Growth of male and female Araucaria araucana trees respond differently to regional mast events, creating sex-specific patterns in their tree-ring chronologies

Abstract

Araucaria araucana is a dioecious evergreen conifer endemic from temperate forests of south Argentina and Chile. It is a long-lived species (maximum age > 1000 years), and it presents a high potential for tree-ring based climate reconstructions. However, the species' dioecious habit can result in distinct sex-specific growth patterns, which introduce novel challenges in the interpretation of tree-ring chronology variations. We used a network of 10 treering chronologies from northwest Patagonia (Argentina) to analyze sex-specific growth patterns in A. araucana and, for the first time, demonstrate that they result from the contrasting responses of ring width index of male (RWImale) and female (RWIfemale) trees to regional mast events (years with high seed production). During the year of seed maturation and seed dispersal, the growth of females was strongly and significantly reduced, while a growth response of similar magnitude was found in male trees in the previous year, corresponding to the year of pollination. We interpret these growth responses as representing contrasting allocation shifts between growth and reproduction in males and females. The sex-specific growth responses associated with mast events resulted in a particularly strong and distinct signal in a RWImale-RWIfemale chronology. Male and female tree-ring chronologies shared a strong common signal, and responded similarly (but not exactly) to broad-scale climatic conditions in the growing season. Our results indicate that sex-specific tree-ring chronologies can be used to isolate mast events in A. araucana chronologies, providing an opportunity to develop unique multi-century reconstructions of large mast events, and improve dendroclimatic calibration for this species.

Araucaria araucana is a dioecious evergreen conifer endemic from temperate forests of south Argentina and Chile. It is a long-lived species (maximum age > 1000 years), and it presents a high potential for tree-ring based climate reconstructions. However, the species' dioecious habit can result in distinct sex-specific growth patterns, which introduce novel challenges in the interpretation of tree-ring chronology variations. We used a network of 10 treering chronologies from northwest Patagonia (Argentina) to analyze sex-specific growth patterns in A. araucana and, for the first time, demonstrate that they result from the contrasting responses of ring width index of male (RWImale) and female (RWIfemale) trees to regional mast events (years with high seed production). During the year of seed maturation and seed dispersal, the growth of females was strongly and significantly reduced, while a growth response of similar magnitude was found in male trees in the previous year, corresponding to the year of pollination. We interpret these growth responses as representing contrasting allocation shifts between growth and reproduction in males and females. The sex-specific growth responses associated with mast events resulted in a particularly strong and distinct signal in a RWImale-RWIfemale chronology. Male and female tree-ring chronologies shared a strong common signal, and responded similarly (but not exactly) to broad-scale climatic conditions in the growing season. Our results indicate that sex-specific tree-ring chronologies can be used to isolate mast events in A. araucana chronologies, providing an opportunity to develop unique multi-century reconstructions of large mast events, and improve dendroclimatic calibration for this species.