Effect of pruning severity and timing of treatment on epicormic sprout development in giant sequoia

Abstract

Summary Giant sequoia ( Sequoiadendron giganteum (Lindl.) Buchh.) trees were pruned monthly over a 12-month period to assess the effects of timing of pruning operations on epicormic sprout development. Trees were pruned to three pruning heights in each month. Periodic counts of total sprouts and measurement of the length of the longest sprout were used to assess sprout development following pruning. Sprouting was initially delayed following pruning during growing season months as compared with non-growing season months. Six years after study initiation, greater numbers of sprouts and larger maximum branch lengths were found from pruning outside the May through September growing season. These differences were most pronounced in the fi rst years following treatment but differences diminished markedly after 6 years. However, a logistic model to predict the probability of sprouting indicates that pruning severity was a much more signifi cant explanatory variable than season of pruning. Seasonal differences in epicormic sprout development may be temporary and are of less importance in affecting sprout development than pruning severity. Epicormic sprouts also occurred with greater frequency on the south or exposed side of pruned tree boles.