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Hydrological Sciences Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/thsj20
Instrumental method for reducing error in compression-derived measurements of rainfall interception for individual trees a
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John T. Van Stan II , Matthew T. Jarvis , Delphis F. Levia Jr & Jan Friesen
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Department of Geography, University of Delaware, Newark, Delaware, 19716-2541, USA
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Independent Scholar, Newark, Delaware, 19713, USA
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Departments of Geography & Plant and Soil Sciences, University of Delaware, Newark, Delaware, 19716-2541, USA d
Department Computational Hydrosystems, Helmholtz Centre for Environmental Research, D-04318, Leipzig, Germany Available online: 09 Sep 2011
To cite this article: John T. Van Stan II, Matthew T. Jarvis, Delphis F. Levia Jr & Jan Friesen (2011): Instrumental method for reducing error in compression-derived measurements of rainfall interception for individual trees, Hydrological Sciences Journal, 56:6, 1061-1066 To link to this article: http://dx.doi.org/10.1080/02626667.2011.590811
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Hydrological Sciences Journal – Journal des Sciences Hydrologiques, 56(6) 2011
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TECHNICAL NOTE Instrumental method for reducing error in compression-derived measurements of rainfall interception for individual trees John T. Van Stan, II1 , Matthew T. Jarvis2 , Delphis F. Levia, Jr3 & Jan Friesen4 1
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Department of Geography, University of Delaware, Newark, Delaware 19716-2541, USA
[email protected] 2
Independent Scholar, Newark, Delaware 19713, USA
[email protected] 3
Departments of Geography & Plant and Soil Sciences, University of Delaware, Newark, Delaware 19716-2541, USA
[email protected] 4
Department Computational Hydrosystems, Helmholtz Centre for Environmental Research, D-04318 Leipzig, Germany
[email protected] Received 29 November 2010; accepted 9 March 2011; open for discussion until 1 February 2012 Citation Van Stan, J. T. II, Jarvis, M. T., Levia, D. F. Jr & Friesen, J. (2011) Instrumental method for reducing error in compressionderived measurements of rainfall interception for individual trees. Hydrol. Sci. J. 56(6), 1061–1066.
Abstract This technical note presents an instrumental method for the precise and timely installation of mechanical displacement sensors to investigate stem compression and relaxation associated with whole-tree rainwater loading and evaporation, respectively. We developed this procedure in response to the conclusions of Friesen et al. (2008), which called for the development of a precision mounting method for strain sensors on inherently-irregular trunk cross-sections so that rainfall interception, storage and evaporation may be distinguished from other strain-related phenomena. To supply precise sensor installation locations, high-resolution trunk profiles are generated using the LaserBarkTM automated tree measurement system. These scans are utilized to approximate the location of neutral bending axes. A routine then instructs a mobile rangefinder along the cross-section to optically indicate exact positioning for strain sensors over the bending axes. As imprecise sensor placement linearly increases error and diminishes signal-to-noise ratio, this automated installation routine is designed to remove significant distortions created by wind throw, off-centre loading within unevenly-distributed canopies, and human error that can lead to erroneous measurements of rainfall interception. Key words forest hydrology; interception; stem compression; mechanical displacement sensor; LaserBarkTM
Méthode instrumentale pour réduire les erreurs sur les mesures par compression de l’interception des précipitations pour les arbres individuels Résumé Cette note technique présente une méthode instrumentale pour l’installation précise et opportune de capteurs de déplacement mécanique pour étudier la compression et la détente de tige associées respectivement au chargement en eaux pluviales et à l’évaporation de l’ensemble de l’arbre. Nous avons développé cette procédure en réaction aux conclusions de Friesen et al., qui appellent à la mise au point d’une méthode de précision pour le montage des capteurs de contrainte sur les sections transversales des troncs afin que l’interception des précipitations, leur stockage et les processus d’évaporation puissent être distingués d’autres phénomènes liés à la contrainte. Pour fournir des emplacements précis d’installation des capteurs, des profils de troncs haute résolution sont générés en utilisant le système automatisé de mesure LaserBarkTM . Ces profils numérisés sont utilisés pour déterminer l’emplacement des axes de flexion neutre. Ensuite un programme ordonne à un télémètre mobile le long de la section transversale d’indiquer d’une manière optique le positionnement exact de capteurs de contrainte sur les axes de flexion. Comme un placement imprécis du capteur augmente les erreurs et diminue le rapport signal sur bruit linéairement, ce programme d’installation automatique est conçu pour éliminer les distorsions importantes créées par les chablis, le chargement excentrique au sein de canopées irrégulièrement réparties, ainsi que l’erreur humaine, qui peuvent conduire à des mesures erronées de l’interception des précipitations. Mots clefs hydrologie forestière; interception; compression de tige; capteur de déplacement mécanique; LaserBarkTM
ISSN 0262-6667 print/ISSN 2150-3435 online © 2011 IAHS Press doi: 10.1080/02626667.2011.590811 http://www.informaworld.com
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INTRODUCTION Intercepted rainfall stored by, and evaporated from, canopy bark and foliar surfaces can diminish incident precipitation inputs beneath the forest canopy by as much as 50% (Muzylo et al. 2009), depending on species and season (Crockford and Richardson 2000, Levia and Frost 2003, Keim et al. 2006, Llorens and Domingo 2007). However, estimates of canopy water storage and evaporation are primarily based on indirect methods and model estimates which are capable of producing >30% error (Muzylo et al. 2009). Error is compounded further if these indirectly-derived interception components are falsely linked to net precipitation measurements by simply treating interception as a “black-box” process (Pollacco and Angulo-Jaramilo 2009), or when splash droplet evaporation is neglected (Murakami 2006, 2007, Dunkerley 2009). The identification of uniquely linked interception mechanisms (Pollacco and Angulo-Jaramilo 2009) and investigation of splash droplet evaporation requires direct canopy interception measurements at the intra-storm scale (Dunkerley 2009). Historically, direct measurements of water fluxes at varying temporal resolutions have been performed using weighing lysimeters (e.g. Fritschen et al. 1973, Edwards 1986, Storck et al. 2002). Although weighing lysimeters have provided valuable insights into the roles of vegetation in hydrological processes (e.g. Seyfried et al. 2001, Petrone et al. 2006, Stumpp et al. 2009), these investigations focus on the whole soil–plant–atmosphere system. Thereby processes such as canopy interception, bark interception and forest floor interception, as well as evaporation and transpiration are observed through one single measurement. To derive a more processbased understanding of plant-specific processes (e.g. canopy interception, evaporation of intercepted water and intra-storm canopy storage), and of soil or surface-specific parameters (e.g. soil evaporation and forest floor interception), it is necessary to observe the different processes as separately as possible. Weighing lysimeters are also expensive and require extensive construction (Sayler et al. 1984), which disturbs the surrounding environment. Friesen et al. (2008) demonstrated that direct measurements of canopy water loadings can be obtained inexpensively at high temporal resolution (∼5 seconds) and sensitivity (
