Paul Hazlett

Logging impacts on the biogeochemistry of boreal forest soils and nutrient export to aquatic systems: A review

Logging disturbances in boreal forest watersheds can alter biogeochemical processes in soils by changing forest composition, plant uptake rates, soil conditions, moisture and temperature regimes, soil microbial activity, and water fluxes. In general, these changes have often led to short-term increases in soil nutrient availability followed by increased mobility and losses by leaching to receiving waters. Among the studies we reviewed, dissolved organic carbon (DOC) exports usually increased after logging, and nitrogen (N) mineralization and nitrification often increased with resulting increased N availability and exports to receiving waters. Similar processes and responses occurred for phosphorus (P), but to a lesser extent than for N. In most cases, base cations were released and exported to receiving waters after logging. Several studies demonstrated that stem-only or partial-harvest logging reduced the impacts on nutrient release and exports in comparison to whole-tree clear-cutting. Despite these log...

Measuring environmental change in forest ecosystems by repeated soil sampling: a North American perspective

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

Development of Stream Water Chemistry during Spring Melt in a Northern Hardwood Forest

The role of snowmelt and subsurface hydrology in determiningthe chemistry of a small headwater stream in the TurkeyLakes Watershed (TLW) was evaluated for the spring meltperiods 1992 to 1996. Spring runoff is the dominanthydrological event at the TLW each year. Processesoccurring within the snowpack during snowmelt wereprincipally responsible for the above-ground changes inchemical fluxes relative to bulk deposition (the effect ofwinter throughfall was minimal). Large changes in chemicalfluxes occurred below ground. Organic matter decomposition,weathering, nitrification, and element cycling are some ofthe more important below-ground processes that operateduring the snow accumulation and ablation season and controlthe composition of the water ultimately appearing in thestream. Maximum stream discharge was accompanied byelevated concentrations of H+, NO3-, K+,NH4+, DOC, Al and Mn, but reduced levels ofCa2+, Mg2+, SO42- and SiO2. Theconcentration-discharge relationships were consistent withwater movement through and above the forest floor duringpeak discharge, a flowpath facilitated by rapid infiltrationof meltwater and the existence of a relatively impermeablelayer in the mineral soil creating a perched water table. Averaged over the five periods of snow accumulation andablation, it was estimated that pre-melt stream flow, andwater routed through the forest floor and through the uppermineral soil contributed 9, 28 and 63%, respectively, ofthe discharge measured at the outlet of the catchment. Theforest floor contribution would be greater at peak dischargeand at higher elevations. An end-member mixing modelestimated concentrations of SO42-, NO3-,Cl-, Ca2+, Mg2+, Na+ and Al that werecomparable to average values measured in the stream. Othervariables (NH4+, H+, K+ and DOC) wereover-estimated implying retention mechanisms operatingoutside the model assumptions.

Hydrologic Pathways during Snowmelt in First-order Stream Basins at the Turkey Lakes Watershed

The chemical composition of stream and soil water collected from two first-order stream basins in the Turkey Lakes Watershed (TLW) during the spring melt periods of 1992–1996 was examined to determine the flowpaths of snowmelt to the stream channel. Soil water was intensively sampled from within the soil organic layers as well as above (shallow soil water) and within (deep soil water) a compact basal till. Stream SiO2 concentrations of the high-elevation basin 47 were the same as the levels found in shallow soil water, and forest-floor percolate SiO2 concentrations were elevated to these levels during intense melting periods. The SiO2 concentrations from the stream and the shallow and deep soil water were similar at the low-elevation basin 31. With the exception of deep soil water, water collected from the soil and stream at basin 47 had higher H+ and Al and lower base cation concentrations than basin 31. Stream Al concentrations were significantly correlated with forest-floor percolate Al concentrations at the high-elevation basin, whereas stream Al concentrations were correlated with mineral soil water Al concentrations at the low-elevation site. There were significant positive correlations between stream and shallow soil water H+ at both basins. Shallow soil water pathways, therefore, were an important contributor to streamflow, and influenced stream chemical response during the spring snowmelt at TLW.

Fine root biomass and nutrient content in a black spruce peat soil with and without alder

non-alder site, respectively. The mass (W/V) of nutrients in fine roots was strongly dependent upon the availability of nutrien ts in the peat. Fine root content had a strong positive relationship with peat available P and exchangeable K contents suggesting tha t P and K may be limiting nutrients for black spruce in this peat soil.

Inter-laboratory variation in the chemical analysis of acidic forest soil reference samples from eastern North America

Long-term forest soil monitoring and research often requires a comparison of laboratory data generated at different times and in different laboratories. Quantifying the uncertainty associated with these analyses is necessary to assess temporal changes in soil properties. Forest soil chemical properties, and methods to measure these properties, often differ from agronomic and horticultural soils. Soil proficiency programs do not generally include forest soil samples that are highly acidic, high in extractable Al, low in extractable Ca and often high in carbon. To determine the uncertainty associated with specific analytical methods for forest soils, we collected and distributed samples from two soil horizons (Oa and Bs) to 15 laboratories in the eastern United States and Canada. Soil properties measured included total organic carbon and nitrogen, pH and exchangeable cations. Overall, results were consistent despite some differences in methodology. We calculated the median absolute deviation (MAD) for each measurement and considered the acceptable range to be the median ± 2.5 × MAD. Variability among laboratories was usually as low as the typical variability within a laboratory. A few areas of concern include a lack of consistency in the measurement and expression of results on a dry weight basis, relatively high variability in the C/N ratio in the Bs horizon, challenges associated with determining exchangeable cations at concentrations near the lower reporting range of some laboratories and the operationally defined nature of aluminum extractability. Recommendations include a continuation of reference forest soil exchange programs to quantify the uncertainty associated with these analyses in conjunction with ongoing efforts to review and standardize laboratory methods.

Biogeography and organic matter removal shape long-term effects of timber harvesting on forest soil microbial communities

The growing demand for renewable, carbon-neutral materials and energy is leading to intensified forest land-use. The long-term ecological challenges associated with maintaining soil fertility in managed forests are not yet known, in part due to the complexity of soil microbial communities and the heterogeneity of forest soils. This study determined the long-term effects of timber harvesting, accompanied by varied organic matter (OM) removal, on bacterial and fungal soil populations in 11- to 17-year-old reforested coniferous plantations at 18 sites across North America. Analysis of highly replicated 16 S rRNA gene and ITS region pyrotag libraries and shotgun metagenomes demonstrated consistent changes in microbial communities in harvested plots that included the expansion of desiccation- and heat-tolerant organisms and decline in diversity of ectomycorrhizal fungi. However, the majority of taxa, including the most abundant and cosmopolitan groups, were unaffected by harvesting. Shifts in microbial populations that corresponded to increased temperature and soil dryness were moderated by OM retention, which also selected for sub-populations of fungal decomposers. Biogeographical differences in the distribution of taxa as well as local edaphic and environmental conditions produced substantial variation in the effects of harvesting. This extensive molecular-based investigation of forest soil advances our understanding of forest disturbance and lays the foundation for monitoring long-term impacts of timber harvesting.

Methods of soil resampling to monitor changes in the chemical concentrations of forest soils

Recent soils research has shown that important chemical soil characteristics can change in less than a decade, often the result of broad environmental changes. Repeated sampling to monitor these changes in forest soils is a relatively new practice that is not well documented in the literature and has only recently been broadly embraced by the scientific community. The objective of this protocol is therefore to synthesize the latest information on methods of soil resampling in a format that can be used to design and implement a soil monitoring program. Successful monitoring of forest soils requires that a study unit be defined within an area of forested land that can be characterized with replicate sampling locations. A resampling interval of 5 years is recommended, but if monitoring is done to evaluate a specific environmental driver, the rate of change expected in that driver should be taken into consideration. Here, we show that the sampling of the profile can be done by horizon where boundaries can be clearly identified and horizons are sufficiently thick to remove soil without contamination from horizons above or below. Otherwise, sampling can be done by depth interval. Archiving of sample for future reanalysis is a key step in avoiding analytical bias and providing the opportunity for additional analyses as new questions arise.

Trends in Water Chemistry in a Maple Forest on a Steep Slope

Year-to-year variation in SO42-,NO3-, Ca2+, K+, and Mg2+concentrations in forest floor and mineral soil percolatefrom a forested, podzolic soil at the Turkey Lakes Watershedon the Precambrian Shield was assessed for monotonic trendsbetween 1986 and 1995. Our objective was to examine howrapidly ion concentrations in soil percolate equilibratedafter stabilization of SO42- concentrations inprecipitation. Significant negative trends were detected inmonthly Ca2+, and Mg2+ concentrations in forestfloor and SO42-, Ca2+, and Mg2+ inmineral soil percolate during the 10-year-period. Thedecline in Ca2+ and Mg2+ was greater than annualdecreases in SO42- and NO3- in forestfloor percolate and proportional to the reduction inSO42- in mineral soil percolate. Response ofmineral soil percolate to a 15 μmolc L-1SO42- decrease in wet-only precipitation between1985 and 1986 was a gradual decline in SO42-concentration through 1995. The five-year meanSO42- concentration in bulk precipitation, forestfloor percolate, and mineral soil percolate decreased 8, 9and 18 μmolc L-1 from 1986–90 to 1991–95.Microbial (mineralization of organic S) and sorption(release from and/or retention in the pool of insolubleSO42-) processes in the soil were logicalexplanations for the observed changes in SO42- inmineral soil percolate.

Quickflow response to forest harvesting and recovery in a northern hardwood forest landscape

School of the Environment, Trent University, Peterborough, ON, Canada Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, Sault Ste Marie, ON, Canada Canada Centre for Inland Waters, Environment and Climate Change Canada, Burlington, ON, Canada Correspondence James M. Buttle, School of the Environment, Trent University, Peterborough, ON, Canada K9L 0G2. Email: jbuttle@trentu.ca