Effect of a Late Spring Frost upon Forest Vegetation in the Wasatch Mountains of Utah

Abstract

The dearth of concrete information on the relative frost hardiness of North American forest trees, as voiced by Phillips (4), remains practically unchanged twelve years after the publication of his paper. Authentic records of frost injury to various species would furnish an excellent scientific basis for determining the relative hardiness of different species in a given locality and of the same species on different sites. In certain cases the relative frost hardiness may prove to be the determining factor in forest succession. Zon (6) has shown that late spring frosts are more dangerous to vegetation than those of early fall. They frequently kill the tender succulent young growth when the air temperature is 2 to 40 F. above the freezing point; and temperatures of as much as 4 to 70 F. above the freezing point, while trees are in blossom, are reported to cause poor seed years. Studies of the biophysics and biochemistry of f rost action (3) have shown that true frost injury, accompanied by ice formation within the tissues, results in plasmolysis, desiccation, precipitation of the proteins, the accumulation of sugars, and consequently a greater density of the cell sap as determined by the depression of the freezing point, and causes changes in the hydrogen-ion and salt concentrations of the juices of injured parts. The premature fall of the leaves is believed by Zon (6) to result in certain chemical changes in the xylem. With the sudden fall of the leaves, mineral salts are carried to the soil which otherwise would be stored in the wood of the tree trunk. Because of the dearth of published information relative to frost injury to most of the species of the forest vegetation of the Wasatch Mountains notes were compiled on an especially severe frost which occurred the last of May, i919, throughout the Intermountain region. Following a period of approximately four weeks of exceptionally warm weather a cold wave, accompanied by rain, hail and snow, resulted in very great damage in the mountainous portions of Utah at elevations above 5,ooo feet. Temperatures were unusually high during practically the entire month, which was the warmest May for i8 years (i). The mean departure from the normal for 43 stations in Utah having records for IO years or more, was 4.50 F. above the mean temperature. The highest temperatures in most cases oc47