Soil Development in an Orographic Toposequence, Eastern Puerto Rico.
Cynthia A. Stiles1, Chien-Lu Ping2, Grizelle González3, and Krista Stensvold1. (1) University of Wisconsin, Dept of Soil Science, 1525 Observatory Drive, Madison, WI 53706-1299, (2) University of Alaska Fairbanks, Ag/Forestry Exp Station, 533 E Fireweed, Palmer, AK 99645, (3) Insititute of Tropical Forestry/USDA Forest Service, Jardín Botánico Sur, 1201 Calle Ceiba, San Juan, PR 00926-1119
Soil characteristics of an altitudinal gradient in eastern Puerto Rico were investigated. The setting is considered an orographic toposequence due to the interaction of strong easterly trade winds and the Luquillo Mountains occurring within 20 km of the coast. All soils formed in granodiorite residuum, colluvium or alluvium, depending on landscape position. The soils in the highest altitude cloud forest (1012 msl; MAP>300cm; clayey, kaolinitic isothermic Typic Endoaquults) were highly enriched in Al and Fe, depleted in Si and base cations (Ca, K, Mg, Na) and had moderate sombric epipedons. In the lower altitude (<50 msl) floodplain, soils ranged from Typic Haplustalfs in the drier windward positions to Aquic Hapludults in the leeward positions of the eastern coast. Soils in these areas had higher base saturation, pH, and slightly higher activity clays than higher altitudes. In the higher altitude positions, soil geochemical properties could be considered accumulating or depleting dependent upon slope morphology and vegetation type. The ashy, smeary nature of the surface horizons, coupled with very high Al contents that differed from parent material composition, suggest that these soils are intercepting aeolian materials and the soil genesis/nutrient cycling may be greatly effected by episodic inputs of ash and dust.