Sylvie A. Quideau

A direct link between forest vegetation type and soil organic matter composition

Total carbon storage and turnover in soils can be simulated as a series of pools with different turnover rates, ranging from seasonal to millennial. This approach has emphasized the importance of climatic controls on soil organic matter (SOM) dynamics, but implicitly assumes that SOM is minimally influenced by the nature of the plant material from which it is derived. Here we test this assumption by contrasting the influence of climate and vegetation (oak, manzanita, and conifers) on SOM composition in granitic-derived soils from California. Soils developed under the same climate in the San Gabriel Mountains were compared to soils with varying climate along an elevational transect in the Sierra Nevada range. Solid state TOSS CPMAS 13C NMR was used to semiquantitatively characterize the chemical structure of organic matter in litter layers, and low-density and fine silt fractions isolated from sampled A horizons. For all soils, there was a progressive decrease in O-alkyl C, and an increase in alkyl and carbonyl C from the litter to the low-density and fine silt fractions. The NMR spectra of the low-density fractions, and even more so of the fine silt fractions exhibited clear differences in SOM composition associated with different plant genera, regardless of climate. The carbonyl C dominated under oak, O-alkyl C prevailed under manzanita, and alkyl C was prominent under coniferous vegetation. These results indicate that vegetation, not climate, was the factor controlling SOM composition in these soils, and should be taken as a caution against a simplistic climatic interpretation of storage and turnover rate of carbon in soils.

Soil organic matter processes: characterization by 13C NMR and 14C measurements

Abstract Soil organic matter (SOM) is a central contributor to soil quality as it mediates many of the chemical, physical, and biological processes controlling the capacity of a soil to perform successfully. SOM properties (e.g. C/N ratio, macro-organic matter) have been proposed as diagnostic criteria of overall soil fitness, but their use is hampered by a poor understanding of the basic biochemical principles underlying SOM processes. The objective of this project was to determine the influence of scrub oak (Quercus dumosa Nutt.) and Coulter pine (Pinus coulteri B. Don) vegetation on decomposition and SOM formation processes in a lysimeter installation constructed in 1936 in the San Gabriel mountains of southern California. Soil samples archived during construction of the installation, and A horizons sampled in 1987, were fractionated according to density and mineral particle size to isolate the water floatable (macro-organic matter), fine silt and clay fractions. Carbon turnover rates were determined on all fractions from AMS 14C measurements. Solid state CPMAS TOSS 13C NMR was used to semiquantitatively characterize the chemical structure of organic matter on fresh litter and soil fractions. For the two soils, there was a progressive decrease in O-alkyl C, and an increase in alkyl and carbonyl C from the litter to the floatable, fine silt and clay fractions. These compositional differences were due to the oxidative degradation of the litter material, with preferential decomposition of the cellulose and hemicellulose entities and selective preservation of recalcitrant waxes and resins. In all soil fractions, turnover rates of carbon were longer for the pine than for the oak lysimeter (up to 10 times longer). Also under pine, there was a gradual increase in turnover rate progressing from the floatable to the clay fraction, and differences in turnover rates among fractions may be explained based on differences in carbon chemistry. In contrast, under oak, rapid carbon turnover for all fractions suggested intense biological activity in this soil.

Recreating a Functioning Forest Soil in Reclaimed Oil Sands in Northern Alberta: An Approach for Measuring Success in Ecological Restoration

During oil-sands mining all vegetation, soil, overburden, and oil sand is removed, leaving pits several kilometers wide and up to 100 m deep. These pits are reclaimed through a variety of treatments using subsoil or a mixed peat-mineral soil cap. Using nonmetric multidimensional scaling and cluster analysis of measurements of ecosystem function, reclamation treatments of several age classes were compared with a range of natural forest ecotypes to discover which treatments had created ecosystems similar to natural forest ecotypes and at what age this occurred. Ecosystem function was estimated from bioavailable nutrients, plant community composition, litter decomposition rate, and development of a surface organic layer. On the reclamation treatments, availability of nitrate, calcium, magnesium, and sulfur were generally higher than in the natural forest ecotypes, while ammonium, P, K, and Mn were generally lower. Reclamation treatments tended to have more bare ground, grasses, and forbs but less moss, lichen, shrubs, trees, or woody debris than natural forests. Rates of litter decomposition were lower on all reclamation treatments. Development of an organic layer appeared to be facilitated by the presence of shrubs. With repeated applications of fertilizers, measured variables for the peat-mineral amendments fell within the range of natural variability at about 20 yr. An intermediate subsoil layer reduced the need for fertilizer and conditions resembling natural forests were reached about 15 yr after a single fertilizer application. Treatments over tailings sand receiving only one application of fertilizer appeared to be on a different trajectory to a novel ecosystem.

Vegetation control on soil organic matter dynamics

Soil organic matter (SOM) formation is one of the least understood steps of the global carbon cycle. An example is uncertainty around the role of plant communities in regulating SOM formation and turnover. Here we took advantage of the highly controlled conditions at the San Dimas lysimeter installation to quantify the influence of oak and pine vegetation on SOM dynamics. SOM turnover rates, estimated using total C and 14C content of litter and physically separable soil fractions, were faster under oak than under pine. In contrast to the rapid turnover for the oak litter (<2 years), the delay in litter incorporation into the mineral soil under pine was a controlling factor of SOM fluxes.

Forest restoration following surface mining disturbance: challenges and solutions

Many forested landscapes around the world are severely altered during mining for their rich mineral and energy reserves. Herein we provide an overview of the challenges inherent in efforts to restore mined landscapes to functioning forest ecosystems and present a synthesis of recent progress using examples from North America, Europe and Australia. We end with recommendations for further elaboration of the Forestry Reclamation Approach emphasizing: (1) Landform reconstruction modelled on natural systems and creation of topographic heterogeneity at a variety of scales; (2) Use and placement of overburden, capping materials and organic amendments to facilitate soil development processes and create a suitable rooting medium for trees; (3) Alignment of landform, topography, overburden, soil and tree species to create a diversity of target ecosystem types; (4) Combining optimization of stock type and planting techniques with early planting of a diversity of tree species; (5) Encouraging natural regeneration as much as possible; (6) Utilizing direct placement of forest floor material combined with seeding of native species to rapidly re-establish native forest understory vegetation; (7) Selective on-going management to encourage development along the desired successional trajectory. Successful restoration of forest ecosystems after severe mining disturbance will be facilitated by a regulatory framework that acknowledges and accepts variation in objectives and outcomes.

Base cation biogeochemistry and weathering under oak and pine : a controlled long-term experiment

Large earthen-walled lysimeters at the San Dimas Experimental Forest in southern California present a unique opportunity to assess vegetation effects on biogeochemical processes and cation release by weathering in controlled soil-vegetation systems where archived samples of soil parent material are available for comparison. The lysimeters were filled in 1937 with homogenized fine sandy loam derived on site from the weathering of diorite, and planted in 1946 with scrub oak (Quercus dumosa) and Coulter pine (Pinus coulteri). Changes in base cation contents were measured in above-ground biomass, and total and exchangeable soil pools to a depth of 1 meter. All cations in the non-exchangeable soil pool decreased relative to the initial fill material, indicating release by weathering. Sodium and K were depleted from both exchangeable and non-exchangeable pools of the soils. Plant uptake of Na was minimal, whereas K storage in vegetation exceeded the loss from the exchangeable soil pool. In both soil-vegetation systems, but especially for oak, there was an increase in exchangeable Ca and Mg. For all base cations, storage in above-ground biomass was greater for oak, whereas losses by weathering from the non-exchangeable soil pool were greater under pine. Strong evidence supports biocycling as a controlling mechanism resulting in greater Ca and Mg release by weathering under pine. In addition, decreases in non-exchangeable Ca and Mg were strongly correlated to decrease in Si under oak, whereas no correlation was observed under pine. We conclude that weathering reactions or stoichiometry differed between vegetation types.

Distribution, accumulation, and fluxes of soil carbon in four monoculture lysimeters at San Dimas Experimental Forest, California

Abstract This research examines how vegetation type controls soil processes involving soil carbon fluxes, accumulation, and transport in a chaparral ecosystem. Carbon concentrations and δ13C values were measured for soil samples collected in 1987 from 1-m depth profiles in four lysimeters in the San Dimas Experimental Forest, southern California, USA. Each lysimeter has sustained a single vegetation type since 1946, the species being Quercus dumosa, Ceanothus crassifolius, Adenostoma fasciculatum, and Pinus coulteri. Archived samples of soil originally used for filling the lysimeters and litter samples from the surface of each lysimeter were analyzed to determine initial and boundary conditions. Although detectable changes in carbon content were limited to the topmost 20 cm of the profiles, variations in δ13C were found to depths of 80 cm, indicating that processing of carbon occurs much deeper than indicated by carbon concentrations alone, underscoring the utility of carbon isotopes in the study of soil carbon dynamics. A one-dimensional model that considers surface carbon input, downward transport, and loss through decomposition is developed to describe the evolution of carbon concentration and stable carbon isotope ratios in the four soil profiles. Comparison of measured and calculated profiles yields estimates of carbon fluxes, turnover rates, and accumulation of soil carbon. A set of physical parameters, including the rate constant of decomposition, downward transport rate of organic carbon, and rate of carbon input from the surface are derived from the model and can be related to the species and environmental conditions. The calculations indicate the importance of species on soil formation and carbon cycles, which is important for understanding the effects of changes in land use on ecosystem processes. Our results also suggest that fire may increase the rate of soil carbon accumulation in a chaparral ecosystem.

Organic carbon sequestration under chaparral and pine after four decades of soil development

Abstract Soils are the largest carbon reservoir of terrestrial ecosystems, and play a central role in the global carbon cycle. The large lysimeter installation at the San Dimas Experimental Forest in southern California allowed quantification of carbon storage in a biosequence of soils under chamise (Adenostoma fasciculatum Hook. and Am.), hoaryleaf ceanothus (Ceanothus crassifolius Torr.), scrub oak (Quercus dumosa Nutt.), and Coulter pine (Pinus coulteri B. Don). After four decades of soil development, carbon sequestration in the lysimeters ranged from 4552 to 17,561 g m−2. Carbon accretion in the mineral soils (0–1 m) under chaparral represented a larger percentage of total above-ground biomass (23–27%) as compared to the pine (13%). Also, contribution of the A horizon to whole soil (0–1 m) OC sequestration was higher under chaparral than under pine. Carbon accretion in the surface horizons was related to earthworm activity, which was intense under scrub oak, but absent under pine. Soils sampled in 1987 and corresponding archived fill materials were fractionated according to density and mineral particle size fractions, and analyzed for OC and N by dry combustion. Carbon and nitrogen concentrations in all mineral soil fractions can be ranked from highest to lowest by plant species: ceanothus > chamise > scrub oak > Coulter pine. Under chaparral, a greater proportion of total soil carbon was recovered in the sand fraction as compared to the pine. The C N ratio of this sand-sized organic matter was higher under chaparral than under pine. This is indicative of fresh plant residues that may not contribute to the long-term carbon storage in soils.

Wood-feeding beetles and soil nutrient cycling in burned forests: implications of post-fire salvage logging.

1 Rising economic demands for boreal forest resources along with current and predicted increases in wildfire activity have increased salvage logging of burned forests. Currently, the ecological consequences of post‐fire salvage logging are insufficiently understood to develop effective management guidelines or to adequately inform policy decision‐makers. 2 We used both field and laboratory studies to examine the effects of post‐fire salvage logging on populations of the white‐spotted sawyer Monochamus scutellatus scutellatus (Say) (Coleoptera: Cerambycidae) and its ecological function in boreal forest. 3 Monochamus s. scutellatus adults were relatively abundant in both burned and clear‐cut logged sites but were absent from salvage logged sites. 4 An in situ mesocosm experiment showed that the abundance of M. s. scutellatus larvae in burned white spruce bolts was linked to changes in total organic nitrogen and carbon in mineral soil. 5 Organic nutrient inputs in the form of M. s. scutellatus frass increased mineral soil microbial respiration rates by more than three‐fold and altered the availability of nitrogen. Changes in nitrogen availability corresponded with decreased germination and growth of Epilobium angustifolium and Populus spp. but not Calamagrostis canadensis. 6 Although the present study focused on local scale effects, the reported findings suggest that continued economic emphasis on post‐fire salvage logging may have implications beyond the local scale for biodiversity conservation, nutrient cycling and plant community composition in forest ecosystems recovering from wildfire.

Laboratory-based nitrogen mineralization and biogeochemistry of two soils used in oil sands reclamation

MacKenzie, M. D. and Quideau, S. A. 2012. Laboratory-based nitrogen mineralization and biogeochemistry of two soils used in oil sands reclamation. Can. J. Soil Sci. 92: 131-142. In the Athabasca oil sands region of Alberta, Canada, peat mineral and upland forest floor mineral soils are salvaged and stockpiled for reclamation. Previous work showed that sites reclaimed with forest floor mineral soil had better understory regeneration and nitrogen dynamics more similar to naturally disturbed ecosystems. Both soils and a mixture of the two were compared in laboratory incubations by examining nitrogen mineralization (over 45 wk) and factorial fertility additions (4 wk trial with NPK) on microbial community structure and nutrient availability. Nitrogen mineralization indicated forest floor mineral soil had lower release rates and a higher estimated labile nitrogen pool than peat mineral soil. Nitrogen mineralization in mixed soil started like peat mineral soil and finished like forest floor mineral soil. Fertility additions influenced microbial community structure less than soil type. Multi-response permutation procedure indicated the forest floor mineral soil microbial community was significantly different from peat mineral and mixed soil communities. Control nutrient profiles differed from those with added NPK. Forest floor mineral soil retained nitrogen as ammonium, while peat mineral and mixed soils were nitrate dominated. Reclamation will require all soil types to be used and these data will help determine soil placement prescriptions.