614 research outputs found
Level and pattern of overstory retention shape the abundance and long-term dynamics of natural and created snags
Standing dead trees, or snags, serve myriad functions in natural forests, but are often scarce in forests managed for timber production. Variable retention (VR), the retention of live and dead trees through harvest, has been adopted globally as a less intensive form of regeneration harvest. In this study, we explore how two key elements of VR systems â level (amount) and spatial pattern of live-tree retention â affect the carryover and post-harvest dynamics of natural and artificially created snags. We present nearly two decades of data from the DEMO Study, a regional-scale experiment in VR harvests of Douglas-fir-dominated forests in the Pacific Northwest. Snag losses to harvest were greater at 15 than at 40% retention (67 vs. 47% declines in density) and greater in dispersed than in aggregated treatments (64 vs. 50% declines). Densities of hard and tall (â„5 m) snags were particularly sensitive to low-level dispersed retention, declining by 76 and 81%, respectively. Despite these losses, post-harvest densities correlated with pre-harvest densities for most snag size and decay classes. In contrast to initial harvest effects, snag densities changed minimally over the post-harvest period (years 1 to 18 or 19), with low rates of recruitment offsetting low rates of loss. Post-harvest survival of snags was greater at 15 than at 40% retention (79 vs. 69%), as were rates of decay (68 vs. 52% of hard snags transitioned to soft). However, pattern had no effect on either process. Snag recruitment did not vary with retention level or pattern at the scale of the 13-ha harvest unit, but was several-fold greater in the 1-ha aggregates (14.3â27.8 snags ha -1) than in the corresponding dispersed treatments (4.2â5.3 snags ha -1). Snag size (diameter) distributions showed greater change in dispersed than in aggregated treatments, reflecting greater loss of smaller snags and recruitment biased toward larger snags. Created snags showed uniformly high survival (97%), irrespective of treatment, but rates of decay were greater at lower retention. If a goal of VR is to sustain snag abundance and diversity through harvest, emphasis should be placed on minimizing initial losses, either by reducing the intensity of felling in areas of dispersed retention or locating forest aggregates in areas of greater initial snag density, diversity, or incipient decay
Explaining the unobserved: why quantum mechanics is not only about information
A remarkable theorem by Clifton, Bub and Halvorson (2003)(CBH) characterizes
quantum theory in terms of information--theoretic principles. According to Bub
(2004, 2005) the philosophical significance of the theorem is that quantum
theory should be regarded as a ``principle'' theory about (quantum) information
rather than a ``constructive'' theory about the dynamics of quantum systems.
Here we criticize Bub's principle approach arguing that if the mathematical
formalism of quantum mechanics remains intact then there is no escape route
from solving the measurement problem by constructive theories. We further
propose a (Wigner--type) thought experiment that we argue demonstrates that
quantum mechanics on the information--theoretic approach is incomplete.Comment: 34 Page
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A comparison of selected parametric and imputation methods for estimating snag density and snag quality attributes
Snags (standing dead trees) are an essential structural component of forests. Because wildlife use of snags depends on size and decay stage, snag density estimation without any information about snag quality attributes is of little value for wildlife management decision makers. Little work has been done to develop models that allow multivariate estimation of snag density by snag quality class. Using climate, topography, Landsat TM data, stand age and forest type collected for 2356 forested Forest Inventory and Analysis plots in western Washington and western Oregon, we evaluated two multivariate techniques for their abilities to estimate density of snags by three decay classes. The density of live trees and snags in three decay classes (D1: recently dead, little decay; D2: decay, without top, some branches and bark missing; D3: extensive decay, missing bark and most branches) with diameter at breast height (DBH) â„ 12.7 cm was estimated using a nonparametric random forest nearest neighbor imputation technique (RF) and a parametric two-stage model (QPORD), for which the number of trees per hectare was estimated with a Quasipoisson model in the first stage and the probability of belonging to a tree status class (live, D1, D2, D3) was estimated with an ordinal regression model in the second stage. The presence of large snags with DBH â„ 50 cm was predicted using a logistic regression and RF imputation. Because of the more homogenous conditions on private forest lands, snag density by decay class was predicted with higher accuracies on private forest lands than on public lands, while presence of large snags was more accurately predicted on public lands, owing to the higher prevalence of large snags on public lands. RF outperformed the QPORD model in terms of percent accurate predictions, while QPORD provided smaller root mean square errors in predicting snag density by decay class. The logistic regression model achieved more accurate presence/absence classification of large snags than the RF imputation approach. Adjusting the decision threshold to account for unequal size for presence and absence classes is more straightforward for the logistic regression than for the RF imputation approach. Overall, model accuracies were poor in this study, which can be attributed to the poor predictive quality of the explanatory variables and the large range of forest types and geographic conditions observed in the data.Keywords: Snag size class, Ordinal regression, Snag density, Snag decay class, Nearest neighbor imputatio
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A comparison of selected parametric and imputation methods for estimating snag density and snag quality attributes
Snags (standing dead trees) are an essential structural component of forests. Because wildlife use of snags depends on size and decay stage, snag density estimation without any information about snag quality attributes is of little value for wildlife management decision makers. Little work has been done to develop models that allow multivariate estimation of snag density by snag quality class. Using climate, topography, Landsat TM data, stand age and forest type collected for 2356 forested Forest Inventory and Analysis plots in western Washington and western Oregon, we evaluated two multivariate techniques for their abilities to estimate density of snags by three decay classes. The density of live trees and snags in three decay classes (D1: recently dead, little decay; D2: decay, without top, some branches and bark missing; D3: extensive decay, missing bark and most branches) with diameter at breast height (DBH) â„ 12.7 cm was estimated using a nonparametric random forest nearest neighbor imputation technique (RF) and a parametric two-stage model (QPORD), for which the number of trees per hectare was estimated with a Quasipoisson model in the first stage and the probability of belonging to a tree status class (live, D1, D2, D3) was estimated with an ordinal regression model in the second stage. The presence of large snags with DBH â„ 50 cm was predicted using a logistic regression and RF imputation. Because of the more homogenous conditions on private forest lands, snag density by decay class was predicted with higher accuracies on private forest lands than on public lands, while presence of large snags was more accurately predicted on public lands, owing to the higher prevalence of large snags on public lands. RF outperformed the QPORD model in terms of percent accurate predictions, while QPORD provided smaller root mean square errors in predicting snag density by decay class. The logistic regression model achieved more accurate presence/absence classification of large snags than the RF imputation approach. Adjusting the decision threshold to account for unequal size for presence and absence classes is more straightforward for the logistic regression than for the RF imputation approach. Overall, model accuracies were poor in this study, which can be attributed to the poor predictive quality of the explanatory variables and the large range of forest types and geographic conditions observed in the data.This is the publisherâs final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/forest-ecology-and-managemen
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Use of created snags by cavity-nesting birds across 25 years
Snags are important habitat features for many forest-dwelling species, so reductions in the number of snags can lead to the loss of biodiversity in forest ecosystems. Intentional snag creation is often used in managed forests to mitigate the long-term declines of naturally created snags, yet information regarding the use of snags by wildlife across long timescales (>20 yr) is lacking and prevents a complete understanding of how the value of created snags change through time. We used a long-term experiment to assess how harvest treatment (i.e., small-patch group selection, 2-story, and clearcut) and snag configuration (i.e., scattered and clustered) influenced nesting in and foraging on 25-27-year-old Douglas-fir (Pseudotsuga menziesii) snags by cavity-nesting birds. In addition, we compared our contemporary measures of bird use to estimates obtained from historical surveys conducted on the same group of snags to quantify how bird use changed over time. Despite observing created snags for >750hours across 2 consecutive breeding seasons, we found limited evidence of nesting activity. Only 11% of created snags were used for breeding, with nesting attempts by 4 bird species (n=36 nests); however, we detected 12 cavity-nesting species present on our study sites. Furthermore, nearly all nests (94%) belonged to the chestnut-backed chickadee (Poecile rufescens), a weak cavity-excavating species that requires well-decayed wood for creating nest cavities. Our surveys also recorded few observations of birds using created snags as foraging substrates, with only 1 foraging event recorded for every 20hours of observation. We detected 82% fewer nests and recorded 7% fewer foraging observations during contemporary field work despite spending >7.5 times more effort observing created snags relative to historical surveys. We conclude that 25-27-year-old created Douglas-fir snags provided limited opportunities for nesting and foraging by most cavity-nesting birds, and that the period of greatest use by this group occurred within 5-15 years of creation. (c) 2018 The Wildlife Society.
We used a long-term experiment to assess how harvest type and snag configuration influenced nesting in and foraging on 25-27-year-old Douglas-fir snags by cavity-nesting birds. Despite observing these snags for >750 hours across 2 consecutive breeding seasons, we conclude that they provided limited opportunities for nesting and foraging by most cavity-nesting birds
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Geostatistical modeling of riparian forest microclimate and its implications for sampling
Les modÚles de prédiction du microclimat pour différentes conditions de station dans les zones riveraines boisées
des cours dâeau de tĂȘte de bassin sont peu dĂ©veloppĂ©s et les procĂ©dures dâĂ©chantillonnage pour caractĂ©riser les gradients
sous-jacents du microclimat riverain sont rares. Nous avons utilisé des données de microclimat riverain collectées le long de
huit cours dâeau de tĂȘte de bassin dans la chaĂźne cĂŽtiĂšre de lâOregon pour comparer le krigeage ordinaire (KO), le krigeage
universel (KU) et le krigeage avec dérive externe (KDE) pour la prédiction localisée de la température moyenne maximale
de lâair (Tair). Plusieurs caractĂ©ristiques topographiques et de la structure de la forĂȘt ont Ă©tĂ© considĂ©rĂ©es comme paramĂštres
spĂ©cifiques Ă la station. LâĂ©lĂ©vation au-dessus du cours dâeau et la distance du cours dâeau Ă©taient les covariables les plus
importantes dans les modĂšles de KDE qui donnaient de meilleurs rĂ©sultats que le KO et le KU en termes dâĂ©cart-type. La
répartition des échantillons a été optimisée sur la base de la variance de krigeage et des moyennes pondérées du critÚre de
la plus courte distance Ă lâaide dâun algorithme de recuit simulĂ©. La rĂ©partition optimisĂ©e des Ă©chantillons donnait de meilleurs
résultats que la répartition systématique en termes de variance moyenne de krigeage, surtout lorsque le nombre
dâĂ©chantillons Ă©tait faible. Ces rĂ©sultats suggĂšrent des mĂ©thodes pour augmenter lâefficacitĂ© du suivi du microclimat dans les
zones riveraines.Predictive models of microclimate under various site conditions in forested headwater stream â riparian areas are poorly developed, and sampling designs for characterizing underlying riparian microclimate gradients are sparse. We used riparian microclimate data collected at eight headwater streams in the Oregon Coast Range to compare ordinary kriging (OK), universal kriging (UK), and kriging with external drift (KED) for point prediction of mean maximum air temperature (T air). Several topographic and forest structure characteristics were considered as site-specific parameters. Height above stream and distance to stream were the most important covariates in the KED models, which outperformed OK and UK in terms of root mean square error. Sample patterns were optimized based on the kriging variance and the weighted means of shortest distance criterion using the simulated annealing algorithm. The optimized sample patterns outperformed systematic sample patterns in terms of mean kriging variance mainly for small sample sizes. These findings suggest methods for increasing efficiency of microclimate monitoring in riparian areas
Non-local Realistic Theories and the Scope of the Bell Theorem
According to a widespread view, the Bell theorem establishes the untenability
of so-called 'local realism'. On the basis of this view, recent proposals by
Leggett, Zeilinger and others have been developed according to which it can be
proved that even some non-local realistic theories have to be ruled out. As a
consequence, within this view the Bell theorem allows one to establish that no
reasonable form of realism, be it local or non-local, can be made compatible
with the (experimentally tested) predictions of quantum mechanics. In the
present paper it is argued that the Bell theorem has demonstrably nothing to do
with the 'realism' as defined by these authors and that, as a consequence,
their conclusions about the foundational significance of the Bell theorem are
unjustified.Comment: Forthcoming in Foundations of Physic
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