Altitudinal Shifts of the Native and Introduced Flora of California in the Context of 20th-Century Warming

Aim: The differential responses of plant species to climate change are of great interest and grave concern for scientists and conservationists. One underexploited resource for better understanding these changes are the records held by herbaria. Using these records to assess the responses of different groups of species across the entire flora of California, we sought to quantify the magnitude of species elevational shifts, to measure differences in shifts among functional groups and between native and introduced species, and to evaluate whether these shifts were related to the conservation of thermal niches. Location: California. Methods: To characterize these shifts in California, we used 681,609 georeferenced herbarium records to estimate mean shifts in elevational and climatic space of 4426 plant taxa.We developed and employed a statistical method to robustly analyse the data represented in these records. Results: We found that 15% of all taxa in California have ranges that have shifted upward over the past century. There are significant differences between range shifts of taxa with different naturalization statuses: 12% of endemic taxa show significant upward range shifts, while a greater proportion (27%) of introduced taxa have shifted upward.We found significant differences between the proportion of significant range shifts across taxa with different seed sizes, but did not find evidence for differences in shift based on life-form (annual versus perennial, herbaceous versus woody). Main conclusions: Our analyses suggest that introduced species have disproportionately expanded their ranges upward in elevation over the past century when compared with native species.While these shifts in introduced species may not be exclusively driven by climate, they highlight the importance of considering the interacting factors of climate-driven range shifts and invasion to understand how floras are responding in the face of anthropogenic change

Structure and Stability of the Twofold Surface of Icosahedral Al-Pd-Mn by Low-Energy Electron Diffraction and X-Ray Photoemission Spectroscopy

We have used low-energy electron diffraction and x-ray photoemission spectroscopy to investigate the structure of the twofold surface of icosahedral Al-Pd-Mn. The regrowth of the surface by annealing after sputtering took place in two distinct stages. The first stage was the appearance of a fine-grained surface phase with icosahedral, or near-icosahedral, symmetry. For higher annealing temperatures (above 800 K) a bulk terminated face-centered icosahedral surface was observed

Influence of nanostructure and nitrogen content on the optical and electrical properties of reactively sputtered FeSiAl(N) films

In this study, the optical properties and dc resistivity of a series of FeSiAl(N) films reactively sputtered with different partial pressures of N were investigated. Spectroscopic ellipsometry was used to measure the real and imaginary parts of the complex dielectric functions. There is a distinct micro/nanostructural transition from single-phase columnar body-centered-cubic (bcc) grains for partial pressure (pp) of nitrogen in sputtering gas ⩽4% to a two-phase nanocomposite of equiaxed bcc nanograins in an amorphous matrix for filmsdeposited with ⩾5% pp N. To assess the effect of surface oxidation on the optical properties, optical measurements were repeated on the 2 and 5% pp N films (representative of the two different types of films with different structures) after they were sputter etched in situ while performing depth profiling of the chemical composition using x-ray photoelectron spectroscopy. The low-nitrogen films(⩽4% pp N) showed a dielectric function typical of a metal whose charge carrier contribution can be described by a classical free electron Drude model. The nanostructured films(⩾5% pp N) showed a positive real part of the dielectric functionε1and no evidence of free-carrier plasmon excitation. The optical conductivity decreased and the dc resistivity increased by about a factor of 2.5 as the film structure changed from a single phase columnar structure to the two-phase material that consisted of nanograins in an amorphous matrix

Surface structures of approximant phases in the Al-Pd-Mn system

We present a study of the surface of the ξ′-Al-Pd-Mn approximant phase based upon scanning tunneling microscopy and low-energy electron diffraction. Several structures are observed on two different samples grown either by the Bridgman technique or by a self-flux method, and which contain various degrees of disorder. We also describe some other complex crystalline phases that are sometimes observed on the fivefold surface of Al-Pd-Mn quasicrystalline samples after the sputter-annealing cleaning process under ultrahigh vacuum conditions. This includes the T approximant phase resulting from surface decomposition after a high-temperature annealing

Laser Cooling of Optically Trapped Molecules

Calcium monofluoride (CaF) molecules are loaded into an optical dipole trap (ODT) and subsequently laser cooled within the trap. Starting with magneto-optical trapping, we sub-Doppler cool CaF and then load $150(30)$ CaF molecules into an ODT. Enhanced loading by a factor of five is obtained when sub-Doppler cooling light and trapping light are on simultaneously. For trapped molecules, we directly observe efficient sub-Doppler cooling to a temperature of $60(5)$ $\mu\text{K}$. The trapped molecular density of $8(2)\times10^7$ cm$^{-3}$ is an order of magnitude greater than in the initial sub-Doppler cooled sample. The trap lifetime of 750(40) ms is dominated by background gas collisions.Comment: 5 pages, 5 figure

Droughts and the ecological future of tropical savanna vegetation

1. Climate change is expected to lead to more frequent, intense and longer droughts in the future, with major implications for ecosystem processes and human livelihoods. The impacts of such droughts are already evident, with vegetation dieback reported from a range of ecosystems, including savannas, in recent years. 2. Most of our insights into the mechanisms governing vegetation drought responses have come from forests and temperate grasslands, while responses of savannas have received less attention. Because the two life forms that dominate savannas—C3 trees and C4 grasses—respond differently to the same environmental controls, savanna responses to droughts can differ from those of forests and grasslands. 3. Drought‐driven mortality of savanna vegetation is not readily predicted by just plant drought‐tolerance traits alone, but is the net outcome of multiple factors, including drought‐avoidance strategies, landscape and neighborhood context, and impacts of past and current stressors including fire, herbivory and inter‐life form competition. 4. Many savannas currently appear to have the capacity to recover from moderate to severe short‐term droughts, although recovery times can be substantial. Factors facilitating recovery include the resprouting ability of vegetation, enhanced flowering and seeding and post‐drought amelioration of herbivory and fire. Future increases in drought severity, length and frequency can interrupt recovery trajectories and lead to compositional shifts, and thus pose substantial threats, particularly to arid and semi‐arid savannas. 5. Synthesis. Our understanding of, and ability to predict, savanna drought responses is currently limited by availability of relevant data, and there is an urgent need for campaigns quantifying drought‐survival traits across diverse savannas. Importantly, these campaigns must move beyond reliance on a limited set of plant functional traits to identifying suites of physiological, morphological, anatomical and structural traits or “syndromes” that encapsulate both avoidance and tolerance strategies. There is also a critical need for a global network of long‐term savanna monitoring sites as these can provide key insights into factors influencing both resistance and resilience of different savannas to droughts. Such efforts, coupled with site‐specific rainfall manipulation experiments that characterize plant trait–drought response relationships, and modelling efforts, will enable a more comprehensive understanding of savanna drought responses