GENDER EXPRESSION IN ABIES PINSAPO BOISS, A MEDITERRANEAN FIR

Gender expression was recorded for three geographically distinct popul ations and two stand densities of pinsapo fir (Abies pinsapo) in south ern 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 floweri ng intensity or in cone crop production was found. The most extreme va riations were correlated with stand density: flowering intensity and c one crop were always greater in low density trees. Abies pinsapo is a monoecious species but all the populations studied showed a predominan ce 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 i n sex expression of individuals al two different stand densities were found, but these were only significant in 1991. In dense stands of pin sapo firs branches were limited to the top of trees and thus, they pro duced mainly female cones,whereas isolated trees had branches from gro und level and as a consequence they were predominantly male, with a hi gher total reproductive effort. The results indicate that relative inv estment in male and female reproductive structures by A. pinsapo indiv iduals is a response to plant architecture, plant resource status and environmental variation. (C) 1997 Annals of Botany Company.