Search

This illustrated review is aimed to provide succinct account of different methods applicable for obtaining objective information about the functional ecology of forest sites and stands (and also, e.g., orchards, watersheds, parks or alleys) for the purposes of phytotechnology or precise forestry. Management strategies must consider preservation of many important functions of forests in the landscape. Management methodologies include classical forestry approaches based on classification of the natural environment according to climatic zones, soil characteristics and composition of herbaceous as well as woody vegetation. One possibility for obtaining objective information came with the development of ecologically applicable instrumentation, allowing studies on the whole tree and stand levels to be undertaken anywhere in the field. Information may be derived at sites that are not permanently observed and are not equipped with additional constructions, such as towers, masts, or greenhouses. These field applicable methods are focused especially on tree and stand macrostructure, water relations and functional parameters of trees. In addition, problems associated with interactions between trees and different organisms are also discussed. A series of methods based on different principles is useful to measure mostly quantitative, operative or effective tree parameters as tree crowns and leaf distribution, stems (or large tree trunks) and root systems including skeleton and absorptive fine roots. This is sometimes possible to do with rather simple methods, but instrumental methods prevail especially for root studies. In addition to several classical measurement principles including anatomical or mechanical sensing, the methods work with sound speed (acoustic tomography) using electromagnetic rays of different wavelength (from radar to optical), electric conductivity or impedance, supersonic air stream and thermodynamics for example. Methods for data evaluation and examples of application are also included. The whole complex system approach should serve for different scientific fields (including hydrology, landscape care, horticulture, forensic engineering, etc.) and especially to support precise forestry.

Graphical abstract Highlights • We conceptualized the approach for measuring three-dimensional crown asymmetry. • Our novel approach separates the effects of crown shift and local crown plasticity. • Smaller trees exhibited higher ability to shift and re-shape their crowns. • Crown models neglecting tree asymmetry were poor predictors of direct competitors. • Light availability computed by geometric crown models were significantly biased. Abstract There are many indications that for a true understanding of aboveground canopy competition, the concept of symmetric trees is oversimplified and unsatisfactory; in spite of that, this concept is still commonly used in forest ecology research. In this study we analyzed and quantified the effect of tree/crown asymmetry on crown-to-crown interactions and canopy light availability with respect to tree size and species. Geometric crown models were used to represent the concept of symmetric trees, while data from terrestrial laser scanning were employed to constitute real crown shapes, positions and mutual crown-to-crown interactions. We developed an original approach for measuring three-dimensional crown asymmetry, separating the effect of positional crown shift and local crown plasticity, and analyzed their effect in aboveground competition for space and light. In comparison with reality, the models neglecting tree asymmetry were only poor predictors of trees mutually competing for space. Geometric models taking the positional crown shift into account were good predictors of 'space competitors' for Norway spruce, but were still insufficient for European beech. This is because for spruce crown shifting seems to be the major neighbor avoidance strategy, while beech in addition exhibited high local crown shape plasticity. Additionally, of the two species beech showed overall greater crown plasticity, which (in contrast to spruce) decreased only slowly with increasing tree size. Importantly, the concept of symmetric trees significantly underestimates the potential canopy light availability (and thus overestimates canopy competition for light), because asymmetric and the plastic 'puzzle-like' arrangement of real tree crowns is more effective than assumed symmetric organization. This most likely inserts a systematic bias into stand growth simulators that are based on the concept of symmetric trees. [ABSTRACT FROM AUTHOR]

Estimation of newly grown needle area, as the most active part of assimilation appa-ratus, is important for better understanding of biochemical processes of trees. This paper investigates the relationship between the projected area of newly grown need-les and other biometric tree parameters (tree height HTREE, diameter at breast height DBH, projected crown area and crown length) of Norway spruce trees. The total pro-jected area of newly grown needles of seven sampled trees was estimated using a detailed inventory of the number and length of shoots. The relationship between this value and other readily measurable biometric tree characteristics was tested to find the best model for estimating total area of newly grown needles. The model using HTREE*DBH with a coefficient of determination of 0.96 had the best performance. The DBH and HTREE inventory of all trees in the studied plot was used to estimate the total projected area of newly grown needles of the entire forest stand (4506.7 m2 per hec-tare). We also investigated specific leaf area (SLA) of newly grown needles in vertical profile of tree crown. SLA increased constantly from the tree top (28.7 cm2.g2) to the crown base (80.3 cm2.g2). [ABSTRACT FROM AUTHOR]

Key message: This study proves the existence of correlative inhibition, and demonstrates that role of light intensity in the growth and death varies among different levels of branching units.Abstract: Within a tree crown, local light conditions vary within a branch and among different branches. Although the role of light intensity in the growth and survival of branches has been studied extensively, the effects of the spatial heterogeneity of light intensity on different levels of branching units are poorly understood. We investigated the effects of light intensity on the growth and death of primary branches (those branching off from the main stem) and secondary branches (those branching off from the primary branches) in the whole crown of Sakhalin spruce (Picea glehnii). The growth of shoot extension on a primary branch or secondary branch may be inhibited on sunlit trees compared to shaded trees when branches under relatively low local light intensity (rPPFD) levels, but it was increased with increasing rPPFD more rapidly on sunlit trees than on shaded trees. A relative importance analysis showed that, in the primary branches, branch growth was mainly influenced by rPPFD, and less influenced by its vertical position within the crown. However, the probability of death of a primary branch was equally influenced by its position within the crown and rPPFD. In contrast, rPPFD played a dominant role in both the growth and death of secondary branches. The results of our study suggest that local light intensity alone cannot fully explain the growth and survival of primary branches simultaneously, and the effects of light intensity vary among different levels of branching units. [ABSTRACT FROM AUTHOR]

The method for evaluation of wind loads and drag coefficients for the trees of different species, size and morphology in natural conditions that does not require special equipment is presented for the first time. Field experiments and numerical simulation were performed for five trees of the Scots pine trees ( Pinus sylvestris L.) under free fall. The field experiments were carried out in the forest for symmetrical 23–27 m tall pine trees. The trees were cut by the chainsaw operator and the videos of a tree falling were obtained. Still images were captured from the video every second after the start of movement. Then the tree stem center lines from the images were obtained. After each run, the length and diameter of the stem and the geometrical characteristics of the tree crown were checked. Numerical experiments were carried out using the deformation model of the tree stem that is inspired by the Cosserat theory of elastic rods. Under the assumption that the drag force is distributed along the tree stem according to a triangular load and increases linearly with velocity, the dynamic global behavior of the real trees was reproduced and the tree stem center lines were obtained. By comparing the data of the two experiments, the drag coefficients of the whole pine trees were found. [ABSTRACT FROM AUTHOR]

Due to the penetration ability of airborne light detection and ranging (lidar) into tree crowns, data pits commonly appear in lidar-derived canopy height models (CHMs). They have a seriously negative effect on the quality of tree detection and subsequent biophysical measurements. To construct a pit-free CHM, an algorithm based on robust locally weighted regression and robust z-score was presented to remove data pits. The significant advantage of the new algorithm is parameter-free, which makes it efficient and robust for practical applications. A numerical test and a real-world example were respectively employed to assess the performance of our method for CHM construction, and its results were compared with those of three classical methods including natural neighbor interpolation of the highest point method, mean and median filters. The numerical test demonstrates that our algorithm is more accurate than the other methods for generating pit-free CHMs under the presence of data pits. The real-world example shows that compared with the classical methods, our method has a better ability of data pit removal. Moreover, our method performs better than the other methods for deriving plot-level maximum tree height from CHMs. In a word, the new method shows high potential for pit-free CHM construction. [ABSTRACT FROM AUTHOR]

Fire severity, defined as the magnitude of fire effects in an ecosystem, is a key factor to consider in planning management strategies for protecting forests against fire. Although prescribed burning has been used as a fuel reduction tool in forest ecosystems, it is quite limited in the Mediterranean region. Furthermore, little is known about how tree crowns are affected by prescribed underburning aimed at reducing fire severity in conifer stands. As part of an ongoing study to assess the effects of prescribed burning on the tree canopy, litterfall is currently being monitored in a network of experimental plots located in mixed ( Pinus nigra and Pinus pinaster ) and pure ( P. nigra ) conifer stands in the Cuenca Mountains (Castilla La Mancha, Spain). A total of 12 study plots (30 m × 30 m) were established in a completely randomized experimental design to determine the effect of burning, with 2 treatments: no burning (control) and burning (i.e. with three replicate plots for each treatment and site). Burning was conducted in May 2016. In each plot, 8 litterfall collectors were installed at regular intervals, according to international protocols (ICP Forests), and all biomass falling into the collectors is being monitored monthly. The specific objective of this study is to assess how prescribed burning affects the rate of generation of foliar and non-foliar litterfall biomass due to the fire. In addition, the Leaf Area Index was estimated before burning and one year later to verify possible changes in the structure of the stands. This information could be used to help minimize the negative impacts of prescribed underburning on litterfall. To our knowledge, this study represents the first attempt to evaluate the effect of prescribed burning on litterfall biomass in Europe. [ABSTRACT FROM AUTHOR]

Sustainable forest management in Zagros Mountains entails accurate information on tree crown density, which could be possibly derived from remote sensing data. Moreover, those remote sensing products need to be objectively evaluated. In this study, the results of three pixel-based classifiers of UltraCam-D aerial imagery were evaluated for classifying Brant`s oak (Quercus brantii Lindl.) crowns in Zagros forests in western Iran. This was carried out by means of receiver operating characteristic (ROC) curve. Therefore, a 30 ha plot was selected in pure Brant`s oak stand, in which the location and crown area of all trees were mapped. The UltraCam-D aerial imagery was classified by maximum likelihood (ML), artificial neural networks (ANNs) and support vector machines (SVMs) classifiers. The classification results were then evaluated by ROC curve and were presented by overall accuracy and Kappa coefficient. Results showed that the ML classified returned the largest area under ROC curve of "tree crowns" (0.894), whereas the lowest rate was found for SVM classifier (0.819). Sensitivity and specificity of "tree crowns" in ML classifier (0.999 and 0.999, respectively) were higher than those in two other classifiers. Although the precision of SVM classifier was the highest in discriminating "tree crowns" (1.000), the achieved accuracy of tree “crown class” was higher for ML classifier (0.999). This study concluded that using ROC curve enables an evaluation accuracy and precision of common pixel-based classifiers of such aerial imagery to discriminate tree crowns.

Data pits commonly appear in lidar-derived canopy height models (CHMs) owing to the penetration ability of airborne light detection and ranging (lidar) into tree crowns. They have a seriously negative effect on the quality of tree detection and subsequent biophysical measurements. In this study, we propose an algorithm based on robust locally weighted regression and robust z-scores for the construction of a pit-free CHM. A significant advantage of the new algorithm is that it is parameter free, which makes it efficient and robust for practical applications. Simulated and airborne lidar-derived data sets are employed to assess the performance of the new method for CHM construction, and its results are compared to those of three classical methods, namely the natural neighbor (NN) interpolation of the highest point method (HPM), mean filter, and median filter. The results from the simulated data set demonstrate that our algorithm is more accurate compared to the three classical methods for generating pit-free CHMs in the presence of data pits. CHM construction using the lidar-derived data set shows that, compared to the classical methods, the new method has a better ability to remove data pits as well as preserving the edges, shapes, and structures of canopy gaps and crowns. Moreover, the proposed method performs better compared to the classical methods in deriving plot-level maximum tree heights from CHMs. Thus, the new method shows high potential for pit-free CHM construction. [ABSTRACT FROM AUTHOR]

• This model is a novel yet simple methodology to quantify the spatially explicit litter loads in frequently burnt longleaf pine forests. • Tree crown objects and estimates of foliage biomass derived from ALS data can be used to characterize patterns of tree leaf litter production and the discontinuity of the litter layer. • Aboveground biomass and YSF are the two major drivers of tree leaf litter accumulation in fire-maintained longleaf pine forests of the southeastern US. The continuity and depth of litter fuelbeds are major drivers of fire spread and fuel consumption. However, no established approach is available for the spatially explicit prediction of litter loads over large areas. Local fuel heterogeneity introduces large uncertainties on estimates derived from field-based models based on the extrapolation of sparse data samples. In fire-maintained pine forests of the southeastern US, litter accumulation and its distribution over the forest floor are mainly driven by vegetation productivity and by the number of years since the last fire (YSF). Some ecological models that simulate fire effects allow for a time-dependent estimation of litter by accounting for the opposing rates of litter deposition and decomposition as a function of YSF at the landscape level, but they do not account for spatial heterogeneity. We developed a conceptually simple approach for wall-to-wall estimation of tree leaf litter loads at high spatial resolution (5 m). The approach involved, first, estimating spatial patterns of tree annual litterfall. We mapped individual tree crowns through segmentation of airborne laser scanning (ALS) data, and we estimated crown foliage biomass using tree inventory data and ALS derived tree crown attributes. Tree annual litterfall was calculated as a fraction of the crown foliage biomass based on leaf turnover rates. We then quantified tree leaf litter accumulation through a spatially explicit implementation of the established Olson (1963) accumulation and negative decay model. We tested and validated our model in several management and research units at Eglin Air Force Base (Florida), Pebble Hill Plantation (Georgia), and Osceola National Forest (Florida), where managers maintain predominantly longleaf pine forests using frequent fire. Pixel-level RMSD and BIAS between tree leaf litter biomass estimated by the proposed model and reference field measurements were 0.21 and 0.01 kg m −2, and area-level RMSD and BIAS were 0.09 and 0.01 kg m −2. We concluded that linking patterns of litterfall and tree leaf litter accumulation to tree crown objects provides a means to characterizing the discontinuity of the litter layer, accounting for spatial heterogeneity largely traceable to tree crown foliage inputs. [ABSTRACT FROM AUTHOR]

Transport caused air pollution is one of the most topical problems in the country. One of the pollutants emitted by the vehicles into the environment is nitrogen dioxide, which adversely affects the plant foliage. At nitrogen dioxide concentration of 30 µg/m3, defoliation process becomes more intense, the growth of trees becomes slower and non-specific leaf choruses symptoms become evident. The aim of research is to investigate of NO2 concentrations and assess the intensity of defoliation process within traffic areas of different intensity. To determine nitrogen dioxide content, the diffusion samplers, which are exhibited after 2 weeks and analyzed in a laboratory, are used. Crown defoliation is determined by comparing the tree to be researched with a reference tree that has all leaves (100%). The main source of nitrogen dioxide in the city is passing vehicles; therefore, research results will reflect the current situation. Santrauka Transporto sukeliama oro tarša yra viena iš aktualiausių problemų šalyje. Vienas iš transporto išmetamų į aplinką teršalų yra azoto dioksidas, kuris neigiamai veikia augalų lapiją. Esant 30 µg/m3 koncentracijai azoto dioksido, suintensyvėja defoliacijos procesas, sulėtėja medžių augimas, atsiranda nespecifinės lapų chlorozės požymių. Tyrimo tikslas − ištirti NO2 koncentracijas ir įvertinti defoliacijos proceso intensyvumą skirtingo intensyvumo eismo zonose. Azoto dioksido kiekiui nustatyti naudojami difuziniai ėmikliai, kurie eksponuojami po 2 savaites ir tiriami laboratorijoje. Lajos defoliacija nustatoma lyginant tiriamą medį su etaloniniu medžiu, kuris turi visus (100 %) lapus. Mieste pagrindinis azoto dioksido šaltinis yra pravažiuojantis transportas, todėl tyrimo rezultatai atspindės esamą situaciją. Reikšminiai žodžiai: azoto dioksidas, defoliacija, oro tarša, automobilių transportas, eismo intensyvumas, medžių laja.

We studied old beech trees individually dispersed in spruce monocultures after having found wildlings in their vicinity. The goal was to define stem and crown dimensions of the trees in dependence on their position in the primary spruce stand and to find out what kind of development they went through before reaching the current condition. We made an inventory of 883 trees in about 800 ha of stands growing in the fir-beech forest altitudinal zone (FAZ). A detailed biometric analysis conducted on two research plots of a total area 19 ha included 110 trees. Their age is 140-180 years as indicated by the analysis of annual rings. Thus, they grow in the second generation of the spruce stand. The fact gives them an absolute competitive advantage, which can be documented by their size (dbh = 49-93 cm as compared with the spruce = 15-66 cm, crown width 8-17 m as compared with the spruce = 1-10 m) as well as by the relation of their disposable (ADISP) and social (ASOC) areas to the size of horizontal crown projection. Regarding the size, the good condition of the crown and the expected recurrent fructification, we can consider these trees suitable for use in the systematic conversion of spruce monocultures into mixed forests for a long time.

In the past, many algorithms have been applied for three-dimensional (3-D) single tree extraction using Airborne Laser Scanner (ALS) data. Clustering based algorithms are widely used in different applications but rarely being they used in the field of forestry using ALS data as an input. In this paper, a comparative qualitative study was conducted using the iterative partitioning and hierarchical clustering based mechanisms and full waveform ALS data as an input to extract the individual trees/tree crowns in their most appropriate shape. The full waveform LIght Detection And Ranging (LIDAR) data was collected from the Waldkirch black forest area in the south-western part of Germany in August 2005 with density of 4–5 points/m2. Both the clustering algorithms were used in their original and modified form for a comparative qualitative analysis of the results obtained in the form of individual clusters containing 3-D points for each tree/tree crown. A total of 378 trees were found in all the 1.2 ha area with height ranging from 15 m to 50.9 m. The forest contains mainly older trees with deciduous, coniferous and mixed stands. The findings showed that among the three kind of clustering methods applied (normal k-means, modified k-means and hierarchical clustering), the modified k-means algorithm using external seed points and scaling down the height for initialization of the clustering process was the most promising method for the extraction of clusters of individual trees/tree crowns. A 3-D reconstruction of extracted individual clusters was carried out using QHull algorithm. In this study, the result was not possible to validate quantitatively due to lack of the field inventory data.

The transparency of trees is the most important indicator for a forest health assessment. This paper presents an efficient method for calculating the crown transparency coefficient from tree binary images. This coefficient is based on the automated quantification of the deep indentation, macro-hole and micro-hole densities. Circular structuring elements are introduced, among other things, to automatically find the significant biological size. The symmetric tree convex hull and the tree smoothed contour are defined to delineate the reference areas necessary to evaluate the above-mentioned densities. Statistical thresholds are proposed to eliminate human operator subjectivity, especially in the automated identification of anatomical elements such as soft and deep crown-indentations or macro and micro crown-holes. A point-wise transparency map is produced to better appreciate the origin of the visible skylight areas in the crown. The crown micro-hole density is calculated from the 0.1-to-0.5 transparency points, the crown macro-hole density from the 0.5-to-1 transparency points. We finally opt for weighting of the above three densities with regard to the importance of the symptoms they describe for a more relevant crown transparency coefficient. A comparative study on several trees from full-size and half-size binary images showed that our method is similar overall to the DSO and less sensitive to scale reduction. [ABSTRACT FROM AUTHOR]

Apart from influencing the amount of leaf-deposited particles, tree crown morphology will influence the local distribution of atmospheric particles. Nevertheless, tree crowns are often represented very rudimentary in three-dimensional air quality models. Therefore, the influence of tree crown representation on the local ambient PM 10 concentration and resulting leaf-deposited PM 10 mass was evaluated, using the three-dimensional computational fluid dynamics (CFD) model ENVI-met ® and ground-based LiDAR imaging. The modelled leaf-deposited PM 10 mass was compared to gravimetric results within three different particle size fractions (0.2–3, 3–10 and >10 μm), obtained at 20 locations within the tree crown. Modelling of the LiDAR-derived tree crown resulted in altered atmospheric PM 10 concentrations in the vicinity of the tree crown. Although this model study was limited to a single tree and model configuration, our results demonstrate that improving tree crown characteristics (shape, dimensions and LAD) affects the resulting local PM 10 distribution in ENVI-met. An accurate tree crown representation seems, therefore, of great importance when aiming at modelling the local PM distribution. [ABSTRACT FROM AUTHOR]

Copyright of Science: Future of Lithuania / Mokslas: Lietuvos Ateitis is the property of Vilnius Gediminas Technical University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Silvicultural regimes that aim at an increased stand structural diversity typically promote small-scale heterogeneity in horizontal and vertical structures, e.g. through the creation of gaps. We used terrestrial laser scanning (TLS) to investigate impacts of altered growing conditions on trees adjacent to artificial gaps as compared to responses of trees in a regularly spaced, thinned forest interior. Based on the TLS-based point clouds we calculated a number of structural tree crown properties that were hypothesized to be sensitive to spatial variability in growing conditions. We found several significant differences between structural properties of trees in the two growing conditions. Compared to trees in regular spacing, border trees near gaps had a lower crown base height (CBH) and a lower height of maximum crown projection. Crown surface area and crown volume of border trees were significantly larger than those of trees growing in a regular spacing. Also, the asymmetry of entire tree crowns of border trees, and in particular of the lower third of crowns, was directed towards the gap center, reflecting the increased light level in the gap. Our results raise concerns that the economic value of border trees is negatively affected by gap creation. These trees had shorter branch free boles and additionally, due to horizontal branch elongation, larger knots. Conversely, the overall increase in structural variability contributed by the border trees in stands with artificial gaps is likely to positively affect several ecosystem functions as well as biodiversity. [ABSTRACT FROM AUTHOR]

Isolated trees in savannas worldwide are known to modify their local environment and interact directly with neighboring plants. Less is known about how related tree species differ in their impacts on surrounding communities, how the effects of trees vary between years, and how composition might change following loss of the tree. To address these knowledge gaps, we explored the following questions: How do savanna trees influence the surrounding composition of herbaceous plants? Is the influence of trees consistent across different species and years? How does this change following the death of the tree? We surveyed herbaceous species composition and environmental attributes surrounding living and dead evergreen and deciduous Quercus trees in California (USA) savannas across several years that differed in their total precipitation. Oak trees of all species created distinct, homogenous understory communities dominated by exotic grasses across several sites. The composition of the low-diversity understory communities showed less interannual variation than open grassland, despite a two-fold difference in precipitation between the driest and wettest year. Vegetation composition was correlated with variation in soil properties, which were strongly affected by trees. Oaks also influenced the communities beyond the edge of the crown, but this depended on site and oak species. Low-diversity understory communities persisted up to 43 years following the death of the tree. A gradual decline in the effect of trees on the physical environment following death did not result in vegetation becoming more similar to open grassland over time. The presence of long-lasting legacies of past tree crowns highlights the difficulty of assigning control of the current distribution of herbaceous species in grassland to their contemporary environment. [ABSTRACT FROM AUTHOR]

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)