Spatial distribution of Austrocedrus chilensis patches with defoliation and mortality in Valle 16 de Octubre, Chubut province, Argentine

Abstract

Cordilleran cypress (Austrocedrus chilensis) is an endemic species of the Andean forests of Patagonia. Widespread mortality of A. chilensis occurs and is locally known as “mal del ciprés”. The objectives of this work were to identify the spatial distribution of patches presenting mal del ciprés syndrome and to quantify the surface showing affected forest. The study was carried out in “16 de Octubre” Valley (Chubut province, 43º10’S), which concentrates 9% of the total surface of A. chilensis pure forests in Argentina. In the field, patches of trees affected by “mal del ciprés” (100), patches of trees in asymptomatic dense forests (50) and patches of trees in asymptomatic thin forests (80) were identified. According to these training sites, the digital numbers for each type of vegetation were determined and a supervised classification was done using SPOT PAN and XS satellite images. Discrimination between “mal del ciprés” and asymptomatic thin patches was hard because both types of vegetation presented similar digital numbers, probably because of the understory influence. Classification accuracy was assessed in the field. In the final map, 70% of patches with “mal del ciprés” were well classified. Eighty five percent of patches with asymptomatic dense forest and 70% of patches with asymptomatic thin forests were well classified. The affected forest covered 1,678 ha (24% of the total surface of A. chilensis in the study area). The asymptomatic dense forest and asymptomatic thin forest covered 2,721 and 2,584 ha, respectively. This study allowed quantifying the magnitude of mal del ciprés and the generated map could be useful for epidemic studies and for forest management.