A new approach for modeling delayed fire‐induced tree mortality

Abstract Global change is expanding the ecological niche of mixed‐severity fire regimes into ecosystems that have not usually been associated with wildfires, such as temperate forests and rainforests. In contrast to stand‐replacing fires, mixed‐severity fires may result in delayed tree mortality driven by secondary factors such as post‐fire environmental conditions. Because these effects vary as a function of time post‐fire, their study using commonly applied logistic regression models is challenging. Here, we propose overcoming this challenge through the application of time‐explicit survival models such as the Kaplan‐Meier (KM‐) estimator and the Cox proportional‐hazards (PH‐) model. We use data on tree mortality after mixed‐severity fires in beech forests to (1) illustrate temporal trends in the survival probabilities and the mortality hazard of beech, (2) estimate annual survival probabilities for different burn severities, and (3) consider driving factors with possible time‐dependent effects. Based on our results, we argue that the combination of KM‐estimator and Cox‐PH models have the potential of substantially improve the analysis of delayed post‐disturbance tree mortality by answering when and why tree mortality occurs. The results provide more specific information for implementing post‐fire management measures

Field investigation of the long-term deformational behavior of a 10,000 m**3 cavity at the Asse salt mine.

This paper reports results of experimental field investigations, which have been performed in a 10,000 m**3 salt cavity excavated in the Stassfurt Halite formation of the Asse salt mine at a depth of 1,000 m. The in situ observations relate to cavity closure measurements over a period of about one year as well as to longterm observations up to nearly 5 years with multiple-point extensometers which have been installed at wall depths up to 40 m. After a short description of the field instrumentation, representative results of the actual cavity closure and of the displacement field around the cavity are examined in detail and presented in diagrams

Optical bistability in InSb at room temperature with two‐photon excitation

We report the observation of optical bistability in an InSb resonator at room temperature. This effect and fringe shifts were caused by nonlinear refraction induced by two‐photon absorption of radiation from a single longitudinal mode injection‐locked pulsed CO2 laser operating at 9.6–10.6 μm. Intensities as low as 100 kW/cm2 were found to be sufficient to tune the 250‐μm‐thick cavity through a fringe maximum. From our results we deduce a value of χ(3) of the order of 10−4 esu over the range of intensities investigated