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A Total Forest Management Plan and Wildland Management Decision Support System
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Frost

See Temperature and Time where degree days are discussed

A table is under development for the growing season or period between frosts for the central point of the area.

Number of Days (with examples) are listed for:
50% - first frost date - 125
50% - last frost date - 277
mean frost free period - 153
10% - first frost date - 143
10% - last frost date - 266
90% - frost free period -122.

FFP = Frost-Free Period

In Ohio (Bringi et al. 1981) there are two GIS zones of frost free periods one with less than 150 days, the other a small area with more than 180 days.

Growing season days are often the count of days between the last frost of winter and first frost of autumn. Degree days may be more appropriate. The growing season concept is useful in agriculture. Nevertheless it is difficult to define and various approaches have been used. In some cases it is the average period between last and first frosts but that has a very wide variance. Most plants native to the eastern US can continue activity at air temperatures below thrity-two-degree F. One sedge initiates root growth at first frost. Definition of growing season should not be based on plant growth alone and should include all biological activities. For instance, nutrient accumulation or release in wetlands can occur in any season depending on local conditions. (This may be an interesting but costly-to implement statement.)

There are few discussions of step-functions in ecology (such as sharp drops in production, etc.) following frost, freezing/thawing, or loss of a vital nutrient, or input of salt by a storm etc.). It seems important to describe several ways to describe "growing period" since it varies for different plants and communities. They all will be similar and may be well within the realm called natural variability. Several types can be described with different brief periods before and after some occurrence of minimum ambient temperature (whether frost is observed or not).

Sream temperature must have parallels with ambient temperatures and associated ecological function shut-downs and start-ups. See literature on "thermal ecology. "

Frost occurs on foliage at various locations in a forest at different temperatures, wind, different exposures to the sky, the ground, and other foliage. Tree spacing, size, shape, foliage density, orientation of the foliage, albedo of the foliage. Frost damage can be considered to result from the fraction of blossoms which are at or below some critical temperature. Frost can kill the terminal bugs of twigs in early autumn, thus altering the shape of plants.

Frost pockets result from cold aid drainage that produce valley temperature inversions. Topographic depressions fill with cold air. Small forest openings may also fill with such air and be frostier than large openings where the air is swept away.

Pockets may produce plant community differences where all other factors seem to be the same.

Cochran (1984) showed that ponderosa pine (Pinus ponderosa Dougl.) survived poorly or not at all in frost pockets as compared to lodgepole pines (Pinus contorta Dougl.) planted in the same areas. Damage from radiation frost resulted in reduced height growth.

Frost patterns need to be studied using GPS. There is much confusion about what is a frost pocket and how they can be located or described for computer mapping. Patterns with GPS should allow them to be mapped readily and avoided for grape vineyards and gardens and for excluding livestock to avoid energy drains on them. Frost areas might be counted as negative influences on wild animal populations of an area, thus possibly explaining population density differences between areas. They may be modified (winds, habitat density, etc.) to reduce winter area suitability indices. They can be avoided, if well known, for habitat improvement efforts.

References

Welles, J.M., J.M. Norman, and J.D. Martsolf 1979. An orchard foliage temperature model. Florida J. Amer. Soc. Horticulture 104(5): 602-610

Bringi, S.K., T.A. Seliga, and L. S. Dochinger. 1981. A method of selecting forest sites for air pollution study, USDA Forest Sevice., NE Forest Exp. Sta, Broomall, PA, Research Paper NE-472

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Last revision July 5, 2004.