Browsing by Author "Vastaranta, Mikko"

Filter results by typing the first few letters
Now showing 1 - 18 of 18
  • Accuracy of Kinematic Positioning Using Global Satellite Navigation Systems under Forest Canopies
    (2015) Kaartinen, Harri; Hyyppä, Juha; Vastaranta, Mikko; Kukko, Antero; Jaakkola, Anttoni; Yu, Xiaowei; Pyörälä, Jiri; Liang, Xinlian; Liu, Jingbin; Wang, Yungshen; Kaijaluoto, Risto; Melkas, Timo; Holopainen, Markus; Hyyppä, Hannu
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Airborne Laser Scanning Outperforms the Alternative 3D Techniques in Capturing Variation in Tree Height and Forest Density in Southern Boreal Forests
    (2018-11) Vastaranta, Mikko; Yrttimaa, Tuomas; Saarinen, Ninni; Yu, Xiaowei; Karjalainen, Mika; Nurminen, Kimmo; Karila, Kirsi; Kankare, Ville; Luoma, Ville; Pyörälä, Jiri; Junttila, Samuli; Tanhuanpää, Topi; Kaartinen, Harri; Kukko, Antero; Honkavaara, Eija; Jaakkola, Anttoni; Liang, Xinlian; Wang, Yunsheng; Vaaja, Matti; Hyyppä, Hannu; Katoh, Masato; Wulder, Michael A.; Holopainen, Markus; Hyyppa, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The objective of this study is to better understand the relationship between forest structure and point cloud features generated from certain airborne and space borne sensors. Point cloud features derived from airborne laser scanning (ALS), aerial imagery (AI), WorldView-2 imagery (WV2), TerraSAR-X, and Tandem-X (TDX) data were classified as features characterizing forest height and density as well as variation in tree height. Correlations between these features and field-measured attributes describing forest height, density and tree height variation were investigated at plot scale. From the field-measured attributes, basal area (G) and the number of trees per unit area (N) were used as forest density indicators whereas maximum tree height (H-max) and standard deviation in tree height (H-std) were used as indicators for forest height and tree height variation, respectively. In the analyses, field observations from 91 sample plots (32 m x 32 m) located in southern Finland were used. Even though ALS was found to be the most accurate data source in characterizing forest structure, AI, WV2, and TDX were also capable of characterizing forest height at plot scale with correlation coefficients stronger than 0.85. However, ALS was the only data source capable of providing separate features for characterizing also the variation in tree height and forest density. Features related to forest height, generated from the other data sources besides ALS, also provided strongest correlation with the forest density attributes and variation in tree height, in addition to H-max. Due to these more diverse characterization capabilities, forest structural attributes can be predicted more accurately by using ALS, also in the areas where the relation between the attributes of interest is not solely dependent on forest height, compared to the other investigated 3D remote sensing data sources.
  • Assessing precision in conventional field measurements of individual tree attributes
    (2017) Luoma, Ville; Saarinen, Ninni; Wulder, Michael A.; White, Joanne C.; Vastaranta, Mikko; Holopainen, Markus; Hyyppä, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Forest resource information has a hierarchical structure: individual tree attributes are summed at the plot level and then in turn, plot-level estimates are used to derive stand or large-area estimates of forest resources. Due to this hierarchy, it is imperative that individual tree attributes are measured with accuracy and precision. With the widespread use of different measurement tools, it is also important to understand the expected degree of precision associated with these measurements. The most prevalent tree attributes measured in the field are tree species, stem diameter-at-breast-height (dbh), and tree height. For dbh and height, the most commonly used measuring devices are calipers and clinometers, respectively. The aim of our study was to characterize the precision of individual tree dbh and height measurements in boreal forest conditions when using calipers and clinometers. The data consisted of 319 sample trees at a study area in Evo, southern Finland. The sample trees were measured independently by four trained mensurationists. The standard deviation in tree dbh and height measurements was 0.3 cm (1.5%) and 0.5 m (2.9%), respectively. Precision was also assessed by tree species and tree size classes; however, there were no statistically significant differences between the mensurationists for dbh or height measurements. Our study offers insights into the expected precision of tree dbh and height as measured with the most commonly used devices. These results are important when using sample plot data in forest inventory applications, especially now, at a time when new tree attribute measurement techniques based on remote sensing are being developed and compared to the conventional caliper and clinometer measurements.
  • Assessing the effects of thinning on stem growth allocation of individual Scots pine trees
    (2020-10-15) Saarinen, Ninni; Kankare, Ville; Yrttimaa, Tuomas; Viljanen, Niko; Honkavaara, Eija; Holopainen, Markus; Hyyppä, Juha; Huuskonen, Saija; Hynynen, Jari; Vastaranta, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Forest management alters the growing conditions and thus further development of trees. However, quantitative assessment of forest management on tree growth has been demanding as methodologies for capturing changes comprehensively in space and time have been lacking. Terrestrial laser scanning (TLS) has shown to be capable of providing three-dimensional (3D) tree stem reconstructions required for revealing differences between stem shapes and sizes. In this study, we used 3D reconstructions of tree stems from TLS and an unmanned aerial vehicle (UAV) to investigate how varying thinning treatments and the following growth effects affected stem shape and size of Scots pine (Pinus sylvestris L.) trees. The results showed that intensive thinning resulted in more stem volume and therefore total biomass allocation and carbon uptake compared to the moderate thinning. Relationship between tree height and diameter at breast height (i.e. slenderness) varied between both thinning intensity and type (i.e. from below and above) indicating differing response to thinning and allocation of stem growth of Scots pine trees. Furthermore, intensive thinning, especially from below, produced less variation in relative stem attributes characterizing stem shape and size. Thus, it can be concluded that thinning intensity, type, and the following growth effects have an impact on post-thinning stem shape and size of Scots pine trees. Our study presented detailed measurements on post-thinning stem growth of Scots pines that have been laborious or impracticable before the emergence of detailed 3D technologies. Moreover, the stem reconstructions from TLS and UAV provided variety of attributes characterizing stem shape and size that have not traditionally been feasible to obtain. The study demonstrated that detailed 3D technologies, such as TLS and UAV, provide information that can be used to generate new knowledge for supporting forest management and silviculture as well as improving ecological understanding of boreal forests.1
  • Can Leaf Water Content Be Estimated Using Multispectral Terrestrial Laser Scanning? A Case Study With Norway Spruce Seedlings
    (2018-03-08) Junttila, Samuli; Sugano, Junko; Vastaranta, Mikko; Linnakoski, Riikka; Kaartinen, Harri; Kukko, Antero; Holopainen, Markus; Hyyppä, Hannu; Hyyppä, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Changing climate is increasing the amount and intensity of forest stress agents, such as drought, pest insects, and pathogens. Leaf water content, measured here in terms of equivalent water thickness (EWT), is an early indicator of tree stress that provides timely information about the health status of forests. Multispectral terrestrial laser scanning (MS-TLS) measures target geometry and reflectance simultaneously, providing spatially explicit reflectance information at several wavelengths. EWT and leaf internal structure affect leaf reflectance in the shortwave infrared region that can be used to predict EWT with MS-TLS. A second wavelength that is sensitive to leaf internal structure but not affected by EWT can be used to normalize leaf internal effects on the shortwave infrared region and improve the prediction of EWT. Here we investigated the relationship between EWT and laser intensity features using multisensor MS-TLS at 690, 905, and 1,550 nm wavelengths with both drought-treated and Endoconidiophora polonica inoculated Norway spruce seedlings to better understand how MS-TLS measurements can explain variation in EWT. In our study, a normalized ratio of two wavelengths at 905 and 1,550 nm and length of seedling explained 91% of the variation (R-2) in EWT as the respective prediction accuracy for EWT was 0.003 g/cm(2) in greenhouse conditions. The relation between EWT and the normalized ratio of 905 and 1,550 nm wavelengths did not seem sensitive to a decreased point density of the MS-TLS data. Based on our results, different EWTs in Norway spruce seedlings show different spectral responses when measured using MS-TLS. These results can be further used when developing EWT monitoring for improving forest health assessments.
  • Comparison of backpack, handheld, under-canopy UAV, and above-canopy UAV laser scanning for field reference data collection in boreal forests
    (2020-10-02) Hyyppä, Eric; Yu, Xiaowei; Kaartinen, Harri; Hakala, Teemu; Kukko, Antero; Vastaranta, Mikko; Hyyppä, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this work, we compared six emerging mobile laser scanning (MLS) technologies for field reference data collection at the individual tree level in boreal forest conditions. The systems under study were an in-house developed AKHKA-R3 backpack laser scanner, a handheld Zeb-Horizon laser scanner, an under-canopy UAV (Unmanned Aircraft Vehicle) laser scanning system, and three above-canopy UAV laser scanning systems providing point clouds with varying point densities. To assess the performance of the methods for automated measurements of diameter at breast height (DBH), stem curve, tree height and stem volume, we utilized all of the six systems to collect point cloud data on two 32 m-by-32 m test sites classified as sparse (n = 42 trees) and obstructed (n = 43 trees). To analyze the data collected with the two ground-based MLS systems and the under-canopy UAV system, we used a workflow based on our recent work featuring simultaneous localization and mapping (SLAM) technology, a stem arc detection algorithm, and an iterative arc matching algorithm. This workflow enabled us to obtain accurate stem diameter estimates from the point cloud data despite a small but relevant time-dependent drift in the SLAM-corrected trajectory of the scanner. We found out that the ground-based MLS systems and the under-canopy UAV system could be used to measure the stem diameter (DBH) with a root mean square error (RMSE) of 2–8%, whereas the stem curve measurements had an RMSE of 2–15% that depended on the system and the measurement height. Furthermore, the backpack and handheld scanners could be employed for sufficiently accurate tree height measurements (RMSE = 2–10%) in order to estimate the stem volumes of individual trees with an RMSE of approximately 10%. A similar accuracy was obtained when combining stem curves estimated with the under-canopy UAV system and tree heights extracted with an above-canopy flying laser scanning unit. Importantly, the volume estimation error of these three MLS systems was found to be of the same level as the error corresponding to manual field measurements on the two test sites. To analyze point cloud data collected with the three above-canopy flying UAV systems, we used a random forest model trained on field reference data collected from nearby plots. Using the random forest model, we were able to estimate the DBH of individual trees with an RMSE of 10–20%, the tree height with an RMSE of 2–8%, and the stem volume with an RMSE of 20–50%. Our results indicate that ground-based and under-canopy MLS systems provide a promising approach for field reference data collection at the individual tree level, whereas the accuracy of above-canopy UAV laser scanning systems is not yet sufficient for predicting stem attributes of individual trees for field reference data with a high accuracy.
  • Comparison of Laser and Stereo Optical, SAR and InSAR Point Clouds from Air- and Space-Borne Sources in the Retrieval of Forest Inventory Attributes
    (2015) Yu, Xiaowei; Hyyppä, Juha; Karjalainen, Mika; Nurminen, Kimmo; Karila, Kirsi; Vastaranta, Mikko; Kankare, Ville; Kaartinen, Harri; Holopainen, Markus; Honkavaara, Eija; Kukko, Antero; Jaakkola, Anttoni; Liang, Xinlian; Wang, Yunsheng; Hyyppä, Hannu; Katoh, Masato
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Effect of forest structure and health on the relative surface temperature captured by airborne thermal imagery – Case study in Norway Spruce-dominated stands in Southern Finland
    (2017) Junttila, Samuli; Vastaranta, Mikko; Hämäläinen, Jarno; Latva-Käyrä, Petri; Holopainen, Markus; Hernández Clemente, Rocío; Hyyppä, Hannu; Navarro-Cerrillo, Rafael M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The effect of forest structure and health on the relative surface temperature captured by airborne thermal imagery was investigated in Norway Spruce-dominated stands in Southern Finland. Airborne thermal imagery, airborne scanning light detection and ranging (LiDAR) data and 92 field-measured sample plots were acquired at the area of interest. The surface temperature correlated most negatively with the logarithm of stem volume, Lorey’s height and the logarithm of basal area at a resolution of 254 m2 (9 m radius). LiDAR-derived metrics: the standard deviations of the canopy heights, canopy height (upper percentiles and maximum height) and canopy cover percentage were most strongly negatively correlated with the surface temperature. Although forest structure has an effect on the detected surface temperature, higher temperatures were detected in severely defoliated canopies and the difference was statistically significant. We also found that the surface temperature differences between the segmented canopy and the entire plot were greater in the defoliated plots, indicating that thermal images may also provide some additional information for classifying forests health status. Based on our results, the effects of forest structure on the surface temperature captured by airborne thermal imagery should be taken into account when developing forest health mapping applications using thermal imagery.
  • Intelligent Open Data 3D Maps in a Collaborative Virtual World
    (2015) Virtanen, Juho-Pekka; Hyyppa, Hannu; Kamarainen, Ali; Hollstrom, Tommi; Vastaranta, Mikko; Hyyppa, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Three-dimensional (3D) maps have many potential applications, such as navigation and urban planning. In this article, we present the use of a 3D virtual world platform Meshmoon to create intelligent open data 3D maps. A processing method is developed to enable the generation of 3D virtual environments from the open data of the National Land Survey of Finland. The article combines the elements needed in contemporary smart city concepts, such as the connection between attribute information and 3D objects, and the creation of collaborative virtual worlds from open data. By using our 3D virtual world platform, it is possible to create up-to-date, collaborative 3D virtual models, which are automatically updated on all viewers. In the scenes, all users are able to interact with the model, and with each other. With the developed processing methods, the creation of virtual world scenes was partially automated for collaboration activities
  • Laserkeilausmenetelmien soveltuvuus jokiympäristöjen mallinnukseen
    (2016) Vaaja, Matti; Kurkela, Matti; Hyyppä, Hannu; Kukko, Antero; Kaartinen, Harri; Jaakkola, Anttoni; Kasvi, Elina; Lotsari, Eliisa; Virtanen, Juho-Pekka; Saarinen, Ninni; Ahlavuo, Marika; Vastaranta, Mikko; Holopainen, Markus; Jalonen, Johanna; Järvelä, Juha; Alho, Petteri; Hyyppä, Juha
     A3 Kirjan tai muun kokoomateoksen osa
    Laserkeilausaineistojen käyttö virtavesien tutkimuksessa on lisääntynyt nopeasti viime vuosina. Perinteisesti virtavesiin liittyviä prosesseja on mallinnettu maastonmuotojen poikkileikkauksien ja virtausmittausten avulla. Laserkeilausmenetelmät ovat tuoneet mahdollisuuden kerätä alueellisia aineistoja entistä suuremmalla resoluutiolla ja tehokkuudella. Laserkeilauksella tuotettuja maanpinnan korkeusmalleja, muutostulkintamalleja ja kasvillisuuden kohdemalleja käytetään muun muassa tulva-alueiden ja -riskien kartoitukseen, jokidynamiikan ja geomorfologian tutkimuksiin sekä sedimentti- ja habitaattimallinnuksiin.
  • Measuring Leaf Water Content with Dual-Wavelength Intensity Data from Terrestrial Laser Scanners
    (2017) Junttila, Samuli; Vastaranta, Mikko; Liang, Xinlian; Kaartinen, Harri; Kukko, Antero; Kaasalainen, Sanna; Holopainen, Markus; Hyyppä, Hannu; Hyyppä, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Decreased leaf moisture content, typically measured as equivalent water thickness (EWT), is an early signal of tree stress caused by drought, disease, or pest insects. We investigated the use of two terrestrial laser scanners (TLSs) employing different wavelengths for improving the understanding how EWT can be retrieved in a laboratory setting. Two wavelengths were examined for normalizing the effects of varying leaf structure and geometry on the measured intensity. The relationship between laser intensity features, using red (690 nm) and shortwave infrared (1550 nm) wavelengths, and the EWT of individual leaves or groups of needles were determined with and without intensity corrections. To account for wrinkles and curvatures of the leaves and needles, a model describing the relationship between incidence angle and backscattered intensity was applied. Additionally, a reflectance model describing both diffuse and specular reflectance was employed to remove the fraction of specular reflectance from backscattered intensity. A strong correlation (R2 = 0.93, RMSE = 0.004 g/cm2) was found between a normalized ratio of the two wavelengths and the measured EWT of samples. The applied intensity correction methods did not significantly improve the results of the study. The backscattered intensity responded to changes in EWT but more investigations are needed to test the suitability of TLSs to retrieve EWT in a forest environment.
  • Multispectral Imagery Provides Benefits for Mapping Spruce Tree Decline Due to Bark Beetle Infestation When Acquired Late in the Season
    (2022-02-01) Junttila, Samuli; Näsi, Roope; Koivumäki, Niko; Imangholiloo, Mohammad; Saarinen, Ninni; Raisio, Juha; Holopainen, Markus; Hyyppä, Hannu; Hyyppä, Juha; Lyytikäinen-Saarenmaa, Päivi; Vastaranta, Mikko; Honkavaara, Eija
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Climate change is increasing pest insects’ ability to reproduce as temperatures rise, resulting in vast tree mortality globally. Early information on pest infestation is urgently needed for timely decisions to mitigate the damage. We investigated the mapping of trees that were in decline due to European spruce bark beetle infestation using multispectral unmanned aerial vehicles (UAV)-based imagery collected in spring and fall in four study areas in Helsinki, Finland. We used the Random Forest machine learning to classify trees based on their symptoms during both occasions. Our approach achieved an overall classification accuracy of 78.2% and 84.5% for healthy, declined and dead trees for spring and fall datasets, respectively. The results suggest that fall or the end of summer provides the most accurate tree vitality classification results. We also investigated the transferability of Random Forest classifiers between different areas, resulting in overall classification accuracies ranging from 59.3% to 84.7%. The findings of this study indicate that multispectral UAV-based imagery is capable of classifying tree decline in Norway spruce trees during a bark beetle infestation.
  • The potential of dual-wavelength terrestrial lidar in early detection of Ips typographus (L.) infestation – Leaf water content as a proxy
    (2019-09-15) Junttila, Samuli; Holopainen, Markus; Vastaranta, Mikko; Lyytikäinen-Saarenmaa, Päivi; Kaartinen, H.; Hyyppä, J.; Hyyppä, H.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Climate change is causing novel forest stress around the world due to changes in environmental conditions. Forest pest insects, such as Ips typographus (L.), are spreading toward the northern latitudes and are now able to produce more generations in their current range; this has increased forest disturbances. Timely information on tree decline is critical in allowing forest managers to plan effective countermeasures and to forecast potential infestation areas. Field-based infestation surveys of bark beetles have traditionally involved visual estimates of entrance holes, resin flow, and maternal-gallery densities; such estimates are prone to error and bias. Thus, objective and automated methods for estimating tree infestation status are required. In this study, we investigated the feasibility of dual-wavelength terrestrial lidar in the estimation and detection of I. typographus infestation symptoms. In addition, we examined the relationship between leaf water content (measured as gravimetric water content and equivalent water thickness) and infestation severity. Using two terrestrial lidar systems (operating at 905 nm and 1550 nm), we measured 29 mature Norway spruce (Picea abies [L.] Karst.) trees that exhibited low or moderate infestation symptoms. We calculated single and dual-wavelength lidar intensity metrics from stem and crown points to test these metrics' ability to discriminate I. typographus infestation levels using regressions and linear discriminant analyses. Across the various I. typographus infestation levels, we found significant differences (p < 0.05) in gravimetric water content, but not in equivalent water thickness due to the latter statistic's high correlation with leaf density. The results show correlations between the lidar intensity metrics and several infestation symptoms: defoliation, discoloration and resin flow. The intensity metrics explain 50% of the variation in the infestation severity (as determined in the field based on canopy and stem symptoms). The overall accuracy with three infestation classes (no, low, or moderate) was 66%, but the overall accuracy with two infestation classes (not infested, or infested) was 90%. The classifiers combine lidar intensity metrics from the stem and the canopy to allow for the detection of bark-beetle infestations in the early, so called green-attack stage. The intensity metrics explain part of the variations in tree-level gravimetric water content and equivalent water thickness, with adjusted R2 values of 0.48 and 0.68, respectively. Terrestrial dual-wavelength lidar shows potential for providing objective tree-decline measurements at tree level: this method can be further used to enhance forest inventories and automate tree-vigor data collection, which has traditionally required expert knowledge.
  • Revealing changes in the stem form and volume allocation in diverse boreal forests using two-date terrestrial laser scanning
    (2021-07) Luoma, Ville; Yrttimaa, Tuomas; Kankare, Ville; Saarinen, Ninni; Pyörälä, Jiri; Kukko, Antero; Kaartinen, Harri; Hyyppä, Juha; Holopainen, Markus; Vastaranta, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Tree growth is a multidimensional process that is affected by several factors. There is a continuous demand for improved information on tree growth and the ecological traits controlling it. This study aims at providing new approaches to improve ecological understanding of tree growth by the means of terrestrial laser scanning (TLS). Changes in tree stem form and stem volume allocation were investigated during a five-year monitoring period. In total, a selection of attributes from 736 trees from 37 sample plots representing different forest structures were extracted from taper curves derived from two-date TLS point clouds. The results of this study showed the capability of point cloud-based methods in detecting changes in the stem form and volume allocation. In addition, the results showed a significant difference between different forest structures in how relative stem volume and logwood volume increased during the monitoring period. Along with contributing to providing more accurate information for monitoring purposes in general, the findings of this study showed the ability and many possibilities of point cloud-based method to characterize changes in living organisms in particular, which further promote the feasibility of using point clouds as an observation method also in ecological studies.
  • Sparse Density, Leaf-Off Airborne Laser Scanning Data in Aboveground Biomass Component Prediction
    (2015) Kankare, Ville; Vauhkonen, Jari; Holopainen, Markus; Vastaranta, Mikko; Hyyppa, Juha; Hyyppa, Hannu; Alho, Petteri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Terrestrial laser scanning in forest inventories
    (2016-05) Liang, Xinlian; Kankare, Ville; Hyyppä, Juha; Wang, Yunsheng; Kukko, Antero; Haggren, Henrik; Yu, Xiaowei; Kaartinen, Harri; Jaakkola, Anttoni; Guan, Fengying; Holopainen, Markus; Vastaranta, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Decision making on forest resources relies on the precise information that is collected using inventory. There are many different kinds of forest inventory techniques that can be applied depending on the goal, scale, resources and the required accuracy. Most of the forest inventories are based on field sample. Therefore, the accuracy of the forest inventories depends on the quality and quantity of the field sample. Conventionally, field sample has been measured using simple tools. When map is required, remote sensing materials are needed. Terrestrial laser scanning (TLS) provides a measurement technique that can acquire millimeter-level of detail from the surrounding area, which allows rapid, automatic and periodical estimates of many important forest inventory attributes. It is expected that TLS will be operationally used in forest inventories as soon as the appropriate software becomes available, best practices become known and general knowledge of these findings becomes more wide spread. Meanwhile, mobile laser scanning, personal laser scanning, and image-based point clouds became capable of capturing similar terrestrial point cloud data as TLS. This paper reviews the advances of applying TLS in forest inventories, discusses its properties with reference to other related techniques and discusses the future prospects of this technique. (C) 2016 The Authors. Published by Elsevier B.V. on behalf of International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licensesiby-nc-nd/11.0/).
  • Terrestrial laser scanning intensity captures diurnal variation in leaf water potential
    (2021-03-15) Junttila, S.; Hölttä, T.; Puttonen, E.; Katoh, M.; Vastaranta, Mikko; Kaartinen, H.; Holopainen, Markus; Hyyppä, H.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    During the past decades, extreme events have become more prevalent and last longer, and as a result drought-induced plant mortality has increased globally. Timely information on plant water dynamics is essential for understanding and anticipating drought-induced plant mortality. Leaf water potential (ΨL), which is usually measured destructively, is the most common metric that has been used for decades for measuring water stress. Remote sensing methods have been developed to obtain information on water dynamics from trees and forested landscapes. However, the spatial and temporal resolutions of the existing methods have limited our understanding of the water dynamics and diurnal variation of ΨL within single trees. Thus, we investigated the capability of terrestrial laser scanning (TLS) intensity in observing diurnal variation in ΨL during a 50-h monitoring period. We aimed to improve the understanding on how large a part of the diurnal variation in ΨL can be captured using TLS intensity observations. We foundthat TLS intensity at the 905 nm wavelength measured from a static position was able to explain 77% of the variation in ΨL for three trees of two tree species with a root mean square error of 0.141 MPa. Based on our experiment with three trees, a time series of TLS intensity measurements can be used in detecting changes in ΨL, and thus it is worthwhile to expand the investigations to cover a wider range of tree species and forests and further increase our understanding of plant water dynamics at wider spatial and temporal scales.
  • Tree Water Status Affects Tree Branch Position
    (2022-05) Junttila, Samuli; Campos, Mariana; Hölttä, Teemu; Lindfors, Lauri; Issaoui, Aimad El; Vastaranta, Mikko; Hyyppä, Hannu; Puttonen, Eetu
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Physiological processes cause movements of tree stems and branches that occur in a circadian rhythm and over longer time periods, but there is a lack of quantitative understanding of the cause-and-effect relationships. We investigated the movement of tree branches in a long-term drought experiment and at a circadian time scale using time-series of terrestrial laser scanning measurements coupled with measurements of environmental drivers and tree water status. Our results showed that movement of branches was largely explained by leaf water status measured as leaf water potential in a controlled environment for both measured trees (R2 = 0.86 and R2 = 0.75). Our hypothesis is that changes in leaf and branch water status would cause branch movements was further supported by strong relationship between vapor pressure deficit and overnight branch movement (R2 = [0.57–0.74]). Due to lower atmospheric water demand during the nighttime, tree branches settle down as the amount of water in leaves increases. The results indicate that the quantified movement of tree branches could help us to further monitor and understand the water relations of tree communities.