The impact of green spruce aphid, Elatobium abietinum (Walker), on the growth of young Sitka spruce in Hafren forest, Wales: delayed effects on needle size limit wood production

• Published in: Forest ecology and management Vol. 157; no. 1; pp. 267 - 283
• Main Authors: Straw, N.A, Fielding, N.J, Green, G, Price, J
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-03-2002; Elsevier
• Subjects: Aphididae; Biological and medical sciences; Defoliation; Elatobium abietinum; Fundamental and applied biological sciences. Psychology; Growth loss; Increment; Needle size; Phytopathology. Animal pests. Plant and forest protection; Picea sitchensis; Protozoa. Invertebrates; Records, symptoms, damages, economic importance, population surveys; United Kingdom; Europe; British Isles, Wales; Elatobium abietinum; Needle size; Defoliation; Growth loss; Increment; Picea sitchensis; Forest stand; Wood; Growth; Insecta; Needle (conifer); Forest production; Plant leaf; Dimension; Pest; Animal plant relation; Arthropoda; Softwood forest tree; Gymnospermae; Coniferales; Spermatophyta; Invertebrata; Damage; Infestation; Photosynthesis
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/S0378-1127(00)00656-3

Defoliation of 3-year-old Sitka spruce (
Picea sitchensis (Bong.) Carr.) by green spruce aphid (
Elatobium abietinum (Walker)), in a field experiment in Hafren forest, Wales, resulted in significantly shorter shoots being produced in the upper canopy in 1994, the year of infestation, and in 1995. The dry weight (DW) of individual needles produced by defoliated trees was also reduced, by up to 19%, but whereas in 1994 the DW of the new needles was reduced only on the most heavily infested branches, in 1995 needle DW decreased throughout the canopy. In 1996, needles produced by previously defoliated trees were 10.4% heavier, on average, than needles produced by undefoliated trees. The total numbers of new needles produced by defoliated and undefoliated trees in 1994 and 1995 were similar, but defoliated trees produced 10% fewer needles in 1996. Consequently, and as a result of the changes in individual needle DW, the total DW of current-year needles on defoliated trees was 11% less than that on undefoliated trees in 1994, 20% less in 1995, and about the same in 1996. Stem volume increment of individual trees was related to the total DW of current-year needles (
r
2=0.43–0.52,
p<0.001), and reductions in increment of 6% in 1994 and 24% in 1995 following
E. abietinum infestation could be attributed to the reductions in total and individual needle DW. These results are in accordance with the known dependency of cambial growth in young conifers on the photosynthetic production of the current foliage, and the changes in individual needle DW provide an explanation, therefore, for the delayed effect of
E. abietinum on diameter and volume increment of the experimental trees. Annual height growth, in contrast, was weakly related to the total DW of current-year needles in 1994 and 1995 (
r
2=0.16–0.26), and showed no relationship in 1996, indicating further that reductions in leader length following infestation, which were not correlated with reductions in stem diameter and volume increment, were caused by a different mechanism. Mechanisms likely to have caused the changes in individual needle DW are discussed.