Northern Coniferous Forests Research Articles

Decay and nutrient dynamics of coarse woody debris in northern coniferous forests: a synthesis

We synthesize current information on input, accumulation, and decay of coarse woody debris (CWD) compared with other aboveground litter to assess the role of CWD in the nutrient cycles of northern coniferous forests. CWD contributes between 3% and 73% of aboveground litter input, but <20% of N, P, K, and Ca. Although CWD accounts for up to 54% of accumulated organic matter (including forest floor and soil), it contributes <5% of the N, <10% of the P, and <25% of the K, Ca, and Mg. Decay rates of CWD in northern forests range from 0.0025 to 0.071 year-1. Nitrogen or P concentrations in CWD increase during decay, depending on the initial N/P ratio, which eventually converges at about 20. CWD is initially a sink for N and (or) P, whichever is least available, but becomes a source later in decay. CWD contributes <5% of the N released annually. There is little evidence that CWD retains significant amounts of excess N following disturbance. We conclude that CWD is of minor importance in the nutrient cycles of northern coniferous forests, and that guidelines for CWD retention should be based on other perceived benefits of CWD.

Red squirrels and predation risk to bird nests in northern forests

Red squirrels (Tamiasciurus hudsonicus) are important predators on bird nests in northern conifer forests, and previous work has shown that nest density of understory birds is low in these forests compared with deciduous forest. Here, we examine the relationships between the risk of squirrel predation and nest distribution at a smaller, within-habitat scale using both experimental and comparative studies. Female squirrels depredated experimental nests more quickly than males in interior forests near the Yukon – British Columbia border, but after 2 weeks, there was no difference in the percentage of nests depredated by males and females. The density of squirrels and the risk of experimental nest predation increased but the index of natural nest density did not decrease with the density of cone-bearing Sitka spruce (Picea sitchensis) trees in coastal conifer forests of Southeast Alaska. Experimental nests in successional deciduous stands had high risks of predation, in part because squirrels occupied small stands of colonizing spruces in the deciduous matrix and foraged widely in the deciduous stands. In the experimental study site, natural nests occurred at similar densities both next to and away from squirrel-occupied spruce stands, but in other areas, there was a "halo" of low nest density in deciduous vegetation next to spruce stands. Overall, there was little evidence that, within habitats, birds chose nest sites that minimized the risk of squirrel predation.

Responses of decomposer community to root-isolation and addition of slash

We studied the causal relationships between forest harvesting and the soil decomposer community focusing on suppression of energy inputs from trees to the soil through root–mycorrhizal network and increased energy input to the soil in the form of slash left on site. We hypothesised that both of these factors would affect the decomposer community, since the soil food web has been regarded as a system in which the amount of resources controls the numbers of consumers. To study the importance of these factors without changes in microclimate, like in sunshine and shade, taking place in clear-felled areas, the experiment was performed in a mature spruce ( Picea abies (L.) Karst.) forest. The experiment with factorial design included two factors, isolation of the tree roots in the study plots from the surrounding soil and addition of slash. The isolation increased soil NH 4 content and promoted growth of herbs. It had no effect on the total microbial or bacterial biomass, but the amount of soil fungi decreased by 40% and community structure of bacteria changed in the isolated plots. At the level of microbivores, fungivorous microarthropods (collembolans and oribatid mites) decreased in their numbers while bacterivorous nematodes slightly increased. In addition, the isolation increased the numbers of enchytraeids with a 2 year delay. No effects on decomposers by slash addition could be detected. The responses of decomposers to the isolation were similar to those observed earlier in clear-felled areas. It was concluded that, in short-term, elimination of root–mycorrhizal connections is one of most important factors affecting the soil decomposer community after harvesting of northern coniferous forest. The effect of slash is, to a large extent, due to its effects on micro-climate and soil moisture.

The importance of leaching from litter collected in litterfall traps.

Litterfall (LF) is usually collected by means of open traps. However, this litter will be subject to leaching by the throughfall which passes through the accumulated litter in the traps. The nutrients lost during this leaching are not taken into account in the calculation of LF nutrient fluxes. We report the results from a 2-month (August-September) study carried out in 8 northern coniferous forest stands to assess the possible importance of leaching from litter in LF traps. Compared to throughfall (TF), the litterfall leachate (LFLgross), which includes a throughfall component, had significantly (p < 0.05) higher concentrations and fluxes of Ca, Mg, Na and S. The average net LFL (i.e., LFLnet = LFLgross - TF) fluxes were 21 (Ca), 7 (Mg), 57 (K), 10 (Na), 10 (N), and 19 (S) mg m-2 mo-1. LFLnet accounted for 42%, 37% and 50% of the LFLgross flux, and for 91%, 51% and 49% of the total litterfall flux (i.e., LF + LFLnet) of Na, S and K, respectively. For Ca, Mg and N, the LFLnet flux accounted for 64%, 58% and 29% of the LFLgross flux, and for < 14% of the total litterfall flux. Compared to TF, LF was the dominant return pathway for Ca, Mg and N to the forest floor regardless of whether LFLnet was included or not. However, for K and S, taking LFLnet into account determined whether TF or LF was the dominant pathway. TF remained the dominant pathway for Na even when LFLnet was included.

Spatial congruence between ecoregions and littoral macroinvertebrate assemblages

The usefulness of ecoregions for discriminating between littoral macroinvertebrate assemblages of 363 Swedish lakes was examined. A relatively good correspondence was found between ecoregion delineations and macroinvertebrate assemblages of the lake littoral zone. Variables describing macroinvertebrate assemblages (abundance, taxon richness, diversity, and Sørensen similarity) had significantly different values in the 6 ecoregions, but the most marked differences occurred between the middle and southern boreal regions, coinciding with the approximate location of the ecotone delineating the northern coniferous (taiga) and southern deciduous forests. Macroinvertebrate assemblages of lakes in the south were generally more diverse, having more taxa, whereas lakes in the north in general and in the arctic–alpine complex in particular were characterized by low richness and the presence of 2 plecopterans, namely Diura nanseni (Kempny) and Capnia atra Morton. Twenty-five variables made significant contributions to explaining the variance among species assemblages. In the constrained ordination of taxa and environmental factors by canonical correspondence analysis, variables indicative of geographic position (latitude and longitude), ecosystem type (water color and lake surface area), and habitat type (pebble substratum) were among the first 5 variables selected. Discriminant analysis of 25 environmental variables and 6 UPGMA (flexible β unweighted pair-group method using arithmetic averages) groups classified 64% of the sites to the correct group.

Response of needle sulphur and nitrogen concentrations of Scots pine versus Norway spruce to SO 2 and NO 2

The results of two field studies and an open-top chamber fumigation experiment showed that the response of mature Scots pine to SO 2 and NO 2 differed from that of mature Norway spruce. Moreover, the response of pine seedlings to SO 2 and NO 2 differed from that of mature trees. The greater increase in the needle total S concentrations of pine suggested more abundant stomatal uptake of SO 2 compared to spruce. Both pine seedlings and mature trees also seemed to absorb more N from atmospheric deposition. Mature pine was able to assimilate SO 4 2− derived from SO 2 into organic S more effectively than mature spruce at the high S and N deposition sites, whereas both pine and spruce seedlings accumulated SO 4-S under NO 2+SO 2 exposure. Spruce, in turn, accumulated SO 4-S even when well supplied with N. Net assimilation of SO 4 2− in conifer seedlings was enhanced markedly by elevated temperature. To protect the northern coniferous forests against the harmful effects of S and N deposition, it is recommended that the critical level for SO 2 as a growing season mean be set at 5–10 μg m −3 and NO 2 at 10–15 μg m −3, depending on the ‘effective temperature sum’ and/or whether SO 2 and NO 2 occur alone or in combination.

A review and synthesis of monoterpene speciation from forests in the United States

The monoterpene composition (emission and tissue internal concentration) of major forest tree species in the United States is discussed. Of the 14 most commonly occurring compounds ( α-pinene, β-pinene, Δ 3-carene, d-limonene, camphene, myrcene, α-terpinene, β-phellandrene, sabinene, ρ-cymene, ocimene, α-thujene, terpinolene, and γ-terpinene), the first six are usually found to be most abundant. Expected regional variability based on the monoterpene composition fingerprints and corresponding tree species distribution and abundance is examined. In the southeast, α-pinene and β-pinene seem to dominate monoterpene emissions, while in the northern forests emissions are distributed more evenly among the six major compounds. In some parts of western forests, β-pinene and Δ 3-carene can be more abundant than α-pinene. Among the other eight compounds, β-phellandrene and sabinene occasionally are significant percentages of expected local monoterpene emissions. Ocimene and ρ-cymene are estimated to be more common in regions dominated by deciduous broadleaf forests, although total emission rates are generally lower for these forests relative to those dominated by conifers. These percentages are compared with monoterpene composition measured in ambient air at various sites. Estimated monoterpene emission composition based on local forest species composition agrees fairly well with ambient measurements for the six major compounds. The past assumption that α-pinene composes approximately 50% of total monoterpene emissions appears reasonable for many areas, except for possibly the northern coniferous forests and some areas in the west dominated by true firs, spruce, and western pines (lodgepole and ponderosa pines). The oxygenated monoterpenes such as camphor, bornyl acetate, and cineole often compose high percentages of the monoterpenes within plant tissues, but are much less abundant in emission samples. Even after adjusting for lower vapor pressures of these compounds, emission rates relative to the hydrocarbon monoterpenes are often lower than would be expected from their internal concentrations. More study is warranted on monoterpene emission rates and composition, especially from the spruces, true firs, hemlocks, cedars, and some deciduous species such as the maples. Non-invasive canopy level and whole ecosystem flux studies are also needed to establish uncertainty estimates for monoterpene emission models.

Managing forest harvesting to maintain old growth in boreal and sub-boreal forests

Old-growth stands can be rare in northern coniferous forests, and hence are worthy of protection and special management. We describe some quantitative guidelines for recognizing old-growth stands and options for maintaining a long-term supply of old-growth values in landscapes managed for timber production. In the Sub-Boreal Spruce forests of central British Columbia, attributes most indicative of old-growth status include stand age, the density of large (&gt; 1.0 m3) snags and downed logs, stand basal area and volume. It is suggested that partial cutting could occur in some old-growth stands, while still maintaining their structural and functional attributes, if large logs, snags and trees are retained at the threshold densities necessary to recognise old-growth status. At the landscape level, the use of extended timber crop rotations is advocated. Planning for a tapered forest age class distribution (with decreasing areas of forest allowed to persist to successively older ages) is suggested as a means of sustainably generating true old-growth, and as an alternative to the use of partial cutting and patch retention. Arithmetic formulas are developed which provide guidelines for the proportion of the forest land base to be kept in each successive age class. This model for regulating human disturbance in commercial forests holds promise as a mechanism for allowing continued timber harvest and even-aged stand management while retaining a near-natural proportion of old-growth forest in northern landscapes. Key words: disturbance regime, even-aged management, extended rotations, forest age class structure, forest management, old-growth attributes, rotation length, silvicultural systems, sub-boreal spruce zone, timber supply planning.

Silvicultural Use of Herbicide in Sub-Boreal Spruce Forest: Implications for Small Mammal Population Dynamics

Vegetation management in northern coniferous forest ecosystems may have implications for small mammal communities. This study was designed to test the hypothesis that herbicide-induced habitat alteration would reduce small mammal populations in early-successional stages of sub-boreal spruce forest. A secondary objective was to determine the long-term influence of herbicide treatment on reproduction, survival, and growth attributes of deer mouse (Peromyscus maniculatus) and southern red-backed vole (Clethrionomys gapperi) populations. Small mammal populations were intensively sampled in 4 pairs of control and treatment sites dominated by early-successional vegetation (5-10 yr after clearcut harvesting) near Prince George, British Columbia, Canada. Sampling was conducted during 1987 (pretreatment year) 1988-89 (first and second posttreatment years), and in 1991-92 (fourth and fifth posttreatment years). Higher mean numbers of red-backed voles (P = 0.03) and shrews (Sorex spp.; P = 0.001) were present on control than treatment sites during 1988-92. Mean abundance of meadow voles (Microtus pennsylvanicus; P = 0.69) and deer mice (P = 0.20) were similar on control and treatment sites throughout the study. Short-tailed weasels (Mustela erminea) and long-tailed weasels (Mustela frenata) were commonly captured on both control and treatment sites. There were no consistent differences between control and treatment populations in body mass, total biomass, or proportion of adult male and female red-backed voles and deer mice in breeding condition. However, there was a higher mean number of successful pregnancies in control than treatment populations of red-backed voles (P = 0.02) but not deer mice (P = 0.18) during posttreatment years. Mean Jolly-Seber estimates of survival of red-hacked voles (P = 0.01) but not deer mice (P = 0.70) were higher in treatment than control populations. The magnitude of observed demographic effects from herbicide treatment were well within the mean values of natural fluctuations of these variables. Herbicide treatment of areas dominated by early-successional vegetation in northern coniferous forests should be staggered in time and space to allow recovery (2-3 yr) of vegetation and small mammal species sucl as red-backed voles and shrews.

Influence of White Pine on Structure and Yields of Mixed Northern Conifer Forests

The presence of white pine (Pinus strobusL.). influenced the structure and yields of mixed-species, multi-cohort, northern conifer stands in Maine. In each of the five stands studied, mean plot volumes were consistently higher where white pine grew with more shade tolerant conifers, than in plots without the additional pine component. However, considerable variability in stand structures among plots resulted in no significant differences in volumes within stands. When plot volumes from the five stands were combined, the larger sample size resulted in the mean volume of pine plots being significantly higher (P < 0.02) than those that had none (355.30 ± 25.24 m3/ha vs. 275.06 ±16.98 m-Vha). Generally, pine's presence enhanced plot volumes but had a negative effect on spruce and hemlock volumes. Whether or not pine was present, plot volumes were greatly affected by variability in age structures. Plots with a representation of two or three cohorts had higher volumes than plots with a single cohort.

Seasonal use by birds of stream‐side riparian habitat in coniferous forest of northcentral British Columbia

To determine use of riparian habitats by birds in the northern coniferous forest of British Columbia, we censused birds and vegetation along 500 m transects placed parallel and perpendicular to three second‐order streams. Censuses were conducted during spring, summer, autumn, and winter to investigate how use of riparian habitat changed seasonally. Stream‐side riparian zones were characterized by a dense understorey of deciduous vegetation not found in the upslope forest. Nine bird species preferred the riparian understorey for breeding, six preferred it only during migration. Neotropical migrants (16 of 46 species) were more closely associated with stream‐sides than year‐round residents (11 species). Some breeding birds (five species) were significantly negatively associated with riparian habitats. The density of riparian birds declined with distance upstream but did not decline up to 250 m away from the stream. The more extensive riparian areas downstream supported a greater density of birds in all seasons compared to upstream areas, but more species only in spring and autumn. Species that nested in non‐riparian areas in summer used riparian habitat in autumn, making riparian corridors in the northern coniferous forest important during migration. Maintaining both riparian and upslope habitats is necessary to preserve species diversity al the landscape level.

Effects of competition mode on spatial pattern dynamics in plant communities

The effects of the mode of competition between individual plants (symmetric versus asymmetric) and the gap formation caused by natural disturbances on the dynamics of spatial configuration pattern of individual size were investigated theoretically based on an individual growth model incorporating competitive effects of neighbouring individuals. The degree of spatial heterogeneity in local size distribution was represented by the CV (coefficient of variation) of averages of local size distributions (CV av), the average of CVs of local size distributions (AV cv) and the CV of CVs of local size distributions (CV cv). Without gap formation, CV av, AV cv and CV cv were larger under asymmetric competition than under symmetric one, suggesting a fine-scale mosaic spatial pattern in asymmetrically competing populations. With gap formation, these statistics under symmetric competition approached those values under asymmetric competition. The spatial configuration pattern of individual size also showed the same trend in terms of the semivariogram. The patchiness index was almost the same in both gap and non-gap cases irrespective of the mode of competition. The semivariogram and patchiness index showed the presence of more uniform and larger patches under symmetric competition than asymmetric competition. Gap formation therefore increased spatial heterogeneity in local size distribution especially under symmetric competition, but there was still a difference in spatial heterogeneity between the two modes of competition even in the gap formation case. The effects of gap formation on spatial pattern dynamics were larger under symmetric competition than under asymmetric competition; under asymmetric competition, the spatial pattern dynamics were similar in both gap and non-gap cases. Therefore, against spatial disturbances (i.e. gap formation), symmetric competition brings about a more variable system than asymmetric competition. These theoretical results can explain spatial pattern dynamics of natural forests (northern coniferous and temperate hardwood forests). In conclusion, both the disturbance regime (gap formation process) and the mode of competition between individuals should be investigated to study the spatial pattern dynamics and species diversity of plant communities. The implications of the mode of between-individual competition for conservation biology are discussed. It is suggested that symmetrically competing plant communities (e.g. northern coniferous forests) should be preserved in larger areas than asymmetrically competing ones (e.g. temperate hardwood forests) if the plant communities are subject to frequent natural disturbances.

Winter Foraging Ecology of Moose on Glyphosate-Treated Clearcuts in Maine

The herbicide glyphosate is widely used in northern coniferous forests of the United States and Canada to promote conifer dominance on clearcut sites by suppressing regeneration of deciduous species. We determined effects of glyphosate treatment of regenerating clearcuts on (1) browse availability (total biomass, by species, and proportion with high digestible energy [DE] content), (2) browse use, and (3) diet quality of moose (Alces alces) in winter in Maine during 2 periods: 1-2 and 7-11 years posttreatment. We measured browse availability and use and collected browse samples for nutritional analyses on 12 clearcuts in January-March 1991 before aerial treatment with glyphosate of 6 of these clearcuts in August 1991. We conducted posttreatment sampling of treated and untreated clearcuts during January-March 1992 and 1993. We also sampled 14 clearcuts that had been treated with glyphosate 7-11 years earlier and 5 untreated clearcuts of similar age in January-March 1992 or 1993. Available biomass (kg/ha) of deciduous browse decreased (P = 0.001) 70% on treated clearcuts relative to untreated clearcuts from pretreatment to year 2, but was not affected (P = 0.29) at 7-11 years posttreatment. Available browse from red maple (Acer rubrum) and paper birch (Betula papyrifera) appeared to decrease less than pin cherry (Prunus pensylvanica) in years 1-2 suggesting that species composition on sites may influence the magnitude of effects on total browse availability. The proportion of deciduous browse biomass with a relatively high DE content (1.8 kcal/g) was not affected (P = 0.37) by treatment at 1-2 years, but was greater (P = 0.047) on treated than untreated clearcuts at 7-11 years posttreatment. Biomass and percent of available deciduous browse eaten by moose were not affected (P > 0.1) by glyphosate in years 1-2, but were 4-5 times greater (P 0.1) by treatment in either time period. Initial reductions in browse availability may decrease the suitability of clearcuts for foraging by moose, but this effect would decrease over the next 5-9 years because browse availability decreases naturally on untreated sites. We concluded that glyphosate did not have important effects on diet quality. Heavy browsing in older treated clearcuts suggests that moose may be attracted to these sites, but this behavior was not directly related to browse availability or nutrition. We discuss management options for minimizing effects of glyphosate treatment on moose habitat.

Use of fluorescence polarization to probe the structure and aluminum complexation of three molecular weight fractions of a soil fulvic acid

A soil fulvic acid isolated from a northern coniferous forest (NCFA) was fractionated by ultrafiltration into three different molecular sizes ranging from less than 500 to 10 000 daltons. The conformation changes of this soil fulvic acid, NCFA, and its molecular weight (MW) fractions were studied using fluorescence polarization as a function of pH and concentration of added ionic inorganic aluminum. Polarization values versus aluminum concentration increased for the lowest molecular weight fraction, whereas they decreased for the higher molecular weight fractions. The change in the polarization values suggests that the lower molecular weight fraction of the fulvic acid molecule does not change conformation when complexed to aluminum, whereas the higher molecular weight fractions changes conformation when complexed to aluminum. The fluorescence intensity versus aluminum concentration increased for all the fractions indicating that the rigidity of the fulvic acid molecule increases as aluminum binds to it. Stability constants were calculated for the aluminum-fulvate complexes using anisotropy values calculated from the polarization data. The log of the stability constants for the aluminum-fulvate complex varied between 4.9 to 5.2 over a pH range of 3.0 to 4.0. The log of the stability constants for the aluminum-fulvate MW fractions varied between 4.2 to 5.1 at a constant pH of 3.5.

Structures for caribou management and their status in the circumpolar north

Large herds of caribou (Rangifer tarandus) in Canada, Alaska, and Russia that winter in northern coniferous forests and summer in tundra of the Arctic have provided a sustainable source of meat and other products for indigenous peoples for thousands of years. Several different administrative structures for management of large caribou herds have emerged throughout the circumpolar North. In Russia under the previous Soviet government, the herd of the Taimyr Region, numbering around 500 000 caribou, was managed under a harvest quota system for both subsistence use by indigenous people and commercial sale of meat and skins. In North America, as indigenous peoples have gained increasing political empowerment, systems for caribou management have been undergoing change. Establishment of the Beverly and Qamanirjuaq Caribou Management Board in Canada, with majority representation from users of the resource, provides a model and a test of the effectiveness of a comanagement system. The Western Arctic Herd in northwestern Alaska, numbering close to 500 000 caribou, has been managed under the traditional American system of game management, with user advisory groups, but with management decisions resting with a statewide Board of Game, whose major representation is from sport-hunting interests. The Porcupine Caribou Herd, which is shared by the United States and Canada, is the focus of an international agreement, in principle designed to assure its continued productivity and well-being. The diversity of systems for caribou management in the circumpolar North provides an opportunity for comparing their effectiveness.

Coastal Massachusetts pond development: edaphic, climatic, and sea level impacts since deglaciation

Kettle ponds in the Cape Cod National Seashore in southeastern Massachusetts differ in their evolution due to depth of the original ice block, the clay content of outwash in their drainage basins, and their siting in relation to geomorphic changes caused by sea-level rise, barrier beach formation, and saltmarsh development. Stratigraphic records of microfossil, carbon isotope, and sediment changes also document late-glacial and Holocene climatic changes. The ponds are separated into 3 groups, each of which follow different development scenarios. Group I ponds date from the late-glacial. They formed in clay-rich outwash, have perched aquifers and continuous lake sediment deposition. The earliest pollen and macrofossil assemblages in Group I pond sediments suggest tundra and spruce-willow parklands before 12 000 yr B.P., boreal forest between 12 000 and 10 500 yr B.P., bog/heath initiation and expansion during the Younger Dryas between 11 000 and 10 000 yr B.P., northern conifer forest between 10 500 and 9500 yr B.P., and establishment of the Cape oak and pitch pine barrens vegetation after 9500 yr B.P. Sedimentation rate changes suggest lowered freshwater levels between 9000 and 5000 yr B.P. caused by decreased precipitation on the Atlantic Coastal Plain. Lake sediment deposition began in the middle Holocene in Group II ponds which formed in clay-poor outwash. These ponds date from about 6000-5000 yr B.P. In these ponds sediment deposition began as sea level rose and the freshwater lens intersected the dry basins. The basal radiocarbon dates of these ponds and stable carbon isotope analyses of the pond sediments suggest a sea-level curve for Cape Cod Bay. Holocene topographic changes in upland and the landscape surrounding the ponds is reconstructed for this coastal area. Group III ponds in the late Holocene landscape of the Provincelands dunes originated as interdunal bogs about 1000 yr B.P. and became ponds more recently as water-levels increased. Peat formation in the Provincelands reflects climatic changes evident on both sides of the Atlantic region.

Fire cycle and fire adaptation of main tree species in Daxing’anling forest region, China

Based on the fire statistics, the Daxing’anling forest area were classified into three fire cycle regions: northern coniferous virgin forest region with a fire cycle ofl 10–120 years, middle conifer-broad-leaved mixed forest region with a fire cycle of 30–40 years, and southern broad-leaved secondary forest region with a fire cycle of 15–20. The percentage of conifers and broad-leaved trees, forest age and natural mature period of main tree species in different fire cycle regions were discussed in concern with fire occurrence. The characteristics of fire adaptation and fire resistance of main tree species, such as sexual and asexual reproduction, were discussed and evaluation of the synthetical fire adaptation was made.

Biogeochemical controls on aluminum chemistry in the O horizon of a red spruce (Picea rubens Sarg.) stand in central Maine, USA

This study examined the biotic and abiotic processes controlling solution chemistry and cycling of aluminum (Al) in the organic horizons of a northern coniferous forest ecosystem. A mass balance budget indicated that aboveground inputs of Al to the O horizon averaged 0.9 kg ha−1 1 yr−1, with major inputs accounted for by litterfall (69%), followed by precipitation (21%), and net canopy throughfall plus stemflow (10%). Estimated leaching losses of Al from the O horizon averaged 2.1 kg Al ha-1 yr1. We hypothesize that the difference between measured Al inputs and outputs can be accounted for by Al release from weathering of soil minerals admixed into the O horizon. Variations in O horizon solution Al chemistry were influenced by a number of factors, including pH, Al equilibria with different solid-phase organic exchange sites, and Al complexation with humic ligands in soil solution.

Similar Patterns of Change in Stemwood Calcium Concentration in Red Spruce and Siberian Fir

Changes in stemwood calcium concentration ((Ca)) for the last 120 years occurred in a common pattern for two sample collections of red spruce (n = 33 and 20) froin the northeastern United States and for one sample collection of Siberian fir (tz = 20) from southcentral Siberia, Russia. The (Caj was measured for wood formed during the periods 1871-90, 1891-1910, 1911-30, 1931-50, 1951-70 and 1971- 90. For each core, the relative increase or decrease in (Ca) for adjacent periods of wood formation was recorded. The relative frequency of positive change in (Caj for each period of wood formation was calculated for the three sample collections. Previous research indicated that under equilibrium condi- tions, (Ca) in stemwood tended to decrease in more recently formed wood, due to declining numbers of Ca binding sites. Consequently, we expected a low frequency of positive changes in (Ca) in successively formed wood. Consistent with expectation, the relative frequency of positive change from the preceding period to the periods 1891-1910, 191 1-30, 1931- 50, and 1971-90 were low. Contrary to expectation, the frequency of positive increases in (Ca) more than dollbled in 1951-70 compared to 1931-50. The frequency of positive increases in the 1951-70 period relative to the preceding period was 48%, significantly greater than all other periods (P S 0.01). The frequencies of positive increases for all other periods were not significantly different from each other (over- all mean = 21 %, SD = 7). This anomaly in the frequency of positive change in (Ca) in wood formed in 1951-70 relative to wood formed in 1931-50 indicated a perturbation in the ion exchange chemistry of stemwood in two widely separated parts of the northern coniferous forest. This anomaly could be due to external or internal factors. Changes in sap chemistry that affected stem- wood chemistry could have been due to changes in the rooting zone. Such changes in rooting zone chemistry could result from the atmospheric deposition of ionic pollutants. Other external factors that could cause the observed anomaly include unusual climatic periods or environmental disturbances such as logging or fire. Internal factors that might produce an anomalously high frequency of positive change of (Caj in- clude heartwood formation, stemwood infection and a hyper- sensitive response of the tree against infection.

Apparent differences in binding site distributions and aluminum(III) complexation for three molecular weight fractions of a coniferous soil fulvic acid

A soil fulvic acid isolated from a northern coniferous forest (NCFA) was fractionated into three different molecular sizes ranging from less than 500 to 10 000 daltons by ultrafiltration and the fractions were studied by synchronous scan fluorescence spectroscopy (SSFS). The SSFS gives three distinct emission peaks (I, II and III) for these fractions of NCFA, which are attributed to different fluorophores. The lower-wavelength peaks (315 and 370 nm) are attributed to fluorophores that consist of a single aromatic ring with carboxyl and/or hydroxyl groups attached to it, whereas the longest-wavelength peak (470 nm) is associated with a fluorophore containing three or four condensed aromatic rings with substituted groups. The ratio of the intensity of peak III to II increases from the lower to higher molecular weight fraction which indicates a higher content of condensed aromatic rings in the high molecular weight fraction. This study also included aluminum(III) binding experiments with the different molecular weight fractions of NCFA. Results showed that the high molecular weight fraction has a stronger affinity for aluminum(III) than the low molecular weight fraction.