Monitoring and modeling short-wave radiation in a broad-leaf forest

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1 F S P M 4 Monitoing and modeling shot-wave adiation in a boad-leaf foest R. Giuliani, M.B. Thonton and K.J. Bown Depatment of Envionmental and Plant Biology, Ohio Univesity, Athens, OH 471 USA Intoduction Among the plant factos, canopy geomety plays a cucial ole in deciding the diving foce fo leaf biological pocesses since it modulates canopy inteception of shot-tem adiation fluxes and it contols thei distibutions thoughout the foliage (Monteith and Unswoth, 199; Jones, 1992). In paticula, it is ecognized the biological ole of PhAR (4-7 nm waveband) in diving the photosynthetic pocess and the ole of global adiation (3-2 nm waveband) in diving the tanspiation activity (Nobel, 1991). Unfotunately, focusing on a foest stand, a fast and convenient method fo the chaacteization of the canopy geomety emains elusive. Only innovative methodologies, e.g. lase-based and imagey emote sensing seem to be pomising (Wulde and Fanklin, 23). Consequently, a spatial distibution of photon and adiant flux densities thoughout the foliage is often modeled assuming canopy geometical simplifications. In paticula, Bee s law has been and is still widely applied, equiing the assumption of foliage geometical homogeneity, to model canopy downwad attenuation of quantum flux density (Monsi and Saeki, 193). Given this context, ou study objectives wee: 1) to measue photosynthetic photon flux density (PPFD, µmol m -2 s -1 ) in a boad-leaf mixed foest stand by using a simple and inexpensive technique poposed by Pake et al. (1996): a custom-built balloon filled with helium was used as a platfom to lift a adiation senso thoughout the foliage; 2) to descibe the distibution of adiation flux densities at inceasing canopy height levels; 3) to pocess the collected adiation data using Bee s law (afte Monsi and Saeki, 193) to estimate spatial distibution in vegetation. Mateials and methods Expeimental site The study was conducted duing Summe 23 in Zaleski State foest, South-East Ohio (39 3 N; 82 6 W) in a mixed-deciduous foest with a 2 m dominant modal height. The foest was located in a hilly aea, at an appoximate elevation of 3 m a.s.l. and a mean slope of 1.7 degees (Fig. 1). Radiation monitoing Radiation measuements wee pefomed by placing a adiation senso on the flat hoizontal top suface of a custom-built balloon filled with helium, which was lifted though the foliage (afte Pake et al., 1996). 1 m Fig. 1. Map of the eseach aea. Dots identify positions chosen fo adiation measuements. 4th Intenational Wokshop on Functional-Stuctual Plant Models, 7-11 june 24 Montpellie, Fance Edited byc. Godin et al., pp. 4-44

2 A method fo 3D econstuction of tee canopy volume fom photogaphs 41 - Helium balloon A balloon was constucted fom a metallized biaxially oiented nylon laminate (Ameican Biaxis Inc., Winnipeg, Manitoba, Canada) with a polyethylene inne coating (Anagam Intl., Eden Paiie, MN, USA). The balloon was paallelogamshaped with a.9*.9 m base and a height of 2.2 m, esulting in a 1.8 m 3 volume and a weight of ~.27 kg. The adopted balloon shape was chosen because it appeaed (Geoffey Pake, p.c.) to confe an adequate dynamic hoizontal stability. Balloon s size made it possible to lift about.8 kg (total weight of balloon plus attached geas to acquie the adiation data) taken into consideation that the lifting capacity of helium is as maximum 1g*l -1 and that B.9 m A E 2.2 m C F D Knob A Switch HOBO # 2 Battey: 4.V - + HOBO #2 Switch On Off F Height: m Knob Linea Potentiomete: 4.7k Ω Resistance:.7 KΩ G Fig. 2. Components of the custom built appaatus to acquie adiation data: A) Quantum senso; B) Balloon filled with helium; C) Bag potecting Hobo H8 data logge #1; D) Cable connecting a adiation senso to the Hobo data logge #1; E) Tethe; F) Altimete attached to the spoole with knob, switch and Hobo H8 #2; G) Electical and font panel schemes of the altimete. the balloon had to win the contay foces exeted by the ai movements (a beeze of km h -1 was most times unavoidable). A 3 m long baided nylon mason s twine maked at 1. m-intevals was used to tethe the balloon. A spoole was used to oll the cable up. The balloon postue was contolled by fou adjustable stings taped to the fou lateal sides and knotted at the same height, all togethe with the tethe, immediately below the balloon. A cosine coected LI-19SA Quantum senso (LI-COR Inc., Lincoln, NE, USA), attached side by side to the top cente balloon suface, was used to detect PPFD (4-7 nm; µmol m -2 s -1 ). The adiation data wee ecoded evey second by a HOBO H8 miniatue data logge (Onset Compute Copoation, Boune, MA, USA) placed below the balloon. A cuent-to-voltage convete was custom-built afte Phillips and Bond (1997) to pocess the cuent (µa) geneated by the quantum senso to a voltage ange (.-2. V) detectable by the data logge. A custom-built device, attached to the tethe spoole made it possible to identify and ecod fom the gound the height (m) to be associated with the ecoded adiation values.the electic pat of this altimete was essentially composed of a battey diven linea potentiomete, a knob able to output thity distinct voltage values ecoded evey second by a second HOBO H8 data logge, and a switch. When the balloon was stopped at each senso height indicated by the labeled tethe, the switch was put in the Off position and the potentiomete voltage was ecoded by the data logge. In paticula, an association between a voltage value, i.e. a knob position, and each senso height was imposed. Vice-vesa while lifting the balloon the switch was put in the On position: a shot-cicuit occued and a backgound signal (. V) was acquied. Pio to use the two data logges, the one ecoding adiation data and the second evealing canopy height, wee synchonized. The components of the custom-built appaatus ae displayed in Fig. 2.

3 42 J. Phattaalephong et al. - Measuements Radiation measuements wee pefomed at full canopy development duing clea sky days in July and August 23 in a time window of two hous aound sola noon. The data wee geneally acquied by a slow elease of the balloon though the canopy until it was completely above the stand: 18 balloon ascents wee completed, wheeas 4 pofiles could not be accomplished because windy conditions. The gound position fo balloon lifting wee andomly chosen among foty locations peviously identified fo a netwok study (FFS Ohio Hills Study Site, Radiation data wee ecoded fom 3. m fom the gound and at each mete canopy height at least 1-1 obsevations wee collected. The balloon displayed some hoizontal movement, typically exploing m 2 aea in elation to wind speed and canopy stuctue. The veticality of the balloon was contolled fom the gound by acting on the tethe, to keep it paallel to a 3. m vetical efeence pole inseted in the soil. When the balloon was not seen in the vetical position, by switching On the altimete the coesponding adiation values could be identified in the data file and excluded. Data pocessing The custom-built altimete made it possible to identify and filte the data fo the values collected at one mete intevals; the est of the data wee excluded. 1) The adiation data associated to each tansect wee gouped in adiation flux density classes and the contibution of each class at the diffeent canopy heights was displayed. The statistics epesenting the data collected at each high level wee also computed. 2) A desciptive statistics based on cluste analysis was applied to the whole data set (the cluste coesponded to the values acquied at the same height in each pofile) (Data not shown). 3) The data of each tansect wee filteed to exclude the values coesponding to sunlit positions (PPFD 12 µmol m -2 s -1 ). Monsi and Saeki (193) equation was used to estimate the Leaf Aea Index (LAI, m 2 m -2 ) to be associated to the each attenuated adiation value. Results ba cb dc The PPFD classes elated to thee balloon ascents, chosen as example, ae displayed in Fig. 3. In paticula, the image a) shows a stong attenuation of PPFD by the uppe canopy faction, wheeas images b) and c) display the vaiability of the adiation values though the canopy. The fequencies of PPFD and LAI classes of a canopy pofile chosen as example ae displayed in Fig. 4a) and Fig. b), espectively Numbe of obsevations pe each PPFD class / collected numbe of obsevations [%] Fig. 3. Thee (a, b, c) vetical PPFD pofiles. The gey scale coesponds, fom black to white, to ten inceasing PPFD classes of 2 µmol m -2 s -1 each. Hoizontal white line at 3. m canopy height coesponds to the stating level fo data collection. SESSION 1 POSTERS

4 A method fo 3D econstuction of tee canopy volume fom photogaphs a b c Numbe of obsevations pe each PPFD class / collected numbe of obsevations [%] Q 28 Q, Q, Q Numbe of, obsevations PPFD 3 [, µmol 4, m -2, s -1 ] Fig. 4. a) Fequencies of PPFD classes associated to a vetical adiation pofile, chosen as example. The gay scale coesponds, fom black to white, to ten inceasing PPFD classes of 2 µmol m -2 s -1 each. Hoizontal white line at 3. m canopy height coesponds to the stating measuing level. b) Coesponding tend of PPFD obsevation numbes collected at the diffeent canopy heights; c) Coesponding mean (..), median (left ) and maximum (ight ) values a b c Numbe of LAI obsevations LAI Numbe of obsevations pe each LAI class / numbe of LAI obsevations [%] LAI [m 2 m -2 ] Fig. ) Infomation elated to the pofile shown in Fig. 4a. a) LAI obsevation numbe at the diffeent canopy heights; b) Coesponding fequencies of LAI: the gey scale coesponds, fom black to white, to 7 inceasing LAI values of 1. m 2 m -2 each. c) Coesponding LAI mean (.), median ( ) and Standad Deviation ( ) fom the mean. Discussion The following points will be consideed: Methodological aspects (Appopiate adiation senso; Veticality of the balloon); Measuement potocol (Numbe of locations to be monitoed and citeia to choose them); Data pocessing (Intepetation of the expeimental data though the application of the Monsi and Saeki (193) equation; Vaiability of the numbe of leaf layes associated to each canopy level).

5 44 J. Phattaalephong et al. Refeences Jones H.G., Plants and micoclimate: a quantitative appoach to envionmental plant physiology. Cambidge Univesity pess, Cambidge, pp Monsi, M. and T. Saeki, 193. Ube den Lictfakto in den Pflanzengesellschaften und sein Bedeutung fu die Stoffpoduktion. Japan J. Bot. 14:22-2. Monteith J.L.and M. H. Unswoth, 199. Pinciples of envionmental physics. Anold, London, pp Nobel P.S., Physicochemical and envionmental plant physiology. Academic Pess, San Diego, pp. 63. Pake G.G., P.J. Stone and D. Bowes, A balloon fo micoclimate obsevations within the foest canopy. J. appl. Ecology 33, Phillips N.G. and B.J. Bond, A mico-powe pecision amplifie fo conveting the output sensos to a voltage eadable by miniatue data logges. Tee Phys. 19: (8) Wulde M.A. and S.E. Fanklin, 23. Remote sensing of foest envionments. Concepts and case studies. Kluwe Academic Publishes, Boston, pp.19. Acknowledgements Funding fo this eseach was povided by the United States Foest Sevice coopeative ageement with Unit RWU NE 413, and the USFS Joint Fie Sciences Pogam. The authos ae gateful to D. Geoffey G. Pake fo his assistance in developing balloon potocols, to Ds Nathan G. Phillips and Babaa J. Bond fo thei assistance with light senso amplifie systems, to Eugenio Magnanini (Univesity of Bologna, Italy) fo the scheme of the custom-built altimete, and to Fabizio Neozzi (ARPA, Bologna, Italy) fo assistance in the statistical data analysis. SESSION 1 POSTERS