Gender Expression inAbies pinsapoBoiss., a Mediterranean Fir

Gender expression was recorded for three geographically distinct populations and two stand densities of pinsapo fir (Abies pinsapo) in southern Spain, during 4 consecutive years (1990–1993). During this period the trees only flowered in 1991 and 1992, and thus only two cone crops could be quantified. No significant geographical variation in flowering intensity or in cone crop production was found. The most extreme variations were correlated with stand density: flowering intensity and cone crop were always greater in low density trees.Abies pinsapois a monoecious species but all the populations studied showed a predominance of female plants, with a few male and monoecious individuals, thus indicating a functionally subdioecious breeding system. No differences in gender expression between populations were recorded. Differences in sex expression of individuals at two different stand densities were found, but these were only significant in 1991. In dense stands of pinsapo firs branches were limited to the top of trees and thus, they produced mainly female cones, whereas isolated trees had branches from ground level and as a consequence they were predominantly male, with a higher total reproductive effort. The results indicate that relative investment in male and female reproductive structures byA. pinsapoindividuals is a response to plant architecture, plant resource status and environmental variation.