Research Note Effect of American bison (Bison bison L.) on the recovery and germinability of seeds of range forage species F. Go ¨ kbulak Istanbul University, Faculty of Forestry, Department of Watershed Management, Istanbul, Turkey Abstract The effect of passage through the digestive tract of Bison bison on the recovery and germinability of undamaged passed seeds of Pseudoroegneria spicata, Elymus cinereus, Oryzopsis hymenoides, Stipa comata, Balsamorhiza sagittata and Sphaeralcea coccinea was tested. Recovery of un- damaged passed seeds peaked 2 days after ingestion and then decreased to the lowest level on day 5 of sample collection for all species used, but the pattern of seed passage through time significantly differed among species. Recovery of passed seeds was greatest for round-shaped, hard seed-coated O. hymenoides and lowest for largest seed-sized B. sagittata. The digestive tract of B. bison did not break seed dormancy of O. hymenoides, S. comata, S. coccinea or B. sagittata. Germination percentage of P. spicata and E. cinereus seeds decreased compared with unpassed seeds of the same species. Keywords: seed passage, seed recovery, germination, forage species, ruminants Introduction Domestic and wild ruminants can play an important role in seed dissemination and affect botanical compo- sition of rangelands (Brown and Archer, 1987; Gar- dener, 1993; Malo and Suarez, 1995). Therefore, seed dispersal by ruminants has received attention from researchers for many years (Lehrer and Tisdale, 1956; Jones and Simao Neto, 1987; Gardener et al., 1993b). To date, seed passage studies have been conducted using cattle (Blackshaw and Rode, 1991; Willms et al., 1995), sheep and goats (Eddy and Smith, 1975; O ¨ zer, 1979; Russi et al., 1992b; Auman, 1996), horse (Janzen, 1981) and deer (Heady, 1954), but no experiments have been conducted using Bison bison L. (American bison). B. bison is an important part of some rangeland ecosystems in North America and their numbers are increasing steadily through the entire United States and Canada (Jones, 2000). Therefore, a seed passage study was carried out using B. bison on Antelope Island in the Great Salt Lake of Utah, USA. The main objective of this study was to determine how B. bison’s digestive system affected the proportion of seed recovered, passage time, and germinability of Pseudoroegneria spicata (Pursh) A. Love (bluebunch wheatgrass), Elymus cinereus Scribn. and Merr. (basin wildrye), Oryzopsis hymenoides (Roemer & Schultes) Ricker. (Indian ricegrass), Stipa comata Trin. & Rupr. (needle and thread), Balsamorhiza sagittata (Pursh) Nutt. (arrowleaf balsamroot), and Sphaeralcea coccinea (Pursh) Rydb. (scarlet globemallow). Previous experiments with cattle showed that maximum seed passage occurred 2–3 days after animals were fed with seeds (Gardener et al., 1993a; Willms et al., 1995) but the pattern of passage rate through time varied depending on seed attributes such as seed size, shape, hardness of seed coat and animal types (Simao Neto et al., 1987; Gardener et al., 1993a). As larger and elongated seeds can pass more slowly than smaller and round seeds, seed size and shape may influence passage rate, retention time, and the chance of being damaged by mastication, chewing and digestion. For example, Russi et al. (1992b) reported that recovery rate of Trifolium campes- tre Schreb. seeds (smallest seeds) was greater than recovery rate of Trifolium stellatum L. seeds (largest seeds). Seed germinability of forage species can increase or decrease after passing through the digestive tract of ruminant animals depending on seed characteristics, type of animals and diet quality (Simao Neto et al., 1987). Moreover, germinability of ingested seeds can be affected by chewing, mastication and digestion (Lieb- erman et al., 1979). Some researchers observed that germination percentage of P. spicata seeds decreased after passing through the digestive tract of animals Present address and correspondence to: Dr F. Go ¨ kbulak, Istanbul University, Faculty of Forestry, Department of Watershed Management, Bahc ¸eko ¨ y 80895-Istanbul, Turkey. E-mail: fgokbulak@istanbul.edu.tr Received 17 September 2001; revised 8 February 2002 Ó 2002 Blackwell Science Ltd. Grass and Forage Science, 57, 395–400 395