Forest vegetation and fuel dynamics following stand-replacing wildfire, re-burn, and postfire management in the Siskiyou Mountains, Oregon

Following high-severity fire, forest succession may take alternate pathways depending on the pattern of the fire and any secondary disturbances during early stand development, with lasting consequences for ecosystem function. The objectives of this research were to quantify: (1) early postfire regeneration as influenced by the spatial pattern of a landscape-scale wildfire, and (2) the influence of secondary disturbances during early succession, specifically recurrent high-severity fire and postfire logging. Four years after the 200,000-hectare Biscuit Fire, patch-scale conifer seedling density was 80% Douglas-fir (Pseudotsuga menziesii) and ranged from 127-6494 stems/ha. Median density (1603 stems/ha) was ~12 times the prefire overstory density of 134 stems/ha. Due to the mixed-severity fire mosaic, ~58% of high-severity area was ≤ 200 m from patches of live trees, and ~81% was ≤ 400 m. Median conifer density exceeded 1000 stems/ha out to 400 m distance before declining rapidly at larger distances. Following a short-interval (15-year) repeat fire, vegetation communities contained nearly all species found in mature/old-growth stands and after a single fire, indicating high community persistence through two severe fires. The short-interval burn had the highest species richness and plant cover with additions of disturbance-adapted forbs and low shrubs, likely associated with a propagule bank that developed between fires. Sprouting capacity of hardwoods and shrubs was unaltered by recurrent fire, and conifer regeneration density (median 1495 stems/ha) was similar to single burn stands. Three to four years after fire, high-intensity postfire logging resulted in a greater proportion (28%) of felled biomass left on site as slash compared to moderate-intensity logging (14%), because tree felling was less selective. However, despite bole removal and slash generation, there was no significant difference in surface woody fuels among logged and unlogged treatments at 17-18 years after fire. Fuel profiles and fire modeling both suggested that regenerating vegetation rather than residual dead wood is the main driver of early seral fire hazard, with low fire potentials 3-4 years postfire and very high potentials at 17-18 years. Postfire logging increased fire potentials within this context due to generation of slash, with differences fading in ~15-20 years. The results from this research underscore the importance of the mixed-severity context in which stand-replacing fire often occurs, both for providing seed sources within a fire and for highly variable disturbances that interact with succession and plant adaptation.Keywords: regeneration, mixed severity, landscape fire, mosaic, high-severity fire, salvage loggin

1FGL J1417.7-4407: A likely gamma-ray bright binary with a massive neutron star and a giant secondary

We present multiwavelength observations of the persistent Fermi-LAT unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary containing a massive neutron star (nearly 2 M_sun) and a ~ 0.35 M_sun giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H-alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk--magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma-ray to X-ray luminosity (~ 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a good candidate to monitor for a future transition between accretion-powered and rotational-powered states, but in the context of a giant secondary.Comment: ApJL in pres

Trait-based approaches to linking vegetation and food webs in early-seral forests of the Pacific Northwest

Both the structure and composition of naturally generated early-seral forests in the Pacific Northwest (PNW) can be profoundly different than that of more developed forest seres, especially in the period after a major disturbance but before conifers re-develop a closed canopy. While it is reasonable to suggest that the unique structure and composition of early-seral forests in the PNW give rise to equally unique functionality, identifying such linkages beyond that inferred by empirical observation is understandably difficult. To address this challenge, we explore the utility of a trait-based approach to identify the vegetation traits most strongly altered by canopy-opening disturbances (using wildfires as an example), and link these traits to secondary production and subsequent food webs. Preliminary analysis, based on original and literature-derived data, suggests that 1) Lepidoptera production, the primary prey base for forest birds in the PNW, is positively correlated with specific leaf area (SLA) which is higher in stands recently opened by canopy disturbance, 2) small mammal production, an important prey base for meso-predators, is positively correlated with SLA, which is higher in stands recently opened by canopy disturbance. These initial results lay the framework for linking disturbance type, disturbance severity, and subsequent successional pathways to trophic processes uniquely provided by the early-seral condition.This is an author's peer-reviewed In Press manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/forest-ecology-and-management/.Keywords: Food webs, Trophic transfer, Early-seral, Post-disturbance succession, Trait analysis, Herbivory, Pacific Northwes

Divergent trends in ecosystem services under different climate-management futures in a fire-prone forest landscape

While ecosystem services and climate change are often examined independently, quantitative assessments integrating these fields are needed to inform future land management decisions. Using climate-informed state-and-transition simulations, we examined projected trends and trade-offs for a suite of ecosystem services under four climate change scenarios and two management scenarios (active management emphasizing fuel treatments and no management other than fire suppression) in a fire-prone landscape of dry and moist mixed-conifer forests in central Oregon, USA. Focal ecosystem services included fire potential (regulating service), timber volume (provisioning service), and potential wildlife habitat (supporting service). Projections without climate change suggested active management in dry mixed-conifer forests would create more open forest structures, reduce crown fire potential, and maintain timber stocks, while in moist mixed-conifer forests, active management would reduce crown fire potential but at the expense of timber stocks. When climate change was considered, however, trends in most ecosystem services changed substantially, with large increases in wildfire area predominating broad-scale trends in outputs, regardless of management approach (e.g., strong declines in timber stocks and habitat for closed-forest wildlife species). Active management still had an influence under a changing climate, but as a moderator of the strong climate-driven trends rather than being a principal driver of ecosystem service outputs. These results suggest projections of future ecosystem services that do not consider climate change may result in unrealistic expectations of benefits

Carbon emissions from decomposition of fire-killed trees following a large wildfire in Oregon, United States

A key uncertainty concerning the effect of wildfire on carbon dynamics is the rate at which fire-killed biomass (e.g., dead trees) decays and emits carbon to the atmosphere. We used a ground-based approach to compute decomposition of forest biomass killed, but not combusted, in the Biscuit Fire of 2002, an exceptionally large wildfire that burned over 200,000 ha of mixed conifer forest in southwestern Oregon, USA. A combination of federal inventory data and supplementary ground measurements afforded the estimation of fire-caused mortality and subsequent 10 year decomposition for several functionally distinct carbon pools at 180 independent locations in the burn area. Decomposition was highest for fire-killed leaves and fine roots and lowest for large-diameter wood. Decomposition rates varied somewhat among tree species and were only 35% lower for trees still standing than for trees fallen at the time of the fire. We estimate a total of 4.7 Tg C was killed but not combusted in the Biscuit Fire, 85% of which remains 10 years after. Biogenic carbon emissions from fire-killed necromass were estimated to be 1.0, 0.6, and 0.4 Mg C ha⁻¹ yr⁻¹ at 1, 10, and 50 years after the fire, respectively; compared to the one-time pyrogenic emission of nearly 17 Mg C ha⁻¹.Keywords: necromass, carbon emissions, forest decomposition, dead wood, wildlif

Burning the legacy? Influence of wildfire reburn on dead wood dynamics in a temperate conifer forest

Dynamics of dead wood, a key component of forest structure, are not well described for mixed-severity fire regimes with widely varying fire intervals. A prominent form of such variation is when two stand-replacing fires occur in rapid succession, commonly termed an early-seral “reburn.” These events are thought to strongly influence dead wood abundance in a regenerating forest, but this hypothesis has scarcely been tested. We measured dead wood following two overlapping wildfires in conifer-dominated forests of the Klamath Mountains, Oregon (USA), to assess whether reburning (15-yr interval, with >90% vegetation mortality) resulted in lower dead wood abundance and altered character relative to once-burned stands, and how any differences may project through succession. Total dead wood mass (standing + down) following the reburn (169 ± 83 Mg/ha [95%CI]) was 45% lower than after a single fire (309 ± 87 Mg/ha). Lower levels in reburn stands were due to, in roughly equal parts, additional combustion and greater time for decay. Although a single fire in mature forest both consumed and created dead wood (by killing large live trees), a reburn only consumed dead wood (few large live trees to kill). Charred biomass (black carbon generation) was higher in reburned stands by a factor of 2 for logs and 8 for snags. Projecting these stands forward (notwithstanding future disturbances) suggests: (1) the near-halving of dead-wood mass in reburn stands will persist for ~50 yr until the recruitment of new material begins, and (2) the reburn signature on dead wood abundance will remain apparent for over a century. These findings demonstrate how a single stochastic variation in disturbance interval can impart lasting influence on dead-wood succession, reinforcing the notion that many temperate forests exist in a state of dead-wood disequilibrium governed by site-specific disturbance history. Accounting for such variation in disturbance impacts is crucial to better understanding forests with complex mixed-severity disturbance regimes and with increasing stochasticity under climatic change

Spatial aspects of tree mortality strongly differ between young and old-growth forests

Rates and spatial patterns of tree mortality are predicted to change during forest structural development. In young forests, mortality should be primarily density dependent due to competition for light, leading to an increasingly spatially uniform pattern of surviving trees. In contrast, mortality in old-growth forests should be primarily caused by contagious and spatially auto-correlated agents (e.g., insects, wind), causing spatial aggregation of surviving trees to increase through time. We tested these predictions by contrasting a three-decade record of tree mortality from replicated mapped permanent plots located in young (\u3c60-year-old) and old-growth (\u3e300-year-old) Abies amabilis forests. Trees in young forests died at a rate of 4.42% per year, whereas trees in old-growth forests died at 0.60% per year. Tree mortality in young forests was significantly aggregated, strong density dependent, and caused live tree patterns to become more uniform through time. Mortality in old-growth forests was spatially aggregated, but was density independent and did not change the spatial pattern of surviving trees. These results extend current theory by demonstrating that density-dependent competitive mortality leading to increasingly uniform three spacing in young forests ultimately transitions late in succession to a more diverse tree mortality regime that maintains spatial heterogeneity through time

Rapid proteasomal degradation of mutant proteins is the primary mechanism leading to tumorigenesis in patients with missense AIP mutations

CONTEXT The pathogenic effect of AIP mutations (AIPmuts) in pituitary adenomas is incompletely understood. We have identified the primary mechanism of loss of function for missense AIPmuts. OBJECTIVE To analyze the mechanism/speed of protein turnover of wild-type (WT) and missense AIP variants, correlating protein half-life with clinical parameters. DESIGN Half-life and protein-protein interaction experiments and cross-sectional analysis of AIPmut positive patients' data were performed. SETTING Clinical academic research institution. PATIENTS Data was obtained from our cohort of pituitary adenoma patients and literature-reported cases. INTERVENTIONS Protein turnover of endogenous AIP in two cell lines and fifteen AIP variants overexpressed in HEK293 cells was analyzed via cycloheximide chase and proteasome inhibition. GST pull-down and quantitative mass spectrometry identified proteins involved in AIP degradation; results were confirmed by co-immunoprecipitation and gene knockdown. Relevant clinical data was collected. MAIN OUTCOME MEASURES Half-life of WT and mutant AIP proteins and its correlation with clinical parameters. RESULTS Endogenous AIP half-life was similar in HEK293 and lymphoblastoid cells (43.5 and 32.7h). AIP variants were divided in stable proteins (median 77.7h [IQR 60.7-92.9]), and those with short (27h [21.6-28.7]) or very short (7.7h [5.6-10.5]) half-life; proteasomal inhibition rescued the rapid degradation of mutant proteins. The experimental half-life significantly correlated with age at diagnosis of acromegaly/gigantism (r=0.411, P=0.002). The FBXO3-containing SCF complex was identified as the E3 ubiquitin-ligase recognizing AIP. CONCLUSIONS AIP is a stable protein, driven to ubiquitination by the SCF complex. Enhanced proteasomal degradation is a novel pathogenic mechanism for AIPmuts, with direct implications for the phenotype

Spatially nonrandom tree mortality and ingrowth maintain equilibrium pattern in an old-growth \u3ci\u3ePseudotsuga–Tsuga\u3c/i\u3e forest

Mortality processes in old-growth forests are generally assumed to be driven by gap-scale disturbance, with only a limited role ascribed to density-dependent mortality, but these assumptions are rarely tested with data sets incorporating repeated measurements. Using a 12-ha spatially explicit plot censused 13 years apart in an approximately 500-year-old Pseudotsuga–Tsuga forest, we demonstrate significant density-dependent mortality and spatially aggregated tree recruitment. However, the combined effect of these strongly nonrandom demographic processes was to maintain tree patterns in a state of dynamic equilibrium. Density-dependent mortality was most pronounced for the dominant latesuccessional species, Tsuga heterophylla. The long-lived, early-seral Pseudotsuga menziesii experienced an annual stem mortality rate of 0.84% and no new recruitment. Late-seral species Tsuga and Abies amabilis had nearly balanced demographic rates of ingrowth and mortality. The 2.34% mortality rate for Taxus brevifolia was higher than expected, notably less than ingrowth, and strongly affected by proximity to Tsuga. Large-diameter Tsuga structured both the regenerating conspecific and heterospecific cohorts with recruitment of Tsuga and Abies unlikely in neighborhoods crowded with large-diameter competitors (P , 0.001). Densitydependent competitive interactions strongly shape forest communities even five centuries after stand initiation, underscoring the dynamic nature of even equilibrial old-growth forests

Forest Fire Impacts on Carbon Uptake, Storage, and Emission: The Role of Burn Severity in the Eastern Cascades, Oregon

This study quantifies the short-term effects of low-, moderate-, and high-severity fire on carbon pools and fluxes in the Eastern Cascades of Oregon. We surveyed 64 forest stands across four fires that burned 41,000 ha (35%) of the Metolius Watershed in 2002 and 2003, stratifying the landscape by burn severity (overstory tree mortality), forest type (ponderosa pine [PP] and mixed-conifer [MC]), and prefire biomass. Stand-scale C combustion ranged from 13 to 35% of prefire aboveground C pools (area − weighted mean = 22%). Across the sampled landscape, total estimated pyrogenic C emissions were equivalent to 2.5% of statewide anthropogenic CO₂ emissions from fossil fuel combustion and industrial processes for the same 2-year period. From low- to moderate- to high-severity ponderosa pine stands, average tree basal area mortality was 14, 49, and 100%, with parallel patterns in mixed-conifer stands (29, 58, 96%). Despite this decline in live aboveground C, total net primary productivity (NPP) was only 40% lower in high- versus low-severity stands, suggesting strong compensatory effects of non-tree vegetation on C uptake. Dead wood respiratory losses were small relative to total NPP (range: 10–35%), reflecting decomposition lags in this seasonally arid system. Although soil C, soil respiration, and fine root NPP were conserved across severity classes, net ecosystem production (NEP) declined with increasing severity, driven by trends in aboveground NPP. The high variability of C responses across this study underscores the need to account for landscape patterns of burn severity, particularly in regions such as the Pacific Northwest, where non-stand-replacement fire represents a large proportion of annual burned area.Keywords: net ecosystem production, net primary productivity, Pinus ponderosa, wildfire, carbon balance, Cascade Range, mixed-severity fire regime, fire emissions, disturbance, heterotrophic respiratio