Abstract
Plant parts used as forage by caribou and reindeer (Rangifer tarandus) have been collected in conjunction with studies of foraging dynamics, nutrition, growth, and population ecology of this arctic ungulate over the course of several years in Alaska and other circumpolar areas. These samples were subjected to proximal analyses for percent nitrogen, phosphorus, sodium, carbohydrate, cell wall (NDF), acid detergent fiber (ADF), lignin, cellulose, and residual ash, and treated to determine in vitro and nylon bag dry matter digestibility (DMD). Among winter vascular plant forage only carbohydrates showed a positive correlation with digestibility, wheras in summer nitrogen, phosphorus, and in some cases sodium, also are positively correlated with digestibility. Forage from shrubs and forbs in early summer had higher nitrogen and carbohydrate levels than later in the season, wheras graminoids show an increase in these levels during the first few weeks of growth. Floral parts during anthesis showed higher nitrogen, phosphorus, and carbohydrate levels and higher digestibility than corresponding leaf material. The annual dietary cycle is the product of adjustment of the physiological cycle to seasonal fluctuation in forage quality and quantity.
Highlights
It is generally accepted that forage type, phenology, and season are primary factors influencing the quality of forage available to ungulates
Considerable variation exists in the quality of natural forage available to caribou and reindeer
The generally accepted correlation between rogen and carbohydrate levels and are therenitrogen and fo- fore of higher quality than similar plants later in rage quality is based on the assumption that nit- the growth period (Klein,1970)
Summary
It is generally accepted that forage type, phenology, and season are primary factors influencing the quality of forage available to ungulates. Forage used by reindeer and caribou is believed to be under these influences, generalizations extrapolated from investigations on other species may be misleading. The foraging pattern or strategy of caribou and reindeer throughout the year is under the control of the physiological-metabolic demands of the animal and the quality and quantity of forage available. A l l of these factors undergo annual fluctuations that are tied to the extreme solar cycle of northern latitudes. This investigation examines variations occurring in vascular plant forage of caribou and reindeer and the Rangifer, Special Issue No 3, 1990
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