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Projeto de investigação
Models for Adaptive Forest Management
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Carbon and nutrients stocks in even-aged maritime pine stands from Portugal
Publication . Nunes, Luís; Patrício, Maria Sameiro; Tomé, José; Tomé, Margarida
To comply with the demands of the Kyoto Protocol, industrialized countries must reliably estimate the stored carbon (C) in different pools of forest ecosystems. The main objective of this study was to quantify the biomass, C and nutrients stocks in the forest floor, understory, downed dead wood (DDW) and mineral soil of even-aged maritime pine (Pinus pinaster Ait.) stands from three contrasting regions of Portugal. Assessing the specific contribution of DDW to the C and nutrients stocks and how C concentration in the plant material differs from 0.50, the reference value used in many practical applications, were also objectives of this research. Biomass content of forest floor was determined by a quadrat method. Sampling units of 1 m2 were used for the understory. The line intersection method was adopted for sampling DDW and the mineral soil was sampled at three depths. Concentrations of C and nutrients were obtained by chemical analysis of samples from soil and milled plant material. Biomass and C in the trees were obtained using published equations. Total C stocks ranged between 100.6 Mg ha–1 and 308.6 Mg ha–1. Mineral soil shared up to 70-74% of global stored C, being the main cause of the global C stock differences among regions. Phosphorous and potassium were at low to very low levels in the mineral soil and plant material. The contribution of DDW to the C and nutrients pools was negligible. The percentage of C in the plant material ranged between 52% and 54%.
Prediction of annual tree growth and survival for thinned and unthinned even-aged maritime pine stands in Portugal from data with different time measurement intervals
Publication . Nunes, Luís; Tomé, José; Tomé, Margarida
An annual individual tree survival and growth model was developed for pure even-aged stands of maritime
pine in Portugal, using a large data set containing irregularly time-spaced measurements and considering
thinning effects. The model is distance-independent and is based on a function for diameter
growth, a function for height growth and a survival function. Two approaches are compared for modeling
annual tree growth. The first approach directly estimates a future diameter or height using well-known
growth functions formulated in difference form. The second approach estimates diameter or height using
a function in differential form estimating the increment over a year period. In both approaches, the function
parameters were related to tree and stand variables reflecting the competition status of the tree as
well as of a thinning response factor. Variable growth and survival rates were assumed in the modeling
approaches. An iterative method was used to continuously update tree and stand attributes using a cutoff
to convert the survival probability for a living or a dead tree. The individual tree diameter growth
model and the survival probability model were fitted simultaneously using seemingly unrelated regression
(SUR). Parameters of the height function were obtained separately as the number of observations for
height was much lower than the number of observations for diameter, which may affect the statistical
inference and the estimation of contemporaneous cross-equation error correlation inherent to the system
of equations. PRESS residuals were used to evaluate the predictive performance of the diameter and the
height growth functions. Additional statistics based in the log likelihood function and also in the survival
probability were computed to evaluate the survival function. The second modeling approach, which integrates
components of growth expansion and decline, performed slightly better than the first approach. A
variable accounting for the thinning response that was tested proved to be significant for predicting
diameter growth, even if the model already included competition-related explanatory variables, namely
the basal area of trees larger than the subject tree. However, this thinning response factor was not significant
for predicting height growth.
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Entidade financiadora
European Commission
Programa de financiamento
FP7
Número da atribuição
226544