Heidmann, L. J.1976. Frost heaving of tree seedlings: A literature review of causes and possible control.USDA For. Serv. Gen. Tech. Rep. 10 p. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo. Frost heaving of tree seedlings is more serious among seedlings less than 1 year old than among transplanted stock. It appears to be a surface soil phenomenon, and occurs because of a segregation of soil water which freezes into layers or lenses of ice. Lens formation causes an uplift of the surface soil and the tree seedling. Upon thawing, the tree remains in an extruded position on the soil surface while the soil recedes to approximately its original level. Segregation of the soil water occurs within the total matrix because of supercooling of the water in smaller soil pores and the water adsorbed on soil particles. The difference in freezing points provides the energy necessary to draw water to the ice lens and to lift the surface. Segregation of soil water is related to soil permeability and negative pressure on the water. A silty soil is more likely to heave because the right combination of permeability and tension can be developed. Heaving in a clay soil is determined to a great extent by the type of clay and the nature of the ions adsorbed by the clay particles. Heaving can be controlled by lowering the freezing point of the soil water, by restricting the water flow to the freezing front, or by cementing the soil particles together. Chemicals such as calcium chloride have been successful in reducing frost heaving by lowering the freezing point of the soil water.Dispersing agents, mainly sodium compounds, reduce heaving by plugging the soil pores, thus limiting water movement to the freezing front and subsequent growth of ice lenses. Cementing agents make the soil less frost susceptible by reducing the proportion of finer soil particles (clay and silt).

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1976. Controlling frost heaving of ponderosa pine seedlings in Arizona. USDA For. Serv. Res. Pap. RM-172, 12 p. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo. 80521. Frost heaving is a three-step process: (1) The surface layer of soil freezes and grips the seedling stem tightly. (2) Ice lenses form below the surface, lifting the seedling and frozen soil. (3) When the soil thaws, it settles back loosely to its original position, leaving the seedling on the surface. Plowing to reduce soil bulk density and adding gypsum to lower the freezing point of soil water will reduce frost heaving.

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