CONICET | Buscador de Institutos y Recursos Humanos

Forest decline, or the premature loss of forest health, is a complex process not yet fully understood.Although reductions of radial growth have previously been recorded for individuals affected by decline,studies describing the whole range of growth patterns from decline-affected stands are rare. We usedprincipal component analysis to identify dominant patterns of radial growth in eleven Nothofagus pumiliostands in northern Patagonia that show external manifestations of forest dieback. At most sites, dominantgrowth patterns significantly different from the stand mean growth chronology were identified usingeither ring widths or basal area increments (BAIs). Due to the pervasive trend of decreasing ring widthwith increasing tree diameter, patterns of tree growth related to forest decline are better captured usingBAIs. Three dominant patterns of growth were identified at most sites: (1) trees with the highest rates ofgrowth during the first decades of the 20th century started a sustained reduction in radial growth in early1940s reaching the lowest increments in the late 20th century; (2) trees with low growth over most ofthe 20th century substantially increased their growth rates in the 1960s concurrent with the growthdecline in the previous group, and (3) trees with intermediate growth rates until mid-20th centuryshowed a subsequent 20?30 year period with high rates of growth followed by a gradual reduction fromthe late 1980s to present. The onset of negative trends in radial growth associated with forest decline(patterns 1 and 3) occurs simultaneously at most stands. Contrary to expectations, large-dominant treeswith the highest rates of growth seem to be the most severely affected by reductions in radial growth.These results are consistent with the concept of ??decline disease stabilizing selection?? where healthydominant fast-growing trees in the forest are selectively affected by a combination of specifically detrimentalfactors. Dominant patterns at stand scale exhibit similar trends in radial growth between sitesseparated by more than 400 km in northern Patagonia suggesting that meso- to macro-scale environmentalforcings modulate regional forest decline. Our results challenge traditional sampling designs used indendroecological and dendroclimatological studies. Traditional sampling strategies, mostly targeted todominant, climate-sensitive trees, will over emphasize the 20th century negative trends in Nothofagusstand growth associated with the largest stand trees. Only by including all individuals within a plot, willsampling provide consistent tree-growth estimates that represent the entire population. Additionally, asendogenous stand dynamics are not clearly reflected in mean growth estimates, dominant growth pat

enviar mensaje