Effect of volcanic ash deposition on length and radial growths of a deciduous montane tree (Nothofagus pumilio)

Abstract Extreme environmental events such as volcanic eruptions can trigger plant responses that largely exceed those recorded for moderate‐intensity disturbances. We assessed the effects of the June 2011 eruption of the Puyehue – Cordón Caulle volcano on the length and radial growths of juvenile Nothofagus pumilio trees at two sites located 20 (with >40 cm ash accretion) and 75 (without ash) km from the volcano. Variations in length and radial growth were evaluated for the periods 1999–2013 and 1993–2013 respectively; pre‐ and post‐eruption growth rates were computed. The length growth of the N. pumilio trees located close to the volcano increased significantly after the eruption: shoot extensions during the growing season after the eruption were, on average, two to three times longer than average according to ontogenetic growth trends. Variations in radial growth after the eruption were comparatively less noticeable than those in length growth. No significant effects of the eruption were observed in those trees located 75 km from the volcano. In order to explain the exceptionally positive response of N. pumilio 's length growth to the volcanic eruption, three non‐exclusive explanations were proposed: (i) thick ash layers increase water retention in the soil; (ii) volcanic ash facilitates the access of plants to nutrients; and (iii) volcanic ashes decrease herbivory and competition. The comparatively lower sensitivity of radial growth to this extreme volcanic event is also noteworthy. These findings highlight the need to further examine how large‐scale volcanic events influence structure and/or functioning of ecosystem in the Patagonian forest.