Forest Views: Shifting Attitudes Toward the Environment in Northeast Oregon

This brief reports on a telephone survey conducted in fall 2014 as part of the ongoing Communities and Forests in Oregon (CAFOR) project. CAFOR focuses on seven counties in the Blue Mountains of northeast Oregon (Baker, Crook, Grant, Umatilla, Union, Wallowa, and Wheeler), where the landscape and local livelihoods are changing in interconnected ways. In an effort to inform policy development around natural resource management, the study seeks to understand how public perceptions of climate change and forest management intersect. Authors Angela Boag, Joel Hartter, Lawrence Hamilton, Forrest Stevens, Mark Ducey, Michael Palace, Nils Christoffersen, and Paul Oester report that 65 percent of those surveyed believe that forests are less healthy than they were twenty years ago. Approximately half of residents support increased user fees to improve forest health on federal land, and a majority believes that climate change is happening, although opinion is split between those who believe it is human-caused and those who believe it is caused by natural forces. The authors conclude that innovative economic and policy solutions are needed across the Inland West to help people and forests regain a strong and productive relationship that both supports livelihoods and sustains working landscapes

Does it matter if people think climate change is human caused?

There is a growing consensus that climate is changing, but beliefs about the causal factors vary widely among the general public. Current research shows that such causal beliefs are strongly influenced by cultural, political, and identity-driven views. We examined the influence that local perceptions have on the acceptance of basic facts about climate change. We also examined the connection to wildfire by local people. Two recent telephone surveys found that 37% (in 2011) and 46% (in 2014) of eastern Oregon (USA) respondents accept the scientific consensus that human activities are now changing the climate. Although most do not agree with that consensus, large majorities (85–86%) do agree that climate is changing, whether by natural or human causes. Acceptance of anthropogenic climate change generally divides along political party lines, but acceptance of climate change more generally, and concerns about wildfire, transcend political divisions. Support for active forest management to reduce wildfire risks is strong in this region, and restoration treatments could be critical to the resilience of both communities and ecosystems. Although these immediate steps involve adaptations to a changing climate, they can be motivated without necessarily invoking human-caused climate change, a divisive concept among local landowners

Inferring ice fabric from birefringence loss in airborne radargrams : application to the eastern shear margin of Thwaites Glacier, West Antarctica

This work is ITGC Contribution No. ITGC-036 and is an output from the Thwaites Interdisciplinary Margin Evolution (TIME) project as part of the International Thwaites Glacier Collaboration (ITGC), supported by Natural Environment Research Council (NERC) research grant #NE/S006788/1 supporting T. J. Young and P. Christoffersen, and National Science Foundation (NSF) research grant #1739027 supporting S. M. Tulaczyk and D. M. Schroeder. Logistics for this project were provided by the NSF-U.S. Antarctic Program and NERC-British Antarctic Survey. R. Culberg is supported by a USA Department of Defense NDSEG Fellowship and N. L. Bienert is supported by an NSF Graduate Research Fellowship.In airborne radargrams, undulating periodic patterns in amplitude that overprint traditional radiostratigraphic layering are occasionally observed, however, they have yet to be analyzed from a geophysical or glaciological perspective. We present evidence supported by theory that these depth-periodic patterns are consistent with a modulation of the received radar power due to the birefringence of polar ice, and therefore indicate the presence of bulk fabric anisotropy. Here, we investigate the periodic component of birefringence-induced radar power recorded in airborne radar data at the eastern shear margin of Thwaites Glacier and quantify the lateral variation in azimuthal fabric strength across this margin. We find the depth variability of birefringence periodicity crossing the shear margin to be a visual expression of its shear state and its development, which appears consistent with present-day ice deformation. The morphology of the birefringent patterns is centered at the location of maximum shear and observed in all cross-margin profiles, consistent with predictions of ice fabric when subjected to simple shear. The englacial fabric appears stronger inside the ice stream than outward of the shear margin. The detection of birefringent periodicity from non-polarimetric radargrams presents a novel use of subsurface radar to constrain lateral variations in fabric strength, locate present and past shear margins, and characterize the deformation history of polar ice sheets.Publisher PDFPeer reviewe

Solid behavior of anisotropic rigid frictionless bead assemblies

We investigate the structure and mechanical behavior of assemblies of frictionless, nearly rigid equal-sized beads, in the quasistatic limit, by numerical simulation. Three different loading paths are explored: triaxial compression, triaxial extension and simple shear. Generalizing recent results [1], we show that the material, despite rather strong finite sample size effects, is able to sustain a finite deviator stress in the macroscopic limit, along all three paths, without dilatancy. The shape of the yield surface is adequately described by a Lade-Duncan (rather than Mohr-Coulomb) criterion. While scalar state variables keep the same values as in isotropic systems, fabric and force anisotropies are each characterized by one parameter and are in one-to-one correspondence with principal stress ratio along all three loading paths.The anisotropy of the pair correlation function extends to a distance between bead surfaces on the order of 10% of the diameter. The tensor of elastic moduli is shown to possess a nearly singular, uniaxial structure related to stress anisotropy. Possible stress-strain relations in monotonic loading paths are also discussed

UAV photogrammetry and structure from motion to assess calving dynamics at Store Glacier, a large outlet draining the Greenland ice sheet

This study presents the application of a cost-effective, unmanned aerial vehicle (UAV) to investigate calving dynamics at a major marine-terminating outlet glacier draining the western sector of the Greenland ice sheet. The UAV was flown over Store Glacier on three sorties during summer 2013 and acquired over 2000 overlapping, geotagged images of the calving front at an ~40 cm ground sampling distance. Stereo-photogrammetry applied to these images enabled the extraction of high-resolution digital elevation models (DEMs) with vertical accuracies of ± 1.9 m which were used to quantify glaciological processes from early July to late August 2013. The central zone of the calving front advanced by ~500 m, whilst the lateral margins remained stable. The orientation of crevasses and the surface velocity field derived from feature tracking indicates that lateral drag is the primary resistive force and that ice flow varies across the calving front from 2.5 m d−1 at the margins to in excess of 16 m d−1 at the centreline. Ice flux through the calving front is 3.8 × 107 m3 d−1, equivalent to 13.9 Gt a−1 and comparable to flux-gate estimates of Store Glacier's annual discharge. Water-filled crevasses were present throughout the observation period but covered a limited area of between 0.025 and 0.24% of the terminus and did not appear to exert any significant control over fracture or calving. We conclude that the use of repeat UAV surveys coupled with the processing techniques outlined in this paper have great potential for elucidating the complex frontal dynamics that characterise large calving outlet glaciers

Internal states of model isotropic granular packings. I. Assembling process, geometry and contact networks

This is the first paper of a series of three, reporting on numerical simulation studies of geometric and mechanical properties of static assemblies of spherical beads under an isotropic pressure. Frictionless systems assemble in the unique random close packing (RCP) state in the low pressure limit if the compression process is fast enough, slower processes inducing traces of crystallization, and exhibit specific properties directly related to isostaticity of the force-carrying structure. The different structures of frictional packings assembled by various methods cannot be classified by the sole density. While lubricated systems approach RCP densities and coordination number z^*~=6 on the backbone in the rigid limit, an idealized "vibration" procedure results in equally dense configurations with z^*~=4.5. Near neighbor correlations on various scales are computed and compared to available laboratory data, although z^* values remain experimentally inaccessible. Low coordination packings have many rattlers (more than 10% of the grains carry no force), which should be accounted for on studying position correlations, and a small proportion of harmless "floppy modes" associated with divalent grains. Frictional packings, however slowly assembled under low pressure, retain a finite level of force indeterminacy, except in the limit of infinite friction.Comment: 29 pages. Published in Physical Review

Modelling climate change responses in tropical forests: similar productivity estimates across five models, but different mechanisms and responses

Accurately predicting the response of Amazonia to climate change is important for predicting climate change across the globe. Changes in multiple climatic factors simultaneously result in complex non-linear ecosystem responses, which are difficult to predict using vegetation models. Using leaf- and canopy-scale observations, this study evaluated the capability of five vegetation models (Community Land Model version 3.5 coupled to the Dynamic Global Vegetation model – CLM3.5–DGVM; Ecosystem Demography model version 2 – ED2; the Joint UK Land Environment Simulator version 2.1 – JULES; Simple Biosphere model version 3 – SiB3; and the soil–plant–atmosphere model – SPA) to simulate the responses of leaf- and canopy-scale productivity to changes in temperature and drought in an Amazonian forest. The models did not agree as to whether gross primary productivity (GPP) was more sensitive to changes in temperature or precipitation, but all the models were consistent with the prediction that GPP would be higher if tropical forests were 5 °C cooler than current ambient temperatures. There was greater model–data consistency in the response of net ecosystem exchange (NEE) to changes in temperature than in the response to temperature by net photosynthesis (An), stomatal conductance (gs) and leaf area index (LAI). Modelled canopy-scale fluxes are calculated by scaling leaf-scale fluxes using LAI. At the leaf-scale, the models did not agree on the temperature or magnitude of the optimum points of An, Vcmax or gs, and model variation in these parameters was compensated for by variations in the absolute magnitude of simulated LAI and how it altered with temperature. Across the models, there was, however, consistency in two leaf-scale responses: (1) change in An with temperature was more closely linked to stomatal behaviour than biochemical processes; and (2) intrinsic water use efficiency (IWUE) increased with temperature, especially when combined with drought. These results suggest that even up to fairly extreme temperature increases from ambient levels (+6 °C), simulated photosynthesis becomes increasingly sensitive to gs and remains less sensitive to biochemical changes. To improve the reliability of simulations of the response of Amazonian rainforest to climate change, the mechanistic underpinnings of vegetation models need to be validated at both leaf- and canopy-scales to improve accuracy and consistency in the quantification of processes within and across an ecosystem.This research was enabled by a grant from the Andes–Amazon Initiative of The Gordon and Betty Moore Foundation. L. Rowland gratefully acknowledges financial support from the Natural Environment Research Council (UK) for a NERC PhD studentship, and NERC grant NE/J011002/1; PM also acknowledges support from ARC FT110100457

Rheophysics of dense granular materials : Discrete simulation of plane shear flows

We study the steady plane shear flow of a dense assembly of frictional, inelastic disks using discrete simulation and prescribing the pressure and the shear rate. We show that, in the limit of rigid grains, the shear state is determined by a single dimensionless number, called inertial number I, which describes the ratio of inertial to pressure forces. Small values of I correspond to the quasi-static regime of soil mechanics, while large values of I correspond to the collisional regime of the kinetic theory. Those shear states are homogeneous, and become intermittent in the quasi-static regime. When I increases in the intermediate regime, we measure an approximately linear decrease of the solid fraction from the maximum packing value, and an approximately linear increase of the effective friction coefficient from the static internal friction value. From those dilatancy and friction laws, we deduce the constitutive law for dense granular flows, with a plastic Coulomb term and a viscous Bagnold term. We also show that the relative velocity fluctuations follow a scaling law as a function of I. The mechanical characteristics of the grains (restitution, friction and elasticity) have a very small influence in this intermediate regime. Then, we explain how the friction law is related to the angular distribution of contact forces, and why the local frictional forces have a small contribution to the macroscopic friction. At the end, as an example of heterogeneous stress distribution, we describe the shear localization when gravity is added.Comment: 24 pages, 19 figure