Germination ecology of neotropical pioneers: Interacting effects of environmental conditions and seed size

T. R. H. Pearson, David Francis Robert Philip Burslem, Christopher Mullins, J. W. Dalling

Research output: Contribution to journalArticle

188 Citations (Scopus)

Abstract

Germination provides many potentially unrecognized sources of variation in the regeneration niche. In this study we relate germination requirements and seed size for 16 species of pioneer trees to microclimatic conditions present in gaps in semi-deciduous rain forest in Panama. We found that, whereas increased duration of direct irradiance can be an effective indicator of the presence of a canopy gap across all scales of canopy openness, diel fluctuations in soil temperature effectively discriminate both understory sites and small gaps (25 m(2)) from larger gaps. Germination response was significantly related to seed size. Small-seeded species (seed mass <2 mg) showed significantly greater germination in response to irradiance of 22.3 mumol.m(-2).s(-1) than in complete darkness. Their germination was unaffected by an increasing magnitude of diel temperature fluctuation up to a species-specific threshold, above which it declined. Large-seeded species (seed mass >2 mg) germinated equally in light and darkness (with one exception) and either showed a positive germination response to an increasing magnitude of temperature fluctuation (four species) or no significant response (four species). The maximum seed burial depth from which seedlings could emerge successfully was strongly positively associated with seed mass. We conclude that photoblastic germination of tropical pioneer trees results in small-seeded species germinating in gaps only when seeds are located in microsites that are suitable for seedling emergence. A positive germination response to increasing temperature fluctuation can stimulate germination of larger-seeded species in larger gaps and when they are buried beneath an opaque soil or litter layer. Therefore, seed size differences constrain the physiological mechanisms of canopy gap detection in tropical pioneer trees and might contribute to observed differences in the distribution of adult plants in relation to canopy gap size.

Original languageEnglish
Pages (from-to)2798-2807
Number of pages9
JournalEcology
Volume83
Issue number10
DOIs
Publication statusPublished - Oct 2002

Keywords

  • Burro Colorado Island, Panama
  • emergence potential
  • germination cue
  • niche diffierentiation
  • pioneer species
  • tropical diversity
  • TROPICAL RAIN-FOREST
  • LIGHT
  • TREE
  • ESTABLISHMENT
  • LITTER
  • SOIL
  • REGENERATION
  • DISPERSAL
  • DIVERSITY
  • RESPONSES

Cite this

Germination ecology of neotropical pioneers: Interacting effects of environmental conditions and seed size. / Pearson, T. R. H.; Burslem, David Francis Robert Philip; Mullins, Christopher; Dalling, J. W.

In: Ecology, Vol. 83, No. 10, 10.2002, p. 2798-2807.

Research output: Contribution to journalArticle

Pearson, T. R. H. ; Burslem, David Francis Robert Philip ; Mullins, Christopher ; Dalling, J. W. / Germination ecology of neotropical pioneers: Interacting effects of environmental conditions and seed size. In: Ecology. 2002 ; Vol. 83, No. 10. pp. 2798-2807.
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AU - Burslem, David Francis Robert Philip

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AB - Germination provides many potentially unrecognized sources of variation in the regeneration niche. In this study we relate germination requirements and seed size for 16 species of pioneer trees to microclimatic conditions present in gaps in semi-deciduous rain forest in Panama. We found that, whereas increased duration of direct irradiance can be an effective indicator of the presence of a canopy gap across all scales of canopy openness, diel fluctuations in soil temperature effectively discriminate both understory sites and small gaps (25 m(2)) from larger gaps. Germination response was significantly related to seed size. Small-seeded species (seed mass <2 mg) showed significantly greater germination in response to irradiance of 22.3 mumol.m(-2).s(-1) than in complete darkness. Their germination was unaffected by an increasing magnitude of diel temperature fluctuation up to a species-specific threshold, above which it declined. Large-seeded species (seed mass >2 mg) germinated equally in light and darkness (with one exception) and either showed a positive germination response to an increasing magnitude of temperature fluctuation (four species) or no significant response (four species). The maximum seed burial depth from which seedlings could emerge successfully was strongly positively associated with seed mass. We conclude that photoblastic germination of tropical pioneer trees results in small-seeded species germinating in gaps only when seeds are located in microsites that are suitable for seedling emergence. A positive germination response to increasing temperature fluctuation can stimulate germination of larger-seeded species in larger gaps and when they are buried beneath an opaque soil or litter layer. Therefore, seed size differences constrain the physiological mechanisms of canopy gap detection in tropical pioneer trees and might contribute to observed differences in the distribution of adult plants in relation to canopy gap size.

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KW - germination cue

KW - niche diffierentiation

KW - pioneer species

KW - tropical diversity

KW - TROPICAL RAIN-FOREST

KW - LIGHT

KW - TREE

KW - ESTABLISHMENT

KW - LITTER

KW - SOIL

KW - REGENERATION

KW - DISPERSAL

KW - DIVERSITY

KW - RESPONSES

U2 - 10.1890/0012-9658(2002)083[2798:GEONPI]2.0.CO;2

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M3 - Article

VL - 83

SP - 2798

EP - 2807

JO - Ecology

JF - Ecology

SN - 0012-9658

IS - 10

ER -