growth ring

growth ring

In a cross section of the stem of a woody plant, the amount of wood added during a single growth period. In temperate regions this period is usually one year, in which case the growth ring may be called an annual ring. In tropical regions growth rings may not be discernible or are not annual. Even in temperate regions growth rings are occasionally missing; and sometimes a second, or “false,” ring may be deposited during a single year (e.g., following defoliation by insects). Nevertheless, annual rings have been used in dating ancient wooden structures, especially those of American Indians in the dry U.S. Southwest. Changes in ring width are a source of information about ancient climates.

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Tambalacoque (Sideroxylon grandiflorum; formerly Calvaria major), also called the Dodo Tree, is a long-lived tree in the family Sapotaceae, endemic to Mauritius. The Dodo Tree is valued for its timber. Tambalacoque is analogous to Peach. Both have a hard endocarp surrounding the seed, but the endocarp naturally splits along a fracture line during germination.

In 1973, it was thought that this species was dying out. There were supposedly only 13 specimens left, all estimated to be about 300 years old. The true age could not be determined because Tambalacoque has no growth rings. Stanley Temple hypothesized that the Dodo, which became extinct in the 17th century, ate tambalacoque fruits, and only by passing through the digestive tract of the Dodo could the seeds germinate. Temple (1977) force-fed seventeen tambalacoque fruits to Wild Turkeys and three germinated. Temple did not try to germinate any seeds from control fruits not fed to turkeys so the effect of feeding fruits to turkeys was unclear. Reports made on tambalacoque seed germination by Hill (1941) and King (1946) found the seeds germinated without abrading.

Temple's hypothesis that the tree required the dodo has been contested. Others have suggested the decline of the tree was exaggerated, or that other extinct animals may also have been distributing the seeds, such as tortoises, fruit bats or the Broad-billed Parrot. Wendy Strahm and Anthony Cheke, two experts in Mascarene ecology, claim that while a rare tree, it has germinated since the demise of the Dodo and numbers a few hundreds, not 13. The difference in numbers is due to the fact that young trees are not distinct in appearance and may easily be confused with similar species. The decline of the tree may possibly be due to introduced pigs and Crab-eating Macaques and competition with introduced plants. Catling (2001) in a summary cites Owadally and Temple (1979), and Witmer (1991). Hershey (2004) reviewed the flaws in Temple's dodo-tambalacoque hypothesis.

To aid the seed in germination, botanists now use turkeys and gem polishers to erode the endocarp to allow germination. This tree is highly valued for its wood in Mauritius, which has led some foresters to scrape the pits by hand to make them sprout and grow.

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