17 research outputs found
Recommended from our members
Modeling light competition in the forests of western Oregon
A plant's immediate neighborhood reflects its realized level of competitive stress, since competition and natural selection act at the individual level. In stands with continuous canopies competition for light is the dominant spatial interaction. Over 100 spatially explicit indices have been used to characterize the local competitive environment in models of individual tree growth. These indices can be divided into those that indirectly characterize the light environment and those that directly characterize the light environment. The three classes of indirect measures are: size-distance, competitive influence zones, growing space and the two classes of direct measures are open sky views and light-interception methods. Studies that have compared the ability of the indirect indices of the light environment have failed to identify a universally superior measure of competition. However, the two direct measures of the light environment have not been included in the comparisons. An examination of the comparative studies showed that most of them identify indices characterizing competition from larger neighbors as superior. This finding leads to the conclusion that competition for light is the dominant spatial interaction in the stands examined. Thus, spatial indices that directly quantify light should explain more variation than those that quantify both above and below ground competition. Light intensity is modeled with the radiation transport equations. SEALS is a program for calculating light intensity in forest stands. It uses the radiation transport equations to model seasonal quantum light flux (SAL). It uses simulated hemispherical photographs to model direct beam light intensity (PCSHS). SAL and PCSHS were compared to three indirect measures of light competition in a planted western hemlock understory and 11 managed Douglas-fir plots. It was found that SAL reduced the residual variation in height growth of understory western hemlock by 48% over a model including only a power of tree height and PCSHS reduced the residual variation by 40%. SAL also reduced residual variation by 48% for overstory Douglas-fir and 18% for understory Douglas-fir while PCSHS reduced the residual variation by 15% and 14% respectively. These reductions were significantly better than those from the indirect classes of spatially explicit index
Recommended from our members
Height-diameter equations for six species in the coastal regions of the Pacific Northwest
Three equations for predicting tree height as a function of diameter (outside
bark) at breast height are presented for six species found in coastal regions of
the Pacific Northwest. Foresters can use these âheightâdiameterâ equations
to avoid the time-consuming task of measuring heights of all individual trees
in an inventory, a stand exam, or a timber cruise. Equation coefficients were
estimated with weighted nonlinear regression techniques. Because the relationship
between a treeâs height and diameter depends on the treeâs competitive
position within the stand, alternative equations, including the average
height and average diameter of the 40 largest-diameter trees/ac, are also
presented. These equations are used in the Stand Management Cooperative
version of ORGANON
Recommended from our members
Predicting height for undamaged and damaged trees in southwest Oregon
Equations for predicting tree height as a function of diameter outside bark at
breast height are presented for various tree species common to southwest
Oregon. Data for damaged and undamaged trees were analyzed with weighted
nonlinear regression techniques. The effects of specific damaging agents and
their severity on the height-diameter relationship were explored. Damage correction
multipliers were estimated, then used to correct predicted height where
damage was noted. Because the relationship between height and diameter
changes with the competitive position of the tree in a stand, alternative equations
are presented that include the average height and diameter of the 40
largest-diameter undamaged conifer trees per acre. Foresters can use these
âheight-diameterâ equations to reduce the time-consuming task of measuring
heights of every tree in an inventory, stand exam, or timber cruise. They
can also use these equations to estimate the change in height as diameter
changes. These equations will be incorporated into the new southwest Oregon
version of ORGANON, which extends the model to older stands and
stands with a heavier component of hardwood species
Recommended from our members
Enhanced mortality equations for trees in the mixed conifer zone of Southwest Oregon
Equations for predicting the probability of a tree's dying in the
next 5 years are presented for eight conifer and eight hardwood
tree species from southwest Oregon. A logistic equation form was
used to characterize the probability of mortality. The parameters
of the equation were estimated using weighted, maximum likelihood
procedures. These equations are being incorporated into the
new southwest Oregon version of ORGANON, a model for predicting
stand development. In particular, the equations extend the previous model to older stands and and stands with a heavier component of hardwood tree species
Recommended from our members
Enhanced diameter-growth-rate equations for undamaged and damaged trees in southwest Oregon
Equations for predicting the 5-yr diameter-growth rate of a tree are presented for eight conifer and nine hardwood tree species from southwest Oregon. Equation parameters for undamaged and damaged trees combined were estimated by weighted nonlinear regression. The resulting equation for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] explained more than 71% of the variation when validated against an independent data set. These equations are being incorporated into the new edition of ORGANON for southwest Oregon, a model for predicting the development of stands. The equations extend the previous model to older stands and stands with a larger component of hardwood. We explored the effects of specific damaging agents on the 5-yr diameter-growth rates of the five most frequently encountered species and estimated damage correction factors. Damaging agents can impact 5-yr diameter-growth rate significantly and, as a result, can lead over time to diversification in stand structure. Therefore, full characterization of stand development should include prediction of the presence and frequency of the agents damaging trees within the stand and their impact on tree attributes such as total height, height-to-crown-base, diameter-growth rate, height-growth rate, and mortality rate
Recommended from our members
Enhanced height-growth-rate equations for undamaged and damaged trees in southwest Oregon
Equations for predicting the 5-yr height growth rate of a tree are presented for six conifer species from southwest Oregon. Equations for the combination of undamaged and damaged trees were estimated with weighted nonlinear regression techniques. These equations are being incorporated into the new southwest Oregon version of ORGANON, a model for predicting the development of stands. The equations extend the previous model to older stands and to stands with a heavier component of hardwood tree species. The effects of specific damaging agents on the 5-yr height growth rate were explored for Douglas-fir, the most frequently encountered species, and damage correction factors were estimated. The findings of this analysis indicated that damaging agents can have a significant impact upon 5-yr height growth rate, and as a result, they can lead, over time, to diversification in within-stand structure. Therefore, a full characterization of stand development should include the prediction of the presence and frequency of the various damaging agents affecting trees within the stand and their subsequent impact upon tree attributes such as total height, height to crown base, diameter growth rate, height growth rate, and mortality rate
Recommended from our members
Reanalysis of the SMC-ORGANON equations for diameter-growth rate, height-growth rate, and mortality rate of Douglas-fir
Using existing data from untreated research plots, we developed equations
for predicting 5-yr diameter-growth rate (ÎDâ
), 5-yr height-growth
rate (ÎHâ
), and 5-yr mortality rate (PMâ
) for Douglas-fir [Pseudotsuga
menziesii (Mirb.) Franco] in the coastal region of the Pacific Northwest.
These equations are revisions of the equations constructed in 1995â1997
for the Stand Management Cooperative's (SMC) version of the ORGANON
growth-and-yield model, and they have been developed with
substantially larger and more comprehensive data sets than were available
in 1995â1997. The new ÎDâ
and ÎHâ
equations were validated with an
independent data set. The PMâ
equation was evaluated by comparing
100-yr predictions of Reineke's (1933) stand density index to behavior
previously reported from measurements taken on long-term research
plots. The new ÎDâ
, ÎHâ
, and PMâ
equations appear to be considerably
superior in predictive ability and behavior to the original equations. The effects of the new equations on stand-level predictions were evaluated
by comparing the maximum mean annual increments (MAI) in
total stem volume (ftÂł) and associated rotation ages (RA) predicted from
the original SMC-ORGANON model to predictions from the revised
SMC-ORGANON model. This analysis was done by making 100-yr
projections using 170 plots in young stands from the SMC data sets.
Some of the ending values for average crown ratio (CR) after 100 yr of
projection were near 15%, however, and predictions of basal area (BA)
for some of these stands peaked and then declined over stand age. Substituting
the HCB equation published by Hann and Hanus in 2004 for
predicting crown recession (ÎHCBâ
) eliminated the problem with BA
peaking over stand age and resulted in somewhat larger average ending
CRs. The 100-yr projections were then made again with the 2004 HCB
equation of Hann and Hanus. On average, the revised model reduced RA
by 2.1 yr (or 4.3%) and maximum MAI by 55.7 ftÂł/ac/yr (18.9%)
Recommended from our members
Predicting height to crown base for undamaged and damaged trees in southwest Oregon
Equations for predicting height to crown base are presented for tree species from southwest Oregon. Equations for undamaged and damaged trees were estimated with weighted nonlinear regression techniques. The effects of specific damaging agents on the height to crown base were explored, and damage correction factors were estimated. The damage correction factors can be used to correct the predicted crown ratio for specific damaging agents and their severity in samples where damage is noted. These equations are being incorporated into the new southwest Oregon version of ORGANON (ORegon Growth ANalysis and projectiON), a model for predicting the growth of individual trees in forest stands. The equations extend the past model to older stands and stands with a heavier component of hardwood tree species
Recommended from our members
Pervasive remagnetization of detrital zircon host rocks in the Jack Hills, Western Australia and implications for records of the early geodynamo
It currently is unknown when Earth's dynamo magnetic field originated. Paleomagnetic studies indicate that a field with an intensity similar to that of the present day existed 3.5 billion years ago (Ga). Detrital zircon crystals found in the Jack Hills of Western Australia are some of the very few samples known to substantially predate this time. With crystallization ages ranging from 3.0â4.38 Ga, these zircons might preserve a record of the missing first billion years of Earth's magnetic field history. However, a key unknown is the age and origin of magnetization in the Jack Hills zircons. The identification of >3.9 Ga (i.e., Hadean) field records requires first establishing that the zircons have avoided remagnetization since being deposited in quartz-rich conglomerates at 2.65â3.05 Ga. To address this issue, we have conducted paleomagnetic conglomerate, baked contact, and fold tests in combination with UâPb geochronology to establish the timing of the metamorphic and alteration events and the peak temperatures experienced by the zircon host rocks. These tests include the first conglomerate test directly on the Hadean-zircon bearing conglomerate at Erawandoo Hill. Although we observed little evidence for remagnetization by recent lightning strikes, we found that the Hadean zircon-bearing rocks and surrounding region have been pervasively remagnetized, with the final major overprinting likely due to thermal and/or aqueous effects from the emplacement of the Warakurna large igneous province at âŒ1070 million years ago (Ma). Although localized regions of the Jack Hills might have escaped complete remagnetization, there currently is no robust evidence for pre-depositional (>3.0 Ga) magnetization in the Jack Hills detrital zircons
Evidence for Two Numerical Systems That Are Similar in Humans and Guppies
Background: Humans and non-human animals share an approximate non-verbal system for representing and comparing numerosities that has no upper limit and for which accuracy is dependent on the numerical ratio. Current evidence indicates that the mechanism for keeping track of individual objects can also be used for numerical purposes; if so, its accuracy will be independent of numerical ratio, but its capacity is limited to the number of items that can be tracked, about four. There is, however, growing controversy as to whether two separate number systems are present in other vertebrate species. Methodology/Principal Findings: In this study, we compared the ability of undergraduate students and guppies to discriminate the same numerical ratios, both within and beyond the small number range. In both students and fish the performance was ratio-independent for the numbers 1â4, while it steadily increased with numerical distance when larger numbers were presented. Conclusions/Significance: Our results suggest that two distinct systems underlie quantity discrimination in both humans and fish, implying that the building blocks of uniquely human mathematical abilities may be evolutionarily ancient, datin