Growth Changes in 20-year-old Sitka Spruce Picea sitchensis After Attack by the Green Spruce Aphid Elatobium abietinum

1993

10 Lit. Ang.

Unselbständiges Werk

12144

200101975

Following a severe attack by Elatobium abietinum (Walker) in 1979-80, annual observations were made for 5 years on 320 pole-size Sitka spruce in a nitrogen and phosphate experiment laid out on oligotrophic blanket bog. Leader length was reduced by 25.5 per cent in 1980-81 compared with the 3 previous years. This reduction was highly correlated with defoliation, being 39,4 per cent for trees that lost all 1977-79 needles and 8.4 per cent in trees that lost no needles. There were strong interactions with fertilizer treatment. Defoliated trees continued to grow less well during the 5 years of observations and were more likely to go into growth check. Early flushing trees suffered significantly less growth reduction following defoliation. The same trees consistently broke bud early over 4 years of observations. Early bud burst was not correlated with height, girth or defoliation. No reattack by aphids was observed in the experiment until 1985-86 and in this minor infestation the trees previously colonized were found to be significantly more likely to be recolonized. A novel measuring-rod for tree height is described.