Sean C Thomas

University of Toronto | U of T · Faculty of Forestry

Pyrolyzed organic matter, or biochar, generally increases the growth of established plants; in some cases, biochar also promotes seed germination in agricultural species, but comparable effects on tree species have received little attention. Potential biochar effects on seed germination and early seedling development were examined in a field experi...

Green roofs are exposed to high winds and harsh environmental conditions that can degrade vegetation and erode substrate material, with negative consequences to ecosystem services. Biochar has been promoted as an effective substrate additive to enhance plant performance, but unprocessed biochars are susceptible to wind and water erosion. Applicatio...

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions. Climate-driven vegetation models typically predict that this tropical forest ‘carbon sink’ will continue for decades. Here we assess trends in the c...

Green roofs have been widely promoted as a means to enhance ecosystem services in cities, but roofs present a harsh growing environment for plants. Biochar is suggested to be a highly beneficial substrate additive for green roof systems due to its low weight, high nutrient and water retention capacity, and recalcitrance. However, biochar is suscept...

Methane (CH4) accounts for 25–30% of anthropogenic climate forcing and is an attractive focus for climate mitigation due to its short half-life in the atmosphere, and the fact that CH4 emissions are unintended and often represent economic inefficiencies. Although forests are globally important both as sources and sinks for CH4, recommendations for...

Co-management is a promising forest governance strategy that integrates local communities' traditional rights and forest dependencies while aiming to improve forest cover and ecosystem health. Bangladesh, facing high deforestation rates and limited per capita forest area, has implemented co-management initiatives since 2003 to restore forest cover...

Seedling establishment is often a critical bottleneck in the revegetation of mine tailings and similar substrates. Biochar and deactivated yeast are potential sustainable materials that could be used in this context as seed coatings to aid in seedling establishment. We conducted a greenhouse study on biochar and deactivated yeast use as seed coatin...

Abstract: Methane (CH4) ranks as the second most significant greenhouse gas after carbon dioxide, contributing substantially ot global warming through its net radiative forcing. Over the past century, atmospheric CH4 concentrations have surged 250%, exacerbating climate change. The Intergovernmental Panel on Climate Change has recommended targeted...

Methane (CH₄) and nitrous oxide (N₂O) are critical biogenic greenhouse gases (GHGs) with global warming potentials substantially greater than that of carbon dioxide (CO₂). The exchange of these gases in tropical forests, particularly via foliar processes, remains poorly understood. We quantified foliar CH₄ and N₂O fluxes among tropical tree species...

Co-management is increasingly recognized as an effective approach of forest governance while recognizing local people's forest dependency and traditional rights. Moreover, co-management is expected to positively impact forest cover and ecosystem health. Bangladesh, facing a rapid decline in forest cover, has one of the lowest per capita forest area...

Seedling establishment is often a critical bottleneck to revegetation of mine tailings and similar substrates with a low capacity to retain water and plant nutrients. Biochar and deactivated yeast are potential sustainable, low-cost materials with high nutrient- and water-holding capacity that could be used in this context as seed coatings to aid i...

Biochar has emerged as a promising amendment for agricultural lands characterized by low fertility and elevated levels of potentially toxic elements (PTEs). Arsenic (As), a highly toxic trace metalloid, has the potential to contaminate food chains, with serious effects on human health. However, the efficacy of biochar in alleviating PTE toxicity in...

Pyrolyzed organic matter, commonly referred to as biochar, generally has positive effects on plant growth and can enhance early seedling development. Biochar-based seed coatings may thus be beneficial, specifically under adverse soil conditions such as high soil salinity. Using a series of lab and greenhouse experiments, we evaluated germination an...

Use of waste wood biomass for bioenergy produces wood ash as a by-product; this ash is typically landfilled, but can potentially play an important role in soil improvement and forest restoration. In particular, high-carbon wood ash biochar (HCWAB) could supply nutrients, improve substrate water-holding capacity and pH, and emulate the ecosystem ben...

Although addition of pyrolyzed organic materials (biochars) to soil generally results in increased growth and physiological performance of plants, neutral and negative responses have also commonly been detected. Toxicity of organic compounds generated during pyrolysis, sorbed by biochars, and then released into the soil solution, has been implicate...

Pyrolyzed organic matter – commonly referred to as biochar – generally has positive effects on plant growth and can enhance early seedling development. Biochar-based seed coatings may thus be beneficial, specifically under adverse soil conditions such as high soil salinity. We evaluated germination and early plant development in radish (Raphinus sa...

Urban areas are at the forefront of climate change impacts, with cities being responsible for ~75% of global GHG emissions. Methane, a GHG 80 times more potent than CO2, is significantly emitted from a range of urban sources including biogenic (e.g., landfills, drainage channels, and wetlands) and abiogenic (e.g., transportation, compressor station...

Background: Urban environments are increasingly recognized as both significant contributors to and primary victims of climate change. Buildings in urban settings are responsible for approximately 33% of global greenhouse gas emissions, while cities themselves are often situated on fertile land with high carbon sequestration potential. To mitigate t...

Urban areas are at the forefront of climate change impacts, with cities being responsible for~75% of global GHG emissions. Methane, a GHG 80 times more potent than CO 2 , is significantly emitted from a range of urban sources including biogenic (e.g., landfills, drainage channels, and wetlands) and abiogenic (e.g., transportation, compressor statio...

Comprising 45% of global forest cover, tropical forests are pivotal in the GHG budgets. Emerging research highlights the significance of tropical trees as CH₄ sources, yet tree-foliage emissions have been minimally investigated. Moreover, the N₂O fluxes from tropical tree foliage remain almost completely unexamined. Objectives: This study presents...

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we inve...

Allelopathy, or chemically mediated interference between co-occurring species, is present in more than half of invasive plant species globally and plays an important role in invasive species dominance in native plant communities. Allelopathy commonly increases the competitive advantage of invasive plants and their ability to displace native species...

Urbanization has degraded ecosystem services on a global scale, and cities are vulnerable to long-term stresses and risks exacerbated by climate change. Green infrastructure (GI) has been increasingly implemented in cities to improve ecosystem functions and enhance city resilience, yet GI degradation or failure is common. Biochar has been recently...

Urbanization has degraded ecosystem services on a global scale, and cities are vulnerable to long-term stresses and risks exacerbated by climate change. Green infrastructure (GI) has been increasingly implemented in cities to improve ecosystem functions and enhance city resilience, yet GI degradation or failure is common. Biochar has been recently...

Canadian cities broadly promote green roofs as a sustainable solution that mitigates urban flooding and combined sewage overflows. This study assessed the performance of eight extensive green roof testbeds for rainwater retention, discharge intensity, and vegetation growth in a highly urbanized area of Toronto, Canada, over a complete growing seaso...

Declining tree health status due to pollutant impacts and nutrient imbalance is widespread in urban forests; however, chemical fertilizer use is increasingly avoided to reduce eutrophication impacts. Biochar (pyrolyzed organic waste) has been advocated as an alternative soil amendment, but biochar alone generally reduces plant N availability. The c...

There is a long-standing, even ancient, belief in Western thought that forests, particularly unmanaged forests relatively free from obvious human impacts, are never-changing; this is the connotation of the German word “urwald” or “original forest” that influenced early thinking on forests from the origins of the emerging scientific disciplines of f...

Unique properties of biochar render it appealing for revegetating and decontaminating historic, barren, and chemically complex mine tailings. Bottom ash from bioenergy facilities can contain high levels of charcoal residue, and thus qualify as a type of biochar; the wide availability of this material at low cost makes it of particular interest in t...

Pyrolyzed waste biomass, or biochar, has been suggested as a means to increase plant growth and mitigate soil salinization, which is a widespread agricultural issue and can reach extreme levels in urban soils impacted by de-icing salts. Soil mixing is enhanced by reduced biochar particle size; however, biochar properties vary with particle size, an...

Pyrolyzed waste biomass, or biochar, has been suggested as a means to increase plant growth and to mitigate soil salinization, which is a widespread agricultural issue and can reach extreme levels in urban soils impacted by de-icing salts. Soil mixing is enhanced by reduced biochar particle size; however, biochar properties vary with particle size...

Many invasive and some native tree species in North America exhibit strong allelopathic effects that may contribute to their local dominance. Pyrogenic carbon (PyC; including soot, charcoal, and black carbon) is produced by the incomplete combustion of organic matter and is widespread in forest soils. Many forms of PyC have sorptive properties that...

Pyrolyzed organic waste, also known as biochar, is commonly used as a soil amendment and has recently been promoted to remediate metal mine tailings by increasing substrate pH, enhancing water and nutrient retention, and reducing bioavailability of toxic metals. Bottom ash from bioenergy facilities can contain high levels of charcoal residue, and t...

Biochar, due to its favourable physiochemical properties, has been promoted as an ideal substrate additive on green roofs, with potential benefits to hydrological function. However, biochar is susceptible to water erosion, which may result in biochar loss and water pollution. The use of granulated biochars or biochars in large particle sizes could...

Tree stems have been identified as globally significant methane (CH4) sources; however, little information exists on emissions from tree wounds and branches. CH4 emissions can occur from the decomposition of anaerobic heartwood, which is also associated with wounds; CH4 may also be transported through the transpiration stream and emitted from branc...

Skid trails and landings are features within managed forest landscapes where soils are moderately to extremely disturbed by forestry vehicles. They have been found to exhibit reduced methane (CH4) oxidation or CH4 emissions six months to a year after a harvest has ended, but little is known about when these changes begin to occur (either during or...

Woody tissue carbon (C) concentration is a key wood trait necessary for accurately estimating forest C stocks and fluxes, which also varies widely across species and biomes. However, coarse approximations of woody tissue C (e.g., 50%) remain commonplace in forest C estimation and reporting protocols, despite leading to substantial errors in forest...

The use of biochar with N-fixing species has been shown to enhance productivity of agricultural systems, both in N-fixing crops, as well as in mixed-species systems. Here we investigate the potential for the use of a granulated mixed conifer biochar and a sugar maple biochar in combination with N-fixing companion plants in an urban forestry context...

Beech Bark Disease (BBD) is a devastating threat to American beech (Fagus grandifolia), spreading through eastern mixed deciduous forests of North America at unprecedented rates. Understanding how and why some beech trees escape severe BBD effects is important; however, the biotic and abiotic factors that underpin the progression of BBD within unma...

Green roof systems have been increasingly implemented to enhance vegetation cover and associated ecosystem services in urban spaces, with primary goals being the reduction of peak surface runoff, enhanced water quality, and mitigation of urban heat island effects. Recently, green roofs have also received attention as a means to enhance carbon seque...

Previous attempts to quantify methane (CH4) fluxes from tree foliage have yielded ambiguous results, and very few studies have measured in situ foliar CH4 fluxes, particularly in upland sites. Here we quantify CH4 fluxes from tree foliage in upland and lowland temperate forests in central Ontario, Canada. Foliar CH4, carbon dioxide, and water vapor...

Many tropical invasive species have allelopathic effects that contribute to their success in native plant communities. Pyrolyzed biomass (“biochar”) can sorb toxic compounds, including allelochemicals produced by invasive plants, potentially reducing their inhibitory effects on native species. Strawberry guava (Psidium cattleianum) is among the mos...

Many invasive species show allelopathic effects that contribute to competitive impacts on native vegetation for which few control measures exist. We investigated the potential for pyrolized organic material used as a soil amendment (“biochar”) to sorb allelochemicals and mitigate allelopathic effects on seed germination and early seedling developme...

Many tropical invasive species have allelopathic effects that contribute to their success in native plant communities. Pyrolyzed biomass (“biochar”) can sorb toxic compounds, including allelochemicals produced by invasive plants, potentially reducing their inhibitory effects on native species. Strawberry guava (Psidium cattleianum) is among the mos...

Aerial-photo interpreted inventories of forest resources, including tree species composition, are valuable in forest resource management, but are expensive to create and can be relatively inaccurate. Because of differences among tree species in their spectral properties and seasonal phenologies, it might be possible to improve such forest resource...

Temperate forest soils are an important sink for methane (CH4); however, disturbance through forest management and the creation of skid trails may significantly decrease soil’s ability to uptake CH4 or in some cases cause CH4 emissions. Skid trails might also be expected to show reductions in carbon dioxide (CO2) flux due to anaerobic conditions an...

Tropical forests store 40-50% of terrestrial vegetation carbon. Spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests. Because of climatic and soil changes with increasing elevation, AGC stocks are lower in tropical montane compared to lowland forests. Here we ass...

Tropical forests store 40–50 per cent of terrestrial vegetation carbon1. However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests2. Owing to climatic and soil changes with increasing elevation3, AGC stocks are lower in tropical montane forests compared with...

A number of processes for post-production treatment of "raw" biochars, including leaching, aeration, grinding or sieving to reduce particle size, and chemical or steam activation, have been suggested as means to enhance biochar effectiveness in agriculture, forestry, and environmental restoration. Here, I review studies on post-production processin...

Log landings are areas within managed forests used to process and store felled trees prior to transport. Through their construction and use soil is removed or redistributed, compacted, and organic matter contents may be increased by incorporation of wood fragments. The effects of these changes to soil properties on methane (CH4) flux are unclear an...

Patterns of structural change associated with monodominant tropical forest complexes have remained enigmatic for decades. Here, we extend previous efforts in presenting a longitudinal, local-scale analysis of forest dynamics in central Africa. Using four 10-ha census plots measured across three time periods (959,312 stems ≥1 cm DBH), we analyzed ch...

Tropical forests are the most diverse and productive ecosystems on Earth. While better understanding of these forests is critical for our collective future, until quite recently efforts to measure and monitor them have been largely disconnected. Networking is essential to discover the answers to questions that transcend borders and the horizons of...

A key uncertainty in quantifying dead wood carbon (C) stocks—which comprise ~8% of total forest C pools globally—is a lack of accurate dead wood C fractions (CFs) that are employed to convert dead woody biomass into C. Most C estimation protocols utilize a default dead wood CF of 50%, but live tree studies suggest this value is an over-estimate. He...

For the first time the electrical conductivity of bamboo biographite-based material reported a ground-breaking milestone of 4.4 × 10⁴ (S/m). This reported conductivity by far exceeded all previous reported conductivity measurements obtained from renewable carbon. Controlled high-temperature thermal carbonization of biomass, notably Asian bamboo, at...

Soil CO2 efflux (FCO2) is a major component of the terrestrial carbon (C) cycle but challenges in explaining local variability hamper efforts to link broad-scale fluxes to their biotic drivers. Trees are the dominant C source for forest soils, so linking tree properties to FCO2 could open new avenues to study plant-soil feedbacks and facilitate sca...

Pyrogenic carbon (PyC) is a ubiquitous legacy of wildfire in terrestrial soils, yet how it affects the growth and function of regenerating plants has received little research attention. We examined responses to a natural gradient of PyC deposition 5 years following a severe fire in a northern boreal forest, based on measurements of growth (height,...

ForestGEO is a network of scientists and long-term forest dynamics plots (FDPs) spanning the Earth's major forest types. ForestGEO's mission is to advance understanding of the diversity and dynamics of forests and to strengthen global capacity for forest science research. ForestGEO is unique among forest plot networks in its large-scale plot dimens...

Soil CO2 efflux (FCO2) plays a dominant role in the terrestrial carbon (C) cycle but interpreting constraints on local observations is impeded by challenges in disentangling belowground CO2 sources. Trees contribute most C to forest soils, so linking aboveground properties to FCO2 could open new avenues to study plant-soil feedbacks and facilitate...

Biochar chemistry varies with feedstock and pyrolysis parameters: fast pyrolysis may not provide sufficient time for volatile compounds – some phytotoxic – to escape from biochar particles. Lettuce and radish seeds were treated with biochar leachate derived from 100 slow pyrolysis biochars (20 wood species, each pyrolyzed at 300–700 oC for 60 min),...

A body of emerging research shows the promise of charcoal soil amendments ("biochars") in restoring fertility in degraded agricultural and forest soils. "Sustainable biochars" derived from locally produced waste biomass and produced near the application site are of particular interest. We tested the effects of surface applications of wood-derived b...

Aims Changes in root functional traits reveal important nutrient acquisition strategies, with well documented patterns in root trait expression within complex communities or along gradients of singular nutrients. In this field study, we investigate intra-root functional trait expression with six soil macro- and micro-nutrients in Theobroma cacao ag...

Alarming increases in tree mortality due to environmental change suggest that contributions of dead wood to global carbon (C) cycles are rapidly increasing 1-3, with dead wood C flux estimates already approximating total annual anthropogenic C emissions 4. Quantifying C in dead wood critically depends on accurate estimates of dead wood C fractions...

The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate contro...

The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate contro...

Urban trees provide natural shade and moderate human exposure to solar ultraviolet radiation. To date, most studies quantifying UV attenuation by urban tree canopies have taken place in Australia, with no studies in North America. Few studies have utilized sensors sensitive to UV-B radiation, although the shorter wavelengths are more important in d...