A modeling approach is essential for quantifying the heterogeneity and complexity of forest composition and dynamics, both spatially and temporally. Simulation models also facilitate the development of guidelines for forest management. To aid in the introduction of indigenous trees on degraded land after the establishment of fast growing tree plantations, we developed models to quantify thinning effects on the growth of canopy trees (Acacia mangium) and understory trees (Hopea odorata, H. ferrea, Xylia xylocarpa var. kerrii) in two-storied plantation forests at the Sakaerat Silvicultural Research Station, Thailand. These models were validated partly using data collected during the monitoring of the 23-year-old Acacia mangium plantation. By employing these models, adequate forest management plans can be selected heuristically, prior to any activity. The models were as follows.
(1) A model to simulate the growth of canopy trees in response to thinning practices; this can predict biomass growth and structural development of forests. This model is applicable to plantation forests containing fast growing species.
(2) “Virtual Forest” to evaluate the light environment under the forest canopy. This is a graphical technique, creating a computer generated virtual forest with various tree sizes and structures. The light environment in the study plots was successfully modeled by “Virtual Forest”, and validated using hemispherical photographs taken in the plots.
(3) A model to estimate the growth of understory trees. The height growth of understory trees depends mainly on the light environment under the forest canopy, particularly in darker conditions. Adopting a logistic growth curve, height growth patterns of understory trees were effectively modeled, demonstrating seasonal step-wise growth.