Physiological Effects of Natural and Artificial Defoliation on the Growth of Young Crops of Lodgepole Pine

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Abstract
Field experiments involving naturally occurring population levels of larval European pine sawfly Neodiprion sertifer (Geoff. ) and artificial defoliation in both field and glasshouse experiments were used to investigate physiological effects of defoliation on lodgepole pine. Reductions in total projected leaf area, annual height and volume increments of 19, 33 and 32 per cent, respectively, were recorded on trees where larvae had consumed all mature foliage. Leader growth was up to 48 per cent less on defoliated trees after two years reflecting a delayed growth impact. Similar effects were found on trees which had been defoliated by hand in a manner resembling sawfly feeding. Artificial defoliation of transplants also showed that this type of damage can have serious consequences on below-ground growth, particularly of fine roots. Root:shoot ratios were found to be 0.64 in undamaged plants and 1. 05 in defoliated plants. A high concentration (1300 ppm) of the insecticide fenitrothion, used to maintain control treatments in the field, was found to have no significant effects on the major growth parameters being assessed.