Forest Floor Samples Research Articles

Vertical stratification of rainforest collembolan (Collembola: Insecta) assemblages: description of ecological patterns and hypotheses concerning their generation

We describe a complex vertical stratification of collembolan assemblages from rainforest leaf litter samples and identify distinct assemblages associated with forest floor, lower canopy and upper canopy samples. Leaf litter samples were collected from the forest floor and deposits of leaf litter suspended in epiphytes in the canopy of a subtropical rainforest site at Lamington National Park in southeast Queensland. The patterns of relationship among assemblages of Collembola extracted from these samples were examined using a variety of analyses of a matrix of similarities between samples. The results of ANOSIM analyses showed that forest floor, lower canopy and tipper canopy samples formed discrete groups. These results permit a discussion of these groups as three distinct collembolan assemblages. Analysis of the dissimilarities between these assemblages revealed a gradient of similarity from the forest floor through the lower to the upper canopy. This gradient represents a more complex vertical stratification than has previously been identified in rainforest canopy arthropods. We suggest that limitations on the dispersal of some forest floor species into the canopy may be responsible for this pattern. We also identify a second gradient of similarities among these assemblages. We show that dissimilarity among samples from forest floor is significantly lower than dissimilarity among samples from within the lower canopy, and that the level of dissimilarity between samples from within the upper canopy is significantly higher again. We suggest that dispersal barriers and higher probabilities of extinction in upper canopy collembolan colonies may be responsible for higher heterogeneity of species composition and abundance among samples from the upper canopy. We outline a number of testable hypotheses aimed at determining the importance of these processes in producing the patterns we have observed.

Characterization of nutrient regimes in some continental subalpine boreal forest soils

To determine whether field-identified soil nutrient regimes (SNRs) can be characterized and segregated by direct soil nutrient measures, we collected samples of forest floor and mineral soil (0 to 30 cm) from a wide range of forest sites throughout the Engelmann Spruce — Subalpine Fir (ESSF) zone of British Columbia. The samples were analyzed for acidity, total C, total N, mineralizable N, and extractable Ca, Mg, K, P, and SO4-S. The study sites were stratified according to an a priori field classification (SNRs) and an a posteriori classification derived from quantitative classification (groups) using all direct measures of nutrients as discriminating variables. The two classification methods had 72% agreement. Regardless of the classification, nitrogen-related variables (C:N ratio, total N, and mineralizable N) in the mineral soil segregated best among SNRs or groups indicating the presence of a steep, N-driven regional soil nutrient gradient. Multiple regression models using SNRs, groups, or direct measures of nutrients together with surrogates of climate (elevation, latitude, and/or longitude) as predictors had the similar accountability for the variation in subalpine fir and Engelmann spruce site index (0.41 ≤ R2 ≤ 0.65). The similarity in the accountability for site index justifies the use of the a priori classification in estimating site quality. Comparison of mineralizable-N values for field-identified SNRs between different climatic regions showed similarities between boreal climates and discrepancies between boreal and cool mesothermal climates. The study gave further evidence that indices of plant-available nitrogen in the upper mineral soil provide useful measures for field-identified SNRs, but indicated that it may be necessary to expand the existing five-class a priori classification to accommodate differences in regional soil nutrient gradients. Key words: Classification, Engelmann spruce, subalpine fir, nitrogen, site index, soil nutrient regime

Carbon and phosphorus transformations during decomposition of pine forest floor with different phosphorus status

Information on the mineralization of inorganic phosphate (Pi) from organically bound P (Po) during decomposition of forest floor and soil organic matter is vital for understanding P supply in forest ecosystems. Carbon (C) and phosphorus (P) fluxes were determined for forest floor samples from three Pinus radiata plots which had received no P (Control), 62.5 kg P ha–1 (Low P) and 125 kg P ha–1 (High P) 20 years before sampling. The P concentration of the forest floor samples had increased with fertilizer application, and the C:P ratio ranged between 585 and 1465. During a 9-week laboratory incubation 8.2–19.0% of the forest floor C was evolved as CO2-C. The amount of CO2 evolved from the forest floor of the Control plot was more than twice the amounts from the Low P and High P plots. There was little change in net P mineralization in the Control and Low P treatments throughout the incubation, but it increased slightly for the High P samples, suggesting a critical forest floor C:P ratio of 550 for net P mineralization. Changes in the 32P-specific activities of the Pi and microbial P pools during incubation, and concurrent changes in microbial-32P and 32Pi, indicated internal P cycling between these pools. The rate of internal P cycling varied with forest floor quality, and was highest in the High P forest floor. The High P samples had microbial C:P ratios of 22 : 1 which remained constant during the incubation, suggesting the microorganisms had adequate P levels.

Forest floor mass and nutrients in two chronosequences of plantations: Jack pine vs. black spruce

The purpose of this study was to determine whether change of forest cover had an effect on the development of the organic surface horizons, particularly on those variables that influence nutrient cycling and forest productivity. Jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] B.S.P.) plantations were selected from among the youngest to oldest (2–16 yr) within a 100 km2 area in southeastern New Brunswick. Natural forests were also included as benchmark sites. The forest floor and tree foliage was sampled and trees measured on 0.05-ha plots. The forest floor samples were used to determine organic mass, nutrient contents and pH. In pine plantations, organic matter accumulated rapidly during the period of exponential tree growth, but leveled off at about 45 Mg ha–1. This was within the range of benchmark sites with mixed conifer-hardwood cover. In spruce plantations, the forest floor mass ranged upward to 77 Mg ha–1. Development was strongly influenced by the nature of the previous forest. Spruce forest floors were on average more acid and had lower nutrient concentrations, particularly N and Ca. The observed differences suggest that nutrients are recycled more rapidly in the pine plantations, partly explaining the superior growth of the latter. Key words: Forest floor, Kalmia angustifolia L., Picea mariana (Mill.) B.S.P., Pinus banksiana Lamb., nutrient cycling, plantation forest

TDR calibration of organic forest floor media

We carried out a time domain reflectometry (TDR) calibration for 25 forest floor samples of five different forest stands. Linear regression was used to estimate the volumetric water content from the refraction index. Due to the presence of bound water, it was impossible to predict the calibration line parameters from theoretical values with a refractive mixing model. However, when the apparent dielectric constant of the water was considered, it was possible to predict the offset parameter because the low forest floor bulk density caused the calibration line slope and offset to be almost reversely proportional. Calibration parameters for different forest floor materials are presented. Allowing a somewhat higher margin of error we could also establish general calibration curves which were in close agreement with a published calibration curve (Malicki et al., 1994). An error analysis showed that decomposition of organic matter, residual water and temperature effects have negligible effects on the calibration parameters. Shrinkage of the organic material significantly influenced both the volumetric water content and the TDR reflection times. If not corrected, both effects yielded systematic errors of approximately 0.02 cm 3 cm −3 for a strongly shrinking H horizon.

A COMPARISON OF SOIL EXTRACTION PROCEDURES FOR 31P NMR SPECTROSCOPY

The effect of extractants on phosphorus determination by 31P NMR spectroscopy was examined using five forest floor samples. The extractants used were: 0.25 M NaOH, 1:6 soil to Chelex in water, 1:6 soil to Chelex in 0.25 M NaOH, and a 1:1 mix of 0.5 M NaOH and o.1 M EDTA. The broadest peaks were produced by the NaOH + EDTA extraction. However, NaOH + EDTA extracts contained the highest percentage of total phosphorus and the greatest diversity of P forms. These extracts were the only ones to show peaks for polyphosphates. Metals analysis indicated that NaOH + EDTA maintained Mn in solution, which seemed to be responsible for the line broadening. The sharpest peaks, with the best separation, were produced with Chelex + NaOH, and these were improved further by increasing the pH with NaOH prior to NMR analysis. Chelex + NaOH extracted 23 to 35% of the total soil P, Chelex in water extracted 10 to 13%, NaOH alone extracted 22 to 34%, and NaOH + EDTA extracted 71 to 90%. This work suggests that, because the extractant used will affect the P forms, care must be taken when interpreting studies of P cycling in soils using 31P NMR spectroscopy and when comparing studies using different extractants.

Carbon mobilization from the forest floor under red spruce in the northeastern U.S.A.

Global climate change may alter soil temperature and moisture conditions, increasing the need to understand how these basic factors affect C dynamics. This is particularly important in boreal forests, which often have large C pools in the forest floor and mineral horizons. We examined the effects of temperature and precipitation frequency on C dynamics in forest floor horizons from eight red spruce sites in the northeastern U.S. using column leaching experiments. Intact and sieved forest floor samples were incubated at 3, 10 or 20°C and leached either daily, once per week, or twice per week during 14 to 39 days using simulated throughfall solutions (pH 2.7 or 4.0). Leachate DOC and CO 2 production were measured along with soil C and N concentrations. For intact samples, losses of C as DOC and as CO 2 increased with increasing temperature, and the increase (Q 10) was usually greater between 3 and 10°C than between 10 and 20°C. There was a greater response of CO 2 to temperature than of DOC (e.g. Howland sieved soil Q 10s of 1.9 and 7.2 for CO 2 and 1.5 and 2.0 for DOC at 3–10 and 10–20°C ranges, respectively). More frequent leaching increased steady state DOC mobilization (e.g. 145 and 58 μg g −1 forest floor d −1 for daily and weekly leachings at 10°C, respectively), but not CO 2 evolution (e.g. 79 and 74 μg CO 2C g −1 forest floor d −1 for daily and weekly leachings at 10°C, respectively). Across the eight sites DOC loss and CO 2 evolution varied by factors of 3.6 and 4.0, respectively. Both CO 2 evolution and DOC in leachates calculated as fluxes were correlated (r = 0.73 and 0.87 respectively, n = 8) with the C-to-N ratios of the samples (C-to-N ratios ranged from 27 to 58), which could be explained by N limitations that triggered selective lignin degradation, differences in degree of humification of the material, or position on a west-to-east pollution gradient. Although higher temperatures and more frequent leaching increased DOC mobilization, and higher temperatures increased CO 2 evolution, both treatments and site to site variation illustrate the complexity of the response of forest-floor C pools to manipulations.

Effect of the inhibitors nitrapyrin and sodium chlorate on nitrification and N2O formation in an acid forest soil

An acid forest soil from beech forest gaps, which were either limed or unlimed, and the undisturbed forest was investigated for the type of nitrifying populations and the process of N2O evolution. To see whether nitrifiers were of heterotrophic or autotrophic origin, the nitrification inhibitors nitrapyrin and sodium chlorate were applied to disturbed soil samples which underwent laboratory incubations. Nitrapyrin inhibits autotrophic nitrification. In different studies, sodium chlorate has been identified as an inhibitor either of autotrophic or of heterotrophic nitrification. In the samples investigated only nitrapyrin inhibited the autotrophic nitrification occurring in the limed soil. Sodium chlorate effectively inhibited heterotrophic nitrification. In the limed forest floor samples, where most autotrophic nitrification occured, sodium chlorate showed no inhibitory effect. In another laboratory incubation experiment, N2O evolution from undisturbed soil columns, to which the above inhibitors were applied, was investigated. In those samples, in which nitrification had been reduced, neither inhibitor significantly reduced N2O evolution. Thus it was concluded that the contribution of nitrification to N2O losses is negligible, and that N2O evolution arises from the activity of denitrifying organisms. Microbial biomass and respiration measurements showed that the inhibitors did not affect microflora negatively.

Watershed liming and pit and mound topography effects on seed banks in the Adirondacks, New York, USA

Seed bank species composition, density, and frequency were evaluated as seedling emergence relative to differences in substrate chemistry associated with watershed liming and pit and mound topography (microsites) on the Woods Lake watershed, western Adirondack Mountains, NY. Liming was expected to affect calcicole and calcifuge species richness and density, while species that form persistent versus transient seed banks were expected to vary with microsite. Two of five subcatchments were limed in October, 1989 with 6.89 t ha −1 of pelletized CaCO 3. Forest floor samples were collected in May 1991 and 1992 from pit, mound, and undisturbed microsites in limed and reference (untreated) subcatchments. Water soluble calcium concentrations in forest floor samples collected in May 1992 from limed subcatchments were almost ten times greater than forest floor samples from reference subcatchments, but there were no differences in soluble calcium concentration among microsites within a subcatchment. Species richness and abundance varied among microsites, but the magnitude depended on year and lime treatment. Relative frequencies of Betula alleghaniensis (yellow birch) and Oxalis acetosella (wood sorrel) exceeded 80% in both years, with a slightly greater frequency from limed than reference subcatchments. Differences in relative frequency for several species between subcatchments were not consistent between years. The relative frequency of all species by microsite was generally greater from limed than reference subcatchments. Total density and the density of individual species by microsite varied between treatments within subcatchments and between years, although some patterns exist. Seed bank patterns vary appreciably between years and among microsites. Differences in seedling emergence from pit versus mound microsites varied between years and depended on whether the microsites were in limed or reference subcatchments. These data suggest that there are no detrimental short-term effects of watershed liming on seed banks of upland deciduous forests. Microsites may affect plant community composition most through germination and survical of propagules.

Decomposition and biomass incorporation of 14c-labeled glucose and phenolics in taiga forest floor: effect of substrate quality, successional state, and season

Forest floor samples from early, intermediate and mature successional sites in the taiga of interior Alaska were exposed to 14C-labeled glucose and two phenolic acids. Our results indicate that microbes present in the taiga forest floor metabolized phenolics. At all sites, biomass incorporation of glucose as measured by the fumigation-extraction technique was approximately twice that for the phenolics, while respiration of 14CO 2 was significantly higher for the phenolic compounds. Major differences in 14C allocation were seen even between phenolic compounds with similar structures. Despite large differences in litter and forest floor composition, the metabolism of our model compounds varied only slightly between successional stages. Seasonal and successional effects were considerably less than those arising from substrate quality with variation greater in the uplands (where succession is firedominated) than in the floodplains (where river erosion and deposition are the controlling factors). Any physiological variation in microbial communities through succession must therefore be in organisms which produce exoenzymes that break down primary polymers, rather than in organisms and pathways that use the monomer breakdown products.

Fuel Loading, Bulk Density, and Depth of Forest Floor in Coast Redwood Stands

Abstract The relationship between forest floor depth and bulk density was examined for purposes of estimating fuel loading and consumption in forests dominated by the coast redwood (Sequoia sempervirens [D. Don] Endl.). Data were obtained from 47 samples at 2 sites. Samples of forest floor varied from 2 to 10 cm deep. For each sample, organic material was excavated in 1 cm strata within a 20 x 20 cm frame. Multiple regression analysis indicated that bulk density increased with strata depth, although a given stratum had lower bulk density in deeper profiles (P = 0.05). In practical terms, these variations have a small effect on the accuracy of estimates of forest floor consumption derived using the constant mean bulk density. For. Sci. 39(3): 617-622.

Kinetics of Microbial Respiration and Nitrogen Mineralization in Great Lakes Forests

AbstractRecent attention has focused on organic matter storage in forested ecosystems because climate change could potentially alter this process. Labile organic matter pools are especially important because they may be most strongly influenced by changes in soil temperature and water availability. We measured rates at which C and N were released from labile organic matter within the forest floor and mineral soil of jack pine (Pinus banksiana Lambert), red pine (P. resinosa Aiton), balsam fir [Abies balsamea (L.) Miller], sugar maple (Acer saccharum Marshall), and quaking aspen (Populus tremuloides Michaux) forests. Forest floor and mineral soil samples were assayed for microbial respiration and N mineralization using a long‐term (32 wk at 35 °C) laboratory incubation. Cumulative amounts of respired C and mineralized N were fit to first‐order rate equations; pools and rate constants were compared among forests. Labile (respired) C pools in forest floor ranged from 67 (jack pine) to 92 g C m−2 (sugar maple), four to six times less than that measured in mineral soil. Rate constants for microbial respiration were statistically different among forest types, but means ranged narrowly in forest floor (0.269–0.299 wk−1) and mineral soil (0.303–0.350 wk−1). Labile (mineralized) N pools ranged from 2.2 (red pine) to 4.1 g N m−2 (sugar maple) in forest floor, an order of magnitude less than those in mineral soil. Rate constants for N mineralization varied from 0.326 to 0.556 wk−1 in forest floor and from 0.043 to 0.069 wk−1 in mineral soil. Regional climatic variables were weakly correlated with labile C and N pools and with rate constants. Annual in situ estimates of microbial respiration and N mineralization were far less than respired C and mineralized N pools, suggesting that only a fraction of labile soil organic matter is annually metabolized within these forests. Local climate, rather than the chemistry of labile organic matter, appears to be an important factor constraining the annual in situ flux of C and N from this pool.

Forest floor and mineral soil development in Casuarina equisetifolia plantations on the coastal sand dunes of Senegal

Forest floor and mineral soil samples were collected from the interdune depressions of 6-, 8-, 17-, and 34-year old Casuarina equisetifolia Forst. & Forst. plantations growing on the coastal sand dunes of Senegal. The accumulation of organic matter as well as all mineral elements in the forest floor except sodium followed a linear pattern. The thickness of the litter layer increased from 4.2 to 8.0 cm. Forest floor biomass increased up to 120.3 Mg ha −1; an average increase of 3.3 Mg ha −1 year −1. Nitrogen in the forest floor accumulated up to 1567 kg ha −1; an average increase of 45 kg ha −1 year −1. Calcium, aluminum, magnesium, iron, potassium and phosphorus in the forest floor accumulated at 6.8, 3.7, 1.8, 1.3, 0.49 and 0.25 kg ha −1 year −1, respectively. In the mineral soil, total phosphorus and exchangeable calcium decreased with plantation age. Nitrogen in the mineral soil increased by 30 kg ha −1 year −1 while organic matter in the mineral soil increased by 61.5 kg ha −1 year −1. The pH of the mineral soil decreased from 7.3 to 6.5. As a result of a particular combination of species characteristics and ecological conditions, C. equisetifolia plantations on these coastal sand dunes appear to accumulate forest floor organic matter at rates comparable to those found in boreal and subalpine forests. A nitrogen to phosphorus ratio in the litter layer of 164:1 indicates that decomposition processes are strongly limited by phosphorus. This suggests that introducing strains of nitrogen-fixing bacteria capable of fixing even greater amounts of nitrogen would do little to improve soil fertility. Since there was no sign that accumulation of either organic matter or mineral nutrients had reached steady-state, a minimum of a 34 year rotation would seem justified if soil improvement is the primary management objective. Since the overwhelming majority of the organic matter and nutrient capital is located in the forest floor and upper 2 cm of mineral soil, proper management of this fragile layer following harvest will be extremely important if the benefits realized in the first rotation are to be capitalized on during subsequent rotations.

Nitrogen availability in radiata pine plantations on former pasture sites in southern New South Wales

Studies of nitrogen availability were carried out in radiata pine (Pinus radiata D. Don) plantations on former pasture sites in N.S.W. in conjunction with studies of the effects of previous land use on tree form. Sites were selected on previously improved pastures (cleared with introduced legumes) and unimproved pastures (partially cleared without legumes) to form age sequences of stands which had been established for periods of up to fifteen years. Mineral-N pools in soils and forest floor samples were determined monthly for thirteen months and nitrification potentials were determined from periodic laboratory incubations.

Carbon Storage in Upland Forests of the Lake States

AbstractCarbon storage and dynamics are receiving increasing attention because of the hypothesized role of CO2 in global climate change. This study was carried out to determine total C storage in Lake States' forests, including C in biomass, forest floor, and mineral soil. Overstory trees were measured and samples of both forest floor and mineral soil (to 1 m) were collected from plots in 169 forest stands across Minnesota, Wisconsin, and Michigan. Five forest types were represented: balsam fir, Abies balsamea (L.) Mill.; jack pine, Pinus banksiana Lamb.; red pine, P. resinosa Ait.; aspen, Populus tremuloides Michx.; and northern hardwoods dominated by sugar maple, Acer saccharum Marsh. There were no strong geographic trends in C storage in biomass, forest floor, or mineral soil across the study area. Storage differed significantly among forest types. Each major C pool was related to a different set of descriptors. Total C storage, the sum of all pools, was related to forest type, stand age, available water, actual evapotranspiration, and soil clay content, explaining about 65% of the variation. Use of soil and site descriptors did not completely account for the strong effects of forest type on C storage. Differences in the size of C pools, as related to time since disturbance and forest type, indicate that C storage in forests of the Lake States can be influenced by forest management activities. Patterns of C storage in these moist temperate ecosystems are not as strongly influenced by climatic variables as is C storage in grasslands to the west.

Biodegradability of Dissolved Organic Matter in Forest Throughfall, Soil Solution, and Stream Water

AbstractHigh concentrations of dissolved organic matter (DOM) were leached into rainwater passing through the canopy and forest floor of an oak (Quercus spp.)‐hickory (Carya spp.) forest in the southern Appalachian Mountains. More than 95% of this dissolved organic C (DOC) and N (DON) was removed as water percolated through the soil profile and left the ecosystem in stream water. Our objective was to examine the importance of decomposition in the removal of DOC and DON. Samples of DOM from throughfall, forest floor water, soil water from A and B soil horizons, and stream water were all adjusted to a common initial DOC concentration, inoculated with soil and stream microbes, and incubated in solution for 134 d. In general, only 14 to 33% of the DOC in forest floor, soil solution, and stream samples decomposed during the incubation. The relative order of average decomposition of DOC from the various strata was, from fastest to slowest; throughfall, Oi horizon (forest floor), Oa horizon (forest floor), B horizon, stream, AB horizon, isolated fulvic acid, and upper A horizon. In short, biodegradability of DOM in the ecosystem profile declined vertically from throughfall to the A horizon and then increased with depth. The DON generally did not decay faster than the DOC — results consistent with the idea that hydrolysis of organic N is linked to mineralization of DOC rather than occurring selectively in response to the biochemical need for N. Throughfall DOM could be decomposed during its passage through the upper soil, but decomposition seems too slow to be responsible for the bulk of removal of DON and DOC that occurs in the mineral soil. Adsorption, rather than biodegradation, is more likely responsible for maintaining low DOC substrate concentrations in the mineral soil and preventing its loss into stream water.

Effects of starch additions on N turnover in Sitka spruce forest floor

Starch and carboxymethyl starch were added to forest floor samples collected from a sitka spruce stand near Aberdeen, Scotland. Samples were incubated for one month and were periodically analyzed for respiration, biomass-C, net and gross N-mineralization/immobilization. Gross mineralization/immobilization was measured by using a 15N-isotope pool dilution technique. Starch additions did not significantly affect respiration rates or biomass-C but caused net immobilization. The mechanism of this appeared to be inhibition of the decomposition of N-containing soil organic matter by the available starch-C, which resulted in decreased gross mineralization. Carboxymethyl starch acted as a biocide, probably as a result of an osmotic effect.

Heavy metal accumulations in forest soils along an urban- rural gradient in Southeastern New York, USA

Heavy metal contents and concentrations of forest floor and mineral soil were determined in nine oak stands situated along an urban-rural gradient. Twelve composite soil and forest floor samples from each stand were analyzed for seven metal cations. Levels of Cu, Ni, and Pb corresponded with the gradient. The mean urban soil and forest floor Pb concentrations were four times those recorded in forests at the rural end of the gradient, whereas Cu and Ni were two times higher in urban sites. Forest floor metal contents provided an unreliable measure of deposition along the gradient.

SPATIAL VARIATION IN CHEMICAL PROPERTIES OF FOREST FLOOR AND SURFACE MINERAL SOIL IN THE NORTH CENTRAL UNITED STATES

Samples of both forest floor and surface mineral soil (0–25 cm) were collected from plots in 171 forest stands across Minnesota, Wisconsin, and Michigan. Five forest types were represented: Abies balsamea (L.) Mill., Pinus banksiana Lamb., Pinus resinosa Ait., Populus tremuloides Michx., and norther

Carbon and nitrogen dynamics in forest floor during short-term laboratory incubations

The supply of N to forest trees depends on seasonal patterns of N turnover. This study was conducted to examine factors that control organic matter decomposition and the relationship between organic matter decomposition and the release of mineral N. Samples of forest floor (organic soil horizons) from plantations of red pine ( Pinus resinosa Ait.,), Norway spruce [ Picea abies (L.) Karst.], sugar maple ( Acer saccharum Marsh) and black locust ( Robinia pseudoacacia L.) were collected periodically from May 1987 to December 1988. Samples were incubated in the laboratory for 20 days at 23°C. Carbon dioxide evolution was measured every 5 days and used to estimate potentially mineralizable carbon, C 0, and decay rate constants, k. Ammonium-N and NO 3 − -N were measured at the beginning and end of incubation for eight sample periods to assess the effects of litter species and season (time of sampling) on N turnover. Forest floor from under the maple stand generally had the largest amount of evolved CO 2 and forest floor from under all stands had relatively large evolution of CO 2 from July to October 1988, following an unexpected, drought-induced litterfall. An exponential decay model and a logistic model were developed from the CO 2 data and were used to predict C 0 and k, but there did not appear to be a predictable difference in these parameters related to species and season. There were no significant ( P <0.10) correlations between evolved CO 2 and net N mineralized in forest floor samples except for three locust samples. Net N mineralization was greatest in forest floor from under the maple, and occurred in all forest floor samples except in all of those collected in September 1988. when N was immobilized. Potential N availability to trees to be significantly influenced by factors other than decomposition rates. High net nitrification in June and October 1988 suggested a potential for loss of N from the soil-plant system.