Canopy Photosynthetically Active Radiation Research Articles

A novel simulation model to predict photosynthetic active radiation interception in micro-irrigated citrus production orchards based on tree spacing, canopy geometry, and row orientation

Diurnal and seasonal patterns of photosynthetically active radiation (PAR) intercepted by tree canopies in production orchards have an important role for eco-physiological processes that determine tree water use and productivity. Under well-watered conditions, PAR intercepted by trees is a reliable predictor of crop consumptive water use, which is regulated by tree spacing, tree row orientation, and by the tree canopy dimensions and geometry. Despite its advantages, only rare attempts have been made by the scientific and fruit production communities to develop canopy PAR interception simulators that rely on analytical principles to inform irrigation planning and management decisions. In this article, a novel model is presented that simulates PAR interception by citrus trees based on the canopy geometry and its shading patterns. The article also illustrates preliminary field testing and validation of the model with data collected in commercial citrus production orchards located in the San Joaquin Valley of California. The testing and validation could enable citrus growers and orchard managers to predict the net radiation for mature, micro-irrigated Navel orange and Page mandarin orchards grown with north–south and east–west tree row orientations and different tree densities. Results from the simulations and field validation showed that the canopy PAR light interception contributed 58.8 (± 0.02) and 71.1 (± 1.60) percent to the overall net radiation for the Navel orange orchards during the periods around summer solstice and autumnal equinox, respectively, whereas for the Page mandarin orchards, PAR light interception contributed 63.0 (±5.60) and 85.7 (±18.87) percent to the overall net radiation during the same time periods. Good correlations were found between daily values of PAR and net radiation for these citrus production orchards grown with the two alternative row orientations, which suggest that the proposed model could be used to inform irrigation planning and management decisions for different site-specific citrus orchard features and growing conditions.

Effects of plastic film mulching on the spatiotemporal distribution of soil water, temperature, and photosynthetic active radiation in a cotton field.

Plastic film mulching (PFM) affects the spatiotemporal distribution of soil moisture and temperature, which in turn affects cotton growth and the spatiotemporal distribution of canopy photosynthetically active radiation (PAR). Due to the spatial heterogeneity of soil moisture, temperature and limited monitoring methods, the issues such as relatively few sampling points and long sampling intervals in most existing studies prevent the accurate quantification of spatiotemporal changes in moisture and temperature along soil profile. To investigate the effects of PFM on spatiotemporal changes in soil moisture, temperature, and canopy PAR in cotton fields, two field trials of plastic film-mulched (M) and nonmulched (NM) cultivations were performed in 2018 and 2019. The grid method was used for the soil information continuous monitoring and multiple-time fixed-site canopy PAR monitoring during the duration of cotton growth. Two-year field trial data showed that, M cultivation increased soil moisture by approximately 13.6%–25% and increased temperature by 2–4 °C in the 0–50 cm soil layer before the first irrigation (June 20) and by 1–2 °C in the 70–110 cm soil layer, compared with NM cultivation. In addition, the temperature difference between the two treatments gradually decreased with the increase in irrigation and air temperature. The M treatment reached the peak PAR interception rate 10 days earlier than the NM treatment. In 2018 and 2019, the PAR peak value under the M treatment was 4.62% and 1.8% higher than that under the NM treatment, respectively, but the PAR interception rate was decreased rapidly in the late growth stage. Overall, PFM had an effect on soil moisture retention during the whole growth period and greatly increased the soil temperature before budding stage, thus promoted the early growth of cotton. Considering this, we suggest that the irrigation quota and frequency could be appropriately decreased in the case of plastic film mulching cultivation. For nonmulching cultivation, the irrigation quota and frequency should be increased, and it is necessary to take measures to improve the soil temperature before middle July.

Coupling of net ecosystem CO2 exchange and evapotranspiration of irrigated maize field in arid areas

Understanding water and carbon fluxes over agroecosystem are fundamental for water resources management in arid areas. However, their dynamics and coupling at different temporal scales have not been well understood. Therefore, in this study, net ecosystem CO2 exchange (NEE) and evapotranspiration (ET) over irrigated maize field were monitored using eddy covariance system during two crop growing seasons in 2017 and 2018. The dynamics of NEE, ET and the resulted water use efficiency (WUE, defined as NEE/ET), and their responses to the meteorological and hydrological factors were investigated. At hourly scale, when ET increased at noon, NEE reached the plateau ahead of ET, which resulted in decreased WUE. The maize WUE changed during the growing season. Average daytime WUE at the heading stage was the largest: 9.52 and 8.57 g (CO2) kg−1 (H2O) in 2017 and 2018, respectively. Photosynthetically active radiation (PAR) was the primary driver controlling diurnal dynamics of NEE and ET in irrigated maize field, while the opposite effects of vapor pressure deficit (VPD) on NEE and ET were identified. When the VPD increased from 0 to 3.3 kPa, the slope of the linear relationship between ET and PAR increased; whereas, the slope of the linear relationship between NEE and PAR decreased. At daily scale, the relationship between NEE and ET was generally linear with a slope of 8.59 g CO2 kg−1 H2O, which could be attributed to their similar sensitivities in response to canopy conductance, PAR and soil water content. In addition, the effect of irrigation on WUE was different depending on the crop development stage and crop physiological activities. This study highlights that high VPD would decrease WUE of maize growing in irrigated agroecosystems in arid areas.

Effects of Planting Density of Spring Soybean on Canopy Photosynthetically Active Radiation and Yield in Northeast China

Soybean is an important legume crop. Planting density of soybean directly affects the distribution of photosynthetically active radiation (PAR) in the canopy, which affects the physiological changes, such as photosynthesis of soybean, and leads to the change of yield. In this experiment, soybean variety Heinong 84 was adopted, and five planting densities were set as 200,000 plants/ha (D20), 250,000 plants/ha (D25), 300,000 plants/ha (D30), 400,000 plants/ha (D40) and 500,000 plants/ha (D50). The canopy PAR intensity was measured based on photosynthetically active radiation recorder, and the effects of different densities on soybean canopy PAR and yield were studied systematically. According to the results, with the extension of growth period, the PAR above and within the canopy of soybean decreased first and then increased, and the rules were consistent under different densities. During each growth period, PAR was above that of canopy > growth point > middle stem > cotyledon scar and decreased with the increase of density. The growth point changed significantly, followed by middle stem, but no significant change happened in cotyledon scar. The absorption photosynthetically active radiation (FPAR) showed a unimodal trend with the increase of density at V4 and R2 and had an upward trend at R4 and R6. The number of effective pods per plant and 100 seed weight of D20 are the highest, and the yield of D25 is the highest.

Effects of row spacing and sowing rate on vertical distribution of photosynthetically active radiation, biomass, and grain yield in winter wheat canopy.

To clarify the effects of row spacing and sowing rate on the vertical distribution of canopy PAR, biomass, and grain yield in winter wheat, a field experiment was conducted without increa-sing water and fertilizer input. There were two row spacing modes, R1 (equal spacing, 20 cm+20 cm) and R2(wide and narrow row spacing, 12 cm+12 cm+12 cm+24 cm), and three sowing rates, D1 (low, 120 kg·hm-2), D2 (medium, 157.5 kg·hm-2), D3 (high, 195 kg·hm-2). The canopy photosynthetically active radiation (PAR) interception and utilization rate in different heights, population photosynthetic capacity, biomass, and grain yield were measured during the main growth stages of winter wheat. The results showed that both total PAR interception and upper layer PAR interception of winter wheat canopy under R1 treatment were significantly higher than those in R2 treatment, but those of the middle layer and lower layer were higher in R2 than in R1, and with significant difference in the middle layer. From flowering to maturity, the photosynthetic potential (LAD), population photosynthetic rate (CAP), PAR conversion rate, and utilization rate in R2 were all significantly higher than those in R1 under the same sowing rate, with the highest value under R2D2 treatment. With the increasing sowing rate, the population biomass (BA) and leaf biomass (BL) at different layers increased, but the individual biomass (BP) showed an opposite trend. Under the same sowing rate, BA, BL and BP in R2 were higher than that in R1 after the flowering stage. Among them, BA and BP had significant difference in row spacing treatments at the maturity stage, with significant difference between the two row spacing treatments being observed in BL of the middle and lower layers under D2 and D3 sowing rates. The spike number, grain number per spike, 1000-kernel weight, and grain yield of winter wheat among different treatments were the highest in R2D3, R2D1, R2D1, and R2D2, respectively. The 1000-kernel weight, grain number per spike and grain yield in R2 treatment were significantly higher than R1. In summary, the PAR interception in the middle and lower layers of winter wheat canopy was improved by changing row spacing, with positive consequence on the photosynthetic capacity of individual plant and population, PAR utilization and transformation efficiency, which finally increased biomass and grain yield. Therefore, optimizing the field structure and shaping the ideal population photosynthetic structure should pay more attention during the high-yield cultivation of winter wheat. Making full use of light resources per unit land area and excavating the photosynthetic production potential of crops were also critical to achieve high yield and efficiency. In this experiment, the population photosynthetic capacity, photosynthetic effective radiation utilization rate, and yield were the highest under the treatment of R2D2.

Characterizing the three-dimensional spatiotemporal variation of forest photosynthetically active radiation using terrestrial laser scanning data

The three-dimensional (3-D) spatiotemporal distribution of forest canopy photosynthetically active radiation (PAR) is a major determinant of within-crown variations of leaf photosynthesis and transpiration. However, it remains challenging to map the 3-D spatiotemporal distribution of PAR within and under the forest canopy due to the limited ability to capture the detailed 3-D structures of forest canopies.This study proposes a simple approach to estimate the 3-D spatiotemporal distribution of forest canopy PAR at a fine spatial resolution based on terrestrial laser scanner (TLS) data by characterizing difference in transfer of incident solar direct PAR and diffuse PAR and by considering the effect of the orientation angles of foliage elements on the 3-D distribution of direct PAR. Estimated PAR was validated using 10-minute PAR measurements from pyranometers at different locations within four forest plots, at which effective leaf area index (LAIe) ranged from 0.83–4.25. It showed that the proposed method captured 85% (N=2831, p<0.001) of the variations in the field pyranometer measurements. Furthermore, the proposed method was also applicable for estimating the vertical distribution of PAR (R2=0.95, N=15, p<0.001). Direct, diffuse, and total PAR exhibited similar vertical distributions changing with LAIe. It was shown that without differentiation of direct and diffuse PAR or ignoring effects of orientation angles of foliage elements may cause errors of about 20% in the estimated 3-D PAR distribution. Furthermore, the results indicated that the proposed method can be used to estimate the vertical distribution of PAR when the average neighbor point distance (NPD) is ≤20 cm. This proposed method will be usable for accurate separation of sunlit and shaded leaves and estimation of vertical distribution of PAR, which will benefit to reduce uncertainties in the estimation of terrestrial carbon fluxes and retrieval of vegetation structural and biochemical parameters.

Novel technique for non-destructive LAI estimation by continuous measurement of NIR and PAR in rice canopy

Although leaf area index (LAI) is a useful index of crop growth, evaluating LAI by destructive sampling is laborious and time-consuming. In the present study, we developed a novel technique to determine rice LAI non-destructively and accurately throughout growth period in paddy field. Near-infrared radiation (NIR) and photosynthetically active radiation (PAR) were measured by a pair of optical sensors inside and outside rice canopy at 1-min intervals. Simple ratio (SR) and NIR to PAR ratio (N/P) were measured depending on growth stage, and the criteria to extract valid SR and N/P that represent LAI accurately were determined. SR and N/P obtained under cloudy conditions were found to represent LAI with high accuracy (R2 = 0.91), and seasonal dynamics of canopy growth curves were successfully drawn for two rice cultivars at two experimental fields. Mathematical analysis revealed that not cumulative PAR but cumulative temperature could trigger exponential canopy growth. The present technique can be used as a powerful tool for evaluating, modelling, and phenotyping crop growth characteristics in various rice cultivars as well as other crops.

Estimating Photosynthetically Active Radiation Intercepted by Almond and Walnut Trees using UAV-Captured Aerial Images and Solar Zenith Angle

Highlights Measurement of canopy light interception data using a ground-based mobile system. Using UAV-captured aerial images and zenith angle to estimate canopy light interception at different times of the day. Identifying boundaries of individual trees using the maximum likelihood estimator and the watershed algorithm. Abstract. Photosynthetically Active Radiation (PAR) absorbed by the leaves is a key piece of information to study the crop response to environmental conditions that could be used to estimate crop production potential. Canopies in a commercial orchard present differences in their capability to intercept light mainly due to the spatial variability in canopy development. There is a need for developing tools that could capture spatial variability in PAR interception to predict potential yield. Unmanned Aerial Vehicles (UAV) present an interesting alternative to provide this information, as they cover a larger area than ground-based systems in a shorter period with high spatial resolution. The objective of this study was to determine the relationship between the shadow of a tree derived from a ground-based canopy light interception scan obtained using a lightbar mounted on a mobile platform and that acquired from UAV Red-Green-Blue (RGB) images. Information acquired by an UAV was classified to separate canopy from its shadow, grass and sunlit soil using maximum likelihood estimator. Boundaries of individual trees were identified based on their positions using watershed transform algorithm. The relationship between canopy PAR interception data, sun angle in the sky (zenith angle), and the information derived from aerial images was analyzed. Coefficient of determination (R2) values of 0.92 and 0.88 were found for the multiple linear regression between PAR, the shadow area and the cosine of zenith angle obtained for almond and walnut crops, respectively. Moreover, R2 values of 0.81 and 0.86 were found for the relationship between the shadow’s area obtained underneath the canopy and the shadow’s area obtained from the UAV images and the cosine of the zenith angle for almond and walnut crops, respectively. The results show that the PAR interception can be estimated using the zenith angle and the area of the shadow, which can be obtained from a RGB aerial image. Keywords: Almond, Canopy segmentation, Image classification, PAR interception, Shadow area, UAV, Walnut.

Incident photosyntehticaly active radiation under and outside the canopy of Acacia nilotica (Linn.) for agroforestry system

The important factor to be considered in biomass production is the maximum light use efficiency. The capture of radiation and its use in dry matter production depends on the fraction of the incident photosynthetically active radiation (PAR). An experiment was conducted in the campus of Dr. Panjabrao Deshmukh Krishi Vidyapeeth Akola, Maharashtra during 2018-2019 with the objective to study microclimatic effect under Babul (Acacia nilotica L.) for checking the suitability of Babul to match the under story agricultural crops and pasture grasses on the basis of microclimatic parameters recorded under and outside the canopy of Babul. Collected data were statistically analyzed with descriptive statistics by calculating mean and standard deviation. Observations on microclimatic parameters Photosynthetically active radiation were recorded from October to December (Rabbi Season). Observations were recorded under and outside the canopy of Babul by selecting ten trees from the 15x15 m plot of Babul plantation site and data were recorded during (9 am, 2pm, and 4pm) in a day by weekly intervals for three months. The results revealed that the microclimatic parameter such as photosynthetically active radiation (PAR) showed lower values under the canopy and higher value outside the canopy, and from West and South direction highest PAR was recorded. In comparison, average PAR values under the canopy from all the three months were lower for the outside canopy PAR value. On the basis of this farmer can chose the suitable understory agricultural crops and pasture grasses.

Natural Regeneration in &lt;i&gt;Strychnos nux-vomica&lt;/i&gt; L. A Commercially Important Non-Timber Forest Product of Tropical Dry Deciduous Forest

Forest is a very complex and dynamic ecosystem and stability of species mainly governed by regeneration success in community. A study was conducted in Chandaka-Damapara wild life sanctuary, Odisha to evaluate the status of natural regeneration of Strychnos nux-vomica in and around canopy of mother tree. A total 16 plots of 1 × 1 m size was laid out per tree at fourdistances (1, 4, 7 and 10 m distances from the trees) in four directions (east, west, south and north) for thirty trees spreading over six sites (Andharua, Sundarpur, Daspur, Kochilaberena, Deras and Ambakhali). Observations on new recruits, un-established seedlings (&lt; 2.0m height) and established regeneration (&gt;2.0m height) were taken in predetermined quadrats and compared for canopy diameter and PAR (Photosynthetically active radiation). Mean number ofregenerates per m 2 per tree was recorded 7.56. Maximum number ofrecruits was observed at 7.0 m distance from mother tree receiving PAR 872.40 μmolm -2 S -2 . Survivability of new recruits at the end of growing season was poor within canopy spread area of mother tree. Only 0.50 established regenerates per m 2 per tree were observed.

Leaf and Crown Optical Properties of Five Early-, Mid- and Late-Successional Temperate Tree Species and Their Relation to Sapling Light Demand

The optical properties of leaves and canopies determine the availability of radiation for photosynthesis and the penetration of light through tree canopies. How leaf absorptance, reflectance and transmittance and radiation transmission through tree canopies change with forest succession is not well understood. We measured the leaf optical properties in the photosynthetically active radiation (PAR) range of five Central European early-, mid- and late-successional temperate broadleaf tree species and studied the minimum light demand of the lowermost shade leaves and of the species’ offspring. Leaf absorptance in the 350–720 nm range varied between c. 70% and 77% in the crown of all five species with only a minor variation from the sun to the shade crown and between species. However, specific absorptance (absorptance normalized by mass per leaf area) increased about threefold from sun to shade leaves with decreasing leaf mass area (LMA) in the late-successional species (Carpinus betulus L., Tilia cordata Mill., Fagus sylvatica L.), while it was generally lower in the early- to mid-successional species (Betula pendula Roth, Quercus petraea (Matt.)Liebl.), where it changed only a little from sun to shade crown. Due to a significant increase in leaf area index, canopy PAR transmittance to the forest floor decreased from early- to late-successional species from ~15% to 1%–3% of incident PAR, linked to a decrease in the minimum light demand of the lowermost shade leaves (from ~20 to 1%–2%) and of the species’ saplings (from ~20 to 3%–4%). The median light intensity on the forest floor under a closed canopy was in all species lower than the saplings’ minimum light demand. We conclude that the optical properties of the sun leaves are very similar among early-, mid- and late-successional tree species, while the shade leaves of these groups differ not only morphologically, but also in terms of the resource investment needed to achieve high PAR absorptance.

In sink-limited spring barley crops, light interception by green canopy does not need protection against foliar disease for the entire duration of grain filling

Disease management in cereals is heavily reliant on the use of fungicides, but development of anti-microbial resistance, effects on non-target organisms and persistence of active ingredients in the environment and food chain challenge the sustainability of this approach. Better targeting of fungicides according to crop need within an integrated pest management (IPM) programme could improve the sustainability of disease management. The objectives of the present study were to determine 1) the duration of protection of post-anthesis canopy light interception required to maximise the yield of spring barley and 2) to relate this to the response of crops to timing of fungicide applications. As the yield of spring barley is considered to be sink-limited (limited by the number and storage capacity of grains) rather than source-limited (limited by the amount of carbon assimilates available for grain filling) in many environments, we hypothesised that the canopy would not need to be protected for the entire grain filling period. Field experiments were conducted at two sites in the UK (Edinburgh and Herefordshire) over four years, providing contrasting climates and soil types. Shading was used to determine the response of grain filling to reductions in light interception over defined intervals, thereby mimicking effects of foliar disease on light interception, as shading is easier to control than the onset and duration of disease epidemics. Shades giving ˜67% reduction in photosynthetically active radiation (PAR) were erected over plots of disease-free crops at weekly intervals commencing at flowering and leaving them in place until harvest. The required duration of protection of light interception was estimated as the period from flowering to the time at which the onset of shading had no effect on yield. In a separate experiment the response to five fungicide timing treatments was determined on three relatively disease-susceptible varieties. Timings were the start of stem extension (referred to here as T1 only) and T1 followed by a second application at either flag leaf emergence (early T2), flowering (mid T2) or the start of rapid grain growth (late T2); untreated plots served as controls. Results showed that canopy PAR interception does not need to be protected for the entire grain filling period in order to maximise yield. The critical period determined from shading was 3–5 weeks after 50% ear emergence depending on the site year, or the first 72–90% of grain filling. There was a significant yield response to fungicide treatment in all site-years of 0.33−0.74 t ha−1 irrespective of the disease severity and yield potential of the site. Where disease severity was low to moderate a T1 application on its own gave sufficient protection during grain filling to maximise yield. Later applications increased healthy area PAR interception further, but effects occurred late during grain filling and did not increase yield. When disease was severe a T1 plus mid T2 application was required to protect PAR interception during the critical early to mid- grain filling period. These results provide the necessary physiological understanding to help target fungicide applications according to crop need.

Estimation of plant area index and phenological transition dates from digital repeat photography and radiometric approaches in a hardwood forest in the Northeastern United States

Long-term, continuous digital camera imagery and tower-based radiometric monitoring were conducted at a representative hardwood forest site in the Northeastern United States, part of the AmeriFlux network. In this study, the phenological metrics of the leaf area index (LAI), plant area index (PAI) and associated transition dates (e.g., timing of the onset of leaf expansion and the cessation of leaf fall) were compared using 4-year of data from Bartlett Experimental Forest. We used digital repeat photography (DRP) imagery collected using two different methods (“canopy cover” and “phenocam” approaches), together with above- and below-canopy measurements of photosynthetically active radiation (PAR). The growth-period LAI estimated from canopy cover images (LAICANOPY) and the above and below canopy PAR measurements (LAIfPARt) were within approximately the same range, in term of magnitude, as previous results for multiple comparative methods, although growing-season LAICANOPY was slightly lower (3.11m2m−2 to 3.35m2m−2) than LAIfPARt (3.19m2m−2 to 3.67m2m−2). In addition, we derived phenological transition dates from PAICANOPY, PAIfPARt, and color-based metrics calculated from the phenocam imagery (green (GCC) and red (RCC) chromatic coordinates). The transition dates in both spring and autumn differed somewhat according to method, presumably due to the vegetation status detection abilities of each vegetation metric. We found that LAI estimation from canopy cover images may be influenced by automatic exposure settings, which limits the ability to detect subtle changes in phenology during the transition phases in both spring and autumn. Particularly in autumn, the color-based metrics calculated from the phenocam imagery are decoupled from leaf area dynamics and thus PAI. While above and below canopy PAR measurements could yield the better indicators for estimating LAI, its seasonal dynamics, and associated phenological transition dates in long-term monitoring, we argue that there are obvious benefits to the multi-sensor approach used here.

Drivers of shortwave radiation fluxes in Arctic tundra across scales

Vegetation composition and water surface area are changing in many tundra regions due to climate warming, which is twice as strong in the Arctic as compared to the global mean. Such land cover changes feed back to climate and permafrost thaw through altering the surface energy budget. We quantified the influence of vegetation type, canopy characteristics, and patchiness on the tundra shortwave radiation components. We used in situ measurements and vegetation mapping to parametrise a 3D radiative transfer model (DART) for summer conditions at the Kytalyk test site in northeast Siberia. We analysed model results assessing the most important drivers of canopy albedo, transmittance, and absorptance of photosynthetically active radiation (PAR). Tundra albedo was strongly influenced by the fractional cover of water surfaces. Albedo decreased with increasing shrub cover. However, plant area index effects on albedo were not statistically significant. Canopy transmittance and PAR absorptance (fAPAR) were almost entirely controlled by plant area index at the landscape scale. Only about one half of the total plant area index consisted of green leaves, while wood and standing dead leaves contributed equally to the other half. While spatial patterns and patch sizes of vegetation types and open water did not significantly influence the radiation budget at the landscape scale, it contributed to the large variability at the local scale. Such local variability of shortwave radiation may impact evapotranspiration and primary productivity at a range of scales. Therefore, the variation of radiation fluxes within single vegetation types potentially affects larger scale energy, water, and carbon fluxes.

Mapping interception of photosynthetically active radiation in sweet cherry orchards

Understanding interception of photosynthetically active radiation (PAR) of individual canopies could help advanced orchard management, thus, enhance fruit productivity and quality. The objective of this research was to develop a canopy PAR interception mapping method in Y-trellis trained sweet cherry orchards. A mobile measurement system was developed for continuously collecting constant spatial resolution PAR data at varying moving speeds. A mathematical model was developed to correct the distortion of the projected canopy shadow due to time of day and/or from orchard latitude. The mapping method was evaluated at both the dormant and full canopy stages. Digital images of 10 trees were used to validate the canopy projection correction method in each test. The measurement system achieved constant spatial resolution of 0.01m·sample−1 within the entire platform speed range of 0–3.8kmh−1. For dormant stage, the relative error in branch elevation angle comparison ranged from 0.1% to 9.6% with a mean of 3.4%±3.1%, and for full canopy stage, the relative error in canopy eccentricity ranged from 1.5% to 10.3% with a mean of 4.8%±2.6%. Combined, the results showed that the measurement system was capable of collecting high-density data with constant spatial resolution in orchards, and the canopy projection correction method can effectively correct the distortion in canopy maps caused by both imperfect sun zenith and azimuth angles at data collection. Light interception of individual tree canopies and the variation between/within canopies could be extracted from the corrected canopy maps, which should be useful for the advanced orchard management.

A Mobile Platform for Measuring Canopy Photosynthetically Active Radiation Interception in Orchard Systems

A mobile platform was developed for measuring midday canopy photosynthetically active radiation (PAR) interception in orchards. The results presented are for almond (Prunus dulcis) and walnut (Juglans regia), but the mobile platform can be used in other orchard crops as well. The mobile platform is adjustable to accommodate orchard row spacing from 4.8 to 7.8 m and is equipped with a global positioning satellite (GPS) receiver and radar for positional assessment as well as three IR thermometers for measuring soil surface temperature. Data from the mobile platform are logged at 10 Hz and stored on a data logger. Custom software has been developed to process the data. The mobile platform was used extensively for mapping midday canopy PAR interception in almond and walnut orchards in 2009 and 2010. The mobile platform produced comparable results to those collected with a handheld light bar with the advantage of being able to cover much larger areas and compare these data to mechanically harvested yield data over the same area. For almond orchards, midday canopy PAR interception peaked at ≈70% at an orchard age of ≈12 years. For walnut orchards, midday canopy PAR interception continued to increase to ≈15 years of age and peaked at a level above 80%. The mobile platform was also able to follow seasonal development of midday canopy PAR interception in young and mature orchards. This technology has potential for evaluating new varieties in terms of productivity per unit PAR intercepted, in evaluating hand pruning or mechanical hedging practices in terms of impact on PAR interception/productivity as well as evaluating effectiveness of insect or disease management treatments. It also has potential as a reference point for grower self-assessment to evaluate orchard canopy development compared with other orchards of similar variety, spacing, etc. Finally, this technology could be used as ground truth referencing for remotely sensed data.

Modelling leaf mass per area in forest canopy as affected by prevailing radiation conditions

Leaf mass per area (LMA) is a key leaf trait, which conditions the assessment of carbon balance and the adaptation of the species to their environment. LMA decreases exponentially within the canopy at a lower rate coefficient ( k LMA) than the extinction coefficient ( k PAR) of photosynthetically active radiation (PAR); consequently the canopy is not fully optimized for the carbon balance. A new algorithm to simulate LMA in forest canopies is developed. The algorithm is based on a relationship between LMA of leaves at a given canopy depth and PAR, that they absorb, during leaf growth. The LMA sub-model is then tested against independent experimental data to demonstrate its validity to assess (i) the LMA vertical distribution inside the canopy, (ii) its evolution during the season and (iii) the variability observed between sites, years and species. Then, the LMA sub-model is coupled with a process-based model simulating carbon, water and energy balances in forest ecosystem. The coupled model is applied to a sensitive analysis for a case study in a beech forest.

(320) Influence of Light Microclimate on the Growth, Yield, and Fruit Quality of Apple

Influence of photosynthetically active radiation (PAR) microclimate in the canopy of four training systems [open-center with high trunk (OH); open-center with middle trunk (OM); open-center with low trunk (OL); and a traditional round canopy (RC)] on the growth, yield and fruit quality of apple were studied in the Beijing area. The results showed that: 1) the growth and yield potential were affected by canopy light microclimate. The average leaf chlorophyll content from OH, OM and OL systems was 12.3% to 18.1% greater than that from the RC system. Trees from OH, OM, and OL systems produced 84.2% to 89.7% of shoot forming flower clusters compared to only 47.3% to 50.9% of the RC shoots. Training system did not affect total yield of 8-year-old trees, but in 10-year-old trees the RC system had lower yields compared with open-center systems. 2) Fruit quality was also affected by canopy light microclimate. The average anthocyanin content in the skin of fruit from OH, OM, and OL systems was 35.9% to 46.1% higher than that from the RC system, but chlorophyll content from the OL system was higher than in the open-center systems. Meanwhile, the contents of TSS and esters in apple flesh from the open-center systems were significantly higher than that from the RC system. 3) When the relative value of PAR in canopy exceeded 33.8%, the growth index of trees (chlorophyll: return-bloom ratio) exceeded 66.6% and the fruit quality index (TSS × anthocyanin) exceeded 94.7%. When PAR was less than 20.6%, the growth index was under 37.2% and the fruit quality index was under 67.5%. PAR value was significantly correlated with the growth and fruit quality index in the four training systems, and the total canopy volume of higher PAR(exceeding 33.8%, relative value) from OH, OM, and OL systems was 37.1% to 45.0% greater than that from the RC system.

Application of vertical skyward wide-angle photography and airborne video data for phenological studies of beech forests in the German Alps

Vertical skyward wide-angle photography, photosynthetically active radiation (PAR) measurements and analysis of leaf parameters were used as ground data for the assessment of phenological change of montane beech forest using airborne video data in the German Alps. The main objectives of the study were: (1) to test the feasibility of wide-angle photographs as ground data for remotely sensed data, (2) to evaluate the feasibility of airborne video data in a change detection study, and (3) to study the phenology of beech forests in different elevation zones to acquire information for regional photosynthesis and evapotranspiration studies. The results showed an increase in canopy closure from April to early June, no changes during the summer months, and a slow decrease in autumn. The results also showed a strong correlation between canopy closure estimation using the photographic method, PAR measurements, and leaf variables. The adjusted r 2 values between photographic canopy closure estimation and PAR ratio ranged from 0.72 to 0.88 and between canopy closure estimation and leaf size from 0.77 to 0.88. The problem of using photographic canopy closure estimation in phenological studies is that canopy closure is difficult to compare with spectral information of remote sensing data. The estimations had high correlation (r 2=0.71) only with the red band of the airborne data, while with green and the near-infrared (NIR) band the correlations were very weak.

Practical Field Methods of Estimating Canopy Cover, PAR, and LAI in Michigan Oak and Pine Stands

Abstract With the increased use of variables such as canopy cover, photosynthetically active radiation (PAR) and overstory leaf area index (LAI) in forestry research, relationships between these variables and traditional forestry variables must be defined before recommended levels of these research variables can be achieved by forestry practitioners on the ground. We measured basal area, canopy cover, Ozalid percent full light, PAR, and overstory LAI in thinned and unthinned plots within oak and pine stands with the objectives of: (1) determining the relationships between these variables in two common forest types, (2) investigating the feasibility of using basal area to estimate and achieve recommended levels of canopy cover, PAR, and LAI in the field, and (3) examining the possibility of using direct canopy cover and Ozalid light measurements for estimating PAR and LAI. Very strong relationships (r² &gt; 0.90 and P &lt; 0.0001) were indicated between basal area and canopy cover, PAR, and LAI. Direct canopy cover and Ozalid light measurements were also strongly related to PAR and LAI. It is likely that the even-aged structure of the stands studied contributed to these results. The strength of the relationships between the measures examined suggest that practical variables such as basal area could potentially be used by forestry practitioners to estimate and achieve recommended levels of canopy cover, PAR, and LAI in similar oak and pine stands. The possibility also exists for strong relationships between these variables in other stand types that resemble those studied in terms of overstory structure. North. J. Appl. For. 16(1):25-32.