Prescribed burning is an effective treatment to reduce the risk of very severe wildfires. Many forests, however, are ill-suited for prescribed fire, because of high fuel loads, high tree densities, or young stands that are vulnerable to low intensity fires. Utilizing prescribed fire in reforested stands established after high-severity fires can protect against further losses from subsequent wildfires (“reburn” fires). Only a handful of studies provide practical guidance on how and when to burn young forests. We apply the concept of “pyrosilviculture” to suggest ways in which pre-fire silvicultural treatments can make prescribed burns more effective across a variety of age classes and structures. We also update results from a study in which several age classes of stands (12-, 22-, 32-, and 100-year-old) were burned experimentally on the same day. This focuses on a key question for managers: how to determine the right stand age at which prescribed fires may become feasible. As expected, older stands were more resistant to damage and had higher survival rates. If tree survival during prescribed fires is a primary objective, then a conservative approach is to wait until stands are age 30 before instituting prescribed fire. This is likely an overestimate of the minimum age, given that the prescribed fires applied in this study occurred during especially dry conditions. Under different objectives, higher mortality may be considered beneficial if it creates low-density, high-complexity stands that are similar to historic conditions.

A monolithic Ku-band phase shifter employing voltage tunable Bi1 5Zn1 0Nb1 5O7 (BZN) thin film parallel plate capacitors is reported. BZN films were deposited by radio frequency magnetron sputtering on single-crystal sapphire substrates. A nine-section distributed coplanar waveguide loaded-line phase-shifter structure was designed. A differential phase shift of 175 was achieved with a maximum insertion loss of 3.5 dB at 15 GHz, giving a figure of merit 50 dB. To the best of our knowledge, this is the first demonstration of a monolithic tunable microwave circuit using BZN thin films.

We tested the release potential of suppressed giant sequoia (Sequoiadendron giganteum) saplings in a plantation that was overgrown with shrubs at Blodgett Forest Research Station, CA in the mixed conifer forest of the Sierra Nevada. As an ancillary case study, we compared the shrub removal method of release with a clear-and-plant method in an adjacent stand. Measurements of various morphological traits were collected prior to shrub removal, then sapling height growth response was measured periodically after the release treatment. In general, giant sequoia responded quickly to the removal of competing shrubs, growing steadily for 20 years following treatment. Among the morphological traits considered, live crown ratio alone was the most important factor in predicting relative height growth following treatment. Other traits were correlated with release, but had lower importance values as indicated by a model selection procedure. The 16-year-old saplings that were released in this study did not grow as large as 2-year-old seedlings that were planted synchronously with release, but both methods resulted in merchantable-sized trees 20 years after treatment. Planted seedlings outgrew released seedlings by 27% in terms of stature and by 37% in terms of diameter. The released stand is projected with a growth model to take 42 years longer than the planted stand to grow to an average diameter of 38 cm. The misperception of giant sequoia as having a low capacity for release may be related to its ambiguous categorization as a shade intolerant species. (c) 2006 Elsevier B.V. All rights reserved.

Planar capacitors employing Bi1.5Zn1.0Nb1.5O7 (BZN) thin films with the pyrochlore structure were fabricated on platinized sapphire substrates. The total device quality factor and capacitance were analyzed in the microwave frequency range (up to 20 GHz) by measuring reflection coefficients with a vector network analyzer. The parasitics due to the probe pads were extracted from the measurements. The total device quality factor, which included losses from the dielectric and the electrodes, was more than 200 up to 20 GHz for devices with an area of 100 ?m2. Based on the frequency-dependence of the impedance, series losses of unknown origin appear to dominate the device quality factor at higher frequencies. No significant dispersion in the device capacitance, as would be associated with a dielectric relaxation of BZN, was measured. The large electric field tunability of the permittivity of BZN films and the high device quality factors make these films attractive for voltage controlled microwave devices.

Replicated circular openings ranging in size from 0.1 to 1 ha were cleared on a Sierran mixed conifer forest in 1996 at the Blodgett Forest Research Station, California and planted with seedlings of six native species. After 3 years of growth, heights of all trees were measured and analyzed according to species, opening size, and location within the opening. To determine the cause of the edge influence on height, we measured differences along north-south transects in extension growth, pre-dawn water potential, and light availability for three species of trees: giant sequoia (Sequoiadendron giganteum), ponderosa pine (Pinus ponderosa), and Douglas-fir (Ptseudotsuga menziesii var. menziesii). The sequence of mean height from tallest to shortest based on species was: giant sequoia > incense cedar > Douglas-fir > ponderosa pine > white fir > sugar pine. For all species combined, a ten-fold increase in the area of the opening corresponded to a 34% increase in mean height. Trees were tallest on average in the north rows and shortest in the south rows. There was no difference in height between trees in the east and west rows. As expected, resource availability was greatest near the center and least near the edges with north edges receiving significantly more light than southern edges. In general, observed edge effects on sapling height growth were correlated with light and water supply. However there were important differences between species in the nature of the co-limitation. Giant sequoia growth was most sensitive to light and water availability. Together they explained more than 47% of the observed variation in giant sequoia height. In contrast, only light was a significant predictor of ponderosa pine performance. Douglas-fir heights were significantly related to both light and water but there was more unexplained variability in the Douglas-fir model compared to the other species. These highly controlled experimental group openings provide a standard reference for silviculturalists using the group selection method of regeneration. (C) 2002 Elsevier Science B.V. All rights reserved.

A significant expansion of prescribed fire activity will be necessary to mitigate growing wildfire hazard in California forests. Forest managers can facilitate this expansion by promoting forest structures that allow for more effective implementation of prescribed fire, for both initial-entry and repeat burns. We analyzed changes in surface fuel during a series of three burns in replicated mixed-conifer stands following a period of over 100 years of fire suppression and exclusion. Total fuel load, proportion of pine present, canopy cover and basal area of live trees were relevant forest-structure components that influenced plot-scale fuel consumption. The study highlighted the importance of pre-fire fuel load and the relative proportion of pine in the overstory, which both led to greater amounts of fuel consumption. The initial-entry burn dramatically reduced all fuel categories (fine fuel, coarse wood and duff). Following each burn, fuel recovered until the next burn reduced loads enough to maintain low fuel levels. We apply the results to provide an example of how to determine the timing of prescribed fires.

The effect of noise figure of different AlGaN/GaN high electron-mobility transistor (HEMT) epitaxy structures is reported. The addition of a thin AlN layer between the barrier and channel gives better performance at biasings other than the best for minimum noise figure. However, varying Al composition in the HEMT barrier does not change the noise performance, contrary to a 2003 study by Lu et al. The measurements are checked with both the Pospieszalski and van der Ziel (Pucel) models. The models are used on six different samples, helping to reinforce the measurements and showing the strengths and weaknesses of each.