1,509 research outputs found
Effects of riparian zone buffer widths on vegetation diversity in southern Appalachian headwater catchments
In mountainous areas such as the southern Appalachians USA, riparian zones are difficult to define. Vegetation is a commonly used riparian indicator and plays a key role in protecting water resources, but adequate knowledge of floristic responses to riparian disturbances is lacking. Our objective was to quantify changes in stand-level floristic diversity of riparian plant communities before (2004) and two, three, and seven years after shelterwood harvest using highlead cable-yarding and with differing no cut buffer widths of 0 m, 10 m, and 30 m distance from the stream edge. An unharvested reference stand was also studied for comparison. We examined: (1) differences among treatment sites using a mixed linear model with repeated measures; (2) multivariate relationships between ground-layer species composition and environmental variables (soil water content, light transmittance, tree basal area, shrub density, and distance from stream) using nonmetric multidimensional scaling; and (3) changes in species composition over time using a multi-response permutation procedure. We hypothesized that vegetation responses (i.e., changes in density, species composition, and diversity across the hillslope) will be greatest on harvest sites with an intermediate buffer width (10-m buffer) compared to more extreme (0-m buffer) and less extreme (30-m buffer and no-harvest reference) disturbance intensities. Harvesting initially reduced overstory density and basal area by 83% and 65%, respectively, in the 0-m buffer site; reduced by 50% and 74% in the 10-m buffer site; and reduced by 45% and 29% in the 30-m buffer site. Both the 0-m and 10-m buffer sites showed increased incident light variability across the hillslope after harvesting; whereas, there was no change in the 30-m and reference sites over time. We found significant changes in midstory and ground-layer vegetation in response to harvesting with the greatest responses on the 10-m buffer site, supporting our hypotheses that responses will be greatest on sites with intermediate disturbance. Ground-layer species composition differed significantly over time in the 0-m buffer and 10-m buffer sites (both P \u3c 0.0001), but did not change in the 30-m buffer and reference sites (both P \u3e 0.100). Average compositional dissimilarity increased after seven years, indicating greater within stand heterogeneity (species diversity) after harvesting. These vegetation recovery patterns provide useful information for evaluating management options in riparian zones in the southern Appalachians
An analysis of the XOR dynamic problem generator based on the dynamical system
This is the post-print version of the article - Copyright @ 2010 Springer-VerlagIn this paper, we use the exact model (or dynamical system approach) to describe the standard evolutionary algorithm (EA) as a discrete dynamical system for dynamic optimization problems (DOPs). Based on this dynamical system model, we analyse the properties of the XOR DOP Generator, which has been widely used by researchers to create DOPs from any binary encoded problem. DOPs generated by this generator are described as DOPs with permutation, where the fitness vector is changed according to a permutation matrix. Some properties of DOPs with permutation are analyzed, which allows explaining some behaviors observed in experimental results. The analysis of the properties of problems created by the XOR DOP Generator is important to understand the results obtained in experiments with this generator and to analyze the similarity of such problems to real world DOPs.This work was supported by Brazil FAPESP under Grant 04/04289-6 and by UK EPSRC under Grant EP/E060722/2
Evaluating the relationship between leaf nitrogen concentration and Minolta SPAD-502 meter readings [abstract]
Abstract only availableOak trees are deciduous trees that can live for up to 200 years and face a variety of environmental stresses. Like all plants, oak trees need nutrients, which vary under different stress conditions. We study nitrogen as an essential element in the growth of plants. Most nitrogen is found in the chlorophyll molecules of a leaf, and we are interested in understanding how nitrogen concentration varies oak species with different responses to flooding. The objectives of this study are to: (1) Determine the relationship between leaf chlorophyll and leaf nitrogen concentration for five different species of oak tree (bur oak, pin oak, swamp white oak, northern red oak and shumard oak) and (2) asses how flood tolerance affects the above relationship. The relationship between total leaf nitrogen concentration and chlorophyll of bur oak (Quercus macrocarpa), pin oak (Q. palustris), northern red oak (Q. rubra), shumard oak (Q. shumardii), and swamp white oak (Q. bicolor) were determined. Each tree species was represented by seedlings raised from acorns collected from both upland and lowland sites with the exception of northern red oak, which was represented by seedlings from a single location. A SPAD-502 Meter (Minolta Corporation ltd., Osaka, Japan) was used to measure chlorophyll in a total of 135 individual seedlings for 5 consecutive weeks. A single leaf was repeatedly sampled on each seedling in each flooded and non-flooded (control) treatment over 5 replications in a greenhouse. The harvested leaves were then oven dried for 72 hours and nitrogen analysis was conducted in the lab by combusting the sample in an induction furnace and measuring the nitrogen via thermal conductivity. Preliminary results indicate a close correlation between chlorophyll and nitrogen content and differing effects of inundation on their relationship.NSF Undergraduate Mentoring in Environmental Biolog
HadISD: a quality-controlled global synoptic report database for selected variables at long-term stations from 1973--2011
[Abridged] This paper describes the creation of HadISD: an automatically
quality-controlled synoptic resolution dataset of temperature, dewpoint
temperature, sea-level pressure, wind speed, wind direction and cloud cover
from global weather stations for 1973--2011. The full dataset consists of over
6000 stations, with 3427 long-term stations deemed to have sufficient sampling
and quality for climate applications requiring sub-daily resolution. As with
other surface datasets, coverage is heavily skewed towards Northern Hemisphere
mid-latitudes.
The dataset is constructed from a large pre-existing ASCII flatfile data bank
that represents over a decade of substantial effort at data retrieval,
reformatting and provision. These raw data have had varying levels of quality
control applied to them by individual data providers. The work proceeded in
several steps: merging stations with multiple reporting identifiers;
reformatting to netCDF; quality control; and then filtering to form a final
dataset. Particular attention has been paid to maintaining true extreme values
where possible within an automated, objective process. Detailed validation has
been performed on a subset of global stations and also on UK data using known
extreme events to help finalise the QC tests. Further validation was performed
on a selection of extreme events world-wide (Hurricane Katrina in 2005, the
cold snap in Alaska in 1989 and heat waves in SE Australia in 2009). Although
the filtering has removed the poorest station records, no attempt has been made
to homogenise the data thus far. Hence non-climatic, time-varying errors may
still exist in many of the individual station records and care is needed in
inferring long-term trends from these data.
A version-control system has been constructed for this dataset to allow for
the clear documentation of any updates and corrections in the future.Comment: Published in Climate of the Past, www.clim-past.net/8/1649/2012/. 31
pages, 23 figures, 9 pages. For data see
http://www.metoffice.gov.uk/hadobs/hadis
Streamflow response to increasing precipitation extremes altered by forest management
Published (Publication status
High elevation watersheds in the southern Appalachians: Indicators of sensitivity to acidic deposition and the potential for restoration through liming
Southern Appalachian high elevation watersheds have deep rocky soils with high organic matter content,
different vegetation communities, and receive greater inputs of acidic deposition compared to low elevation sites within the region. Since the implementation of the Clean Air Act Amendment in the 1990s, concentrations of acidic anions in rainfall have declined. However, some high elevation streams continue to show signs of chronic to episodic acidity, where acid neutralizing capacity (ANC) ranges from 0 to
20 µeq L-1. We studied three 3rd order watersheds (North River in Cherokee National Forest, Santeetlah Creek in Nantahala National Forest, and North Fork of the French Broad in Pisgah National Forest) and selected four to six 1st order catchments within each watershed to represent a gradient in elevation (849–1526 m) and a range in acidic stream ANC values (11–50 leq L-1). Our objectives were to (1) identify biotic, physical and chemical catchment parameters that could be used as indices of stream ANC, pH and Ca:Al molar ratios and (2) estimate the lime required to restore catchments from the effects of excess acidity and increase base cation availability. We quantified each catchment’s biotic, physical, and chemical characteristics and collected stream, O-horizon, and mineral soil samples for chemical analysis seasonally for one year. Using repeated measures analysis, we examined variability in stream chemistry and catchment characteristics; we used a nested split-plot design to identify catchment characteristics that were correlated with stream chemistry. Watersheds differed significantly and the catchments sampled provided a wide range of stream chemical, biotic, physical and chemical characteristics. Variability in stream ANC, pH, and Ca:Al molar ratio were significantly correlated with catchment vegetation characteristics (basal area, tree height, and tree diameter) as well as O-horizon nitrogen and aluminum concentrations. Total soil carbon and calcium (an indicator of parent material), were significant
covariates for stream ANC, pH and Ca:Al molar ratios. Lime requirement estimates did not differ among watersheds but this data will help select catchments for future restoration and lime application studies. Not surprisingly, this work found many vegetation and chemical characteristics that were useful indicators of stream acidity. However, some expected relationships such as concentrations of mineral soil extractable Ca and SO4 were not significant. This suggests that an extensive test of these indicators across the southern Appalachians will be required to identify high elevation forested catchments that would benefit from restoration activities
Genetic algorithm dynamics on a rugged landscape
The genetic algorithm is an optimization procedure motivated by biological
evolution and is successfully applied to optimization problems in different
areas. A statistical mechanics model for its dynamics is proposed based on the
parent-child fitness correlation of the genetic operators, making it applicable
to general fitness landscapes. It is compared to a recent model based on a
maximum entropy ansatz. Finally it is applied to modeling the dynamics of a
genetic algorithm on the rugged fitness landscape of the NK model.Comment: 10 pages RevTeX, 4 figures PostScrip
Properties of Nucleon Resonances by means of a Genetic Algorithm
We present an optimization scheme that employs a Genetic Algorithm (GA) to
determine the properties of low-lying nucleon excitations within a realistic
photo-pion production model based upon an effective Lagrangian. We show that
with this modern optimization technique it is possible to reliably assess the
parameters of the resonances and the associated error bars as well as to
identify weaknesses in the models. To illustrate the problems the optimization
process may encounter, we provide results obtained for the nucleon resonances
(1230) and (1700). The former can be easily isolated and thus
has been studied in depth, while the latter is not as well known
experimentally.Comment: 12 pages, 10 figures, 3 tables. Minor correction
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