1 distribution patterns of riparian species in relation to

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atrocinerea, Populus nigra and Nerium oleander. The general results of the study indicate that the 3 species have a different tolerance to inundation and ...
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7 ISE & 8 HIC Chile, 2009

DISTRIBUTION PATTERNS OF RIPARIAN SPECIES IN RELATION TO CHANNEL BED IN TWO MEDITERRANEAN RIVERS V. GARÓFANO-GÓMEZ, F. MARTÍNEZ-CAPEL Instituto de Investigación para la Gestión Integrada de Zonas Costeras (IGIC), Universidad Politécnica de Valencia. Ctra. Nazaret-Oliva s/n, 46730 Grao de Gandia. Valencia (Spain) Tel.: +34-962849458, Fax: +34-962849309, e-mail: [email protected] F. FRANCÉS Instituto de Ingeniería del Agua y Medio Ambiente (IIAMA). Universidad Politécnica de Valencia. Camino de Vera s/n, 46022 Valencia, (Spain), e-mail: [email protected] The spatial distribution patterns of the most representative riparian species in relation to elevation above the channel bed (thalweg) was analysed in 3 study sites in the Júcar River Basin. Two study sites were located in the Mijares River and another in the Serpis River. Sampling by transects allowed the comparison of 3 species present in the 2 rivers. A clear trend was observed, with significant differences among the 3 species Salix atrocinerea, Populus nigra and Nerium oleander. The general results of the study indicate that the 3 species have a different tolerance to inundation and corroborate that elevation above thalweg is a key variable to explain the riparian plants distribution. The comparison among sites indicated that the elevation above thalweg, for some species, could be transferable to other Mediterranean rivers with similar climate conditions. In this way, the vegetation model RibAV will be able to contribute to the occurrence prediction for the main riparian species along typical cross-sections as a function of the river flow regime. Keywords: Salix, Populus, distribution patterns, flow regime, Mediterranean rivers. INTRODUCTION The knowledge of the riparian forests, regarding their distribution and composition has been largely expanded since the 1980’s (Hupp & Osterkamp [1], Nilsson [2], Salo et al. [3], Slater et al. [4]). Also the relations between riparian species and streams hydrology have been developed (Stromberg [5], Shafroth et al. [6], Mahoney & Rood [7]). Among such studies, some have used variables related to river morphology to explain the species distribution (Stromberg & Patten [8], Van Coller et al. [9], Nakamura et al. [10]). Others have developed dynamic models to simulate growth and processes of succession/retrogression in the riparian ecosystem (Inamdar et al. [11], Glenz [12], Egger et al. [13]).

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2 In the context of Mediterranean rivers, the riparian vegetation is highly influenced by factors such as flow regime, soil moisture and ground water availability (Tabacchi et al. [14]). In the framework of a Spanish research project, a model for soil moisture, coupled with a hydrological distributed model (Francés et al. [15]), was developed in order to predict the probability of occurrence for riparian species and functional groups (Morales & Francés [16], in this volume). This model, RibAV, is aimed to predict how the community changes with different scenarios of hydrological alteration, in relation with dam operation and climate change. One of the keys in the development and validation of vegetation models is the definition of functional groups (USDA-NRCS, [17], Lite et al. [18]). For this task it is necessary to distinguish if different species are affected in the same way by the hydrological events, and what species show significant differences. Other question arising is the applicability of the empirical results of a species (for example, in tolerance to inundation) in rivers with diverse physical conditions. This is essential for the validation, in other rivers than the ones where the models were calibrated. In consequence with these ideas, this study was developed in two rivers of the Comunidad Valenciana (East Spain), in order to address these questions: - Are there significant differences in tolerance to inundation among the main riparian species in each study site? - Is the location of certain species, in relation to the river channel thalweg, transferable from one site to others? STUDY AREA The rivers Serpis and Mijares are two of the most important in the Júcar River Basin (East Spain). Both are permanent rivers which end is in the Mediterranean Sea. One study site, 240 m long, was located in the river Serpis (site 1, 38º51’15.42’’N, 0º18’41.34’’W) which flows from southwest to northeast, in the south of the Comunidad Valenciana. Two more study sites were located in the north of the Comunidad Valenciana, in the river Mijares. The first one, 180 m long, was located near the small town of Cirat (site 2, 40º3’35.38’’N, 0º27’46.06’’W) and the second, 150 m long, was located 7 km downstream the former, near the small town of Tormo (site 3, 40º3’35.19’’N, 0º24’50.28’’W). The three sites have a notable scenic value and the impact of the agricultural activities is relatively low, except for the site 2, where the river channel and the floodplain were constrained by them. It is important the hydrological alteration of both rivers by large dams, which store water for irrigating during the summer. The total catchment area of the river Mijares is approximately 4028 km2, and the main stem has a total length of 156 km; for river Serpis the catchment area is approximately 753 km2, and the main stem is 74.5 km long. The three sites have similar altitude (site 1: 340 m, site 2: 360 m, and site 3: 310 m), but the difference of latitude between the 2 rivers is relevant within Spain, as they are in the north and south of the Comunidad Valenciana, with a straight distance of 140 km approximately. Based on

3 previous studies (Confederación Hidrográfica del Júcar [19]), the α-diversity was not very different in the 3 sites, being 2.82, 2.38 and 2.50 for the sites 1, 2, and 3, respectively. METHODS First part of this study was the survey of the riparian plant species (helophytes, shrubs and trees) along transects perpendicular to stream flow, following the “line intercept method” (FIREMON, [20]). In each study site, 9 linear transects were made including the river channel and the riparian zone (until the point where species of terrestrial vegetation were dominant). In those lines, all the intercepting individual plants were surveyed, by recording the points at the beginning and the end of the vertical projection of the plant (or crown of the tree) on the cross section. Total station and GPS were used to obtain georeferenced data. Abundances (in percentage) of the riparian species in each site were obtained. From such data, the most representative species present in the two rivers were selected for analysis. Since one of the objectives was to differentiate the species by their tolerance to inundation, stream flow and plants position were the basic information needed. However, in this study, distance and elevation above the channel thalweg (m) were used (Harris [21]) to observe differences in tolerance to inundation, with a “static” point of view based on the actual morphology. In this way, the surveys showed the result of many hydrological cycles and repeated processes of vegetation succession and retrogression. Therefore, the geo-referenced locations of the selected target species were used to calculate distance and elevation above the channel thalweg. For the first objective, the locations of the target species in each site were compared based on the two variables, distance and elevation above the channel thalweg. For the second objective, the results in the two variables were compared for each target species among study sites; all the comparison were done with the non-parametric test of KruskalWallis (P