A simple and efficient method to estimate microsite light availability under a forest canopy

1996 ◽  
Vol 26 (1) ◽  
pp. 151-154 ◽  
Author(s):  
Sylvain Parent ◽  
Christian Messier
Keyword(s):  
Efficient Method ◽  
Forest Canopy ◽  
Light Availability ◽  
Photosynthetic Photon Flux Density ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Broadleaf Forest ◽  
The Mean ◽  
Sky Conditions ◽  
Overcast Sky

This study presents a new, simple, and efficient method for estimating microsite light availability in the understory of a forest. The percentage of above-canopy photosynthetic photon flux density (%PPFD) transmitted above 16 microsites in the understory of a mixed conifer–broadleaf forest was measured every minute between 07:00 and 19:00 for both a completely overcast and a cloudless day. Instantaneous measures of %PPFD were also taken at different times on 3 overcast days. The instantaneous measures of %PPFD were strongly and directly related (P < 0.001) among themselves and with mean daily %PPFD values. These results demonstrate the usefulness of using an instantaneous measure of %PPFD taken under overcast sky conditions for estimating the mean daily %PPFD at any microsite under a forest canopy.

Spatial and temporal variation in the Bight environment of developing Scots pine stands: the basis for a quick and efficient method of characterizing Bight

1995 ◽  
Vol 25 (2) ◽  
pp. 343-354 ◽  
Author(s):  
Christian Messier ◽  
Pasi Puttonen
Keyword(s):  
Scots Pine ◽  
Efficient Method ◽  
Spatial And Temporal Variation ◽  
Photon Flux ◽  
Photon Flux Density ◽  
The Mean ◽  
Pine Stands ◽  
Sky Conditions ◽  
Overcast Sky ◽  
Scots Pine Stands

Spatial and temporal variations in photosynthetic photon flux density (PPFD) at 1 m above the forest floor were measured under and between dominant pines and in 21- to 52-m2 gaps under developing Scots pine (Pinussylvestris L.) stands in southern Finland. For each stand, PPFD data were collected continuously every 10-s and then averaged for every 5-min period during 4-6 days under completely clear and overcast sky conditions. Measurements were made during 102 consecutive days within two different areas in each of 10 different Scots pine stands ranging in age from 7 to 105 years. Mean daily percent PPFD in the understory varied from 7.5% in the 20-year-old stands to 38% in the 7-year-old stands, and did not differ significantly between completely clear and overcast sky conditions. Mean daily percent PPFD did not vary significantly between the different sensor locations within closed pine stands, indicating that at high latitudes mean daily percent PPFD does not vary much spatially under closed Scots pine forests. Measurements of PPFD made at different periods during the day under clear sky conditions, one of the main approaches used in the literature, were not representative of the whole-day conditions. Two different results suggest that PPFD can be better characterized under completely overcast sky conditions. First, the 5-min percent PPFD in the understory was fairly constant between 06:00 and 20:00 for all stand ages under completely overcast sky conditions. Second, there was an almost perfect 1:1 relationship of the mean daily percent PPFD measured at 40 different locations in the 10 stands between clear and overcast sky conditions. These two results suggest that an instantaneous measure of percent PPFD obtained under completely overcast sky conditions is representative of the mean daily percent PPFD for both sky conditions. These results provide the basis for a quick and efficient method of estimating the mean daily percent PPFD in the understory of closed forests.

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

1989 ◽  
Vol 19 (11) ◽  
pp. 1470-1477 ◽  
Author(s):  
Christian Messier ◽  
Terry W. Honer ◽  
James P. Kimmins
Keyword(s):  
Forest Floor ◽  
Photosynthetic Photon Flux Density ◽  
Western Hemlock ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Photosynthetic Photon Flux ◽  
Light Requirement ◽  
Red Cedar ◽  
Sky Conditions ◽  
Overcast Sky

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 light requirement for salal survival is between 3.9 and 11.1 μmol•m−2•s−1 (1.2 to 3.3% of global PPFD measured in an adjacent clearing) and 4.5 and 27.2 μmol•m−2•s−1 (0.3 to 1.8% of global PPFD measured in the clearing) under overcast and clear sky conditions, respectively. The global PPFD and red:far-red ratio measured 30 cm above the forest floor (beneath the salal) did not vary widely among the three stands. At this level, global PPFD values were very low, ranging from 0.15 to 0.35% and 0.58 to 0.75% of the global PPFD measured in the clearing under clear and overcast sky conditions, respectively. Red:far-red ratios at the forest floor level varied from 0.13 to 0.25 and 0.40 to 0.58 under clear and overcast sky conditions, respectively. The silvicultural implications of the results are discussed.

scholarly journals Estimation of Global and Diffuse Photosynthetic Photon Flux Density under Various Sky Conditions Using Ground-Based Whole-Sky Images

2019 ◽  
Vol 11 (8) ◽  
pp. 932
Author(s):  
Megumi Yamashita ◽  
Mitsunori Yoshimura
Keyword(s):  
Flux Density ◽  
Photosynthetic Photon Flux Density ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Diffuse Component ◽  
Photosynthetic Photon Flux ◽  
Physiological Processes ◽  
Sky Conditions ◽  
Mean Square Errors ◽  
Relative Root

A knowledge of photosynthetic photon flux density (PPFD: μmol m−2 s−1) is crucial for understanding plant physiological processes in photosynthesis. The diffuse component of the global PPFD on a short timescale is required for the accurate modeling of photosynthesis. However, because the PPFD is difficult to determine, it is generally estimated from incident solar radiation (SR: W m−2), which is routinely observed worldwide. To estimate the PPFD from the SR, photosynthetically active radiation (PAR: W m−2) is separated from the SR using the PAR fraction (PF; PAR/SR: unitless), and the PAR is then converted into the PPFD using the quanta-to-energy ratio (Q/E: μmol J−1). In this procedure, PF and Q/E are considered constant values; however, it was reported recently that PF and Q/E vary under different sky conditions. Moreover, the diffuse ratio (DR) is needed to distinguish the diffuse component in the global PAR, and it is known that the DR varies depending on sky conditions. Ground-based whole-sky images can be used for sky-condition monitoring, instead of human-eye interpretation. This study developed a methodology for estimating the global and diffuse PPFD using whole-sky images. Sky-condition factors were derived through whole-sky image processing, and the effects of these factors on the PF, the Q/E of global and diffuse PAR, and the DR were examined. We estimated the global and diffuse PPFD with instantaneous values using the sky-condition factors under various sky conditions, based on which the detailed effects of the sky-condition factors on PF, Q/E, and DR were clarified. The results of the PPFD estimations had small bias errors of approximately +0.3% and +3.8% and relative root mean square errors of approximately 27% and 20% for the global and diffuse PPFD, respectively.

scholarly journals A Consideration for the Light Environmental Modeling under Tropical Rainforest Canopies

2014 ◽  
Vol XL-7 ◽  
pp. 217-220 ◽  
Author(s):  
M. Yoshimura ◽  
M. Yamashita
Keyword(s):  
Solar Radiation ◽  
Tropical Rainforest ◽  
Light Condition ◽  
Photosynthetic Photon Flux Density ◽  
Environmental Modeling ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Forest Region ◽  
Direct Light ◽  
Sky Conditions

Photosynthetic Active Radiation (PAR) is the most important light source for plant photosynthesis. It is known that most of PAR from solar radiation is well absorbed by the surface. The canopy is the surface in forest region, consists an aboveground portion of plant community and formed by plant crowns. On the other hand, incident solar radiation is fluctuating at all times because of fluctuating sky conditions. Therefore, qualitative light environmental measurements in forest are recommended to execute under stable cloudy condition. In fact, it is quite a few opportunities to do under this sky condition. It means that the diffuse light condition without the direct light is only suitable for this measurement. <br><br> In this study, we challenged the characterization the forest light environment as its representativeness under no consideration of sky conditions through analysis huge quantities of instantaneous data which obtained under the different sky conditions. All examined data were obtained under the different sky conditions at the tropical rainforest canopy as one of the typical fluctuating sky conditions regions. An incident PAR is transmitted and scattered by different forest layers at different heights. Various PAR data were measured with quantum units as Photosynthetic Photon Flux Density (PPFD) at different forest heights by the quantum sensors. By comparing PPFDs at different heights with an incident PPFD, relative PPFDs were calculated, which indicate the degree of PPFD decrease from the canopy top to lower levels. As the results of these considerations, daily averaging is confirmed to be cancelled sky fluctuating influences.

Effets d'un gradient de lumière sur la croissance en hauteur et la morphologie de la cime du sapin baumier régénéré naturellement

1995 ◽  
Vol 25 (6) ◽  
pp. 878-885 ◽  
Author(s):  
Sylvain Parent ◽  
Christian Messier
Keyword(s):  
Photosynthetic Photon Flux Density ◽  
Height Growth ◽  
Balsam Fir ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Light Gradient ◽  
Cone Type ◽  
Crown Shape ◽  
Crown Morphology ◽  
The Mean

This study characterized the height growth and crown form of 14-year-old balsam fir regenerated naturally under a light gradient varying from 3 to 83% of photosynthetic photon flux density (PPFD). After 14 years, total height growth was correlated with percent PPFD (R2 = 0.766; p < 0.001). From 3 to 25% of PPFD, balsam firs went from a suppressed stage with an umbrella type crown shape to a full grown stage with a cone type crown shape. This morphological change was caused by a greater increase in leader length compared to the mean nodal branches length. The number of nodal and internodal branches increased with PPFD. Balsam fir crown morphology showed a strong plasticity with a light gradient going from 3 to 83% of PPFD.

scholarly journals Photosynthetic Active Radiation, Solar Irradiance and the CIE Standard Sky Classification

2020 ◽  
Vol 10 (22) ◽  
pp. 8007
Author(s):  
Ana García-Rodríguez ◽  
Sol García-Rodríguez ◽  
Montserrat Díez-Mediavilla ◽  
Cristina Alonso-Tristán
Keyword(s):  
Plant Growth ◽  
Flux Density ◽  
Photosynthetic Photon Flux Density ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Photosynthetic Photon Flux ◽  
Clear Sky ◽  
Experimental Campaign ◽  
Sky Type ◽  
Overcast Sky

Plant growth is directly related to levels of photosynthetic photon flux density, Qp. The improvement of plant-growth models therefore requires accurate estimations of the Qp parameter that is often indirectly calculated on the basis of its relationship with solar irradiation, RS, due to the scarcity of ground measurements of photosynthetic photon flux density. In this experimental campaign in Burgos, Spain, between April 2019 and January 2020, an average value of the Qp/Rs ratio is determined on the basis of measurements at ten-minute intervals. The most influential factor in the Qp/Rs ratio, over and above any daily or seasonal pattern, is the existence of overcast sky conditions. The CIE standard sky classification can be used to establish an unequivocal characterization of the cloudiness conditions of homogeneous skies. In this study, the relation between the CIE standard sky type and Qp/Rs is investigated. Its conclusions were that the Qp/Rs values, the average of which was 1.93±0.15 μmol·J−1, presented statistically significant differences for each CIE standard sky type. The overcast sky types presented the highest values of the ratio, while the clear sky categories presented the lowest and most dispersed values. During the experimental campaign, only two exceptions were noted for covered and partial covered sky-type categories, respectively, sky types 5 and 9. Their values were closer to those of categories classified as clear sky according to the CIE standard. Both categories presented high uniformity in terms of illumination.

Comparing indices of understory light availability between hemlock and hardwood forest patches

2009 ◽  
Vol 39 (10) ◽  
pp. 1949-1957 ◽  
Author(s):  
Michael F. Tobin ◽  
Peter B. Reich
Keyword(s):  
Sugar Maple ◽  
Forest Canopy ◽  
Light Availability ◽  
Canopy Structure ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Canopy Openness ◽  
Forest Patches ◽  
Two Indices

We evaluated whether two indices of light availability resolved differences among microsites within deeply shaded understories (<12% of above-canopy photosynthetic photon flux density (PPFD)) and also whether marked differences in forest canopy structure affected how the two indices related to direct measures of incident photosynthetically active radiation (PAR). Incident PAR was measured with gallium–arsenide–phosphide photodiodes at numerous points in two adjacent forest patches in Michigan, USA: one dominated by the evergreen conifer eastern hemlock ( Tsuga canadensis (L.) Carrière), and the other by the deciduous hardwood sugar maple ( Acer saccharum Marsh.). The two indices tested were canopy openness, measured with the LI-COR LAI-2000 plant canopy analyzer, and the percentage of above-canopy PPFD measured in the understory during overcast conditions (%PPFD). Canopy openness and %PPFD did not effectively predict the long-term mean of daily PPFD. However, both indices reliably predicted the long-term mean of daily median PPFD, an alternative standard of directly measured incident PAR that reduces the relative contribution of sunflecks. The relationships of both indices with mean daily median PPFD differed between hemlock and hardwood patches. Hence, the effect of canopy structure should be considered when using these indices to draw conclusions about differences in light availability between forest patches, particularly when narrow ranges of light availability in deep shade are important.

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