A Polyurethane Stemflow Collector for Trees and ShrubsAuthor(s): Gene E. Likens and John E. EatonSource: Ecology, Vol. 51, No. 5 (Sep., 1970), pp. 938-939Published by: Ecological Society of AmericaStable URL: http://www.jstor.org/stable/1933996 .

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A POLYURETHANE STEMFLOW COLLECTOR FOR TREES AND SHRUBS'

GENE E. LIKENS AND JOHN S. EATON

Section of Ecology and Systematics, Cornell University, Ithaca, New York

Abstract. A collar of polyurethane foam was developed for collecting stemflow from hard- wood trees. This collector is economical, chemically inert, and easy to install on stems of various textures, sizes, and shapes.

The diversion of precipitation down stems of plants has been shown by several workers to be important in studies of nutrient cycling in forested ecosystems. For example, Carlisle, Brown, and White (1967) showed that stemflow contributed 3-6%o of the total yield (litter and rainfall) of potassium, calcium, magnesium, and sodium to the forest floor. Thus, as a part of our studies of nu- trient cycling in the Hubbard Brook Ecosystem in New Hampshire (Bormann and Likens 1967), it was necessary to make quantitative chemical anal- yses of stemflow.

Stemflow is collected from forest trees by plac- ing a collecting collar or trough around the bole of the tree. Major considerations in the construc- tion of such collars are (1) cost, particularly if a large number must be constructed; (2) ease of attachment; and (3) a tight seal against the bole of the tree. If the stemflow is to be used for chemical analysis, the collar should be chemically inert.

Various devices have been used to collect stem- flow from trees. In many studies, however, the intent was to measure water volume, and precau- tions were not taken to avoid chemical contamina- tion (e.g., Ovington 1954, Leonard 1961). Leo- nard (1961) used zinc collars attached to the tree with nails and soldered in place. The collar was made water tight with asphalt roofing cement. Kaul and Billings (1965) used an aluminum foil collar affixed to the tree with modeling clay, and Carlisle et al. (1967) used a lead gutter sealed with an inert plastic filler and painted with an inert bitumastic paint. Chemical analyses of the stem- flow were undertaken in the latter two studies.

At Hubbard Brook we needed to construct a 1 Contribution no. 21 of the Hubbard Brook Ecosystem

Study. Financial support was provided by National Sci- ence Foundation Grants No. GB6742, GB6757, GB14289, and GB14325. We thank F. H. Borman for collaborative support and suggestions. Published as a contribution to the U. S. Program of the International Biological Pro- gram and the International Hydrological Decade. The work was done through the cooperation of the North- eastern Forest Experiment Station, Upper Darby, Penn- sylvania. (Received January 26, 1970; accepted May 13, 1970).

large number of stemflow collars around northern hardwood species of various sizes and to analyze the collected samples primarily for Ca++, Mg++, K+, Na+, and total N content. We found that polyurethane foam was convenient to use and met all of our requirements. The polyurethane was purchased from Isocyanate Products, Inc. as two liquid components. When these solutions were mixed in equal amounts the resulting solution produced a foam, with a volume increase of about 35 times, which hardened in a few minutes. The cost of a 2-gal kit was about $25.

The collars were formed around the tree by placing a polyethylene sheet (0.16 cm thick) around the tree in the form of a temporary collar. The two polyurethane liquid ingredients were then mixed in a separate container. As soon as the foaming action was observed (about 45 sec) the solution was poured around the tree into the tem- porary collar. Due to its expansion and foaming action, the polyurethane had a tendency to work itself into the crevices and around the rough bark. However, in the deeper crevices the foam was worked into the depressions with a polyethylene stirring rod or "policeman." We made no attempt to smooth the bark prior to adding the foam collar, although this could be done if necessary. After the foam hardened (about 15-30 min) the poly- ethylene sheet was easily removed since the foam did not adhere to it. A trough was fashioned in the top of the collar with a sharp knife.

The collars projected some 5-10 cm from the trunk of the tree depending on the species and the design of the collar. A wide trough is sometimes necessary to collect water that drips from the ends of curly bark or branch stubs (Leonard 1961). At the lowest point in the collar a hole or slot was made. A funnel, attached by tygon tubing to a 1-liter polyethylene collection bottle, was positioned below the hole (Fig. 1). A larger collection ves- sel is required if the apparatus is to be unattended for a long period of time, or during very heavy rainstorms, as very large volumes of water may be channelled into stemflow from large trees. Leonard (1961) found at Hubbard Brook that a

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Late Summer 1970 A POLYURETHANE STEMFLOW COLLECTOR 939

FIG. 1 Polyurethane foam collar and collection appa- ratus attached to a yellow birch (Betula alleghaniensis) tree.

beech tree of 25I4 cm dbh could produce some 1 10 liters of stemfiow during a 2.54-cm rainstorm.

To determine whether various nations or nitro- gen were leached from the foam, a number of small pieces of hardened foam with a total surface area of 43.4 cm2 were agitated with 100 ml of deionized water for a period of 5 min. This sam- ple and a deionized water blank were analyzed by

atomic absorption spectrophotometry for Ca+ +, Mg++, K+, and Na+. Total nitrogen was de- termined by the micro-Kjeldahl technique. In all cases these elements were not detectable by our techniques.

This type of stemflow collar is economical and easy to install on the boles of hardwood trees. The foam is readily adaptable in the field to various sizes and shapes. It could be used to collect stem- flow from small shrubs, woody vines, or even herbs. Also the foam is chemically inert with regard to Ca++, Mg++, K+, Na+, and total N. The foam collar appeared to be very durable. We used it successfully throughout the summer of 1969. Sunlight causes the surface of the foam to become brownish, but the manufacturer states that no serious deterioration results. We anticipate that the collars will not rupture during the winter,2 and because the foam is somewhat flexible even in the "hardened" condition, it should withstand small expansion of the tree diameter with growth.

LITERATURE CITED

Bormann, F. H., and G. E. Likens. 1967. Nutrient cycling. Science 155: 424-429.

Carlisle, A., A. H. F. Brown, and E. J. White. 1967. The nutrient content of tree stem flow and ground flora litter and leachates in a sessile oak (Quercus petraea) woodland. J. Ecol. 55: 615-627.

Kaul, 0. N., and W. D. Billings. 1965. Cation content of stem flow in some forest trees in North Carolina. Indian Forester 91: 367-370.

Leonard, R. E. 1961. Interception of precipitation by northern hardwoods. U. S. Forest Serv. Northeast- ern Forest Exp. Sta. Pap. 159. 16 p.

Ovington, J. D. 1954. A comparison of rainfall in dif- ferent woodlands. Forestry 26: 41-53. 2 In May 1970 only one of the stemflow collars installed

during June 1969 had been damaged during the winter.

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