Using soil-based and physiographic variables to improve stand growth equations in Uruguayan forest plantations

Abstract

Biogeosciences and Forestry Biogeosciences and Forestry Using soil-based and physiographic variables to improve stand growth equations in Uruguayan forest plantations Cecilia Rachid-Casnati (1) , Euan G Mason (2) , Richard C Woollons (2) Information provided by traditional growth models is an essential input in decision making processes for managing planted forests. They are generally fitted using inventory data guaranteeing robustness and simplicity. The introduction of explanatory factors affecting tree development in age-based sigmoidal growth and yield equations attempts not only to improve the quality of predictions, but also to add useful information underpinning forest management decisions. This study aimed to assess the use of the following soil-based and physiographic predictors: potentially available soil water (PASW), elevation (Elev), aspect (α) and slope (β) in a system of empirical stand equations comprising: dominant height (hdom), basal area (G), maximum diameter at breast height (dmax), and standard deviation of diameters (SDd). Augmented models were compared with the base models through precision and bias of estimations for two contrasting species: Pinus taeda (L.), and Eucalyptus grandis (Hill ex. Maiden), planted commercially in Uruguay. Soil-based and physiographic information significantly improved predictions of all the state variables fitted for E. grandis, but just hdom and G for P. taeda. Only PASW was consistently significant for the augmented models in P. taeda and E. grandis, while the contribution of other predictors varied between species. From a physiological point of view, predictors on the augmented models showed consistency. Models with such augmentation produced decrease of errors between 3 to 10.5%, however decreases in the prediction errors calculated with the independent dataset were lower. Results from this study contributed to add information to the decision-making process of plantations' management.

Modelling growth of Pinus taeda and Eucalyptus grandis as a function of light sums modified by air temperature, vapour pressure deficit, and water balance

“…Consequently, the independent variables were not directly measured, as is the case with age, and were therefore susceptible to error. However, summarising several growth factors that interact and vary with location and plantation period is an advantage over time-based formulations that consider only one growth factor (Woollons et al 1997a;Maestri 2003;Pinjuv et al 2006;Scolforoet al 2019a) or that consider surrogate variables (Rachid-Casnati et al 2019).…”

“…Previous studies showed that potentially available soil water influences the asymptote of dominant height and basal area growth equations for E. grandis and P. taeda, and maximum diameter growth equations for E. grandis (Rachid-Casnati et al 2019). Therefore, this possibility was also assessed for light-based equations.…”

“…A comparison of the hybrid approach with timebased formulations in terms of precision and bias was undertaken given that an identical dataset was used by Rachid-Casnati et al (2019) to model the same state variables through time-based equations. In this other study, two formulations: (1) simple (based solely on time); and (2) augmented equations were developed.…”

“…We hypothesise that models for projecting maximum diameter at breast height and standard deviation of diameters could be improved when using potentially useable radiation sums. Previous studies showed that the inclusion of variables related to site quality or site characteristics, improved the precision of models for pine and eucalypts (Methol 2008(Methol , 2001Rachid-Casnati et al 2019).…”

“…Pinus taeda is the most planted pine species (nearly 180,000 ha) (MGAP-DGF 2018) for producing saw logs and plywood. Growth and yield systems predicting the effect of factors limiting productivity are of increasing importance for intensively-managed plantations of these species, and their development has been an increasingly important research goal (Soares & Leite 2000;Maestri 2003;Temps 2005;Carrero 2012;Munhoz 2016;Rachid-Casnati et al 2019;Schons et al 2019;Scolforo et al 2019). However, the performance of PULSE applied to those species has not been analysed.…”