompassed the range of elevation and environmental conditions at the restoration site, although none individually was representative. The vegetation at the reference sites was sampled annually at fixed grid points. Hierarchical cluster analyses identified assemblages of perennial and annual species that were differently distributed among the reference sites. BIO-ENV analysis showed that the distribution of perennial assemblages was determined by elevation, annual hydroperiod, and salinity. More labile annual assemblages were loosely associated with particular perennial ones. Species composition fluctuated over the seven years, in concert with rainfall and hydroperiod, but showed no directional change. Understanding the hydro-chemical drivers of spatio-temporal variation in vegetation across multiple sites has established a rationale for defining reference conditions for large, heterogeneous wetland restoration sites

Disentangling elevation, annual flooding regime and salinity as hydrochemical determinants of halophyte distribution in non-tidal saltmarsh

“…Hanley et al, 2019). Improved understanding of the hydrochemical processes underlying the composition and structure of the vegetation of non-tidal marshes in general, and the internationally important Doñana National Park (Vélez-Martín et al, 2018) in particular, and will be valuable in informing their future conservation and restoration. Table 1.…”

“…The vegetation consists of a mosaic of halophytic shrubs of the Amaranthaceae ('chenopods'), more numerous annual species of halophyte, and emergent or submerged aquatic macrophytes in more flooded areas (Rivas-Martínez et al, 1980;Marañón et al, 1989;García et al, 1993;Espinar, 2009). The site is described in more detail by Vélez-Martín et al (2018).…”

“…We sampled an area of 3,580 ha near the north-eastern boundary of the Doñana National Park comprising five compartments centred on 37°02´N, 6°18´W. We established 170 permanent sampling locations on a rectilinear grid designed to provide even coverage across the five compartments of the site; locations were arranged in linear groups of three, to be consistent with an adjoining area designated for restoration, but wide spacing between locations (62.5 m within triplets and 1 km between them) would have minimised the possibility of spatial autocorrelation (see Vélez-Martín et al, 2018 for further details). We sampled the vegetation in the period June-July from 2004 to 2010, during the dry season, when both plant cover and site accessibility were greatest.…”

“…Typically, they are tidal and experience frequent, usually semi-diurnal, inundations with seawater (Adam, 1990). Less well-known, however, are non-tidal saltmarshes (Costa et al, 2003), especially those with limited hydrological connectivity with the sea (Vélez-Martín et al, 2018), where the dominant cycle of inundation is much longer i.e. seasonal rather than semi-diurnal.…”

“…The saltmarshes of Doñana National Park (south-west Spain) are largely isolated from tidal influence by embankments and dune ridges (Vélez-Martín et al, 2018). Because they occupy shallow clay basins, rainfall in their catchment area causes flooding and surface runoff, whereas evapotranspiration in summer can leave the soil surfaces dry and cracked, with efflorescing salts.…”