Photosynthetic photon flux density, red:far-red ratio, and minimum light requirement for survival of Gaultheriashallon in western red cedar–western hemlock stands in coastal British Columbia

Measurements of photosynthetic photon flux density (PPFD; global, diffuse, and direct: 400–700 nm) and red:far-red ratio (660:730 nm) were made above and below an understory of salal (Gaultheriashallon Pursh) within three western red cedar (Thujaplicata Donn)–western hemlock (Tsugaheterophylla (Raf.) Sarg.) stands on the northern end of Vancouver Island, British Columbia. These stands were chosen to represent a wide range of canopy closure and understory salal cover. The measurements were repeated under both clear and overcast sky conditions. Within each stand, the percent cover, height, number of stems per hectare, and leaf morphology of the salal were measured. As expected, there was a decrease in both the salal cover and in the global PPFD and red:far-red ratio measured directly above salal as the percent tree cover increased. Salal leaf thickness and specific leaf weight decreased, whereas its leaf area increased, as global PPFD and red:far-red ratio decreased. The results indicate that the minimum li...