Some observations on the spectral distribution characteristics of short‐wave radiation within Pinus radiata D. Don canopies

Abstract

Measurements of the photosynthetic photon flux density (400-700 nni) and of the spectral distribution of photon flux density across the 370-800 nm waveband, were made under both clear and overcast sky conditions above and at various positions within two Pinus radiata canopies of diflerent stocking but similar leaf area indices. The spectra obtained for the daylight conditions (i.e. above forest canopy) were generally similar to those published previously. The spectra for shadelight within the forest canopy showed no blue peak which was characteristic of previously reported measurements which were restricted to the difluse radiation component. There was almost neutral absorption within the 400-700 nm waveband, and typical lower attenuation in the 700-800 nm waveband. The blue: red ratio was largely unchanged by either canopy type or sky conditions and varied between 0.57 and 0.81. The red: far-red ratio in shadelight was between 0.22 and 0.41 under clear sky and between 0.68 and 0.95 under overcast sky conditions. Values for daylight were between 1.16-1.22. Calculated phytochrome photoequilibrium values in shadelight were approximately 0.35 under clear sky and 0.46 under overcast sky conditions. In each case there appeared to be no dilTerences between the two canopies with respect to these minimum values.A.Vr-u' ()/v/.

Transmissivity of solar radiation within a <i>Picea sitchensis</i> stand under various sky conditions

“…It is also shown, quite independently, by the extent to which the diffuse irradiation is relatively higher at the forest floor and by the distribution of ground-level data between transmission classes (data not shown here). The same phenomenon was shown by Morgan et al (1985) for pine canopies and by Leuchner et al (2005), Navratil et al (2007) and Urban et al (2007Urban et al ( , 2012 for Norway spruce.…”

“…This aspect of light quality has received much attention. The decline in the red : far-red ratio has long been known and has been linked in numerous studies to aspects of photomorphogenesis (see reviews by Federer and Tanner, 1966;Smith, 1982;Woodward, 1983;Morgan et al, 1985;Endler, 1993). In the present study, we have found that the red : far-red ratio in the canopy is much lower under clear skies (Hertel et al, 2011), indicating a lower photomorphogenical "light quality" (sensu Smith, 1982) than under diffuse conditions.…”

Predicting and managing light in the understory of boreal forests

“…On sunny days, this decline is steeper than on cloudy days (Endler 1993;Messier and Puttonen 1995). This has been noted for hardwood stands (Messier and Bellefleur 1988), Scots pine (Messier and Puttonen 1995), radiata pine (Morgan et al 1985), and mixed conifers (Federer and Tanner 1966). On sunny days, R:FR may vary from 0.1 under dense eastern hardwoods (Messier and Bellefleur 1988) to 1.0 in large gaps (Turnbull and Yates 1993;Lei et al 1998) and from 0.4 under dense conifer canopies to 1.0 in large gaps (Messier et al 1989;Messier and Puttonen 1995;Ritchie 1997;Mailly and Kimmins 1997).…”

Shade responses of five grasses native to southwestern U.S. Pinus ponderosa forests

“…The target values of photosynthetic photon flux density (PPFD; 400-700 nm) and R/FR of the shade treatments were based on a literature review of light quantity and quality under conifer canopies (e.g., Morgan et al 1985;Ross et al 1986;Messier et al 1989). Full sun is characterized by a R/FR of 1.15 (Smith 1982), while dense conifer stands transmit only 5-10% of PPFD and have an average R/FR of 0.40.…”