Novel Application of ALMANAC: Modelling a Functional Group, Exotic Warm-season Perennial Grasses

Abstract

Aim: To determine the efficacy of the ALMANAC model in simulating leaf canopy growth and biomass production of a plant functional group, specifically “exotic warm-season perennial grasses,” represented by buffelgrass [Pennisetum ciliare (L.) Link] and “Old World Bluestems” (Bothriochloa Kuntze, Capillipedium Stapf, and Dichanthium Willemet). Study Design: Leaf area index (LAI) over the growing season, the light extinction coefficient (k) for Beer's Law, and the radiation use efficiency (RUE) were quantified for Old World Bluestems and buffelgrass.  Place and Duration of Study: This study was conducted in central Oklahoma in 2005 and 2007 and in south-central Texas in 2008 and 2009. Methodology: Serial dates of measurement over the growing season of leaf area index, light extinction coefficient for Beer's Law, and the radiation use efficiency were used to quantify these growth parameters for simulation modeling. Results: All assayed grasses in the exotic warm-season perennial grasses functional group had similar values for LAI (mean = 4), k (mean = -0.5), and RUE (mean = 1.3 g MJ-1 IPAR).  Conclusion: When these parameters were applied in a simulation model, the model successfully simulated mean yields near the reported yields for exotic warm-season perennial grasses on all simulated soils in Texas and Oklahoma and in Mexico. These results suggest that with further parameterization, the applicability of such process-based models could be expanded from species simulation to functional group simulation, whereby land managers could determine potential adaptability, water use, soil erosion, and forage productivity of various plant functional groups over a wide range of soils and climatic conditions