Soil texture and altitude, respectively, largely determine the floristic gradient of the most diverse fog oasis in the Peruvian desert

Abstract: Studying species turnover along gradients is a key topic in tropical ecology. Crucial drivers, among others, are fog deposition and soil properties. In northern Peru, a fog-dependent vegetation formation develops on mountains along the hyper-arid coast. Despite their uniqueness, these fog oases are largely uninvestigated. This study addresses the influence of environmental factors on the vegetation of these unique fog oases. Accordingly, vegetation and soil properties were recorded on 66 4 × 4-m plots along an altitudinal gradient ranging from 200 to 950 m asl. Ordination and modelling techniques were used to study altitudinal vegetation belts and floristic composition. Four vegetation belts were identified: a low-elevation Tillandsia belt, a herbaceous belt, a bromeliad belt showing highest species richness and an uppermost succulent belt. Different altitudinal levels might reflect water availability, which is highest below the temperature inversion at around 700 m asl. Altitude alone explained 96% of the floristic composition. Soil texture and salinity accounted for 88%. This is in contrast with more humid tropical ecosystems where soil nutrients appear to be more important. Concluding, this study advances the understanding of tropical gradients in fog-dependent and ENSO-affected ecosystems. RESUMEN El estudio de recambio de especies a lo largo de gradientes es un tema clave en la ecología tropical. Los conductores cruciales, entre otros, son la deposición de niebla y las propiedades del suelo. En el norte de Perú, una formación vegetal dependiente de las nubes estratos se desarrolla en las montañas a lo largo de la costa hiperárida. A pesar de su singularidad, estos oasis de niebla están en gran parte sin investigar. Este estudio aborda la influencia de los factores ambientales sobre la vegetación de estos oasis de niebla únicos. En consecuencia, las propiedades de la vegetación y el suelo se registraron en 66 parcelas de 4 × 4-m a lo largo de un gradiente altitudinal que oscila entre 200 y 950 m.s.n.m. Técnicas de ordenación y modelos fueron utilizados para estudiar los cinturones altitudinales de vegetación y composición florística. Se identificaron cuatro pisos de vegetación: a baja altitud un cinturón de Tillandsia, un cinturón de herbáceas, luego un cinturón de bromelias mostrando elevada riqueza de especies y finalmente un cinturón en la parte superior constituido por suculentas. Los diferentes niveles altitudinales podrían reflejar la disponibilidad de agua, la cual es más alta por debajo de la inversión de temperatura a unos 700 m.s.n.m. La altitud sola explicó el 96% de la composición florística. La textura del suelo y la salinidad representaron el 88%. Esto está en contraste con los ecosistemas tropicales más húmedos donde los nutrientes del suelo aparecen ser más importantes. En conclusión, este estudio ayuda a la comprensión de los gradientes en los ecosistemas tropicales tanto de los dependientes de la niebla así como de los afectados por ENSO.

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