Hemispherical Photography Research Articles

Natural and Anthropogenic Variation of Stand Structure and Aboveground Biomass in Niger Delta Mangrove Forests

Mangrove forests are important coastal wetlands because of the ecosystem services they provide especially their carbon potential. Mangrove forests productivity in the Niger Delta are poorly quantified and at risk of loss from oil pollution, deforestation, and invasive species. Here, we report the most extensive stem girth survey yet of mangrove plots for stand and canopy structure in the Niger Delta, across tidal and disturbance gradients. We established twenty-five geo-referenced 0.25-ha plots across two estuarine basins. We estimated aboveground biomass (AGB) from established allometric equations based on stem surveys. Leaf area index (LAI) was recorded using hemispherical photos. We estimated a mean AGB of 83.7 Mg ha–1 with an order of magnitude range, from 11 to 241 Mg ha–1. We found significantly higher plot biomass in close proximity to a protected site and tidal channels, and the lowest in the sites where urbanization and wood exploitation was actively taking place. The mean LAI was 1.45 and ranged fivefold from 0.46 to 2.41 and there was a significant positive correlation between AGB and LAI (R2 = 0.31). We divided the plots into two disturbance regimes and three nipa palm (Nypa fruticans) invasion levels. Lower stem diameter (5–15 cm) accounted for 70% of the total biomass in disturbed plots, while undisturbed regimes had a more even (∼25%) contribution of different diameter at breast height (DBH) size classes to AGB. Nipa palm invasion also showed a significant link to larger variations in LAI and the proportion of basal area removed from plots. We conclude that mangrove forest degradation and exploitation is removing larger stems (>15 cm DBH), preferentially from these mangroves forests and creates an avenue for nipa palm colonization. This research identifies opportunities to manage the utilization of mangrove resources and reduce any negative impact. Our data can be used with remote sensing to estimate biomass in the Niger Delta and the inclusion of soil, leaf properties and demographic rates can analyze mangrove-nipa competition in the region.

Electromagnetic Induction Is a Fast and Non-Destructive Approach to Estimate the Influence of Subsurface Heterogeneity on Forest Canopy Structure

The spatial forest structure that drives the functioning of these ecosystems and their response to global change is closely linked to edaphic conditions. However, the latter properties are particularly difficult to characterize in forest areas developed on karst, where soil is highly rocky and heterogeneous. In this work, we investigated whether geophysics, and more specifically electromagnetic induction (EMI), can provide a better understanding of forest structure. We use EMI (EM31, Geonics Limited, Ontario, Canada) to study the spatial variability of ground properties in two different Mediterranean forests. A naturally post-fire regenerated forest composed of Aleppo pines and Holm oaks and a monospecific plantation of Altlas cedar. To better interpret EMI results, we used electrical resistivity tomography (ERT), soil depth surveys, and field observations. Vegetation was also characterized using hemispherical photographs that allowed to calculate plant area index (PAI). Our results show that the variability of ground properties contribute to explaining the variability in the vegetation cover development (plant area index). Vegetation density is higher in areas where the soil is deeper. We showed a significant correlation between edaphic conditions and tree development in the naturally regenerated forest, but this relationship is clearly weaker in the cedar plantation. We hypothesized that regular planting after subsoiling, as well as sylvicultural practices (thinning and pruning) influenced the expected relationship between vegetation structure and soil conditions measured by EMI. This work opens up new research avenues to better understand the interplay between soil and subsoil variability and forest response to climate change.

Stemflow and throughfall on several tree architectural models

The aim of developing urban forests for steep areas is to prevent erosion. Erosion can be caused by stemflow and throughfall. The difference in stemflow and throughfall is thought to be due to differences in the tree architecture model. The study investigates the effects of several tree architectural models on the amount of stemflow and throughfall. It is hoped that data and information of this research can be taken into consideration in selecting tree species for the benefit of soil and water conservation in urban forest areas that have the potential for erosion and sedimentation. The collection and processing of data comprised the rainfall data obtained from Meteorological Climatological and Geophysical Agency, measurement of leaf area index using a hemispherical photograph and Hemiview 2.1 software, measurement of stemflow and throughfall in five tree architectural models (Massart, Aubreville, Koriba, Rauh, and Troll). Afterward, the relationship between the dependent and independent variables is known through multiple linear regression analysis using Minitab 16 software. The result showed that the tree architectural model influences stemflow and throughfall. The tree architectural model with the highest stemflow and throughfall is Rauh, and the lowest belongs to the Massart architectural model. The tree architectural model that can be used for land and water conservation is Massart; the species is Diospyros discolor Willd.

Percentage of Mangrove Canopy Cover and Mollusks Abundance in Benoa Bay Mangrove Ecosystem

This research was conducted to determine the condition of the mangrove ecosystem based on its canopy cover and to determine the types of mollusks (Bivalves and Gastropods) associated with the Benoa Bay mangrove ecosystem. Hemispherical photography is a method for observing mangrove canopy cover and line transect method for mollusks. The composition of mangrove species found in the research location were five species, namely Rhizophora stylosa, Rhizophora mucronata, Rhizophora apiculata, Bruguiera gymnorrhiza, and Avicennia marina. The percentage of mangrove canopy cover in the Benoa Bay mangrove ecosystem is in a good category (average = 76.59%). There are eight types of mollusks found in the research location. There are two types of bivalves (Polymesoda bengalensis and Gafrarium pectinatum) and six types of gastropods (Nerita balteata, Nerita picea, Neritina turrita, Pila ampullacea, Cassidula aurisfelis, and Littoraria melanostoma). The relationship between the percentage of mangrove canopy cover and abundance of mollusks in the Benoa Bay mangrove ecosystem is very strong (r) of 0.920. The higher the percentage value of mangrove canopy cover, the higher the mollusks abundance.

Changes in Long-Term Light Properties of a Mixed Conifer—Broadleaf Forest in Southwestern Europe

Natural and anthropogenic factors affect forest structure worldwide, primarily affecting forest canopy and its light properties. However, not only stand-replacing events modify canopy structure, but disturbances of lower intensity can also have important ecological implications. To study such effects, we analyzed long-term changes in light properties of a conifer–broadleaf mixed forest in the Southwestern Pyrenees, placed in the fringe between the Mediterranean and Eurosiberian biogeographical regions. At this site, a thinning trial with different intensities (0%, 20%, and 30–40% basal area removed) took place in 1999 and 2009, windstorms affected some plots in 2009 and droughts were recurrent during the sampling period (2003, 2005, 2011). We monitored light properties during 14 years (2005–2019) with hemispherical photographs. We applied partial autocorrelation functions to determine if changes between years could be attributed to internal canopy changes or to external disturbances. In addition, we mapped the broadleaf canopy in 2003, 2008, and 2016 to calculate broadleaf canopy cover and richness at the sampling points with different buffer areas of increasing surface. We applied generalized linear mixed models to evaluate the effects of light variables on canopy richness and cover. We found that light variables had the most important changes during the period 2008 to 2010, reacting to the changes caused that year by the combined effects of wind and forest management. In addition, we found that an area of 4.0 m radius around the sampling points was the best to explain the relationship between light properties and species richness, whereas a radius of 1.0 m was enough to estimate the relationship between light and canopy cover. In addition, light-related variables such as diffuse light and leaf area index were related to species richness, whereas structural variables such as canopy openness were related to canopy cover. In summary, our study demonstrates that non stand-replacing disturbances such as windstorms, thinning, or droughts can have an important role in modifying structural and light-related canopy properties, which in turn may influence natural processes of stand development and ecological succession.

Continuous Parameterization of Leaf Area Index and Phenological Phases Within Deciduous Forests Based on Temperature Measurements

The Leaf-Area-Index (LAI) is commonly used to characterize the plant canopy and is a fundamental indication of plant vitality and photosynthetic activity. The forest health status is not only vital for economical reasons, but also has a significant impact on global carbon sequestration. The LAI has a highly dynamic character among deciduous forests and is prone to significant seasonal fluctuations. Accurate continuous LAI measurements do provide valuable information on growth characteristics, but they require considerable measurement effort. In this study, we tested a novel method that would allow for continuous low-effort LAI parameterizations. For our study we used temperature measurements from 2011 to 2019 obtained at two meteorological stations: Station one is an open land station, station two is located inside a forest stand characterized by European beech (measurements were undertaken as part of the ICP Forests program), both are located in Klausen Leopoldsdorf (Austria). We chose the difference in daily maximum temperature between the two sites for our LAI parametrization (LAIpar) since the forest canopy has a significant impact on local radiation conditions. We were able to identify phenological events such as leaf unfolding, the end of leaf growth, and the beginning and end of defoliation by examining at the average course of the year for LAIpar. The resultant LAIpar values were compared to annual values derived from hemispheric photographs taken near the stand temperature sensor. For the years 2011–2017, we found a strong correlation of 0.93 between LAI measures and LAIpar, which dropped to 0.69 after adding the year 2018 and 0.32 after adding 2019. We further compared the phenological events obtained from LAIpar to phenological observations. The impact of forests on their site climate, according to our findings, can be utilized to identify phenological and growth characteristics. The proposed method, however, is not a replacement for conventional LAI measurements.

Remote sensing based forest canopy opening and their spatial representation

The use of remote sensing in natural resource management is an easily accessible input for obtaining detailed information on the ground and landscape. There is a wide range of procedures to analyze the forest canopy through satellite images. The purpose of this work is to obtain a map of forest opening with remote sensing by relating several vegetation indices, Kauth-Thomas transformation and texture filters, to a Landsat 8OLI image. A factor analysis was made to evaluate the contribution of these variable to identify the opening of the forest cover, yielding a σ2 = 76%. The results show that the Modified Soil Adjusted Vegetation Index (MSAVI), Soil Adjusted Vegetation Index (SAVI), and brightness factor have the best correlation (0.225–0.216 component coefficient). The resulting model was reclassified into five categories of forest opening and associated with land use data from the National Institute of Statistics and Geography (INEGI-México). Thus, 95% of human settlements have a canopy opening between medium and very high, the crops areas 72%, and the low deciduous forest with secondary shrub vegetation 100% of the opening. Coniferous and mixed forests have a low to very low canopy opening 46% and 55%, respectively of their surface. The forests with secondary vegetation, both shrub and arboreal, present greater openness than the same forests in the primary state. Verification of the spatial representation data of canopy opening was made by comparing 94 hemispheric photographs with 94 sites located in open areas obtaining an r = 0.57. This work offers a simple and straightforward methodology, easily replicable in different types of vegetation using free satellite imagery. Hence, it is a helpful tool for decision-makers when considering the general status of conservation of forest systems and their spatial distribution.

Mangrove condition at Selayar Island based on field data and NDVI

Mangrove monitoring in Selayar is part of Reef Health Monitoring which starts from 2015 to 2019 as a result of collaboration between Coremap CTI and Hasanuddin University. The results of satellite image analysis show that the estimated mangrove area in Selayar is 695 hectares, spatially distributed over 9 islands and 24 villages. This study aims to map the condition of mangroves in Selayar and Pasi Island based on canopy cover and NDVI. There were six mangrove locations visited on the field, four locations at Selayar Island, and two locations at Pasi Island. Each station was divided into three observation plots where positions are determined as detail as possible using GNSS, laser distance meter, and compass. There were 18 observed plots. The canopy cover was measure using the hemispherical photo method. Sentinel 2A satellite image was use to mapping NDVI and mangrove condition based on its canopy cover. The correlation between canopy cover and NDVI was 0.96. The coefficient of determination of the regression was 91.3%, and the RMSE value was 5.3%. Referring to KLH standards, mangroves in Selayar and Pasi Island classified as dense, moderate and sparse was 34%, 39%, and 27% recpectively of the total 274 hectares. Mangroves in damaged condition are about 75 hectares scattered on Selayar Island. These results are expected to become a benchmark to monitor mangrove conditions in the Selayar Islands and its vicinity.

Extracting Canopy Closure by the CHM-Based and SHP-Based Methods with a Hemispherical FOV from UAV-LiDAR Data in a Poplar Plantation

Canopy closure (CC), a useful biophysical parameter for forest structure, is an important indicator of forest resource and biodiversity. Light Detection and Ranging (LiDAR) data has been widely studied recently for forest ecosystems to obtain the three-dimensional (3D) structure of the forests. The components of the Unmanned Aerial Vehicle LiDAR (UAV-LiDAR) are similar to those of the airborne LiDAR, but with higher pulse density, which reveals more detailed vertical structures. Hemispherical photography (HP) had proven to be an effective method for estimating CC, but it was still time-consuming and limited in large forests. Thus, we used UAV-LiDAR data with a canopy-height-model-based (CHM-based) method and a synthetic-hemispherical-photography-based (SHP-based) method to extract CC from a pure poplar plantation in this study. The performance of the CC extraction methods based on an angular viewpoint was validated by the results of HP. The results showed that the CHM-based method had a high accuracy in a 45° zenith angle range with a 0.5 m pixel size and a larger radius (i.e., k = 2; R2 = 0.751, RMSE = 0.053), and the accuracy declined rapidly in zenith angles of 60° and 75° (R2 = 0.707, 0.490; RMSE = 0.053, 0.066). In addition, the CHM-based method showed an underestimate for leaf-off deciduous trees with low CC. The SHP-based method also had a high accuracy in a 45° zenith angle range, and its accuracy was stable in three zenith angle ranges (R2: 0.688, 0.674, 0.601 and RMSE = 0.059, 0.056, 0.058 for a 45°, 60° and 75° zenith angle range, respectively). There was a similar trend of CC change in HP and SHP results with the zenith angle range increase, but there was no significant change with the zenith angle range increase in the CHM-based method, which revealed that it was insensitive to the changes of angular CC compared to the SHP-based method. However, the accuracy of both methods showed differences in plantations with different ages, which had a slight underestimate for 8-year-old plantations and an overestimate for plantations with 17 and 20 years. Our research provided a reference for CC estimation from a point-based angular viewpoint and for monitoring the understory light conditions of plantations.

Estimation of Leaf Area Index of Moso Bamboo Canopies

ABSTRACT All ground-based estimations of leaf area index (LAI) of Moso bamboo canopies are currently conducted based on indirect remote sensing methods. However, the relatively small values of LAI estimated by previous studies conflict with the expected values of such extremely dense canopies of Moso bamboo. This is the first attempt to accurately estimate the LAI of Moso bamboo canopies using an allometric model based on destructive measurements. The results indicate that (1) LAI of Moso bamboo canopies range was 6.7–30.6 m2·m−2, which is clearly higher than the range 2.2–6.5 m2·m−2 estimated by previous studies; (2) there is a strong linear relationship between LAI and crown density (R2 = 0.947, RMSE = 1.343); (3) LAI is largely underestimated using the digital hemispherical photography (DHP) because of the overestimation of clumping index; and (4) there is a strong exponential relationship between LAI and effective leaf area (Le) estimated using DHP (R2 = 0.734, RMSE = 3.011). Based on the results, three methods are recommended for LAI estimations of Moso bamboo canopies using the allometric relationship, the empirical relationship with crown density, and the empirical relationship with Le.

Canopy parameters for tree and shrub species compositions in differently intervened land uses of an urban park landscape

Emirgan Park, which covers almost 43 ha hosting variable tree and shrub species, is situated near the Bosphorus at the European side of İstanbul, Turkey. Different tree and shrub species and, their compositions display different canopy parameter values dependent particularly upon their diversity and characteristics. Our study investigated some canopy parameters of the coniferous and deciduous trees, and shrubs within the 30 differently intervened land uses of the Emirgan Park landscape. Therefore, April, May, June LAI values and LT-GF percentages of 242 tree and shrub canopies were analysed using the hemispherical photographing and then image analysis techniques. In total, 726 hemispherical photographs were taken from these 242 different canopy points of the Emirgan Park.The result data were evaluated and discussed based on the land uses these canopies were in and on the ten different compositions their canopies were aggregated into. The highest mean value of LAI with 2.34 m2 m−2 were recorded for the relatively less intervened and pine dominating Picnic Site V, while the lowest LT and GF were recorded both for the Picnic Site V and Secondary Entrance, with respectively 19% and 10% in June. The second canopy composition which is dominated by the coniferous trees with relatively vast canopy, showed the mean highest LAI values with 1.24 m2 m−2, 1.60 m2 m−2 and 2.19 m2 m−2 for the consecutive three months respectively. Nevertheless, LT-GF percentages were also the lowest for this second composition, being 38-22%, 33-18%, 24-13% respectively along the same period. On the other hand, the level of constructional interventions and associated spacing between the canopies have led to the diminishment of LAI values and increment of LT-GF principally within the built land uses, which were confirmed by the pairwise comparisons (LSDs below 0.01) between the land uses. However, this negative situation occurred even though the land uses had diverse tree and shrub species compositions.

Estimating canopy fuel load with hemispherical photographs: A rapid method for opportunistic fuel documentation with smartphones

Abstract Canopy fuel load (CFL) affects wildfire intensity and is a critical input for fire behaviour models; however, measuring CFL in the field is time‐consuming and costly. Until recently, hemispherical photographs have been unable to adequately describe canopy metrics in non‐diffuse light conditions. Recent developments allow calculation of canopy openness (CO) and leaf area index (LAI) using hemispherical photographs taken in sunny conditions. We describe an inexpensive and effective method for estimating CFL in the field opportunistically using CO and LAI values derived from hemispherical photographs taken in variable lighting conditions with a smartphone and fisheye lens attachment. Implications of this work include: new data for modelling effects of forest structure on fire behaviour; inexpensive assessment and monitoring of forest structure changes over time and in relation to management actions; and decision support for fuel treatment planning and prescribed burning operations.

Niche differentiation between Malus sylvestris and its hybrid with Malus domestica indicated by plant community, soil and light

AbstractQuestionMalus sylvestris is considered an endangered tree species in Central Europe. Hybridization with Malus domestica poses a serious threat to the genetic integrity of the wild species. Here we investigate whether M. sylvestris and the hybrid M. domestica × sylvestris occur in the same habitat or have different ecological niches and whether M. sylvestris is threatened by displacement by the hybrid.LocationNorthern Bavaria.MethodsTaxon delimitation was accomplished using six genetic microsatellite markers and 613 Germany‐wide references of M. sylvestris and 75 cultivars. To determine differences in the ecological niches between M. sylvestris and hybrids, light availability for the trees was estimated via gap fractions in hemispherical photographs. Soil particle size fractions and pH values were determined for each horizon. Vegetation relevé data were collected, and mean Ellenberg indicator values calculated. For habitat differences, means in combination with frequency patterns of the parameters were compared, and logistic models and detrended correspondence analysis (DCA) of community data were calculated.ResultsGenetic markers identified 22 M. sylvestris and 11 hybrid specimens, meaning that in the study area the wild taxon is much more frequent than the hybrid. Ecological site differences between M. sylvestris and its hybrid with M. domestica were best explained by light availability, pH and mean Ellenberg moisture value. In contrast to the ecological demands of the hybrid, Malus sylvestris tolerated wet soil and flooding and even somewhat shadier conditions in the later successional stages. DCA revealed that differences in the composition of the plant communities in which the taxa were found were primarily driven by soil moisture.ConclusionsOur data suggested different ecological niches, which are appropriate to reduce the risk of replacement of M. sylvestris by the hybrid M. domestica × sylvestris. Hence, these findings provide important implications for a more targeted planning of in‐situ conservation strategies of M. sylvestris genomes with low levels of admixture and help to protect plant communities suitable for the threatened wild apple.

Comparative Evaluation of Algorithms for Leaf Area Index Estimation from Digital Hemispherical Photography through Virtual Forests

The in situ leaf area index (LAI) measurement plays a vital role in calibrating and validating satellite LAI products. Digital hemispherical photography (DHP) is a widely used in situ forest LAI measurement method. There have been many software programs encompassing a variety of algorithms to estimate LAI from DHP. However, there is no conclusive study for an accuracy comparison among them, due to the difficulty in acquiring forest LAI reference values. In this study, we aim to use virtual (i.e., computer-simulated) broadleaf forests for the accuracy assessment of LAI algorithms in commonly used LAI software programs. Three commonly used DHP programs, including Can_Eye, CIMES, and Hemisfer, were selected since they provide estimates of both effective LAI and true LAI. Individual tree models with and without leaves were first reconstructed based on terrestrial LiDAR point clouds. Various stands were then created from these models. A ray-tracing technique was combined with the virtual forests to model synthetic DHP, for both leaf-on and leaf-off conditions. Afterward, three programs were applied to estimate PAI from leaf-on DHP and the woody area index (WAI) from leaf-off DHP. Finally, by subtracting WAI from PAI, true LAI estimates from 37 different algorithms were achieved for evaluation. The performance of these algorithms was compared with pre-defined LAI and PAI values in the virtual forests. The results demonstrated that without correcting for the vegetation clumping effect, Can_Eye, CIMES, and Hemisfer could estimate effective PAI and effective LAI consistent with each other (R2 > 0.8, RMSD < 0.2). After correcting for the vegetation clumping effect, there was a large inconsistency. In general, Can_Eye more accurately estimated true LAI than CIMES and Hemisfer (with R2 = 0.88 > 0.72, 0.49; RMSE = 0.45 < 0.7, 0.94; nRMSE = 15.7% < 24.21%, 32.81%). There was a systematic underestimation of PAI and LAI using Hemisfer. The most accurate algorithm for estimating LAI was identified as the P57 algorithm in Can_Eye which used the 57.5° gap fraction inversion combined with the finite-length averaging clumping correction. These results demonstrated the inconsistency of LAI estimates from DHP using different algorithms. It highlights the importance and provides a reference for standardizing the algorithm protocol for in situ forest LAI measurement using DHP.

Characterizing Canopy Openness Across Large Forested Landscapes Using Spherical Densiometer and Smartphone Hemispherical Photography

AbstractCanopy openness is an important forest characteristic related to understory light environment and productivity. Although many methods exist to estimate canopy openness, comparisons of their performance tend to focus on relatively narrow ranges of canopy conditions and forest types. To address this gap, we compared two popular approaches for estimating canopy openness, traditional spherical densiometer and modern smartphone hemispherical photography, across a large range of canopy conditions (from closed canopy to large gaps) and forest types (from low-elevation broadleaf to high-elevation conifer forests) across four states in the northeastern United States. We took 988 field canopy openness measurements (494 per instrument) and compared them across canopy conditions using linear regression and t-tests. The extensive replication allowed us to quantify differences between the methods that may otherwise go unnoticed. Relative to the densiometer, smartphone photography overestimated low canopy openness (<10%) but it underestimated higher canopy openness (>10%), regardless of forest type.

Assessing Forest Level Response to the Death of a Dominant Tree within a Premontane Tropical Rainforest

Small-scale treefall gaps are among the most important forms of forest disturbance in tropical forests. These gaps expose surrounding trees to more light, promoting rapid growth of understory plants. However, the effects of such small-scale disturbances on the distribution of plant water use across tree canopy levels are less known. To address this, we explored plant transpiration response to the death of a large emergent tree, Mortoniodendron anisophyllum Standl. & Steyerm (DBH > 220 cm; height ~40 m). Three suppressed, four mid-story, and two subdominant trees were selected within a 50 × 44 m premontane tropical forest plot at the Texas A&M Soltis Center for Research and Education located in Costa Rica. We compared water use rates of the selected trees before (2015) and after (2019) the tree gap using thermal dissipation sap flow sensors. Hemispherical photography indicated a 40% increase in gap fraction as a result of changes in canopy structure after the treefall gap. Micrometeorological differences (e.g., air temperature, relative humidity, and vapor pressure deficit (VPD)) could not explain the observed trends. Rather, light penetration, as measured by sensors within the canopy, increased significantly in 2019. One year after the tree fell, the water usage of trees across all canopy levels increased modestly (15%). Moreover, average water usage by understory trees increased by 36%, possibly as a result of the treefall gap, exceeding even that of overstory trees. These observations suggest the possible reallocation of water use between overstory and understory trees in response to the emergent tree death. With increasing global temperatures and shifting rainfall patterns increasing the likelihood of tree mortality in tropical forests, there is a greater need to enhance our understanding of treefall disturbances that have the potential to redistribute resources within forests.

Competitive effects of a dominant palm on sapling performance in a Neotropical rainforest

AbstractEradication of herbivores, due to human disturbances, produces a demographic outburst of highly competitive prey species, which in turn reduces plant species diversity. This happens at Los Tuxtlas tropical rainforest, Mexico, where a population outburst of the understory palm Astrocaryum mexicanum is ostensibly excluding tree species, but how this is occurring is still unknown. We used a neighborhood approach to explore the effects of palm shading and palm crowding on the survival and growth (RGR) of saplings of six common tree species. Sixteen to 32 saplings (1.5–2.5 m height) per species were used as focal individuals of circular neighborhoods (4 m radius), which included palms ≥ 1cm stem length potentially competing for light or soil resources. Shading was estimated using hemispherical photographs. Overall, survivorship was high combining all species (93.8%/yr). In most species, shading produced a displacement of the crown, which increased with specific leaf area of species. In three species, shading had a negative effect on RGR without any effect of crowding, the contrary occurred in two species, and in one species no effects were found. No effects due to trees (DBH ≥1cm) crowding were detected. The shading effect increased with species leaf dry matter content (LDMC), while the effect of crowding declined with LDMC and increased with sapling total leaf area. We argue that the species‐dependent palm shading/crowding effects were related to the shade tolerance of sapling species. In the long‐term, such species‐specific responses could have consequences for forest structure and composition, as saplings develop to mature stages.Abstract in Spanish is available with online material.

Structure, environmental patterns and impact of expected climate change in natural beech-dominated forests in the Cantabrian Range (NW Spain)

The European beech (Fagus sylvatica L.) occurs in the Cantabrian Range (NW Spain), at the southwestern limit of the wide distribution area of the species in Europe, forming relatively unmanaged forests of high biodiversity value. In this study, we measured three-dimensional positions, diameter at breast height and height of all the trees present in 112 inventory plots established in beech-dominated forests in the north-western Cantabrian Range, in which hemispherical photographs were taken and a detailed floristic inventory was carried out. In addition, we measured 56 spatially continuous environmental variables in each plot to enable examination of environmental patterns in structural features and prediction of the effects of climate change. Forest structure was analyzed by using indices that evaluated spatial tree distribution, plant richness and tree species diversity, diversity of tree dimensions and vertical structure, stand density and average tree size, standing deadwood, canopy geometry and light regime. The stands exhibited a moderate clustered spatial arrangement at young stages, becoming more regular as they matured. The stands are generally monospecific, with low plant richness, never monostratified, with very close canopies, greater variation in diameter than in height and are usually overstocked. Only 25% of the stands included some standing dead trees. Random Forest models were used to describe structural features as a function of environmental variables. Although some of the models were complex and included many predictor variables, they revealed some interesting patterns. Thus, we found that spatial tree distribution was only related to lithostratigraphy, and tree species richness and vertical structure were related to isothermality. Shrub and herbaceous richness were related to soil pH and several thermal variables, while intermingling of tree species was mainly explained by soil-related variables. Climatic variables explained differences in tree diameter, whereas edaphic variables were more important for predicting differences in tree height. Stocking degree was mainly related to soil variables, while dominant height was related to thermal variables and standing dead wood to climatic variables. Projections under the moderate RCP 4.5 and pessimistic RCP 8.5 climate change scenarios predict a shift in beech forests towards increased shrub and plant richness and species diversity, but also increased stocking degree and standing deadwood basal area. These findings appear to confirm a drastic reduction in the suitable habitat for beech in the region (deterioration of future growth conditions), which could anticipate a loss of competitive advantage over other species and indicate a shift in this beech-dominated forest to more resilient mixed stands.

Variation of intra-daily instantaneous FAPAR estimated from the geostationary Himawari-8 AHI data

The fraction of absorbed photosynthetically active radiation (FAPAR) quantifies the efficiency of light absorption by vegetation. The intra-daily variation in FAPAR is important for monitoring vegetation growth but current studies to estimate the intra-daily FAPAR from remote sensing are limited. This study proposes to estimate the intra-daily variations of the direct, diffuse, and total FAPARs on clear days from the geostationary Himawari-8 AHI data. A look-up table inversion method was developed based on simulations of a radiative transfer model that couples a soil reflectance (GSV, General Spectral Vectors), canopy (PROSAIL), and atmospheric models (6SV, Second Simulation of a Satellite Signal in the Solar Spectrum). Field measurements were conducted over paddy rice fields in Northeast China from June 22 to August 25, 2019, to obtain continuous FAPAR measurements using an AccuPAR ceptometer and digital hemispherical photography. The instantaneous FAPAR values were analyzed and evaluated with field measurements and MODIS and GEOV2 FAPAR products. The results show that the retrieved AHI FAPAR values are consistent with the field measurements (R2 > 0.75). The AHI, MODIS, and GEOV2 FAPAR values display similar spatial and temporal patterns over the growing season (R2 > 0.66). The intra-daily variations in the total and direct FAPAR values agree with the field measurements, and both show a “bowl-shaped” pattern with the smallest value found at noon. The diffuse FAPAR remains stable before 16:00 local solar time (LST). The instantaneous total and direct FAPAR values at 10:00 – 10:30 LST usually assumed to be daily values underestimate the daily values, while the values at 9:30 and 14:30 LST can better represent the daily FAPAR. As a future study, global intra-daily instantaneous and daily FAPAR products could be generated by combining all geostationary satellite data.

Vertical structure heterogeneity in broadleaf forests: Effects on light interception and canopy photosynthesis

Foliage clumping refers to the aggregation of leaves around branches and tree crowns. It has been shown to influence considerably light interception in forests and is increasingly being used in terrestrial biosphere models (TBMs) to estimate canopy photosynthesis, represented by a single value encompassing all spatial scales (shoot, branch, crown and plot): the clumping factor (Ω). Several studies have pointed to possible vertical variations in foliage clumping, and a recent study confirmed very low clumping factor values (high leaf aggregation) at the top of deciduous broadleaf forests. However complete profiles of clumping factors have never been described in tall forest canopies. As TBMs are currently moving towards multilayer schemes for the computation of photosynthesis, we investigated whether vertical profiles of foliage clumping should be considered within those schemes. We first used ground lidar combined with hemispherical photos to characterise branch level clumping factor (Ωv) at different heights in a deciduous broadleaf forest. We then applied the branch level clumping factor profile to four forests plots where complete 3D structure derived from ground lidar was available to produce vertical profiles (30 cm resolution) for foliage clumping (Ωl) and leaf area index (LAI). We ran radiative transfer simulations using different scenarios for representing vertical structure to assess its effect on canopy photosynthesis (without considering energy balance, temperature, kinetics or water balance). We found that when considering branch level clumping, the plot level clumping factor values were considerably lower (leaves more clumped together) than the average values commonly used for broadleaf forests. Modeling light fluxes using this lower value increased canopy photosynthesis because of a combination of greater light penetration to lower layers and non-linearity in the light-response curve. Considering the vertical profiles of foliage clumping further increased canopy photosynthesis through a greater contribution from shaded leaves in the lower and upper canopy levels. Further, we find that there is an optimal range of value for clumping factor which maximises photosynthesis, and the four sites surveyed (LAIs above 4) display clumping factors values close to this optimum. Solely on the basis of the effect of radiative transfer, we did not find notable differences in canopy photosynthesis when the LAI profile was considered. We find that it may be of interest to consider foliage clumping vertical profiles within TBM multilayer schemes, and we present a generic profile equation for use in dense deciduous forests.