Effects of simulated climate change on the reproductive phenology of tussock cottongrass: implications for growth and reproduction of reindeer on the Seward Peninsula, Alaska

Abstract

I investigated the experimental effects of manipulations of snowmelt on the flowering phenology and forage chemistry (digestibility and nitrogen concentration) of tussock cottongrass on the Seward Peninsula, Alaska. The early snowmelt treatment (1) accelerated reproductive phenology by 11 days, and (2) resulted in higher floral digestibility but is associated with decreased nitrogen concentration in flowers. Therefore, changes in climate that lead to changes in the timing of snowmelt can alter the timing of flowering of E. vaginatum and, consequently, its value as reindeer and caribou forage. I then used relationships between forage chemistry and body weight gain of caribou derived from White (1983) to model the possible effects of altered forage chemistry on food intake and growth in reindeer. Reindeer foraging on cottongrass flowers can potentially increase their intake of digestible dry matter and therefore energy, by selecting to forage on early-emergent inflorescences over late-emergent ones. The multiplicative effects of forage quality and food intake can result in large increases in the rate of body weight gain that have positive feedbacks on the health and reproductive status of reindeer at both the individual and population level. Comparison of effects on reindeer and caribou populations on the Seward Peninsula indicate that early emergence of cottongrass flowers may confer a greater benefit on reindeer.