Estimating tree volume components is an essential element in sustainable forest management. Compatible taper and merchantable outside-bark volume systems based on volume ratio models were globally ...fitted to four pine species (reduced models) with the aim to select the best reduced model and to fit it with dummy variables and additive effects using Pinus pseudostrobus Lindl as a base species. The study was carried out in the northern mountains of Oaxaca, Mexico. To fit the taper, merchantable volume, stem volume, branch volume, and total tree volume (stem volume and branch volume) equations, a taper dataset of 222, 230, 245, and 333 trees of Pinus douglasiana Martínez (Pd), Pinus oaxacana Mirov (Po), Pinus patula Schltd (Pp), and Pinus pseudostrobus Lindl (Pps), respectively, was used. In general, the compatible systems explained more than 97% in the observed variability for the four studied components: outside-bark diameter (d), merchantable outside-bark volume (Vm), stem outside-bark volume (Vs), and total tree volume (Vt). Alternatively, more than 52% of the observed variability for branch volume (Vb) was also explained. The developed compatible systems based on volume ratio models are a simple and consistent alternative for estimating the outside-bark diameter and variable outside-bark volume, as well as the components of commercial species for uneven-age and mixed-species forests in Oaxaca, Mexico.
Key message
We evaluated the use of low-density airborne laser scanning data to estimate diameter distributions in radiata pine plantations. The moment-based parameter recovery method was used to ...estimate the diameter distributions, considering LiDAR metrics as explanatory variables. The fitted models explained more than 77% of the observed variability. This approach can be replicated every 6 years (temporal cover planned for countrywide LiDAR flights in Spain).
Context
The estimation of stand diameter distribution is informative for forest managers in terms of stand structure, forest growth model inputs, and economic timber value. In this sense, airborne LiDAR may represent an adequate source of information.
Aims
The objective was to evaluate the use of low-density Spanish countrywide LiDAR data for estimating diameter distributions in
Pinus radiata
D. Don stands in NW Spain.
Methods
The empirical distributions were obtained from 25 sample plots. We applied the moment-based parameter recovery method in combination with the Weibull function to estimate the diameter distributions, considering LiDAR metrics as explanatory variables. We evaluated the results by using the Kolmogorov–Smirnov (KS) test and a classification tree and random forest (RF) to relate the KS test result for each plot to stand-level variables.
Results
The models used to estimate average (
d
m
) and quadratic (
d
g
) mean diameters from LiDAR metrics, required for recovery of the Weibull parameters, explained a high percentage of the observed variance (77 and 80%, respectively), with RMSE values of 3.626 and 3.422 cm for the same variables. However, the proportion of plots accepted by the KS was low. This poor performance may be due to the strictness of the KS test and/or by the characteristics of the LiDAR flight.
Conclusion
The results justify the assessment of this approach over different species and forest types in regional or countrywide surveys.
Even though the site index is a popular method for describing forest productivity, its use is limited in uneven-aged multispecies forests. Accordingly, the site form (SF) is an alternative measure of ...productivity to the site index based on the tree height–diameter relationship. Our study aims to evaluate SF as a measure of productivity in the temperate uneven-aged multispecies forests of Durango, Mexico, applying three methods to estimate SF: (i) as the mean height of dominant trees at a reference diameter (SFH-D); (ii) as the expected mean height of dominant trees at a reference mean diameter (SFMH-MD), and (iii) as the expected height at a reference diameter for a given site (SFh-dbh). We assess the effectiveness of the SF based on two hypotheses: (i) the SF correlates to the total volume production, and (ii) the SF is independent of stand density. The SFH-D and the SFh-dbh showed a high correlation with productivity. However, they also did so with density. Contrary to this, the SFMH-MD had a weak correlation with density and productivity. We conclude that the SF is a suitable approach to describe site quality. Nonetheless, its effectiveness as a site quality indicator may be affected according to the method used.
Context
The scaling-up approach (which requires the use of individual tree biomass equations and data) is one of the most commonly used methods for estimating stand biomass at a local scale. However, ...biomass prediction over large management areas requires more efficient methods.
Aims
Two methods of estimating aboveground stand biomass were developed and compared: stand biomass equations (SBE) including observed stand variables, and SBE including biomass expansion factors (BEF) and stand volume.
Methods
Two types of systems of additive equations were fitted simultaneously for components and total aboveground stand biomass, to ensure additivity. Inherent correlations among biomass components were also taken into account in the fitting process.
Results
The systems explained a high percentage of the observed variability. The SBE systems that included observed stand variables provided more accurate estimates than those that included BEF and stand volume. However, the latter were found to be more precise for stem wood and total aboveground biomass prediction.
Conclusions
Both approaches provide a direct link between forest inventory data, outputs from whole-stand growth models, and biomass estimates at stand level. Taking into account that the inventory effort is similar for both alternatives, the choice of which to use will depend on the data available and on the relative importance of the biomass components for the end-users.
Resumen Las distribuciones diamétricas son un factor importante en la caracterización del rodal, ya que el diámetro, generalmente, está correlacionado con otras variables de interés como la altura, ...volumen, biomasa, etcétera, esto permite conocer el tipo de productos que pueden obtenerse del bosque. El objetivo de la presente investigación fue desarrollar una estrategia para ajustar las FDP Weibull, Beta y S B Johnson, así como reconstruir (modelación) la distribución diamétrica futura con el método de recuperación de parámetros. En una primera etapa, se estudió comparativamente la calidad de ajuste de tres funciones de distribución de probabilidad (FDP: Weibull, S B Johnson y Beta) mediante los métodos de momentos y máxima verosimilitud para recuperar los parámetros y describir la distribución diamétrica de 2 252 parcelas temporales de muestreo ubicadas en bosques naturales de Pueblo Nuevo, Durango, México. En general, los mejores resultados en términos de precisión y parsimonia en la etapa de ajuste, evaluados mediante el sesgo medio y la Raíz del Error Medio Cuadrático, se obtuvieron con la FDP Weibull ajustada con el método de los momentos; mientras que las distribuciones S B Johnson y Beta se ubicaron en segundo y tercer lugar, respectivamente. Por tanto, la FDP Weibull biparamétrica fue seleccionada para modelar las distribuciones diamétricas de los rodales estudiados. La técnica de la recuperación de parámetros evidenció que 62 % de las parcelas modeladas siguen una distribución teórica tipo Weibull con 20 % de nivel de significancia en la prueba de Kolmogorov-Smirnov.
Considering that, the temporal trend in stocking, expressed as number of trees per unit area, is the opposite of that of growth, and that both trajectories are sigmoidal, we derived a temporal ...trajectory of density decrease by reversing the temporal trend of a generalized growth function. We derived and analysed twelve stand-level mortality models by using four data sets from monospecific even-aged stands. Stand dominant height rather than stand age was incorporated as an indicator of the growth stage and a careful examination of the models conformity with the essential logical properties of the stand-level survival models was conducted. We first tested the models adequacy and general predictive performance by fitting them to parameterization data sets and subsequently assessing them with validation data. The regression equations were re-fitted afterwards over the total data sets to make use of all available information in the final parameter estimates. Nine model formulations were successfully fitted and four of them were the most adequate in describing stand density decrease with dominant height growth. The site-specific effect was incorporated in the newly derived models through the predictor variable and the stand-specific starting density was accounted for through a specific model parameter. These new dominant height-dependent mortality equations can be considered for inclusion in the framework of stand-level growth models as transition functions.
Lack of knowledge of individual tree growth in species-rich, mixed forest ecosystems impedes their sustainable management. In this study, species-specific models for predicting individual diameter at ...breast height (dbh) and total tree height (h) growth were developed for 30 tree species growing in mixed and uneven-aged forest stands in Durango, Mexico. Growth models were also developed for all pine, all oaks, and all other species of the genus Arbutus (strawberry trees). A database of 55,158 trees with remeasurements of dbh and h of a 5-year growth period was used to develop the models. The data were collected from 217 stem-mapped plots located in the Sierra Madre Occidental (Mexico). Weighted regression was used to remove heteroscedasticity from the species-specific dbh and h growth models using a power function of the tree size independent variables. The final models developed in the present study to predict dbh and total tree height growth included size variables, site factors, and competition variables in their formulation. The developed models fitted the data well and explained between 98 and 99% and of the observed variation of dbh, and between 77 and 98% of the observed variation of total tree height for the studied species and groups of species. The developed models can be used for estimating the individual dbh and h growth for the analyzed species and can be integrated in decision support tools for management planning in these mixed forest ecosystems.
Several model forms were analyzed to develop a height-diameter (h-d) relationship for even-aged, birch-dominated stands (8,454 h-d pairs of 198 plot-inventory combinations) in northwestern Spain. A ...basic model (which includes only d as predictor) and a generalized model (which also considers stand variables as regressors) were selected from among available models. Fixed and mixed forms of these models were evaluated. An approximate Bayesian estimator was used to obtain a calibrated response (prediction with fixed parameters and random effects) of the mixed models from prior height measurements of trees selected by different strategies. From a practical point of view, the calibrated basic mixed model is recommended if a randomly selected sample of 4-11 trees is available or if only the 3 trees that are the diameter quartiles are measured. If the random sample includes more than 11 trees, the basic fixed model should be locally fitted, and the generalized fixed model is recommended when only dominant height is known. Finally, the predictions of the latter model may be outperformed by the calibrated generalized mixed model, which also requires inclusion of the height of the smaller diameter trees.
The parsimonious taper function proposed by Riemer et al. (1995. Allg. Forst.- Jagdztg.
166
(7): 144–147) was fitted for radiata pine (Pinus radiata D. Don) stems in Spain by using a nonlinear mixed ...modelling approach. Eight candidate models (all possible expansion combinations of the three fixed parameters with random effects) were assessed, and the mixed model with three random effects performed the best according to the goodness-of-fit statistics. An evaluation data set was used to assess the performance of these models in predicting stem diameter along the bole, as well as total stem volume. Four prediction approaches were compared: one subject (tree) specific (SS) and three population specific (ordinary least squares (OLS), mean (M), and population averaged (PA)). The SS responses for a tree were estimated from a prior stem diameter measurement available for that tree, whereas OLS, M, and PA were obtained from the fixed-effects model, from the fixed parameters of mixed-effects models, and by computing mean predictions from the mixed-effects models over the distribution of random effects, respectively. Prediction errors were greater for the M and PA responses than for the OLS response, and therefore, from the prediction point of view, the use of the mixed-effects models is not recommended when an additional stem diameter measurement is not available. The mixed model with three random effects was also selected as the best model for SS estimations. Measurement of an additional stem diameter at a relative tree height of approximately 0.5 provided the best calibrations for stem diameters along the bole and total stem volume predictions. The SS approach increased the flexibility and efficiency of the selected mixed-effects model for localized predictions and thus improved the overall predictive capacity of the base model.
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