Normalized Difference Perennial Dominance Index

This Google Earth Engine web application provides visualization and analysis of the Normalized Differenced Perennial Dominance Index and fires. NDPDI is an indicator of rangeland plant functional group dominanced intended for use in the Great Basin. When analyzed through time, NDPDI can help to assess ecological resilience to fire and disturbance and resistance to invasive plants (R&R). For example, locations that maintain high values of NDPDI following fire likely have high R&R.

  • Project lead Eric Jensen
  • Collaborators Jody Vogeler
  • Website Web application
  • Tools Google Earth Engine, R, ArcGIS Pro
  • Completed December 2020


Visit the NDPDI web application here!

What is NDPDI?

A significant challenge in conducting regional-scale analysis of vegetation recovery following disturbance is identifying an ecologically meaningful response variable. Many vegetation modeling studies in the Great Basin use recovery of shrub or sagebrush cover percentages as an indicator of post-fire recovery. However, such approaches have two limitations in regional-scale analysis, 1) they may not account for regional variability in plant density, productivity, and site potential and 2) they are unable to account for annual grass invasion which often occurs in plant interspaces. Here, we introduce an alternative metric that overcomes these limitations, the normalized differenced perennial dominance index (NDPDI). NDPDI differences percent cover of perennial plants against annual plants, below.

The NDPDI is bound from 0–2, with values of less than 1 being dominated by annual plants and values greater than 1 being dominated by perennial plants. This measure is most useful in the Great Basin where most annual plants are introduced and noxious (e.g. Bromus tectorum, Taeniatherum caput-medusae, Salsola traegus, Sisymbrium altissimum, etc.) and most perennial plants are native to their ecosystems. One of the advantages of NDPDI is that it is unbiased for low or high vegetation cover systems. For example, mountain sagebrush systems naturally have much denser vegetation cover than salt desert shrub. It is, however, important to note the limitation of NDPDI that it treats all perennial functional groups the same, which can gloss over ecologically important distinctions. Yet, in many areas in the Great Basin simply establishing perennial plants in the post-fire environment is viewed as a restoration success. Thus, we propose NDPDI as a scalable metric for evaluating trajectories of plant communities for the Great Basin and Snake River Plain.

About the NDPDI Web Application

This application allows you to explore NDPDI time-series data in the context of fire frequency. Use the layer selector to switch between NDPDI and fire frequency data. The year slider allows you to evaluate spatial patterns and vegetation change through time. The example locations demonstrate high, moderate, and low R&R locations. Click any location on the map to see fire information and NDPDI data for any location.

See the one-page fact sheet, below: