Elk survey data were collected from three distinct sites Davison Meadows and Boyes Meadow, in the Prairie Creek drainage, and the Bald Hills Meadows in the lower Redwood Creek drainage (Fig.2 ). We primarily selected Boyes Meadow and Bald Hills Meadows because there were no elk population irruptions, as there was in the Davison Meadows, between 1989 and 2011. Another reason for selection was that female elk in Boyes and Davison Meadows displayed strong meadow tenacity (Starns et al. 2014 ). Rarely (observed <1% of time) did the female elk population (defined below) from Boyes Meadow use Davison Meadows, and the Davison females were never observed in the Boyes Meadow (Julian et al. 2013 ). The female population inhabiting the Bald Hills were geographically separated from Boyes and Davison Meadows to the extent that it was unlikely females from these meadows used the Bald Hills or vice versa. Furthermore, the population dynamics of elk in Boyes Meadows and Bald Hills Meadows were very different (see Results). Consequently, to more robustly evaluate the influence of elk herbivory on NDVI during an irruption, temporal patterns in NDVI values in Davison Meadows were compared to NDVI values in Boyes Meadows and the Bald Hills Meadows across the same time period.
All sites are in Redwood National and State Parks in northern Humboldt County, California (Fig.2 ). The Prairie Creek drainage encompasses about 100 km2 and flows into Redwood Creek. Elevation ranges from near sea level in Davison Meadows to about 1050 m at the highest peak of the Bald Hills. Forest in the Prairie Creek drainage consists mainly of second-growth and old-growth redwood–conifer forests dominated by coast redwood, Sitka spruce (Picea sitchensis), Douglas-fir (Pseudotsuga menziesii), and western hemlock (Tsuga heterophylla). Small meadows (13–51 ha in size) are dispersed throughout the forest. Bald Hills forest consists of a mix of evergreens such as Douglas-fir, with a large component of hardwoods: tanoak (Lithocarpus densiflorus), madrone (Arbutus menziesii), big-leaf maple (Acer macrophyllum), California bay (Umbellularia californica), and red alder (Alnus rubra). Meadows in the Bald Hills are situated near one another and total about 1000 ha. Meadow vegetation at all sites is a mix of perennial and annual grasses such as California oat grass (Danthonia californica), redtop (Agrostis alba) and soft chess (Bromus hordeaceus). Common forbs are hairy cat's ear (Hypochoeris radicata) and narrow-leaved plantain (Plantago lancelata) (Harper 1962 ; Weckerly et al. 2001 ). Since 1997, there has been an apparent increase in reed canary grass (Phalaris arundinacea) in the Davison Meadows.
Regional climate is maritime with mild, dry summers and rainy winters. Coastal fog occurs throughout the year, but is more frequent in summer. Mean minimum and maximum temperatures in the Prairie Creek drainage during winter are approximately 2°C and 10°C, respectively, with mean temperatures in summer ranging from 10 to 20°C (Veirs 1987 ). Annual precipitation is usually greater than 150 cm, with rainfall mostly occurring from autumn to early spring. Snowfall in Boyes and Davison Meadows is rare, and daytime winter temperatures prohibit snow accumulation. The Bald Hills, however, receives snow more frequently and accumulations of 20–40 cm may persist for 1–2 weeks. About 35 km inland, Bald Hills temperatures are more extreme than those found in Boyes and Davison Meadows, with mean summer minimum and maximum temperatures ranging from 20 to 26°C, respectively. Mean minimum and maximum winter temperatures range from 0 to 10°C, respectively.
All sites are in Redwood National and State Parks in northern Humboldt County, California (Fig.
Regional climate is maritime with mild, dry summers and rainy winters. Coastal fog occurs throughout the year, but is more frequent in summer. Mean minimum and maximum temperatures in the Prairie Creek drainage during winter are approximately 2°C and 10°C, respectively, with mean temperatures in summer ranging from 10 to 20°C (Veirs 1987 ). Annual precipitation is usually greater than 150 cm, with rainfall mostly occurring from autumn to early spring. Snowfall in Boyes and Davison Meadows is rare, and daytime winter temperatures prohibit snow accumulation. The Bald Hills, however, receives snow more frequently and accumulations of 20–40 cm may persist for 1–2 weeks. About 35 km inland, Bald Hills temperatures are more extreme than those found in Boyes and Davison Meadows, with mean summer minimum and maximum temperatures ranging from 20 to 26°C, respectively. Mean minimum and maximum winter temperatures range from 0 to 10°C, respectively.
