What is the PnET-Succession Extension?

The PnET-Succession extension implements succession with cohorts defined by age ranges and including biomass per cohort. Most parameters can change over time, due to climate change for example.

The PnET-Succession extension was originally based on the Biomass Succession extension of Scheller and Mladenoff (2004), embedding elements of the PnET-II ecophysiology model of Aber et al (1995) to simulate growth as a competition for available light and water, replacing the existing competition for “growing space” algorithms (De Bruijn et al. 2014). PnET (Photosynthesis and EvapoTranspiration) is a simple, lumped parameter model of carbon and water balances of forests (Aber and Federer 1992), built on two principal relationships: 1) maximum photo-synthetic rate is a function of foliar nitrogen concentration, and 2) stomatal conductance is a function of realized photosynthetic rate. PnET-Succession uses one PnET simulation for each tree species-age cohort and uses water and light consumption by these cohorts to implement competition. PnET-Succession calculates resources in terms of Non-Structural Carbon (NSC) for each cohort in its PnET part and assumes that cohorts die when their NSC level drops below a threshold. The PnET-Succession extension also tracks dead biomass over time, divided into two pools: woody and leaf litter.

Release Notes

• Latest official release: Version 6.0.3 — January 2026
• This version has functionality identical to v5.1, with documentation below. The new release is simply for compatibility with LANDIS-II v.8. This also means that calibrations performed for v5.1 should apply to simulations using this version.
• Download the User Guide here: PnET-Succession v6.0 User Guide.
• Download the Climate Library guide here: User guide for Climate Library
• Full release details can be found in the User Guide and on GitHub.
• A detailed description of the model can be found in this updated document: Description of PnET-Succession v5.1.pdf
• A spreadsheet that demonstrates some of the specific model functions is available to explore the impacts of certain parameter choices: PnET-Succession function worksheet v6.0.xlsx
• This version is compatible with all officially released extensions – unless a restriction to a specific extension is otherwise identified.

Requirements

To use PnET-Succession, you need:

• The LANDIS-II model v8.0 installed on your computer.

Download

Version 6.0.3 installer can be downloaded here: PnET-Succession v6.0.3 Installer. To install it on your computer, launch the installer.

Example Files

LANDIS-II requires a global parameter file for your scenario, and separate parameter files for each extension.

Example files using PnET-Succession are here: Examples.

Citation

Gustafson, Eric J., Brian R. Sturtevant, Brian R. Miranda, Zaixing Zhou. 2023. PnET-Succession v 6.0.3: Comprehensive description of an ecophysiological succession extension within the LANDIS-II forest landscape model. Published by the LANDIS-II Foundation. URL: https://github.com/LANDIS-II-Foundation/Foundation-Publications/blob/main/Description of PnET-Succession v5.1.pdf.

Support

If you have a question, please contact Brian Sturtevant. You can also ask for help in the LANDIS-II users group.

If you come across any issue or suspected bug, please post about it in the issue section of the Github repository (GitID required).

Authors

Arjan de Bruijn: originally Purdue University; Eric Gustafson (emeritus), Brian Miranda, Brian Sturtevant:; US Forest Service, and Zaixing Zhou (University of New Hampshire)

Mail : brian.r.sturtevant@usda.gov