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1. Plant facilitation usually changes to competition as plants age. In dioecious plants, females should be affected more negatively than males by stressful conditions because of the greater costs of female reproduction.

2. We investigated the gender effects on the post-facilitation performance of adult plants of two dioecious Juniperus species from the high mountains of eastern Spain: J. sabina L. acts as a nurse plant for J. communis L. We compared physiological (water potential, carbon isotope discrimination and nitrogen concentration), vegetative (shoot growth) and reproductive (number of male flowers, and number of fruits and seeds) characters of associated and non-associated plants of both species, to test the hypothesis that this association represents a more stressful condition for females than for males because of the greater costs of female reproduction.

3. Despite their close phylogenetic relatedness, both species showed a distinct performance pattern after the facilitation phase. Association with the nurse plant reduced the growth and reproductive capacity of both genders in J. communis, the facilitated species. In contrast, the association with J. communis did not affect the fitness of the nurse plant, J. sabina, although in accordance with our hypothesis a gender effect was found on several physiological parameters. Thus J. sabina-associated females had a more negative water potential and carbon isotope discrimination than the associated males, but there were no differences between genders when growing in isolation.

4. The consequences of the post-facilitation interaction between the two long-lived woody Juniperus species are asymmetrical: harmful for the facilitated species, but harmless for the nurse.

5. Gender had also asymmetrical consequences on some functional traits of the nurse - but not the facilitated - species.