Exotic annual grass (EAG) phenology estimates for western U.S. rangelands based on 30-m HLS NDVI (ver. 4.0, August 2025)

Phenological dynamics reflect the vegetation response to changes in weather, vegetation composition, plant life stages pertinent to both agricultural and fire management and are thus important to monitor operationally. The Exotic Annual Grass (EAG) phenology in the western U.S. rangeland based on 30-m Harmonized Landsat and Sentinel-2 (HLS) Normalized Difference Vegetation Index (NDVI) weekly composites between 2016 and 2024 (Dahal et al., 2022) were processed using these 3 methods: (1) NDVI threshold-based method, (2) manual phenological metrics, and (3) modeling and mapping. The EAG phenology model produced two metrics (Start of Season Time [SOST] and End of Season Time [EOST]) and calculated six metrics for identifying the sustained growth characteristics of 15 EAG species throughout 190 million hectares of western U.S. rangeland for 2017 to 2024. The current suite of phenological metrics are SOST; Start of Season NDVI (SOSN); EOST; End of Season NDVI (EOSN); Maximum Time (MAXT); Maximum NDVI (MAXN); Duration (DUR); and Amplitude (AMP). Datasets from 2017 to 2021 were developed using manually interpreted training data specific to each year, while datasets from 2022 to 2024 were produced using the same training set supplemented with additional automated datasets.

References:
Dahal, D.; Pastick, N.J.; Boyte, S.P.; Parajuli, S.; Oimoen, M.J.; Megard, L.J. Multi-Species Inference of Exotic Annual and Native Perennial Grasses in Rangelands of the Western United States Using Harmonized Landsat and Sentinel-2 Data. Remote Sensing 2022, 14, doi:10.3390/rs14040807.

First release: 2022

Revised: April 4, 2024 (ver. 2.0)
Revised: September 3, 2024 (ver. 3.0)
Revised: August 27, 2025 (ver. 4.0)