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 ﬁrst of which is the allocation of resources to reproductive structures as opposed to vegetative growth. Among ﬂowering plants, that comprise the majority of tree species, allocation to reproductive structures such as ﬂowers, 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 ﬂowers, while others (e.g., Dipterocarpus) produce only a few hundred relatively large ﬂowers. Flower number and morphology reﬂect 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 ﬁrst of two stages by which gene ﬂow is affected, by gamete dispersal within populations. Seed dispersal represents a second opportunity for gene ﬂow as seeds are transported to new locations by a variety of dispersal vectors.
[...] Tropical trees generally have hermaphroditic ﬂowers but are mostly incapable of self-fertilization due to physiological self- incompatibility mechanisms. Spatial separation of ﬂowers 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 ﬂowering 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 efﬁciency is thought to have contributed substantially to the ﬂexibility 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. [...]
[...] of tree reproductive strategies in temperate and tropical forests, emphasizing ﬂower and seed life stages. General Reproductive Strategies Vegetative reproduction Plants as sessile organisms reproduce by means of their modular architecture and their capacity for reiterative growth indeed, all plants are potentially clonal in that each module contains both reproductive and somatic tissue. However, production of independent offspring by means of vegetative growth is rare among trees, although detached branches of willows and poplars can sprout if maintained in moist conditions. [...]
[...] Flowers of bat-pollinated trees open at dusk or soon after and are typically large, white or pale, have a musky odor, and produce copious amounts of nectar. While this is energetically costly, gene ﬂow by bat-dispersed pollen is potentially very great. In the neotropics hummingbirds are the main avian pollinators and feed exclusively on nectar, although they primarily visit understory shrubs rather than trees. Their Old World counterparts are sunbirds which visit a wide variety of trees but also feed on insects. [...]
[...] Regeneration of many forest trees is usually conﬁned to gaps, and composition of the regenerating community is a function of gap size, shape, and location, and the coincidence between gap formation and a fruiting event. The establishment of some tropical trees, such as mahogany, is entirely dependent on large clearings created by high winds and subsequent ﬁres, while seedlings of other species simply need canopy openings for further growth. Yet other species, such as beech and hemlock, are shade- tolerant and regenerate under closed canopies. [...]
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