Frost Injury to Aspen in Colorado

Aspen, Populus tremuloides, was seriously injured in Colorado by early June frost, 1947. Most buds had opened. Injury varied from no killing to over 90% of new growth being injured or killed. Recovery varied with degree of injury. Leaves with frosted margins survived and sometimes grew to several times normal size but remained much deformed in shape, When several leaves were killed but twig survived, later formed leaves were several times normal size. Where both twig and leaves were killed, entire twig including several year's growth was dehisced. Development of adventitious or resting buds was slow and often failed to produce mature leaves. Extent of killing was correlated with color of tree bark. Yellowish-white barked trees averaged 15% killing; greyish-white barked trees aver-aged 80% killing. Latter were also injured by early September frost re-sulting in unusual type of leaf-fall. Correlation existed even when two trees were side by side.