scholarly journals A dynamic equation for a published Sitka spruce site-dependent height-age model

2002 ◽  
Vol 78 (5) ◽  
pp. 690-694 ◽  
Author(s):  
Chris J Cieszewski ◽  
Gordon D Nigh
Keyword(s):  
Numerical Solutions ◽  
Function Analysis ◽  
Real Data ◽  
Sitka Spruce ◽  
Site Index ◽  
Picea Sitchensis ◽  
Fixed Base ◽  
Richards Function ◽  
Age Model ◽  
Pseudo Data

We present a new Sitka spruce (Picea sitchensis (Bong.) Carr) site-dependent height-age model that is based on a dynamic site equation simulating previously published height-age curves for various productivity sites. The new model is an improvement over the previous model because it uses any arbitrary height-age pair to directly predict a height at another age, instead of using a fixed base-age site index as the older model does. Consequently, it can also be used directly to compute height at any age from site index or site index from any height and age instead of relying on numerical solutions for site index computations. The model predicts the same heights for any site as the original fixed base-age model and has the same desirable properties of polymorphism, inflection point, variable asymptotes, logical behaviour, theoretical basis, parsimony, and improved extrapolation. The model is offered as an algebraic improvement only, and therefore it was calibrated on pseudo-data generated from the old model’s predictions rather than on real data. The proposed equation mimics the old model better than the other dynamic equations tested in this study, which is illustrated using examples with the Chapman-Richards function. Analysis with the real data might offer further improvements to the model predictions. Key words: Base-age invariance, height-age model, model properties, nonlinear regression, Sitka spruce, site index

A Sitka spruce height-age model with improved extrapolation properties

1997 ◽  
Vol 73 (3) ◽  
pp. 363-369 ◽  
Author(s):  
Gordon D. Nigh
Keyword(s):  
British Columbia ◽  
Serial Correlation ◽  
Sitka Spruce ◽  
Analysis Data ◽  
Site Index ◽  
Picea Sitchensis ◽  
Stem Analysis ◽  
Queen Charlotte Islands ◽  
Extrapolation Model ◽  
Age Model

The height-age model for Sitka spruce (Picea sitchensis (Bong.) Carr.) currently recommended for use in British Columbia has poor extrapolation properties. Therefore, a new height-age model for Sitka spruce using stem analysis data collected from the Queen Charlotte Islands was developed. Care was taken to meet the standard regression assumptions. In particular, accounting for within-plot serial correlation improved the extrapolation abilities of the model by eliminating the crossing-over effect. The new model is being recommended for use in British Columbia because it offers better extrapolated height and site index estimates without sacrificing accuracy at young ages. Key words: Sitka spruce, site index, height-age model, serial correlation, nonlinear regression, extrapolation, model properties

Site index of Sitka spruce (Picea sitchensis) in relation to different measures of site quality in Ireland

2011 ◽  
Vol 41 (2) ◽  
pp. 265-278 ◽  
Author(s):  
Niall Farrelly ◽  
Áine Ní Dhubháin ◽  
Maarten Nieuwenhuis
Keyword(s):  
Chemical Properties ◽  
Soil Nutrient ◽  
Sitka Spruce ◽  
Site Index ◽  
Picea Sitchensis ◽  
Site Quality ◽  
Physical And Chemical Properties ◽  
Edaphic Variables ◽  
Physical And Chemical ◽  
And Chemical Properties

To examine the relationships between Sitka spruce (Picea sitchensis (Bong.) Carr.) site index and site quality variables, we sampled 201 Sitka spruce stands covering the entire range of sites supporting the growth of the species in Ireland. Site index varied significantly with climate and climate surrogate variables, some site quality variables, soil physical and chemical properties, edatopes (combinations of soil nutrient and moisture regimes), rotation types, provenance, and fertilizer regimes. We developed a series of models to predict site index using climate, site, soil physical and chemical properties, edaphic variables, and management factors as predictor variables. Soil nutrient regime (SNR) exhibited the strongest relationship of all variables examined in the study, explaining 51% of the variation in site index, with site index increasing with increasing SNR. We found that edaphic variables of soil moisture regime and SNR produced the best prediction of site index. The species showed the best development on fresh to very moist sites, with rich to very rich soil nutrient regimes. We also developed a composite model explaining 62% of the variation in site index and an elevation zone model (>300 m) explaining 74% of the variation in site index.

scholarly journals A fractional order epidemic model for the simulation of outbreaks of Ebola

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Weiqiu Pan ◽  
Tianzeng Li ◽  
Safdar Ali
Keyword(s):  
Numerical Solution ◽  
Root Mean Square ◽  
Fractional Order ◽  
Relative Error ◽  
Numerical Solutions ◽  
Real Data ◽  
Mean Square ◽  
Order Model ◽  
The Real ◽  
Fractional Orders

AbstractThe Ebola outbreak in 2014 caused many infections and deaths. Some literature works have proposed some models to study Ebola virus, such as SIR, SIS, SEIR, etc. It is proved that the fractional order model can describe epidemic dynamics better than the integer order model. In this paper, we propose a fractional order Ebola system and analyze the nonnegative solution, the basic reproduction number $R_{0}$ R 0 , and the stabilities of equilibrium points for the system firstly. In many studies, the numerical solutions of some models cannot fit very well with the real data. Thus, to show the dynamics of the Ebola epidemic, the Gorenflo–Mainardi–Moretti–Paradisi scheme (GMMP) is taken to get the numerical solution of the SEIR fractional order Ebola system and the modified grid approximation method (MGAM) is used to acquire the parameters of the SEIR fractional order Ebola system. We consider that the GMMP method may lead to absurd numerical solutions, so its stability and convergence are given. Then, the new fractional orders, parameters, and the root-mean-square relative error $g(U^{*})=0.4146$ g ( U ∗ ) = 0.4146 are obtained. With the new fractional orders and parameters, the numerical solution of the SEIR fractional order Ebola system is closer to the real data than those models in other literature works. Meanwhile, we find that most of the fractional order Ebola systems have the same order. Hence, the fractional order Ebola system with different orders using the Caputo derivatives is also studied. We also adopt the MGAM algorithm to obtain the new orders, parameters, and the root-mean-square relative error which is $g(U^{*})=0.2744$ g ( U ∗ ) = 0.2744 . With the new parameters and orders, the fractional order Ebola systems with different orders fit very well with the real data.

Validation of forest height–age models

1996 ◽  
Vol 26 (5) ◽  
pp. 810-818 ◽  
Author(s):  
Gordon D. Nigh ◽  
Vera Sit
Keyword(s):  
Forest Management ◽  
Confidence Intervals ◽  
Error Variance ◽  
Site Index ◽  
Random Coefficients ◽  
Multivariate Technique ◽  
Forest Height ◽  
Preliminary Validation ◽  
Age Model ◽  
Validation Procedure

Forest height–age models are used in forest management to estimate height and (or) site index. It is useful to know the bias and precision of these models in order to evaluate their applicability. Methods are available for validating the models; however, many problems exist with the methods because of a lack of independence in the data and nonconstant error variance across a range of ages. A validation procedure is presented that overcomes these problems by using a multivariate technique (random coefficients) to model the structure of the errors associated with the models. Confidence intervals for bias and precision can then be constructed based on the error structure. This method of validation was demonstrated on the white spruce (Piceaglauca (Moench) Voss) height–age model for British Columbia, Canada. The preliminary validation showed the model to be unbiased for estimating both height and site index; however, its precision was poor.

Predicting the longitudinal modulus of elasticity of Sitka spruce from cellulose orientation and abundance

Holzforschung ◽  
2010 ◽  
Vol 64 (4) ◽  
Author(s):  
J. Paul McLean ◽  
Robert Evans ◽  
John R. Moore
Keyword(s):  
Bulk Density ◽  
Modulus Of Elasticity ◽  
Microfibril Angle ◽  
Sitka Spruce ◽  
Picea Sitchensis ◽  
Model Parameters ◽  
Bending Tests ◽  
Wood Stiffness ◽  
Using Data ◽  
Longitudinal Modulus

Abstract Sitka spruce (Picea sitchensis) is the most widely planted commercial tree species in the United Kingdom and Ireland. Because of the increasing use of this species for construction, the ability to predict wood stiffness is becoming more important. In this paper, a number of models are developed using data on cellulose abundance and orientation obtained from the SilviScan-3 system to predict the longitudinal modulus of elasticity (MOE) of small defect-free specimens. Longitudinal MOE was obtained from both bending tests and a sonic resonance technique. Overall, stronger relationships were found between the various measures of cellulose abundance and orientation and the dynamic MOE obtained from the sonic resonance measurements, rather than with the static MOE obtained from bending tests. There was only a moderate relationship between wood bulk density and dynamic MOE (R2=0.423), but this relationship was improved when density was divided by microfibril angle (R2=0.760). The best model for predicting both static and dynamic MOE involved the product of bulk density and the coefficient of variation in the azimuthal intensity profile (R2=0.725 and 0.862, respectively). The model parameters obtained for Sitka spruce differed from those obtained in earlier studies on Pinus radiata and Eucalyptus delegatensis, indicating that the model might require recalibration before it can be applied to different species.

Heritability of height growth in 10-year-old Sitka spruce

1985 ◽  
Vol 27 (6) ◽  
pp. 729-734 ◽  
Author(s):  
Francis C. Yeh ◽  
Sven Rasmussen
Keyword(s):  
Sitka Spruce ◽  
Height Growth ◽  
Picea Sitchensis ◽  
Breeding Program ◽  
Progeny Test ◽  
Northwest Coast ◽  
Phenotypic Variance ◽  
Family Selection ◽  
Sources Of Variation

Ten-year height growth for Picea sitchensis (Bong.) Carr. was studied in a progeny test of 42 wind-pollinated families from seven stands on the northwest coast of Vancouver Island. Although stand and family-within-stand effects were significant sources of variation, 79% of the phenotypic variance in 10-year height was associated with differences among trees within family plots. Estimates of heritability ([Formula: see text], [Formula: see text], and [Formula: see text]) indicate that a combination of stand, family-within-stand, and progeny-within-family selection will be effective for a long-term breeding program to increase tree heights in Sitka spruce.Key words: Picea, heritability, quantitative.

Genetic relationships between wood quality traits and diameter growth of juvenile core wood in Sitka spruce

2013 ◽  
Vol 43 (1) ◽  
pp. 1-6 ◽  
Author(s):  
S.G. Kennedy ◽  
A.D. Cameron ◽  
S.J. Lee
Keyword(s):  
Growth Rate ◽  
Genetic Correlation ◽  
Modulus Of Elasticity ◽  
Genetic Relationships ◽  
Wood Quality ◽  
Wood Properties ◽  
Sitka Spruce ◽  
Acoustic Velocity ◽  
Picea Sitchensis ◽  
Good Growth

The trend towards shorter rotations in planted conifer stands has resulted in a reduction in the proportion of mature wood relative to juvenile core wood, raising concerns that the mechanical performance of sawn battens will be affected. The potential to improve the wood quality of the juvenile core of Sitka spruce (Picea sitchensis (Bong.) Carrière) without compromising growth rate was investigated. Rapid and inexpensive indirect methods of assessing wood properties on standing trees using a Pilodyn gun and acoustic velocity were compared with direct measurements made on wood samples cut from the juvenile core. Strong genetic correlations were observed between Pilodyn gun values and direct measures of density (–0.76) and between the square of acoustic velocity and modulus of elasticity (0.73). The genetic correlation between the square of acoustic velocity and microfibril angle was also strong (–0.84). These results suggest that indirect assessments of wood properties within juvenile core wood are sufficiently reliable for these techniques to be used in the Sitka spruce breeding programme. Although a strong negative genetic correlation between diameter at breast height and density was noted (–0.79), sufficient variation exists within the breeding population to select families with both good growth rate and high modulus of elasticity wood.

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