Introduction

The seedling debarking weevil (Hylobuis congener) has been found to cause damage and mortality to conifer seedlings planted in newly harvested sites in Nova Scotia and Prince Edward Island. Reduced growth and mortality of the planted seedlings negatively impacts upon the objectives and criteria of sustainable forest management.

Recent studies in Europe have revealed that the damage from the pine weevil (Hylobius abietis) can be reduced by conducting partial harvests and leaving residual overstory trees to shade newly planted seedlings. The shade prevents the ground surface temperatures from getting as high as they would with total overstory removal, which in turn reduces the development and feeding activity of the pine weevil. The reduction in damage is thought to be directly related not to weevil numbers but to an environmental modification which influences the insect's behavior.

Objective

Since morphology, physiology, and feeding habits of the seedling debarking weevil and the pine weevil are similar, the objective of this study was to test and evaluate the influence of harvest block size and residual overstory shade on the occurrence and frequency of damage and mortality of planted black spruce (Picea marianna) seedlings.

Methodology

Plots were established in which spruce seedlings were planted in 2 by 2 meter spacings. The plots were replicated twice in three cutover sizes and under three light conditions. The occurrence and frequency of seedling damage and mortality were measured and will be related to:

• harvest block size and amount of edge;
  
• the amount of slash, moss, and ground cover;
  
• soil texture and drainage; and
  
• crown closure and the amount of light reaching the ground.
  
• Results and Conclusions

As with the European studies, the amount of seedling damage and mortality from the seedling debarking weevil was demonstrated to intensify with increasing harvest block size. However, for the first time it has been shown that damage and mortality can be reduced and controlled by regulating the residual overstory and thus the amount of light that reaches the forest floor.

Management Implications

The planting of shade tolerant softwoods, such as red (Picea rubens) and black spruce, under residual forest canopies left after partial harvests or commercial thinnings may become an effective silvicultural tool in reducing the damage and mortality caused by the seedling debarking weevil.

More information is required to determine the amount of light that should be reaching the forest floor to adequately control the seedling debarking weevil and to ensure that the planted seedlings maintain acceptable growth rates.