1. Process-based forest models (PBMs) are important tools for quantifying forest growth and vulnerability, particularly under climate change. The 3-PG model (Physiological Processes Predicting Growth) is one of the most widely used forest growth simulators for this purpose worldwide.
2. Here, we present r3PG, a new Fortran implementation of 3-PG, wrapped into an r package. r3PG can simulate monospecific as well as mixtures of evergreen and deciduous tree species in even-aged or uneven-aged stands.
3. The combination of Fortran functions with an r interface makes the model extremely fast. This facilitates the use of r3PG for extensive computer experiments and sensitivity analysis. We demonstrate this in a case study including (a) single model runs; (b) a sensitivity analysis and a full Bayesian calibration of the model and (c) spatial simulations of forest growth across Switzerland.
4. r3PG is faster and easier to use than previous implementations of 3-PG in visual basic. We believe that this will make 3-PG even more useful and popular for ecologists and climate change scientists.