Supporting data for publication: Painter, L.E.; R.L. Beschta; W.J. Ripple. 2023 in press. Bison alter the northern Yellowstone ecosystem by breaking aspen saplings. Ecology and Evolution.

1. Description of methods used for collection/generation of data: In the northern ungulate winter range of northern Yellowstone National Park, we visited 87 aspen stands that had been randomly selected and sampled in previous studies in 1997-98 and 2012 (see Painter, L.E., R.L. Beschta, E.J. Larsen, and W.J. Ripple. 2014. After long-term decline, are aspen recovering in northern Yellowstone? Forest Ecology and Management 329:108-117.) A single sampling plot 2x30 m began at the live, standing dead, or fallen aspen tree closest to the GPS locations recorded in 2012, and extending toward the centriod of the stand. We recorded the number of aspen saplings (>2 m tall and <=5 cm diameter-at-breast-height, dbh), the number of dead saplings stripped of bark and girdled, and the number of broken sapling stumps (>2 cm in diameter at 0.5 m height). We also recorded the number of young aspen trees (6-20 cm dbh). We estimated density of elk and bison fecal piles in two belt transect plots 2x50 m, placed about 10 m from the stand and spaced 10 m apart, in the nearest xeric grassland or forest edge. Mesic grassland was avoided due to the low likelihood of scat persistence or detection in this substrate.