Ecological correlates of seed desiccation tolerance in tropical African dryland trees

Authors:
  • BFBenjamin J. Fletcher
    Benjamin J. Fletcher
  • CGChristiane S. Gaméné
    Christiane S. Gaméné
  • HMHeriel P. Msanga
    Heriel P. Msanga
  • WOWilliam Omondi
    William Omondi
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Abstract
In the tropics, species with recalcitrant or desiccation‐sensitive, Type III seeds are largely restricted to regions with comparatively high rainfall, because desiccation‐induced seed death will be minimal in these environments. However, species with recalcitrant seeds do occur in drylands, although little is known about ecological adaptations to minimize seed death in these environments. Here we present data for the seed desiccation tolerance of 10 African dryland species and examine the relationships between seed size, rainfall at the time of seed shed, and desiccation tolerance for these and a further 70 species from the scientific literature. The combined data set encompasses species from 33 families. Three species (Syzygium cumini, Trichilia emetica, and Vitellaria paradoxa) had desiccation‐sensitive seeds, and the remaining seven species investigated were desiccation‐tolerant. The desiccation‐sensitive species had large (>0.5 g) seeds, germinated rapidly, and had comparatively small investments in seed physical defenses. Furthermore, seed was shed in months of high rainfall (>60 mm). In comparison, for species with desiccation‐tolerant seeds, seed mass varied across five orders of magnitude, and seed was shed in wet and dry months. Although infrequent in dryland environments (approximately 11% of the species examined here), species with desiccation‐sensitive seeds do occur; large size, rapid germination, and the timing of dispersal all reduce the likelihood of seed drying. Furthermore, desiccation‐sensitivity may be advantageous for large‐seeded species by increasing the efficiency of resource use in seed provisioning.
Funding Information
  • International Plant Genetic Resources Institute
  • Danida Forest Seed Centre
  • Millennium Commission
  • The Wellcome Trust and Orange plc
  • The Royal Botanic Gardens

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