An online resource based on the award-winning nature guide

Phloem

Yellow-bellied Sapsuckers Drilling Wells & Lapping Sap

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Yellow-bellied Sapsuckers have returned and in between sending their Morse code messages, are drilling into over 1,000 species of woody plants to obtain sap.  At this time of year, sap wells are drilled into xylem tissues (transport water and nutrients from roots to branches) to feed on sap that is moving upward; after deciduous species leaf out, sap wells tap phloem tissues (transport sugars and other nutrients made in the leaves to other parts of the tree).  Unlike sap drawn from the xylem which contains from 2-3% sugar, phloem sap may contain 20-30% sugar.

Sapsucker tongues have a fringe of hair-like projections along the edges which enable the sapsucker to lap up the sap that accumulates in a well (“saplapper” would be a more accurate name for these woodpeckers).  Recently a female sapsucker landed on the trunk of a nearby Sugar Maple and tapped eight wells.  She then spent the better part of the afternoon inserting her brush-like tongue into the wells and drinking the sap that collected.  The entire time she was drinking sap, she was constantly (8 times per hour) evacuating a stream of clear liquid (as opposed to the typical uric acid excreted by birds).  Apparently much of what goes in must come out.

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Living Hollow Trees

12-31-14 hollow yellow birch 027Occasionally one comes across a living tree with a portion of its trunk, or its entire trunk, hollow. How is it possible for a tree to thrive even when its center, or heart, has completely decayed? It comes down to the different kinds of wood that are produced by a tree: sapwood and heartwood.

Sapwood (often light-colored) is the younger, living, outermost portion of a woody branch or tree trunk (just beneath the bark), while heartwood (often dark-colored) is the dead, inner wood. All wood in a tree is first formed as sapwood. Sapwood’s principal functions are to conduct water from the roots to the leaves (via xylem tissue) and to disperse nutrients made by the leaves to the rest of the tree (via phloem tissue). Heartwood (so called because of its central position, not because it is essential to the health of the tree) is basically non-functioning xylem tissue that has become blocked with resins, tannins, and oils. Although the dead heartwood can lend stability to a tree, it is no longer part of the transport system, and therefore, not vital to the tree.

Cavities and hollows typically result from an injury to a tree (usually caused by fire, storms, lightning, insects or birds) that exposes the heartwood. Bacteria and fungi lose no time moving in and beginning the decaying process, which can result in a hollow tree. Because the sapwood, and therefore the transport system, is still intact, the tree lives, despite the loss of its inner heartwood.

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