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

Abstract

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.

Juvenile growth and crown morphological plasticity of eastern white pines (Pinus strobus L.) planted along a natural light gradient: Results after six years

“…Light measurements were taken under completely overcast sky conditions following the method proposed by Messier and Puttonen (1995) and Parent and Messier (1996). These studies have shown that instantaneous measurements obtained under completely overcast sky conditions are a good estimate of the mean daily percent PPFD under both overcast and clear sky conditions.…”

Effets d'un gradient de lumière et de compétition intraspécifique sur la croissance et la morphologie de la cime du sapin baumier (Abies Balsamea (L.) Mill.) /

“…Cette proportion représentait la moyenne journalière de lumière incidente reçue à l'apex de l'arbre étudié (Messier et Puttonen 1995a).…”

Effects of overstory paper birch (Betula Papyrifera March) on physiology, growth, and biomass responses of under-planted conifer seedlings

“…Single measurements of light taken at midday in midsummer have been used widely to characterize light environments (Messier and Puttonen 1995;Parent and Messier 1996). Instantaneous measurements of transmittance on overcast days using single sensors show stronger correlation with growing season transmittance than do midday or entire-day measurements on sunny days (Messier and Puttonen 1995;Comeau et al 1998;Lieffers et al 1999).…”

“…There have been many studies comparing methods for estimating light under different types of stands (Messier and Puttonen 1995;Yanhong and Naoki 1997;Comeau et al 1998;Jennings et al 1999). Comeau et al (1998) found that growing season light under a paper birch mixedwood stand can be reasonably estimated using quantum sensors (>r=0.89), hemispherical photographs, and LAI-2000 plant canopy analyzers.…”

“…Leaf area index measured in 1999 were greater than measurements in 1997 suggesting that the crowns of paper birch are getting larger (Jian Wang unpublished). It has been reported that small increases in percent PAR found in gaps can result from an increase in diffuse light penetrating into the understory from the gaps (Messier and Puttonen 1995 (Chen eta/. 1996;Constabel and Lieffers 1996;Mencuccini and Grace 1996;Chen and Klinka 1997;Man and Lieffers 1997).…”