Cindy Prescott

 
Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.

Professor

Research Classification

Ecological and Ecophysiological Processes
Ecosystem (Aquatic and Terrestrial)
Landscape and Restoration
Land and Soil

Research Interests

ecological restoration
soil organic matter
nutrient cycling

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Mar 2019)
The effects of variable-retention harvesting and stand age on fine-root decomposition and fungal communities in coastal temperate rainforests (2018)

Fine-root litter is the principal source of carbon (C) stored in forest soils and a dominant source of C for fungal decomposers. Differences in decomposer capacity among fungi may be an important determinant of fine-root decomposition. Variable-retention harvesting (VRH) provides refuge for ectomycorrhizal fungi, but its influence on fine-root decomposers is unknown, as are the effects of functional shifts in fungal communities on C cycling. I compared fungal communities decomposing fine-roots (in litterbags) under VRH (aggregate and dispersed retention), clearcut, and uncut stands at two sites (6- and 13-years post-harvest), and two decay stages (43-days and 1 year after burial), in Douglas-fir forests in coastal British Columbia. Fungal species and guilds were identified from fine-roots using high-throughput sequencing. Aggregate-retention maintained fungal communities similar to those found in uncut stands, but only at the 6-year post-harvest site. Ericoid and ectomycorrhizal guilds were not more abundant under VRH, but stand-age treatments (6-, 13-, and 70-years post-harvest) significantly structured species composition. Ectomycorrhizal abundance on decomposing fine roots may partially explain why fine roots typically decompose slower than surface litter. Stand age was a good predictor of vegetation and soil chemistry; grass and forb abundance, and nitrogen availability, were highest in young stands, whereas soil C and N increased in older stands. Despite differences among stand-age treatments, environmental factors were poor predictors of fungal community composition. However, in a 2-year decomposition study, environmental differences among treatments at the 6-year post-harvest site resulted in faster fine-root decomposition rates under clearcut harvesting, whereas 15-19% more C was retained under VRH and in uncut stands. As nitrate availability correlated with decomposition rate, management practices that reduce post-harvest nitrate availability are likely to result in lower C losses from fine-root decomposition. The effect of harvesting was not persistent as fine roots decomposed at similar rates in forests and openings at the 13-year post-harvest site. Altogether, aggregate-retention harvesting preserved fungal communities more commonly found in uncut stands, and slowed fine-root decomposition relative to clearcut harvesting. As such, this is a recommended harvesting practice in coastal British Columbia if fungal conservation and reduced harvesting-related C losses are management objectives.

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Biomass, productivity and allocation patterns in tropical old-growth and logged-over forests in Ghana (2017)

Understanding how tropical forest structure and function change during the decades after logging is a key research challenge. This thesis reports functional traits, forest structure, biomass, net primary productivity (NPP) and allocation, as well as their controlling factors in an old-growth forest and a 54-year-old logged-over forest in Ghana. By analyzing root traits, I found fine-root biomass, root length, surface area, and root tissue density were higher in the logged-over forest, whereas the old-growth forest had higher specific root length and specific root area. I also found divergent exploitation strategies between the two forests; plants in the old-growth forest produced thinner roots, which increase resource uptake efficiency, while plants in the logged-over forest had thicker roots, which are associated with greater resource conservation. Through correlation analysis, I found that fine-root mass correlated positively to relative humidity, while absorbed photosynthetically active radiation and fine-root biomass were also positively correlated. Fine-root mass and soil K were also positively correlated, and fine-root necromass correlated positively with soil P. I then explored the relationships between leaf traits, taxonomic (e.g., species richness) or structural (e.g., tree diameter) variables and aboveground biomass (AGB) or coarse wood productivity (CWP) in the two forests. Leaf K related positively to tree biomass in the logged-over forest. Leaf N and P were significantly and positively related to tree productivity in the old-growth forest and logged-over forest. AGB and CWP were mostly explained by the structural variables. The shape and magnitude of the relationships between tree species richness and AGB or CWP differed between the two forests. In addition, I found that leaf area index, mean tree diameter and height were similar between the two forests, but stand density and basal area were higher in the logged-over forest than in the old-growth forest. Total biomass and annual NPP were comparable in both forests, but there was a shift in NPP allocation between wood and fine roots. I conclude that the forest structure, biomass and productivity of the logged-over forest have largely recovered, but the legacy of logging still persists, which is reflected in differences in functional traits and allocation patterns.

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Incorporating stand-health metrics into monitoring the effects of soil disturbance during logging on long-term forest productivity (2016)

Stand volumes at rotation are usually predicted from models based on tree growth, assuming that fast-growing trees are, and will remain, healthy. However, greater-than-expected disease occurrence on dominant trees has been reported in regenerating forests in British Columbia (BC), suggesting that forest-productivity monitoring should include health measurements. In this thesis, I assess growth and health of lodgepole pine at six installations of the Long-Term Soil Productivity (LTSP) project 15 to 20 years after soil-disturbance treatments (organic-matter removal and soil compaction). To determine treatment effects on forest health, 5400 lodgepole pine seedlings at six sites were examined for vigour and pest occurrence. Treatment effects differed among sites, suggesting that the effects of the soil-disturbance treatments on forest health are context-dependent. Larger trees generally had higher frequency of disease, contradicting the assumption that fast-growing trees are healthy. Spectral-reflectance indices of greenness calculated from aerial images correlated with ground-based measures of tree vigour and foliar disease, indicating a role for remote-sensing techniques in forest health monitoring. Topsoil-nutrient content was reduced in the forest-floor removal treatment plots, with foliar phosphorus and potassium concentrations (%) being reduced in the three older sites in the sub-boreal spruce zone. The forest-floor removal treatment was also associated with lower abundance of ectomycorrhizae, but greater abundance Suillus sp., a fungus that is associated with nitrogen-fixing diazatrophic bacteria. The main predictive growth-and-yield model used in BC (called TASS with the interface TIPSY), underestimated tree height (m) but overestimated stand density (stems/ha) at the six sites, suggesting greater-than-predicted tree mortality. Monitoring forest health in conjunction with tree growth after free-to-grow standards are met is recommended for more accurate management of long-term forest productivity.

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Relationships among soil carbon, climate, and vegetation in forests of British Columbia (2014)

No abstract available.

Relationships between cyanolichen communities and nutrient cycling in sub-boreal spruce forests (2010)

Cyanolichens (lichens with cyanobacterial symbionts) form a distinct assemblage of epiphytes strongly associated with humid microclimatic conditions in inland British Columbia. Disparate abundance patterns in sub-boreal forests are examined in relation to the influence of overstorey tree species. A comparison of lichens on conifer saplings beneath five overstorey tree species revealed that saplings beneath Populus support a disproportionately abundant and species-rich community of cyanolichens. Cyanolichens also grew more rapidly and had lower rates of mortality beneath Populus than beneath conifer overstorey trees. That cyanolichens were observed beneath Populus in stands that were otherwise climatically unsuitable suggests that Populus facilitates cyanolichen communities by providing a factor that compensates for sub-optimal conditions. Chemical analyses of throughfall precipitation from beneath Populus, Picea, Abies, Pseudotsuga and Betula failed to explain the variation in lichen community structure. However, glucose-rich nectar, exuded from extrafloral nectaries on Populus leaves, may instead be supporting cyanolichen communities. The nectar accumulates during dry periods, is washed off during subsequent rain events, and may be intercepted and metabolized by cyanolichens on conifer saplings beneath mature Populus canopies. C-flux measurements and phospholipid fatty-acid analyses with experimental applications of ¹³C₆-labelled glucose revealed a strong physiological response to glucose and a rapid incorporation of exogenous-¹³C into cyanolichen fatty-acid tissues. Field evidence further supports this hypothesis with higher rates of cyanolichen establishment observed on Picea branches under treatment of 2% glucose solution compared to water. The exogenous C may enable cyanolichens to become established in regions that are otherwise too dry to support them by providing a source of C despite drought-induced inactivity of the cyanobacterial partner. The abundant communities of nitrogen-fixing cyanolichens in wet, mature forests and beneath Populus are important to ecosystem function. The contribution of cyanolichens to N-cycling is calculated at sites with varying lichen abundances from measured rates of lichen litter deposition, decomposition and nutrient release. Cyanolichen litter biomass represents up to 11.5% of the total N-input from aboveground litterfall and is estimated to release 2.1 kg N ha⁻¹ yr⁻¹ of newly-fixed N that would otherwise be unavailable in these mature sub-boreal forests.

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The effects of excessive moisture on soil carbon and nitrogen mineralization and forest productivity (2010)

Conifers of regenerating cedar-hemlock (CH) forests exhibit slow growth and nutrient deficiencies (N and P), which are not observed on adjacent cutovers of hemlock-amabilis fir (HA) forests. I test the theory that excessive moisture and resulting low oxygen availability in CH sites create the low N supply and poor growth in these ecosystems. A field experiment determined: 1) whether CH and HA forests differ in soil moisture and aeration, 2) whether decomposition rate and soil C stores differ in CH and HA forests, 3) whether composition of plant communities are related to soil moisture and aeration, and 4) the impact of harvesting CH and HA forests on moisture and aeration conditions. A laboratory experiment investigated the effects of moisture levels, from field capacity to saturation level, on C and N mineralization rates. Lastly, a field trial was carried out to assess drainage as a potential forest management solution in wetland forests by comparing C dynamics in drained and un-drained sites. As hypothesized, CH forests were wetter, less aerated, had shallower aerated depth and higher frequency of anaerobic conditions compared with HA forests. Composition of plant species was related to soil moisture and aeration, however plant diversity was not. Soil aeration was the most important factor, explaining 25% of the variability of species within plant communities. Compared with HA forests with well-aerated soils, soils in HA clearcuts were anaerobic, had slower decomposition rate and shallower rooting depth. Microbial biomass, C mineralization and the soluble inorganic N: soluble organic N (SIN:SON) ratio all declined under water-saturated conditions. Concentrations of SIN increased with increasing moisture in HA soils; whereas in CH humus and soil, the SIN pool was small and decreased with increasing moisture. The results indicate that the low N availability on CH sites results from synergistic effects of litter quality and greater frequency of waterlogging. Drainage could be a useful silvicultural practice for improving the productivity of cedar-swamp ecosystems without stimulating loss of soil C, provided that redox levels are maintained at less than +300 mV, at which level oxygen is sufficient for plant growth but not for aerobic microbial decomposition.

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Effects of nurse tree species on growth environment and physiology of underplanted Toona ciliata Roemer in subtropical Argentinean plantations (2009)

Toona ciliata Roem. plantations require a nurse-tree overstorey to minimize damage from drought and frost in north-eastern Argentina. Nurse-species vary in their facilitative and competitive abilities, thus influencing trade-offs among T. ciliata establishment success, stem quality and productivity, and ultimately stand revenues. The first objective was to quantify the influence of nurse species (G. robusta A. Cunn., Pinus elliottii Englm. x Pinus caribaea Morelet, P. taeda L.) and thinning density on mortality, stem morphology and growth of under-planted T. ciliata. Trade-offs among performance traits were considered in developing recommendations for nurse species selection and density management. The second objective was to examine interspecific interaction mechanisms by determining the effects of nurse species and thinning intensities on light, soil water and nutrient availability to T. ciliata. The final objective was to link T. ciliata establishment success and early growth to soil water availability, by calibrating the two-dimensional forest hydrology model, ForWaDy. To develop a stand management tool for guiding establishment of T. ciliata plantations it was found that T. ciliata responded more to nurse species identity than density. G. robusta was less competitive with T. ciliata for soil nutrients and soil water than either of the pine species: P. elliottii x P. caribaea was an strong competitor for water while P. taeda was a strong competitor for nutrients. G. robusta, by contrast, increased water and phosphorus availability to T. ciliata. Density effects varied with nurse species and performance traits. ForWaDy had good predictive capability for early T. ciliata performance, and was especially discriminatory among nurse species effects. This study shows that nurse species and thinning effects depend on management objectives, but that nurse species choice can be more important than thinning for increasing early T. ciliata performance. Future research employing a greater range of overstorey species, thinning densities, tree ages and environmental conditions will improve predictions of mixed stand productivity under a broader range of conditions. The study contributes to a better understanding of competitive and facilitative interactions in nurse tree plantations and emphasize the need for long-term empirical and modeling studies of mixed species stand dynamics.

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Functional and compositional responses of microorganisms to reclamation of surface-mined boreal forest soils (2009)

Over the last four decades, surface mining of oil sands in the boreal forest of western Canada has created large areas of disturbed land. The current regulatory framework requires that derelict land be reclaimed to pre-disturbance conditions. This has prompted the need to assess the effectiveness of reclamation, which relies on the use of salvaged materials (e.g., tailings sand and overburden), on key ecosystem components such as soil microorganisms. In this thesis, I examined landscape-scale changes in soil microbial community composition and function in response to different reclamation amendments and in natural sites comprising a regional environmental gradient. Using molecular fingerprinting (phospholipid fatty acids and denaturing gradient gel electrophoresis) and phylogenetic analyses of 16S rRNA genes, I found that microbial communities in natural soils differed from those of reclaimed soils. This dissimilarity was driven by increasing abundances of fungal and actinomycetal biomarkers in natural soils. After 30 years, however, reclamation did not place soil microbial communities on a predictable recovery path. The composition of microorganisms was particularly affected by tailings sand-based amendments. Functional potential, determined with assays targeting the activities of enzymes responsible for macromolecule degradation, was mainly impacted by prescriptions containing overburden. Variance partitioning analyses indicated that microbial responses to reclamation were partially determined by vegetation cover development, soil pH, and the fungal-to-bacterial biomass ratio. pH effects on bacterial composition were partly driven by the abundance of Acidobacteria. The relative abundances of several bacterial biomarkers covaried with individual enzyme activities, suggesting certain sub-sets of the microbial communities were functionally relevant. I tested this idea experimentally by assembling a laboratory-scale reciprocal transplant of microorganisms sourced from two distinct peat types. My main finding was that differences in initial microbial community composition were functionally significant for lignin depolymerization, while the activities of nutrient-acquiring enzymes (a more ubiquitous function) were mostly influenced by peat type. Overall, my results indicate that the responses of abundant microbial populations to reclamation were largely accounted for by abiotic properties of reclamation materials and, indirectly, by the effects of reclamation on plant growth.

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Master's Student Supervision (2010-2017)
How well do plant functional traits and leaf-litter traits predict rates of litter decomposition? (2016)

Foliar functional traits have been shown to strongly co-vary with each other and with rates of litter decomposition, demonstrating an “after-life effect” of foliar traits on ecosystem processes. Leaf-litter traits are often used to indicate substrate quality in decomposition studies. Chemical traits have been studied more extensively in the context of decomposition than physical traits such as specific leaf area (SLA) and leaf toughness, which impart information on litter structure and decomposer access. I investigated relationships among foliar and litter traits, and between traits and early mass-loss, in 14 plant species native to British Columbia. Both physical and chemical traits were measured in foliage and leaf litter of each species. Foliar traits novel to this kind of study include cuticle thickness and distance to lumen (DTL); novel litter traits include leaching loss and water uptake after 2 and 24 hours. Decomposition, as net proportion of mass lost over time, was measured in litterbags installed in a temperate rain forest at the University of British Columbia Farm in Vancouver. Mass loss was divided into two phases: Phase I from 0 to 3 months, and Phase II from 3 to 12 months. Foliar traits co-varied in ways predicted by the leaf economics spectrum hypothesis, and litter traits similarly co-varied. Trait-based relationships among species differed when using foliar traits and using litter traits, suggesting that the same traits measured in foliar and litter impart different meaning in the context of decomposition. Phase I was best predicted by leaching loss and litter traits, suggesting that leaching dominates Phase I, and Phase II was best predicted by foliar functional traits such as leaf dry matter content and nitrogen that relate to relative mesophyll abundance, suggesting that decomposer activity dominates Phase II. Physical traits predicted mass loss as well or better than chemical traits, and using both types of traits in correlative studies may provide insights into the processes that underlie litter decomposition.

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Soil carbon stabilization under three reclaimed vegetation types in the Alberta oil sands (2015)

Prior to oil sands extraction, mineral soil from local boreal forest is salvaged and stored, together with additional peat obtained from local peatlands, for future reclamation use. The ability of reclaimed soils to stabilize carbon is an important indicator of soil functioning and successful reclamation. The objective of this research was to compare total soil carbon and the distribution of carbon in chemically and physically protected pools between three reclaimed vegetation treatments, and naturally fire-disturbed boreal forest sites. Twenty sites that were reclaimed or disturbed 20 – 40 years ago were chosen, and the top 10 cm of mineral soil was sampled. Density and size fractionation was used to separate soil organic carbon (SOC) into unprotected light fraction C, physically protected C, and chemically protected C. Aggregate size distribution, microbial biomass C, root biomass, and exchangeable cation concentrations were also measured. Reclaimed sites had three times more total SOC than natural sites and similar or greater SOC in physically and chemically protected pools. However, reclaimed sites were also estimated to have reached carbon saturation in chemically protected C pools, and half of the total SOC on average was unprotected, compared to 9 % unprotected C at natural sites. Accumulation of SOC in unprotected pools and C saturation in chemically protected pools at reclaimed sites suggest that further incorporation of SOC into chemically protected pools may be limited, possibly by soil texture (
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Formica integroides of Swakum Mountain : a qualitative and quantitative assessment and narrative of Formica mounding behaviors influencing litter decomposition in a dry, interior Douglas-fir forest in British Columbia (2014)

Formica spp. mound construction is fundamental to northern forests as their activities govern and shape forest floor dynamics and litter decomposition. The interior Douglas-fir forest at Swakum Mountain contains a super colony of Formica integroides whose presence and monolithic structures dramatically demonstrate their impact on the landscape. Through a series of observations, natural and controlled experiments I examine the effects of Formica mounding on litter decomposition. The basic measurements of temperature, moisture, evolved CO2, and mass loss reveal that Formica mounds buffer litter decomposition as Douglas-fir needles are carefully stacked, stockpiled, and assembled into thatch, where at the depth of ~ 8 cm thatch mass loss minimizes and begins to stabilize. The function of Formica mounding further exacerbates the prevailing arid conditions endemic to this forest type. Cotrufo's Microbial Efficiency-Matrix Stabilization (MEMS) framework sets forth a conceptual model where labile plant constituents are efficiently utilized by microbes and stabilized into soil organic matter (SOM). I integrate my findings within this framework while conceptualizing aspects of complexity theory as potential ecological drivers contributing to soil organic matter formation relating to Formica mounds. Through natural and controlled experiments my overall objective is to describe and explain litter decomposition involving Formica spp. within an interior Douglas-fir forest. I have included descriptive observations, sketches, and photographs involving the forest floor and Formica spp. behaviors and ecology to provide a holistic perspective describing litter decomposition within this local forest type. The framework of scientific methodology combined with a novel approach, provides further empirical and qualitative support for the findings of my research.

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Organic matter accumulation in reclaimed soils beneath different vegetation types in the Athabasca oil sands (2014)

As of 2008, 60,234 ha of boreal forest had been disturbed by strip mining in the Athabasca Oil Sands in northern Alberta. Reclamation of this area is proceeding concurrently with mine operations, and 6,687 ha are considered to be reclaimed by industry (Hrudey et al. 2010). My study focused on understanding how vegetation planting prescriptions affect soil organic matter (SOM) accumulation in the mineral section of peat/mineral mix (PMM) reclaimed soils. SOM concentration is important in reclaimed soils, as it increases soil fertility and is directly related to site productivity (Farnden et al. 2013). Reclaimed sites which are not particularly wet or dry are planted with either deciduous or spruce trees, and in some cases, grasses. I assessed SOM accumulation, and its source, in different vegetation treatments. Three research questions were developed: (1) Does organic matter content of mineral soil differ between reclaimed and natural soils? (2) What are the dominant sources of organic matter accumulation in the mineral soil of each reclamation treatment? (3) Has SOM accumulated quickest in soils under replanted deciduous (Populus tremuloides/balsamifera), spruce (Picea glauca) or grasses? Seventeen sites were studied, 4 each of the reclaimed deciduous and grassland, 5 reclaimed spruce, and 4 natural forest analogues. At each site, vegetation, forest floor and soils were surveyed. In the laboratory, soil samples from four depths at each site were tested for several properties, including organic matter concentration. The SOM content of all reclaimed soils was significantly higher than the natural analogues. The mechanisms by which SOM accumulates differed for each vegetation treatment: dissolved organic matter and macrofaunal activity were the dominant sources of SOM in deciduous sites; root litter and macrofaunal activity were the dominant sources of SOM in the grassland sites; there was no sign of SOM accumulation at the spruce sites. SOM accumulated quickest in the deciduous sites, intermediate in the grassland sites, and not at all in the spruce sites.

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Productivity analysis of silvicultural treatments in cedar and hemlock stands on northern Vancouver Island (2012)

Due to many favourable characteristics such as a moist and mild climate year round, the absence of fire or a major insect infestation and disease, the coastal coniferous forests of northern Vancouver Island are among the most productive forests in British Columbia. However, the productivity rates can vary in a mosaic pattern of two very distinctive forest types: low-productivity “CH” and medium-productivity “HA”. In 1987-88 a trial was established to analyse growth effects of fertilization on western red cedar (Thuja plicata Donn ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) at these two different sites. Previous projects measured the height and the DBH after 10 and 15 growing seasons, and have been recently re-measured again after 22 years since establishment. Fertilizer was applied three times after planting; stand density was established at: 500, 1500 and 2500 stems/ha. Fertilization significantly increased the height and volume of both species at all treatment. Depending on the site fertility and treatment used, the stand volume of fertilized red cedar increased from 123% to 351% and fertilized hemlock volume increased from 106% to 2190% compared to the non-fertilized counterparts. In most cases, higher densities had much greater volume per hectare than lower density stands; however, density caused a significant decrease in the average height of both species at CH sites. Biomass and carbon content were also estimated in this study. Results indicated a positive growth response of total biomass generated by fertilization. CH sites have shown the best increment response to fertilization; however, averages were still low if compared to HA sites. Overall, the best treatments were found to be high density fertilized hemlock stands on HA sites. This treatment not only had the greatest height, volume and biomass, but was also the most efficient for C capture. After 22 growing seasons, the results of this research reinforces the idea that fertilization is a reliable and effective tool to increase nutrient availability and productivity of these forests; it suggests that the focus of silvicultural treatments such as fertilization and increased stand density should be directed mostly towards the more productive HA sites.

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The effects of millipedes (Harpaphe haydeniana) on microbial decomposition of leaf litter (2012)

Most estimates of litter decomposition rates do not account well for the effects of soil macrofauna, and so are suspect in ecosystems in which litter-transforming soil fauna are abundant. In coastal rainforests, millipedes consume substantial amounts of leaf litter, most of which is egested as faecal pellets. Little is known about the fate of this material, which hinders estimation of realistic rates of litter decomposition in these ecosystems. In this study, I assess the influence of feeding by the millipede (Harpaphe haydeniana) on decomposition of leaf litter by comparing rates of CO₂ release during laboratory incubation from leaf litter which has been ingested by millipedes and transformed into faecal pellets with that from litter which has not been ingested by millipedes. Changes in litter microbial communities as a consequence of millipede ingestion are assessed by comparing the PLFA profiles of faeces and uningested litter during incubation. Rates of CO₂ release from faeces and litter were similar. CO₂ release was higher in maple litter than Douglas-fir litter, and this difference persisted in the faeces from litter that millipedes fed on. Differences in bacterial abundance between litter types were also retained during millipede gut passage. Grinding of litter increased CO₂ release, as did grinding of faeces, indicating that structure of litter and millipedes’ faecal pellets may restrict microbial access and thus decrease the decomposition rates. Microbial activity and abundance did not differ between leaf litter and faeces incubated alone vs together.

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Thinning and prescribed fire for ecosystem restoration in Rocky Mountain forests of British Columbia : changes in physical, chemical and biological properties of forest floors and soil (2011)

Prevention of uncontrolled wildfire and restoration of Rocky Mountain forests can be accomplished through ecosystem restoration practices such as thinning followed by prescribed fire. The objective of this study is to determine how much thinned fuel can be left on the ground without causing fire temperatures high enough to impair soil physical, chemical and biological properties. I assess the effects of different fuel loadings on soil properties (forest floor depth, soil pH, carbon and nutrient levels, and soil bacteria and fungal communities) during the first year after fire and explore relationships among fuel loadings, fire temperatures and indicators of soil health. Five fuel management treatments were assessed: large piles, small piles, areas of cut-and-leave, deep litter and an unburned control. In all burned treatments, fuel loadings were greatly reduced and maximum temperatures at the forest floor surface ranged from 60 to 850°C. Temperatures were over 300°C for over 3 hours in the large-pile treatment but were lower and of shorter duration in the small-pile and cut-and-leave treatments. The deep-litter treatment had temperatures above 200°C for over 2 hours and complete combustion of the forest floor occurred. The low moisture content and resulting consumption of the forest floor in the deep-litter treatment resulted in the largest negative impacts on soil chemical and microbiological properties, while few significant differences were evident among the other treatments. Higher nitrate availability and significant increases in pH were found in the forest floors of burned plots and in the mineral soil of the deep-litter treatment. Microbial abundance did not recover to pre-fire levels in any burned treatments after one year, which may be attributed to the persistence of significant increases in pH.

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Nitrous oxide emissions, nutrient dynamics and nitrifier communities following fertilization of western hemlock, lodgepole pine and Douglas-fir forests (2010)

I explored effects of fertilization on soil N₂O fluxes and underlying soil nutrients using short-term (up to 7 mo.) simulated operational fertilization with urea-nitrogen or nitrogen, phosphorus, potassium, and micronutrients (a N + micronutrients mix) in lodgepole pine, western hemlock, and Douglas-fir forests in British Columbia. The effect on the structure of ammonia- oxidizing bacterial (AOB) communities in the three forest ecosystems was also studied using polymerase chain reaction coupled with denaturing gradient gel electrophoresis (PCR-DGGE). Urea appeared to be rapidly mineralized to ammonium, and nitrification (relative to controls) was only observed in the lodgepole pine site and represented only 0.5% of added nitrogen. Across all sites and treatments, soils were as likely to consume as emit nitrous oxide, and among treatment replicates, rates were never significantly different from zero, with the exception of one efflux of 1.5 μg m-² hr-¹ on the warmest day in the study. I conclude from this pilot study that in acidic, unpolluted (with regard to nitrogen deposition) upland conifer forest soils in western Canada fertilized once or infrequently with urea or ammonium or a combination of nutrients, soil greenhouse-gas flux dynamics are generally not altered over the short-term, with soils remaining neutral with regards to flux of nitrous oxide.

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