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Global change is altering interactions between ecological disturbances. We review interactions between tropical cyclones and fires that affect woody biomes in many islands and coastal areas. Cyclone-induced damage to trees can increase fuel loads on the ground and dryness in the understory, which increases the likelihood, intensity, and area of subsequent fires. In forest biomes, cyclone-fire interactions may initiate a grass-fire cycle and establish stable open-canopy biomes. In cyclone-prone regions, frequent cyclone-enhanced fires may generate and main-tain stable open-canopy biomes (e.g., savannas and woodlands). We discuss how global change is transforming fire and cyclone regimes, extensively altering cyclone-fire interactions. These altered cyclone-fire interactions are shifting biomes away from historical states and causing loss of biodiversity.

Effects of invasive species on ecosystem processes are often thought to underlie the effects of invaders on community dynamics. Specifically, positive feedbacks in which invasive species alter ecosystem function in ways that favour their own growth have been suggested as an important mechanism contributing to the success of invasion. In this study, we analysed the impacts of the invasive exotic tree Acer platanoides on survival and growth of conspecific and native tree seedlings, and explored whether these impacts can be explained by the ecosystem effects of the invader. Seedlings of Acer platanoides, Acer saccharum, Fraxinus americana and Prunus serotina were monitored in quadrats in three forest stands in northwestern Connecticut. Soil resources and light levels were quantified in the same quadrats. Maximum-likelihood methods were used to predict seedling survival and growth as a function of the size and spatial configuration of A. platanoides trees in the immediate neighbourhood (0–25 m). The abundance of A. platanoides in the neighbourhood had moderate negative effects on survival of first-year conspecific seedlings, but did not affect survival of older conspecific or native seedlings. These negative effects on conspecifics were not correlated with soil nutrients or light levels, but were presumably related to Janzen-Connell effects. In contrast, A. platanoides had strong positive effects on the growth of seedlings of all four species. These positive effects appear to be related to the positive impacts of the invader on soil fertility. Our results support the importance of canopy-seedling feedbacks as a mechanism regulating the rate of invasion in forests. However, they also indicate that the net consequences of feedbacks on the process of invasion are probably determined by the balance of positive and negative feedbacks acting at the same time on different aspects of regeneration (i.e. survival vs. growth). Synthesis: Because the species with the highest inhere

Part I - Dipole Properties of Atoms and Molecules in the Random Phase Approximation: A random phase approximation (RPA) calculation and a direct sum over states is used to calculate second-order optical properties and van der Waals coefficients. A basis set expansion technique is used and no continuum-like functions are included in the basis. However, unlike other methods we do not force the basis functions to satisfy any sum-rule constraints but rather the formalism (RPA) is such that the Thomas Reiche-Kuhn sum rule is satisfied exactly. Central attention is paid to the dynamic polarizability from which most of the other properties are derived. Application is made to helium and molecular hydrogen. In addition to the polarizability and van der Waals coefficients, results are given for the molecular anisotropy of H_2, Rayleigh scattering cross sections and Verdet constants as a function of frequency. Agreement with experiment and other theories is good. Other energy weighted sum-rules are calculated and compare very well with previous estimates. The practicality of our method suggests its applications to larger molecular systems and other properties. Part II - Photoionization Cross Sections for H_2 in the Random Phase Approximation with a Square-Integrable Basis: Total photoionization cross sections for H_2 are calculated in the Random Phase Approximation (RPA) through a numerical analytic continuation procedure applied to the polarizability for complex valuesof the frequency. The representation of the polarizability that is required is obtained from a discrete set of excitation energies and oscillator strengths that satisfies the Thomas-Reich-Kuhn sum rule exactly and other energy-weighted sum rules approximately. The fact that the excitation spectrum is obtained through a solution of the RPA equations with no continuum functions added to the basis makes the method well suited for general molecular photoionization calculations. The results are compared with experime

Part I - Dipole Properties of Atoms and Molecules in the Random Phase Approximation: A random phase approximation (RPA) calculation and a direct sum over states is used to calculate second-order optical properties and van der Waals coefficients. A basis set expansion technique is used and no continuum-like functions are included in the basis. However, unlike other methods we do not force the basis functions to satisfy any sum-rule constraints but rather the formalism (RPA) is such that the Thomas Reiche-Kuhn sum rule is satisfied exactly. Central attention is paid to the dynamic polarizability from which most of the other properties are derived. Application is made to helium and molecular hydrogen. In addition to the polarizability and van der Waals coefficients, results are given for the molecular anisotropy of H_2, Rayleigh scattering cross sections and Verdet constants as a function of frequency. Agreement with experiment and other theories is good. Other energy weighted sum-rules are calculated and compare very well with previous estimates. The practicality of our method suggests its applications to larger molecular systems and other properties. Part II - Photoionization Cross Sections for H_2 in the Random Phase Approximation with a Square-Integrable Basis: Total photoionization cross sections for H_2 are calculated in the Random Phase Approximation (RPA) through a numerical analytic continuation procedure applied to the polarizability for complex valuesof the frequency. The representation of the polarizability that is required is obtained from a discrete set of excitation energies and oscillator strengths that satisfies the Thomas-Reich-Kuhn sum rule exactly and other energy-weighted sum rules approximately. The fact that the excitation spectrum is obtained through a solution of the RPA equations with no continuum functions added to the basis makes the method well suited for general molecular photoionization calculations. The results are compared with experime

Part I - Dipole Properties of Atoms and Molecules in the Random Phase Approximation: A random phase approximation (RPA) calculation and a direct sum over states is used to calculate second-order optical properties and van der Waals coefficients. A basis set expansion technique is used and no continuum-like functions are included in the basis. However, unlike other methods we do not force the basis functions to satisfy any sum-rule constraints but rather the formalism (RPA) is such that the Thomas Reiche-Kuhn sum rule is satisfied exactly. Central attention is paid to the dynamic polarizability from which most of the other properties are derived. Application is made to helium and molecular hydrogen. In addition to the polarizability and van der Waals coefficients, results are given for the molecular anisotropy of H_2, Rayleigh scattering cross sections and Verdet constants as a function of frequency. Agreement with experiment and other theories is good. Other energy weighted sum-rules are calculated and compare very well with previous estimates. The practicality of our method suggests its applications to larger molecular systems and other properties. Part II - Photoionization Cross Sections for H_2 in the Random Phase Approximation with a Square-Integrable Basis: Total photoionization cross sections for H_2 are calculated in the Random Phase Approximation (RPA) through a numerical analytic continuation procedure applied to the polarizability for complex valuesof the frequency. The representation of the polarizability that is required is obtained from a discrete set of excitation energies and oscillator strengths that satisfies the Thomas-Reich-Kuhn sum rule exactly and other energy-weighted sum rules approximately. The fact that the excitation spectrum is obtained through a solution of the RPA equations with no continuum functions added to the basis makes the method well suited for general molecular photoionization calculations. The results are compared with experime