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1 The University of Notre Dame Foliage Production by Thuja occidentalis L. from Biomass and Litter Fall Estimates Author(s): William A. Reiners Reviewed work(s): Source: American Midland Naturalist, Vol. 92, No. 2 (Oct., 1974), pp Published by: The University of Notre Dame Stable URL: Accessed: 06/02/ :59 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. The University of Notre Dame is collaborating with JSTOR to digitize, preserve and extend access to American Midland Naturalist.

2 Foliage Production by Thuia occidentalis L. from Biomass and Litter Fall Estimates WILLIAM A. REINERS Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire ABSTRACT: Foliage production by members of Cupressaceae is difficult to measure by direct methods because of the growth and abscission pattern of the foliage sprays. An estimate of production was calculated for Thuja occidentalis by estimating foliage turnover as a ratio of litter fall to foliage biomass. Thuja foliage litter was 103 g/m2 in a T. occidentalis swamp in E-Central Minnesota. Total litter fall was 422 g/m2. A correction factor of 1.17 was derived from analyses of weight/area ratios of dead, fallen foliage fragments, and dried samples of live foliage. The ratio of corrected litter weight (120 g/m2) to an estimate of foliage biomass from an earlier study (563 g/m2) was INTRODUCTION In an earlier paper I described difficulty in estimating foliage production by Thuja occidentalis L. (Reiners, 1972). Thuja foliage consists of much-branched, two-ranked sprays of appressed, scalelike leaves. Growth of this foliage involves both apical extension of the sprays and thickening of the persistent leaves. While some axes of the branchlets develop into long-lived twigs, other axes are eventually deciduous. Based on a search of the literature and inquiries among plant morphologists and ecologists, it appears that no one has analyzed this pattern of branch growth, and that there is no known way to separate current growth from old growth for purposes of estimating productivity in Thuja. Other productivity studies involving T. occidentalis and other members of Cupressaceae have followed methods avoiding direct measurement of growth on a plant organ basis (Ovington, 1956; Young and Carpenter, 1967). The family Cupressaceae includes genera world-wide, and five genera in North America: Juniperus, Cupressus, Chamaecyparis, Thuja and Libocedrus (Lawrence, 1951). Because some of these genera are of considerable ecological importance, it is surprising that the problem of estimating foliage production has not already been resolved. Perhaps this problem has inhibited more detailed productivity studies in ecosystems in which members of Cupressaceae are important. In my earlier work involving Thuja occidentatis, I estimated foliage production by simply multiplying biomass by 0.35 (Reiners, 1972). The 35% figure was essentially a rough guess based on productivity of foliage in other conifers, all in Pinaceae. This paper describes an indirect approach for estimating the percentage of Thuja foliage which represents annual production. It involves measuring litter fall under a Thuja-dominated stand for which foliar mass has already been estimated and calculating the foliage turnover percentage from a ratio of litter fall to biomass. 340

3 1974 REINERS: T. OCCIDENTALIS FOLIAGE PRODUCTION 341 A production measurement based on this method of estimating turnover is subject to several assumptions. First, it assumes that the year-to-year changes in foliage mass are low compared with litter fall so that turnover is a good estimate of production. Second, it assumes that the Thuja foliage-litter collected is a reasonable average for longterm losses. Third, it assumes that there is no difference in weight of deciduous foliar fragments and dried green fragments, or that this difference can be systematically corrected. Finally, if the turnover percentage calculated in this study is to be applied to other stands, it must be assumed that the turnover percentage does not change with the age of individual trees or developmental age of mixed-age stands. The study area.-this study was conducted at a site described in detail in earlier papers (Reiners and Anderson, 1968; Reiners, 1968; Reiners and Reiners, 1970; and Reiners, 1972). It is situated in a peat-filled basin on the Anoka Sand Plain, Anoka Co., Minn. This swamp forest apparently was clear-cut or leveled by windfall about 1867 and then partially disturbed about Dominant canopy trees are either about 70 years old, or years old. Tree species in this stand, according to their percentage contributions to shoot biomass, are: Thuja occidentalis 56%, Betula papyrifera Marsh. 24%, Fraxinus nigra Marsh. 7%, Betula lutea Michx. 6%, Ulmus americana L. 5%, Larix laricina (Du Roi) K. Koch 3%o Acer rubrum L.<1%, Alnus rugosa (Du Roi) Spreng. <1 %, Cornus alternifolia L. <1%. Thuja density and basal area were 1100 stems/ha and 27.4 m2/ha, respectively, out of totals of 2755 stems/ha and 42.2 m2/ha for all species. METHODS Litter collection.-litter was collected in eight traps distributed in a stratified random pattern within an area 20 by 80 m. The traps were square, screen-bottomed boxes 0.5 M2 in area with sides 15.2 cm high. The screen bottoms were supported in light contact with the litter layer of the forest floor. Litter deposited in these traps was collected monthly in June, July and August, and weekly in September, October and the 1st 3 weeks of November Due to a continuous snow cover, litter was next collected in late April 1972, and then in mid-may and mid-june. Litter was dried for 48 hr at 55 C, sorted into Thuja foliage fragments and other components, redried for 30 min at 55 C to remove -moisture derived from atmospheric humidity, and weighed to 0.1 mg precision. Correction for weight changes.-as mentioned above, weight changes in foliage fragments prior to death and loss must be known in order to compare them with living foliage. To make this correction, freshly fallen foliage and living foliage were collected from various crown positions, and on N- and S-facing sides of Thuja occidentalis trees in Hanover, N.H. These fragments were then dried for 48 hr at 55 C and their outlines traced on bond paper. These tracings were

4 342 THE AMERICAN MIDLAND NATURALIST 92(2) then cut out, dried briefly and weighed. By use of the known area/ weight relationship of the paper, the areas of the foliage fragments were indirectly estimated. The weight/area relations of living and dead foliage fragments were then compared by regression analysis. This method assumes that there is no difference in shrinkage in area between foliage fragments which died and were then dried, and those which were living, cut and dried. RESULTS AND DISCUSSION Litter fall.-weights of various complonents of the litter collected over the full annual cycle (12 June June 1972) are given in Table 1. The grand total, g/m2, is significantly lower at the 0.90 confidence level than the total of g/m2, but is not significantly lower than the total of (Reiners and Reiners, 1970). Measures of variation are standard errors. A small part of this low total may be attributed to a severe infestation of deciduous leaves by the variable oak leaf caterpillar, Heterocampa manteo Dbldy. Using the estimate of Gosz et al. (1972) of 14% retention of leaf material by other species of Heterocampa, the weight for frass in Table 1 actually represents another 30 g/m2 of angiosperm leaf litter. The weight of insect parts in the frass component of Table 1 is trivial. Loss of frass through the screen floors of the traps probably caused an underestimate of frass fall and angiosperm leaf loss. Heterocampa manteo is not believed to feed on coniferous trees, even accidentally (Prof. H. M. Kulman, Univ. of Minnesota, pers. comm.), so this infestation probably did not influence litter fall of Thuja foliage. Thuja foliage fall was only 68% of angiospenn leaf fall even though Thuja foliage mass was estimated to be 260% of the mass of angiosperm foliage (Reiners, 1972) and angiosperms suffered defoliation. Thus, even with 2.6 times the foliage mass, Thuja contributed less to forest floor accretion than did the angiosperms because of the low foliage turnover rate in Thuja. Angiosperm leaf fall data provide an opportunity to estimate grazing intensity by defoliators. The sum of litter components (151 g for leaves + 26 g for frass + 4 g calculated for ingested leaf material) is TABLE 1.-Disposition of litter fractions in a Thuja occidentalis swamp. Standard errors of means are given with means for eight samples Litter fraction g/m2 Thuja foliage 103.0? 18.6 Thuja cones 26.9? 8.0 Thuja seeds 5.8? 0.6 Larix needles 0.7? 0.3 Angiosperm leaves 150.9? 16.9 Betula seeds and scales 47.7? 8.1 Bark and twigs 61.6? 23.9 Frass and insects 25.8? 8.6 Total 422.4? 34.2

5 1974 REINERS: T. OCCIDENTALIS FOLIAGE PRODUCTION g/m2. Consumption of angiosperm litter is thus 2% of the angiosperm leaf standing crop; destruction is 18%. These data also permit a check of the original estimate of angiosperm leaf biomass (213 g/m2). The difference between these estimates is about 15% of the biomass estimate. A weight loss correction for leaves prior to, abscission and for fallen leaves would probably bring this difference close to 10%. Measured Thuja cone and seed fall, and Betula seed and scale fall provide further opportunities to compare original estimates of production to those of the present study. The central axes of birch aments are included in the seed and scale category. The sum of Thuja cones and seeds, 33 g/m, is about twice the estimated production value of 16 g/m2 (Reiners, 1972); the weight of birch seeds and scales (48 g/m2) is about 1.6 times the estimated production value of 30 g/m2 for Betula lutea and B. papyrifera combined. These large differences can be attributed to several factors in unknown proportions. First, seeds and scales probably gained dry weight between measurement of their biomass in August and their dispersal later in the year. Second, there could be sizable differences between seed crops in 1967 and Third, there is biomass sampling error itself. The high variability in cone and ament distribution and the resulting high errors of estimate in the regression equations were discussed earlier (Reiners, 1972). In view of the statistical measures of error for these regressions, it is satisfying that discrepancies are only factors of 2.0 and 1.6. Unfortunately, the weights of individual Thuja seeds were not determined. With such data, a value for the Thuja seed rain could be calculated. In general, Thuja foliage and seeds, Larix needles and angiosperm leaves fell mainly in the autumn. The fall of Betula seeds and scales and Thuja cones was most concentrated in late autumn and winter. Frass fall was basically a summer phenomenon and bark and twigs fell sporadically, dependent on storms of summer or winter. Correction for weight changes of Thuja foliage.-the regression expressing the foliage weight in grams as a function of area in cm2 for all live segments is y (X) (n = 68, standard error of estimate = , correlation coefficient =.96, F ratio = 810.7). The analogous regression for dead segments is y = (X) (n = 48, standard error of estimate = , correlation coefficient = 0.99, F ratio = ). The intercepts of both regressions are virtually zero and the slopes are significantly different at the 0.99 confidence level. The difference between slopes represents the difference in weight/area ratios of the two, kinds of samples. From this analysis, it appears that dry weight per unit area of live foliage segments is 1.17 times higher than that of dead, fallen foliage segments. Thuja foliage turnover.-corrected Thuja litter fall is 103 g/m2 x 1.17, or 120 g/m2. Since the foliage biomass was estimated at 563 g/m2 (Reiners, 1972), the ratio of litter to biomass gives a turnover value of A range of variation for this ratio might extend from a minimum

6 344 THE AMERICAN MIDLAND NATURALIST 92(2) estimate of Thuja litter fall divided by a maximum estimate of foliage biomass, to a maximum estimate of litter divided by a minimum estimate of biomass. The mean for litter fall plus and minus the standard error gives a minimum of 84 and a maximum of 122 g/m2. Corrected for dry weight loss, these values become 98 and 143 g/m2. Rather than use the ambiguous standard error associated with the regression for estimating foliage biomass (Reiners, 1972), I will simply apply an arbitrary variation of +- 10% to the estimate of 563 g/m2. Turnover ratios resulting from these extremes are 0.16 and 0.28 compared with the calculated value of A turnover of 21% is somewhat low compared with turnover values for other conifers. Kimura (1963) estimated average longevities of Abies veitchii Lindl. and A. mariesii Mast. needles to be 4.4 and 6.1 years, respectively, equivalent to turnover ratios of 23 and 16%. His ratio of litter fall to estimated leaf biomass for old forests composed of these species, however, was 2.2/20.8 or only 1 %. Nihlg'ard (1972) estimated needle production in a 55-year-old Picea abies (L.) Karst. stand as 2.6 metric tons (mt) /ha compared with a biomass of 18 mt/ha, resulting in a turnover estimate of only 14%. Litter fall, on the other hand, was 4.4 t/ha yielding a turnover estimate of 24%. Nihlg'ard attributed this discrepancy to a recent history of thinning followed by canopy closure so that litter fall temporarily exceeded needle production. Analogous estimates of other conifer species are 26% for Abies balsamea (L.) Mill. (Baskerville, 1965), 35% for Picea glauca (Moench) Voss (Clark, 1961), 45% for Pinus rigida Mill. (Whittaker and Woodwell, 1969), and ca. 50% for Pinus echinata Mill. (Whittaker, et al., 1963). Many more comparisons are necessary to determine if Thuja occidentalis foliage turnover is indeed on the low end of the scale, and if this is a characteristic of all members of Cupressaceae. Such comparisons would also be of interest in searching for common turnover characteristics within genera, and for relationships of turnover with environments and productivities of genera and species. By coincidence, a turnover of 21 % is very close to an alternative low percentage of 20% I originally presented for a range of possible values (Reiners, 1972). The alternative aerial production value of 9.5 mt/ha based on 20% turnover ghould replace the published estimate of 10.1 mt/ha based on 35% turnover. Acknowledgments.-This work was funded through National Science Foundation grants GB-7148 and GB I am grateful for the field assistance of Mr. Donald L. Tilton, University of Minnesota, and for the cooperation of Dr. David Parmalee, Director of Cedar Creek Natural History Area. Mrs. Helen Vitousek provided a critical reading of the manuscript.

7 1974 REINERS: T. OCCIDENTALIS FOLIAGE PRODUCTION 345 REFERENCES BASKERVILLE, G. L Dry matter production in immature balsam fir stands. Forest Sci. Monogr p. CLARK, J Photosynthesis and respiration in white spruce and balsam fir. N.Y. State Univ. Coll. Forest. Syracuse Univ. Tech. Publ p. Gosz, J. R., G. E. LIKENS AND F. H. BORMANN Nutrient content of litter fall on the Hubbard Brook Experimental Forest, New Hampshire. Ecology, 53: KIMURA, M Dynamics of vegetation in relation to soil development in northern Yatsugatake Mountains. lap. J. Bot., 18: LAWRENCE, G. H. M Taxonomy of vascular plants. The Macmillan Co., New York. 823 p. NIHLGARD, B Plant biomass, primary production and distribution of chemical elements in a beech and a planted spruce forest in South Sweden. Oikos, 23: OVINGTON, J. D The form, weights and productivity of tree species grown in close stands. New Phytol., 5-5: REINERS, W. A Carbon dioxide evolution from the floor of three Minnesota forests. Ecology, 49: AND R. 0. ANDERSON CO2 concentrations in forests along a topographic gradient. Amer. Midl. Natur., 80: AND N. M. REINERS Energy and nutrient dynamics of forest floors in three Minnesota forests. J. Ecol., 58: Structure and energetics of three Minnesota forests. Ecol. Monogr., 42: WHITTAKER, R. H., N. COHEN AND J. S. OLSON Net production relations of three tree species at Oak Ridge, Tennessee. Ecology, 44: AND G. M. WOODWELL Structure, production and diversity of the oak-pine forest at Brookhaven, New York. J. Ecol., 57: YOUNG, H. E. AND P. M. CARPENTER Weight, nutrient element and productivity studies of seedlings and saplings of eight tree species in natural ecosystems. Maine Agr. Exp. Sta. Bull. Tech. Ser p. SUBMITTED 30 JULY 1973 ACCEPTED 21 SEPTEMBER 1973