William Arthur Hoffmann

William Arthur Hoffmann
North Carolina State University | NCSU · Department of Plant and Microbial Biology

Ph.D.

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187
Publications
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Publications

Publications (187)
Article
Forest encroachment into savannas is a widespread phenomenon, the rate of which may depend on soil conditions, species composition, or changes in stand structure. As savanna specialist trees are replaced by generalist species, rates of stand development may increase. Because generalists can persist in forests, they are likely to grow more quickly a...
Article
Prior to European settlement the longleaf pine (Pinus palustris) ecosystem covered over 92 million hectares in the southeastern United States. Historically, fire was an important driver of species composition in the longleaf pine ecosystem, but fire exclusion since the early 20th century has led to the degradation of longleaf pine communities and h...
Article
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Key Message Frost-sensitive and frost-resistant Cerrado tree species differ in their morphological and physiological traits, which are linked with their resprout strategies and can affect their persistence under recurrent frost events. AbstractAlthough fire is the most common disturbance affecting neotropical savannas, frost events are locally comm...
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Fulltext at: https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2664.13994 1. Woody encroachment into grassy biomes is a global phenomenon, often resulting in a nearly complete turnover of species, with savanna specialists being replaced by forest‐adapted species. Understanding the mechanisms involved in this change is important fo...
Article
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Savanna tree communities occurring in confluence zones with other biomes likely experience different environmental pressures, resulting in shifts in the selection of individual traits, the combinations of such traits, and species composition. In seasonally dry fire-prone environments, plant survival is presumably associated with adaptive changes in...
Article
Under fire suppression, many tropical savannas transform into forests. Forest expansion entails changes in environmental variables and plant community structure. We hypothesized that forest expansion into savanna results in a shift in community‐weighted mean functional traits from stress tolerance to competitiveness, with generalist species having...
Article
The heat plume associated with fire has been hypothesized to cause sufficient water loss from trees to induce embolism and hydraulic failure. However, it is unclear whether the water transport path remains sufficiently intact during scorching or burning of foliage to sustain high water loss. We measured water uptake by branches of Magnolia grandifl...
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Global change has resulted in chronic shifts in fire regimes. Variability in the sensitivity of tree communities to multi-decadal changes in fire regimes is critical to anticipating shifts in ecosystem structure and function, yet remains poorly understood. Here, we address the overall effects of fire on tree communities and the factors controlling...
Article
Exotic grasses and high-nutrient availability are common factors that may limit recovery of herbaceous diversity in derived savannas, while tree encroachment is a threat to diversity in old-growth savannas. To understand the impacts of these factors on herbaceous communities, we studied the effect of nutrient addition, and the resulting increase in...
Article
Aim. In savannas, a grass dominated ground layer is key to ecosystem function via grass-fire feedbacks that maintain open ecosystems. With woody encroachment, tree density increases, thereby decreasing light in the ground layer and potentially altering ecosystem function. We investigated how light availability can filter individual grass species di...
Preprint
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Global change has shifted fire regimes, but the long-term consequences for ecosystems are uncertain because of variability in environmental conditions, fire types, and plant composition. We tested how fire-frequency manipulations of 16-64 years affect tree communities and traits using 374 plots from 29 sites on four continents. More frequently burn...
Article
1. Disentangling species strategies that confer resilience to natural disturbances is key to conserving and restoring savanna ecosystems. Fire is a recurrent disturbance in savannas, and savanna vegetation is highly adapted to and often dependent on fire. However, although the woody component of tropical savannas is well studied, we still do not un...
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Vegetation‐fire feedbacks are important for determining the distribution of forest and savanna. To understand how vegetation structure controls these feedbacks, we quantified flammability across gradients of tree density from grassland to forest in the Brazilian Cerrado. We experimentally burned 102 plots, for which we measured vegetation structure...
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Although savannas are fire-adapted ecosystems, prescribing fire for biodiversity conservation remains controversial at least in some regions where savannas occur. Faced with uncertainty, many decision makers and even scientists are still reluctant to prescribe fire for conservation purposes in fire-prone ecosystems, invoking the precautionary princ...
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Bastin et al .’s estimate (Reports, 5 July 2019, p. 76) that tree planting for climate change mitigation could sequester 205 gigatonnes of carbon is approximately five times too large. Their analysis inflated soil organic carbon gains, failed to safeguard against warming from trees at high latitudes and elevations, and considered afforestation of s...
Article
Bastin et al.’s estimate (Reports, 5 July 2019, p. 76) that tree planting for climate change mitigation could sequester 205 gigatonnes of carbon is approximately five times too large. Their analysis inflated soil organic carbon gains, failed to safeguard against warming from trees at high latitudes and elevations, and considered afforestation of sa...
Article
Fire controls tree cover in many savannas by suppressing saplings through repeated topkill and resprouting, causing a demographic bottleneck. Tree cover can increase dramatically if even a small fraction of saplings escape this fire trap, so modelling and management of savanna vegetation should account for occasional individuals that escape the fir...
Preprint
Full-text available
Global change impacts on the Earth System are typically evaluated using biome classifications based on trees and forests. However, during the Cenozoic, many terrestrial biomes were transformed through the displacement of trees and shrubs by grasses. While grasses comprise 3% of vascular plant species, they are responsible for more than 25% of terre...
Article
Global change impacts on the Earth System are typically evaluated using biome classifications based on trees and forests. However, during the Cenozoic, many terrestrial biomes were transformed through the displacement of trees and shrubs by grasses. While grasses comprise 3% of vascular plant species, they are responsible for more than 25% of terre...
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The original version of this article unfortunately contained a mistake. The Electronic supplementary material (ESM) was accompanying this article by mistake.
Article
Background: Fire has been reported to trigger the production of flowers and fruits in many fire-prone ecosystems around the world. However, for tropical savannas, little is known about the effects of fire on flower production at community and species scale, especially for the ground-layer. Aims: We assessed the role of fire as a trigger to short-te...
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1.The ability of vegetation to ameliorate or exacerbate environmental extremes can generate feedbacks that mediate the distribution of biomes. It has been suggested that feedbacks between vegetation and frost damage may be important for maintaining savanna, particularly at the edge of the tropics. 2.We quantified frost damage and air temperature ac...
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Roughly 3% of the Earth’s land surface burns annually, representing a critical exchange of energy and matter between the land and atmosphere via combustion. Fires range from slow smouldering peat fires, to low-intensity surface fires, to intense crown fires, depending on vegetation structure, fuel moisture, prevailing climate, and weather condition...
Article
Fire-promoting, open-canopy ecosystems are under threat of conversion to a fire-deterring, closed-canopy condition due to woody encroachment. This conversion of vegetation structure has been fostered by introduced woody plant species. We performed a field experiment to quantify growth, survival, and establishment success of six invasive, woody spec...
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Bastin et al. (Reports, 12 May 2017, p. 635) infer forest as more globally extensive than previously estimated using tree cover data. However, their forest definition does not reflect ecosystem function or biotic composition. These structural and climatic definitions inflate forest estimates across the tropics and undermine conservation goals, lead...
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Over the past 10 million years, tropical savanna environments have selected for small growth forms within woody plant lineages. The result has been the evolution of subshrubs (geoxyles), presumably as an adaptation to frequent fire. To evaluate the traits associated with the shift from tree to subshrub growth forms, we compared seed biomass, germin...
Article
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Fire frequencies are changing in Neotropical savannas and forests as a result of forest fragmentation and increasing drought. Such changes in fire regime and climate are hypothesized to destabilize tropical carbon storage, but there has been little consideration of the widespread variability in tree fire tolerance strategies. To test how abovegroun...
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Tropical savannas have been increasingly viewed as an opportunity for carbon sequestration through fire suppression and afforestation, but insufficient attention has been given to the consequences for biodiversity. To evaluate the biodiversity costs of increasing carbon sequestration, we quantified changes in ecosystem carbon stocks and the associa...
Article
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Soybean [Glycine max (L.) Merr.] genotype PI 471938 expresses a slow-wilting phenotype in the field, and the progeny of this genotype have shown to have high yield under water deficit conditions. However, the physiological basis for the slow-wilting trait in PI 471938 remains unclear, and failure to understand the causal mechanism may limit future...
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Key message: Along a fire frequency gradient, we found a savanna tree species had the greatest below ground decay compartmentalization after coppicing as compared to other resprouting species located at mesic gradient positions. Abstract: In pyrophilic ecosystems, woody plants are repeatedly injured or topkilled (i.e. aboveground tissue is killed...
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Fire regimes in savannas and forests are changing over much of the world. Anticipating the impact of these changes requires understanding how plants are adapted to fire. In this study, we test whether fire imposes a broad selective force on a key fire-tolerance trait, bark thickness, across 572 tree species distributed worldwide. We show that inves...
Article
Future climate change is expected to increase temperature (T) and atmospheric vapor pressure deficit (VPD) in many regions, but the effect of persistent warming on plant stomatal behavior is highly uncertain. We investigated the effect of experimental warming of 1.9-5.1 °C and increased VPD of 0.5-1.3 kPa on transpiration and stomatal conductance (...
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Production of reactive oxygen species (ROS) can be accelerated under various biotic and abiotic stresses causing lipid peroxidation, protein degradation, enzyme inactivation, and DNA damage. Superoxide reductase (SOR) is a novel antioxidant enzyme from Pyrococcus furiosus and is employed by this anaerobic hyperthermophilic archaeon for efficient de...
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Numerous predictions indicate rising CO2 will accelerate the expansion of forests into savannas. Although encroaching forests can sequester carbon over the short-term, increased fires and drought-fire interactions could offset carbon gains, which may be amplified by the shift towards forest plant communities more susceptible to fire-driven dieback....
Article
Bacterial growth in vase solutions can lead to stem vasculature blockage causing petal and leaf wilt, bent neck, or similar symptoms related to water stress that reduce vase life. In these studies we isolated, identified, and evaluated the effects of several bacteria species on the vase life of cut Zinnia elegans L. 'Benary's Giant Wine'. Nine bact...
Article
The probability of stem survival after fire is strongly influenced by energy allocation to bark because bark thickness affects heat transfer during fire. Greater relative investment in inner bark versus outer bark should also enhance survival because of greater moisture content of inner bark. We measured stem diameter, bark thickness, and habitat p...
Article
Anthropogenic climate change has altered temperate forest phenology, but how these trends will play out in the future is controversial. We measured the effect of experimental warming of 0.6-5.0 °C on the phenology of a diverse suite of 11 plant species in the deciduous forest understory (Duke Forest, North Carolina, USA) in a relatively warm year (...
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In the eastern United States, winter temperature has been increasing nearly twice as fast as summer temperature, but studies of warming effects on plants have focused on species that are photosynthetically active in summer. The terrestrial orchid Tipularia discolor is leafless in summer and acquires C primarily in winter. The optimum temperature fo...
Conference Paper
Positive feedbacks influenced by direct and indirect interactions between fire, vegetation, and microclimate can allow pyrophilic and pyrophobic ecosystems to co-occur in the same landscape, resulting in the juxtaposition of flammable and non-flammable vegetation. To quantify the drivers of these feedbacks, we combined measurements of vegetation, f...
Conference Paper
Background/Question/Methods Post-fire resprouting from underground storage reserves is an essential persistence strategy for plants in fire prone habitats. However, it is difficult to disentangle the relative contribution of new assimilates and storage reserves to post-fire resprouting. Furthermore, frequent fire tends to promote small statured p...
Conference Paper
Background/Question/Methods In longleaf pine savannas, fire plays an important role in the maintenance of species composition. Small inclusional wetlands with drastically different vegetation often occur within these fire-adapted savannas, creating a hydrological gradient. Most species found in these wetlands are restricted to the wetlands and th...
Conference Paper
Background/Question/Methods Increasing temperature has the potential to affect vegetative and reproductive phenology of temperate forest ecosystems in the future. The impact of warming on temperate forest communities is highly uncertain in part because warming experiments have focused on open ecosystems such as tundra, alpine meadows, and grassla...
Conference Paper
Background/Question/Methods With drought an increasing concern in many areas due to climate change, it becomes critical to understand how ecosystem composition and ecosystem-climate feedbacks change with drought. Yet we do not fully understand the relationship between drought, tree carbon assimilation, and tree mortality. Tree species have differ...
Article
In resprouting species, fire-induced topkill causes a reduction in height and leaf area without a comparable reduction in the size of the root system, which should lead to an increase in the efficiency of water transport after fire. However, large plants undergo a greater relative reduction in size, compared with small plants, so we hypothesized th...
Article
Tropical grassy biomes (TGBs) are globally extensive, provide critical ecosystem services, and influence the earth-atmosphere system. Yet, globally applied biome definitions ignore vegetation characteristics that are critical to their functioning and evolutionary history. Hence, TGB identification is inconsistent and misinterprets the ecological pr...
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Genetic factors such as decreased genetic diversity and increased homozygosity can have detrimental effects on rare species, and may ultimately limit potential adaptation and exacerbate population declines. The Gulf and Atlantic Coastal Plain physiographic region has the second highest level of endemism in the continental USA, but habitat fragmenta...
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The expansion of tropical forest into savanna may potentially be a large carbon sink, but little is known about the patterns of carbon sequestration during transitional forest formation. Moreover, it is unclear how nutrient limitation, due to extended exposure to fire-driven nutrient losses, may constrain carbon accumulation. Here, we sampled plots...
Article
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Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the m...
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The ecology of forest and savanna trees species will largely determine the structure and dynamics of the forest–savanna boundaries, but little is known about the constraints to leaf trait variation imposed by selective forces and evolutionary history during the process of savanna invasion by forest species. We compared seasonal patterns in leaf tra...
Article
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Aims The effects of fire ensure that large areas of the seasonal tropics are maintained as savannas. The advance of forests into these areas depends on shifts in species composition and the presence of sufficient nutrients. Predicting such transitions, however, is difficult due to a poor understanding of the nutrient stocks required for different c...
Article
Plant species distributions and transitions between vegetation types are determined by numerous factors, including disturbances such as fire. Documentation of past changes in the distribution and structure of fire-dependent ecosystems is necessary to assess the success of land management in maintaining historic vegetation types. In our study system...
Article
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Globally, fire maintains many mesic habitats in an open canopy state by killing woody plants while reducing the size of those able to resprout. Where fire is frequent, tree saplings are often suppressed by a "fire trap" of repeated topkill (death of aerial biomoass) and resprouting, preventing them from reaching adult size. The ability to tolerate...
Article
The higher flammability of tropical savanna, compared with forest, plays a critical role in mediating vegetation‐environment feedbacks, alternate stable states, and ultimately, the distribution of these two biomes. Multiple factors contribute to this difference in flammability, including microclimate, fuel amount and fuel type. To understand this t...
Conference Paper
Background/Question/Methods Species that resprout after fire undergo a reduction in height and leaf area after fire without a comparable reduction in the size of the root system, and this reduction is likely to be greater for larger-statured species. An increase in the root:shoot biomass ratio post-fire should lead to an increase in the efficienc...
Conference Paper
Background/Question/Methods Most climate predictions agree that the southern US will be 2-4°C warmer by the end of the 21st century, whereas the average temperature increase in North Carolina over the last century was 0.7°C. Studies of the effects of warming on native plants have focused on plants that are photosynthetically active in summer; muc...
Conference Paper
Background/Question/Methods Because of its substantial effects on demographic vital rates, fire has been used successfully to manage for fire-dependent plant species in a number of ecosystems. However, not all plant species respond positively to fire, even in fire-dependent ecosystems, making it particularly important to study the effects of fire...
Conference Paper
Background/Question/Methods Fire is critical to the maintenance of many ecosystems because it is able to limit the success of certain plant species while promoting others. To effectively use fire as a management tool, it is important to understand the differences in plant responses to fire, but we lack a mechanistic framework from which to build...
Article
Fire can have dramatic effects on the vital rates of plant species and has been used successfully for management in a number of ecosystems. However, the demographic response of species to fire in fire-dependent ecosystems is variable, making it important to study the effects of fire on rare and threatened species. We quantified the effects of fire...