Remote Sensing of Land Surface Phenology

Phenology is the study of periodic tion documenting trends in ecology and life-cycle events (for example, flower- detecting the impacts of climate change ing, insect emergence, nesting, migra- on ecosystems at multiple scales. tion) and how these stages are affected Remote sensing of land-surface by climate and environment. Phenology phenology can characterize vegetation describes how organisms are specifically changes during the growing season and adapted to the environmental cycles that documents specific events such as start surround them and it applies to nearly and end of season and growing season all aspects of life on Earth including the duration (table 1). These indicators can abundance, distribution, and diversity reveal broad-scale phenological trends of organisms, ecosystem services, food that are difficult to detect over large areas webs, and the global cycles of water and using traditional ground-based methods carbon. Phenological events are sensitive (fig. 1). Remote Sensing Phenology indi- to climate variation; therefore, phenology cators developed by the U.S. Geological Figure 2. A U.S. Geological Survey data provide important baseline informa- Survey (USGS) RSP program are used scientist records ground data that are 120° 110° 100° used (along with other datasets) with start of season phenology indicator to model cheatgrass (Bromus tectorum) growth in

EXPLANATION the Northern Great Basin (photograph by 45° Matthew Rigge, USGS). Maximum Normalized Difference Vegetation by government agencies, universities, Index (NDVI) and conservation groups, among others, No data to model the growth of noxious weeds, 0–0.1 0.1–0.2 assess forage production, characterize 0.2–0.3 40° 0.3–0.4 climate and phenology interactions, and 0.4–0.5 model fire potential (fig. 2). 0.5–0.6 0.6–0.7 Land-surface phenology indicators 0.7–0.8 0.8–0.9 developed by the USGS RSP program 0.9–1 Water are derived from the Normalized Differ- ence Vegetation Index (NDVI) and are Base map generated from digital phenology data 0 250 MILES http://phenology.cr.usgs.gov/ processed to highlight vegetation changes. 0 250 KILOMETERS Nine phenology indicators are available Figure 1. Example of a phenology indicator. The indicator shown is maximum Normalized at 250-meter and 1,000-meter resolu- Difference Vegetation Index (NDVI) and can be used to estimate peak canopy photosynthetic tion, and can be downloaded from http:// activity during the growing season. phenology.cr.usgs.gov/index.php (table 1).

Table 1. Remote sensing phenology data at 250-meter and 1,000-meter resolution available at http://phenology.cr.usgs.gov/index.php. [NDVI, Normalized Difference Vegetation Index]

Phenology metric Acronym Description Amplitude AMP Maximum increase in canopy photosynthetic activity above the baseline. Duration DUR Length of photosynthetic activity (the growing season). End of season NDVI EOSN Level of photosynthetic activity at the end of measurable photosynthesis. End of season time EOST End of measurable photosynthesis in the vegetation canopy. Maximum NDVI MAXN Maximum level of photosynthetic activity in the canopy. Maximum time MAXT Time of maximum photosynthesis in the canopy. Start of season NDVI SOSN Level of photosynthetic activity at the beginning of measurable photosynthesis. Start of season time SOST Beginning of measurable photosynthesis in the vegetation canopy. Time-integrated NDVI TIN Canopy photosynthetic activity across the entire growing season.

U.S. Department of the Interior Fact Sheet 2014–3052 U.S. Geological Survey May 2014 To promote an understanding of “Phenology is an under- how the RSP indicators relate to actual lying indicator of vegetation field conditions, the RSP program is change, when it is scaled-up collecting on-the-ground phenologi- cal data in conjunction with the USA by remote sensing it can show National Phenology Network (USA– potentially significant changes NPN). The USA–NPN promotes a to populations in both time and broad understanding of plant and space.” animal phenology and its relationship —Jake Weltzin, Executive with environmental change. The net- Director, USA National Phenol- work is a consortium of individuals and Figure 3. Volunteers at the U.S. Geological organizations that collect, share, and ogy Network Survey Earth Resources Observation and use phenology data, models, and related Science Center (USGS EROS) in Sioux information. Falls, South Dakota, monitor the timing of seasonal events (bud burst, flowering, and A EXPLANATION leaf drop). Start of season time The USGS Earth Resources Observa- No data tion and Science (EROS) Center is build- Previous year ! Jan. ing a record of the vegetation phenology Silverton Feb. week 1 of 14 species around its South Dakota Feb. week 2 campus using Nature’s Notebook (https:// Feb. week 3 www.usanpn.org/natures_notebook), Feb. week 4 which is a phenology monitoring program Mar. week 1 that relies on “citizen scientists” to record Mar. week 2 Mar. week 3 plant and animal life-cycle events (fig. 3). Mar. week 4 These life-cycle data are made available Apr. week 1 by the USA–NPN to anyone interested in Apr. week 2 studying the phenology of species in their B Apr. week 3 local areas and the response of species to Apr. week 4 their environment. These local observa- Apr. week 5 May week 1 tions provide important ground data for ! May week 2 scientists who study climate and vegeta- Silverton May week 3 tion interactions. May week 4 Phenology indicators reveal impor- June week 1 tant environmental data about the vegeta- June week 2 tion around us. For example, the moun- June week 3 tains of southwestern Colorado often June week 4 July week 1 receive heavy snow in spring, though July week 2 2002 was a remarkably dry spring (Wor- July week 3 rall et al., 2013). RSP data were used to Map generated from digital phenology data 0 5 10 MILES July week 4 show the start of vegetation growth [in http://phenology.cr.usgs.gov/ July week 5 0 5 10 KILOMETERS a sample area]. Figure 4 compares the 110° 115° Aug. 2002 start of season with the 2007 start of Sept. to Dec. Water season for a sample area in southwestern 40° COLORADO Colorado. In 2002, the start of season for elevations above 3,000 meters occurred Area of interest during the last week of March and the first week of April. Whereas, in 2007 the start of season occurred a month later during late April and early May. Figure 4. Start of season in the mountains of southwestern Colorado in A, 2002 and B, 2007. For more information contact:

References Cited [email protected] or USGS Earth Resources and Observation Worrall, J.J., Rehfeldt, G.E., Hamann, A., Hogg, E.H., Marchetti, S.B., Michaelian, M., Science (EROS) Center and Gray, L.K., 2013, Recent declines of Populus tremuloides in North America 47914 252nd Street linked to climate: Forest Ecology and Management, v. 299, p. 35–51. Sioux Falls, SD 57198

ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20143052