Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Non-destructive tree volume estimation through quantitative structure modelling: Comparing UAV laser scanning with terrestrial LIDAR
Brede, Benjamin ; Calders, Kim ; Lau, Alvaro ; Raumonen, Pasi ; Bartholomeus, Harm M. ; Herold, Martin ; Kooistra, Lammert - \ 2019
Remote Sensing of Environment 233 (2019). - ISSN 0034-4257
Above-Ground Biomass (AGB) product calibration and validation require ground reference plots at hectometric scales to match space-borne missions' resolution. Traditional forest inventory methods that use allometric equations for single tree AGB estimation suffer from biases and low accuracy, especially when dealing with large trees. Terrestrial Laser Scanning (TLS) and explicit tree modelling show high potential for direct estimates of tree volume, but at the cost of time demanding fieldwork. This study aimed to assess if novel Unmanned Aerial Vehicle Laser Scanning (UAV-LS) could overcome this limitation, while delivering comparable results. For this purpose, the performance of UAV-LS in comparison with TLS for explicit tree modelling was tested in a Dutch temperate forest. In total, 200 trees with Diameter at Breast Height (DBH) ranging from 6 to 91 cm from 5 stands, including coniferous and deciduous species, have been scanned, segmented and subsequently modelled with TreeQSM. TreeQSM is a method that builds explicit tree models from laser scanner point clouds. Direct comparison with TLS derived models showed that UAV-LS reliably modelled the volume of trunks and branches with diameter ≥30 cm in the mature beech and oak stand with Concordance Correlation Coefficient (CCC) of 0.85 and RMSE of1.12 m3. Including smaller branch volume led to a considerable overestimation and decrease in correspondence to CCC of 0.51 and increase in RMSE to 6.59 m3. Denser stands prevented sensing of trunks and further decreased CCC to 0.36 in the Norway spruce stand. Also small, young trees posed problems by preventing a proper depiction of the trunk circumference and decreased CCC to 0.01. This dependence on stand indicated a strong impact of canopy structure on the UAV-LS volume modelling capacity. Improved flight paths, repeated acquisition flights or alternative modelling strategies could improve UAV-LS modelling performance under these conditions. This study contributes to the use of UAV-LS for fast tree volume and AGB estimation on scales relevant for satellite AGB product calibration and validation.

Tree Biomass Equations from Terrestrial LiDAR: A Case Study in Guyana
Lau, Alvaro ; Calders, Kim ; Bartholomeus, Harm ; Martius, Christopher ; Raumonen, Pasi ; Herold, Martin ; Vicari, Matheus ; Sukhdeo, Hansrajie ; Singh, Jeremy ; Goodman, Rosa - \ 2019
Forests 10 (2019)6. - ISSN 1999-4907 - 18 p.
Large uncertainties in tree and forest carbon estimates weaken national efforts to accurately estimate aboveground biomass (AGB) for their national monitoring, measurement, reporting and verification system. Allometric equations to estimate biomass have improved, but remain limited. They rely on destructive sampling; large trees are under-represented in the data used to create them; and they cannot always be applied to different regions. These factors lead to uncertainties and systematic errors in biomass estimations. We developed allometric models to estimate tree AGB in Guyana. These models were based on tree attributes (diameter, height, crown diameter) obtained from terrestrial laser scanning (TLS) point clouds from 72 tropical trees and wood density. We validated our methods and models with data from 26 additional destructively harvested trees. We found that our best TLS-derived allometric models included crown diameter, provided more accurate AGB estimates ( R2 = 0.92–0.93) than traditional pantropical models ( R2 = 0.85–0.89), and were especially accurate for large trees (diameter > 70 cm). The assessed pantropical models underestimated AGB by 4 to 13%. Nevertheless, one pantropical model (Chave et al. 2005 without height) consistently performed best among the pantropical models tested ( R2 = 0.89) and predicted AGB accurately across all size classes—which but for this could not be known without destructive or TLS-derived validation data. Our methods also demonstrate that tree height is difficult to measure in situ, and the inclusion of height in allometric models consistently worsened AGB estimates. We determined that TLS-derived AGB estimates were unbiased. Our approach advances methods to be able to develop, test, and choose allometric models without the need to harvest trees.
An architectural understanding of natural sway frequencies in trees
Jackson, T. ; Shenkin, A. ; Moore, J. ; Bunce, A. ; Emmerik, T. Van; Kane, B. ; Burcham, D. ; James, K. ; Selker, J. ; Calders, K. ; Origo, N. ; Disney, M. ; Burt, A. ; Wilkes, P. ; Raumonen, P. ; Gonzalez De Tanago Menaca, J. ; Lau, A. ; Herold, M. ; Goodman, R.C. ; Fourcaud, T. ; Malhi, Y. - \ 2019
Journal of the Royal Society, Interface 16 (2019)155. - ISSN 1742-5689 - 9 p.
The relationship between form and function in trees is the subject of a longstanding debate in forest ecology and provides the basis for theories concerning forest ecosystem structure and metabolism. Trees interact with the wind in a dynamic manner and exhibit natural sway frequencies and damping processes that are important in understanding wind damage. Tree-wind dynamics are related to tree architecture, but this relationship is not well understood. We present a comprehensive view of natural sway frequencies in trees by compiling a dataset of field measurement spanning conifers and broadleaves, tropical and temperate forests. The field data show that a cantilever beam approximation adequately predicts the fundamental frequency of conifers, but not that of broadleaf trees. We also use structurally detailed tree dynamics simulations to test fundamental assumptions underpinning models of natural frequencies in trees. We model the dynamic properties of greater than 1000 trees using a finite-element approach based on accurate three-dimensional model trees derived from terrestrial laser scanning data. We show that (1) residual variation, the variation not explained by the cantilever beam approximation, in fundamental frequencies of broadleaf trees is driven by their architecture; (2) slender trees behave like a simple pendulum, with a single natural frequency dominating their motion, which makes them vulnerable to wind damage and (3) the presence of leaves decreases both the fundamental frequency and the damping ratio. These findings demonstrate the value of new three-dimensional measurements for understanding wind impacts on trees and suggest new directions for improving our understanding of tree dynamics from conifer plantations to natural forests.
The Importance of Consistent Global Forest Aboveground Biomass Product Validation
Duncanson, L. ; Armston, J. ; Disney, M. ; Avitabile, V. ; Barbier, N. ; Calders, K. ; Carter, S. ; Chave, J. ; Herold, M. ; Crowther, T.W. ; Falkowski, M. ; Kellner, J.R. ; Labrière, N. ; Lucas, R. ; Macbean, N. ; Mcroberts, R.E. ; Meyer, V. ; Næsset, E. ; Nickeson, J.E. ; Paul, K.I. ; Phillips, O.L. ; Réjou-méchain, M. ; Román, M. ; Roxburgh, S. ; Saatchi, S. ; Schepaschenko, D. ; Scipal, K. ; Siqueira, P.R. ; Whitehurst, A. ; Williams, M. - \ 2019
Surveys in Geophysics 40 (2019)4. - ISSN 0169-3298 - p. 979 - 999.
Several upcoming satellite missions have core science requirements to produce data for accurate forest aboveground biomass mapping. Largely because of these mission datasets, the number of available biomass products is expected to greatly increase over the coming decade. Despite the recognized importance of biomass mapping for a wide range of science, policy and management applications, there remains no community accepted standard for satellite-based biomass map validation. The Committee on Earth Observing Satellites (CEOS) is developing a protocol to fill this need in advance of the next generation of biomass-relevant satellites, and this paper presents a review of biomass validation practices from a CEOS perspective. We outline the wide range of anticipated user requirements for product accuracy assessment and provide recommendations for the validation of biomass products. These recommendations include the collection of new, high-quality in situ data and the use of airborne lidar biomass maps as tools toward transparent multi-resolution validation. Adoption of community-vetted validation standards and practices will facilitate the uptake of the next generation of biomass products.
Finite element analysis of trees in the wind based on terrestrial laser scanning data
Jackson, T. ; Shenkin, A. ; Wellpott, A. ; Calders, K. ; Origo, N. ; Disney, M. ; Burt, A. ; Raumonen, P. ; Gardiner, B. ; Herold, M. ; Fourcaud, T. ; Malhi, Y. - \ 2019
Agricultural and Forest Meteorology 265 (2019). - ISSN 0168-1923 - p. 137 - 144.
Critical wind speed - Finite element analysis - Resonant frequency - Terrestrial laser scanning - TLS - Wind damage

Wind damage is an important driver of forest structure and dynamics, but it is poorly understood in natural broadleaf forests. This paper presents a new approach in the study of wind damage: combining terrestrial laser scanning (TLS) data and finite element analysis. Recent advances in tree reconstruction from TLS data allowed us to accurately represent the 3D geometry of a tree in a mechanical simulation, without the need for arduous manual mapping or simplifying assumptions about tree shape. We used this simulation to predict the mechanical strains produced on the trunks of 21 trees in Wytham Woods, UK, and validated it using strain data measured on these same trees. For a subset of five trees near the anemometer, the model predicted a five-minute time-series of strain with a mean cross-correlation coefficient of 0.71, when forced by the locally measured wind speed data. Additionally, the maximum strain associated with a 5 ms−1 or 15 ms-1 wind speed was well predicted by the model (N = 17, R2 = 0.81 and R2 = 0.79, respectively). We also predicted the critical wind speed at which the trees will break from both the field data and models and find a good overall agreement (N = 17, R2 = 0.40). Finally, the model predicted the correct trend in the fundamental frequencies of the trees (N = 20, R2 = 0.38) although there was a systematic underprediction, possibly due to the simplified treatment of material properties in the model. The current approach relies on local wind data, so must be combined with wind flow modelling to be applicable at the landscape-scale or over complex terrain. This approach is applicable at the plot level and could also be applied to open-grown trees, such as in cities or parks.

Geometric Tree Modelling with UAV-based Lidar
Brede, B. ; Raumonen, Pasi ; Calders, Kim ; Lau Sarmiento, A.I. ; Bartholomeus, H.M. ; Herold, M. ; Kooistra, L. - \ 2018
Assessing biomass and architecture of tropical trees with terrestrial laser scanning
Lau Sarmiento, Alvaro Ivan - \ 2018
Wageningen University. Promotor(en): M. Herold, co-promotor(en): H. Bartholomeus; K. Calders. - Wageningen : Wageningen University - ISBN 9789463434720 - 157
Assessing the structural differences between tropical forest types using Terrestrial Laser Scanning
Decuyper, Mathieu ; Mulatu, Kalkidan Ayele ; Brede, Benjamin ; Calders, Kim ; Armston, John ; Rozendaal, Danaë M.A. ; Mora, Brice ; Clevers, Jan G.P.W. ; Kooistra, Lammert ; Herold, Martin ; Bongers, Frans - \ 2018
Forest Ecology and Management 429 (2018). - ISSN 0378-1127 - p. 327 - 335.
Increasing anthropogenic pressure leads to loss of habitat through deforestation and degradation in tropical forests. While deforestation can be monitored relatively easily, forest management practices are often subtle processes, that are difficult to capture with for example satellite monitoring. Conventional measurements are well established and can be useful for management decisions, but it is believed that Terrestrial Laser Scanning (TLS) has a role in quantitative monitoring and continuous improvement of methods. In this study we used a combination of TLS and conventional forest inventory measures to estimate forest structural parameters in four different forest types in a tropical montane cloud forest in Kafa, Ethiopia. Here, the four forest types (intact forest, coffee forest, silvopasture, and plantations) are a result of specific management practices (e.g. clearance of understory in coffee forest), and not different forest communities or tree types. Both conventional and TLS derived parameters confirmed our assumptions that intact forest had the highest biomass, silvopasture had the largest canopy gaps, and plantations had the lowest canopy openness. Contrary to our expectations, coffee forest had higher canopy openness and similar biomass as silvopasture, indicating a significant loss of forest structure. The 3D vegetation structure (PAVD – Plant area vegetation density) was different between the forest types with the highest PAVD in intact forest and plantation canopy. Silvopasture was characterised by a low canopy but high understorey PAVD, indicating regeneration of the vegetation and infrequent fuelwood collection and/or non-intensive grazing. Coffee forest canopy had low PAVD, indicating that many trees had been removed, despite coffee needing canopy shade. These findings may advocate for more tangible criteria such as canopy openness thresholds in sustainable coffee certification schemes. TLS as tool for monitoring forest structure in plots with different forest types shows potential as it can capture the 3D position of the vegetation volume and open spaces at all heights in the forest. To quantify changes in different forest types, consistent monitoring of 3D structure is needed and here TLS is an add-on or an alternative to conventional forest structure monitoring. However, for the tropics, TLS-based automated segmentation of trees to derive DBH and biomass is not widely operational yet, nor is species richness determination in forest monitoring. Integration of data sources is needed to fully understand forest structural diversity and implications of forest management practices on different forest types.
New perspectives on the ecology of tree structure and tree communities through terrestrial laser scanning
Malhi, Yadvinder ; Jackson, Tobias ; Bentley, Lisa Patrick ; Lau, Alvaro ; Shenkin, Alexander ; Herold, Martin ; Calders, Kim ; Bartholomeus, Harm ; Disney, Mathias I. - \ 2018
Interface Focus 8 (2018)2. - ISSN 2042-8898
Branching - Metabolic scaling theory - Terrestrial laser scanning - Tree architecture - Tree surface area - Wind speed
Terrestrial laser scanning (TLS) opens up the possibility of describing the three-dimensional structures of trees in natural environments with unprecedented detail and accuracy. It is already being extensively applied to describe how ecosystem biomass and structure vary between sites, but can also facilitate major advances in developing and testing mechanistic theories of tree form and forest structure, thereby enabling us to understand why trees and forests have the biomass and three-dimensional structure they do. Here we focus on the ecological challenges and benefits of understanding tree form, and highlight some advances related to capturing and describing tree shape that are becoming possible with the advent of TLS. We present examples of ongoing work that applies, or could potentially apply, new TLS measurements to better understand the constraints on optimization of tree form. Theories of resource distribution networks, such as metabolic scaling theory, can be tested and further refined. TLS can also provide new approaches to the scaling of woody surface area and crown area, and thereby better quantify the metabolism of trees. Finally, we demonstrate how we can develop a more mechanistic understanding of the effects of avoidance of wind risk on tree form and maximum size. Over the next few years, TLS promises to deliver both major empirical and conceptual advances in the quantitative understanding of trees and tree-dominated ecosystems, leading to advances in understanding the ecology of why trees and ecosystems look and grow the way they do.
Estimation of above-ground biomass of large tropical trees with terrestrial LiDAR
Gonzalez De Tanago, Jose ; Lau, Alvaro ; Bartholomeus, Harm ; Herold, Martin ; Avitabile, Valerio ; Raumonen, Pasi ; Martius, Christopher ; Goodman, Rosa C. ; Disney, Mathias ; Manuri, Solichin ; Burt, Andrew ; Calders, Kim - \ 2018
Methods in Ecology and Evolution 9 (2018)2. - ISSN 2041-210X - p. 223 - 234.
1. Tropical forest biomass is a crucial component of global carbon emission estimations. However, calibration and validation of such estimates require accurate and effective methods to estimate in situ above-ground biomass (AGB). Present methods rely on allometric models that are highly uncertain for large tropical trees. Terrestrial laser scanning (TLS) tree modelling has demonstrated to be more accurate than these models to infer forest AGB. Nevertheless, applying TLS methods on tropical large trees is still challenging. We propose a method to estimate AGB of large tropical trees by three-dimensional (3D) tree modelling of TLS point clouds. 2. Twenty-nine plots were scanned with a TLS in three study sites (Peru, Indonesia and Guyana). We identified the largest tree per plot (mean diameter at breast height of 73.5 cm), extracted its point cloud and calculated its volume by 3D modelling its structure using quantitative structure models (QSM) and converted to AGB using species-specific wood density. We also estimated AGB using pantropical and local allometric models. To assess the accuracy of our and allometric methods, we harvest the trees and took destructive measurements. 3. AGB estimates by the TLS–QSM method showed the best agreement in comparison to destructive harvest measurements (28.37% coefficient of variation of root mean square error [CV-RMSE] and concordance correlation coefficient [CCC] of 0.95), outperforming the pantropical allometric models tested (35.6%–54.95% CV-RMSE and CCC of 0.89–0.73). TLS–QSM showed also the lowest bias (overall underestimation of 3.7%) and stability across tree size range, contrasting with the allometric models that showed a systematic bias (overall underestimation ranging 15.2%–35.7%) increasing linearly with tree size. The TLS–QSM method also provided accurate tree wood volume estimates (CV RMSE of 23.7%) with no systematic bias regardless the tree structural characteristics. 4. Our TLS–QSM method accounts for individual tree biophysical structure more effectively than allometric models, providing more accurate and less biased AGB estimates for large tropical trees, independently of their morphology. This non-destructive method can be further used for testing and calibrating new allometric models, reducing the current under-representation of large trees in and enhancing present and past estimates of forest biomass and carbon emissions from tropical forests.
Tropical forest canopies and their relationships with climate and disturbance: results from a global dataset of consistent field-based measurements
Pfeifer, Marion ; Gonsamo, Alemu ; Woodgate, William ; Cayuela, Luis ; Marshall, Andrew R. ; Ledo, Alicia ; Paine, Timothy C.E. ; Marchant, Rob ; Burt, Andrew ; Calders, Kim ; Courtney-mustaphi, Colin ; Cuni-sanchez, Aida ; Deere, Nicolas J. ; Denu, Dereje ; Gonzalez De Tanago Meñaca, J. ; Hayward, Robin ; Lau Sarmiento, A.I. ; Macía, Manuel J. ; Olivier, Pieter I. ; Pellikka, Petri ; Seki, Hamidu ; Shirima, Deo ; Trevithick, Rebecca ; Wedeux, Beatrice ; Wheeler, Charlotte ; Munishi, Pantaleo K.T. ; Martin, Thomas ; Mustari, Abdul ; Platts, Philip J. - \ 2018
Forest Ecosystems 5 (2018). - ISSN 2095-6355 - 14 p.
Background: Canopy structure, defined by leaf area index (LAI), fractional vegetation cover (FCover) and fraction of absorbed photosynthetically active radiation (fAPAR), regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics. Methods: Here, we introduce the Global LAI database: a global dataset of field-based canopy structure measurements spanning tropical forests in four continents (Africa, Asia, Australia and the Americas). We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences. Results: Using data collected from 887 tropical forest plots, we show that maximum water deficit, defined across the most arid months of the year, is an important predictor of canopy structure, with all three canopy attributes declining significantly with increasing water deficit. Canopy attributes also increase with minimum temperature, and with the protection of forests according to both active (within protected areas) and passive measures (through topography). Once protection and continent effects are accounted for, other anthropogenic measures (e.g. human population) do not improve the model. Conclusions: We conclude that canopy structure in the tropics is primarily a consequence of forest adaptation to the maximum water deficits historically experienced within a given region. Climate change, and in particular changes in drought regimes may thus affect forest structure and function, but forest protection may offer some resilience against this effect.
Capturing forest structure and change – 5 years of laser scanning and future perspectives using UAV based LiDAR
Bartholomeus, H.M. ; Lau Sarmiento, A.I. ; Gonzalez de Tanago Meñaca, J. ; Herold, M. ; Brede, B. ; Kooistra, L. ; Calders, Kim - \ 2017
In: SilviLaser 2017 Program. - Blacksburg : Virginia Tech - p. 61 - 62.
Above-ground biomass assessment of tropical trees with Terrestrial LiDAR and 3D architecture models
Lau Sarmiento, A.I. ; Gonzalez de Tanago Meñaca, J. ; Bartholomeus, H.M. ; Herold, M. ; Avitabile, V. ; Raumonen, Pasi ; Martius, Christopher ; Goodman, R.C. ; Disney, Mathias ; Manuri, Solichin ; Burt, Andrew ; Calders, Kim - \ 2017
In: SilviLaser 2017 Program. - Blacksburg : Virginia Tech - p. 123 - 124.
Ecosystem structure
Mücher, C.A. ; Calders, K. ; Petrou, Z.I. ; Reiche, J. - \ 2017
In: A Sourcebook of Methods and Procedures for Monitoring Essential Biodiversity Variables in Tropical Forests with Remote Sensing / Gill, Mike, Jongman, Rob, Luque, Sandra, Mora, Brice, Paganini, Marc, Szantoi, Zoltan, Wageningen : GOFC-GOLD Land Cover Project Office, Wageningen University, The Netherlands (Report version UNCBD COP-13 ) - p. 67 - 82.
Data acquisition considerations for Terrestrial Laser Scanning of forest plots
Wilkes, Phil ; Lau Sarmiento, Alvaro ; Disney, Mathias ; Calders, Kim ; Burt, Andrew ; Gonzalez De Tanago Meñaca, J. ; Bartholomeus, Harm ; Brede, Benjamin ; Herold, Martin - \ 2017
Remote Sensing of Environment 196 (2017). - ISSN 0034-4257 - p. 140 - 153.
The poor constraint of forest Above Ground Biomass (AGB) is responsible, in part, for large uncertainties in modelling future climate scenarios. Terrestrial Laser Scanning (TLS) can be used to derive unbiased and non-destructive estimates of tree structure and volume and can, therefore, be used to address key uncertainties in forest AGB estimates. Here we review our experience of TLS sampling strategies from 27 campaigns conducted over the past 5 years, across tropical and temperate forest plots, where data was captured with a RIEGL VZ-400 laser scanner. The focus is on strategies to derive Geometrical Modelling metrics (e.g. tree volume) over forest plots (≥1 ha) which require the accurate co-registration of 10s to 100s of individual point clouds. We recommend a 10 m × 10 m sampling grid as an approach to produce a point cloud with a uniform point distribution, that can resolve higher order branches (down to a few cm in diameter) towards the top of 30+ m canopies and can be captured in a timely fashion i.e. ∼3–6 days per ha. A data acquisition protocol, such as presented here, would facilitate data interoperability and inter-comparison of metrics between instruments/groups, from plot to plot and over time.
Evaluation of the Range Accuracy and the Radiometric Calibration of Multiple Terrestrial Laser Scanning Instruments for Data Interoperability
Calders, Kim ; Disney, Mathias I. ; Armston, John ; Burt, Andrew ; Brede, Benjamin ; Origo, Niall ; Muir, Jasmine ; Nightingale, Joanne - \ 2017
IEEE Transactions on Geoscience and Remote Sensing 55 (2017)5. - ISSN 0196-2892 - p. 2716 - 2724.
Terrestrial laser scanning (TLS) data provide 3-D measurements of vegetation structure and have the potential to support the calibration and validation of satellite and airborne sensors. The increasing range of different commercial and scientific TLS instruments holds challenges for data and instrument interoperability. Using data from various TLS sources will be critical to upscale study areas or compare data. In this paper, we provide a general framework to compare the interoperability of TLS instruments. We compare three TLS instruments that are the same make and model, the RIEGL VZ-400. We compare the range accuracy and evaluate the manufacturer's radiometric calibration for the uncalibrated return intensities. Our results show that the range accuracy between instruments is comparable and within the manufacturer's specifications. This means that the spatial XYZ data of different instruments can be combined into a single data set. Our findings demonstrate that radiometric calibration is instrument specific and needs to be carried out for each instrument individually before including reflectance information in TLS analysis. We show that the residuals between the calibrated reflectance panels and the apparent reflectance measured by the instrument are greatest for highest reflectance panels (residuals ranging from 0.058 to 0.312).
Data from: "African savanna-forest boundary dynamics: a 20-year study"
Cuni-sanchez, Aida ; White, Lee J.T. ; Calders, K. ; Jeffery, Kathryn J. ; Abernethy, Katharine ; Burt, Andrew ; Disney, Mathias ; Gilpin, Martin ; Gomez-dans, Jose L. ; Lewis, Simon L. - \ 2016
Recent studies show widespread encroachment of forest into savannas with important consequences for the global carbon cycle and land-atmosphere interactions. However, little research has focused on in situ measurements of forest-savanna boundary change over time. Using long-term inventory plots we quantify changes in above-ground biomass (AGB), vegetation structure and biodiversity over 20 years for five vegetation types (savanna, colonising forest or F1, successional monodominant forest or F2, Marantaceae forest or F3 and mixed forest or F4) along a savanna-forest transition of central Gabon, all occurring on similar soils. Additionally, we use novel 3D terrestrial laser scanning (TLS) measurements to assess forest structure differences across the transition. Overall, F1 and F2 forests increased in AGB, mainly as a result of adding stems (recruitment in F1) or increased Basal Area (F2). Some plots of F3 and F4 increased in AGB while some decreased. Changes in biodiversity and species’ dominance were small. After 20 years no plot could be classified as having moved to the next stage in the succession. TLS vertical plant profiles showed very distinctive differences amongst the vegetation types. We highlight two relevant points: (i) as forest colonises, changes in biodiversity are much slower than changes in forest structure or AGB; and (ii) all forest types store important quantities of Carbon. Decades long-term monitoring is likely to be required to assess the speed of transition between vegetation types, ideally with TLS, as this provides more objective forest classifications than inventory monitoring.
3D Measurements of Tropical Forest Structure for BIOMASS, Morphology and Calibration and Validation of Satellite Observations
Disney, Mathias ; Burt, Andrew ; Calders, K. ; Raumonen, P. ; Herold, M. ; Lewis, P. ; Lewis, S. ; Boni Vicari, M. ; Rowland, L. ; Meir, P. ; Mitchard, Edward - \ 2016
Influence of tree crown characteristics on the local PM10 distribution inside an urban street canyon in Antwerp (Belgium): A model and experimental approach
Hofman, Jelle ; Bartholomeus, Harm ; Janssen, Stijn ; Calders, Kim ; Wuyts, Karen ; Wittenberghe, Shari Van; Samson, Roeland - \ 2016
Urban Forestry and Urban Greening 20 (2016). - ISSN 1618-8667 - p. 265 - 276.
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 PM10 concentration and resulting leaf-deposited PM10 mass was evaluated, using the three-dimensional computational fluid dynamics (CFD) model ENVI-met® and ground-based LiDAR imaging. The modelled leaf-deposited PM10 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 PM10 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 PM10 distribution in ENVI-met. An accurate tree crown representation seems, therefore, of great importance when aiming at modelling the local PM distribution.
Forest inventory with terrestrial LiDAR : A comparison of static and hand-held mobile laser scanning
Bauwens, Sébastien ; Bartholomeus, Harm ; Calders, Kim ; Lejeune, Philippe - \ 2016
Forests 7 (2016)6. - ISSN 1999-4907
Digital elevation model - Forestry - Hand-held mobile laser scanning - HMLS - SLAM - Stem mapping - Terrestrial laser scanning - TLS

The application of static terrestrial laser scanning (TLS) in forest inventories is becoming more effective. Nevertheless, the occlusion effect is still limiting the processing efficiency to extract forest attributes. The use of a mobile laser scanner (MLS) would reduce this occlusion. In this study, we assessed and compared a hand-held mobile laser scanner (HMLS) with two TLS approaches (single scan: SS, and multi scan: MS) for the estimation of several forest parameters in a wide range of forest types and structures. We found that SS is competitive to extract the ground surface of forest plots, while MS gives the best result to describe the upper part of the canopy. The whole cross-section at 1.3 m height is scanned for 91% of the trees (DBH > 10 cm) with the HMLS leading to the best results for DBH estimates (bias of -0.08 cm and RMSE of 1.11 cm), compared to no fully-scanned trees for SS and 42% fully-scanned trees for MS. Irregularities, such as bark roughness and non-circular cross-section may explain the negative bias encountered for all of the scanning approaches. The success of using MLS in forests will allow for 3D structure acquisition on a larger scale and in a time-efficient manner.

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