The accuracy of traditional dendrometrics when estimating diameter at breastheight and basal area of tree stems, in regard to the non-circularity of tree stem

I skogbruket behandles trær som om de er sirkulære i form. Trær er tilnærmet sirkulære i form men de er ikke perfekt sirkulære. Berettigelsen for denne påstanden er at de fleste trestammer har ulike diameterlengder i ulike retninger og den maksimale og minimale diameterlengden ofte krysser i omtrent 90 graders vinkel. Det vil derfor bli undersøkt hvilken av målemetodene; kryssklaving eller enkeltklaving som tar høyde for treets noe uregelmessige sirkulæritet, med andre ord hvilke av målemetodene som gir det mest nøyaktige estimatet på treets brysthøydediameter og grunnflateareal. Det vil også bli undersøkt om størrelsen på treets stammeform har en innvirkning på hvor stor forskjell i diameter estimat de ulike målemetodene vil gi. For å finne ut av dette ble det forutsatt at måling med målebånd vil gi et forventingsrett estimat på trestammens brysthøydediameter og grunnflateareal. Målemetodene ble testet på 150 trær i Evenstadlia. Trærne ble stratifisert i tre ulike klasser med ulike diametermål, 50 trær i hver klasse. Hvert tre ble dermed målt 3 ganger, en gang for hver metode; kryssklaving, enkeltklaving og måling med målebånd. Etter endt studium gis det støtte til bruken av kryssklaving i stedet for enkeltklaving ved måling av brysthøydediameter på trær over 35 cm. i diameter. Likevel vil diskusjonen om bruk av kryssklaving inkludere flere faktorer som må tas i betraktning og det vil derfor ikke kunne gis en definitiv konklusjon på om det i enkelte tilfeller bør benyttes kryssklaving ved måling av brysthøydediameter i prøveflatetaksering.In forestry, tree stems are treated as if their shape were perfectly circular. However, tree stem are approximate circular in shape, but their shape are not perfectly circular. The justification offered for the approach of non-circularity is that most stems have different diameters in different directions, and that maximum and minimum diameters often intersect at approximately right angles. That is why the following measurement methods; cross-calipering, single calipering and girth measurement will be tested for the ability to account for the non-circularity of the tree stems, in other words, which of the measurement methods would give the most accurate estimate of the breastheight and basal area of the tree. There will also be investigations to see if the size of the tree stem has an impact on the difference in diameter estimates that each of the measurement methods will provide. To determine this, it was assumed that girth measurement would provide the right expectation of estimate when it comes to breastheightdiameter and basal area of the tree stem. The measurement methods were tested on 150 trees in Evenstadlia. The trees were stratified into three different classes with specific diameter measurements, 50 trees in each class. Every tree where measured three times, one time for each different method; cross-calipering, single calipering and girth measurement. In the end of the study, there has been found support to the use of cross-calipering instead of single calipering when trees of breastheightdiameter over 35 cm. are measured. However, the discussion of the use of cross-calipering when measuring tree stems will involve several factors which has to be concluded before there will be given a definitive conclusion if there should be practiced cross-calipering when measuring breastheightdiameter of the tree stems in field sampling

Precise Measurement of Stem Diameter by Simulating the Path of Diameter Tape from Terrestrial Laser Scanning Data

Accurate measurement of stem diameter is essential to forest inventory. As a millimeter-level measuring tool, terrestrial laser scanning (TLS) has not yet reached millimeter-level accuracy in stem diameter measurements. The objective of this study is to develop an accurate method for deriving the stem diameter from TLS data. The methodology of stem diameter measurement by diameter tape was adopted. The stem cross-section at a given height along the stem was determined. Stem points for stem diameter retrieval were extracted according to the stem cross-section. Convex hull points of the extracted stem points were calculated in a projection plane. Then, a closed smooth curve was interpolated onto the convex hull points to simulate the path of the diameter tape, and stem diameter was calculated based on the length of the simulated path. The stems of different tree species with different properties were selected to verify the presented method. Compared with the field-measured diameter, the RMSE of the method was 0.0909 cm, which satisfies the accuracy requirement for forest inventory. This study provided a method for determining the stem cross-section and an efficient and precise curve fitting method for deriving stem diameter from TLS data. The importance of the stem cross-section and convex hull points in stem diameter retrieval was demonstrated

Measuring and Modeling the Structure of Coniferous Trees with Point Clouds Data

Coniferous trees are a major North American crop that has been intensively managed for its commercial value, while also serving as critical habitat for abundant wildlife and as carbon sinks. Having diverse functions, North American temperate coniferous forests have become a research hotspot for numerous scientific studies aiming to integrate ecological and economic objectives, such as examining the contribution of the conifer crown architecture to long-term forest management schemes. Point clouds have become an important source of forest inventory data and forest ecological studies, as provide accurate and comprehensive estimates of many structural variables. The present thesis aims to improve the understanding of conifer crown structure by estimating crown variables and developing stem and crown models using point clouds derived from images or laser scanning. The utilizations of point clouds were tested on loblolly pine plantations and mature Douglas-fir trees in a natural stand. Various types of 3D models were constructed for tree stems and branch attributes using point clouds. The 3D models provide direct volume estimates, as well as estimates of tree structural variables including tree height, stem diameter, branch basal diameter, length, insertion angle, and azimuth. The variable extractions were executed with semi-automatic methods, which combine human interpretation with an automatic estimation algorithm. The accuracy and reliability of point-clouds-based estimates were assessed with ground measurements and estimates from existing equations through simulations. Stem taper equations were developed using point-clouds-based stem diameter estimates. Nonlinear models of branch variables, as well as systematic crown models, were developed using lidar-based estimates by considering neighboring competition effects. The results demonstrate the reliability and efficiency of using point clouds data as alternatives or complements to traditional fieldwork. Stem and branch variables estimated nondestructively from lidar and photogrammetry point clouds agreed with ground measurements and fit in the range of observations from existing equations. Workflows developed and presented in this thesis can be employed by forestry practitioners and researchers to acquire fast and accurate tree structural variables, while models of stem and branch attributes can guide forest inventory and silvicultural practices as well as advance ecological research