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A floristic and vegetational study of a latitudinal gradient of salt marshes in South-Central Chile.

2006; Pontifical Catholic University of Chile; Volume: 33; Issue: 1 Linguagem: Inglês

10.7764/rcia.v33i1.326

0718-3267

Cristina San Martín, M. Subiabre, Carlos Ramírez,

Botany, Ecology, and Taxonomy Studies

Salt marshes are brackish swamps formed in the estuaries of the rivers. The flora and vegetation of three marshes located at Puerto Saavedra (Cautin province, 38o 46' S and 73o 24' W), Mehuin (Valdivia province, 39o 26' S and 73o 12' W), and Quillaipe (Llanquihue province, 41o 32' S and 72o 44' W), distributed along 400 km in south-center Chile, were studied in 2000. Salt marshes are azonal plant formations independently of the macroclimate. A plant-sociological methodology was used to characterize these salt marshes. However, salt marshes studies should not differ in terms of floristic and vegetational characteristics. In each salt marsh, 10 sampling plots were equidistantly established along a 100-m-long transect beginning at the lower vegetation limit. Eighteen halophilic species were identified, and four were alochtonous: Cotula coronopifolia , Spergularia rubra , Leontodon saxatilis and Lolium multiflorum . The first specie was identified in the three salt marshes and it was the dominant specie in Mehuin. The other three species were detected only in Mehuin, suggesting that Mehuin was the most intervened place. The floristic similarity analysis demonstrated scarce affinity between marshes but, distant vegetation was more similar than closer one. Indeed, high affinity was detected between Mehuin and Quillaipe while low affinity was found between Puerto Saavedra and Quillaipe. These results were unexpected because Mehuin and Quillaipe were geographically more distant than Mehuin and Puerto Saavedra. According to the multivariate statistical analysis, flooding and salinity explained the altitutinal distribution pattern found for the plant species detected at each salt marsh. Floristic differences between salt marshes suggested the presence of a latitudinal gradient that contradicted the azonality condition described for salt marshes. These finding may be explained by differences in the coastal topography and it is also possible that differences in the substrate characteristics may existed along the latitudinal gradient. Las marismas son pantanos salobres que se forman en los estuarios de los rios. Se estudio la flora y la vegetacion de tres marismas ubicadas en Puerto Saavedra (Provincia de Cautin, 38o 46' S y 73o 24' W), Mehuin (Provincia de Valdivia, 39o 26' S y 73o 12' W), y Quillaipe (Provincia de Llanquihue, 41o 32' S y 72o 44' W), distribuidos en una gradiente latitudinal de alrededor de 400 km, en el centrosur de Chile. Por tratarse de formaciones vegetales azonales, que no dependen del macroclima, se esperaria altas similitudes floristicas y vegetacionales entre ellas. Se trabajo con metodologia fitosociologica, muestreando 10 parcelas por marisma, a lo largo de un transepto de 100 m iniciado en el limite inferior de la vegetacion. Se determinaron 18 especies halofitas, de las cuales solo cuatro fueron aloctonas: Cotula coronopifolia , Spergularia rubra , Leontodon saxatilis y Lolium multiflorum . La primera especie se identifico en las tres marismas, pero domino en Mehuin. Las otras tres especies solo se detectaron en Mehuin. Esto sugiere que Mehuin ha sido el lugar mas intervenido. La similitud floristica demostro baja afinidad entre marismas, pero se encontro mayor similitud entre Mehuin y Quillaipe y menor entre Puerto Saavedra y Quillaipe. La mayor similitud floristica entre Mehuin y Quillaipe se contrapone con la lejania geografica y climatica entre esos lugares. Mehuin esta mas proximo a Puerto Saavedra. La vegetacion de los extremos del gradiente latitudinal resulto mas homogenea que aquella del lugar intermedio. Segun los analisis estadisticos multivariados, los factores de anegamiento y salinidad aparecen como responsables de la distribucion de las especies en la gradiente altitudinal en cada lugar. La diferencia floristica entre los lugares sugiere la presencia de una gradiente latitudinal que no corresponde al caracter azonal de las marismas. La inclinacion de la gradiente litoral y la naturaleza del sustrato en los diferentes lugares, podrian ser los factores responsables de las diferencias encontradas.