Impacts of anthropogenic disturbances on forest succession in the mid-montane forests of Central Himalaya

We studied the influence of anthropogenic drivers on the distribution and regeneration of tree species in vegetation at different stages of succession from grasslands to oak forests in mid-montane Central Himalaya. We found fire, grazing, and lopping as the main factors hindering a progressive successional regime towards a late-successional oak community. Succession was studied in five vegetation formations (grasslands, pine, pine–oak, open oak, and dense oak), with similar site conditions, representing a theoretical successional sequence from early- to late-successional stages. A structured survey with uniform distribution of sampling plots in the five selected vegetation formations was conducted to gather information abut the vegetation communities. Early-successional grasslands and pine forests were found to harbour high densities of pine and oak seedling and sapling regeneration. However, recurring fires and chronic unsustainable levels of grazing in these vegetation formations obstructed progressive succession by eliminating regenerating seedling and saplings from the forest understorey. Similarly, in intermediate- and late-successional stages (including pine–oak, open oak, and dense oak), overexploitation of existing oaks trees via lopping and grazing of regenerating oak seedlings and saplings hampered oak regeneration and development. The possibility to convert pine forests into oak as well as the conservation of existing oak forests through controlled grazing and lopping are management options that can contribute to an enhanced functioning of forest ecosystems in the study area. We conclude that with strategic management that restricts the current anthropogenic disturbances, the extent of oak forest in the study area can be increased.     

The effect of agricultural utilization on the composition and yield of phenolic acids in low peat soils

Summary Levels of benzoic and cinnamic acids in low peat soils, maintained for 25 years under four different cropping systems, were studied in field experiments. The soil samples were obtained from four horizons of thirteen selected profiles. Seven phenolic acids were identified by high performance liquid chromatographic (HPLC) techniques and their amounts were determined quantitatively. The concentration of phenolic acids in the soils depended on the cropping system and the depth of the soil profiles. Permanent grassland had the highest yield of phenolic compounds in peat soils. Much smaller amounts were found in the order forest, alternate and field utilization. Thus, phenolic compounds may be useful markers with which to follow the decomposition in peat soils. The content of phenolic acids decreased with the depth of the profiles, but in some cases the 25–30 cm soil layers contained higher amounts of phenols than the 5–10 cm layers. Compared with the surface layers the deeper horizons (55–60 cm and 95–100 cm) were low in phenolic acids.     

Potential use of organomineral complex (OMC) for bioremediation of pentachlorophenol (PCP) in soil

Adsorption/desorption characteristics for the organic pollutant pentachlorophenol (PCP) were determined for the organomineral complex (OMC) prepared in the laboratory with clay mineral (zeolite–clinoptilolite) and organic matter (humic acids), both natural products with excellent sorption properties. Sorption experiments were carried out in three characterized soil samples, Calcaro-haplic Chernozem, Gleyic Fluvisol, and Arenic Regosol. The results of this study indicate that OMC has better retention abilities than the clay minerals alone. Higher amounts of humic acids (HAs), bound to zeolite, enhance its potential to adsorb and retain PCP. An OMC containing approx. 5 mg HA g⁻¹ of zeolite possessed the best retention ability for PCP and presented an optimal economic solution from the preparation point of view. Then biodegradation of PCP was studied in the same types of sterilized soils bioaugmented with the bacterial isolate Comamonas testosteroni CCM 7350, with and without the addition of OMC. The immobilization effect of OMC in relation to PCP depends on the concentration of PCP and the content of organic carbon in the soil. The activity of the microorganisms and the effect of acid rain led to the gradual release and biodegradation of the irreversibly bound PCP, without any initial toxic effect on indigenous or bioaugmented microorganisms. OMC appeared to be a good adsorbant for PCP, with potential application in remediation technology. Fast and effective adsorption and low desorption may serve as a pretreatment step for bioremediation technology for reducing PCP content in soil and thus for reducing its potential toxicity, reducing bioavailability, and in this way facilitating biodegradation.     

Biogeochemical cycles in natural forest and conifer plantations in the high mountains of Colombia

Plant litter production and decomposition are two important processes in forest ecosystems, since they provide the main organic matter input to soil and regulate nutrient cycling. With the aim to study these processes, litterfall, standing litter and nutrient return were studied for three years in an oak forest (Quercus humboldtii), pine (Pinus patula) and cypress (Cupressus lusitanica) plantations, located in highlands of the Central Cordillera of Colombia. Evaluation methods included: fine litter collection at fortnightly intervals using litter traps; the litter layer samples at the end of each sampling year and chemical analyses of both litterfall and standing litter. Fine litter fall observed was similar in oak forest (7.5 Mg ha/y) and in pine (7.8 Mg ha/y), but very low in cypress (3.5 Mg ha/y). Litter standing was 1.76, 1.73 and 1.3 Mg ha/y in oak, pine and cypress, respectively. The mean residence time of the standing litter was of 3.3 years for cypress, 2.1 years for pine and 1.8 years for oak forests. In contrast, the total amount of retained elements (N, P, S, Ca, Mg, K, Cu, Fe, Mn and Zn) in the standing litter was higher in pine (115 kg/ha), followed by oak (78 kg/ha) and cypress (24 kg/ha). Oak forests showed the lowest mean residence time of nutrients and the highest nutrients return to the soil as a consequence of a faster decomposition. Thus, a higher nutrient supply to soils from oaks than from tree plantations, seems to be an ecological advantage for recovering and maintaining the main ecosystem functioning features, which needs to be taken into account in restoration programs in this highly degraded Andean mountains.     

Plant species effect on the decomposition and chemical changes of leaf litter in grassland and pine and oak forest soils

Aims

The aim of this study was to examine the effect of plant species differing in functional and phylogenetic traits on the decomposition processes of leaf litter in a grassland of Japanese pampas grass (Miscanthus sinensis) and adjacent forests of Japanese red pine (Pinus densiflora) and Japanese oak (Quercus crispula), representing sequential stages of secondary succession.

Methods

The litterbag experiments were carried out for 3 years in a temperate region of central Japan.

Results

The decomposition constant (Olson’s k) was 0.49, 0.39, and 0.56/year for grass, pine, and oak, respectively. Nitrogen mass decreased in grass leaf litter during decomposition, whereas the absolute amount of nitrogen increased in leaf litter of pine and oak during the first year. Holocellulose in grass leaf litter decomposed selectively over acid-unhydrolyzable residues more markedly than in leaf litter of pine and oak. ¹³C nuclear magnetic resonance analysis also revealed a decrease in the relative area of O-alkyl-C in grass.

Conclusions

The different decomposition among the three litter species implied that the secondary succession from grassland to pine forest and from pine to oak forests could decrease and increase, respectively, the rate of accumulation and turnover of organic materials and N in soils.     

Driving factors of a vegetation shift from Scots pine to pubescent oak in dry Alpine forests

An increasing number of studies have reported on forest declines and vegetation shifts triggered by drought. In the Swiss Rhone valley (Valais), one of the driest inner‐Alpine regions, the species composition in low elevation forests is changing: The sub‐boreal Scots pine (Pinus sylvestris L.) dominating the dry forests is showing high mortality rates. Concurrently the sub‐Mediterranean pubescent oak (Quercus pubescens Willd.) has locally increased in abundance. However, it remains unclear whether this local change in species composition is part of a larger‐scale vegetation shift. To study variability in mortality and regeneration in these dry forests we analysed data from the Swiss national forest inventory (NFI) on a regular grid between 1983 and 2003, and combined it with annual mortality data from a monitoring site. Pine mortality was found to be highest at low elevation (below 1000 m a.s.l.). Annual variation in pine mortality was correlated with a drought index computed for the summer months prior to observed tree death. A generalized linear mixed‐effects model indicated for the NFI data increased pine mortality on dryer sites with high stand competition, particularly for small‐diameter trees. Pine regeneration was low in comparison to its occurrence in the overstorey, whereas oak regeneration was comparably abundant. Although both species regenerated well at dry sites, pine regeneration was favoured at cooler sites at higher altitude and oak regeneration was more frequent at warmer sites, indicating a higher adaptation potential of oaks under future warming. Our results thus suggest that an extended shift in species composition is actually occurring in the pine forests in the Valais. The main driving factors are found to be climatic variability, particularly drought, and variability in stand structure and topography. Thus, pine forests at low elevations are developing into oak forests with unknown consequences for these ecosystems and their goods and services.     

Bird population in the pine and birch forests of Kungurskii Raion (Perm’; Krai) under anthropogenic load of various levels

In 1995—2006, the birds inhabiting the pine and birch forests as well as pine plantations were studied in and near the town of Kungur (Perm’ krai). The greatest faunal and biocenotic similarity of the bird populations was revealed in the pine forests in the town and raion, the lowest, in the birch forests. It was found that anthropogenic impact is the highest in the town birch forests, where it is seen in all studied parameters of ornitocenosis—density of bird population, species diversity and domination.     

Effect of temperate forest tree species on soil dehydrogenase and urease activities in relation to other properties of soil derived from loess and glaciofluvial sand

We investigated the effects of several tree species on dehydrogenase and urease activities in soils derived from two different parent materials (glaciofluvial sand and loess) in forested areas in southern Poland. We hypothesized that coniferous forests (pine, spruce) alter the soil cation exchange capacity (CEC) and decrease soil pH and, therefore, might decrease soil enzyme activities compared with broadleaf species growing on similar soils. Eight paired plots (12 × 12 m) were established on glaciofluvial sand in pine (Pinus sylvestris) + oak (Quercus robur) and spruce (Picea abies) + pine stands, as well as on loess-derived soils: beech (Fagus sylvatica) + pine and hornbeam (Carpinus betulus) + pine stands. Each plot was a 4 × 4 m grid with 16 sampling points. In soil samples pH, soil texture, and organic carbon, nitrogen, base cation contents, dehydrogenase and urease activities were determined. On both parent materials, the soil pH was lower under coniferous species than under broadleaf species. The acidifying effect of tree species on sandy soil was in the order of spruce = pine > oak, while that on loess was pine > beech > hornbeam. Hornbeam and oak increased the soil pH and stimulated enzyme activity in the soil. The content of fine fraction enhanced potential enzyme activities in soils, thus the loess soils had greater dehydrogenase and urease activity. The results suggest that pine stores more soil organic C in association with silt increasing the pool of stabilized soil organic C.     

In situ gross nitrogen transformations differ between temperate deciduous and coniferous forest soils

Despite long-term enhanced nitrogen (N) inputs, forests can retain considerable amounts of N. While rates of N inputs via throughfall and N leaching are increased in coniferous stands relative to deciduous stands at comparable sites, N leaching below coniferous stands is disproportionally enhanced relative to the N input. A better understanding of factors affecting N retention is needed to assess the impact of changing N deposition on N cycling and N loss of forests. Therefore, gross N transformation pathways were quantified in undisturbed well-drained sandy soils of adjacent equal-aged deciduous (pedunculate oak (Quercus robur L.)) and coniferous (Scots pine (Pinus sylvestris L.)) planted forest stands located in a region with high N deposition (north Belgium). In situ inorganic ¹⁵N labelling of the mineral topsoil (0–10?cm) combined with numerical data analysis demonstrated that (i) all gross N transformations differed significantly (p?<?0.05) between the two forest soils, (ii) gross N mineralization in the pine soil was less than half the rate in the oak soil, (iii) meaningful N immobilization was only observed for ammonium, (iv) nitrate production via oxidation of organic N occurred three times faster in the pine soil while ammonium oxidation was similar in both soils, and (v) dissimilatory nitrate reduction to ammonium was detected in both soils but was higher in the oak soil. We conclude that the higher gross nitrification (including oxidation of organic N) in the pine soil compared to the oak soil, combined with negligible nitrate immobilization, is in line with the observed higher nitrate leaching under the pine forest.     

Amino acid distribution in some fungal melanins and of soil humic acids from Brazil

Summary Humic acids from four Brazilian topsoils of different origins and four soil fungal melanins, synthesized under two cultural conditions, were subjected to 6N HCl hydrolysis and their amino acid distribution patterns qualitatively and quantitatively determined. Both soil and fungal polymers showed similar patterns with aspartic acid, glutamic acid, glycine and alanine as the dominant amino acids. Some variations noted were more quantitative than qualitative, the similarities were more pronounced than differences, indicating that the fungal melanins may play a significant role in the formation of soil humic acid polymers. The humic acids of Brazilian soils had amino acid distribution patterns similar to those reported for humic acids of other tropical and temperate soils.     

Influence of radiata pine seedlings on chemical properties of some New Zealand montane grassland soils

Interaction between soil acidity and vegetation phenolic concentration was investigated to identify mechanisms by which forests sustain productivity on extremely acidic, infertile soils. Contrasting soils on well-preserved marine terraces of the “Ecological Staircase’ near Mendocino, CA comprise an extreme edaphic gradient. Pygmy forests of dwarf (< 5m) Mendocino cypress (Cupressus pygmaea), Bolander pine (Pinus contorta var. bolanderi), and Bishop pine (Pinus muricata) are found on the oldest, most acidic soils, and along a gradient that includes three distinct levels of soil acidity, with pH(CaCl₂) ranging from 5.0 to 3.0 in the upper mineral soil and from 4.0 to 2.0 in the litter layer where fine roots are concentrated. Mature foliage was collected from five sites on this edaphic gradient. Aqueous methanol extracts of the samples were analyzed for concentrations of total phenols and condensed tannin by the Prussian blue and acidified vanillin assays, respectively. There were significant differences (p<0.05) in foliar condensed tannin and phenolic concentrations within each species and concentrations were inversely related to soil pH, approximately doubling along the gradient. Natural selection for soil-regulated variation in polyphenol concentration is interpreted in the context of plant-litter-soil interactions as an adaptation that permits these conifers to survive in extremely acidic soils. H Lambers Section editor     

The effects of ferulic acid on the mineral nutrition of grain sorghum

The combined effects of whole-tree harvesting (WTH) and soil leaching by both acid deposition and naturally-produced carbonic acid were evaluated in a mixed oak and a loblolly pine forest growing on similar soils in the Ridge and Valley province of eastern Tennessee. It was hypothesized that nutrient export via WTH would be greater in a mixed oak stand than in the loblolly pine stand because of greater nutrient concentrations in oak and hickory species than in pine. This hypothesis was true for N,P, and particularly Ca at the time of harvest, but not for K or Mg. When expressed on an annual basis, exports of N,P,K, and Mg were greater in the loblolly pine site and only Ca export was greater in the mixed oak site. It was also hypothesized that the large accumulation of Ca in the oak and hickory vegetation would cause lower exchangeable Ca²⁺ in soils, and, consequently, lower Ca²⁺ leaching in the mixed oak site than in the loblolly pine site. This hypothesis was supported by the data, which indicated 340–370% more exchangeable Ca and 100% more Ca²⁺ leaching in the loblolly pine site than in the mixed oak site. Research sponsored by the U.S. Environmental Protection Agency under Interagency Agreement No. 79-D-X0533 and Biofuels and Municipal Waste Technology Division, U.S. Department of Energy, under Contract No. De-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. Publication No. 2933, Environmental Sciences Division, ORNL.     

Microbial community utilization of recalcitrant and simple carbon compounds: impact of oak-woodland plant communities

Little is known about how the structure of microbial communities impacts carbon cycling or how soil microbial community composition mediates plant effects on C-decomposition processes. We examined the degradation of four ¹³C-labeled compounds (starch, xylose, vanillin, and pine litter), quantified rates of associated enzyme activities, and identified microbial groups utilizing the ¹³C-labeled substrates in soils under oaks and in adjacent open grasslands. By quantifying increases in non-¹³C-labeled carbon in microbial biomarkers, we were also able to identify functional groups responsible for the metabolism of indigenous soil organic matter. Although microbial community composition differed between oak and grassland soils, the microbial groups responsible for starch, xylose, and vanillin degradation, as defined by ¹³C-PLFA, did not differ significantly between oak and grassland soils. Microbial groups responsible for pine litter and SOM-C degradation did differ between the two soils. Enhanced degradation of SOM resulting from substrate addition (priming) was greater in grassland soils, particularly in response to pine litter addition; under these conditions, fungal and Gram + biomarkers showed more incorporation of SOM-C than did Gram – biomarkers. In contrast, the oak soil microbial community primarily incorporated C from the added substrates. More ¹³C (from both simple and recalcitrant sources) was incorporated into the Gram – biomarkers than Gram + biomarkers despite the fact that the Gram + group generally comprised a greater portion of the bacterial biomass than did markers for the Gram – group. These experiments begin to identify components of the soil microbial community responsible for decomposition of different types of C-substrates. The results demonstrate that the presence of distinctly different plant communities did not alter the microbial community profile responsible for decomposition of relatively labile C-substrates but did alter the profiles of microbial communities responsible for decomposition of the more recalcitrant substrates, pine litter and indigenous soil organic matter.     

Degradation and Preservation of Vascular Plant-derived Biomarkers in Grassland and Forest Soils from Western Canada

The total solvent extracts (TSE) of mineral and organic horizons of selected soils and overlying vegetation were analyzed using gas chromatography–mass spectrometry (GC–MS) to determine the composition of solvent-extractable (‘free’) lipids in soils and to study the degradation and possible preservation of vascular plant-derived molecular markers (biomarkers) in soils. Major compound classes in the TSE of soils and vegetation included a homologous series of aliphatic lipids (alkanoic acids, alkanols, alkanes), steroids, and terpenoids. Characteristic patterns of aliphatic and cyclic biomarkers derived from the overlying, native vegetation were recognized in the associated soil samples indicating the preservation of lipids from the external waxes of vascular plants in the soil organic matter (SOM). The observed biomarker patterns in the grassland soils (Brown Chernozems) were similar to the compounds identified in their major source vegetation, Western Wheatgrass. A similar composition of biomarkers was observed in Aspen leaves and the soil horizons of the forest–grassland transition soil (Dark Gray Chernozem). The Lodgepole Pine needles yielded a characteristic pattern of diterpenoids that was also detected in leaf litter and the O horizon of the associated forest soil (Brunisol). The results demonstrate that solvent extractable biomarkers derived from vascular plants maintain their characteristic pattern of aliphatic and cyclic lipids despite ongoing degradation processes and are thus valuable molecular markers for the determination of the sources of SOM. Furthermore, the abundance of aliphatic wax lipids in plant material and soils decreased at higher rates than the steroids and terpenoids indicating the preferential degradation of aliphatic over cyclic biomarkers. Most of the plant-derived steroids and terpenoids identified in the soils were unaltered, preserved biomolecules as observed in the source vegetation, but minor amounts of their degradation products were also present. Oxidation products of plant sterols are reported here for the first time in soils. The detected alteration products of steroids and diterpenoids are consistent with the oxidative degradation of free cyclic biomarkers in decomposing plant material and soils.     

Macrofungal diversity and ecology in four Irish forest types

The macrofungal communities of Irish native tree species (ash and oak) and exotic tree species (Scots pine and Sitka spruce) forests were examined through the collection of sporocarps over 3 yr. Sampling of 27 plots revealed 186 species of macrofungi, including 10 species new to Ireland. The species richness of non-native Sitka spruce and Scots pine forests was similar to that of native oak forests. However, specific communities of macrofungi existed in each of the forest types as confirmed by non-metric multidimensional scaling and multi-response permutation procedure. Indicator species analysis was used to identify macrofungi which are indicative of the four forest types. The oak community lacked certain species/genera known to be distinctive of oak woods in Britain, possibly due to low inoculum availability as a result of historic removal of Ireland’s oak forests. Our results indicate that, while being similar to native forests in species richness, non-native forests of Sitka spruce and Scots pine in Ireland harbour many fungal species which are not typical of native forests, particularly members of the genus Cortinarius.     

Natural oak forest vs. ancient pine plantations: lizard microhabitat use may explain the effects of ancient reforestations on distribution and conservation of Iberian lizards

Natural vegetation in Europe appears nowadays deeply modified by human activities. In the Guadarrama Mountains (Central Spain), ancient reforestations with Scots pines, Pinus sylvestris, replaced original deciduous pyrenean oak, Quercus pyrenaica, forests (since the Roman period). However, the effect of reforestations on fauna remains little known, especially in reptiles. We described patterns of microhabitat selection in several species of Lacertid lizards, and analyzed whether the modification of the original vegetation affected distribution and population densities of lizards. The species of lacertid lizards found in oak forests (Psammodromus algirus, Lacerta lepida and Podarcis hispanica) were different to those of in pine plantations (Podarcis muralis and Podarcis hispanica). Lizards did not use habitat at random and this could explain differences in species found in both forests, which differed in some microhabitat structure characteristics. Most lizards selected microhabitats with rocky outcrops, with low cover of trees, and close to refuges. These microhabitat preferences also explained abundance of lizards in transects. From the perspective of conservation and management of lizards, pine plantations seem not to contribute too much to the diversity of lizard species because species typical from oak forests were lost. This study has implications for pine reforestation management, because allowing the recolonization by understory␣oaks, and leaving some open areas, without trees but with dense shrubs and rocks inside reforestations would contributed to maintain lizard populations.     

Mediterranean pine and oak distribution in southern Spain: Is there a mismatch between regeneration and adult distribution?

Questions: What is the current distribution of pine and oak species along environmental gradients in southern Spain? Do pine and oak regeneration niches differ from the environmental niches of adults? Is oak species regeneration favoured under the canopy of pine forests? Location: Forest areas of Andalusia (～87 600 km², southern Spain). Methods: We compiled extensive forest inventory data to explore differences in abundance (basal area, m² ha^?1) patterns of adults (dbh >7.4 cm) and regeneration (dbh ≤7.4 cm) of five pine and five oak species. Canonical correspondence analysis (CCA) and generalized linear models were applied to explore species–environment relationships along climatic, edaphic, topographic and fire‐frequency gradients. Results: Both pines and oaks segregated along complex environmental gradients, with pines generally dominating in more severe (colder and drier) environments, while oaks dominated in milder, wetter winter areas. In 40‐55% of mature pine stands there was a lack of regeneration in the understorey, while in two oak species (Q. suber and Q. canariensis) 70% of stands did not show regeneration. Pine recruits were found at a higher frequency and abundance under the canopy of their congeners, whereas some oaks (Q. ilex) had greater regeneration under mixed pine–oak canopies. Conclusions: Climatic limitations and soil properties partly explained the regional distribution of pines and oaks. We found evidence for an upward shift of Q. ilex recruits towards areas with colder conditions in pine forests, which could be explained by a possible facilitative effect of the pine canopy on seedling establishment.     

Natural acidophilous Quercus and Pinus forests in the northern Vosges,France, from a geographical perspective

Abstract. A phytosociological study of forests on Vosges sandstone in the basins of Pays de Bitche (Bitcherland) resulted in the identification of three plant communities: Luzulo-Quercetum, Leucobryo-Pinetum, and Vaccinio uliginosi-Pinetum. The Luzulo-Quercetum is an association with a typically sub-continental distribution; the two communities with Pinus sylvestris are clearly more continental. The Luzulo-Quercetum oak forest represents a climatic climax and the pine forests are considered edaphic climaxes linked to very dry soils (Leucobryo-Pinetum) or peaty soils (Vaccinio uliginosi-Pinetum). These three associations determine a forest sequence that is typical of sub-continental areas in which Quercus petraea dominates in the climatic climax. In more continental areas, it is gradually replaced by Pinus sylvestris. Thus, the forest sequence in Pays de Bitche represents a remarkable subcontinental link in the transition from Atlantic oak forests to continental pine forests.     

Development of secondary pine forests after pine wilt disease in western Japan

Abstract. The development of secondary Pinus densiflora (Japanese red pine) forests after pine wilt disease was studied through phytosociological analysis, estimation of forest structure before disease and size-structure, tree ring and stem analyses. Following the end of the disease, the growth of previously suppressed small oak trees was accelerated. This is quite different from the development of forests following fire, which starts with the establishment of pine seedlings. Pine wilt disease shifted the dominance of secondary forests from Pinus densiflora to Quercus serrata oak forest. In pine forests, disturbance by fire is important for forest maintenance. In contrast, disturbance by pine wilt disease leads to an acceleration of succession from pine forest to oak forest.     

Soil amino-acid availability across a temperate-forest fertility gradient

Despite increasing recognition that free amino acids can be an important source of N for plant uptake, we have a poor understanding of environmental variation in the availability of amino-acid N in soils outside of arctic, alpine and boreal regions. I investigated patterns of amino-acid availability along a temperate forest fertility gradient ranging from low mineral N availability, oak-dominated forests to high mineral N availability, maple-basswood forests (5 sites). I measured standing pools of free amino acids, soluble peptides, ammonium and nitrate, rates of amino acid production (native proteolysis activity) and rates of consumption of a ¹⁵N-labeled leucine tracer. Standing pools of amino acid N decreased consistently along the fertility gradient from the low fertility black oak/white oak system to the high fertility sugar maple/basswood system, with a 25-fold difference in pool sizes between the poorest and richest sites. Standing pools of soluble peptides varied little among sites, instead, the relationship between free amino acids and peptides changed markedly across the gradient. At low fertility sites free amino acids were positively correlated with soluble peptides, whereas free amino acid pools were universally low at high fertility sites, regardless of peptide pools. Assays for native proteolysis activity indicated that amino acid production did not vary significantly among sites. Recovery of leucine tracer in inorganic (NH₄ ⁺ and NO₃ ⁻) pools and in residual soil organic matter both increased with increasing soil fertility; however, total consumption of the added amino-acid tracer did not vary among sites. Results from this study demonstrate that free amino acids can make an important contribution to potentially plant-available N pools in temperate forest soils, particularly at low fertility sites.