Top Of Canopy Research Articles

An enhanced method for reconstruction of full SIF spectrum for near-ground measurements

Recently the applications of remotely sensed Solar-Induced chlorophyll Fluorescence (SIF) in the study of photosynthesis, stress conditions, and gross primary production have increased significantly. The full SIF spectrum spans over a spectral region of 650 ∼ 850 nm with two characteristic peaks around 685 nm and 740 nm. Over recent decades, many retrieval algorithms have been developed to estimate SIF at Top-Of-Canopy (TOC) using in-situ measurements of solar irradiance and canopy radiance spectra. Although the majority of retrieval methods retrieve SIF at a narrow spectral window, there exists a potential for retrieval of SIF in the full emission spectrum. Moreover, solar irradiance and canopy radiance spectra should ideally be measured at the same time but are usually measured sequentially with a certain time lag, raising potential errors in SIF retrieval. In this study, an enhanced retrieval algorithm of the full SIF spectrum at TOC is proposed. The proposed algorithm attempts to minimize the errors owing to time mismatch in measurements of solar irradiance and canopy radiance spectra. As an improvement to the previous algorithm (advanced Fluorescence Spectrum Reconstruction, aFSR), this proposed algorithm (aFSR-SVE) models the SIF-free contribution with principal components using the singular value decomposition technique. The optimal parameter settings in the forward model were determined for the experimental data collected by spectrometers used in the study. Firstly, the proposed algorithm was used to reconstruct full SIF spectrum for simulated data. The results were compared with known reference SIF values. After achieving satisfying results from simulated data, the proposed algorithm was compared with retrievals from established algorithms using experimental data. The results show improved SIF retrieval accuracy, without the need to simultaneously measure solar irradiance and canopy radiance spectra. The retrieval values comply with the results of previous algorithms in terms of spectral shape, diurnal trend, and temporal variations. The induced errors in SIF retrievals due to non-simultaneous measurements of solar irradiance and canopy radiance spectra were also investigated and the proposed algorithm was found to be less prone to such errors. Hence, the proposed algorithm is an improvement in reconstructing the full SIF spectrum with near-ground measurements. With the help of the proposed algorithm, field measurements using sequential systems and automated measurements of multiple targets can be performed effectively as it relaxes the requirement of concurrent measurement of solar irradiance and canopy radiance spectra. For future work, the applicability of this method can be investigated under more variable illumination conditions, like high cirrus clouds, passing clouds or persistent thin clouds.

Agronomic Evaluation and Yield Potentials of Grafting of Piper nigrum and Piper colobrinum

Foot rot disease (Phytophthora capsica) is Indonesia's primary challenge in cultivating pepper (Piper nigrum). Grafting to another Piper species, Piper coclobrinum, or melada (the local name), is a potential solution to increase resistance to this disease. The use of melada as rootstock has shown promising results during the seedling phase, but it has not been thoroughly evaluated during the production phase. The study was conducted in the pepper grower’s location in Puput and Simpang Katis Villages, Central Bangka, Bangka Belitung Islands Province. The study used kapok (Ceiba petandra) as the standard; plant morphology, leaf area, leaf thickness, and crown diameter for grafted melada and non-grafted pepper were recorded. Harvest variables included panicle length, panicle weight, the number of fruits per panicle, and fruit diameter, measured in three different areas of the canopy: the lower area (0-1 meter above the ground surface), the middle area (1-2 meters above the ground surface), and the top area (more than 2 meters above the ground surface). Physiological variables measured included rates of photosynthesis, stomatal conductance, transpiration rate, intercellular CO2, and CO2 conductance. The study demonstrated that the grafted pepper plants had a larger leaf area than the non-grafted pepper plants; the panicle weight and the number of fruits per panicle were higher. Panicles located in the middle zone of the plant canopy tended to be longer for grafted and non-grafted peppers. Panicle weight, fruit size, and the number of fruits per panicle were generally more significant at the top of the plant canopy. In all parts of the canopy, grafted peppers exhibited larger fruit size, greater panicle weight, and a higher number of fruits per panicle than non-grafted “Nyelungkup” peppers, highlighting the potential of melada as a rootstock for pepper plants.

A Wind Tunnel Test for the Effect of Seed Tree Arrangement on Wake Wind Speed

Changes in canopy structures caused by harvesting and regeneration practices can significantly alter the wind environment. Therefore, it is essential to understand the wind patterns influenced by seed tree arrangements for predicting seed dispersal by winds and ensuring the success of natural regeneration. This study aimed to identify how wind speed responds to seed tree arrangement designs with differing horizontal distances, vertical positions, and free-stream wind speeds. A wind tunnel test was conducted using pine saplings for a scale model of various seed tree arrangements, and the change in wake speed was tracked. The wake’s relative wind speed averaged 71%, ranging from 3.5% to 108.5%, depending on the seed tree arrangement, distance from saplings, and vertical position. It peaked within the patch of three seed trees compared to other arrangements and at the top canopy layer. The empirical function effectively described the wind speed reduction and recovery with distance from saplings. For instance, the minimum wind speed was reached at 0.6–2.2 times the canopy height, and a wind speed reduction of over 20% of the free-stream wind speed was maintained at a 1.6–7.6 canopy height. A negative relationship between the seed tree leaf area and the relative wind speed was observed only at the top canopy layer. This study presents empirical evidence on the patterns of wake winds induced by different types of heterogeneous canopy structures.

Improving the accuracy of SIF quantified from moderate spectral resolution airborne hyperspectral imager using SCOPE: assessment with sub-nanometer imagery

Hyperspectral imaging of solar-induced chlorophyll fluorescence (SIF) is required for plant phenotyping and stress detection. However, the most accurate instruments for SIF quantification, such as sub-nanometer (≤1-nm full-width at half-maximum, FWHM) airborne hyperspectral imagers, are expensive and uncommon. Previous studies have demonstrated that standard narrow-band hyperspectral imagers (i.e., 4–6-nm FWHM) are more cost-effective and can provide far-red SIF quantified at 760 nm (SIF760), which correlates strongly with precise sub-nanometer resolution measurements. Nevertheless, narrow-band SIF760 quantifications are subject to systematic overestimation owing to the influence of the spectral resolution (SR). In this study, we propose a modelling approach based on the Soil Canopy Observation, Photochemistry and Energy Fluxes (SCOPE) model with the objective of enhancing the accuracy of absolute SIF760 levels derived from standard airborne hyperspectral imagers in practical settings. The performance of the proposed method was evaluated using airborne imagery acquired from two airborne hyperspectral imagers (FWHM ≤ 0.2-nm and 5.8-nm) flown in tandem on board an aircraft that collected data from two different wheat and maize phenotyping trials. Leaf biophysical and biochemical traits were first estimated from airborne narrow-band reflectance imagery and subsequently used as SCOPE model inputs to simulate a range of top-of-canopy (TOC) radiance and SIF spectra at 1-nm FWHM. The SCOPE simulated radiance spectra were then convolved to match the spectral configuration of the narrow-band imager to compute the 5.8-nm FWHM SIF760. A site-specific model was constructed by employing the convolved 5.8-nm SR SIF760 as the independent variable and the 1-nm SR SIF760 directly simulated by SCOPE as the dependent variable. When applied to the airborne dataset, the estimated SIF760 at 1-nm SR from the standard narrow-band hyperspectral imager matched the reference sub-nanometer quantified SIF760 with root mean square error (RMSE) less than 0.5 mW/m2/nm/sr, yielding R2 = 0.93–0.95 from the two experiments. These results suggest that the proposed modelling approach enables the interpretation of SIF760 quantified using standard hyperspectral imagers of 4–6 nm FWHM for stress detection and plant physiological condition assessment.

Validation and Error Minimization of Global Ecosystem Dynamics Investigation (GEDI) Relative Height Metrics in the Amazon

Global Ecosystem Dynamics Investigation (GEDI) is a relatively new technology for global forest research, acquiring LiDAR measurements of vertical vegetation structure across Earth’s tropical, sub-tropical, and temperate forests. Previous GEDI validation efforts have largely focused on top of canopy accuracy, and findings vary by geographic region and forest type. Despite this, many applications utilize measurements of vertical vegetation distribution from the lower canopy, with a wide diversity of uses for GEDI data appearing in the literature. Given the variability in data requirements across research applications and ecosystems, and the regional variability in GEDI data quality, it is imperative to understand GEDI error to draw strong inferences. Here, we quantify the accuracy of GEDI relative height metrics through canopy layers for the Brazilian Amazon. To assess the accuracy of on-orbit GEDI L2A relative height metrics, we utilize the GEDI waveform simulator to compare detailed airborne laser scanning (ALS) data from the Sustainable Landscapes Brazil project to GEDI data collected by the International Space Station. We also assess the impacts of data filtering based on biophysical and GEDI sensor conditions and geolocation correction on GEDI error metrics (RMSE, MAE, and Bias) through canopy levels. GEDI data accuracy attenuates through the lower percentiles in the relative height (RH) curve. While top of canopy (RH98) measurements have relatively high accuracy (R2 = 0.76, RMSE = 5.33 m), the accuracy of data decreases lower in the canopy (RH50: R2 = 0.54, RMSE = 5.59 m). While simulated geolocation correction yielded marginal improvements, this decrease in accuracy remained constant despite all error reduction measures. Some error rates for the Amazon are double those reported in studies from other regions. These findings have broad implications for the application of GEDI data, especially in studies where forest understory measurements are particularly challenging to acquire (e.g., dense tropical forests) and where understory accuracy is highly important.

Numerical investigation of a three-dimensional flow structure influenced by the lateral expansion of a partially distributed submerged canopy

This study employed numerical simulations to investigate the three-dimensional hydrodynamic structure of a channel obstructed by submerged rigid canopies. After validating the model using existing experimental data, a series of numerical experiments varying the canopy density and the blocking ratio were conducted. The results indicate that submerged canopy, different from emergent canopies, triggers the generation of three-dimensional coherent vortices. When canopies expand laterally, the scale, location, and evolution characteristics of cross-sectional secondary flows vary. The direction of secondary circulation at the canopy top of the fully covered vegetation channel is affected by the river width/depth ratio. Three-dimensional coherent vortices are jointly controlled by vertical and transverse Reynolds stresses. When the channel is seriously blocked, the degree of momentum exchange in the mixing layer does not change significantly. The boundary friction effect dominates the momentum exchange process near the wall. An equation coupling the drag length scale and blocking ratio with the vertical coherent vortex penetration length is proposed, indicating that the penetration length increases exponentially with both variables. Higher canopy density exhibits a stronger resistance to the vertical coherent vortex penetration length. In the process of canopy lateral expansion, the evolution time of the outer vortex to scale stability is longer than that of the inner vortex. The significance of research on the three-dimensional vortex structure of rigid submerged vegetation is established based on previous studies and existing conclusions.

Evaluating airborne, mobile and terrestrial laser scanning for urban tree inventories: A case study in Ghent, Belgium

In urban tree inventories, structural measurements such as diameter at breast height (DBH), tree height (H), crown projection area (CPA) and crown volume (CV) are essential for diverse applications, including accurate ecosystem service estimation and management decisions. Traditionally, tree measurements are obtained using range finders and diameter tape. These measurements can be integrated into urban tree inventories through 3D laser scanning (also known as LiDAR). Multiple platforms for laser scanning exist, each with its own advantages and disadvantages, which have not yet been compared explicitly for urban tree inventories. We collected terrestrial laser scanning (TLS), mobile laser scanning (MLS) and airborne laser scanning (ALS) in leaf-on (TLS, MLS, ALS) and leaf-off conditions (TLS, MLS) in Ghent, Belgium. We evaluated the DBH, H, CPA and CV of 95 individual trees acquired from each acquisition platform, benchmarking against TLS. Our results show accurate DBH derivation from both TLS and MLS (bias < 2 cm, concordance correlation coefficient (CCC) ≈ 1). However, during leaf-on conditions, occlusion from shrubs and ivy is observed. For leaf-on MLS, point clouds of large trees exhibited occlusion in the top canopy, impacting crown volume (CV MLS leaf-on: bias = −116 m², CCC=0.85) and, to a lesser extent, tree height (H MLS leaf-on: bias = −0.38 m, CCC=0.99). Crown projected area was less affected (bias = 0.49 m², CCC=0.99), with differences more attributed to varying point precision among sensors. The difference between the metric and benchmark increased with tree size and the structural complexity of the surroundings (e.g. buildings), especially for MLS, for which limited GNSS coverage, traffic, and suboptimal walking patterns impeded ideal data collection. Our results will help city councils and tree managers choose the most optimal LiDAR platform for urban tree inventories, accounting for their purpose, site complexity and budget.

Morning Transition of the Coupled Vegetation Canopy and Atmospheric Boundary Layer Turbulence according to the Wind Intensity

Abstract Turbulence in canopy plays a crucial role in biosphere–atmosphere exchanges. Traditionally, canopy turbulence has been analyzed under stationary conditions based on atmospheric thermal stability, disregarding the time of the day and the atmospheric boundary layer (ABL) depth, although recent studies have suggested that daytime canopy turbulence might be influenced by ABL-scale motions. The morning transition offers an intriguing period when the ABL grows and when an increasing influence of large-scale motions on canopy turbulence might be anticipated. Using large-eddy simulations resolving both canopy and ABL turbulence, we investigate here how the turbulence and exchanges at the canopy top change along the morning transition according to the wind intensity. Under significant wind, simulations show that canopy turbulence and exchanges are dominated by mixing-layer-type motions whose characteristics remain constant during the morning transition even though ABL-scale motions imprint on the canopy’s instantaneous velocity fields as the ABL grows. Under low wind, the canopy turbulence is dominated by plumes, whose horizontal sizes extend with the ABL, while their vertical sizes reach a limit before the morning transition ends. In the early morning, canopy-top exchanges are influenced by sources from both the canopy top and the ABL entrainment zone, explaining some of the dissimilarity in turbulent transport between scalars, apart from the differences in the location of canopy scalar sources. When reaching the residual layer, the ABL grows quicker, with intense water vapor and carbon dioxide exchanges, dominated by large-scale motions penetrating deep within the canopy, releasing into the atmosphere the nocturnal accumulated carbon dioxide.

Plant Growth Regulators Enhance Maize (Zea mays L.) Yield under High Density by Optimizing Canopy Structure and Delaying Leaf Senescence

Shaping the canopy architecture and delaying leaf senescence in maize are pivotal strategies for extending the crop’s photosynthetic period and improving yield. The application of plant growth regulators (PGRs) is a critical cultivation measure, with the timing of application being of paramount importance. To explore the effects of PGR application time on maize canopy structure, leaf senescence characteristics and yield, a comparative two-year field study was undertaken during the 2019–2020 growing seasons at the Gongzhuling Experimental Station of the Jilin Academy of Agricultural Sciences, utilizing a PGR containing ethephon as the active ingredient. The experiment was structured with two plant densities of 60,000 and 90,000 plants ha−1, and three distinct PGR application protocols: T10 (application of PGR at the 10th leaf stage), T15 (application at the 15th leaf stage), and CK (control group sprayed with water). The result indicated that the yield increased by 5.62% following T15 treatment compared to the CK under high density (90,000 plants ha−1). Furthermore, the kernel per ear and the 1000-kernel weight increased by 3.93% and 5.62% respectively, while the abortion rate decreased. Correlation analysis showed that yield and yield components were correlated with plant morphology, physiology, and aging characteristics under 90,000 plants ha−1. Pollen density was also positively correlated with the top leaf area and the top leaf angle (p &lt; 0.01). Furthermore, relative green leaf area at maturity (RGLAM) showed positive correlations with chlorophyll b, superoxide dismutase activity (SOD), peroxidase activity (POD), catalase activity (CAT), and soluble protein content (p &lt; 0.01), while displaying a negative correlation with malondialdehyde content (MDA) (p &lt; 0.01). Spraying plant growth regulators at the 15-leaf stage under high density can effectively enhance the top canopy structure of the maize and reduce the upper leaf area and angle, increase pollen density, and boost the number of grains. Furthermore, it delayed the senescence of leaves, prolonged the functional period of the leaves, increased kernel weight, optimized light resource utilization, and ultimately enhanced the maize yield.

Downscaling canopy photochemical reflectance index to leaf level by correcting for the soil effects

The photochemical reflectance index (PRI) is a promising remote sensing signal for monitoring vegetation physiology. Variations in leaf PRI are usually attributed to either the energy-dependent xanthophyll cycle or the carotenoid-chlorophyll ratio, both indicative of leaf physiology. However, canopy PRI is subject to soil, canopy structure, and incident and viewing angles, and thus has a weaker and more complicated relationship with vegetation photosynthetic activity or leaf pigment composition. Therefore, downscaling canopy PRI to the leaf level is essential for accurate remote sensing of vegetation physiology using PRI. An earlier investigation (P.Yang, RSE, 279, 113,133, 2022) illustrates that structural and angular variations in canopy PRI primarily result from varying degrees of soil interference. In this study, a soil correction method is proposed to mitigate the soil effects on top-of-canopy (TOC) reflectance at the PRI bands. The soil effects on TOC reflectance at 531 nm and 570 nm are respectively estimated as R531soil×R675/R675soil and R570soil×R675/R675soil, where R675 is TOC red reflectance, Rλsoil soil reflectance at wavelengthλ. R675/R675soil approximates the fraction of the observed sunlit soil, as leaves are nearly black at 675 nm due to strong absorption of chlorophyll, and R675 is mainly contributed from soil. To assess the effectiveness of the soil correction method, a wheat field dataset, a corn field dataset, and a simulated dataset, were utilized. The soil-adjusted and the original canopy PRI were compared with the leaf PRI for the real and synthetic scenarios that had various soil brightness, leaf chlorophyll content and canopy structure. Both the field and numerical experiments demonstrate that, for the canopies with low vegetation coverage and substantial soil contamination, the original canopy PRI was largely different from the leaf PRI, displaying substantial structural and angular dependence. In comparison, the soil-adjusted canopy PRI was more closely aligned with the PRI observed in the sunlit leaves in all three datasets. This study shows that accounting for the soil effects with TOC red reflectance allows downscaling canopy PRI to the leaf level. The soil-adjusted canopy PRI contributes to remote sensing of the xanthophyll cycle or the carotenoid-chlorophyll ratio from canopy PRI.

Numerical Investigation of Observational Flux Partitioning Methods for Water Vapor and Carbon Dioxide

AbstractWhile yearly budgets of CO2 flux (Fc) and evapotranspiration (ET) above vegetation can be readily obtained from eddy‐covariance measurements, the separate quantification of their soil (respiration and evaporation) and canopy (photosynthesis and transpiration) components remains an elusive yet critical research objective. In this work, we investigate four methods to partition observed total fluxes into soil and plant sources: two new and two existing approaches that are based solely on analysis of conventional high frequency eddy‐covariance (EC) data. The physical validity of the assumptions of all four methods, as well as their performance under different scenarios, are tested with the aid of large‐eddy simulations, which are used to replicate eddy‐covariance field experiments. Our results indicate that canopies with large, exposed soil patches increase the mixing and correlation of scalars; this negatively impacts the performance of the partitioning methods, all of which require some degree of uncorrelatedness between CO2 and water vapor. In addition, best performances for all partitioning methods were found when all four flux components are non‐negligible, and measurements are collected close to the canopy top. Methods relying on the water‐use efficiency (W) perform better when W is known a priori, but are shown to be very sensitive to uncertainties in this input variable especially when canopy fluxes dominate. We conclude by showing how the correlation coefficient between CO2 and water vapor can be used to infer the reliability of different W parameterizations.

Investigating Fire–Atmosphere Interaction in a Forest Canopy Using Wavelets

Wildland fire–atmosphere interaction generates complex turbulence patterns, organized across multiple scales, which inform fire-spread behaviour, firebrand transport, and smoke dispersion. Here, we utilize wavelet-based techniques to explore the characteristic temporal scales associated with coherent patterns in the measured temperature and the turbulent fluxes during a prescribed wind-driven (heading) surface fire beneath a forest canopy. We use temperature and velocity measurements from tower-mounted sonic anemometers at multiple heights. Patterns in the wavelet-based energy density of the measured temperature plotted on a time–frequency plane indicate the presence of fire-modulated ramp–cliff structures in the low-to-mid-frequency band (0.01–0.33 Hz), with mean ramp durations approximately 20% shorter and ramp slopes that are an order of magnitude higher compared to no-fire conditions. We then investigate heat- and momentum-flux events near the canopy top through a cross-wavelet coherence analysis. Briefly before the fire-front arrives at the tower base, momentum-flux events are relatively suppressed and turbulent fluxes are chiefly thermally-driven near the canopy top, owing to the tilting of the flame in the direction of the wind. Fire-induced heat-flux events comprising warm updrafts and cool downdrafts are coherent down to periods of a second, whereas ambient heat-flux events operate mainly at higher periods (above 17 s). Later, when the strongest temperature fluctuations are recorded near the surface, fire-induced heat-flux events occur intermittently at shorter scales and cool sweeps start being seen for periods ranging from 8 to 35 s near the canopy top, suggesting a diminishing influence of the flame and increasing background atmospheric variability thereat. The improved understanding of the characteristic time scales associated with fire-induced turbulence features, as the fire-front evolves, will help develop more reliable fire behaviour and scalar transport models.

Forest top canopy bacterial communities are influenced by elevation and host tree traits

BackgroundThe phyllosphere microbiome is crucial for plant health and ecosystem functioning. While host species play a determining role in shaping the phyllosphere microbiome, host trees of the same species that are subjected to different environmental conditions can still exhibit large degrees of variation in their microbiome diversity and composition. Whether these intra-specific variations in phyllosphere microbiome diversity and composition can be observed over the broader expanse of forest landscapes remains unclear. In this study, we aim to assess the variation in the top canopy phyllosphere bacterial communities between and within host tree species in the temperate European forests, focusing on Fagus sylvatica (European beech) and Picea abies (Norway spruce).ResultsWe profiled the bacterial diversity, composition, driving factors, and discriminant taxa in the top canopy phyllosphere of 211 trees in two temperate forests, Veluwe National Parks, the Netherlands and Bavarian Forest National Park, Germany. We found the bacterial communities were primarily shaped by host species, and large variation existed within beech and spruce. While we showed that there was a core microbiome in all tree species examined, community composition varied with elevation, tree diameter at breast height, and leaf-specific traits (e.g., chlorophyll and P content). These driving factors of bacterial community composition also correlated with the relative abundance of specific bacterial families.ConclusionsWhile our results underscored the importance of host species, we demonstrated a substantial range of variation in phyllosphere bacterial diversity and composition within a host species. Drivers of these variations have implications at both the individual host tree level, where the bacterial communities differed based on tree traits, and at the broader forest landscape level, where drivers like certain highly plastic leaf traits can potentially link forest canopy bacterial community variations to forest ecosystem processes. We eventually showed close associations between forest canopy phyllosphere bacterial communities and host trees exist, and the consistent patterns emerging from these associations are critical for host plant functioning.

Harsh environmental conditions promote cooperative behavior in an epiphytic fern

ABSTRACT Harsh, unpredictable environments are known to favor cooperative groups in animals. Whether plants exhibit similar relationships is unknown. Staghorn ferns (Platycerium bifurcatum, Polypodiaceae) are epiphytes that form cooperative groups which build communal water and nutrient ‘nests’ at the tops of trees, a habitat characterized by water and nutrient stress. We conducted field observations to test whether staghorn ferns continue to live in large, reproductively active groups after they become dislodged from the canopy and fall to the forest floor, where they are less limited by water and nutrient deprivation. To rule out the potentially confounding effects of light limitation on the forest floor, we also conducted a multi-year glasshouse experiment where we transplanted individual plants into soil and onto vertically oriented boards under standardized light conditions. Results from field observations showed that dislodged colonies formed smaller groups that reproduced less than epiphytic colonies. Results from the glasshouse experiment showed that even when growing in full sun, terrestrial individuals tended to remain solitary, while epiphytic individuals tended to recruit new individuals into colonies. Results also showed that plants growing in potting soil and exposed to full sunlight sporulated more heavily than plants growing epiphytically. However, localities that are characterized by both elevated soil and light resources are generally not available to staghorn ferns in the wild, perhaps with the exception of large, epiphytic colonies with well-developed nests at the top of tree canopies. Overall results indicate that the harsh environmental conditions at the tops of trees trigger the formation of colonies in staghorn ferns, similarly to group living animals.

Assessment of Temperate Deciduous Forest Communities and Structures after Restoration through the Multi-Reference Ecosystems Framework

The reference forest serves as a model for forest ecosystem restoration and can be employed to assess the vegetation of the Restored Forest, thereby confirming the success of restoration. When evaluating restoration, employing multireference forests is advantageous for discerning gradual changes in Restored Forests. However, in previous studies, their utilization has been limited to comparisons with individual ecosystems. Therefore, this study investigates the status of Restored Forests in previously damaged areas and their resemblance to reference forests across four forest types, namely Climax Forest (CF), Secondary Forest (SF), Restored Forest (RF), and Planted Forest (PF). Reference forests, serving as model targets for restoration, include CF and SF, while RF and PF represent the restoration forests. Six target sites within two temperate deciduous forests (Quercus acutissima and Quercus variabilis) were selected, and a comparative analysis of species diversity, dominance, and evenness was conducted. This study revealed that the dominant species in the top canopy of restoration forests mirrored those in reference forests, with Q. variabilis and Q. acutissima being prevalent. A similarity index of over 60% and a high correlation of 0.987 were observed in the top canopy layer between the reference and restored ecosystems (CF-RF/SF-PF). These findings enhance our understanding of the current status of Restored Forests and advocate for the utilization of multiple reference forests for successful restoration efforts.

A SIF-based approach for quantifying canopy photosynthesis by simulating the fraction of open PSII reaction centers (qL)

Advances in retrieval of solar-induced chlorophyll fluorescence (SIF) provide a promising and independent approach for quantifying gross primary production (GPP) across spatial scales. Recent studies have highlighted the prominent role of qL, the fraction of open Photosystem II (PSII) reaction centers, in mechanistically modeling GPP from remote sensing SIF. However, due to the limited availability of simulated and experimental data, a comprehensive understanding of qL responses to environmental and physiological variations has yet to emerge, and as a consequence, prediction of qL across leaf and canopy scales is still in an early stage. Based on a global sensitivity analysis of a recently developed mechanical model of photosynthesis, we find that the broadband total SIF emitted from PSII (SIFTOT_FULL_PSII) and leaf temperature (TLeaf) are the two major predictors of qL. A leaf-level instrument is designed to obtain concurrent measurements of qL, SIFTOT_FULL_PSII, and TLeaf over a wide range of environmental conditions. From these measurements, we show that qL can be modelled as a hyperbolic function of SIFTOT_FULL_PSII with only one temperature-related parameter m which increases with temperature, but decreases rapidly as temperatures exceed the optimum temperature. It is suggested that m can be mathematically modelled by a peaked function. The results of the leaf-level experiments on winter wheat demonstrate that the proposed model predicts qL with high accuracy (R2 ≥ 0.91, rRMSE ≤ 8.46%) under diverse light and temperature conditions. The essential steps necessary to apply it at canopy scale, including estimating the escape fraction, removing fluorescence emitted from Photosystem I, and reconstructing SIFTOT_FULL_PSII from top-of-canopy (TOC) narrowband SIF, are also presented. Our results confirm that estimated GPP using SIF-informed qL agrees well with measured GPP at a winter wheat site (R2 = 0.81, rRMSE = 12.03%). The key benefit of SIF-informed approach is that SIFTOT_FULL_PSII provides critical information on the collective influence of the sub-canopy light environment on qL, avoiding the requirement to explicitly estimate qL at different canopy depths, potentially promoting the ability of SIF to mechanistically quantify photosynthetic CO2 assimilation at large scales.

Vegetation moisture estimation in the Western United States using radiometer-radar-lidar synergy

Monitoring vegetation moisture conditions is paramount to better understand and assess drought impacts on vegetation, enhance crop yield predictions, and improve ecosystem models. Passive microwave remote sensing allows retrievals of the vegetation optical depth (VOD; [unitless]), which is directly proportional to the vegetation water content (VWC; in units of water mass per unit area [kg/m2]). However, VWC is largely dependent on the dry biomass and structure imprints on the VOD signal. Previously, statistical models have been used to isolate the water component from the biomass and structure components. Physically-based approaches have not yet been proposed for this goal. In this study, we present a multi-sensor semi-physical approach to retrieve the vegetation moisture from the VOD and express it as Live Fuel Moisture Content (LFMC [%]; the percentage of water mass per dry biomass unit). The study is performed in the western United States for the period April 2015 – December 2018. There, in situ LFMC samples are available for assessment. We rely on a VOD model based on vegetation height data from GEDI/Sentinel-2 and radar backscatter from Sentinel-1, which account for the biomass and structure components. Vegetation moisture is retrieved at L-, X- and Ku-bands by minimizing the difference between the modeled VOD and the VOD estimates from SMAP (L-band) and AMSR-2 (X- and Ku-band) satellites. Results show that the LFMC retrievals are independent of canopy height, land cover, and radar backscatter, demonstrating the capability of the proposed algorithm to separate water dynamics from the biomass/structure component in VOD. LFMC estimates at X- and Ku-bands reproduce well the expected spatio-temporal dynamics of in situ LFMC. Results show good agreement with in situ at a regional scale, with Pearson's correlations (r) between in situ LFMC samples and LFMC estimates of 0.64 (Ku-band), 0.60 (X-band) and 0.47 (L-band). Similar results are obtained independently for shrub and forest sites at X- and Ku-bands. In most comparisons between in situ and estimated LFMC, biases are below 10% of the dynamic range of LFMC. Performance at L-band is limited by the fact that this frequency senses the full vertical extent of the canopy, while in situ samples are taken only from top of canopy leaves to which X- and Ku-bands are much more sensitive. More insight will be needed for grasslands (r = 0.44 at X-band) using time-dynamic canopy height data. Furthermore, a pixel-scale assessment is conducted, showing a good agreement in most sites (r > 0.6). The proposed method can be tailored to exploit the synergies of past (e.g., AMSR-E), current (e.g., AMSR-2) and future satellite sensors such as CIMR and ROSE-L for global vegetation moisture mapping at different canopy layers.

Drivers of deciduous forest near-infrared reflectance: A 3D radiative transfer modeling exercise based on ground lidar

The fraction of near infrared (NIR) solar energy reflected by forest canopies has been shown to correlate with leaf nitrogen availability and photosynthesis. But the canopy properties behind this relation are unclear, partly because whole canopy reflectance and albedo results from multiple complex interactions between photons and tree parts, and also because modeling these interactions has been challenging due to difficulties in representing forest canopies with sufficient detail. Ground lidar technology has been applied to this problem in recent years; it is used here to provide highly detailed forest canopy representations as inputs into a ray tracing radiative transfer model. These structural representations are coupled with the best available field data on leaf optical properties to produce simulated images of canopy reflectance in the NIR, as well as the detailed 3D mapping of NIR energy absorption within the canopy. The simulations performed for two deciduous forests in the northeastern USA were first compared to airborne hyperspectral observations to assess their accuracy. The radiative transfer model was then used to quantify the sensitivity of whole canopy reflectance and vertical absorption of NIR to changes in model parametrization in an attempt to identify the main drivers of canopy reflectance. The results point to the arrangement of leaves in the topmost canopy layers, both in terms of leaf angles and leaf clumping within shoots, and to the leaf-level absorptance in all canopy layers as the dominant factors affecting canopy reflectance and albedo. These findings emphasize the need for improving our understanding of leaf arrangement in canopy tops – including what it covaries with – and for including measurements of leaf transmission when measuring leaf spectral properties in the field.

Differential Tree Growth Response to Management History and Climate in Multi-Aged Stands of Pinus pinea L.

The possible differential response to the climatic fluctuations of co-occurring trees of different ages is still poorly known and rather controversial. Moreover, in managed forests, such a picture is further complicated by the impact of silvicultural practices. With this concern, in a multi-aged umbrella pine stand in the Maremma Regional Park (Tuscany, Italy), the spatial patterns and tree-ring response to the climate were investigated by differentiating trees into three classes, i.e., young, mature, and old. The aim was to assess the role of past management in shaping the current stand structure and affecting the growth dynamics at different ages, as well as to evaluate the possible shifting of tree adaptation to the climatic variables throughout plant aging. Our outcomes proved that the current mosaic of even-aged small patches results from a multifaceted forest management history. Until the 1960s, silvicultural treatments seemed more suitable in promoting tree growth and regeneration. Later on, inappropriate and/or untimely thinning probably triggered excessive competition from the top canopy trees, involving reduced stem and root system development in the younger plants living in the understory. Also, the intra-annual growth response to the climate showed some dependence on age. Younger trees are assumed not to be able to efficiently exploit water resources from the deep aquifer during the dry season, probably due to an insufficiently developed taproot, differently than older trees. Accordingly, appropriate and timely thinning, simulating frequent natural disturbances on small areas, could be a suitable management approach to promote sustained growth rates and regeneration processes, as well as healthy and vital trees at all life stages.

Future of Transparent Wood: A Preliminary Review

The wood has unique structure and excellent mechanical properties. Wood is important natural source for human civilization. Wood is anisotropy structure. Wood was the important material and natural resource in human civilization. Wood is widely used in many sectors such as building, fuel, tools and other. In the ancient, wood played an important role in human cultural, economic, act and building. As a natural and sustainable material, wood has excellent mechanical properties cause by unique structures relative to its cost. Wood due to its natural growth can define as renewable and sustainable material. Due to the hierarchical and anisotropy structure, wood have properties of high strength, good durability, high moisture content and high strength. Wood is porous and fibrous structural tissue of wood. Roots and stems of wood made by natural cellulose fibres growing upward all the way to the top of canopy. This paper will present a preliminary review about the future of transparent wood.