CONICET | Buscador de Institutos y Recursos Humanos

Forest decline, or the premature senescence of forests, is a global phenomenon associated with crown dieback and reduction in radial growth, eventually leading to massive tree mortality. Although poor health in a tree is expected to be associated with low growth rates, only few studies have linked tree external conditions with radial growth. In this study, we explore the relationships between radial growth patterns and external variables commonly related to N. pumilio forest decline at 11 stands along the northern Patagonian Andes in Argentina. The external characteristics of trees compared with radial growth were 1) the percentage of crown mortality, 2) the diameter at breast high (DAP), 3) the percentage of dead bark, 4) the abundance of holes left by borer insects; 5) the abundance of holes left by woodpeckers, 6) the presence of tumors produced by fungi (llao-lao), 7) the number of hemiparasite plants in the crown and 8) lichen coverage along the principal stem. Crown mortality, which was classified in four categories (0-25, 25-50, 50-75 and 75-100% dead crown), is the parameter most closely related to the growth patterns. Individuals showing the larger percentages of crown mortality show lower rates of growth and negative growth trends in recent decades. In addition, low rates of growth and high percentages of crown mortality are related to larger DAPs. Other variables statistically related to both low growth rates and large percentages of crown mortality were the bark health condition and the number of holes left by boring insects and woodpeckers. Conversely, the presence of tumors produced by fungi, hemiparasites and lichens showed no difference between forest-decline affected and unaffected individuals. This study shows that low rates of radial growth, percentages of crown and bark mortality as well as the abundance of holes left by boring insects and woodpeckers can be used as indicators to assess N. pumilio forests decline.