Plant sample collection and processing
At each site, samples of the three most common plant species in haypiles and the three most common available plant species were collected from growing vegetation. Collection from intact plants was standardized by cutting specimens at ground level and in full sun to eliminate influence of dew on initial weights and minimize environmental variation caused by differences in light availability. Multiple source plants of each species were selected from the area within 30 m of a pika haypile at each site. Samples from intact plants were collected in paper bags and samples were immediately weighed to the nearest 0.25 g with a 60 g spring scale.
Quantities: 3 most common cached species + 3 most common available species per site, multiple source plants within 30 m of haypiles, weighed to nearest 0.25 gDuration: Not specifiedConditions: Specimens cut at ground level in full sun to eliminate dew influence
Equipment: 60 g spring scale (PESOLA AG, Rebmattli 19, CH-6340 Baar, Switzerland), paper bags
Laboratory analysis of plant samples
Plant samples were thoroughly air-dried in a mesh bag at the University of Colorado and then dried in an oven for 24 h at 60°C. Samples were weighed immediately after drying to assess water content. Water content was computed as the total percent weight lost during drying (weight at harvest vs. weight following oven drying). For nitrogen analysis, 0.5 g of each sample was finely ground and adding liquid nitrogen does not change the chemical composition of the sample but facilitates the grinding process. Samples were packaged 3 to 5 mg of each sample in 5 × 9 mm tin capsules and run through a Costech ECS 4010 elemental CHNSO analyzer.
Quantities: 24 h drying at 60°C, 0.5 g samples ground, 3-5 mg in tin capsules (5 × 9 mm)