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    The amount of wood produced by a tree each year depends on tree condition, genetic programming, and growing conditions. Wood is mature xylem, the result of inward cell divisions by the vascular cambium, the new cell generator located between the wood and the inner bark (phloem). In temperate climatic zones, where a spring and summer growing season alternates with winter dormancy, the vascular cambium usually produces a single layer or increment of wood each year. Tree rings are annual growth layers seen in cross section. In Mediterranean dry and tropical climates, rings of earlywood are formed when seasonal moisture is available and may not be strictly annual. Tropical trees also produce wood in flushes of growth but usually do not produce rings that can be easily correlated with the calendar. The formation of latewood in tropical species is sometimes associated with environmental changes, such as el Niño and la Niña cycles.

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    Smith, Kevin T. 2011. Tree rings and the local environment. Arborist News. 20(3): 12-15.

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