Linking growth and yield and process models to estimate impact of environmental changes on growth of loblolly pine

PTAEDA2 is a distance-dependent, individual tree model that simulates the g rowth and yield of a plantation of loblolly pine (Pinus taeda L,) on an ann ual basis. The MAESTRO model utilizes an array of trees in a stand to calcu late and integrate the effects of biological and physical variables on the photosynthesis and respiration processes of a target tree on an hourly basi s. PTAEDA2 sums the quantities for individual trees to obtain stand results ; MAESTRO computes values for one tree at a time. These models were linked to provide a tool for further understanding stand, climatic, and edaphic ef fects on tree and forest productivity. PTAEDA2 predicts the characteristics of trees grown at a given stand density, on a given site, for a given leng th of time. These characteristics (outputs) are then used as direct inputs into MAESTRO which assesses the expected impact of environmental changes on tree function, The results from MAESTRO are fed back into PTAEDA2 to updat e future predictions by modifying the site index driver variable of the gro wth and yield model. An equation that predicts changes in site index as a f unction of net photosynthesis, age, and trees per unit area is the backbone of the dynamic linkage, The model changes required to link PTAEDA2 to MAES TRO were developed and reported earlier. This article reviews the earlier w ork and reports research results quantifying the relationships between net photosynthesis and the PTAEDA2 growth predictors, thus providing the basis for the MAESTRO to PTAEDA2 feedback process and integration of these two mo dels.