Sex-related spatial segregation and growth in a dioecious conifer along environmental gradients in northwestern Patagonia

Abstract

The separation of sexes in plants (dioecy) implies differences in reproductive biology that in many cases favour sexual dimorphism and spatial segregation. Females of the dioecious conifer Austrocedrus chilensis have higher reproductive effort than males. We examined the spatial distribution of male and female Austrocedrus trees along a range of environmental conditions and sex-related growth patterns in northwestern Patagonia. Males were more abundant on high-radiation slopes (M:F ≈ 1.7), while low-radiation slopes had higher abundances of females (M:F ≈ 0.6). This pattern was consistent and equally strong in mesic and xeric sites along a strong rainfall gradient, suggesting that moisture is not the only triggering factor for tree distribution. Austrocedrus females tended to occupy the moister aspects, but genders were not isolated at large geographical scales, avoiding detrimental effects on species fitness. As evidenced by ring widths, males grew ~100% more per year than females on high-radiation exposures, while on low-radiation aspects, males and females did not differ significantly, suggesting that in moister, low-radiation exposures female trees are able to compensate for the reproductive expenses they have. Alternatively, reproductive effort may differ between male and females on different slopes.