Foliage Density Research Articles

An Efficient Detection of the Pitaya Growth Status Based on the YOLOv8n-CBN Model

The pitaya is a common fruit in southern China, but the growing environment of pitayas is complex, with a high density of foliage. This intricate natural environment is a significant contributing factor to misidentification and omission in the detection of the growing state of pitayas. In this paper, the growth states of pitayas are classified into three categories: flowering, immature, and mature. In order to reduce the misidentification and omission in the recognition process, we propose a detection model based on an improvement of the network structure of YOLOv8, namely YOLOv8n-CBN. The YOLOv8n-CBN model is based on the YOLOv8n network structure, with the incorporation of a CBAM attention mechanism module, a bidirectional feature pyramid network (BiFPN), and a C2PFN integration. Additionally, the C2F module has been replaced by a C2F_DCN module containing a deformable convolution (DCNv2). The experimental results demonstrate that YOLOv8n-CBN has enhanced the precision, recall, and mean average precision of the YOLOv8n model with an IoU threshold of 0.5. The model demonstrates a 91.1% accuracy, a 3.1% improvement over the original model, and an F1 score of 87.6%, a 3.4% enhancement over the original model. In comparison to YOLOv3-tiny, YOLOv5s, and YOLOv5m, which are highly effective target detection models, the mAP@0.50–0.95 of our proposed YOLOv8n-CBN is observed to be 10.1%, 5.0%, and 1.6% higher, respectively. This demonstrates that YOLOv8n-CBN is capable of more accurately identifying and detecting the growth status of pitaya in a natural environment.

Comparable diameter resulted in larger leaf area and denser foliage in the park trees than in street trees: A study on Norway maples of Karlsruhe city, Germany

The leaf area of trees is the main surface of energy and matter exchange between the plant canopy and the atmosphere. A better understanding of canopy structure variations in cities is a prerequisite to evaluating leaf area and ecosystem services. We selected 58 single-standing and healthy Norway maple trees (Acer platanoides L.), equally distributed between the park and street at the same tree size for canopy structure and leaf area measurements. The canopy structures of street trees and park trees were different. Street trees had significantly higher dieback (p < 0.01), crown damage (p < 0.01), and branch-free bole length (p < 0.001) than park trees. Even though we sampled trees with similar diameters, park tree crowns tended to be healthier and denser than street trees. The crown volume, crown projection area (CPA), light availability (Crown Light Exposure or CLE), and foliage density were lower in street trees than in park trees. The average foliage density of street trees is 20 % lower than park trees. All the above differences in crown volume and foliage density lead to a significantly lower leaf area in street trees. The total leaf area of a single street tree was only 83 m2 on average, compared to 186 m2 among park trees. We demonstrated that crown volume and growing habitats (i.e., park or street) are important explanatory variables for leaf area. We conclude that a precise and site-specific evaluation of leaf areas is a prerequisite for accuracy in quantifying ecosystem services from urban trees.

Responses of stomatal density and carbon isotope composition of sugar maple and yellow birch foliage to N, P and CaSiO3 fertilization.

Stomatal density, stomatal length and carbon isotope composition can all provide insights into environmental controls on photosynthesis and transpiration. Stomatal measurements can be time-consuming; it is therefore wise to consider efficient sampling schemes. Knowing the variance partitioning at different measurement levels (i.e., among stands, plots, trees, leaves and within leaves) can aid in making informed decisions around where to focus sampling effort. In this study, we explored the effects of nitrogen (N), phosphorus (P) and calcium silicate (CaSiO3) addition on stomatal density, length and carbon isotope composition (δ13C) of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton). We observed a positive but small (8%) increase in stomatal density with P addition and an increase in δ13C with N and CaSiO3 addition in sugar maple, but we did not observe effects of nutrient addition on these characteristics in yellow birch. Variability was highest within leaves and among trees for stomatal density and highest among stomata for stomatal length. To reduce variability and increase chances of detecting treatment differences in stomatal density and length, future protocols should consider pretreatment and repeated measurements of trees over time or measure more trees per plot, increase the number of leaf impressions or standardize their locations, measure more stomata per image and ensure consistent light availability.

Green Infrastructure with Actual Canopy Parameterization: A Simulation Study for Heat Stress Mitigation in a Hot-Humid Urban Environment

Abstract Background The urban heat island (UHI) phenomenon, resulting from rapid urbanization and aggravated by persistent climate change, is intensifying heat stress and temperature anomalies inside the urban microclimate, requiring the implementation of suitable adaptation measures for sustainable development. The integration of street trees inside the urban landscape is a strategy to alleviate the thermal stress of pedestrians. However, trees have variable potential for the regulation of thermal comfort depending on their different canopy shapes/drag. Therefore, a holistic understanding of tree plantings and species with respect to a particular climate is necessary for urban sustainability. Methods In this study, computational fluid dynamics (CFD) that employ unsteady Reynolds-averaged Navier-Stokes (URANS) equations were performed using FLUENT solver to analyze the cooling potential of isolated tree species based on 5 morphological characteristics and canopy shapes (i.e., tree height, trunk height, crown width, crown height, and leaf area density) in an urban area. Results Results revealed a variable temperature regulation (i.e., 0.6 to 1.2 °K) depending on the tree species. Overall, the cooling effect was only observed in the vicinity of the tree canopy. This was due to the availability of shading and increased moisture content provided by the canopy foliage, which blocked shortwave radiation from the sun, as compared to its surroundings. Conclusions The study findings show that leaf area density is the morphological trait that has the greatest impact on thermal comfort, as it results in low ambient air temperature irrespective of the type of urban density. Additionally, the most effective way to reduce thermal stress is to implement taller trees with uniform foliage density, which will produce a well-ventilated environment.

Modelling aboveground biomass of a multistage managed forest through synergistic use of Landsat-OLI, ALOS-2 L-band SAR and GEDI metrics

To better understand forest carbon budgets and design forest-based climate change mitigation solutions, reliable biomass estimation is critical. Integrating multi-sensor remote sensing data can improve forest monitoring and evaluation. This study adopted a one-hectare plot size sampling design to improve the integration of GEDI footprints with in-situ, optical, and SAR data for the estimation of forest above-ground biomass (AGB). The study was carried out for a managed tropical forest in the Himalayan foothills of India. The space-borne GEDI retrieved the canopy height of the study area with an RMSE of 3.36 m and Adj. R2 of 0.70. Extrapolating GEDI footprint heights (RH95) with Landsat 8 indices using Random Forest (RF) yielded a spatial canopy height of the study area with an R2 of 0.97 and RMSE of 2.32 m. Using the GEDI canopy height, foliage density, and plant area index, the AGB at GEDI footprints level was estimated using RF, with an R2 of 0.91 and an RMSE of 20.10 Mg ha−1. The spatial AGB model that only considered ALOS-2 SAR variables had an R2 of 0.61 and an RMSE of 18.27 Mg ha−1, whereas the RF model that considered both SAR variables and canopy height had a superior R2 of 0.77 and a lower RMSE of 13.86 Mg ha−1. The addition of canopy height data reduced the RMSE of the AGB model by 4.41 Mg ha−1 and also predicted a higher range of AGB. The study demonstrates the effectiveness of combining GEDI data with other sensors (optical and SAR data) to provide precise AGB of multistage managed forests using a one-hectare plot size sampling design.

Visual rating and the use of image analysis for assessing canopy density in a pecan provenance collection during leaf fall

A collection representing the native range of pecan was planted at the USDA − ARS Southeastern Fruit and Tree Nut Research Station, Byron, GA. The collection (867 trees) is a valuable genetic resource for characterizing important horticultural traits. Canopy density during leaf fall is important as the seasonal canopy dynamics provides insights to environmental cues and breeding potential of germplasm. The ability of visual raters to estimate canopy density on a subset of the provenance collection (76 trees) as an indicator of leaf shed during autumn along with image analysis values was explored. Mean canopy density using the image analysis software was less compared to visual estimates (11.9% vs 18.4%, respectively). At higher canopy densities, the raters overestimated foliage density, but overall agreement between raters and measured values was good (ρc = 0.849 to 0.915), and inter-rater reliability was high (R2 = 0.910 to 0.953). The provenance from Missouri (MO-L), the northernmost provenance, had the lowest canopy density in November, and results show that the higher the latitude of the provenance, the lower the canopy density. Based on regression, the source provenance latitude explained 0.609 of the variation using image analysis, and 0.551 to 0.640 when based on the rater estimates of canopy density. Visual assessment of pecan canopy density due to late season leaf fall for comparing pecan genotypes provides accurate and reliable estimates and could be used in future studies of the whole provenance collection.

Dynamically simulating spruce budworm in eastern Canada and its interactions with wildfire

Eastern Spruce Budworm (ESBW) is a major agent of disturbance in Eastern Canada's boreal forests. Outbreaks have historically led to widespread defoliation of its preferred host trees, fir and spruce species, leading to high rates of mortality. This in turn can result in significant economic losses and enhancement of fire potential in the region. Representation of such biotic disturbance has rarely been included in Dynamic Global Vegetation Models (DGVM), which have become essential tools in understanding and predicting forest dynamics in present and future contexts. We present novel representation of host-specific defoliation in a DGVM (LPJ-LMfire), to better represent disturbance regimes in the boreal forest of eastern Canada. Using host foliage density to trigger outbreak, we were able to calibrate and simulate general spatial patterns of defoliation relative to historical aerial sketch map data. Return intervals were thus sensitive to the growth rates of host trees. Modeled return intervals tended to be significantly longer than 30 years, the approximate observed return interval. A factorial experiment was performed on the interactions of ESBW with wildfire, which was found to be slightly enhanced in terms of burned areas after outbreaks due to increased fuel loads. Interactions between ESBW and fire were found to have higher interaction strength in the drier Western region of the boreal forest. Our study demonstrates that biotic disturbance and its interaction with wildfire can be effectively simulated in a DGVM. We show that bottom-up climatic controls are sufficient to drive simulated spatiotemporal patterns of ESBW that can be calibrated to generally match historical observations.

Investigating above- vs. below-ground competition by accounting for azimuth of competitors in native eucalypt forests

Competition for both above-ground and below-ground resources plays a crucial role in shaping the structure and dynamics of plant communities. Above-ground competition for light may be more azimuthal and size-asymmetric than below-ground competition. However, there has been limited research on azimuthal effects in competition and development of related methods that may help distinguish between above- vs. below-ground competition. The aims of this study were to 1) develop novel approaches to evaluate the azimuthal effect of competition; 2) illustrate and evaluate these approaches by applying them to dominant eucalypt species in two mid-latitude Mediterranean climate forests; and 3) show how these methods can provide insights into the relative importance of above- vs. below-ground competition in these different species. We developed, applied and evaluated three new methods to evaluate azimuthal differences in competition, using models predicting DBH growth in two different forests (Eucalyptus marginata, jarrah and Corymbia callophyla, marri) and karri forest (E. diversicolor, karri; and Corymbia callophylla, marri) of south-west Western Australia. The foliage density of karri/marri is higher than that of jarrah, and the karri/marri site had higher rainfall. Both sites included thinned (thinning from below) and unthinned plots, regenerated naturally, and aged 100 year (jarrah) and 50 year (karri and marri). First, we compared the ability to predict growth using competitors in specific azimuths only vs. all competitors together. Second, we investigated whether weighting competitive effects of neighbours according to their azimuth could improve growth predictions. Third, we investigated whether growth prediction could be improved by accounting for relative size of competitors as well as their azimuth. We found evidence of an azimuthal effect of competition on growth in jarrah, karri and marri forest through all three new approaches. The third approach showed the existence of size-asymmetric competition. Improvement in model prediction was relatively small when accounting for the azimuth, which suggests that above-ground competition for light is low and most competition in jarrah, karri and marri forests is for below-ground resources. The three approaches developed and illustrated in this study can potentially help identify, distinguish and understand above- vs. below-ground competition for tree species in different parts of the world where competition among trees is one of the limiting factors of forest growth, dynamics and health.

Effects of Competition on the Vertical Distribution of Foliage Biomass within the Crowns of Planted Korean Pine Trees in Northeast China

The characteristics and distribution of foliage biomass are important aspects of the crown structures of trees. In this study, we developed a foliage biomass distribution model at the branch level and annual shoot level (i.e., all branches on an annual increment of the main tree bole) using a sample of 51 Korean pine trees that were destructively sampled in Liaoning Province, northeast China. A variety of independent variables, including branches, trees, and forest competition, were used as explanatory variables in the model development. Our results indicated that foliage biomass at the branch level increased with an increasing relative distance from the tree tip into the crown. The peak of the foliage biomass distribution shifted to the tree tip with increasing tree age. A power function, including branch diameter and competition variables, showed excellent performance in modeling branch foliage at the branch level. The final model, which included branch diameter, competition variables, and relative distance to branch base for the relative foliage density, showed best performance. The trees that showed advantageous growth ability also had a larger amount of foliage biomass.

Diverse morphological and molecular patterns of tomato (Solanum lycopersicum Linn.) accessions

Field and molecular experiments were conducted between May and August 2021 at the research farm of the Department of Botany, University of Ibadan and International Institute of Tropical Agriculture, Ibadan respectively. Morphological and molecular variability in 40 tomato accessions were investigated in this study. Five accessions from local markets in Ibadan, two varieties from seed companies, three varieties from Benue State and Oyo State, and thirty accessions from the National Center for Genetic Resources and Biotechnology (NACGRAB) were evaluated. The experiment was arranged in a randomised complete block design (RCBD) with three replicates. Significant (p < 0.05) variation was observed for days to germination, hypocotyl colour, primary leaf length, primary leaf width, number of leaves, plant height, number of leaves under first inflorescence, number of inflorescence, days to first fruiting, foliage density and internode length (cm). The cumulative values for the first three components (74.80%) accounted for variation among the 40 accessions in the principal component analysis. All yield related characters correlated positively with both the number of leaves and plant height. The study revealed that NGB/05081, NGB/00714, NGB/05075, NGB/00696, NGB/00735b and Hausa (Dugbe) accessions performed the best in growth and yield characters, while NGB/00735b and NGB/00759 were early maturing accessions. The Tp 124 and Tp 121 primers were highly polymorphic and had high gene diversities. Sixteen tomato accessions were amplified for marker genes nodZ-A and nodZ-B. Five of these accessions showed high growth, while seven produced high yield, implying positive influence on the improvement of these accessions. However, the nifh marker gave no amplification.

Evaluation of a dill (Anethum graveolens L.) gene bank germplasm collection using multivariate analysis of morphological traits, molecular genotyping and chemical composition to identify novel genotypes for plant breeding.

Dill (Anethum graveolens L.) is an aromatic herb widely used in the food industry, with several commercial cultivars available with different qualitative characteristics. Commercial cultivars are usually preferred over landraces due to their higher yield and also the lack of improved landraces than can be commercialized. In Greece, however, traditional dill landraces are cultivated by local communities. Many are conserved in the Greek Gene Bank and the aim here was to investigate and compare the morphological, genetic, and chemical biodiversity of twenty-two Greek landraces and nine modern/commercial cultivars. Multivariate analysis of the morphological descriptors, molecular markers, and essential oil and polyphenol composition revealed that the Greek landraces were clearly distinguished compared with modern cultivars at the level of phenological, molecular and chemical traits. Landraces were typically taller, with larger umbels, denser foliage, and larger leaves. Plant height, density of foliage, density of feathering as well as aroma characteristics were desirable traits observed for some landraces, such as T538/06 and GRC-1348/04, which were similar or superior to those of some commercial cultivars. Polymorphic loci for inter-simple sequence repeat (ISSR) and start codon targeted (SCoT) molecular markers were 76.47% and 72.41% for landraces, and 68.24% and 43.10% for the modern cultivars, respectively. Genetic divergence was shown, but not complete isolation, indicating that some gene flow may have occurred between landraces and cultivars. The major constituent in all dill leaf essential oils was α-phellandrene (54.42-70.25%). Landraces had a higher α-phellandrene and dill ether content than cultivars. Two dill landraces were rich in chlorogenic acid, the main polyphenolic compound determined. The study highlighted for the first-time Greek landraces with desirable characteristics regarding quality, yield, and harvest time suitable for breeding programs to develop new dill cultivars with superior features.

Understory plant communities fail to recover species diversity after excluding deer for nearly 20 years

White-tailed deer ( Odocoileus virginianus) have been overabundant in eastern North America for more than five decades, resulting in depauperate understories and ricocheting effects on higher trophic levels. Even after deer populations are reduced, understory plant communities may fail to recover for an unknown length of time due to persistent legacy effects. We surveyed understory plant communities in six deer exclosures and paired reference plots in northwestern Pennsylvania to determine the degree to which 19 years of deer exclusion was sufficient for recovery of species richness, diversity, percent cover, and understory structural complexity. We observed a 2.3-fold increase in tree cover and a 60% reduction in fern cover in the ground layer, as well as a 114-fold increase in foliage density between 80 and 200 cm above ground level, in exclosures compared to reference plots. However, the exclosures did not permanently support higher overall percent cover, species richness, or diversity in the ground layer, nor did we detect any meaningful divergence in community composition between exclosures and reference plots. We conclude that 19 years of release from chronic over-browsing are sufficient to restore understory structural complexity, but recovery of diversity in the ground layer will require more time or direct intervention.

Airborne dual-wavelength waveform LiDAR improves species classification accuracy of boreal broadleaved and coniferous trees

Tree species identification constitutes a bottleneck in remote sensing applications. Waveform LiDAR has been shown to offer potential over discrete-return observations, and we assessed if the combination of two-wavelength waveform data can lead to further improvements. A total of 2532 trees representing seven living and dead conifer and deciduous species classes found in Hyytiälä forests in southern Finland were included in the experiments. LiDAR data was acquired by two single-wavelength sensors. The 1064-nm and 1550-nm data were radiometrically corrected to enable range-normalization using the radar equation. Pulses were traced through the canopy, and by applying 3D crown models, the return waveforms were assigned to individual trees. Crown models and a terrain model enabled a further split of the waveforms to strata representing the crown, understory and ground segments. Different geometric and radiometric waveform attributes were extracted per return pulse and aggregated to tree-level mean and standard deviation features. We analyzed the effect of tree size on the features, the correlation between features and the between-species differences of the waveform features. Feature importance for species classification was derived using F-test and the Random Forest algorithm. Classification tests showed significant improvement in overall accuracy (74→83% with 7 classes, 88→91% with 4 classes) when the 1064-nm and 1550-nm features were merged. Most features were not invariant to tree size, and the dependencies differed between species and LiDAR wavelength. The differences were likely driven by factors such as bark reflectance, height growth induced structural changes near the treetop as well as foliage density in old trees.

Key Technologies for an Orchard Variable-Rate Sprayer: Current Status and Future Prospects

An orchard variable-rate sprayer applies the appropriate amount of plant protection products only where they are needed based on detection data from advanced sensors, a system that has attracted increasing attention. The latest developments in the detection unit, variable control unit, and signal-processing algorithm of the variable-rate sprayer are discussed. The detection of target position and volume is realized with an ultrasonic sensor, a laser scanning sensor, or other methods. The technology of real-time acquisition of foliage density, plant diseases and pests and their severity, as well as meteorological parameters needs further improvements. Among the three variable-flow-rate control units, pulse width modulation was the most widely used, followed by pressure-based, and variable concentration, which is preliminarily verified in the laboratory. The variable air supply control unit is tested both in the laboratory and in field experiments. The tree-row-volume model, the leaf-wall-area model, and the continuous application mode are widely used algorithms. Advanced research on a variable-rate sprayer is analyzed and future prospects are pointed out. A laser-based variable-rate intelligent sprayer equipped with pulse width modulation solenoid valves to tune spray outputs in real time based on target structures may have the potential to be successfully adopted by growers on a large scale in the foreseeable future. It will be a future research direction to develop an intelligent multi-sensor-fusion variable-rate sprayer based on target crop characteristics, plant diseases and pests and their severity, as well as meteorological conditions while achieving multi-variable control.

Pest and disease risk and management in high-density perennial crops: Current knowledge and areas of future research

High-density production has been increasing for numerous perennial crops in different parts of the world. Recent work suggests that high-density systems improve yields, fruit quality, and harvest efficiency. Yet, despite the increasing amount of acreage in high-density production, there has been surprisingly little comparative research on pest and disease patterns in such systems compared to conventional systems. Given the significantly different structure of high-density plantings compared to conventional orchards, pest abundance, disease prevalence, and appropriate management strategies are likely to differ. Here we describe the characteristics of high-density plantings and how their management and infrastructure are likely to have direct and indirect effects on pest abundance and disease prevalence. We also describe how high-density structure, management, infrastructure, fruit abundance, and microclimate present challenges and opportunities for pest and disease management strategies. For example, the compact structure of high-density plantings may mean smaller quantities of inputs are required while, at the same time, the high foliage density may reduce penetration of pesticide sprays and other inputs. Finally, we propose critical areas for future research including 1) patterns of pest and disease prevalence among rootstocks and varieties, 2) how infrastructure and timing of high-density management affect pest and disease prevalence, 3) how microclimate and fruit abundance vary across canopy levels, with associated impacts on pest and disease prevalence, and 4) types of pest and disease management that are likely to be effective in high-density systems.

Wind-flow dynamics and spore-like particle dispersal over agroforestry systems: Impact of the tree density distribution

Agroforestry systems associating trees with crops are gaining a growing interest due to their environmental benefits in a context of climate change and biodiversity loss. Still, the impact of trees on the wind dynamics within agroforestry systems remains poorly understood despite the key role played by the wind in energy and mass exchanges, including disease and pest propagation. Here, we present the first detailed analysis of the wind dynamics over agroforestry systems, combining in situ measurements and instantaneous airflow simulations, with a numerical application on spore-like particle dispersion from an infection point source at crop top. Simulations reproduce remarkably well most characteristics of the turbulent wind flow within the agroforestry system. Simulations reveal the presence of two inflection points on the mean wind velocity profile, at crop and tree tops, both inducing the development of mixing-layer type eddies, controlling most of the turbulent exchanges within the agroforestry system. Relative to the local wind, the turbulence at the crop scale is more intense and intermittent in presence of trees. With increasing tree density, the turbulence at crop top becomes dominated by tree-scale motions developing at tree top. The presence of trees has a different impact on particle dispersion according to the particle size and the wind intensity. Trees accentuate the vertical and transversal dispersal of submicron spores while they enhance the short-range deposition of coarser spores on crops, the more as the wind is low, and thus limit the long-range dispersal of coarse spores. Finally, a simple parameterization of the mean wind velocity vertical profile is proposed for agroforestry systems, depending only on the foliage densities and heights of the tree and crop layers. This parameterization leads to an indication of the agroforestry system efficiency to limit spore propagation through an estimation of the Rouse number at crop top.

The Role of Habitat Amount and Vegetation Density for Explaining Loss of Small-Mammal Diversity in a South American Woodland Savanna

The focus of research and conservation in tropical regions is mainly devoted to forest ecosystems, usually neglecting the processes underlying widespread, more open biomes, like savannas. Here we test a wide range of sampled woodland sites across the South American savanna for the direct and indirect effects of habitat loss and vegetation density on the diversity of small-mammal species. We quantify the direction and magnitude of the effects of habitat amount (habitat loss), vegetation density (tree or foliage density), and patch size (species-area effect) on species composition and richness. We also test whether the relative effect sizes of landscape and patch-related metrics predict a persistence gradient from habitat specialist to generalist species across 54 sites. We used structural equation models (SEM) to test our predictions. After 22,032 trap-nights considering all sampled sites and 20 small-mammal species identified, the structural equation model explained 23.5% of the variance in the richness of small-mammal species. Overall, we found that landscape-level metrics were more important in explaining species richness, with a secondary role of patch-level metrics such as vegetation density. The direct effect of local landscape was significant for explaining species richness variation, but a strong positive association between regional and local landscapes was also present. Furthermore, considering the direct and indirect paths, SEM explained 46.2% of the species composition gradient. In contrast to species richness, we recorded that the combined landscape-level and patch-level metrics are crucial to determining small-mammal species composition at savanna patches. The small mammals from the South American woodland savanna exhibit clear ecological gradients on their species composition and richness, driven by habitat specialist (e.g.,Thrichomys fosteri,Monodelphis domestica, andThylamys macrurus) and generalist (e.g.,Didelphis albiventris,Rhipidomys macrurus, andCalomys callosus) species’ responses to habitat amount and/or vegetation density, as seen in dense-forest Neotropical biomes.

Validation of the hot-spot model with terrestrial laser scanning

Validation of the hot-spot theoretical model was carried out with extensive terrestrial laser scanning (TLS) measurements in the Järvselja RAMI pine stand. A 120 m × 120 m × 12 m point cloud of laser hits of 1 cm resolution was built to describe the spatial structure of the crown layer. From this point cloud, foliage density was found at 1 dm resolution, and a Fourier analysis of the spatial structure of the crown layer was performed. The autocorrelation function of the transmittance of 1 dm slices of the crown layer, which controls the hot-spot profile of directional reflectance, was estimated directly from the point cloud. The determined value of the hot-spot parameter was found to agree well with the value estimated indirectly from the measurements of reflectance profile in the principal plane.

The needle percentage in the leafy shoot biomass of Scots pine in climate gradients of Eurasia

The efficiency of using photosynthetically active radiation by trees largely depends on the architecture of the assimilation apparatus in their crown. It is known that an increase in the level of atmospheric pollution is accompanied, on the one hand, by an increase in the foliage density on the leafy shoot length, and on the other hand, by an increase in the transparency of the crown due to the expansion of the leafless inner part of the crown. On this basis, we assume that the foliage percentage of leafy shoots (PL) is a sensitive indicator of changes in growing conditions not only due to environmental pollution, but also in broader ecological aspects, in particular, in the geographical or climatic gradients of Eurasia. For this purpose, a database of empirical data has been formed in the amount of 558 model trees of Scots pine of natural and artificial origin from 6 regions of Northern Eurasia with a measured percentage of needle in the leafy shoot biomass. A regression model has been designed, in which the contributions of mensuration variables (tree age and stem diameter), climatic variables (temperature and precipitation) and the origin of stands (natural and artificial) to explain the variability of the desired PL indicator are 15, 53 and 30 %, respectively. It is concluded that with a decrease in annual precipitation from 600 to 300 mm, there is an increase in PL by 0.2..0.3% for every 10 mm of annual precipitation, both in natural stands and in plantations. When the January temperature decreases from 0°C to -20 °C, PL increases by 0.8...1.0% for each 1°C. Thus, the foliage percentage of leafy shoots of Scots pine is an indicator of changes in growing conditions in the climate gradients of Eurasia.

Mixed-species flocking is associated with low arthropod detectability and increased foraging efficiency by Yungas forest birds in Argentina

AbstractMixed-species flocks presumably provide birds with antipredator and foraging benefits. The foraging benefits hypothesis predicts that a reduction in arthropod abundance will trigger flocking activity; however, flocking activity may also be influenced by the difficulty of detecting arthropods, a seldom explored possibility. We found that environmental traits (temperature and foliage density) combined with arthropod abundance explained arthropod detection by birds in the Yungas foothill forest of NW Argentina. Prey detection was inversely related to ambient temperature and foliage density while positively associated with arthropod abundance. Based on this result, we built a structural equation model using a latent proxy variable for arthropod detectability, arthropod crypsis, integrating ambient temperature, foliage density, and proportion of immature arthropods. This model allowed us to compare the relative importance of arthropod abundance and the difficulty in detecting prey items as predictors of flocking propensity. After 2 yr of studying 129 mixed-species flocks, 1,351 bird foraging sequences, and 25,591 arthropod captures, we found that the flocking propensity of birds was only significantly correlated with arthropod detectability and not with arthropod abundance. Flocking propensity peaked when the arthropod community was comprised of proportionately more immature and non-flying arthropods, the temperature was low, and the foliage cover was denser; all factors are contributing to a low arthropod detectability. Finally, we evaluated whether joining mixed-species flocks provided foraging benefits such as increased foraging efficiency. Individuals benefited from joining flocks by an average increase of their prey-capture attempt rate of 40%, while the search rate increased by 16%. Our results add a new perspective on the drivers of mixed-species flocking by showing that the capacity to find prey items may have a more significant effect than prey abundance per se.