Expressions and Variables

In iLand, text-based mathematical expressions and dynamic variables are used extensively to define species-specific behaviors, customize forest management activities, evaluate logical selection criteria, and inspect simulation results.

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Expressions

An Expression is a mathematical formula provided in text form (such as 3*x + 2 or dbh > 30 and leafarea < 1). In iLand, expressions are parsed once and compiled into high-performance internal programs that run at speeds comparable to hard-coded C++. * Read the Expressions documentation to learn about basic arithmetic, logical operators, constants, built-in functions (mathematical, logical, and helper functions), and performance linearization.

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Variable Reference Lists

The variables available within an expression depend on the context it is evaluated in. Refer to the reference pages below for the specific variables exposed for different entities:

• Tree Variables: Variables representing individual living trees, such as dbh, height, volume, basalarea, leafarea, stress, and age metrics.
• Sapling Variables: Variables representing sapling cohorts on a resource unit, such as height, age, cohortCount, and species-specific indicators.
• Dead Tree Variables: Variables for standing and downed dead wood (snags), representing their diameter, height, decomposition state, and species.
• Resource Unit Variables: Landscape-level variables representing resource unit conditions (typically 1-hectare blocks), including climate variables, soil indicators, site productivity, and aggregated tree metrics.