A new drought tipping point for conifer mortality

(Huang et al 2015 Environ. Res. Lett. 10 024011) present a method for predicting mortality of ponderosa pine (Pinus ponderosa) and pinyon pine (Pinus edulis) in the Southwestern US during severe drought based on the relationship between the standardized precipitation–evapotranspiration index (SPEI) and annual tree ring growth. Ring growth was zero when SPEI for September to July was −1.64. The threshold SPEI of −1.64 was successful in distinguishing areas with high tree mortality during recent severe drought from areas with low mortality, and is proposed to be a tipping point of drought severity leading to tree mortality. Below, I discuss this work in more detail

Bulk viscosity of a gas of neutrinos and coupled scalar particles, in the era of recombination

Bulk viscosity may serve to damp sound waves in a system of neutrinos coupled to very light scalar particles, in the era after normal neutrino decoupling but before recombination. We calculate the bulk viscosity parameter in a minimal scheme involving the coupling of the two systems. We add some remarks on the bulk viscosity of a system of fully ionized hydrogen plus photons.Comment: 6 pages, 4 figure

Observation of a quenched moment of inertia in a rotating strongly interacting Fermi gas

We make a model-independent measurement of the moment of inertia of a rotating, expanding strongly-interacting Fermi gas. Quenching of the moment of inertia is observed for energies both below and above the superfluid transition. This shows that a strongly interacting Fermi gas with angular momentum can support irrotational flow in both the superfluid and collisional normal fluid regimes.Comment: 4 pages 5 figure

Tree growth and regeneration response to climate and stream flow in a species-rich southwestern riparian forest

We studied the influence of climate variables, stream flow, and topography on regeneration and growth of several riparian tree species (Acer negundo, Alnus oblongifolia, Fraxinus velutina, Juglans major, Platanus wrightii, Populus fremontii, Salix spp.) at an unregulated perennial stream, West Clear Creek, in central Arizona. A pulse of seedling regeneration occurred for Alnus, Fraxinus, Platanus, Populus, and Salix in 1995 and 1996 following high winter and spring surface flows in 1993 and high spring surface flow in 1995. In contrast, little regeneration occurred for Acer and Juglans under these conditions. Most seedlings occurred at the active channel topographic location, and few seedlings occurred at abandoned channel, gravel-boulder bar, and bench locations. Relationships between environmental variables and annual radial stem growth varied among species and between constrained and unconstrained reaches. High spring or winter surface flows were negatively related to growth of Acer, Alnus, and Platanus, whereas high spring surface flow was positively related to growth of Fraxinus. Positive relationships between precipitation and growth occurred only for Fraxinus and Juglans, suggesting greater use of surface soil water by these species. Annual radial growth was high for Platanus and Alnus, medium for Acer and Fraxinus, and low for Juglans. Overall, the tree species in our study responded individually, rather than collectively, in regeneration and growth to changes in stream flow and climatic variables

Impacts of pear thrips on a Pennsylvania sugarbush: Third year results

Pear thrips, Taeniothrips inconsequens (Uzel) (Thysanoptera: Thripidae), were first positively identified as causing damage to sugar maple (Acer saccharum Marsh.) in forest environments in the United States in 1980. Damage in Pennsylvania from this insect has occurred consistently since 1980, with the most extensive impact in 1988 (0.5 mfllon ha). Sap characteristics and crown condition were monitored for three years following a 1989 thrips attack in a Pennsylvania sugarbush on 56 trees representing a range of thrips damage. Heavy damage in 1989 was associated with increased crown transparency for two summers following the attack. Calculated syrup production was greatest in all years for trees with light damage and lowest for trees with heavy damage. Reduced syrup production in trees with heavy damage resulted from lower sap volume in all years and lower sap sugar concentration in 1990 and 1992 compared to trees with light damage. The results indicate that pear thrips damage in 1989 had a detrimental impact on sugar maple health and syrup production for three years following the attack

Teaching silvics: Student performance and evaluations in web-based and traditional classroom courses

There is interest in Web delivery of lower-division forestry courses at Northern Arizona University to accommodate transfer students and scheduling conflicts. We have taught “Trees and Forests of North America,” a sophomore-level required course for forestry majors, for five years with good results as measured by student performance on exams and student evaluations. Fall semester 2001 marks our first completely Web- based version of the course; 25 students enrolled with 30% of the class residing outside of the Flagstaff area. Students covered the course material using a combination of linked Web sites and a commercially available dendrology CD set following a weekly schedule based on the classroom course. We used student evaluations and identical test questions to compare student performance in the Web-based and classroom courses. These data provide a preliminary indication of the feasibility of using a self-directed, Web-based approach to teaching silvics in forestry curricula

Inflatonless Inflation

We consider a 4+N dimensional Einstein gravity coupled to a non-linear sigma model. This theory admits a solution in which the N extra dimensions contract exponentially while the ordinary space expand exponentially. Physically, the non-linear sigma fields induce the dynamical compactification of the extra dimensions, which in turn drives inflation. No inflatons are required.Comment: 12 pages, version to appear in IJMP

Physiological response to groundwater depth varies among species and with river flow regulation

We investigated the physiological response of two native riparian tree species (Populus fremontii and Salix gooddingii) and one exotic species (Tamarix chinensis) to groundwater availability along gradients of depth to groundwater at two rivers in Arizona. Depth to groundwater (DGW) at the dam-regulated Bill Williams River (BWR) was relatively constant and shallow (,4 m). Populus fremontii at BWR did not experience reduced water availability at deeper groundwater depths, as evidenced by high predawn water potential. However, leaf gas exchange of P. fremontii was sensitive to high vapor pressure deficit where surface flow was ephemeral at BWR. Lower predawn water potentials of S. gooddingii at BWR suggested reduced water availability at deeper groundwater depths, but these reductions did not adversely affect net photosynthetic rate. Along the range of depth to groundwater at BWR, all three species suffered little canopy dieback, and dieback was not related to depth to groundwater. Depth to groundwater at the free-flowing Hassayampa River (HRP) was much greater and declined more rapidly in the ephemeral reaches than at BWR. Both P. fremontii and S. gooddingii experienced reduced water availability at deeper groundwater depths at HRP, as evidenced by lower predawn water potential. Both species also experienced reduced leaf gas exchange at deeper groundwater depths. Canopy dieback of all species was higher at HRP than at BWR and increased with increasing DGW, especially when DGW fell below 3 m. There was evidence to support branch sacrifice in these three riparian tree species as a means of improving water status in the surviving shoot. However, branch sacrifice was insufficient to prevent mortality in some of the native trees where DGW fell below 3 m at HRP. In contrast to the native species, T. chinensis showed no change in water availability, leaf gas exchange, or canopy dieback with increasing DGW at either river. Leaf gas exchange was lower and dieback was greater for T. chinensis at HRP where depth to groundwater was greater than at BWR, but there was no mortality at either river. Our results show that deep groundwater is more detrimental to the physiological condition of P. fremontii and S. gooddingii than it is to T. chinensis. Also, the pronounced differences in DGW and tree physiological performance between BWR and HRP suggest that dam regulation can increase water availability to mature trees in some desert riparian ecosystems. Finally, our study also provides estimates of the range of DGW that can maintain healthy, mature P. fremontii and S. gooddingii trees

Growth sensitivity to drought of co-occurring Pinus Spp. along an elevation gradient in northern Mexico

Climate change is predicted to increase the frequency of severe drought, yet little information exists on the impacts of drought on dominant trees of Mexican pine forests, which are among the most biologically diverse forests in the world. We conducted the first comparison of growth sensitivity to drought of two co-occurring Pious species in Mexico to understand whether growth of dominant pines of the Sierra Madre Occidental in northern Mexico is sensitive to drought and temperature variation and to understand how sensitivity differs between tree species and elevations. We sampled and analyzed tree-ring data across a 400-m elevation gradient for the years 1945-2004 for co-occurring Pinus engelmannii and Pious lumholtzii at Basaseachi National Park, Chihuahua, Mexico. We hypothesized that growth sensitivity to drought would be highest at low elevations, annual basal area increment (BAI) would be lowest at low elevations, and winter precipitation would covary positively with BAI at all elevations. Growth sensitivity to drought, as measured by a wet-dry ring-width index ratio (W:D), was significantly higher for both species at low elevations (W:D range 2.2-2.8) than at intermediate and high elevations (W:D range 1.5-1.9). Pious engelmannii had significantly higher W:D (2.2) than P. lumholtzii (1.8). Annual BAI did not differ between elevations or species. Annual ring width index was positively and significantly associated with winter (December April) precipitation. This association was stronger at low elevations than at high elevations. Other seasons of precipitation and other climatic variables were not significantly associated with annual growth. Our results suggest that the increasing frequency and severity of drought predicted for this region in the coming decades will reduce growth of P. engelmannii and P lumholtzii, with greater impacts on low-elevation populations and on P engelmannii