Search results for " spatial pattern"
showing 10 items of 39 documents
Rainfall statistics changes in Sicily
2013
Abstract. Changes in rainfall characteristics are one of the most relevant signs of current climate alterations. Many studies have demonstrated an increase in rainfall intensity and a reduction of frequency in several areas of the world, including Mediterranean areas. Rainfall characteristics may be crucial for vegetation patterns formation and evolution in Mediterranean ecosystems, with important implications, for example, in vegetation water stress or coexistence and competition dynamics. At the same time, characteristics of extreme rainfall events are fundamental for the estimation of flood peaks and quantiles which can be used in many hydrological applications, such as design of the mos…
Structural analysis of woody species in Mediterranean old fields.
2008
The first part of this study provides an overview on Sicilian olive systems. Subsequently, the study describes the different typologies of cultivated agroforestry systems present in South-Eastern Sicily employing olive trees in association with other Mediterranean tree species, in particular for the production of firewood, coal and animal food (downy or pubescent oak, holm oak, cork oak), but also in association with forage or grazing species (oat, barley, vetch, etc.) or cereals. The study shows that Sicilian agroforestry systems are much more diversified than it was known so far. In the second part, the study describes the spontaneous colonization processes by plants, observed in abandone…
Pre- and post-ictal brain activity characterization using combined source decomposition and connectivity estimation in epileptic children
2019
In this research, the study of functional connectivity between sources of electroencephalogram (EEG) activity assessed for different classes (well before seizure, preictal and post-ictal) was performed. EEG recordings were acquired from 12 subjects with focal epilepsy. Then, ten common spatial patterns (CSP) were obtained for EEG segments describing 95% of Riemannian distance between pairs of classes, followed by estimation of multivariate autoregressive (MVAR) models’ coefficients. The MVAR models were further used to extract coherence as a functional connectivity measures. Our results show that the coherence between CSP sources differs between baseline and pre-ictal segments: it has the l…
Pleistocene and Holocene aeolian sediments of different location and geological history: A new insight from rounding and frosting of quartz grains
2014
Abstract Rounding and frosting of quartz grains in aeolian sediments of the known stratigraphic position and unique geological setting was explored in Finnish, Estonian, Latvian, and Polish localities and in Fuerteventura Island. The aim of the study is to characterize the variability of the spatial pattern of rounding and frosting of quartz grains in the sandy (0.5–0.8 mm) fraction and to evaluate the factors influencing it. The relationships between rounded and non-abraded, as well as matt- and shiny-type quartz grains were calculated for 159 samples and evaluated against the aeolian subenvironment, substratum and presumed age of the locations. The obtained relations do not confirm meridi…
Measuring soil erosion by field plots: Understanding the sources of variation
2006
Soil erosion plots of different types and sizes are widely used to investigate the geomorphological processes related to soil erosion. This field method has provided a variety of results, depending on the characteristics of the plots, on their suitability to reflect the ecosystem's characteristics and on the objectives of each particular research. The coupling of real soil loss at patch and slope scale within a landscape and the values obtained by field plots depend, among other things, on how good the methodology performs over a set of ecosystem properties, such as those related with temporal and spatial scale issues, disturbance and representation of natural conditions, and the ability to…
Lost in space? Using geo-narratives to interpret land use changes in a rural landscape of inner Sicily
2021
Intercropping landscapes characterised by the presence of certain plant features (i.e. old-century olive trees) are usually considered traditional landscapes, extremely important for their biocultural heritage. Olive agroforestry systems were widespread in the past throughout Sicily. Recent evolution processes involving intensification have switched to olive grove monocultures. Here we present ongoing work on the application of geo-narratives to interpret transformation dynamics of land use practices in a rural landscape of inner Sicily. Based on the assumption that spatial patterns are the expression of transformation processes, where the spatial variation of human activities is a signific…
An “Uncertainty Principle” for the Mediterranean annual dry grasslands
2009
Preliminary results of diachronic researches on the spatial arrangement and species richness in Mediterranean annual dry grasslands (Tuberarietea guttatae) demonstrated that the patchiness resulted minimized and the temporal stability maximized at elevations offering the best compromise between the summer drought stress and the winter cold stress. Moreover, the temporal stability of the Mediterranean annul dry grasslands could not necessarily be related with their demographic inertia, meaning that the turnover and rearrangement of species within the community do not necessarily implicate significant changes in the average species composition over time. On the other hand, the survival chance…
The 1970 US Draft Lottery Revisited: A Spatial Analysis
2004
Summary We revise the result of the 1970 selective service draft lottery in the USA following an open question that was suggested by Fienberg in a paper published in Science in 1971. The result of the drawings can be viewed as a particular spatial pattern which can be analysed by using general spatial tools adapted to our context. Approaches for assessing the complete spatial randomness for this spatial process on a finite support are proposed. More specifically, these approaches involve the number of events in a square window and a k(r)-based function used to analyse stationary spatial point processes.
A spatial analysis of Italian unemployment differences
2008
Using spatial econometric models, this paper focuses attention on the spatial structure of provincial unemployment disparities of Italian provinces for the year 2003. On the basis of findings from the economic literature and of the available socio-economic data, various model specifications including supply- and demand-side variables are tested. Further we use ESDA analysis as equivalent to integration analysis on time series; therefore it is applied on each variable, dependent and independent, involved in the statistical model. The suggestions of ESDA lead us to the most adequate statistical model, which estimates indicate that there is a significant degree of neighbouring effect (i.e. pos…
New method for field studies on the parapatric distribution of sibling species
1999
Abstract Spatial segregation (parapatry) often occurs between closely related species. The distributions of the two species are sometimes defined with a small overlapping zone (called a `sympatric area') which generally shifts. Exclusion is necessary to explain the persistence and shift of such a spatial pattern. Field studies are carried out to identify the type of interaction that leads to the required exclusion. This is usually achieved by estimating competition and predation parameters to define the type of interaction strong enough to imply exclusion. But interaction parameters are estimated by quantitative methods which require prolonged observation (5–10 years). These estimations are…