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Media type:
E-Article
Title:
Crown Illumination Limits the Population Growth Rate of a Neotropical Understorey Palm (Geonoma macrostachys, Arecaceae)
Contributor:
Svenning, Jens-Christian
Published:
Kluwer Publishers, 2002
Published in:
Plant Ecology, 159 (2002) 2, Seite 185-199
Language:
English
ISSN:
1385-0237;
1573-5052
Origination:
Footnote:
Description:
The importance of light as a limiting factor for growth and reproduction in tropical understorey plants is well known, but the population-level consequences of light limitation remain little explored. Here, I use demographic modelling to examine if the effect of canopy gaps on individual-level performance in a tropical understorey palm translates into an effect on the population growth rate. The demographic effects of heterogeneity in crown illumination (index of hemispherical canopy openness), forest-phase, and other microenvironmental parameters were quantified using data on 2592 individuals of all sizes in permanent plots followed over a 1.5 year period. Supplementary experiments investigating the effects of canopy conditions on seedling recruitment were also conducted. Among the microenvironmental parameters only crown illumination and forest-phase had strong and consistent demographic effects. Growth and fecundity generally increased with increasing crown illumination. Under open forest-phase conditions growth tended to increase and survival to decrease (due to increased physical damage). Seedlings transplanted into gap centres were damaged by solarization. The population-level effect of heterogeneity in crown illumination and forest-phase was investigated using transition matrix models. The overall population growth rate was 0.999, and not significantly different from 1. Illumination-specific models showed that G. macrostachys would be unable to persist at permanently low illumination, but would increase in density under higher illumination. Forest-phase-specific models gave similar, but weaker results. Thus, in G. macrostachys effects of canopy openness on individual-level performance strongly limit the population growth rate. The present study thereby shows that fine-scale spatiotemporal variation in canopy openness in the tropical rain forest understorey can play a central role in the population ecology of shade-tolerant understorey plants.