Proposed mechanisms of initial injury-causing apical dieback in red spruce at high elevation in eastern North America

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Abstract
Observations of apical dieback and tree declines of high-elevation red spruce (Picearubens Sarg.) were made from hundreds of random plant samples that exhibited recent injury. This recent and predominant injury related to red spruce decline was not a result of secondary injury to other tissues. Samples of recently injured branches were collected on Whiteface Mountain, NY, Mount Mitchell, NC, and Clingman's Dome, TN. Visible recent injury at Whiteface Mt. was much more intensive and extensive than at Mt. Mitchell. Moreover, few symptoms were present at Clingman's Dome. In the normal growth pattern of red spruce, three buds elongate from each twig terminus during spring. These buds elongate the next growing season and three new buds will form on each of the three elongated twigs. During late winter and early spring of 1985, recent tissue injury occurred on twigs that elongated during the spring of 1984. This recent twig injury and necrosis occurred on 1st-year twigs that retained injured or necrotic needles. No bud enlargement occurred on affected 1st-year twigs. Injury to only one or two of the 1st-year twigs on a branch was the most common injury symptom observed, while injury to all three 1st-year twigs on a branch was rare. On a branch with one or two injured 1st-year twigs, adjacent 1st-year twigs on the same branch had no visible injury. In addition to having all needles of affected twigs exhibiting the same degree of injury simultaneously, injury and necrosis of all portions of affected needles occurred simultaneously. In this manner, affected tissues (twigs and needles) on a branch exhibited a uniform appearance of injury. There was no chlorotic mottle or bands of living and necrotic tissues that has been described for conifer needles exposed to gaseous air pollutants. These results are discussed in relation to possible causes.

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