Demography of the vegetable ivory palm Phytelephas seemannii in Colombia, and the impact of seed harvesting.
Abstract
The demography of the vegetable ivory palm Phytelephas seemannii was studied on the Pacific coast of Colombia and a female-based matrix model was used to determine the proportion of seed that can be sustainably harvested from the population. The density of the palm stands ranged from 240 to 420 adult palms/ha. The sex ratio was 1:1 and palms of both sexes produced leaves at the same rate. Seedlings produced 1.2 leaves per year on average, juveniles 1.8, and adults 6.1-7.4. Adult females had fewer leaves than males (18.5 vs. 21.3 on average). Leaves of females lasted about 2.7 years in the crown, those of males about 3.2 years. Stems creep on the ground, growing at the apex and often dying behind, the extant portion not always reflecting the total age of the palm. The longest stem of a female palm in the study plots was 2.5 m, corresponding to an 'extant' age of 85 years; the longest stem recorded was that of a male (outside the plots) 10.5 m long, corresponding to an 'extant' age of 184 years. It was considered that these figures reflect differences in growth habit, not in longevity. Reproduction began at about 24 years, when the palm still lacked an aboveground stem. The population growth rate λ was 1.059, and was most sensitive to changes in survival of juveniles and adults, and relatively insensitive to changes in fecundity and growth. River channel migration was the most important cause of adult mortality. P. seemannii is apparently an efficient colonizer of the understorey in the late phases of riverine forest succession. It is considered that the population could tolerate a harvesting rate of 86% of all seeds before λ decreases to the equilibrium level of 1.00. Monitoring of populations under intensive harvesting is required.