Plant nutrient concentrations inform white-tailed deer diet limitations

Management of large herbivores often involves increasing availability of forages sufficient in nutrient density to allow animals to meet dietary demands. Nutritional carrying capacity (NCC) models commonly are used to compare plant communities and management strategies, but failure to use the most limiting nutrient could result in overestimating NCC. Moreover, the relationship between limiting nutrients often is not considered, which may influence the utility of NCC models based on a single nutrient, especially when herbivores must simultaneously meet multiple constraints. We examined crude protein and phosphorus concentrations in 131 plant species commonly eaten by white-tailed deer (Odocoileus virginianus) to determine whether they would meet a minimum 14% crude protein and 0.3% phosphorus constraint for a lactating female. Crude protein and phosphorus demands were met in 43.9% and 18.8% of sampled forages, respectively. Concentrations of crude protein and phosphorus were greatest in young forb tissue, with an average of 18.6% crude protein and 0.28% phosphorus. Protein and phosphorus concentrations were positively correlated, but not all plants which met protein requirements simultaneously provided sufficient phosphorus. We created NCC models using crude protein and phosphorus and documented phosphorus tended to be more limiting, but variation existed among sites. Given that limiting nutrients may vary spatiotemporally, focusing conservation efforts on providing a diversity of plants, particularly to include forbs that simultaneously meet multiple nutritional demands, is likely the most practical management approach.