Estimating leaf area index in different types of mature forest stands in Switzerland: a comparison of methods
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Leaf area index (LAI) was estimated at 15 sites in the Swiss Long-Term Forest Ecosystem Research Programme (LWF) in 2004–2005 using two indirect techniques: the LAI-2000 plant canopy analyzer (Licor Inc.) and digital hemispherical photography, applying several exposure settings. Hemispherical photographs of the canopy were analysed using Hemisfer, a software package that offers several new features, which were tested here: (1) automatic thresholding taking the gamma value of the picture into account; (2) implementation of several equations to solve the gap-fraction inversion model from which LAI estimates are derived; (3) correction for ground slope effects, and (4) correction for clumped canopies. In seven broadleaved stands in our sample set, LAI was also estimated semi-directly from litterfall. The various equations used to solve the gap-fraction inversion model generated significantly different estimates for the LAI-2000 measurements. In contrast, the same equations applied in Hemisfer did not produce significantly different estimates. The best relationship between the LAI-2000 and the Hemisfer estimates was obtained when the hemispherical photographs were overexposed by one to two stops compared with the exposure setting derived from the reading of a spotmeter in a canopy gap. There was no clear general relationship between the litterfall and the LAI-2000 or the hemispherical photographs estimates. This was probably due to the heterogeneity of the canopy, or to biased litterfall collection at sites on steep slopes or sites subject to strong winds. This study introduces new arguments into the comparison of the advantages and drawbacks of the LAI-2000 and hemispherical photography in terms of applicability and accuracy.
KeywordsLAI Digital hemispherical photography LAI-2000 Litterfall
We are very grateful to A. Brechbühl, N. Hajjar, O. Schramm, D. Trummer and the staff from the forest services for collecting the litterfall samples on the LWF plots. A. Brechbühl also participated in sorting the litterfall samples. We warmly thank O. Schramm and P. Waldner for their participation in the field campaign 2005. We also thank M. Nobis for his technical advice on the analysis of hemispherical photographs and S. Dingwall for editing the English. We gratefully acknowledge the financial support of the Federal Office for the Environment (FOEN).
- Anderson MC (1971) Radiation and crop structure. In: Sestak Z, Catsky J, Jarvis PG (eds) Plant photosynthetic production: manual of methods. Junk, The Hague, pp 412–466Google Scholar
- Graf Pannatier E, Dobbertin M, Schmitt M, Thimonier A, Waldner P (2007) Effects of the drought 2003 on forests in Swiss Level II plots. In: Eichhorn J (ed), Forests in a changing environment. Results of 20 years ICP forests monitoring, Göttingen, Germany, October 25–28, 2006. Schriften aus der Forstlichen Fakultät der Universität Göttingen und der Nordwestdeutschen Forstlichen Versuchsanstalt, vol 142, pp 128–135Google Scholar
- Li-Cor (1992) LAI-2000 plant canopy analyzer—Operating manual. LI-COR, Inc, LincolnGoogle Scholar
- Mussche S, Samson R, Nachtergale L, De Schrijver A, Lemeur R, Lust N (2001) A comparison of optical and direct methods for monitoring the seasonal dynamics of leaf area index in deciduous forests. Silva Fenn 35:373–384Google Scholar
- Nobis M (2003) Sideview 1.0—imaging software to extract vertical vegetation structure from true-colour photographs; http://www.appleco.de
- Norman JM, Campbell GS (1989) Canopy structure. In: Pearcy RW, Ehleringer JR, Mooney HA, Rundel PW (eds) Plant physiological ecology: field methods and instrumentation. Chapman and Hall, London, pp 301–325Google Scholar
- Ross J (1981) The radiation regime and architecture of plant stands. Junk, The HagueGoogle Scholar
- Soudani K, Trautmann J, Walter JM (2001) Comparison of optical methods for estimating canopy openness and leaf area index in broad-leaved forests. C R Acad Sci Ser III-Sci Vie 324:381–392Google Scholar
- Strachan IB, McCaughey JH (1996) Spatial and vertical leaf area index of a deciduous forest resolved using the LAI-2000 plant canopy analyzer. For Sci 42:176–181Google Scholar
- Thimonier A, Schmitt M, Cherubini P, Kräuchi N (2001) Monitoring the Swiss forest: building a research platform. In: Anfodillo T, Carraro V (eds) Monitoraggio ambientale: metodologie ed applicazioni Atti del XXXVIII Corso di Cultura in Ecologia, 2001. San Vito di Cadore, Centro Studi per l’Ambiente Alpino, Università degli Studi di Padova, pp 121–134Google Scholar
- Wang YS, Miller DR, Welles JM, Heisler GM (1992) Spatial variability of canopy foliage in an oak forest estimated with fisheye sensors. For Sci 38:854–865Google Scholar