Assessing wood properties in standing timber with laser scanning

Managed forests play crucial roles in ongoing climatic and environmental changes. Among other things, wood is capable of sinking and storing carbon in both standing timber and wood products. To promote these positive effects, more precise planning is required that will ensure sustainable forest management and maximal deposition of harvested wood for long-term applications. Information on wood properties plays a key role; i.e. the wood properties can impact the carbon stocks in forests and the suitability of wood for structural timber. With respect to the theoretical background of wood formation, stem, crown, and branching constitute potential inputs (i.e. wood quality indicators) to allometric wood property, tree biomass, and wood quality models. Due to the complex nature of wood formation, measurements of wood quality indicators that could predict wood properties along the relevant directions of variation have previously been elusive in forest inventories. However, developments in laser scanning from aerial and terrestrial platforms support more complex mapping and modeling regimes based on dense three-dimensional point clouds. The aim here was to determine how wood properties could be estimated in remote-sensing-aided forest inventories. For this purpose, methods for characterizing select wood quality indicators in standing timber, using airborne and terrestrial laser scanning (ALS and TLS, respectively) were developed and evaluated in managed boreal Scots pine (Pinus sylvestris L.) forests. Firstly, the accuracies of wood quality indicators resolved from TLS point clouds were assessed. Secondly, the results were compared with x-ray tomographic references from sawmills. Thirdly, the accuracies of tree-specific crown features delineated from the ALS data in predictive modeling of the wood quality indicators were evaluated. The results showed that the quality and density of point clouds significantly impacted the accuracies of the extracted wood quality indicators. In the assessment of wood properties, TLS should be considered as a tool for retrieving as dense stem and branching data as possible from carefully selected sample trees. Accurately retrieved morphological data could be applied to allometric wood property models. The models should use tree traits predictable with aerial remote sensing (e.g. tree height, crown dimensions) to enable extrapolations. As an outlook, terrestrial and aerial remote sensing can play an important role in filling in the knowledge gaps regarding the behavior of wood properties over different spatial and temporal extents. Further interdisciplinary cooperation will be needed to fully facilitate the use of remote sensing and spatially transferable wood property models that could become useful in tackling the challenges associated with changing climate, silviculture, and demand for wood.Hoidetuilla metsillä on useita tärkeitä rooleja muuttuvassa ilmastossa ja ympäristössä. Puu sitoo ja varastoi hiiltä niin kasvaessaan, kuin pitkäikäisiksi puutuotteiksi jalostettuna. Näiden vaikutusten huomioiminen metsänhoidossa vaatii tarkkaa suunnittelua, jolla varmistetaan metsänhoidon ja puunkäytön kestävyys. Tieto puuaineen ominaisuuksista on keskeisessä osassa, sillä ne vaikuttavat hiilivarastojen suuruuteen metsissä, sekä puun käytettävyyteen pitkäikäisenä rakennesahatavarana. Puunmuodostuksen teoreettisen taustan mukaisesti, runko, latvus ja oksarakenne ovat potentiaalisia selittäviä muuttujia (eli puun laatuindikaattoreita), kun mallinnetaan puuaineen ominaisuuksia, puubiomassaa ja puun laatua. Puunmuodostuksen monimutkaisuudesta ja moniulotteisesta vaihtelusta johtuen, tarvittavien laatuidikaattorien mittaaminen osana metsävarojen inventointia ja riittävällä yksityiskohtaisuudella on ollut aiemmin mahdotonta. Monialustaisen laserkeilauksen kehittyminen kuitenkin tukee aiempaa monipuolisempien kartoitus- ja mallinnusjärjestelmien rakentamista, jotka perustuvat tiheisiin kolmiulotteisiin pistepilviin. Tämän työn tavoitteena oli määritellä, kuinka puuaineen ominaisuuksia voidaan arvioida kaukokartoitusta hyödyntävässä metsävarojen inventoinnissa. Tätä tarkoitusta varten kehitettiin menetelmiä puun laatuindikaattorien mittaamiseksi hoidetuissa männiköissä (Pinus sylvestris L.) lento- ja maastolaserkeilauksen avulla, ja arvioitiin niiden toimivuutta. Ensin arvioitiin laatuindikaattorien mittatarkkuus pistepilvissä. Toiseksi verrattiin pistepilvimittauksia röntgentomografiamittauksiin teollisilla sahoilla. Kolmanneksi arvioitiin lentolaserkeilauksella tuotettujen latvuspiirteiden tarkkuutta laatuindikaattorien ennustamisessa. Tuloksien perusteella pistepilvien laatu ja pistetiheys vaikuttivat merkittävästi mitattujen laatuindikaattorien tarkkuuteen. Puuaineen ominaisuuksien arvioimisessa, maastolaserkeilausta tulisi käyttää työkaluna mahdollisimman yksityiskohtaisten runko- ja oksikkuustietojen keräämiseen tarkkaan valikoiduista näytepuista. Tarkasti mitatut laatuindikaattorit voivat selittää puuaineen ominaisuuksia mallinnuksessa. Käytettyjen mallien tulisi perustua laatuindikaattoreille, jotka voidaan ennustaa lentolaserkeilausaineistosta (esim. puun pituus ja latvuksen mittasuhteet), jotta ennusteet ovat yleistettävissä laajoille alueille. Tulevaisuudessa, maasta ja ilmasta tehtävällä kaukokartoituksella voi olla tärkeä rooli puuaineen ominaisuuksien aikaan ja paikkaan sidotun vaihtelun tutkimuksessa. Lisää poikkitieteellistä työtä tarvitaan, jotta kaukokartoitusta ja puuaineen ominaisuuksia ennustavia spatiaalisia malleja voidaan täysimittaisesti hyödyntää kiihtyvän ilmastonmuutoksen, muuttuvan metsänhoidon ja lisääntyvän puunkäytön tuomien haasteiden kohtaamisessa

Wood quality of Norway Spruce in uneven-aged forests

Tutkielma on osa Metsätutkimuslaitoksen hanketta Eri-ikäisrakenteisten ja monijaksoisten metsien käsittely (ERIKA). Tavoitteena oli tutkia eri-ikäisrakenteisissa metsiköissä kahdella eri paikkakunnal-la Etelä-Suomessa kasvaneiden kuusien sisäistä kasvunopeutta ja -rytmiä sekä kuusien puuaineen sisäistä laatua kuitujen pituuden, puuaineen kuiva-ilmakuivatiheyden, akustisella menetelmällä määri-tetyn dynaamisen kimmokertoimen sekä visuaalisen laatulajittelun perusteella. Kuidunpituudet mitat-tiin 64 puusta, tiheysmittaukset ja akustinen mittaus sekä laatulajittelu tehtiin 40 puun saheille, yh-teensä 355 kpl. Kuitujen pituuden vaihtelua suhteessa etäisyyteen ytimestä ja lustojen leveyteen mal-linnettiin sekamallilla. Tiheyden, kimmokertoimen ja visuaalisen laadun vaihtelua suhteessa sijaintiin rungossa analysoitiin kaksisuuntaisella varianssianalyysillä ja suhteessa kasvuun regressioanalyysillä. Tuloksien perusteella kuidunpituus, tiheys ja kimmokerroin eivät poikenneet kuuselle tavanomaisista arvoista ja suurin osa hajonnasta oli puidenvälistä. Sahatavaran visuaalisen laatulajittelun perusteella A-laatua oli melko hyvin (~ 20 %), mutta C-laatua oli enemmän (> 33 %) kuin B-laatua ( 33 %) was more common than class B (> 25 %): Timber was knotty especially near pith and loose knots were dense on lumber boards. Twisting was high near pith in timber boards but did not differ from the usual. There was remarkable amount of compression wood and decay in the material. The within-tree variation of visual grade was equal to the among-tree varia-tion. Due to the small sample size the results are not yet applicable to uneven-aged forests in general, but they give an impression that there might not be any major differences between the quality of even-aged and uneven-aged wood. First of all, the results give light to the characteristics of uneven-aged spruce wood properties that might be of interest for further research

Tracheid dimensions of Norway spruce in uneven-aged stands

Tracheid length and width patterns from pith to bark at a height of 0.6 m in uneven-aged Norway spruce (Picea abies L. (H.) Karst) trees were addressed. The identification of the main factors and a comparison with even-aged stands were also pursued. 96 trees were sampled from experimental stands in Southern Finland. The material encompassed the variation in tracheid properties from early years to silvicultural maturity, i.e. from corewood to outerwood up to a cambial age of 111 years. Data from 39 Norway spruce trees from even-aged stands we utilized for comparison. Models fitted to the data indicated that annual ring widths did not influence mean tracheid dimensions but the latewood proportion showed a significant influence on tracheid dimensions. Tracheids in uneven-aged stands were slightly wider and longer at the base of the stem with a similar tree diameter, cambial age, and annual ring number.Tracheid length and width patterns from pith to bark at a height of 0.6 m in uneven-aged Norway spruce (Picea abies (L.) Karst.) trees were studied. Identification of the main factors and a comparison with even-aged stands were also carried out. Ninety-six trees were sampled from experimental stands in southern Finland. The material encompassed the variation in tracheid properties from early years to silvicultural maturity, i.e., from corewood to outerwood up to a cambial age of 111 years. Data from 39 Norway spruce trees from even-aged stands were utilized for comparison. Models fitted to the data indicated that annual ring widths did not influence mean tracheid dimensions but that the latewood proportion had a significant influence on tracheid dimensions. Tracheids in uneven-aged stands were slightly wider and longer at the base of the stem in trees with a similar diameter, cambial age, and annual ring number.Peer reviewe

Comparison of Terrestrial Laser Scanning and X-ray Scanning in Measuring Scots Pine (Pinus sylvestris L.) Branch Structure

While X-ray scanning is increasingly used to measure the interior quality of logs, terrestrial laser scanning (TLS) could be used to collect information on external tree characteristics. As branches are one key indicator of wood quality, we compared TLS and X-ray scanning data in deriving whorl locations and each whorl's maximum branch and knot diameters for 162 Scots pine (Pinus sylvestris L.) log sections. The mean number of identified whorls per tree was 37.25 and 22.93 using X-ray and TLS data, respectively. The lowest TLS-derived whorl in each sample tree was an average 5.56 m higher than that of the X-ray data. Whorl-to-whorl mean distances and the means of the maximum branch and knot diameters in a whorl measured for each sample tree using TLS and X-ray data had mean differences of -0.12 m and -6.5 mm, respectively. One of the most utilized wood quality indicators, tree-specific maximum knot diameter measured by X-ray, had no statistically significant difference to the tree-specific maximum branch diameter measured from the TLS point cloud. It appears challenging to directly derive comparative branch structure information using TLS and X-ray. However, some features that are extractable from TLS point clouds are potential wood quality indicators.Peer reviewe

Quantitative Assessment of Scots Pine (Pinus Sylvestris L.) Whorl Structure in a Forest Environment Using Terrestrial Laser Scanning

State-of-the-art technology available at sawmills enables measurements of whorl numbers and the maximum branch diameter for individual logs, but such information is currently unavailable at the wood procurement planning phase. The first step toward more detailed evaluation of standing timber is to introduce a method that produces similar wood quality indicators in standing forests as those currently used in sawmills. Our aim was to develop a quantitative method to detect and model branches from terrestrial laser scanning (TLS) point clouds data of trees in a forest environment. The test data were obtained from 158 Scots pines (Pinus sylvestris L.) in six mature forest stands. The method was evaluated for the accuracy of the following branch parameters: Number of whorls per tree and for every whorl, the maximum branch diameter and the branch insertion angle associated with it. The analysis concentrated on log-sections (stem diameter > 15 cm) where the branches most affect wood's value added. The quantitative whorl detection method had an accuracy of 69.9% and a 1.9% false positive rate. The estimates of the maximum branch diameters and the corresponding insertion angles for each whorl were underestimated by 0.34 cm (11.1%) and 0.67 degrees (1.0%), with a root-mean-squared error of 1.42 cm (46.0%) and 17.2 degrees (26.3%), respectively. Distance from the scanner, occlusion, and wind were the main external factors that affect the method's functionality. Thus, the completeness and point density of the data should be addressed when applying TLS point cloud based tree models to assess branch parameters.Peer reviewe

Assessing the Dependencies of Scots Pine (Pinus sylvestris L.) Structural Characteristics and Internal Wood Property Variation

Wood density is well known to vary between tree species as well as within and between trees of a certain species depending on the growing environment causing uncertainties in forest biomass and carbon storage estimation. This has created a need to develop novel methodologies to obtain wood density information over multiple tree communities, landscapes, and ecoregions. Therefore, the aim of this study was to evaluate the dependencies between structural characteristics of Scots pine (Pinus sylvestris L.) tree communities and internal wood property (i.e., mean wood density and ring width) variations at breast height. Terrestrial laser scanning was used to derive the structural characteristics of even-aged Scots pine dominated forests with varying silvicultural treatments. Pearson’s correlations and linear mixed effect models were used to evaluate the interactions. The results show that varying silvicultural treatments did not have a statistically significant effect on the mean wood density. A notably stronger effect was observed between the structural characteristics and the mean ring width within varying treatments. It can be concluded that single time terrestrial laser scanning is capable of capturing the variability of structural characteristics and their interactions with mean ring width within different silvicultural treatments but not the variation of mean wood density

Assessing the Effects of Sample Size on Parametrizing a Taper Curve Equation and the Resultant Stem-Volume Estimates

Large and comprehensive datasets, traditionally based on destructive stem analysis or other labor-intensive approaches, are commonly considered as a necessity in developing stem-volume equations. The aim here was to investigate how a decreasing number of sample trees affects parametrizing an existing taper curve equation and resultant stem-volume estimates. Furthermore, the potential of terrestrial laser scanning (TLS) in producing taper curves was examined. A TLS-based taper curve was derived for 246 Scots pines (Pinus sylvestris L.) from southern Finland to parametrize an existing taper curve equation. To assess sensitivity of the parametrization regarding sample size, the number of Scots pines included in the parametrization varied between full census and 1 Scots pine at a time. Root mean square error of stem-volume estimates remained ≤20.9% and the mean absolute difference was relatively constant (≤9.0%) between stem-volume estimates when the sample size included ≥46 Scots pines. Thus, it can be concluded that, with a rather small sample size, a taper curve equation can be re-parametrized for local conditions using point clouds from TLS to produce consistent stem-volume estimates

Variability of wood properties using airborne and terrestrial laser scanning

Information on wood properties is crucial in estimating wood quality and forest biomass and thus developing the precision and sustainability of forest management and use. However, wood properties are highly variable between and within trees due to the complexity of wood formation. Therefore, tree-specific field references and spatially transferable models are required to capture the variability of wood quality and forest biomass at multiple scales, entailing high-resolution terrestrial and aerial remote sensing methods. Here, we aimed at identifying select tree traits that indicate wood properties (i.e. wood quality indicators) with a combination of terrestrial laser scanning (TLS) and airborne laser scanning (ALS) in an examination of 27 even-aged, managed Scots pine (Pinus sylvestris L.) stands in southern Finland. We derived the wood quality indicators from tree models sampled systematically from TLS data and built prediction models with respect to individual crown features delineated from ALS data. The models were incapable of predicting explicit branching parameters (height of the lowest dead branch R2 = 0.25, maximum branch diameter R2 = 0.03) but were suited to predicting stem and crown dimensions from stand, tree, and competition factors (diameter at breast height and sawlog volume R2 = 0.5, and live crown base height R2 = 0.4). We were able to identify the effect of canopy closure on crown longevity and stem growth, which are pivotal to the variability of several wood properties in managed forests. We discussed how the fusions of high-resolution remote sensing methods may be used to enhance sustainable management and use of natural resources in the changing environment.Peer reviewe

Assessing the Effects of Sample Size on Parametrizing a Taper Curve Equation and the Resultant Stem-Volume Estimates

Large and comprehensive datasets, traditionally based on destructive stem analysis or other labor-intensive approaches, are commonly considered as a necessity in developing stem-volume equations. The aim here was to investigate how a decreasing number of sample trees affects parametrizing an existing taper curve equation and resultant stem-volume estimates. Furthermore, the potential of terrestrial laser scanning (TLS) in producing taper curves was examined. A TLS-based taper curve was derived for 246 Scots pines (Pinus sylvestris L.) from southern Finland to parametrize an existing taper curve equation. To assess sensitivity of the parametrization regarding sample size, the number of Scots pines included in the parametrization varied between full census and 1 Scots pine at a time. Root mean square error of stem-volume estimates remained ≤20.9% and the mean absolute difference was relatively constant (≤9.0%) between stem-volume estimates when the sample size included ≥46 Scots pines. Thus, it can be concluded that, with a rather small sample size, a taper curve equation can be re-parametrized for local conditions using point clouds from TLS to produce consistent stem-volume estimates