Do Spatial Simulations Change Reference Conditions?

Background The reference condition is the expected proportions of reference vegetation classes per ecological system (hereafter, system) within an area and has been measured with non-spatial state-and-transition simulation models (STSM). Aims Demonstrate that reference conditions varied between non-spatial and spatial STSMs from an eastern Nevada, USA landscape. Methods The same STSM database was used to simulate the non-spatial and spatial reference conditions, except additional input were added for spatial simulations. The reference condition was obtained from averaged vegetation class proportions of replicated simulations. Key results Mean fire return intervals (MFRI) were always shorter in spatial than non-spatial simulations. The dissimilarity between the spatial and non-spatial reference conditions was generally higher for smaller systems and those with long MFRIs (≥100 years). Conclusions Non-spatial and spatial reference conditions were comparable for large systems with 50–100-year MFRI. The proportions of older vegetation classes for spatial systems were smaller for large systems with long MFRIs compared to non-spatial results, but those proportions were larger for smaller systems with shorter MFRIs, likely because fires can spatially exit small narrow systems. Implications National and local assessments that use departure from non-spatial reference conditions to determine vegetation treatments should recognize that spatial simulations can lead to revisions of treatment decisions.