Soil properties and Austrocedrus chilensis decline in Central Patagonia, Argentina

LA MANNA L., RAJCHENBERG M.

PLANT AND SOIL

Kluwer

Lugar: Amsterdam; Año: 2004 vol. 263 p. 25 - 37

0032-079X

Austrocedrus chilensis forests in Argentina suffer a widespread mortality, locally known as ‘mal del ciprés’, whose causes remain unknown. ‘Mal del ciprés’ occurs throughout the cypress range in Argentina, being Río Grande Valley, in Central Patagonian Andes, an area where the disease has notoriously increased its extension and importance in the last years. The purpose of this work was to characterize Río Grande Valley soils where declining cypress stands develop and to determine what soil properties are associated with the disease. Four sampling sites with pure cypress forests expressing ‘mal del ciprés’ were selected. In each of them, 3 declining and 3 asymptomatic plots were established and were characterized by edaphic features. Selected morphological, physical and chemical soil properties were related to the occurrence of the decline by means of analysis of variance. The cypress forest developed in a wide range of soils with different parent materials: glacifluvial, alluvial, volcanic with a glacifluvial discontinuity, volcanic on an andesitic substratum, and soils derived fromandesite alteration. All the soils presented dark superficial horizons, rich in organic matter and with granular structure. Cypress growing on volcanic soils with a glacifluvial discontinuity presented symptoms of decline in areas where the discontinuity, and therefore the clayey horizon and the redoximorphic features, were close to the surface. In soils derived from andesite alteration, the declining forest was also present on shallow soils with redoximorphic features near the surface. In volcanic soils with a lithological discontinuity of andesite, the decline was restricted to areas near a water stream. In alluvial soils, declining trees appeared related with the flood plain of the river; healthy forest stands developed on higher lands, where soils were well drained. Glacifluvial soils, presenting clayey textures and great difficulties for rooting, were the soils submitted to the worst drainage conditions. In these soils, the decline presented a random pattern of distribution, suggesting that the whole area is prone to develop the decline. Results showed cypress capacity to inhabit different soils; however microsite features related to poor drainage (i.e., low slope, nearness to water streams, the presence of clay and redoximorphic features near to the surface) determined a higher risk of disease occurrence.