Relative Photosynthetic Photon Flux Research Articles

Factors controlling germination and seedling growth of an endangered Saussurea species (Asteraceae) endemic to serpentine areas in Japan

AbstractSaussurea ochiaiana Kadota (Asteraceae) is a perennial herb endemic to serpentine areas in western Japan. To date, only two locations are known habitats for this species of unknown ecological requirements. Therefore, this study aimed to clarify the environmental factors that limit the germination and seedling growth of this species, which is an essential requirement for designing a suitable conservation strategy. Our germination experiments, in which the achenes were subjected to a gradually increasing temperature and a gradually decreasing temperature after short (1 month) or long (4 months) storage, indicated that the achenes required a long cold stratification for germination. In an experiment where plants collected at the study site were potted individually, they did not grow under strongly shaded conditions consisting of only 10% relative photosynthetic photon flux density (RPPFD), but grew well under moderately shaded conditions (50% RPPFD). No significant differences in seedling growth were observed among the three pH conditions tested (pH 4, 6, and 8). Although average seedling shoot weight was significantly larger at low Ca:Mg molar ratios (0.6 and 0.3) than at high substrate Ca:Mg molar ratios (15 and 1.5) in pot culture experiments, the difference between treatments was not very large (<20%). Habitat conditions suitable for the regeneration of this species are decreasing because of climate change and the depopulation of rural communities (reduction in management); therefore, urgent conservation strategies, including ex situ conservation, are needed.

Photosynthetic nitrogen utilization of Robinia pseudoacacia, an invasive species, grown in contrasting light conditions: A leaf scale approach

AbstractRobinia pseudoacacia (black locust), an alien species in Japan, has been commonly planted to rehabilitate degraded land and as a resource for the production of honey. Although very few R. pseudoacacia adult trees are found in established mature forests, the management of R. pseudoacacia is a vital and urgent matter because of astounding growth potential, which negatively affects biodiversity and native vegetation. For this reason, we evaluated the seasonal shade‐acclimation capacity of black locusts from the viewpoint of photosynthetic nitrogen use (PNU) and their partitioning. We assessed in situ photosynthetic N use traits of R. pseudoacacia leaves at open sites (relative photosynthetic photon flux density: (rPPFD) > 90%) and shaded sites (rPPFD < 22%) on the forest floor in larch (Larix kaempferi Carr.) plantations. Leaf unfolding started in late May and leaves turned yellow by mid‐October just before leaf shedding. Shoot length at open sites was three times longer than at shaded sites. R. psudoacacia at open sites has more the leaflet number of each pinnate compound leaf than shaded sites from mid‐August to October, and the size of leaflets at shaded sites was about 20% smaller than it was at the open sites. Leaf mass per area showed (mean ± standard deviation) 40.00 ± 2.14 g m−2 at the open sites and 22 ± 1.56 g m−2 at the shaded sites from June to October. The light‐saturated photosynthetic rate peaked at 22 μmol m−2 s−1 at the open sites in July. At the shaded sites, it gradually increased to 7–10 μmol m−2 s−1 around August, and then decreased at both sites toward zero in mid‐October. The total N content during the growth period was 1.60 ± 0.17 g m−2 at open sites and 1.16 ± 0.15 g m−2 at shaded sites. Unlike other tree species, N partitioning to photosynthetic organs was not affected by light conditions. These findings suggested R. psudoacacia cannot acclimate to shady conditions.

Estimating Three-Dimensional Distribution of Leaf Area Using Airborne LiDAR in Deciduous Broad-Leaved Forest

We examined the performance of airborne light detection and ranging (LiDAR) data obtained in 2011 for leaf area estimation in deciduous broad-leaved forest using the Beer–Lambert law in Takayama, Gifu, Japan. We estimated leaf area index (LAI, allometry-LAI) and vertical leaf area density (LAD) using field survey data by applying allometric equations to estimate leaf-area of trees and a Weibull distribution equation to estimate vertical leaf distribution. We then estimated extinction coefficients (Ke) of LiDAR data for three height layers from the ground to the canopy top using the vertical LAD and vertical laser pulse distribution. The estimated PAI (LiDAR-PAI) using the Beer–Lambert law and Ke, when treating the canopies as three height layers, showed a significant linear relationship with allometry-LAI (p < 0.001). However, LiDAR-PAI when treating the canopies as single layer saturated at a PAI of six. It was similar to the lesser PAI estimation by hemispherical photography or relative photosynthetic photon flux density which treated the canopy as a single layer, compared to LAI measurements by litter traps. It is therefore important to allocate distinct Ke values to each of the multiple height layers for an accurate estimation of PAI and vertical PAD when applying the Beer–Lambert law to airborne LiDAR data.

Chemical and cultural control of Ipomoea hederacea var. integriuscula in narrow‐row soybean in southwestern Japan

AbstractIn Japan, the spread of morning glory (Ipomoea spp.) in soybean fields has become a serious issue. To establish a control approach for Ipomoea species, this study considered the optimal system combining cultural and chemical control methods. Field experiments were conducted for 3 years to investigate the effects of no‐tillage compared with tillage seeding in narrow‐row soybean and of application timing of selective post‐emergence herbicides bentazone and fluthiacet‐methyl. The cumulative emergence of entireleaf morning glory (Ipomoea hederacea [L.] Jacq. var. integriuscula A. Gray) in no‐tillage was 25–79% of that in tillage, and the initial growth was suppressed. In no‐tillage, the dry matter weight of I. hederacea var. integriuscula was suppressed compared to tillage methods. However, in no‐tillage, initial soybean growth was inferior, and reduction of the relative photosynthetic photon flux density (RPPFD) in the soybean canopy was delayed. A combination of selective post‐emergence herbicide applications at the second and fourth trifoliate leaf stages (TLS) of soybean was most effective in I. hederacea var. integriuscula suppression. The initial growth of soybean greatly fluctuated yearly, and the period when the RPPFD became less than 50% varied at the fourth through seventh TLS. Therefore, if the initial soybean growth is good, the end of the required period for weed control can be defined as the fourth TLS. No‐tillage cultivation combined with management to promote soybean growth, such as adequate soil moisture control by subirrigation systems, may be effective in controlling I. hederacea var. Integriuscula.

Effects of Light Intensity and Girdling Treatments on the Production of Female Cones in Japanese Larch (Larix kaempferi (Lamb.) Carr.): Implications for the Management of Seed Orchards

To ensure sustainable forestry, it is important to establish an efficient management procedure for improving the seed production capacity of seed orchards. In this study, we evaluated the effects of girdling and increasing light intensity on female cone production in an old L. kaempferi (Lamb.) Carr. seed orchard. We also evaluated whether there is a genotype-specific reproductive response to these factors among clones. The results showed that female cone production was augmented by girdling and increasing light intensity. There was a difference in the effectiveness of girdling treatment levels, and the probability of producing female cones increased markedly at higher girdling levels. At light intensities where the relative photosynthetic photon flux density was higher than 50%, more than half of the trees tended to produce female cones, even in intact (ungirdled) trees, and the genotype-specific response to light intensity was more apparent in less-reproductive clones. These findings suggested that girdling less-reproductive trees combined with increasing light intensity was an effective management strategy for improving cone production in old seed orchards.

Evaluation of validity and limitations of the soybean canopy height‐to‐row spacing ratio as an onsite index to control weeds using diverse soybean accessions

A canopy height‐to‐row spacing ratio (CHRSR) of 1.0 is expected to be a simple and practical onsite index for soybean growers to determine when further weed control is no longer necessary. This is decided when relative photosynthetic photon flux density (PPFD) reaches 50% under the soybean canopy. To evaluate the validity of this index, a 2‐year field experiment was conducted to compare days after sowing (DAS) to reach a relative PPFD of 50% (defined as PPFD50) and DAS to reach a CHRSR of 1.0 (defined as CHRSR1.0) in 190 accessions with different canopy architectures from a soybean core collection. A total of 104 accessions, for which final relative PPFD reached <10% in 2014, were examined for the differences between CHRSR1.0 and PPFD50. The mean and median values of the difference in 2014 were 0.02 and 2.2, respectively. Similarly, the mean and median values in 2015 were 2.8 and 2.6, respectively. Thus, CHRSR1.0 tended to be achieved slightly later than PPFD50, so a consideration was made that there would be a negligible risk of failure if growers used CHRSR1.0 to determine the termination time for weed control in the most of accessions. Although there were some accessions with a standing type of morphological characteristics or with a smaller or narrower leaf, showing negative differences between CHRSR1.0 and PPFD50 larger than 1 week, a CHRSR of 1.0 could be used to estimate PPFD50 in most of accessions without risk of failure to control weeds.

Early growth pattern of <i>Miscanthus sinensis</i> and two subordinate species in nutrient-poor soil as a key issue for the restoration of <i>M. sinensis</i> community

There were few researches in Japan on revegetation techniques for the restoration or reclamation of semi-natural grasslands. Miscanthus sinensis is a major dominant species in the Japanese semi-natural grasslands, which sometimes produces species-rich plant communities. The present study aimed to describe the early stage of growth patterns in M. sinensis and two subordinate species, Aster microcephalusand Potentilla freyniana, taking competitive interaction for light into account. We made a one-year pot experiment observing the growth of the subordinate species surrounded by pots with M. sinensis with and without fertilizer input in a hexagonal design. Results showed that M. sinensis in unfertilized pots failed to establish closed canopy within a single season. M. sinensis in fertilized pots had quarto biomass compared with that in unfertilized M. sinensis. Relative photosynthetic photon flux density at the ground level was 20% after one and a half month onwards after establishment. P. freyniana significantly decreased biomass due to its low statue by the severe shade of M. sinensis compared with those in unfertilized treatment, while A. microcephalus did not decrease the biomass escaping from shade by developing leaves at vertically higher position than that in unfertilized treatment. Possibility for the persistence of subordinate species under the predominance of M. sinensis with or without fertilizer input was further discussed.

Characterization of the Spectrum of Solar Irradiance under Different Crop Protection Coverings in Mediterranean Conditions and Effect on the Interception of Photosynthetically Active Radiation

Plants use visible light and part of adjacent ultraviolet and near infrared regions for photosynthesis. Crop protection coverings enable plant cultivation in areas or seasons not suitable open field. However, the use of covering materials is a detriment to solar irradiance, which may decrease the photosynthetic rate. Here, the effect of two different covering materials, tempered glass and white polyethylene mesh, on solar irradiance was compared to open field (control) under real farming conditions. Relative irradiance (RI) and photosynthetic photon flux density (PPFD) were recorded along 380-780 nm wavelength spectrums in the two conditions at 10:00 h and 13:00 h. Also the efficiency of Capsicum peppers in capturing solar irradiance was evaluated in leaves as the reflectance of both RI and PPFD under the mentioned growing conditions. Low differences in RI among the three conditions were found, and the lowest values corresponded to glasshouse conditions. Differences were more obvious in PPFD and, compared to open field, both mesh greenhouse and glasshouse conditions provoked remarkable decreases in all the spectral bands, 50-55% and 75-80% respectively. Covering materials also differed on the ratio of reflected PPFD and incident PPFD. Glasshouse plants displayed the highest reflectance at both 10:00 h and 13:00 h (0.05-0.20), followed by mesh greenhouse (0.05-0.10), suggesting that glasshouse conditions might decrease the photosynthesis rate due to both PPFD decrease and reflectance, although the effect of polyethylene mesh should not be disregarded as it also decreases considerably PPFD. Our results have important implications for the physiology and the productivity of crops under different covering materials.

Effects of sika deer browsing on soil mesofauna in a thinned Japanese cypress plantation

ABSTRACTWe examined the indirect effects of sika deer (Cervus nippon) overabundance on soil mesofauna in a thinned plantation. We compared the understory vegetation, environmental conditions at the forest floor, and soil mesofauna inside and outside of a fenced area established at a plantation of Japanese cypress in central Japan about 6 years after thinning. Deer browsing had reduced the volume of understory plants outside the fence; this tended to not cause a reduction in the litter mass and an increase in the soil bulk density, but caused an increase in the relative photosynthetic photon flux density reaching the forest floor. As a result, the relative humidity at the forest floor was lower outside the fence than inside. The abundances of detritivores and fungivores and predators in the soil mesofauna declined significantly in areas with deer. This could be due to desiccation in the litter layer inhabited by many detritivores and fungivores and predators that are sensitive to changes in moisture conditions. Thus, deer browsing had a negative effect on the soil mesofauna as well as on the aboveground fauna in the understory vegetation.

Patterns of Branch Growth and Death in Crowns of Sakhalin Spruce, Picea glehnii (F. Schmidt) Mast

The development of crown architecture strongly affects tree growth and survival. Growth and death of primary branches (those branching off from the main stem) and secondary branches (those from a primary branch) in the lowest part of the crown were investigated for Picea glehnii in an even-aged plantation. Probability of death of a primary branch decreased as the length between its basal location and the crown base (LCB) increased (p = 0.04), but this probability was not significantly related to the relative photosynthetic photon flux density (rPPFD) above the primary branch (p = 0.18). The probability of producing one or more current-year shoots on a primary branch increased with increasing rPPFD above the primary branch (p = 0.01); however, this probability was unrelated to LCB (p = 0.29). Secondary branches at the distal part of a primary branch produced more current-year shoots and exhibited a lower probability of death than proximal branches (p < 0.01), probably because rPPFD above the distal secondary branches was greater than the proximal branches (p < 0.01). Our results suggest that, while local light conditions are relevant to shoot production and shoot death on a primary branch, the death of an entire primary branch may be related to some morphological attributes concerning the length to the crown base.

Canopy height‐to‐row spacing ratio as a simple and practical onsite index to determine the time for terminating Ipomoea coccinea control in the Japanese soybean‐growing systems

In order to determine the time for terminating Ipomoea coccinea control in Japanese soybean‐growing systems, the relationship between the relative photosynthetic photon flux density at the emergence time of I. coccinea seedlings and their fate in competition with a Japanese determinate soybean cultivar, “Hatayutaka”, was investigated. A 2 year field study was conducted, in which I. coccinea was seeded at 0, 5 and 7 weeks after seeding of the soybean in 2010 and once per week between 0 and 7 weeks after seeding in 2011, while soybean was seeded in six plots at three different seeding times and two different row‐spacing arrangements with the same intrarow spacing. The results showed that the I. coccinea seedlings that emerged at a relative photosynthetic photon flux density of <49% grew weak or died. At this value, the canopy height‐to‐row spacing ratio of soybean was very stable, regardless of the row spacing, in both study years. This ratio was also stable when tested on 11 different soybean cultivars that covered all cultivation areas of Japan and had various growth speeds during the early growing period. A canopy height‐to‐row spacing ratio of 1.0 could be a simple and practical onsite index for determining the time to terminate I. coccinea control in Japanese soybean‐growing systems.

Carbon gain optimization in five broadleaf deciduous trees in response to light variation within the crown: correlations among morphological, anatomical and physiological leaf traits

AbstractLeaf trait variations in five deciduous species (Quercus robur, Corylus avellana, Populus alba, Acer campestre, Robinia pseudoacacia) growing in an old broadleaf deciduous forest in response to light variation within the tree crown was analyzed. Net photosynthetic rate (PN), leaf respiration rate (R) and the photosynthetic nitrogen use efficiency were, on average, more than 100% higher in sun than in shade leaves. A. campestre and C. avellana sun leaves had the highest specific leaf area (SLA, 156.0 ± 17.9 cm2 g-1) and the lowest total leaf thickness (L, 101.9 ± 8.8 μm) underlining their shade-tolerance. Among the shade-intolerant species (Q. robur, P. alba and R. pseudoacacia), Q. robur had the lowest SLA and the highest L in sun leaves (130.6 ± 10.0 cm2 g-1 and 160.8 ± 9.6 μm, respectively) since shade-intolerant species typically have thicker leaves. The higher PN decrease in respect to R decrease from sun to shade leaves attested the higher sensitivity of PN than R to light variations within the crown. This determined a 69% lower R/PN in sun than in shade leaves. This result is further attested by the significant correlation between PN and the relative photosynthetic photon flux density. The shade-tolerant species have a 76% higher R/PN ratio than the shade-intolerant ones. The measured leaf phenotypic plasticity (PI = 0.35) was in the range of broadleaf deciduous species. Plasticity is a key trait useful to quantify plant response to environmental stimuli. It is defined as the ability of a genotype to produce different phenotypes depending on the environment. Among the considered species, Q. robur showed the highest PI (0.39) and P. alba the lowest (0.29). Knowledge on phenotypic plasticity is important in making hypotheses about the dynamics of the studied forest in consideration of environmental stress factors, including invasive species competition and global climate change.

A Consideration for the Light Environmental Modeling under Tropical Rainforest Canopies

Abstract. 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. 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.

Effects of shade on growth, biomass allocation and leaf morphology in European yew (Taxus baccata L.)

The impact of shade on the growth of European yew (Taxus baccata L.) saplings was investigated over a three-year period using artificial shading to simulate four different light regimes (3, 7, 27 and 100 % relative photosynthetic photon flux density, RPPFD). There was no mortality attributable to shading even under the 3 % RPPFD treatment. Increasing shade was positively associated with specific leaf area, leaf length, leaf width and total chlorophyll content, but negatively associated with plant height, stem diameter, total dry weight and root to leaf and shoot ratio. Discoloration of the foliage occurred in plants grown in 100 % RPPFD conditions (resulting in reduced growth rates) and those transferred to 100 % RPPFD conditions after being shade-acclimated for 2 years. Evidence suggests that T. baccata has the ability to regenerate beneath a lighter canopy but beneath denser canopies gap dynamics will play an important role in facilitating successful regeneration and this needs to be reflected in management of natural populations of this declining species.

The effects of plant size and light availability on male and female reproductive success and functional gender in a hermaphrodite tree species,Magnolia stellata

Plant size and light availability may affect male and (or) female reproductive success and their relative contribution (functional gender). To test this hypothesis, we identified parents of 184 seedlings in a local population within a metapopulation of a hermaphroditic, insect-pollinated tree species, Magnolia stellata (Siebold & Zucc.) Maxim., using 14 nuclear and 3 chloroplast microsatellite markers. Parent pairs of all the seedlings were determined, and both seed and pollen parents could be distinguished for 49.5% of the seedlings. We also measured the parents’ plant size (diameter at breast height of the thickest ramet within each genet; DBHt) and the relative photosynthetic photon flux density (rPPFD) they received. The proportion of seedlings that originated from selfing was 20.7%. The number of seedlings parental trees produced as seed parents (S) was positively affected by DBHtand rPPFD. DBHt(but not rPPFD) also positively affected the number of seedlings sired as pollen parents (P). The femaleness of the parental trees (S/(S + P)) was positively affected by DBHt, probably because DBHthad a stronger effect on the trees’ reproductive success as seed parents than on their success as pollen parents. These results suggest that plant size affects not only reproductive success (male and female), but also functional gender.

Optimal Leaf-to-Root Ratio and Leaf Nitrogen Content Determined by Light and Nitrogen Availabilities

Plants exhibit higher leaf-to-root ratios (L/R) and lower leaf nitrogen content (N area) in low-light than in high-light environments, but an ecological significance of this trait has not been explained from a whole-plant perspective. This study aimed to theoretically and experimentally demonstrate whether these observed L/R and N area are explained as optimal biomass allocation that maximize whole-plant relative growth rate (RGR). We developed a model which predicts optimal L/R and N area in response to nitrogen and light availability. In the model, net assimilation rate (NAR) was determined by light-photosynthesis curve, light availability measured during experiments, and leaf temperature affecting the photosynthesis and leaf dark respiration rate in high and low-light environments. Two pioneer trees, Morus bombycis and Acer buergerianum, were grown in various light and nitrogen availabilities in an experimental garden and used for parameterizing and testing the model predictions. They were grouped into four treatment groups (relative photosynthetic photon flux density, RPPFD 100% or 10%×nitrogen-rich or nitrogen-poor conditions) and grown in an experimental garden for 60 to 100 days. The model predicted that optimal L/R is higher and N area is lower in low-light than high-light environments when compared in the same soil nitrogen availability. Observed L/R and N area of the two pioneer trees were close to the predicted optimums. From the model predictions and pot experiments, we conclude that the pioneer trees, M. bombycis and A. buergerianum, regulated L/R and N area to maximize RGR in response to nitrogen and light availability.

The effects of early and intense pruning on light penetration, tree growth, and epicormic shoot dynamics in a young hybrid larch stand

We examined the effect of early and intense pruning on light intensity under the canopy, individual growth, diameter–height relationships, and epicormic shoot dynamics in young hybrid larch (Larix gmelinii var. japonica × L. kaempferi) to establish a new effective management method for hybrid larch plantations. The objective is to produce high-quality wood while reducing silviculture costs using a combination of low-density planting and early and intense pruning. In a young hybrid larch plantation, we pruned branches to two different heights (2 and 4 m above ground level) using a no-pruning treatment as a control. Although the growth rates were lower in the heavy pruning treatment (4 m above the ground level) than in other treatments in the year following pruning, when measured 4 years later, growth did not differ between treatments. The number of epicormic shoots increased in the year following pruning, as did the relative photosynthetic photon flux density (rPPFD). The number of epicormic shoots was also dependent on the size of individual trees. However, survival of epicormic shoots was not sufficiently high to be problematic for high-quality timber production. If branches are pruned carefully such that the rPPFD does not rise above 20%, the emergence of epicormic shoots can also be controlled. Our results indicate that early and intense pruning is an effective component of a new management system for hybrid larch plantations.

Examination of the coexistence mechanism of two major conifers in Hokkaido, northern Japan, based on differences in suitable germination conditions and shade tolerance

The coexistence mechanism of Abies sachalinensis and Picea jezoensis, which usually regenerate on fallen logs, was examined with respect to differences in suitable conditions for germination and shade tolerance in Hokkaido, northern Japan. Germination conditions were evaluated through the effect of log hardness, moss height, light condition, and shading by taller seedlings on fallen logs, and shade tolerance was evaluated by physiological and morphological traits and survival dynamics in a natural coniferous forest. In contrast to P. jezoensis, the number of germinated seedlings of A. sachalinensis increased with moss height. The number of germinated seedlings decreased with shading only in P. jezoensis. Consequently, it is suggested that germination of P. jezoensis is limited to fresh, recently fallen logs. The survival rate of A. sachalinensis under low-light conditions (< 5% of relative photosynthetic photon flux density) was higher than that of P. jezoensis. Abies sachalinensis had a higher leaf mass ratio (total leaf mass/total mass) and leaf area ratio (total leaf area/total mass) than P. jezoensis. In conclusion, earlier establishment of P. jezoensis on fallen logs and higher shade tolerance of A. sachalinensis are suggested to contribute to the coexistence of these 2 species.

Forest floor light conditions in a secondary tropical rain forest after artificial gap creation in northern Borneo

Forest floor light conditions were monitored in a field experiment regarding alternative approaches to canopy gap creation. To establish gaps, three pioneer canopy treatments (canopy tree felling, girdling and untreated control) were combined with two sub-canopy treatments (slashing or untreated control). The canopy treatments were performed within sub-plot circles (radius 5 m) while the sub-canopy treatment was confined to the central parts (2.5 m radius). Pioneer canopy felling and girdling (stripping of the bark) treatments affected 31% (mean value) of the initial mean standing basal area (39 m 2 ha −1). Relative photosynthetic photon flux densities (PPFD R) and canopy openness were measured (1.5 m above the forest floor) in the sub-plots before and immediately after treatment and at subsequent intervals of 6, 18 and 30 months. During the study period all treatments resulted in increased PPFD R and canopy openness compared to pre-treatment mean values (PPFD R: 1.8–2.3%, canopy openness: 8.8–10.7%). Felling selected pioneer canopy trees provided distinct but transient shade reduction; mean PPFD R values were 12.5% after 6 months and 8.5% 30 months after initial treatment, while canopy openness averaged 14.2 and 11.8% after 6 and 30 months, respectively. Girdling effects were less drastic but after 30 months forest floor openness and PPFD R averaged values similar to, or slightly higher than the felling treatment. Sub-canopy slashing resulted in 2.4–5.1% higher PPFD R and 2.0–2.4% higher canopy openness compared to the untreated control plots and this effect persisted throughout the study period.

Relationships between flowering phenology and female reproductive success in the Japanese tree species Magnolia stellata

We have examined the earliness, duration, and amplitude of flowering genets in a Magnolia stellata (Sieb. et Zucc.) Maxim. population in relation to their size, environmental factors (temperature and light), and female reproductive success (ovule survival rate) over three consecutive years. Average flowering durations of individual flowers, genets, and the whole population in these 3 years were 10.2, 15.2, and 29.0 d, respectively. A bisexual phase (with both female and male phase flowers) in genets spanned 62.9% of the total flowering period, suggesting that geitonogamy can occur. The earliness, duration, and amplitude of flowering genets were all significantly correlated, indicating that genets flower early and long periods have high flowering amplitudes. The three parameters were also significantly correlated with the size of the genets (represented by the diameter at breast height of its thickest ramet) and relative photosynthetic photon flux density at the top of their crowns. Therefore, genets that are large and located in well-lit sites tend to have many flowers, and blossom both earlier and longer. Later-flowering genets have higher female reproductive success, probably because M. stellata is protogynous. Significantly positive correlation between flowering amplitude and female reproductive success suggests that large numbers of flowers increase the attractiveness of genets for pollinators, and this outweighs the negative effects of geitonogamy.