Unravelling the pedogenetic development of forest soils in Northern Patagonia, Argentina

Abstract

The mountain forests of Northern Patagonia represent a steep hydroclimatic gradient, with a udic to xeric soil water balance from west to east, alongside pronounced elevation gradients. This study aimed to elucidate forest soil formation along these interacting gradients and to disentangle the various influencing factors. We collected 45 soil profile and 66 topsoil samples along 16 elevational transects along two west-to-east valley transects. Based on standard chemical soil analyses, 24 profiles were further characterised by selective dissolution analysis of short-range order minerals and PO₄-retention, and 5 profiles were analysed for bulk and clay mineralogical composition.

We found distinct patterns of soil development along the hydroclimatic gradient, along the elevation (thermal) gradient, and with changing litter quality characterised by the C:N ratio. The distinct plant species composition of the forest types plays a significant role in shaping soil properties through the C:N ratio of the ecto-organic layer and topsoil. Volcanic ash deposition regularly rejuvenates soils, particularly in the humid west, influencing the pedogenetic development. We observed a less pronounced expression of andic properties (e.g. higher bulk density, less amorphous Fe and Al, less PO₄-retention) in the east, and attributed this partly to aeolian deposition of non-volcanic material, reflected by a significant share of mica, quartz and K-feldspar. These factors lead to a shift in the reference soil groups, from Andosols to Cambisols.

Our findings reveal a complex interplay between climate, vegetation, and volcanic deposition, which has implications for understanding pedogenetic development and the effects of climate change in the Northern Patagonian forests.