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Anisotropic shock sensitivity and detonation temperature of pentaerythritol tetranitrate single crystal Electrical resistivity of singlecrystal Al2O3 shockcompressed in the pressure range 91-220 GPa (0.91-2.20 Mbar) Experimental investigation of shear stress effects on shockinduced phase transition in InSb single crystal AIP Conf.The shock response of single crystals of the explosive pentaerythritol tetranitrate was studied from 3.4 to 19 GPa. Four orientations, (llO), (OOl), (lOl), and (100) were studied. The shock Hugoniot and shock initiation sensitivities were measured in wedge tests. Intermediate velocity transitions were noted. A sensitivity anomaly near 4 GPa was discovered for (110) orientations. Chemiluminescent phenomena associated with this anomaly were studied using framing photography and uv/visible spectroscopy. Both plane-wave explosive and gas-gun impact experiments were done. Analysis of the steric hindrance occurring during edge dislocation motion in the shear flow associated with shockinduced uniaxial strain was done. The results corroborate the hypothesis that the orientation dependence of shock initiation sensitivity is due to the anisotropy of plastic flow, that is, the relative ease of slip in different orientations. 3572

The volume and complexity of their vascular systems make the dynamics of long-distance water transport in large trees difficult to study. We used heat and deuterated water (D 2 O) as tracers to characterize whole-tree water transport and storage properties in individual trees belonging to the coniferous species Pseudotsuga menziesii . Tracer residence time and half-life increased as tree diameter increased, independent of species. Species-independent scaling of tracer velocity with sapwood-specific conductivity was also observed. When data from this study were combined with similar data from an earlier study of four tropical angiosperm trees, species-independent scaling of tracer velocity and residence time with sapwood hydraulic capacitance was observed. Sapwood capacitance is an intrinsic tissue-level property that appears to govern whole-tree water transport in a similar manner among both tracheid-and vesselbearing species.

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Dwarf mistletoe ( Arceuthobium spp.) is a hemiparasite that is said to be the single-most destructive pathogen of commercially valuable coniferous trees in many regions of the world. Although its destructive nature is well documented in many respects, its effects on the physiology of its host are poorly understood. In the present study, water and carbon relations were characterized over a range of scale from leaf to whole tree in large ( C values were 2.8‰ more negative in infected than in uninfected individuals, consistent with the absence of stomatal adjustment to diminished photosynthetic capacity. Adjustments in hydraulic architecture of infected trees thus contributed to homeostasis of water transport efficiency and transpiration on a leaf area basis, whereas both carbon accumulation and photosynthetic water use efficiency were sharply reduced at both the leaf and whole-tree scale.

The Wind River old-growth forest, in the southern Cascade Range of Washington State, is a cool (average annual temperature, 8.7°C), moist (average annual precipitation, 2223 mm), 500-year-old Douglas-fir 4 -western hemlock forest of moderate to low productivity at 371-m elevation on a less than 10% slope. There is a seasonal snowpack (November-March), and rain-on-snow and freezing-rain events are common in winter. Local geology is characterized by volcanic rocks and deposits of Micocene/Oligocene Micocene-Oligocene 5 (mixed) Micocene and Quaternary age, as well as intrusive rocks of Miocene age. Soils are medial, mesic, Entic Vitrands 6 that are deep (2-3 m), well drained, loams and silt loams, generally stone free, and derived from volcanic tephra. The vegetation is transitional, between the Western Hemlock Zone and the Pacific Silver Fir Zone, and the understory is dominated by vine maple, salal, and Oregon grape. Stand structural parameters have been measured on a 4-ha plot. There are eight species of conifers, with a stand density of 427 trees ha )1 and basal area of 82.9 m 2 ha )1 . Dominant conifers include Douglas-fir (35 trees ha )1 ), western hemlock (224 trees ha )1 ), Pacific yew (86 trees ha )1 ), western red cedar 7 (30 trees ha )1 ), and Pacific silver fir (47 trees ha )1 ). The average height of Douglas-fir is 52.0 m (tallest tree, 64.6 m), whereas western hemlock averages 19.0 m (tallest tree, 55.7 m). The regional disturbance regime is dominated by high-severity to moderateseverity fire, from which this forest is thought to have originated. There is no evidence that fire has occurred in the forest after establishment. Primary agents of stand disturbance, which act at the individual to small groups of trees scale, are wind, snow loads, and drought, in combination and interacting with root-rot and butt-rot fungi, heart-rot fungi, dwarf mistletoe, and bark beetles. The forest composition is slowly shifting from dominance by Douglas-fir, a shade-intolerant species, to western hemlock, western red cedar, Pacific yew, and Pacific silver fir, all shade-tolerant species. The Wind River old-growth forest fits the regional definition of Douglas-fir ''old growth'' on western hemlock sites.