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

Field experiments involving naturally occurring population levelsof larval European pine sawfly Neodiprion sertifer (Geoff. )and artificial defoliation in both field and glasshouse experimentswere used to investigate physiological effects of defoliationon 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 consumedall mature foliage. Leader growth was up to 48 per cent lesson defoliated trees after two years reflecting a delayed growthimpact. Similar effects were found on trees which had been defoliatedby hand in a manner resembling sawfly feeding. Artificial defoliationof transplants also showed that this type of damage can haveserious consequences on below-ground growth, particularly offine roots. Root:shoot ratios were found to be 0.64 in undamagedplants and 1. 05 in defoliated plants. A high concentration(1300 ppm) of the insecticide fenitrothion, used to maintaincontrol treatments in the field, was found to have no significanteffects on the major growth parameters being assessed.