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1 :'.«".';.;. v United States ' ' EHK 'Y<\ Department of P;; Agriculture.rtA *af,,.-/ ' Z^'' Fores! Service Pacific Northwest Forest and Range Experiment Station General Technical Report PNW-163 December 1883 I ES 'Vast'S3 I m B i p f "35 n HC"^) r^> l\ ~f> ( J "^i \s2;^ U «a 4i/ *«i«j L 1 u \i il H C^4 va> E/ cs^ Cw 3 /f^x T n ^4f f i fits S I" j /"^ (' ^? o i i C?^ U U VJ^' ^4is 5^S ^-4^ 1:

2 I.U.RR.O. Symposium on Forest Site and Continuous Productivi'ty Seattle, Washington August 22-28, 1982 Russell Ballard and Stanley P. Gessel Technical Editors Sponsored by: USDA Forest Service, Pacific Northwest Forest and Range Experiment Station Northwest Forest Soils Council Weyerhaeuser Company University of Washington, College of Forest Resources Published by: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station, Portland, Oregon General Technical Report PNW-163 December 1983

3 FOREST MANAGEMENT PRACTICES AND THE NUTRIENT STATUS OF A LOBLOLLY PINE PLANTATION David H. Van Lear, Wayne T. Swank, James E. Douglass, and Jack B. Waide ABSTRACT: Nutrient budgets for N, P, K, and Ca over a 41-year rotation were estimated for two loblolly pine (Pinus taeda L.) watersheds on poor sites in the upper Piedmont of South Carolina. Whole-tree ing of above-stump biomass removed more than twice the N and P, and almost twice the K and Ca, as conventional of boles only. Nutrient outputs exceeded inputs for P, K, and Ca on even the conventionally ed watershed. Harvesting and/or prescribed burning were the major causes of N and P loss from both watersheds, and stormflow and leaching were major sources of cation loss. Precipitation and N fixation were major sources of nutrient input to the ecosystems. Findings suggest that of boles only on rotations of moderate length and leaving the forest floor and logging slash in place will help minimize adverse effects of clearcutting on the nutrient status, and thus the productivity, of these sites. INTRODUCTION Maintenance of site productivity in perpetuity is a basic tenet of forest resource stewardship. Forest soil scientists, ecologists, and silviculturists have recently become concerned that some intensive forest management practices may have an adverse impact on long-term productivity of the sites. Of special concern is the relatively new practice of whole-tree ing, which is becoming increasingly attractive to the wood-using industry as a means of increasing fiber production from a given land base (Boyle et al. 1973, Weetman and Webber 1972, White 1974). Others see whole-tree ing as a method of supplementing current and projected energy supplies in the United States (Office of Technology and Assessment 1979). Research sponsored by the Biomass Energy Systems Division, U.S. Department of Energy, under contract W-7405-eng-26 with the Union Carbide Corporation. DAVID H. VAN LEAR is a professor, Department of Forestry, Clemson University, Clemson SC; WAYNE T. SWANK is a principal plant ecologist and JAMES E. DOUGLASS is a principal hydrologist, Coweeta Hydrologic Laboratory, USDA Forest Service, Franklin NC; and JACK B. WAIDE is a research ecologist, U.S. Army Engineers Waterways Experiment Station, Vicksburg MS. 252 Concern that intensive forestry will reduce forest site quality is more than academic. Reports from abroad have documented productivity declines in spruce in Saxony (Wiedemann 1923), and radiata pine in Australia (Keeves 1966) and New Zealand (Stone and Will 1965, Whyte 1973). Although actual declines in site productivity in response to management practices have not been documented in the United States, declines have been predicted on the basis of theoretical analyses, either from computer simulation (Swank and Waide 1980) or from nutrient budget analyses (Wells and Jorgensen 1975). Effects of conventional and whole-tree (abovestump) ing on the nutrient status of two sites within a near-maturity loblolly pine plantation in the Piedmont of South Carolina are presented. Data collected from the last few years prior to and the first 2 years following cutting were used to estimate nutrient inputs and outputs from each site over a rotation beginning with regeneration on freshly clearcut areas. STUDY AREA The study was conducted in an old field plantation of loblolly pine growing on the Clemson University Experimental Forest. Within the plantation, four small watersheds, ranging from 0.40 to 2.18 ha had been delineated in a previous study. Three of these watersheds were used in the present study: one served as the uncut

4 control, another was whole-tree ed of all biomass above stump (whole tree), and the third was conventionally ed. The 41-year-old stand was ed between mid- December 1979 to mid-january It had been thinned twice prior to. Basal area of the pine overstory ranged from 15 to 22 m^/ha. Growth rates were extremely low for the 5 years preceding but are considered typical for older loblolly pine plantations in the highly eroded upper Piedmont. The soil was Pacolet fine sandy loam (Typic Hapludult, kaolim'tic, thermic) and was well drained (slopes averaged percent). Erosion has removed up to 75 percent of the A horizon of similar soils in the Piedmont (Byrd 1972). Perhaps due to past land use history, the whole-tree ed watershed was not eroded as badly and supported about 33 percent more biomass than the other two watersheds. Precipitation averages 130 cm yearly and is generally well distributed. Prior to, three consecutive prescribed fires were conducted on the watersheds at yearly intervals to control understory hardwoods and prepare a seedbed. Strip head fires with ignition lines across the slope were used to accomplish the burning. Regeneration after was accomplished naturally using clearcutting with seed in place (Lotti 1961). METHODS Biomass and nutrient content of trees in the plantation were estimated from regression equations developed from 16 trees growing in the stand (Van Lear et al. 1983). Data on biomass and nutrient content of each tree component were related to diameter at breast height (d.b.h.) in the model: Log 1n Y = a + b Iog 1n d.b.h. '10 lo 1 - where Y is the biomass or nutrient content of the tree component in kilograms and d.b.h. is expressed in centimeters. Diameters of all trees >7.6 cm were measured for each watershed. Forest floor (0^ and 02 layers) and soil (0- to 8-, 15- to 23-, and 46- to 53-cm depths) were sampled quarterly after from five 5- x 5-m locations on each watershed. The Oj layer was collected within 1-m^ quadrats, whereas the much thicker 02 layer was sampled in an interior 0.09-m 2 quadrat. Because there is considerable mixing of soil with forest floor material, nutrient content of the forest floor is expressed on an ash-free basis. Potential N fixation was measured on samples collected quarterly for 2 years from control and treatment watersheds using the acetylene reduction assay method (Hardy et al. 1968). Fieldmoist subsamples were transported to the laboratory in an ice chest. Approximately 100 g of soil or 10 g or 0\ and 02 layers were transferred to 125-ml Erlenmeyer flasks fitted with serum stoppers; and 25 ml of -2^2 were injected into each flask. Three extra flasks of soil and litter were used for endogenous controls, and three empty flasks were used as acetylene controls. Samples were incubated for 24 hours at 18 C and then a 1-ml gas sample was extracted for analysis. Ethylene was determined by gas chromatography. Dissolved nutrient output in stormflow was determined over a 3.7-yr pre period ( ) by sampling storm runoff from ephemeral stream channels with a 0.61-m-diameter Coshocton wheel set below 0.3-m H flumes. Stage height during storms was recorded on an analog-to-digital punch tape recorder. Flow sampled by the Coshocton wheel was diverted into plastic sample barrels from which subsamples were collected at weekly intervals for analysis. Concentration data were multiplied by stormflow quantities to calculate dissolved nutrient export. Sediment loss of nutrients in stormflow was predicted by multiplying annual sediment export during the calibration period by the total nutrient concentration in soil samples from the 0-8-cm depth of each watershed. Nutrient loss in stormflow over the rotation is the sum of the dissolved nutrients and nutrients in sediment. Loss to leaching was determined from nutrient concentrations in the soil solution collected at monthly intervals. Porous-cup tube lysimeters (suction set at 0.1 atm) were placed in the soil to a 50-cm depth at five locations per watershed. The volume of water moving beyond this depth was estimated by the difference in precipitation and potential evapotranspiration for the Clemson area. This difference was separated into stormflow and deep seepage components. Because of differences in channel morphology, only about 3 percent of precipitation was stormflow on watershed 64; 14 percent was stormflow on watershed 66 (Douglass and Van Lear 1983). Lysimeters were installed after, so nutrient concentrations used for calculation of leaching losses within the latter part of the rotation were based on a 2-year record from the control, watershed 63. During the early years of the rotation, elevated losses of nutrients occurred because of the lack of ground cover and the increase in both runoff and deep seepage. For this reason, stormflow and leaching losses of nutrients were calculated for the first 10 years of the rotation using concentration data from the first year after and assuming a linear recovery rate to base-line condition; i.e., concentration prior to. Three low-intensity prescribed fires were applied to both watersheds prior to clearcutting to prepare the seedbed and to control understory hardwoods. Nutrient losses were calculated from measured weight reductions of the forest floor

5 during burning and nutrient concentrations of the Ql layer following burning. McKee (1982) summarized prescribed burning effects on soil chemical properties and concluded that most of the cations and P in burned litter enters the mineral soil. Others have documented nutrient loss to ash convection (Clayton 1976, Kodama and Van Lear 1980, Lewis 1974). Therefore, we arbitrarily assumed 25 percent of the cations and P were lost in ash convection during the fires, and 75 percent was leached into the soil profile. Nutrients leached into the soil were considered to be part of the nutrient reserve. Nitrogen in the consumed litter was assumed lost to volatilization. Input of nutrients in precipitation was collected in 1979 and Analyses were performed after rains produced a volume greater than 250 ml. Mass balance differences (i.e., an index of potential weathering) were calculated as the difference between hydrologic outputs and precipitation inputs (Clayton 1979). Leaching and stormflow losses and precipitation inputs during the last years of the rotation were used to compute weathering input. Water samples were analyzed for N03-N, NH4-N, P04-P, Ca, and K on a Technicon Autoanalyzer and atomic absorption spectrophotometer. Total N in water, plant, and soil samples was measured by Kjeldahl analysis, and total P in plant and soil samples by perchloric acid digestion. Total K and Ca in plant tissue were determined by perchloric acid digestion, and total cations in soil were obtained by lithium metaborate fusion (Suhr and Ingamells 1966). Exchangeable K and Ca and extractable P04-P in soils were measured in a 0.05N HC N H 2 S0 4 extract. RESULTS AND DISCUSSION Nutrient Inputs Nutrient inputs in bulk precipitation (includes both wet and dry deposition) in 1979 and 1980 averaged 6.2 kg.ha.-v~ 1 for N(N03-N + NH^-N), and 0.2, 1.6, and 2.8 kg.ha.-lyr' 1 for P, K, and Ca, respectively. These figures are similar to precipitation input at Hubbard Brook, New Hampshire (Likens et al. 1977) and at Coweeta Hydrologic Laboratory, North Carolina (Swank and Douglass 1977). Total input from precipitation over the 41-year rotation was estimated to be 254, 8, 66, and 115 kg/ha for N, P, K, and Ca, respectively (table 1). lable 1 Nutrient inputs in two loblolly pine watersheds (WS) over a 41-year rotation Whole-tree Conventional (WS 64) (WS 66) N P K Ca N P K Ca (kg.ha.-mlyrs- 1 ) Inputs Precipitation N fixation Weathering Total input A summary of potential N-fixation data from free living organisms for the three catchments over a 2-year period showed an annual rate for the control of 3.7 kg.ha.-lyr-^. Estimates for the ed catchments indicated a depression ir fixation with rates of 2.4 and 1.7 kg.ha.-lyr~^ for the commercial and whole-tree s, respectively. Fixation rate over the course of a year appeared to respond most closely to moisture conditions. On the ed sites, moisture content of the litter and surface soil samples were lower than for the control site, particularly in the summer and fall periods. For the calculation of input in table 1, we assumed that fixation rates exhibit a linear recovery to control rates over 5- and 7-year periods for commercial clearcut and whole-tree ing treatments, respectively. Nitrogen accretion from fixation is a major input over the rotation and accounts for about 37 percent of the total input of N. Input from weathering, as indexed by mass balance differences. ranged between 0.2 and 0.4 kg.ha.-lyr-i for K and Ca on the two ed watersheds. These rates are within the estimated weathering rates for K and Ca in other Piedmont studies (Cleaves et al. 1970, Cleaves et al. 1974). Inputs of P in precipitation exceeded losses to leaching and stormflow, so weathering input is shown as 0. Piedmont soils, such as the extremely old and highly weathered Pacolet series, would be expected to have low rates of nutrient release from parent material and primary minerals. Diffraction analysis of soil samples from ed watersheds indicates that plagioclase feldspar and weathered mica are the primary sources of Ca and K, respectively.i/ During short rotations of 20 years or so, nutrient loss in stormflow and leaching plus the rapid accumulation of nutrients in biomass and forest floor materials, may be too large to be compensated by weathering, as suggested by data from Wells and Jorgensen (1975). Using the mass balance equation in short rotations would predict unrealistically high rates of nutrient release in weathering. - Personal communication, Steven C. Hodges, soil chemist, Clemson University, Clemson SC. 254

6 Nutrient Outputs Nutrient outputs, or removals, from the site are accelerated by whole-tree ing (table 2). Whole-tree removed more than twice as much N and P as did conventional, and almost twice the K and Ca. The relatively nutrient-rich portions of the tree (i.e., foliage, branches, and upper stem) are removed in whole-tree, whereas conventional took only the bole to a 15-cm top, which has a lower nutrient concentration. Comparison of nutrient removal between the two ed watersheds must be tempered by the fact that, at, watershed 64 contained about 133 t/ha above-stump biomass whereas watershed 66 had 100 t/ha. Nevertheless, if both watersheds had equal biomass, the magnitude of nutrient loss between the two methods would still be dramatic. Table 2--Nutrient outputs from two loblolly pine watersheds (WS) over a 41-year rotation Outputs Final Burning 160 Thinning 16 (stems only) Stormflow 11 N Whole-tree (WS 64) Conventional (WS 66) K Ca (kg.ha.-ulyrs- 1 ) Ca Leaching Total output Forest-floor weight losses averaged about kg/ha for the two treatment watersheds for the first burn, kg/ha for the second burn, and about kg/ha for the third burn. Because watershed 64 contained more fuel, greater quantities of nutrients were lost from that site during the three burns. Nitrogen loss to volatilization during burning was a major avenue of nutrient output, accounting for 44 and 43 percent of total output on watersheds 64 and 66, respectively. Others have reported large losses of volatile N during fire (Allen 1964, DeBell and Ralston 1970). Some of the N loss may be offset by an increased rate of N fixation from legumes, which were prevalent on burned and ed watersheds, but symbiotic N fixation was not measured. Loss of cations and P to ash convection were estimated to be relatively small from these cool prescribed fires. If burning had been accomplished after logging, the convection loss of nutrients would have been much greater. In addition, most of the N in the forest floor and logging slash would have been volatilized. Burning, as used in this study, caused no significant losses of nutrients in stormflow (Douglass and Van Lear 1983). Thinnings, which removed stems only, accounted for less than 10 percent of total output of N, P, K, and Ca (table 2). Thinnings, where branches and foliage are left on site, are a conservative method of in regard to nutrients. In addition, the quantity of nutrients removed at final is reduced in thinned stands. Stormflow was about 3 and 14 percent of total precipitation for watersheds 64 and 66, respectively. These differences are due primarily to the effect of channel morphology; i.e., watershed 66 had a long, deeply incised channel that was highly responsive to precipitation events, and the channel in watershed 64 was relatively short, shallow, and less responsive. Nutrient loss to stormflow was therefore much greater from watershed 66 (table 2). Conversely, leaching loss was less from watershed 66 than from watershed 64. The large quantity of nutrients lost to stormflow in a rotation is often overlooked. Ephemeral stream channels (i.e., gullies) that are relatively long and deeply incised carry away relatively large quantities of nutrients even after they are stabilized by a deep cover of pine needles. For certain cations (e.g., K from watershed 66) this may be the major mechanism of nutrient output. Leaching losses were calculated from nutrient concentrations in lysimeters and estimated volumes of soil moisture passing beyond the porous cup (table 2). Although the porous cup was inserted to a depth of only cm, probably 90 percent of the feeder roots of loblolly pine are above this depth on eroded Piedmont sites. Therefore, the majority of nutrients leaching beyond this depth presumably percolate to groundwater or move laterally downslope beyond the watershed boundaries. We used this hypothesis even though it needs field verification. In contrast to stormflow losses, leaching losses of nutrients, except for P, were much greater on watershed 64 than on watershed 66. A much greater proportion of precipitation percolated deeply on watershed 64, because stormflow was only 3 percent of precipitation. The site specificity of nutrient cycling processes is dramatically indicated in the comparison of stormflow and leaching losses between these two adjacent watersheds. Input of N exceeded output over the length of the rotation for both the conventionally and wholetree ed watersheds (table 3). However, N input exceeded output on the whole-tree ed watershed by only 9 percent whereas inputs exceeded outputs by 84 percent on the conventionally ed watershed. We should point out that potential N loss by denitrification was not measured in this study, although losses to this process are thought to be low on these welldrained sites. Also, symbiotic N fixation was not measured but could have contributed significant amounts of N input since leguminous species were observed on both sites. Outputs of P exceeded inputs for both watersheds, but the 255

7 deficit was five times as great on the whole-tree ed watershed. This difference in net P balance can be attributed to ing method alone, because burning, thinning, and hydrologic losses were the same for both watersheds. Outputs of K and Ca exceeded inputs on both watersheds. Table 3 Net balance of nutrients in two loblolly pine watersheds over a 41-year rotation Watershed number Nutrient Item N P K Ca - (kg.ha.-ml yrs' 1 ) - 64 Input (whole-tree Output ) Net balance Input (conventional Output ) Net balance Results of this nutrient budget analysis indicate that inputs of certain nutrients (e.g., P, K, and Ca) are not keeping pace with outputs on these poor Piedmont sites even under conventional ing systems. Under whole-tree ing, nutrient drain is greater (although this is not clearly shown for K because of the greater hydrologic loss of this element on watershed 66). Nutrient Reserves Nutrients in the mineral soil are considered reserves because mineral soil supplies a small proportion of the stand's annual requirements, especially after the forest floor reaches an equilibrium mass. Early in the rotation, nutrients supplied by the soil may be much more important. Total N in the mineral soil was about 10 percent higher on watershed 64 (table 4), which supported 33 percent more biomass. The striking difference, however, is that watershed 64 contained more than twice the total calcium of watershed 66. Whether high concentrations and quantities of Ca in watershed 64 are due to past land-use history or to geologic differences is not known. The forest floor is a ready source of nutrients for regeneration, because of accelerated decomposition following clearcutting (Bormann et al. 1968). Nitrogen was the most abundant nutrient in the forest floor just prior to ; i.e., 176 and 132 kg/ha for watersheds 64 and 66, respectively (table 5). Phosphorus was the least abundant of the elements analyzed in the forest floor with 12 kg/ha for watershed 66 and 17 kg/ha for watershed 64. Table 4--Total and extractable nutrient content in the mineral soil of two loblolly pine watersheds in the Piedmont of South Carolina Depth Whole-tree (WS 64) N K (kg/ha) - Ca Total (0-60 cm) Extractable I/ (0-8 cm) (9-34 cm) (35-60 cm) Conventional (WS 66) Total (0-60 cm) Extractable-/ (0-8 cm) (15-23 cm) (46-53 cm) Extractable P expressed as PO.-P Table 5 Nutrient reserves from organic residues Whole-tree Conventional (WS 64) (WS 66) Source N P K Ca N P K Ca (kg.ha.-mi Forest floor decomposition Logging residues Thinning residues Stumps and roots Total Foliage on logging slash releases its nutrients rather quickly, but woody logging debris does not contribute nutrients until much later when the Crelement ratio becomes more favorable for net mineralization and uptake (Covington 1981). The amount of nutrients in logging debris on watershed 66 appears low compared to data of Wells and Jorgensen (1975). Differences are attributed to site, stand, and management factors. This site was an eroded upland of poor to average site 256

8 quality, whereas the site studied by Wells and Jorgensen was a high quality old-field site. Their stand was a vigorous 16-year-old plantation nearing a peak nutrient-accumulation rate, and our 41-year-old plantation was near biological maturity. In this study whole watersheds, which contained a logging road and old skid trails, rather than small plots were used. Another important feature contributing to difference in biomass of the two studies is that the 41-yearold plantation had been thinned twice. Management records indicate that about 21 tons/ha of stem biomass was removed in light low thinnings before the study began with about 14 percent of total tree biomass in branch and foliage remaining on site following thinning. Estimated nutrient reserves from thinning residues ranged from 2 kg/ha for P to 13 kg/ha for N. Nutrient reserves in root systems were not measured but were estimated from published relationships between nutrient content of tops and roots of loblolly pine in the Piedmont of North Carolina (Wells and Jorgensen 1975). While fine roots certainly decompose rapidly, larger roots decompose rather slowly. Because of the high C:element ratio of these large roots, decomposition may immobilize significant quantities of N and P (Ralston 1978). As the C:element ratio decreases during subsequent decay, elements are released for uptake by the plant. In this respect, nutrient dynamics in large decomposing roots and woody logging debris are similar; i.e., both provide N and P for stand nutrition after the regeneration period. At first glance, nutrient removal in, erosion, burning, or leaching seems insignificant when compared to nutrient reserves in the mineral soil and those available from decomposition of organic reserves. It is the rate of nutrient availability that is important to productivity; however, nearly all the N and a large portion of the P in southern forest soils are located in a rather stable humus (mineral soil organic complex) fraction that has developed over centuries (Pritchett and Wells 1978). Mineralization of the soil humus fraction and the larger forms of the organic residues are slow and likely would not be adequate to satisfy nutritional demands of a rapidly growing new stand. Rates of N mineralization as affected by of these sites are currently under study and will be reported later. Nutrient inputs from weathering indices are low for this soil and deficits of P, K, and Ca may contribute to potential declines in site productivity, especially where whole-tree ing is practiced on eroded Piedmont sites. The negative net balance of P, K, and Cc (table 3) is a significant portion of the extractable quantities of these nutrients (table 4). SUMMARY AND CONCLUSIONS Management practices have a major effect on the nutrient status of loblolly pine ecosystems. Assuming stands of equal biomass, whole-tree ing removes about percent more N and P and 37 percent more K and Ca than would conventional. Frequent prescribed fires, even those of low intensity, can be a major source of N loss through volatilization. Conversely, thinning removes stem biomass of relatively low nutrient content and leaves the nutrient-rich foliage and branches to decompose on the site. Topography and hydrology affect nutrient flux. Adjacent watersheds with similar vegetation and overall slope but differing in channel depth and length exhibit markedly different nutrient output for some elements. Potential weathering rates are low for these weathered kaolinitic soils. Nutrient release from weathering appears to be unable to replace those removed in ing, especially whole-tree ing. Results indicated that even conventional ing had an adverse impact on P, K, and Ca status of the ecosystem. Output of these nutrients exceeded inputs on both ed watersheds. This net drain represented a significant percentage of the extractable nutrient pool. Whole-tree ing increased the net deficit of P and Ca. In addition, N inputs exceeded outputs by only 9 percent on the whole-tree ed watershed. When nutrient losses exceed nutrient gains to the ecosystem, reserves from the mineral soil and organic sources will have to compensate for the deficit to maintain current productivity levels. The question is for how many rotations can this reserve be taxed without adversely affecting site productivity. The length of the rotation is important in evaluating nutrient status. The shorter the rotation, the greater the rate of nutrient loss to stormflow and leaching. In addition, the rate of nutrient accumulation in biomass is greatest during the early phase of the rotation, and therefore rate of nutrient removal at is greater. Finally, a short rotation does not provide adequate time for nutrient accumulations through precipitation, weathering, and N fixation. For these reasons, nutrient drain is faster for short rotations. Whole-tree ing and frequent prescribed burning can markedly accelerate nutrient losses from loblolly pine ecosystems. On these eroded, highly weathered Piedmont soils, of boles only on relatively long rotations while leaving logging slash and forest floor in place will helo reduce the impact of ing operations on site nutrient status. LITERATURE CITED Allen, S. E Chemical aspects of heather burning. J. Appl. Ecol. 1: Borman, F. H., Likens, G. E., Fisher, W. D., and Pierce, R. S Nutrient loss accelerated by clearcutting of a forest ecosystem. Science 159: Boyle, J. R., Phillips, J. J., and Ek, A. R "Whole tree" ing: a nutrient budget evaluation. J. For. 71: Byrd, Huger S Soil survey of Pickens County, South Carolina. U.S. Oep. Agric. Soil Cons. Serv. 70 p.

9 Covington, W. W Changes in forest floor organic matter and nutrient content following clearcutting in northern hardwoods. Ecology 62: Clayton, J. L Nutrient gains to adjacent ecosystems during a forest fire: an evaluation. For. Sci. 22: Clayton, James L Nutrient supply to soil by rock weathering. In Leaf, A. L. (ed.) Proc. Impact of intensive ing on forest nutrient cycling, p State Univ. New York, Sch. of Forestry, Syracuse, New York. Cleaves, E. T., Godfrey, A. E., and Bricker, 0. P Geochemical balance of a small watershed and its geomorphic implications. Geol. Soc. Am. Bull. 81: Cleaves, E. T., Fisher, D. W., and Bricker, 0. P Chemical weathering of serpentine in the eastern Piedmont of Maryland. Geol. Soc. Am. Bull. 85: DeBell, D. S., and Ralston, C. W Release of nitrogen by burning light forest fuels. Soil Sci. Soc. Am. Proc. 34: Douglass, J. E., and Van Lear, D. H Prescribed burning and water quality of ephemeral streams in the Piedmont of South Carolina. For. Sci. 29: Hardy, R. W. F., Holstein, R. D., Jackson, E. K., and Burns, R. C The acetyleneethylene assay for N2 fixation: laboratory and field evaluation. Plant Physiology 43: Reeves, A Some evidence of loss of productivity with successive rotation of Pinus radiata in the southeast of South Australia. Aust. For. 30: Kodama, H. E., and Van Lear, D. H Prescribed burning and nutrient cycling relationships in young loblolly pine plantations. South J. App. For. 4: Lewis, W. W., Jr Effects of fire on nutrient movement in a South Carolina pine forest. Ecology 55: Likens, G. E., Bormann, F. H., Pierce, R. S., Eaton, J. S., and Johnson, N. M Biogeochemistry of a forested ecosystem. Springer-Verlag, New York. 146 p. Lotti, Thomas The case for natural regeneration. In Advances in management of southern pines, p Proc. 10th Annual Forestry Symposium. Louisiana State Univ. McKee, W. H., Jr Changes in soil fertility following prescribed burning of Coastal Plain sites. USOA Forest Serv. S.E. Forest Exp. Stn. Res. Pap. SE p. Office of Technology Assessment Energy from biological processes. Washington, D.C. Pritchett, W. L., and Wells, C. G Harvesting and site preparation increase nutrient mobilization. In Tippin, Tom (ed.) Proc: A Symposium on Principles of Maintaining Productivity on Prepared Sites, p Mississippi State Univ. MS. Ralston, C. W The Southern pinery: forests, physiography, and soils. In Proc: A Symposium on Principles of Maintaining Productivity on Prepared Sites, p Mississippi State Univ. MS. Stone, E. L., and Will, G. M Nitrogen deficiency of second generation radiata pine in New Zealand. In C. T. Youngb.rg (ed.) Forest soil relationships in North America, p Oregon State Univ. Press, Corvallis. Suhr, N. H., and Ingamells, C Solution technique for analysis of silicates. Anal. Chem. 38: Swank, Wayne T., and Waide, Jack B Interpretation of nutrient cycling research in a management context: evaluating potential effects of alternative management strategies on site productivity. In Forests: fresh perspectives from ecosystem analysis, p Proc. 40th Annu. Biol. Colloq. Oregon State Univ. Press. Swank, W. T., and Douglass, J. E A comparison of nutrient budgets for undisturbed and manipulated hardwood forest ecosystems in the mountains of North Carolina. In Howell, F. G., Gentry, J. B., and Smith, M. H. (eds.) Watershed Research in eastern North America, p ERDA Symp. Series (CONF ). Van Lear, D. H., Waide, J. B., and Teuke, M. J Biomass and nutrient content of a 41- year-old loblolly pine (Pinus taeda L.) plantation. For. Sci. (in press). Wells, C. G., and Jorgensen, J. R Nutrient cycling in loblolly pine plantations. In Bernier and Winget (eds.) Forest soils and forest land management, p Les Presses de 1'Universite Laval, Quebec, Canada. Weetman, G. F., and Webber, B The influence of wood ing on the nutrient status of two spruce stands. Can. J. For. Res. 2: White, E. H Whole-tree ing depletes soil nutrients. Can. J. For. Res. 4: Whyte, A. G. D Productivity of first and second crops of Pinus radiata on the Moutere gravel soils of Nelson, New Zealand. J. For. 53: Wiedemann, E Zuwachsruckgang and Wuchestockungen der Fichte in den Mittleren und den unteren Hohenlagen der sachischen Staatsforsten. Tharandt. [Papers in increment and growth interruptions of spruce in the middle and lower altitudes of the Saxon state forests.] 181 p. (U.S. Dep. Agric. For. Serv. 258 T,~ansl. Mo, 302, 1936.)