Simulating Secondary Forest Growth and Composition Dependency on Prior Land Use, Time of Abandonment, and Seed Availability
Authors
Polly Thornton1* (polly.buotte@berkeley.edu), Charles Koven2, Eileen Helmers3, Lara Kueppers1,2, Jeffrey Chambers1,2
Institutions
1University of California–Berkeley, CA; 2Lawrence Berkeley National Laboratory, Berkeley, CA; 3International Institute of Tropical Forestry, USDA Forest Service, San Juan, PR
URLs
Abstract
Land abandonment after agricultural use is a common phenomenon in tropical forest regions. Prior land use, time of abandonment, and seed availability influence secondary forest growth rates and trajectories of composition. Puerto Rico is an ideal setting to evaluate the ability to simulate secondary forest growth following land abandonment. Most of the island was under agricultural cultivation and subsequently abandoned over the course of the 20th century.
Island-wide estimates of forest age and current biomass allow for benchmarking E3SM Land Model–Functionally Assembled Terrestrial Ecosystem Simulator (ELM-FATES) simulations of secondary forest growth. The team has developed robust parameterizations for nine tropical plant functional types (PFTs), representing seven evergreen and two deciduous tree strategies. The evergreen PFTs are differentiated along axes of mature tree height, shade tolerance, and growth rates. The two deciduous PFTs are differentiated by mature tree height. These PFTs have been evaluated at a wet and dry site in Puerto Rico. Researchers created workflows to evaluate the relative importance of prior land use, time of abandonment, and seed availability within the current ELM-FATES infrastructure. Prior land use is evaluated by starting one set of simulations with established grass and another with a shade-tree coffee plantation. Seed availability is evaluated by manually editing the restart files to represent a dense and a sparse seed bank. Time since abandonment and the effects of the realized climate conditions will be evaluated by starting one set of simulations in 1936 and a second set in 1976 as those years correspond to the most common current forest age classes. All simulations are forced with 1-km climate data generated with the Daymet algorithm at Oak Ridge National Laboratory. Results from these simulations allow the team to understand and prioritize model development tasks needed to effectively simulate secondary forest growth following agricultural land abandonment in the tropics.