Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0-5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in -N accumulation during the incubation was accompanied by decreases in both exchangeable -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater -N levels in the forest soil.     

Conservation of beetles in boreal pine forests: the effects of forest age and naturalness on species assemblages

The effort of boreal forest conservation has emphasised the preservation of old-growth forests while the role of young successional stages in maintaining biodiversity has remained largely unstudied. We compared the richness of beetle species and composition of species assemblages between managed and seminatural forests in five stages of forest succession. The sites were in boreal sub-xeric pine-dominated forests in eastern Finland. Seminatural study sites, especially the recently burned sites, were important habitats for threatened and near-threatened species. We propose that young stages of natural succession should be included in the network of protected forest areas. On the other hand, the composition of saproxylic species assemblages in seminatural forests differed from the assemblages in managed forests, indicating also the need to improve the forest management guidelines so that they better address the requirements of species protection. Regeneration methods applied should resemble or mimic the natural disturbances more closely.     

Decoupled stoichiometric,isotopic, and fungal responses of an ectomycorrhizal black spruce forest to nitrogen and phosphorus additions

Many northern forests are limited by nitrogen (N) availability, slight changes in which can have profound effects on ecosystem function and the activity of ectomycorrhizal (EcM) fungi. Increasing N and phosphorus (P) availability, an analog to accelerated soil organic matter decomposition in a warming climate, could decrease plant dependency on EcM fungi and increase plant productivity as a result of greater carbon use efficiency. However, the impact of altered N and P availability on the growth and activity of EcM fungi in boreal forests remains poorly understood despite recognition of their importance to host plant nutrition and soil carbon sequestration. To address such uncertainty we examined above and belowground ecosystem properties in a boreal black spruce forest following five years of factorial N and P additions. By combining detailed soil, fungal, and plant δ¹⁵N measurements with in situ metrics of fungal biomass, growth, and activity, we found both expected and unexpected patterns. Soil nitrate isotope values became ¹⁵N enriched in response to both N and P additions; fungal biomass was repressed by N yet both biomass and growth were stimulated by P; and, black spruce dependency on EcM derived N increased slightly when N and P were added alone yet significantly declined when added in combination. These findings contradict predictions that N fertilization would increase plant P demands and P fertilization would further exacerbate plant N demands. As a result, the prediction that EcM fungi predictably respond to plant N limitation was not supported. These findings highlight P as an under appreciated mediator of the activity of denitrifying bacteria, EcM fungi, and the dynamics of N cycles in boreal forests. Further, use of δ¹⁵N values from bulk soils, plants, and fungi to understand how EcM systems respond to changing nutrient availabilities will often require additional ecological information.     

Parasitoids (Hymenoptera, Ichneumonoidea) of Saproxylic beetles are affected by forest successional stage and dead wood characteristics in boreal spruce forest

The habitat requirements and effects of forest management on insects belonging to higher trophic levels are relatively unknown in forest ecosystems. We tested the effect of forest successional stage and dead wood characteristics on the saproxylic parasitoid (Hymenoptera, Ichneumonoidea) assemblage in boreal spruce-dominated forests in northern Sweden. Within each of nine areas, we selected three sites with different management histories: (1) a clear-cut (2) a mature managed forest and (3) an old-growth forest. Parasitoids were collected in 2003 using eclector traps mounted on fresh logs, which were either untreated (control), burned, inoculated with fungi, or naturally shaded, and on artificially-created snags.Both forest type and dead wood characteristics had a significant effect on parasitoid assemblages. Grouped idiobionts and some species, such as Bracon obscurator and Ontsira antica, preferred clear-cuts, while others, such as Cosmophorus regius (Hym., Braconidae) and other koinobionts, were associated with older successional forest stages. No single dead wood substrate was sufficient to support the entire community of parasitoids in any forest type, even when the regular host was present. In particular, snags hosted a different assemblage of species from other types of dead wood, with parasitoids of Tetropium spp. such as Rhimphoctona spp. (Hym., Ichneumonidae) and Helconidea dentator (Hym., Braconidae) being abundant. These results indicate that a diversity of dead wood habitats is necessary to support complete assemblages of beetle-associated parasitoids from early successional stages of dead wood and that parasitoids may be more sensitive to habitat change than their hosts.     

Charcoal mineralisation potential of microbial inocula from burned and unburned forest soil with and without substrate addition

Effects of fire on the functioning of the soil microbial community are largely unknown. In this study, we addressed the charcoal mineralisation potential of microbial inocula extracted from burned and unburned soil. The mineralisation of charcoal was analysed during a 1 month incubation experiment under controlled conditions with and without substrate addition. The aim of the study was to elucidate (1) the indirect effect of fire on the functioning of the soil microbial community in terms of charcoal degradation and (2) the possibility to stimulate this degradation by addition of two substrates of increasing complexity. Our conceptual approach included the monitoring of CO₂ emission from microcosms containing laboratory-made charcoal and microbial inocula from burned and unburned soil with and without ¹³C labelled glucose and cellulose.Our results showed higher charcoal mineralisation without substrate addition in microcosms with the inocula from unburned soil compared to burned soil. Charcoal mineralisation was stimulated by the addition of glucose, whereas cellulose addition did not induce a priming effect. We observed a higher stimulation of charcoal mineralisation induced by glucose for the inoculum from burned soil compared to the inoculum from unburned soil. We concluded that fire did affect the functioning of the soil microbial community in terms of charcoal degradation and that the important priming effect induced by glucose may be explained by an increase of the overall microbial activity, rather than selective stimulation of charcoal degrading microbial communities.     

Indices of dissolved organic nitrogen, ammonium and nitrate across productivity gradients of boreal forests

Organic nitrogen (N) uptake, rather than solely inorganic N (DIN), is considered a significant pathway for plant nutrition, especially in arctic, alpine and boreal ecosystems. Assays of plant-available N in these ecosystems might therefore be improved with measures of dissolved organic N (DON). We examined DON and DIN abundance from an in situ 5-week incubation across plant associations that represent the widest range in site potential in southern boreal forests of British Columbia, Canada. The supply of N from forest floors and mineral soils (20 cm depth) was measured separately and then combined (kg ha⁻¹) to facilitate comparisons of sites. DON was the predominant form of extractable N, and was increasingly supplemented, rather than replaced, by NH₄⁺ and NO₃⁻ on productive sites. The amount of DIN produced in the soils was very low, perhaps too small to support forest needs, and the correlation of DIN to asymptotic stand height (a measure of site potential) was significant but nonlinear. The combined amount of DON+DIN was considered a more effective index of plant-available N because it was strongly significant as a linear correlation to stand height and more typical of annual forest N uptake. The relative shift in N forms, from a predominance of DON to progressively greater ratios of DIN:DON, was consistent with the current paradigm of N forms across gradients of N availability, although the actual amounts of DON increased, rather than decreased, with site potential. Based on this, we suggest organic N uptake has the potential to contribute to plant nutrition across the entire productivity gradient of soils in southern boreal forests. Although other N indices were effective in characterizing forest productivity, a combined assay of DON+DIN production could provide new insights into functional differences in plant-available N.     

Controls over pathways of carbon efflux from soils along climate and black spruce productivity gradients in interior Alaska

Small changes in C cycling in boreal forests can change the sign of their C balance, so it is important to gain an understanding of the factors controlling small exports like water-soluble organic carbon (WSOC) fluxes from the soils in these systems. To examine this, we estimated WSOC fluxes based on measured concentrations along four replicate gradients in upland black spruce (Picea mariana [Mill.] BSP) productivity and soil temperature in interior Alaska and compared them to concurrent rates of soil CO₂ efflux. Concentrations of WSOC in organic and mineral horizons ranged from 4.9 to 22.7 g C m⁻² and from 1.4 to 8.4 g C m⁻², respectively. Annual WSOC fluxes (4.5-12.0 g C m⁻² y⁻¹) increased with annual soil CO₂ effluxes (365-739 g C m⁻² y⁻¹) across all sites (R²=0.55, p=0.02), with higher fluxes occurring in warmer, more productive stands. Although annual WSOC flux was relatively small compared to total soil CO₂ efflux across all sites (<3%), its relative contribution was highest in warmer, more productive stands which harbored less soil organic carbon. The proportions of relatively bioavailable organic fractions (hydrophilic organic matter and low molecular weight acids) were highest in WSOC in colder, low-productivity stands whereas the more degraded products of microbial activity (fulvic acids) were highest in warmer, more productive stands. These data suggest that WSOC mineralization may be a mechanism for increased soil C loss if the climate warms and therefore should be accounted for in order to accurately determine the sensitivity of boreal soil organic C balance to climate change.     

Seasonal variations in enzyme activity and organic carbon in soil of a burned and unburned hardwood forest

This study examined variations in soil organic C content and the activity of acid phosphatase, α-glucosidase, phenol oxidase, chitinase, and l-glutaminase in ultisols of burned and unburned areas in Quercus-dominated forests in Ohio, USA. The low intensity, prescribed fires were conducted in April 2001, with temperature 10 cm above the forest floor averaging 160-240 °C. Sampling was conducted throughout the six month growing season (May-October) of 2003, two years after the fire. Organic C content in these ultisols varied between 20 and 30 g C/kg soil, and varied little through the growing season, except for a late season increase to ∼32 g C/kg soil in the burned areas. When enzyme activity was expressed per unit soil organic C, there was no statistically significant variation among sample dates in soil enzyme activity except l-glutaminase, which demonstrated a distinct maximum in activity in spring. Non-metric multidimensional scaling (NMS) ordination resulted in no clear separation of burned and unburned sample areas based on soil organic C and enzyme activity. When the growing season was divided into three segments (early spring, late spring/early summer, and late summer/early autumn), there was again a lack of separation between burned and unburned areas in the earlier two segments, whereas in the late summer/early autumn segment the burned and unburned areas were clearly separated on the basis of differences in soil organic C and l-glutaminase activity. As environmental factors (e.g. soil temperature, moisture) and substrate availability do not vary in parallel through the growing season in this region, seasonal patterns often differ among enzyme systems based on their predominant control mechanism. Sampling time during the growing season appears to have little effect on holistic judgments of fire effects based on soil enzymes, except under restrictive conditions.     

Learning from a “benign neglect strategy” in a national park: Response of saproxylic beetles to dead wood accumulation

Increasing demands for firewood owing to rising energy costs have accelerated discussions about the amount of dead wood needed for conservation. A sharp increase in dead wood caused by bark beetles in a German national park provides lessons for management of commercial and protected forests. We investigated the effects of dead wood due to bark beetle infestation as well as tree senility on abundance and richness of saproxylic species of beetles. Increasing amounts of spruce dead wood and opening of the canopy by bark beetles had positive effects on the abundance of host-generalist, conifer-specialist, and red-listed saproxylic beetles. Broadleaf specialists were positively associated with the amount of broadleaf dead wood and negatively associated with canopy openness. Gradient analysis of beetle assemblages revealed two major environmental axes: canopy openness and amount of dead wood. We found a threshold for community divergence at a canopy openness of 23% (confidence interval CI: 11-49) and at an amount of dead wood of 64 m³ ha⁻¹ (CI: 35-160). Critically endangered species served as indicators of dense and open forests, but only when the amount of dead wood was high. Our results suggest that, to maintain saproxylic beetle assemblages, the amount of dead wood in commercial montane forests (at present ≈15 m³ ha⁻¹) needs to be tripled, with a focus on broadleaf wood in dense stands and spruce wood in open stands. For large protected areas in Europe, our data suggest that bark beetle infestation and senescence without active forest management improves habitat conditions for saproxylic beetles.     

Changes in mineral nitrogen, soil organic matter fractions and microbial community level physiological profiles after application of digested pig slurry and compost from municipal organic wastes to burned soils

In this study, mineralization of digested pig slurry and compost from municipal organic wastes in burned soils was followed for 60 days. The effects of amendments on organic matter fractions and microbial community level physiological profiles (CLPP) were also investigated at the end of the incubation period. Soil from a forest 10 days after a fire had a greater basal respiration, and more organic matter that a nearby soil that was not affected by fire, presumably as a consequence of black ash addition following the wildfire. Nitrification was inhibited in soils treated at 105 and 250 °C in the laboratory, but amendment application allowed nitrification to take place in the latter soil, and led to significant flushes of mineralization. Slurry amendment resulted in greater increases in mineral N compared with compost. Soil treated at 250 °C had the greatest content of water-extractable compounds (WE) at the expense of acid-extractable compounds (AE), but during the incubation the variations in these two fractions had an opposite trend, i.e. soil gained AE and lost WE fractions. The variation in N-acetyl-glucosamine-induced respiration was different between compost- and slurry-amended soils, with the greater values in the former. The effect of amendments could be further differentiated by principal component (PCA) and cluster analyses based on the variations in organic matter fractions and CLPP between the beginning and the end of the incubation period. Amendment application led to shifts on the PCA maps that depended both on the amendment and soil treatment. In fresh soil and in that treated at 250 °C, the unamended, compost- and slurry-amended treatments remained relatively close on the PCA maps and had linkage distances <1.0. In contrast, amendment application to other soils led to large shifts on the PCA maps and to linkage distances >1.0. Pig slurry led to the greatest changes in burned soil, while compost induced the greatest shifts in soil treated at 105 °C.This study suggests that an application of organic amendments after a severe fire event may contribute to a faster recovery of soil functions.     

Contribution of fine roots to ecosystem biomass and net primary production in black spruce, aspen, and jack pine forests in Saskatchewan

Fine root (<2 mm) processes contribute to and exhibit control over a large pool of labile carbon (C) in boreal forest ecosystems because of the high proportion of C allocated to fine root net primary production (NPP), and the rapid decomposition of fine roots relative to aboveground counterparts. The objective of this study was to determine the contribution of fine roots to ecosystem biomass and NPP in a mature black spruce (Picea mariana Mill.) (OBS), aspen (Populus tremuloides Michx.) (OA), and jack pine (Pinus banksiana Lamb.) (OJP) stand, and an 11-year-old harvested jack pine (HJP) stand in Saskatchewan. Estimates of fine root biomass and NPP were obtained from nine minirhizotron (MR) tubes at each of the four Boreal Ecosystem Research and Monitoring Sites (BERMS). Fine root data were collected once a month for May–September in 2003 and 2004. Additional C biomass and NPP data for various components of the forest stands were obtained from Gower et al. (1997) and Howard et al. (2004). Annual fine root biomass averaged 3.10 ± 0.89, 1.71 ± 0.49, 1.62 ± 0.32, and 2.96 ± 0.67 Mg C ha⁻¹ (means ± S.D.) at OBS, OA, OJP, and HJP, respectively, comprising between 1 and 6% of total stand biomass. Annual fine root NPP averaged 2.66 ± 0.97, 2.03 ± 0.43, 1.44 ± 0.43, and 2.16 ± 0.81 Mg C ha⁻¹ year⁻¹ (means ± S.D.) at OBS, OA, OJP, and HJP, respectively, constituting between 41 and 71% of total stand NPP. Results of this study indicate that fine roots produce a large amount of C in boreal forests. It is speculated that fine root NPP may control a large amount of labile C-cycling in boreal forests and that fine root responses to environmental and anthropogenic stress may be an early indicator of impaired ecosystem functioning.     

Processing of 13C glucose in mineral soil from aspen,spruce and novel ecosystems in the Athabasca Oil Sands Region

Microbial composition is known, on similar soil types, to vary based on differing organic matter inputs, or stand composition. Fine-textured luvisolic soils, which dominate the upland boreal forests of Western Canada, support a canopy cover of aspen (Populus tremuloides Michx.), white spruce (Picea glauca (Moench) Voss) or a mixture of the two. These soils then reflect different belowground biogeochemical processing of organic matter. Novel, anthropogenic soils formed from a combination of peat litter and fine textured mineral soil, are now also a part of the landscape in the western boreal. This study set out to determine if a simple labeled compound (¹³C glucose) was processed differently by soils from the two dominant stand types (aspen and spruce) and from an anthropogenic (newly reclaimed) site. Results indicate that while all three soils rapidly incorporated and respired the labeled carbon, each maintained a distinct microbial community structure (as evidenced by phospholipid fatty acid analysis) throughout the 300 hour experiment. Therefore soils with different microbial communities from varied organic matter inputs decompose organic carbon by different processes, even in the case of simple labile compounds.     

Different effect of drying on the fluxes of dissolved organic carbon and nitrogen from a Norway spruce forest floor

The forest floor represents the major source of dissolved organic carbon (DOC) and nitrogen (DON) in forest soils. The release mechanisms of DOC and DON from forest floors and their environmental controls as well as the dynamics of concentrations and fluxes are still poorly understood. We investigated the effect of drying and rewetting on the release of DOC and DON from a Norway spruce forest floor. Undisturbed soil columns of 17 cm diameter and 15—20 cm height were taken with 7 replicates from the forest floor of a mature Norway spruce (Picea abies [L.] Karst.) site and established at 10°C in the laboratory. Columns were exposed to different periods of drying (3, 5, 10, 20 days). Each drying period was followed by a rewetting for 5 days at an irrigation rate of 10 mm d^—1 with a natural throughfall solution. The percolates from the forest floor were collected daily and analyzed for DOC, total N, NH₄, NO₃, pH, electrical conductivity and major ions. Drying for 10 and 20 days decreased the water content of the Oi horizon from 280% dry weight to about 30%. The water content of the Oe and the Oa horizon only changed from about 300% to 200%. The fluxes of DOC from the forest floor were moderately effected by drying and rewetting with an increase after 3 and 5 days of drying, but a decrease after 10 and 20 days. On the contrary, the drying for 10 and 20 days resulted in a drastic increase of the DON fluxes and a subsequent decrease of the DOC/DON ratios in the forest floor percolates from about 50 to 3.3. These results suggest that the mechanisms for DOC release in forest floors differ from those for DON and that drying and rewetting cause temporal variations in the DOC/DON ratios in forest floor percolates.     

Threats, conservation strategies, and prognosis for suckers (Catostomidae) in North America: insights from regional case studies of a diverse family of non-game fishes

Catostomid fishes are a diverse family of 76+ freshwater species that are distributed across North America in many different habitats. This group of fish is facing a variety of impacts and conservation issues that are somewhat unique relative to more economically valuable and heavily managed fish species. Here, we present a brief series of case studies to highlight the threats such as migration barriers, flow regulation, environmental contamination, habitat degradation, exploitation and impacts from introduced (non-native) species that are facing catostomids in different regions. Collectively, the case studies reveal that individual species usually are not threatened by a single, isolated factor. Instead, species in general face numerous stressors that threaten multiple stages of their life history. Several factors have retarded sucker conservation including widespread inabilities of field workers to distinguish some species, lack of basic natural history and ecological knowledge of life history, and the misconception that suckers are tolerant of degraded conditions and are of little social or ecological value. Without a specific constituent group lobbying for conservation of non-game fishes, all such species, including members of the catostomid family, will continue to face serious risks because of neglect, ignorance, and misunderstanding. We suggest that conservation strategies should incorporate research and education/outreach components. Other conservation strategies that would be effective for protecting suckers include freshwater protected areas for critical habitat, restoration of degraded habitat, and design of catostomid-friendly fish bypass facilities. We believe that the plight of the catostomids is representative of the threats facing many other non-game freshwater fishes with diverse life-history strategies globally.