Shrub facilitation increases plant diversity along an arid scrubland-temperate rainforest boundary in South America

Theoretical models predict nurse plant facilitation enhances species richness by ameliorating stressful environmental conditions and expanding distributional ranges of stress-intolerant species into harsh environments. We studied the role of nurse facilitation on the recruitment of perennial plants along an arid scrubland–temperate rain forest boundary to test the following predictions: (1) nurse shrub canopy increases seedling abundance and species richness along the rain forest–scrubland boundary; (2) scrubland species are less dependent on facilitative interactions than temperate rain forest species, especially at the moister, upper end of the gradient

Oak Persistence in Mediterranean Landscapes: The Combined Role of Management, Topography, and Wildfires

Mediterranean ecosystems have been shaped by a history of human and ecological disturbances. Understanding the dynamics of these social-ecological systems requires an understanding of how human and ecological factors interact. In this study, we assess the combined role of management practices and biophysical variables, i.e., wildfire and topography, to explain patterns of tree persistence in a cork oak (Quercus suber L.) landscape of southern Portugal. We used face-to-face interviews with landowners to identify the management practices and the incentives that motivated them. We used aerial photographs and a Geographic Information System (GIS) to classify vegetation patch-type transitions over a period of 45 years (1958-2002) and logistic regression to explain such changes based on management and biophysical factors. The best model explaining vegetation transitions leading to cork oak persistence in the landscape included both biophysical and management variables. Tree persistence was more likely to occur on steeper slopes, in the absence of wildfires, and in the absence of understory management. We identified ecological, ideological, and economical barriers that preclude oak persistence and that are important to consider in implementing efficient environmental policies for adequate conservation and reforestation programs of Mediterranean cork oak landscape

Intra-hour cloud index forecasting with data assimilation

We introduce a computational framework to forecast cloud index (CI)fields for up to one hour on a spatial domain that covers a city. Such intra-hour CI forecasts are important to produce solar power forecasts of utility scale solar power and distributed rooftop solar. Our method combines a 2D advection model with cloud motion vectors (CMVs)derived from a mesoscale numerical weather prediction (NWP)model and sparse optical flow acting on successive, geostationary satellite images. We use ensemble data assimilation to combine these sources of cloud motion information based on the uncertainty of each data source. Our technique produces forecasts that have similar or lower root mean square error than reference techniques that use only optical flow, NWP CMV fields, or persistence. We describe how the method operates on three representative case studies and present results from 39 cloudy days

Source Parameters of Induced Seismicity in North America

Source parameters of earthquakes play a key role in the understanding of earthquake behavior and modelling of seismic hazard. They describe the size of earthquakes, including how much energy is generated during the rupture, and how the ground motion is distributed over different frequency bands and azimuths. The last decade’s increase in induced seismicity caused by oil and gas production has led to an interest in understanding the underlying earthquake processes and how they can be modelled. This thesis is divided into three studies, each examining source parameters of induced earthquakes in North America. In the first study, I show that for earthquakes in Central US the variability of ground-motion prediction equations (GMPEs), known as sigma, can be reduced by adjusting the basic input source parameters of location and magnitude. Sigma is an important seismic hazard parameter because it exerts significant control over the expected ground motions at return periods used in seismic design. Refinements in magnitude were shown to reduce sigma more than refinements in location. This reflects that between-event variability is not completely accounted for by magnitude in the GMPE, as it is also influenced by other source parameters such as stress drop. In the second study, I examine stress drop and corner frequency in the Western Canada Sedimentary Basin (WCSB) using the Empirical Green’s Function (EGF) method. Large azimuthal variations are found in the corner frequencies for earthquakes, which indicates rupture directivity, a phenomenon which can have implications for observed high-frequency ground motion. By modelling the directivity using a Haskell (1964) model, earthquake corner frequencies are retrieved despite the region’s sparse seismic network. Finally, in the third study, I show that the stress drops obtained from the previous WCSB EGF study can be used as proxies for the GMPE “stress parameter”. I also test whether they provide equivalent measures of the high-frequency content of the earthquake source. I find that GMPE stress parameters tend to yield lower corner frequency values in the forward rupture directivity direction when comparing individual earthquake records. This can be partly attributed to the trade-off between source and site effects in GMPE modeling

An observation of LHR noise with banded structure by the sounding rocket S29 Barium-GEOS

The measurement of electrostatic and obviously locally produced noise near the lower hybrid frequency made by the sounding rocket S29 Barium-GEOS is reported. The noise is strongly related to the spin of the rocket and reaches well below the local lower hybrid resonance frequency. Above the altitude of 300 km the noise shows banded structure roughly organized by the hydrogen cyclotron frequency. Simultaneously with the banded structure, a signal near the hydrogen cyclotron frequency is detected. This signal is also spin related. The characteristics of the noise suggest that it is locally generated by the rocket payload disturbing the plasma. If this interpretation is correct we expect plasma wave experiments on other spacecrafts, e.g., the space shuttle to observe similar phenomena

The future of coffee and cocoa agroforestry in a warmer Mesoamerica

Climate change threatens cofee production and the livelihoods of thousands of families in Mesoamerica that depend on it. Replacing cofee with cocoa and integrating trees in combined agroforestry systems to ameliorate abiotic stress are among the proposed alternatives to overcome this challenge. These two alternatives do not consider the vulnerability of cocoa and tree species commonly used in agroforestry plantations to future climate conditions. We assessed the suitability of these alternatives by identifying the potential changes in the distribution of cofee, cocoa and the 100 most common agroforestry trees found in Mesoamerica. Here we show that cocoa could potentially become an alternative in most of cofee vulnerable areas. Agroforestry with currently preferred tree species is highly vulnerable to future climate change. Transforming agroforestry systems by changing tree species composition may be the best approach to adapt most of the cofee and cocoa production areas. Our results stress the urgency for land use planning considering climate change efects and to assess new combinations of agroforestry species in cofee and cocoa plantations in Mesoamerica

Are drought and wildfires turning Mediterranean cork oak forests into persistent shrublands?

In the Iberian Peninsula Mediterranean oak forests have been transformed into a mosaic landscape of four main patch-types: forests, savannas, shrublands and grasslands. We used aerial photographs over a period of 45 years (1958-2002) to quantify the persistence and rates of transitions between vegetation patch-types in southern Portugal, where cork oak is the dominant tree species. We used logistic regression to relate vegetation changes with topographical features and wildfire history. Over the 45 years, shrublands have been the most persistent patch-type (59%), and have been expanding; forests are also persistent (55%) but have been decreasing since 1985; savannas and grasslands were less persistent (33% and 15%, respectively). Shrublands persistence was significantly correlated with wildfire occurrence, particularly on southern exposures after 1995. In contrast, forest persistence decreased with wildfire occurrence, and forests were more likely to change into shrublands where wildfire had occurred after 1995