Effects of artificial shade on early performance of white spruce seedlings planted on clearcuts

摘要

Chlorophyll fluorescence, chlorophyll content, growth, and mortality of white spruce (Picea glauca [Moench] Voss) seedlings were monitored for 2 years after planting under three scenarios of artificial shade: no-shade (control), shade in summer only, and shade all year. The shade frames allowed 50–60% light transmission, with limited effects on air temperature, relative humidity, soil temperature, and soil moisture around seedlings. Based on fluorescence yield and chlorophyll content measurements, summer-only shade reduced photoinhibition and photooxidation, especially in summer and fall; extending to all year shading did not further reduce either photoinhibition or photooxidation. Shade tended to reduce seedling diameter and mortality, but after 2 years the cumulative effect on mortality was not statistically significant. Study results support the establishment of white spruce seedlings under partial forest canopy, especially on sites with harsh environmental conditions.