Earth Interactions d Volume 23 (2019) d Paper No. 4 d Page 1

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Changes in Vegetation Cover of the Arctic National Wildlife Refuge Estimated from MODIS Greenness Trends, 2000–18

Christopher Pottera NASA Ames Research Center, Moffett Field, California

Received 5 October 2018; in final form 18 December 2018

ABSTRACT: Trends and transitions in the growing-season normalized dif- ference vegetation index (NDVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor at 250-m resolution were analyzed for the period from 2000 to 2018 to understand recent patterns of vegetation change in ecosystems of the Arctic National Wildlife Refuge (ANWR) in . Statistical analysis of changes in the NDVI time series was conducted using the breaks for additive seasonal and trend method (BFAST). This struc- tural change analysis indicated that NDVI breakpoints and negative 18-yr trends in vegetation greenness over the years since 2000 could be explained in large part by the impacts of severe wildfires. At least one NDVI breakpoint was detected in around 20% of the MODIS pixels within both the and Coleen River basins of the study area. The vast majority of vegetation cover in the ANWR Brooks Range and coastal plain ecoregions was detected with no (positive or negative) growing-season NDVI trends since the year 2000. Results suggested that most negative NDVI anomalies in the 18-yr MODIS record have

a Corresponding author: Christopher Potter, [email protected]

DOI: 10.1175/EI-D-18-0018.1

Unauthenticated | Downloaded 09/29/21 01:06 AM UTC Earth Interactions d Volume 23 (2019) d Paper No. 4 d Page 2 been associated with early spring thawing and elevated levels of surface moisture in low-elevation drainages of the northern ANWR ecoregions. KEYWORDS: Climate records; Remote sensing; Ecosystem effects; Forest fires; Regional effects

1. Introduction The Arctic National Wildlife Refuge (ANWR) was established by the Alaska National Interest Lands Conservation Act of 1980 and covers 19 million acres (77 000 km2) in northeast Alaska. Proponents of development in the ANWR view its 1.6 million acre (6475 km2) coastal plain as a promising onshore oil reserve (Comay et al. 2018). Nonetheless, wildlife habitats in the ANWR are vulnerable to long-lasting effects from any disturbance, in part because short growing seasons in the Arctic provide limited time for species to recover. Caribou (Rangifer tarandus) are the most numerous large animals in the ANWR. The Porcupine herd (named after the Porcupine River) numbers approximately 150 000 animals. The herd’s Arctic Village–South Brooks Range spring migration route within Alaska and the ANWR crosses the East Fork of the Chandalar River, the Sheenjek River, and upper Coleen River, and follows the Firth River into Canada where it joins the Old Crow migration route. Caribou herds will use areas in the northern foothills of the Brooks Range during summer at elevations of 300– 600 m, with vegetation communities consisting of graminoid meadows, dwarf shrub, and alpine tundra communities (Nicholson et al. 2016). Caribou consume a variety of vegetation including fungi, lichens, woody browse, graminoids, and forbs (Thompson et al. 2015; Denryter et al. 2017). Barboza et al. (2018) reported that female caribou and their calves in northern Alaska select a mixture of graminoids, browse, and forbs to achieve adequate dietary concentrations of digestible energy and nitrogen requirements. Graminoids were the most abundant forage, accounting for 77% of the digestible nitrogen and 74% of the digestible energy in forage biomass. Localized patterns of vegetation growth and decline in the ANWR may be affecting the survival and reproduction of the