Growth and climatic response of male and female trees of Austrocedrus chilensis, a dioecious conifer from the temperate forests of southern South America

ROVERE, A.E.; AIZEN, M.A.; KITZBERGER, T.

ECOSCIENCE (SAINTE-FOY)

UNIVERSITE LAVAL

Año: 2003 vol. 10 p. 195 - 203

1195-6860

Abstract: In dioecious plants, males and females usually differ in the amount of resources devoted to reproduction. As a consequence of potential tradeoffs between reproductive and vegetative functions, sexes can exhibit distinctive growth patterns. We analyzed differences between male and female trees in average radial growth, interannual radial growth variation, and, through dendrochronological reconstruction, growth response to temperature and rainfall in 15 stands of the dioecious conifer Austrocedrus chilensis, occurring in Nahuel Huapi National Park, Argentina. Patterns of resource allocation in this species are typical of most dioecious plants in that females invest several times more carbon and nitrogen into reproduction than males. Consistent with theory, we found that in seven stands males grew faster than females. In three stands, however, females grew faster than males, whereas in the other five no significant differences between sexes were detected. In addition, within a stand one sex could grow faster than the other during some periods, while at other times the reverse was true. We found no evidence that females exhibited higher interannual growth variation than males. Growth responded positively to precipitation and negatively to temperature over the growing season. However, neither the direction nor the magnitude of the correlations between annual growth and seasonal climatic variables differed between males and females. Possible factors that could contribute to reducing the differences in the cost of reproduction between males and females in A. chilensis are i) the photosynthetic activity of developing female cones, ii) differences in carbon assimilation efficiency between sexes, and iii) a more strict regulation of the number of reproductive structures produced annually among the females. We hypothesize that the spatio-temporal mosaic in growth differences between sexes we report here might be attributed to chance colonization of disturbed sites by either fast- or slow-growing male and female genotypes rather than by stand characteristics. A general implication is that very little might be concluded about the consequences of the differential cost of reproduction between sexes in any dioecious species from studies focused on a single population or even a few populations.