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Reproductive ecology of forest trees

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  1. Introduction.
  2. General reproductive strategies.
    1. Vegetative reproduction.
    2. Sexual reproduction.
  3. Pollination of angiosperms.
    1. Pollination by vertebrates.
    2. Pollination by invertebrates.
    3. Wind pollination.
  4. Breeding systems and incompatibility.
  5. Seed morphology and dispersal.
    1. Seed size.
    2. Seed dispersal.
  6. Seed and seedling banks.
  7. Natural disturbance.
  8. Conclusion.

Plant reproductive processes encompass biotic interactions, such as pollination and seed predation and dispersal, and abiotic elements, notably disturbance that creates differential reproductive opportunities for plant groups and thereby maintains diverse forest formations.

There are several important stages in the regeneration of trees, the ?rst of which is the allocation of resources to reproductive structures as opposed to vegetative growth. Among ?owering plants, that comprise the majority of tree species, allocation to reproductive structures such as ?owers, seeds, and fruit may vary enormously and may comprise a substantial portion of photosynthate. Even within plant families some trees (e.g., some dipterocarps of the genus Shorea) produce several million tiny ?owers, while others (e.g., Dipterocarpus) produce only a few hundred relatively large ?owers. Flower number and morphology re?ect pollinator syndromes while the trade-off between seed size and number has also generated a huge variety of options for reproductive success. Beyond being a crucial step in seed production, pollination is the ?rst of two stages by which gene ?ow is affected, by gamete dispersal within populations. Seed dispersal represents a second opportunity for gene ?ow as seeds are transported to new locations by a variety of dispersal vectors.

[...] Tropical trees generally have hermaphroditic ?owers but are mostly incapable of self-fertilization due to physiological self- incompatibility mechanisms. Spatial separation of ?owers by dioecy is also common among tropical species. In tropical lowland forests of Guanacaste in Costa Rica, for example of trees are dioecious and a further 54% are physiologically self-incompatible. Seed morphology and dispersal Seed Size Seed size varies among ?owering plants from less than 10^-6 g in orchids to more than 10^4 g in coco-de-mer. Small seeds can be produced in greater numbers but have less chance of establishing successfully, owing to fewer stored reserves, and size is largely a trade-off between these two selection pressures. [...]

[...] Increased reproductive ef?ciency is thought to have contributed substantially to the ?exibility of reproductive strategies and to the current dominance and diversity of the angiosperms. The ovules of angiosperms are completely enclosed within the carpel (hence angiosperm, meaning hidden seed), a development that may have arisen to protect the ovules and pollen from insects. A pollen grain landing on the stigmatic surface germinates and extends a pollen tube through the style to fertilize the ovule. The fertilized embryo develops within a seed that may be enclosed in a nut or fruit to attract animal dispersal agents, or may be formed so as to facilitate dispersal by wind, water, or passive animal transport. [...]

[...] Quite different reproductive strategies exist among forest trees within and among communities. The most obvious is the overwhelming dependence of tropical trees on animal interactors for pollination and seed dispersal, compared to temperate species, for which abiotic agents are comparatively more important. Such differences in pollination and seed dispersal vectors are re?ected in the ef?ciency of gene transfer and patterns of gene ?ow, and information about seed production and gene ?ow is critical for the design of forest management plans and strategies for the conservation of plant genetic resources. [...]

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