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Quantifying changes in soil carbon (C) and nutrient stocks after timber harvesting is needed to inform C management and to ensure that forest productivity is sustained over time. Our objective was to assess changes in soil C, nitrogen (N), and phosphorus (P) 1 year after timber harvesting in temperate northern hardwood forests. We established permanent plots in forest stands for measuring forest attributes before and after harvesting. We collected soils from quantitative soil pits, which were associated with permanent plots, to determine total C, total N, and extractable P stocks and concentrations. Mean post‐harvest fine fraction organic (O) horizon C was less than the pre‐harvest stock, but we did not detect a statistically significant change in total O horizon or mineral soil C stocks. For the fine fractions of the O horizon and mineral soil from the 0–5 and 5–30 cm depth increments of the B horizon, total N and extractable P stocks were positively correlated with total C stocks. For all of these soil components, extractable P stocks and concentrations declined over time, which could be related to post‐harvest stand conditions that favored microbial activity and immobilization of available P. These findings indicate that P availability could be a concern in these forests and that long‐term monitoring is needed to consider potential management actions for ensuring that forest productivity is sustained. We quantified changes in soils after harvesting in old forests to inform C and forest productivity objectives.For most of our operationally defined soil components, we did not detect a reduction in total C stocks.For all soil components, total N and extractable P stocks were positively correlated with total C stocks.We detected a reduction in soil extractable P stocks and concentrations 1 year after harvesting.Monitoring soils over time will be needed to determine future recovery or continued declines in extractable P.

Evaluating and refining methods to minimize soil compaction during timber harvesting is important for maintaining soil health and long‐term forest productivity. This is especially important when harvesting methods change over time. In this study, a hybrid harvesting method was used with the trees cut by one machine, in‐forest processing of trees by other machines, and transporting the wood to the roadside by a forwarder on silt loam soils during the summer months. Two methods for sampling soils with mixed horizons in logging trails were developed to determine the baseline values of soil bulk density for long‐term monitoring and to compare soils from nonmixed B horizons with those of B horizons from nontrafficked areas. For both methods, paired soil samples, in and outside of logging trails, were collected to determine the difference in bulk density between trails and nontrafficked areas. Soil compaction in trails was greatest where the soils adjacent to trails had low bulk densities and for locations that were closest to landings. These results are important in the context of climate change, as more summer logging is expected to occur in areas traditionally cut in the winter because of longer frost‐free periods and more winter precipitation occurring as rain. More logging during the expanding snow‐free season could translate to a greater degree of compaction and longer soil recovery times over a larger portion of the forested landscape.

Elevated greenhouse gas (GHG) emissions have resulted in growing societal interest in natural climate solutions that include enhancing soil organic carbon (SOC). This study evaluated SOC from three USDA soil databases for Maine, a state that is nearly 90% forested. These databases were: (1) Forest Inventory and Analysis (FIA), (2) NRCS Soil Survey Geographic (SSURGO), and (3) Rapid Carbon Assessment (RaCA). We compared estimates of SOC density and concentration among databases and analyzed relationships between key soil properties and SOC densities and concentrations. Estimates of SOC density to a 20 cm depth which allows comparison among all three databases were 77 ± 1.2 Mg ha−1, 95 ± 0.3 Mg ha−1, and 39 ± 2.2 Mg ha−1for SSURGO, RaCA, and FIA, respectively. Significant differences existed among databases in SOC density at shallow depth increments, and marked differences existed among databases in the soil depths measured. Analysis of the influence of soil texture and drainage class on SOC highlighted the importance of silt and clay in SOC retention. A hypothetical increase in forest and agricultural SOC was compared to reported Maine GHG emissions to illustrate potential policy implications in the use of soil databases. We conclude that all three databases are valuable but not interchangeable. The database should be carefully chosen to match the objectives of the user.

Chronic N enrichment increased N exports, although ecosystem N retention was still high.Soil was the largest ecosystem N pool, but it was not significantly altered by chronic N enrichment.Chronic N enrichment increased biomass N accumulation in hardwood but not in softwood stands. We examine the temporal trend of input–output N fluxes and net ecosystem N retention, and estimate a mass balance for ecosystem soil and vegetation pools, after 25 yr of chemical manipulation at the Bear Brook Watershed in Maine (BBWM). The BBWM is a paired whole watershed manipulation experiment designed to study the effects of elevated N and S deposition on forest ecosystem function. Starting in 1989, 25.2 kg N ha−1was added annually to the West Bear (treated) watershed. The N additions in West Bear stimulated N loss through stream exports, and West Bear retained 81% of the annual N inputs, compared to 94% retention in the reference, East Bear. After 25 yr of N additions, the West Bear watershed had accumulated ∼700 kg ha−1more N than East Bear in soils and vegetation, with ∼10% of the accumulated N stored in forest biomass. The treatment increased recent biomass N accumulation rates in the hardwood stands, but not in the softwoods. Soils did not show detectable differences in total N content between watersheds, although the organic soils had greater N in West Bear. This paper presents a unique set of findings from one of the few long‐term whole forest ecosystem N enrichment studies in the world. While N dynamics were clearly altered in West Bear, with evidence of accelerated N cycling, the treated watershed did not attain an advanced stage of N saturation during the study period, based on the evidence from forest growth and stream N exports.

Anthropogenic emissions have altered the N status of forests in the northeastern United States, highlighting the importance of our imperfect understanding of the interaction between nitrogen (N) and phosphorus (P) in response to atmospheric N deposition. We investigated soil N and P dynamics at the Bear Brook Watershed in Maine (BBWM), a long‐term paired watershed experiment established to study ecosystem response to experimental N enrichment. One watershed (West Bear [WB]) was treated bimonthly for 25 yr with ammonium sulfate, and the reference East Bear (EB) received only ambient N deposition. We conducted field and laboratory studies to examine the interaction between N and P in O horizon soils in both EB and WB. In the “Field Addition” study, an addition of 100 kg P ha−1resulted in an overall 38% decrease in extractable ammonium (NH4+–N) due to increased immobilization. Even under ambient N deposition rates, EB displayed parallel, although lower, evidence of P limitation compared with WB. In contrast, in the “Laboratory Addition” study, soils incubated in the laboratory at rates of 0 to 200 kg P ha−1showed increases in potential net N mineralization (PNNM) and NH4+–N concentrations in response to P additions. There was no effect of N status in the Laboratory Addition study, but hardwood soils showed a faster response and greater rates of PNNM compared with softwood soils. Despite contrasting responses, both the field and laboratory studies suggested that N dynamics at BBWM were P limited and that N status and forest type influenced the N and P interaction. N transformations in Maine's forest soils are P limited.P limitation is greater in N‐enriched soils.Hardwood soils show greater response to P additions than softwood soils.

Little is known about the regional extent and variability of nitrate from atmospheric deposition that is transported to streams without biological processing in forests. We measured water chemistry and isotopic tracers (δ18O and δ15N) of nitrate sources across the Northern Forest Region of the U.S. and Canada and reanalyzed data from other studies to determine when, where, and how unprocessed atmospheric nitrate was transported in catchments. These inputs were more widespread and numerous than commonly recognized, but with high spatial and temporal variability. Only 6 of 32 streams had high fractions (>20%) of unprocessed atmospheric nitrate during baseflow. Seventeen had high fractions during stormflow or snowmelt, which corresponded to large fractions in near-surface soil waters or groundwaters, but not deep groundwater. The remaining 10 streams occasionally had some (<20%) unprocessed atmospheric nitrate during stormflow or baseflow. Large, sporadic events may continue to be cryptic due to atmospheric deposition variation among storms and a near complete lack of monitoring for these events. A general lack of observance may bias perceptions of occurrence; sustained monitoring of chronic nitrogen pollution effects on forests with nitrate source apportionments may offer insights needed to advance the science as well as assess regulatory and management schemes.

Widespread changes in dissolved organic carbon (DOC) concentrations in lakes of the Northern Hemisphere are well documented, and there is a need to understand the ecological implications for changes in cold‐water refugia. DOC controls thermal structure in small, wind‐sheltered lakes, thus influencing the volume and persistence of the hypolimnion and cold‐water habitat. We explored the relationship between the quantity and quality of DOC and the availability of cold‐water habitat over the course of summer stratification in small lakes of varying depths. The ratio of the hypolimnetic volume to total lake volume was calculated to assess the relative changes in cold‐water habitat availability in each lake over time. DOC concentration, maximum lake depth, and the interaction between DOC concentration and maximum lake depth explained 87% of the variability in percent change in hypolimnion volume ratio across studied lakes. Hypolimnion compression was greater in shallow, low DOC lakes, whereas deeper, intermediate DOC lakes had more persistent hypolimnion volumes over the course of summer stratification. These results demonstrate that depth moderates the effect of DOC on the volume and persistence of cold‐water refugia availability in north temperate lakes, advancing our understanding of differing lake sensitivity in a rapidly changing physical and chemical environment. Dissolved organic carbon concentration, maximum lake depth, and their interaction explained 87% of the variability in hypolimnion volume ratioThe relative change in hypolimnion volume ratio over the course of summer stratification had a strong, negative correlation with mean Schmidt stability Dissolved organic carbon concentration, maximum lake depth, and their interaction explained 87% of the variability in hypolimnion volume ratio The relative change in hypolimnion volume ratio over the course of summer stratification had a strong, negative correlation with mean Schmidt stability

Environmental change is monitored in North America through repeated measurements of weather, stream and river flow, air and water quality, and most recently, soil properties. Some skepticism remains, however, about whether repeated soil sampling can effectively distinguish between temporal and spatial variability, and efforts to document soil change in forest ecosystems through repeated measurements are largely nascent and uncoordinated. In eastern North America, repeated soil sampling has begun to provide valuable information on environmental problems such as air pollution. This review synthesizes the current state of the science to further the development and use of soil resampling as an integral method for recording and understanding environmental change in forested settings. The origins of soil resampling reach back to the 19th century in England and Russia. The concepts and methodologies involved in forest soil resampling are reviewed and evaluated through a discussion of how temporal and spatial variability can be addressed with a variety of sampling approaches. Key resampling studies demonstrate the type of results that can be obtained through differing approaches. Ongoing, large‐scale issues such as recovery from acidification, long‐term N deposition, C sequestration, effects of climate change, impacts from invasive species, and the increasing intensification of soil management all warrant the use of soil resampling as an essential tool for environmental monitoring and assessment. Furthermore, with better awareness of the value of soil resampling, studies can be designed with a long‐term perspective so that information can be efficiently obtained well into the future to address problems that have not yet surfaced.

Imperfectly drained soils under forests can occupy extensive areas of the landscape and understanding how they might differ from upland forest soils can be critical for understanding soil organic carbon (SOC) across forested landscapes. Research on forest SOC across drainage gradients has been limited. This research was a case study at the Bear Brook Watershed in Maine (BBWM), a long‐term ecological research site, that focused on SOC pools and fluxes across three soil drainage classes (moderately well drained‐MWD, somewhat poorly drained‐SWPD, poorly drained‐PD) and two forest types (coniferous‐CF, broadleaved deciduous‐BLD). Soil respiration (RS), soil temperature, soil moisture content, and extractable soluble C were measured from May through November to assess Rsas an indicator of biological activity. The MWD mineral soil had significantly higher C concentrations(0.71 g kg−1) compared to SWPD (0.30 g kg−1) and PD (0.34 g kg−1). The MWD soils in CF had significantly greater C content (433.3 Mg C ha−1) compared to SWPD (113.95 Mg C ha−1) and PD (103.3 Mg C ha−1). Soil C concentration and content was not significantly different between SWPD and PD soils. Mean mineral soil C fraction concentrations (active, stable, passive) expressed as a percent of the total soil mass were significantly different among soil drainage classes. Results from this case study suggest that pedogenesis, above and belowground plant productivity, and moisture availability across the growing season play important roles in determining SOC dynamics in these forests.

We used P fractionation techniques to study the accumulation, mobilization, and availability of soil P in six watersheds of the eastern United States and Europe, two of which included paired long‐term acidification experiments. Although total soil P concentrations varied widely among these watersheds, the proportions of P fractions were relatively uniform. The mean for the P fraction operationally defined as being associated with Al in the reference watersheds was 71% of total extractable P (SE ≤ 1%). Experimental whole‐watershed acidification resulted in significant depletion of Al‐P concentrations from the upper mineral soil in treated watersheds due to the dissolution of Al hydroxide by acidic solutions traveling along shallow flow paths. Acidic soil solutions mobilize both Al and P, leading to P depletion from the Al‐P fraction in the mineral soils. Across this suite of watersheds, lower pH appears to decrease Al/P ratios in the Al‐P fraction of these mineral soils through changes in Al solubility. Biocycling in these forests can play a critical role in linking subsurface mineral soil P to surface O horizon available P. In this study, sites with the lowest mineral subsoil Al/P ratios generally had the lowest mineral soil pH values and the highest O horizon available P concentrations. The net effect was to leave subsoil P more bioavailable at the lower pH values because of a lower Al/P ratio in the mineral subsoil at the pH range of 3.1 to 4.6 found in this study. These results suggest that changes in soil acidity due to management, air pollutants, or pedogenesis could shift P availability by altering acidity and the Al/P balance.

In the northeastern United States interest in the use of biosolids on forest lands is growing due to the prevalence of extensive forests and market incentives for waste disposal, yet much of the regulatory framework for biosolids land application is based on agronomic practice. This study evaluated the response of soils in a young (∼20 yr old) deciduous forest to lime‐stabilized biosolids amendments focusing on (i) the temporal and spatial evolution of the pH response, (ii) soil exchangeable cation response, (iii) the risk of trace metal accumulations, and (iv) a bioindicator of treatments (i.e., foliar chemistry). Eighteen plots were established in two study phases with lime‐stabilized biosolids loading targets of 0 (control), 4.5, 6.7, 13.4, 20.2, 26.9, and 33.6 Mg (megagram) calcium carbonate equivalents (CCE) ha−1, with the lowest target rate of addition representing the current regulated loading limit for forest biosolids applications in Maine. The pH of the O horizon increased immediately >2 pH units, and then declined with time, while B horizon pH increased gradually, taking over 1 yr to achieve ∼1.0 pH unit increase at the highest loading target. O‐horizon exchangeable Ca concentration increases dominated soil chemical change and resulted in decreases in exchangeable H and Al. Few significant increases in soil trace metal concentrations had occurred at any soil depth after 1 yr of treatment. Foliar response generally reflected changes in soil chemistry, with Ca concentration increases most significant. This research provides critical insights on forest soil response to application of lime‐stabilized biosolids and suggests opportunities for higher loading targets in forests should be examined.

It is believed that atmospheric deposition of S and N in the Adirondack Mountains of New York has depleted soil‐base cation pools, reduced soil base saturation (BS), and contributed to enhanced acidification of soils and surface waters. However, data to determine changes in soil characteristics are generally lacking. It is expected that soil acid‐base status will improve as acidic deposition declines in response to atmospheric emissions controls. We studied edaphic characteristics at 199 locations within 44 statistically selected Adirondack lake‐watersheds, plus 26 additional watersheds that are included in long‐term lakewater monitoring programs. The statistically selected watersheds were chosen to be representative of Adirondack watersheds containing lakes larger than 1 ha and deeper than 1 m that have lakewater acid neutralizing capacity (ANC) less than or equal to 200 μmolcL−1Results of soil analyses were extrapolated to the watersheds of 1320 low ANC lakes. In general, the concentrations of exchangeable base cations, base saturation, and soil pH were low. More than 75% of the target lakes received drainage from watersheds having average B horizon exchangeable Ca concentrations < 0.52 cmolckg−1, base saturation < 10.3%, and pH (H2O) < 4.5. Variations in the effective cation exchange capacity in both O and B horizons were closely correlated with soil organic matter content. These data provide a baseline against which to compare future changes in regional soil chemistry, and provide input data for aquatic and terrestrial effects models intended to project future changes in surface water chemistry, biological conditions, and forest health.

There is concern that changes in atmospheric deposition, climate, or land use have altered the biogeochemistry of forests causing soil base‐cation depletion, particularly Ca. The Bear Brook Watershed in Maine (BBWM) is a paired watershed experiment with one watershed subjected to elevated N and S deposition through bimonthly additions of (NH4)2SO4Quantitative soil excavations in 1998 measured soil pools of exchangeable base cations 9 yr after treatments began. Stream sampling at the weirs on a weekly and event basis, and weekly precipitation sampling, were used for input‐output estimates. The treated watershed had lower concentrations of exchangeable Ca and Mg in all horizons, with evidence for the greater depletion in the O horizon compared to underlying mineral soils, and in softwoods compared to hardwoods. This difference between watersheds is interpreted to be treatment‐induced base‐cation depletion, which was reinforced by model simulations. The difference between watersheds was 66 and 27 kg ha−1of exchangeable Ca and Mg, respectively, after accounting for soil mass differences between watersheds. This was comparable with the total cumulative excess stream Ca and Mg export in West Bear after 9 yr of treatment of 55 and 11 kg ha−1, respectively. Model simulations of watershed response to treatments predicted excess soil exchangeable Ca and Mg losses in the treated watershed of 47 and 9 kg ha−1, respectively. These results indicate that the response to a step‐increase in N and S deposition during the first decade of treatments in this experimental forested watershed was to invoke cation‐exchange buffering, resulting in a net decline in soil exchangeable base cations.

Northern forest soils represent large reservoirs of C and N that may be altered by ecosystem perturbations. Soils at three paired watershed in Maine were investigated as case studies of experimentally elevated N deposition, wildfire, and whole‐tree harvesting. Eight years of experimental (NH4)2SO4additions at the Bear Brook Watershed in Maine significantly reduced forest‐floor C/N ratios from 30.6 to 23.4. Forest‐floor C and N pools were lower in the treated watershed (38 Mg C ha−1, 1612 kg N ha−1) compared with the reference (75 Mg C ha−1, 2372 kg N ha−1). Fifty years after wildfire at Acadia National Park, the burned watershed with hardwood regeneration had significantly lower forest‐floor C and N concentrations (208 g C kg−1soil, 9.9 g N kg−1soil) than the reference watershed dominated by a softwoods (437 g C kg−1soil, 12.8 g N kg−1soil). Forest‐floor C and N pools were lower in the burned watershed (27 Mg C ha−1, 1323 kg N ha−1) compared with the reference (71 Mg C ha−1, 2088 kg N ha−1). At the Weymouth Point, the harvested watershed regenerated to spruce‐fir, the dominant stand type that existed before the harvest, and it had significantly lower forest‐floor C concentrations and pools (406 g C kg−1soil, 24 Mg C ha−1) than the reference (442 g C kg−1soil, 39 Mg C ha−1) after 17 yr. All perturbations studied were associated with lower forest‐floor C pools.

The primary objective of this study was to evaluate the use of uncomposted, de‐watered pulp sludge as the organic matter component in a manufactured topsoil. Seven manufactured topsoils, containing 5.1, 8.8, 9.6, 10.9, or 13.8% pulp sludge and 0, 8.4, or 20.7% flume grit on a dry weight basis, were applied to an abandoned gravel pit. Manufactured topsoils and a control topsoil were evaluated for (i) impacts on soil and soil solution chemistry and (ii) effectiveness as a growing medium for a grass conservation mix and hybrid poplars (Populusspp.). Significant N mineralization was evident in all of the manufactured topsoils within the first field season. Soil cation exchange capacity (CEC), pH and P availability were positively correlated to pulp sludge loading rate. In soil solution, the highest concentrations of solutes were detected within 2 mo of topsoil placement and were dominated by NO3‐N and Ca. Cumulative grass yields from the 15 mo following topsoil placement were greater than those in the control topsoil and ranged from 3.9 to 7.3 Mg ha−1in the manufactured topsoils. Tree height, diameter growth, and foliar nutrient concentrations responded positively to the manufactured topsoils. Results from this study indicate that topsoils manufactured with pulp sludge as the organic matter component can be an environmentally sound alternative to natural topsoil for the reclamation of sites on which existing conditions necessitate importing topsoil for revegetation.

The chemistry of a first‐order stream in Amherst, ME, with a catchment area of 103 ha has been strongly altered as a result of road salt application at a rate of approximately 4 t of NaCl per year in the lower 15% of the catchment. Downstream from the road, elevated stream Cl is accompanied by elevated Ca, K, Mg, and Na. The chemistry of the stream was deconstructed to identify the impact of the salt on total stream chemistry. Components quantified include precipitation (including dry deposition), chemical weathering, road salt, and cation exchange. Sodium from the road salt displaces Ca, K, and Mg from the soil on an equivalent basis. The displacement was at a maximum in late Fall and early Spring, indicating a long residence time for the NaCl. The exchange process was reversible. With continued loading of NaCl the water chemistry should reach a steady state such that Na and Cl move through the soil in a relatively conservative way, when the soils are at equilibrium with elevated concentrations of Na. Concentrations of Ca, K, and Mg in stream water should concurrently return to pre‐salting values under the new steady state.

Increased rates of litter decay due to projected global warming could substantially alter the balance between C assimilation and release in forest soils, with consequent feedbacks to climate change. This study was conducted to investigate the effects of soil warming on the decomposition of red spruce (Picea rubensSarg.) and red maple (Acer rubrumL.) foliar litter at Howland, ME. Experimentally increased Oa horizon soil temperatures (increase of 4–5°C) were maintained during the snow‐free season from 1993 through 1995 in replicated 15 by 15 m plots using heat‐resistance cables. For red maple litter, significant treatment effects included greater loss of mass (27%) and C (33%), and greater accumulation of Zn (54%) during the first 6 mo of decay in the heated plots than the control plots. After 30 mo of decay, significant treatment effects were no longer evident for red maple litter. Few treatment effects were observed for red spruce litter during the initial 18 mo of decay. However, after 30 mo of decay, significant treatment effects included greater loss of mass (19%), C (19%), N (24%), Ca (27%), Mg (12%), K (4%), Zn (60%), and cellulose (40%) in red spruce litter in the heated plots than the control plots. We conclude that a modest increase in Oa horizon soil temperature (4–5°C) can significantly increase litter decay rates and alter litter decay dynamics in this coniferous forest stand, and that these changes exhibit variations in their temporal development as a function of species and litter quality attributes.

To characterize soil CO2under different forest types and several years after a clear‐cut harvest, soil CO2evolution and soil air CO2concentrations were measured at three sites in Maine: the Howland Integrated Forest Study (HIFS) site, the Bear Brook Watershed in Maine (BBWM) site, and the Letter E township (Letter E) site. Soil CO2evolution means ranged from 0.19 to 0.32 g m−2h−1among sites, whereas soil air CO2concentration means ranged from 1023 µL L−1for the O horizon to 3296 µL L−1for the C horizon for the 1990 growing season. Soil CO2evolution and soil air CO2concentrations were similar under deciduous and coniferous forests and 4 to 6 yr after harvest. Limited multiple‐year data suggest that significant annual variations in temporal patterns of these properties exist as a function of short‐term climatic factors. These data suggest that soil CO2evolution and soil air CO2concentrations may be somewhat similar across a diversity of soil types, forest types, and forest conditions at any point in time for northern New England.

A spruce‐fir forest in central‐Maine, USA, has been the site of dry and wet atmospheric deposition measurements since 1988. Precipitation flux of hydrogen ions (H+) and sulfate (SO2−4) decreased by 24 and 42%, respectively, during the study period, but no temporal trends occurred for precipitation H+or SO2−4concentrations. Decreased precipitation fluxes were likely due to a 33% decrease in precipitation amounts during the latter years of the study. Both H+and SO2−4concentrations and fluxes in throughfall decreased, corresponding to decreases in dry deposition of those constituents. No nitrate (NO−3) concentration or flux trends occurred in precipitation, throughfall, or dry deposition. Hydrogen, NO−3, and NH+4had a negative net canopy exchange (NCE) attributable to N deficiency at this site and acid neutralization in the canopy. Sulfate and magnesium (Mg2+) were conservative and had no NCE. Calcium (Ca2+) and potassium (K+) had a positive NCE due to canopy leaching. A comparison of bulk and wet‐only precipitation collectors showed that SO2−4, Ca2+, and K+concentrations were greater in solutions from a bulk collector compared with a wet‐only collector. The differences were partially attributable to dry deposition. Throughfall H+, Ca2+, and dissolved organic carbon (DOC) concentrations were higher in weekly wet‐only collections composited monthly, compared with weekly bulk collections composited either weekly or monthly. Nitrate concentration, however, was lowest in the wet‐only throughfall collections. Differences likely resulted from spatial variability. Ongoing research is attempting to further define trends apparent to date, and to determine the mechanisms controlling these characteristics.

Changes in soil and soil solution chemistry were studied for 2 yr after application of wood ash to an acidic forest Spodosol. Application rates to four 50 m2plots were: 0 (control), 6, 13, and 20 Mg CaCO3equivalents per hectare (Mg ha−1). In soil solution, the 13 and 20 Mg ha−1treatments caused large but generally transient increases in base cations, pH, and anions. At 20 Mg ha−1, solution concentrations of H, acid neutralizing capacity (ANC), K, and SO4remained elevated for 20 mo. There was minimal response in soil solutions at 6 Mg ha−1, suggesting that this rate may represent a threshold below which there is only minor response in soil solution chemistry. Loss of soil N into soil solution (as NO3) at the two higher application rates may have decreased available‐N in the already N‐limited soil. In the O horizon, all treatments resulted in increased pH and higher exchangeable Ca, K, Mg, CEC, and percent base saturation; Mn and Al decreased. In the B horizon, exchangeable Ca, K, Mg, and percent base saturation were higher than in the control. Responses in soil chemistry were not generally proportional to the ash application rate. Furthermore, the responses in soil chemistry at different application rates were generally not distinguishable from each other after 25 mo. The treatment rate of 6 Mg ha−1ash was sufficient to favorably alter soil exchange chemistry, without seriously affecting solution chemistry. Above 6 Mg ha−1, soil exchange sites were unable to buffer ash amendments, resulting in substantial changes in solution chemistry.

Although N is typically a growth‐limiting factor in northeastern forest soils, few studies have demonstrated the best analytical approach for determining available N in this heavily forested region. To address this information need, seedlings of balsam fir [Abies balsamea(L.) Miller], red spruce (Picea rubensSarg.), and white pine (Pinus strobusL.) were grown for 26 wk in the greenhouse using soil materials representative of commercial forest sites in Maine. Soils included two O horizons and two B horizons from Spodosols derived in till, and an Ap and B horizon from an Inceptisol derived in marine sediments. Six different indices of available N were evaluated for each horizon, and results were compared with seedling‐growth parameters. Three available‐N indices were chemical and three were biological. Seedlings grew markedly better in O horizons than in mineral soils. Of the species examined, white pine had the greatest dry‐weight yields, and was the only species to exhibit visible evidence of root mycorrhizal infection. Although N‐availability indices were correlated with seedling‐growth parameters, the 1‐ and 2‐wk anaerobic incubations generally exhibited the highest correlation coefficients. Of the chemical indices, the simple KCl extraction appeared best correlated with seedling growth. Of the seedling characteristics examined, foliar N concentration was not highly correlated with soil N availability due to dilution effects. In contrast, foliar N uptake was highly correlated with N availability.

Research and modeling efforts to evaluate soil‐soil solution chemical interactions must take into account solution equilibria with soil air CO2. Measurements of soil air CO2and soil temperature were made in the major horizons of a forest soil in eastern Maine through the 1985 growing season. Soil air CO2concentration ranged from 0.10 to 0.35%, 0.10 to 1.25%, and 0.20 to 1.20% in the O, B, and C horizons respectively. Peak soil air CO2concentration occurred in July and early October which coincided with high points in soil temperature during the growing season.