Search results for "wood"
showing 10 items of 818 documents
Adjacency matrices of random digraphs: singularity and anti-concentration
2017
Let ${\mathcal D}_{n,d}$ be the set of all $d$-regular directed graphs on $n$ vertices. Let $G$ be a graph chosen uniformly at random from ${\mathcal D}_{n,d}$ and $M$ be its adjacency matrix. We show that $M$ is invertible with probability at least $1-C\ln^{3} d/\sqrt{d}$ for $C\leq d\leq cn/\ln^2 n$, where $c, C$ are positive absolute constants. To this end, we establish a few properties of $d$-regular directed graphs. One of them, a Littlewood-Offord type anti-concentration property, is of independent interest. Let $J$ be a subset of vertices of $G$ with $|J|\approx n/d$. Let $\delta_i$ be the indicator of the event that the vertex $i$ is connected to $J$ and define $\delta = (\delta_1, …
An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape
2016
Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrubâgrassland site in central Oregon (USA) using a modified version of Cellular Automata TreeâGrassâShrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics represented by the model were first evaluated using satellite-derived leaf area index and measured evapotranspiration data. Reconstruc…
Assessing and Modeling Soil Detachment Capacity by Overland Flow in Forest and Woodland of Northern Iran
2020
Land use has significant effects on the erosion process, since it influences the soil detachment capacity by causing an overland flow (Dc). The effects of different land uses on the rill detachment capacity have not been explained in depth, and the hydraulic parameters providing accurate estimates of this soil property have not been completely identified. This study quantifies Dc at low flow rates in woodland and forestland, compared to two other land uses (cropland and grassland), in the Saravan watershed (Northern Iran), and develops prediction models of Dc and rill erodibility (Kr). Dc was measured on undisturbed soil samples, collected in the four land uses, and characterized in terms o…
Large-scale, millennial-length temperature reconstructions from tree-rings
2018
Supported by the German Science Foundation, grants # Inst 247/665-1 FUGG and ES 161/9-1. SSG acknowledges support by the Alexander von Humboldt Foundation, KJA by US National Science Foundation grants AGS-1501856 and NSF AGS-1501834, and JL and LS by the Belmont Forum and JPI-Climate, Collaborative Research Action INTEGRATE. Over the past two decades, the dendroclimate community has produced various annually resolved, warm season temperature reconstructions for the extratropical Northern Hemisphere. Here we compare these tree-ring based reconstructions back to 831 CE and present a set of basic metrics to provide guidance for non-specialists on their interpretation and use. We specifically d…
Firewood and hearths: Middle Palaeolithic woody taxa distribution from El Salt, stratigraphic unit Xb (Eastern Iberia)
2017
Abstract Spatial analyses of Palaeolithic sites typically defined by hearth-related assemblages have been mostly based on lithic and faunal remains. By using spatial analysis methods in conjunction with analytical units with higher temporal resolution than typical stratigraphic units, synchronic and diachronic relationships between artifacts deposited during successive occupation events have been elucidated. Spatial analyses applied to archaeobotanical remains are scarce, and when available, are typically focused on carpological remains (seeds and fruits). The lack of spatial indicators among anthracological remains hampers obtaining significant data linked to the relationships established …
The past distribution of Abies nebrodensis (Lojac.) Mattei: results of a multidisciplinary study
2019
The present study provides a critical review of the available historical data on the distribution of Abies nebrodensis, a fir tree endemic to Sicily. The only (somewhat ambiguous) references to its occurrence on Mount Etna date back to the 1st century bc and refer back to the 3rd century bc. Although the botanical and forestry literature and the very few surviving herbarium specimens do not prove that A. nebrodensis grew outside the Madonie mountain range, several indications suggest its past occurrence on other Sicilian mountain ranges such as the Erei, Nebrodi, and probably also Sicani mountains. The results of the most recent pollen investigations (still ongoing) point to the disappearan…
Personal body ornamentation on the Southern Iberian Meseta: An archaeomineralogical study
2016
Beads and pendants from the Castillejo del Bonete (Terrinches, Ciudad Real) and Cerro Ortega (Villanueva de la Fuente, Ciudad Real) burials were analysed using XRD, micro-Raman and XRF in order to contribute to the current distribution map of green bead body ornament pieces on the Iberian Peninsula which, so far, remain undetailed for many regions. XRD, micro-Raman and XRF analyses showed that most of the beads from Castillejo del Bonete (Late 3rd millennium cal. BC) were made from variscite or green phyllosilicates, while Cerro Ortega's (Late 4th millennium cal. BC) beads were made out of fossil wood or Clinochlore. Significantly enough, while XRD pointed to variscite as the main crystallo…
Understanding woodworking in Paleolithic times by means of use-wear analysis
2020
Abstract Throughout prehistory, wood working was a frequent activity. The indices of this activity comes from rare found wooden remains, and the analysis of use-wear on them. In most recent periods, there are stone polished tools and metal tools, that increase the capability of wood transformation. This is not the case for older times, from which only knapped tools are available. The woodworking chaine operatoire includes activities of selection and acquisition of raw material, but also the transformation and the finish of objects and structures. Use-wear analysis in many sites illustrates this. However, a systematic compilation of published traceological analysis has not been made recently…
New tree-ring evidence for the Late Glacial period from the northern pre-Alps in eastern Switzerland
2018
Abstract The rate and magnitude of temperature variability at the transition from the Last Glacial Maximum into the early Holocene represents a natural analog to current and predicted climate change. A limited number of high-resolution proxy archives, however, challenges our understanding of environmental conditions during this period. Here, we present combined dendrochronological and radiocarbon evidence from 253 newly discovered subfossil pine stumps from Zurich, Switzerland. The individual trees reveal ages of 41–506 years and were growing between the Allerod and Preboreal (∼13′900–11′300 cal BP). Together with previously collected pines from this region, this world's best preserved Late…
Dead wood gathering among Neanderthal groups: Charcoal evidence from Abric del Pastor and El Salt (Eastern Iberia)
2017
International audience; We present here a new approach combining the microscopic characterization of fungal decay features and the fragmentation degree of the charcoal remains from Middle Palaeolithic combustion structures: features H4 and H11 from Abric del Pastor, unit IV (>75 ka BP) and features H50 and H57 from El Salt, unit Xb (ca. 52 ka BP), Eastern Iberia. The observation of wood degradation patterns that occurred prior to charring followed by their quantitative analysis according to previous experimental studies revealed differences between the alteration degrees of the firewood used in the hearths, highlighting the existence of firewood acquisition criteria based on dead wood gathe…