Modeling individual tree mortality for crimean
pine plantations
Mehmet Misir*, Nuray Misir
and Hakki Yavuz
Faculty of
Forestry, Karadeniz
Technical University,
Trabzon-610 80, Turkey
(Received:
November 23, 2005 ; Revised received: July 21, 2006; Accepted: August 11, 2006)
Abstract: Individual tree mortality model was
developed for crimean pine (Pinus
nigra subsp. pallasiana) plantations in Turkey. Data came from 5 year remeasurements of the permanent sample plots. The data
comprises of 115 sample plots with 5029 individual trees. Parameters of the
logistic equation were estimated using weighted nonlinear regression analysis.
Approximately 80% of the observations were used for model development and 20%
for validation. The explicatory variables in the model were ratio of diameter
of the subject tree and basal area mean diameter of the sample plot as measure
of competition index for individual trees, basal area and site index. All
parameter estimates were found highly significant (p<0.001) in predicting
mortality model. Chi-square statistics indicate that the most important
variable is , the second most important is site index, and the third most
important predictor is stand basal area. Examination of graphs of observed vs.
predicted mortality rates reveals that the mortality model is well behaved and
match the observed mortality rates quite well. Although the phenomenon of
mortality is a stochastic, rare and irregular event, the model fit was fairly
good. The logistic mortality model passed a validation test on independent data
not used in parameter estimation. The key ingredient for obtaining a good
mortality model is a data set that is both large and representative of the
population under study and the data satisfy both requirements. The mortality
model presented in this paper is considered to have an appropriate level of
reliability.
Key words: Growth model, Individual trees,
Mortality, Logistic function
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