In temperate oak forests in Ohio, USA, we examined variability in forest communities within containment treatment sites for oak wilt (
Bretziella fagacearum
), a fungal pathogen lethal to susceptible ...oak species. Containment treatments included quarantine lines in soil for limiting belowground fungal spread and sanitation cutting of 1–3 mature black oak (
Quercus velutina
) trees within oak wilt infection patches. At 28 sites, we compared tree structure and understory plant communities across a gradient of 1- to 6-year-old treatments and reference forest (untreated and without evidence of oak wilt). While oak seedlings were abundant, oak saplings (1–10 cm in diameter) were absent. In contrast, many native understory plant community measures were highest in oak wilt treatments. Plant species richness 100 m
−2
doubled in treatments, regardless of age, compared with reference forest. Plant cover increased with treatment age, with 6-year-old treatments exhibiting 5 × more cover than reference forest. Non-native plants averaged only a small proportion (< 0.12) of cover across treatments and reference forest. Variability in understory communities was mostly predictable using treatment age, tree canopy cover, and geographic location, as 20 of 25 understory measures had at least 72% of their variance modeled. While oak wilt treatments did not facilitate oak regeneration nor many conservation-priority species of open savanna-woodland habitats, the treatments did diversify and increase cover of native understory communities with minimal invasion of non-native plants.
We report the first observation of the parity-violating gamma-ray asymmetry A_{γ}^{np} in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the ...Spallation Neutron Source at Oak Ridge National Laboratory. A_{γ}^{np} isolates the ΔI=1, ^{3}S_{1}→^{3}P_{1} component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless effective field theory. We measured A_{γ}^{np}=-3.0±1.4(stat)±0.2(syst)×10^{-8}, which implies a DDH weak πNN coupling of h_{π}^{1}=2.6±1.2(stat)±0.2(syst)×10^{-7} and a pionless EFT constant of C^{^{3}S_{1}→^{3}P_{1}}/C_{0}=-7.4±3.5(stat)±0.5(syst)×10^{-11} MeV^{-1}. We describe the experiment, data analysis, systematic uncertainties, and implications of the result.
Open-structured habitats, such as heathlands, grasslands, and savannas, support unique plant diversity but are threatened by woody plant encroachment in diverse locations globally. During 20 years of ...vegetation management aimed at restoring and sustaining oak savannas, woodlands, and wet prairies in a Midwestern USA oak savanna region, we examined change in 17 plant community metrics ranging from cover of rare species to pollinator floral resources. Metrics indicative of open-habitat quality increased rapidly but also declined rapidly with time since disturbance spanning a first decade of intensive management (tree cutting and 4–5 fires/decade) and a second decade of less-intensive management (> 4 years between fires). After initial restoration treatments reduced overstory tree density, changes in cover of open-habitat specialist species correlated with fluctuations of a brushy layer of small trees 1–10 cm in stem diameter. Between 2002 and 2018, 92% of sites where small trees increased by over 100/ha had declines in open-habitat species, whereas 72% of sites not experiencing that level of woody encroachment had sustained or increasing open-habitat species. Conserving open habitats in contemporary environments likely requires perpetually frequent low-severity disturbance (at least every 3–4 years), periodic severe disturbance (e.g., growing-season fires), or multiple treatment types (e.g., managed herbivory and fire) to synergistically limit woody encroachment. Fluctuations between positive and negative trends in the 20-year dataset also highlight that perhaps restoration success should not be evaluated on the basis of a net change from beginning to end, but rather on a time-weighted accrual of restoration benefits.
Abstract
Delayed tree mortality can contribute to variability in fire effects in forests, but its prevalence is not well understood in eastern North American oak forests where a management goal is ...using prescribed fire to shape forest density and composition. To assess potential delayed mortality after prescribed fires, we tracked the fates of 690 trees of four species in burned and 542 trees in unburned oak forests in northwestern Ohio, USA, and modeled survival using tree diameter and bole char. Delayed mortality, occurring 3–4 growing seasons after fire and in addition to initial mortality (1–2 growing seasons after fire), varied with species and tree diameter. Compared to initial mortality, delayed mortality resulted in eleven times more small-diameter (1–13 cm) red maple (Acer rubrum) dying after fire. White oak (Quercus alba), 1–25 cm in diameter, also incurred delayed mortality (five-times increase in dead trees). Neither sassafras (Sassafras albidum) nor black oak (Quercus velutina) displayed delayed mortality. Background tree mortality in unburned sites was minimal (0.4% per year across species). Logistic regression to model canopy survival selected only stem diameter for burned red maple trees, whereas both diameter and bole char related to survival in other species. Results suggest that (1) monitoring postfire tree mortality in oak forests should extend for at least four growing seasons to detect delayed mortality in some species, and that (2) single surface fires may eventually reduce encroaching red maple in oak forests more than initial postfire years indicate.
The ultracold neutron (UCN) source at Los Alamos National Laboratory (LANL), which uses solid deuterium as the UCN converter and is driven by accelerator spallation neutrons, has been successfully ...operated for over 10 years, providing UCN to various experiments, as the first production UCN source based on the superthermal process. It has recently undergone a major upgrade. This paper describes the design and performance of the upgraded LANL UCN source. Measurements of the cold neutron spectrum and UCN density are presented and compared to Monte Carlo predictions. The source is shown to perform as modeled. The UCN density measured at the exit of the biological shield was 184(32) UCN/cm3, a fourfold increase from the highest previously reported. The polarized UCN density stored in an external chamber was measured to be 39(7) UCN/cm3, which is sufficient to perform an experiment to search for the nonzero neutron electric dipole moment with a one-standard-deviation sensitivity of σ(dn)=3×10-27ecm.
We present a search for possible spin dependent interactions of the neutron with matter through exchange of spin 1 bosons with axial vector couplings as envisioned in possible extensions of the ...Standard Model. This was sought using a slow neutron polarimeter that passed transversely polarized slow neutrons by unpolarized slabs of material arranged so that interactions would tilt the plane of polarization and develop a component along the neutron momentum. The result for the rotation angle, ϕ′=2.8±4.6(stat.)±4.0(sys.)×10−5 rad/m is consistent with zero. This result improves the upper bounds on the neutron-matter coupling gA2 by about three orders of magnitude for force ranges in the mm– μm regime.
An uncertainty in ecological restoration is how natural disturbances occurring during restoration might influence restoration outcomes. The unplanned nature of natural disturbances makes them ...difficult to study, and their effects hinge on the resistance or resilience of ecosystem components that may change during restoration. In 2010, a tornado struck a 23-year-old oak woodland-savanna restoration site in northwestern Ohio, USA, providing a rare opportunity to determine how a major natural disturbance could influence the course of restoration. Restoration burning had begun at the site in 1988. We monitored tree and understory metrics before restoration, in 10 of the 22 years during restoration before the tornado, and in two of five years after the tornado until 2015. Trajectories in floristic quality and conservation-priority plant species (e.g., state-listed rare species) were resistant to change by the tornado, non-native plants were resilient (which was desirable as they quickly declined to near pre-tornado levels after an initial increase), and the oak overstory was neither resistant nor resilient. Overstory density was halved after the tornado, moved from woodland toward savanna, and then changed little. Forbs and oaks in the understory were the main increasers after the tornado. The tornado disturbance altered the pathway of restoration but remained consistent with restoration goals, given that both woodlands and savannas were part of reference conditions and conservation-priority forbs increased.
Status of the UCN τ experiment Pattie, R.W.; Callahan, N.B.; Cude-Woods, C. ...
EPJ Web of Conferences,
2019, Letnik:
219
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
The neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics beyond the standard model. Measurements of neutron lifetime and ...β-decay correlation coefficients with precisions of 0.02% and 0.1%, respectively, would allow for stringent constraints on new physics. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with
in situ
counting of surviving neutrons to measure the neutron lifetime, τ
n
= 877.7s (0.7s)
stat
(+0.4/−0.2s)
sys
. We discuss the recent result from UCNτ, the status of ongoing data collection and analysis, and the path toward a 0.25 s measurement of the neutron lifetime with UCNτ.
The Nab experiment will measure the correlation a between the momenta of the beta particle and antineutrino in neutron decay as well as the Fierz term b which distorts the beta spectrum.
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