The decline of Austrocedrus chilensis forests in Patagonia, Argentina: soil features as predisposing factors

The forests of Austrocedrus chilensis in southern Argentina suffer mortality from “mal del cipres”, whose causes remain unknown. The purpose of this work was to establish the relation of soil features with the occurrence of the disease. In Rio Grande Valley, Chubut Province, Argentina, 14 areas with “mal del cipres” were selected for study. The spatial pattern of the decline varied among the different areas and was classified as aggregated and disaggregated. In each area, symptomatic and asymptomatic plots were established and characterized by 11 edaphic and topographic variables. Three forest areas where the disease was totally absent were also included. Site features were related to the occurrence of the decline using principal component analysis and cluster analysis. Results indicated that soil properties related to poor internal drainage, such as the proximity to water streams, non-allophanized soils of fine textures, and redoximorphic features, act as predisposing factors to the development of “mal del cipres”. Poor soil drainage was strongly associated not only with the occurrence of the disease, but also with its spatial pattern. Symptomatic and asymptomatic plots presented similar edaphic features in areas with a disaggregated distribution of the decline and were grouped together in the multivariate analysis. This result suggests that large areas with such a pattern are prone to develop the decline.