Nutritional ecology of elk during summer and autumn in the Pacific Northwest

Abstract

Elk (Cervus elaphus) in the western United States are an economically and socially valuable wildlife species. They have featured species status for federal land management planning; hence, considerable modeling focused on habitat evaluation and land management planning has been undertaken for elk. The extent to which these and other habitat models for large ungulates account for influences of nutritional resources varies greatly, probably because of varying recognition of the importance of nutrition and uncertainty about how to measure and model nutrition. Our primary goals were to 1) develop greater understanding of how habitat conditions influence foraging dynamics and nutrition of elk in summer and autumn; and 2) illustrate an ecological framework for evaluating and predicting nutritional resources so that nutritional needs of elk can be integrated within landscape‐scale plans, population models, and habitat evaluation models. We evaluated foraging responses of elk to clearcut logging and commercial thinning, forest succession, and season across ecological site potentials. We also identified the extent to which plant communities satisfied nutritional requirements of lactating female elk and their calves. Our study was conducted in the temperate rainforests of the Pacific Northwest on industrial and public timberlands. We evaluated relations between habitat conditions and elk nutrition in plant communities representing a range in stand age and ecological conditions at 3 study areas, 1 near the Canadian border in the north Cascades Mountains (Nooksack), 1 in the Coast range southwest of Olympia, Washington (Willapa Hills), and the third in the central Cascades near Springfield, Oregon (Springfield), from late June to November, 2000–2002. In 98–143 macroplots per study area, we measured forage abundance by plant species, digestible energy content by plant life‐form group, and forest overstory. In a subset of these macroplots (∼30 per study area), we held 4 tame lactating elk with calves in electrified pens (n = 15–25 adult elk per year), and sampled activity budgets, dietary composition, forage selection, and other measures of foraging behavior; dietary digestible energy (DE; kcal/g) and protein (DP; %) levels; and intake rates of these nutrients. In 15 of these pens, we held elk for extended periods (13–21 days) to monitor changes in body fat of adults and growth of calves. We developed equations to predict dietary DE and DP and per‐minute intake rates of each in a nutrition prediction model that reflected vegetation attributes and ecological site influences. Total abundance of forage in the western hemlock series after clearcut logging in low to moderate elevations (≤1,000 m) ranged from a peak of 3,000–4,500 kg/ha in 5‐ to 10‐year‐old stands to 100–300 kg/ha in 20‐ to 50‐year‐old stands with only moderate increases through late succession. Patterns were similar in higher elevation forests (1,000–1,800 m), although peaks and troughs in forage abundance developed more slowly. Deciduous shrubs, forbs, an...

Straight from the caribou’s (Rangifer tarandus) mouth: detailed observations of tame caribou reveal new insights into summer–autumn diets

“…The tame caribou defined what is accepted as "food" in each plant community sampled, allowing us to assess variability in the forage base. Accepted biomass and similar forager-defined metrics have the potential to generate biologically informative caribou-habitat relationships, as they have been related to intake rates and to diet quality in multiple ungulate species (White and Trudell 1980;Wickstrom et al 1984;Rominger et al 1996;Cook et al 2016). These studies, along with our own, demonstrate the need for biologically sensitive indicators to assess suitability of habitats for foraging (Searle et al 2007).…”

“…Although selection indices do not indicate true forage preference (which may only be determined through cafeteria-style foraging trials where abundance of all items is equal), they are informative and widely used (e.g., Holleman and Luick 1977;Thompson and Barboza 2014;Cook et al 2016). An apparent limitation of selection studies is the difficulty in determining selection for rare species, which we also documented.…”

Land management alters traditional nutritional benefits of migration for elk

“…In general, forests in earlier seral stages and with more open canopies provide higher forage quality for elk, particularly at high elevations (Cook et al ). More work is needed, however, to fully assess the effects of different logging techniques and thinning practices on elk nutritional resources (Cook et al ) and to compare the effects of timber and fire management. Additionally, the extent to which the quality of forage available in alpine ecosystems differs from that in irrigated agricultural lands remains largely unexplored; our study area lacked alpine meadows commonly used by migratory elk in other populations (Morgantini and Hudson , Luccarini et al ).…”

Nutritional carrying capacity for cervids following disturbance in hardwood forests

“…Closed‐canopy mature forests currently dominate the landscape across much of the eastern United States and limit available sunlight to stimulate and support understory vegetation (Anderson and Katz , Rossell et al , Webster et al , Shaw et al , McCord et al ). Closed‐canopy forests limit food and cover resources for many wildlife species that benefit from a well‐developed forest understory or early successional vegetation communities, including elk and white‐tailed deer (Beck and Harlow , Johnson et al , Lashley et al , McCord et al , Cook et al ). The prominence of closed‐canopy forest in the eastern United States threatens the success of elk restoration so techniques to increase nutritional carrying capacity should be evaluated if elk populations are expected to thrive in these areas.…”