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1. Northern red oak regeneration in burned and unburned stands in the White Mountain National Forest, New Hampshire, USA, 2023-2024

   https://doi.org/10.6073/pasta/f488d29e300ce386fd6c99920e2d5f3b  

   Ton, Khanh; Vadeboncoeur, Matthew A; Cleavitt, Natalie; Asbjornsen, Heidi (July 2025, Environmental Data Initiative)

   This project aimed to determine whether prescribed burning of managed forest stands improves the regeneration of Quercus rubra near its northern range limit in New Hampshire. We measured oak seedling density and growth rates in three pairs of managed stands in which one had received a prescribed burn since 2017. We also measured the density of competing seedlings and shrubs, leaf area index above seedling height, soil nutrients, mycorrhizal colonization, foliar carbon/nitrogen ratio, and stable isotopes of nitrogen and carbon. We found greater oak seedling density and faster oak seedling growth rates in burned stands relative to unburned stands. A subset of these measurements were also collected in additional burned and unburned study stands in the region. A companion mesocosm experiment showed faster growth in oak seedlings grown in soil from burned vs. unburned stands. Together these studies show that the benefits of fire to oak regeneration are mediated both via greater light availability as well as effects mediated via soil. 

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2. Hydrodynamic Limitations to Mangrove Seedling Retention in Subtropical Estuaries

   https://doi.org/10.3390/su14148605  

   Kibler, Kelly M.; Pilato, Christian; Walters, Linda J.; Donnelly, Melinda; Taye, Jyotismita (July 2022, Sustainability)

   Mangrove-forest sustainability hinges upon propagule recruitment and seedling retention. This study evaluates biophysical limitations to mangrove-seedling persistence by measuring anchoring force of two mangrove species (Rhizophora mangle L. and Avicennia germinans (L.) L.). Anchoring force was measured in 362 seedlings via lateral pull tests administered in mangrove forests of two subtropical estuaries and in laboratory-based experiments. Removal mechanism varied with seedling age: newly established seedlings failed due to root pull-out while seedlings older than 3 months failed by root breakage. The anchoring force of R. mangle seedlings was consistently and significantly greater than A. germinans (p = 0.002); however, force to remove A. germinans seedlings increased with growth at a faster rate (p < 0.001; A. germinans: 0.20–0.23 N/g biomass; R. mangle: 0.04–0.07 N/g biomass). Increasing density of surrounding vegetation had a positive effect (p = 0.04) on anchoring force of both species. Critical velocities at which seedlings become susceptible to instantaneous uprooting estimated from anchoring forces measured in the field were 1.20 m/s and 1.50 m/s, respectively, for R. mangle and A. germinans. As estimated critical velocities exceed typical flow magnitudes observed in field sites, removal of established seedlings likely occurs following erosion of sediments from the seedling base. 

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3. Soil biotic and abiotic thresholds in sugar maple and American beech seedling establishment in forests of the northeastern United States

   https://doi.org/10.1007/s11104-023-06123-2  

   Tourville, Jordon C; Zarfos, Michael R; Lawrence, Gregory B; McDonnell, Todd C; Sullivan, Timothy J; Dovčiak, Martin (October 2023, Plant and Soil)

   Aims: Climate change is expected to shift climatic envelopes of temperate tree species into boreal forests where unsuitable soils may limit range expansion. We studied several edaphic thresholds (mycorrhizae, soil chemistry) that can limit seedling establishment of two major temperate tree species, sugar maple (arbuscular mycorrhizal, AM) and American beech (ectomycorrhizal, EM). Methods: We integrate two field surveys of tree seedling density, mycorrhizal colonization, and soil chemistry in montane forests of the Adirondack and Green Mountains (Mtns) in the northeastern United States. We conducted correlation and linear breakpoint analyses to detect soil abiotic and biotic thresholds in seedling distributions across edaphic gradients. Results: In the Green Mtns, sugar maple seedling importance (an index of species relative density and frequency, IV) declined sharply with low pH (< 3.74 in mineral soil) and low mycorrhizal colonization (< 27.5% root length colonized). Sugar maple importance was highly correlated with multiple aspects of soil chemistry, while beech was somewhat sensitive to pH only; beech mycorrhizal colonization did not differ across elevation. Mycorrhizal colonization of sugar maple was positively correlated with soil pH and conspecific overstory basal area. In the Adirondacks, sugar maple importance, but not beech, plateaued above thresholds in soil calcium (~ 2 meq/100 g) and magnesium (~ 0.3 meq/100 g). Conclusions: The establishment of sugar maple, but not beech, was impeded by both biotic and abiotic soil components in montane conifer forests and by soil acidity in temperate deciduous forests. These differences in species sensitivity to edaphic thresholds will likely affect species success and future shifts in forest composition. 

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4. Mycorrhizal fungi as critical biotic filters for tree seedling establishment during species range expansions

   https://doi.org/10.1002/ecm.1634  

   Tourville, Jordon C; Horton, Thomas R; Dovciak, Martin (November 2024, Ecological Monographs)

   Abstract Global warming has been shifting climatic envelopes of many tree species to higher latitudes and elevations across the globe; however, unsuitable soil biota may inhibit tree migrations into these areas of suitable climate. Specifically, the role of mycorrhizal fungi in facilitating tree seedling establishment beyond natural species range limits has not been fully explored within forest ecosystems. We used three experiments to isolate and quantify the effects of mycorrhizal colonization and common mycorrhizal networks (CMN) on tree seedling survival and growth across (within and beyond) the elevational ranges of two dominant tree species in northeastern North America, which were associated with either arbuscular mycorrhiza (AMF,Acer saccharum) or ectomycorrhiza (EMF,Fagus grandifolia). In order to quantify the influence of mycorrhiza on seedling establishment independent of soil chemistry and climate, we grew seedlings in soils from within and beyond our study species ranges in a greenhouse experiment (GE) as well as in the field using a soil translocation experiment (STE) and another field experiment manipulating seedling connections to potential CMNs (CMNE). Root length colonized, seedling survival and growth, foliar nutrients, and the presence of potential root pathogens were examined as metrics influencing plant performance across species' ranges. Mycorrhizal inoculum from within species ranges, but not from outside, increased seedling survival and growth in a greenhouse setting; however, only seedling survival, and not growth, was significantly improved in field studies. Sustained potential connectivity to AMF networks increased seedling survival across the entire elevational range ofA. saccharum. Although seedlings disconnected from a potential CMN did not suffer decreased foliar nutrient levels compared with connected seedlings, disconnected AM seedlings, but not EM seedlings, had significantly higher aluminum concentrations and more potential pathogens present. Our results indicate that mycorrhizal fungi may facilitate tree seedling establishment beyond species range boundaries in this forested ecosystem and that the magnitude of this effect is modulated by the dominant mycorrhizal type present (i.e., AM vs. EM). Thus, despite changing climate conditions beyond species ranges, a lack of suitable mutualists can still limit successful seedling establishment and stall adaptive climate‐induced shifts in tree species distributions. 

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5. Rates and controls of nitrogen fixation in postfire lodgepole pine forests

   https://doi.org/10.1002/ecy.70016  

   Heumann, Robert E; Turner, Monica G; Cleveland, Cory C (February 2025, Ecology)

   Abstract Severe, stand‐replacing wildfire substantially depletes nitrogen (N) stocks in subalpine conifer forests, potentially exacerbating N limitation of net primary productivity in many forested regions where fire frequency is increasing. In lodgepole pine (Pinus contortavar.latifolia) forests in the Greater Yellowstone Ecosystem (GYE), long‐term data show surface soil and biomass N stocks are replenished during the first few decades following wildfire, but the source(s) of that N are unclear. We measured acetylene reduction rates in multiple cryptic niches (i.e., lichen, moss, pine litter, dead wood, and mineral soil) in 34‐year‐old lodgepole pine stands in the GYE to explore the rates, temporal patterns, and climate controls on cryptic N fixation. Acetylene reduction rates were highest in late May (0.376 nmol C₂H₄g⁻¹ h⁻¹) when moisture availability was high compared with early August and mid‐October when moisture was relatively low (0.112 and 0.002 nmol C₂H₄g⁻¹ h⁻¹, respectively). We observed modest rates of nitrogenase activity in a few niches following a mid‐summer rain event, suggesting that moisture is an important factor regulating field‐based N fixation rates. In a laboratory experiment, moss responded more strongly to temperature and moisture variation than all other niches. Acetylene reduction rates in dead wood increased with temperature but not moisture content. No other niches showed clear responses to either moisture or temperature manipulation. Together, the field and laboratory results suggest that frequent asynchrony between favorable temperature and moisture conditions may limit N fixation rates in the field. Overall, total annual cryptic N fixation inputs (mean: 0.26; range: 0.07–2.9 kg N ha⁻¹year⁻¹) represented <10% of the postfire biomass and surface soil N accumulation in the same stands (39.4 kg N ha⁻¹year⁻¹), pointing to a still unknown source of ecosystem N following fire. 

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