Transcript HEARTWOOD
Wood with no living cells. Hoadley: “The central core of wood in mature stems that was at one time sapwood but no longer conducts sap or has living cells. In most species, infiltration of extractives imparts a perceptibly darker color to this wood.” NOT ALL HEARTWOOD HAS A DARKER COLOR THAN THE SAPWOOD Some species have light-colored heartwood • Spruce (Picea) • Aspen (Populus) The number of sapwood rings varies with species. Catalpa Walnut Oaks S. Yellow Pine Tupelo 1-2 10 - 15 10 - 15 15 - 25 100+ Ponderosa Pine 150 - 200 Most ring porous species have 10 or fewer rings of sapwood Changes Sapwood to Heartwood • Nuclei in parenchyma cells degenerate • Decrease in nitrogenous materials • Moisture content changes • Decrease in starch • Accumulation of extractives These changes can be “abrupt” or gradual. Death of the Parenchyma Cell • Spatial control -- Distance from the cambium & secondary phloem • Temporal Control -- Age of the parenchyma cell (programmed to die after a certain age). Which factor is most important varies from species to species, and can be a combination of the two. EXTRACTIVES • Organic compounds (e.g, gums, tannins, oils) manufactured by the parenchyma cells. • Extractives can be removed (extracted) by water, alcohol, or other solvents EXTRACTIVES • Not “structural elements” of cell walls • May or may not be colored • May be in the cell walls or in cell lumens Heartwood Properties If extractives go into the cell wall, If a lot of extractives deposited in cell wall, Then may be some increase in the compressive strength of the heartwood relative to “like-aged” sapwood. Effects of Extractives Some, not all extractives are toxic to decay organisms or insects. Heartwood then will be more durable, last longer than sapwood. This may be heartwood gets considered “stronger” than sapwood -in some species it lasts longer. Extractive Effects If extractives coat cell wall and pit membranes, Then will reduce permeability. Sapwood Intervessel Pit Heartwood Intervessel Pits Undesirable Effects of Extractives • Increased chemical consumption for pulping and bleaching • Tannins can corrode metals • Can interfere with setting of paints, glues, and varnishes • Can migrate during drying cause discoloration. Desirable Effects of Extractives •Color •Durability •Dimensional Stability