Microscale patterns of tree establishment near upper treeline, Snowy Range, Wyoming, USA

We report tree seedling (mostly Picea engelmannii, some Abies lasiocarpa, v ery infrequent Pinus contorta) invasion into meadows at upper timberline in the Snowy Range, Wyoming, from 1994 to 1996. We used gradient analysis to relate this to environmental patterns, particularly plant community structu re (as aggregates of plant life-forms) and persistence of snowpack in 1995 and 1996. Tree seedlings established best at sites where snow melted earlie st; the site with the shortest growing season had fewest seedlings. Microsi tes dominated by vascular plants admitted few or no seedlings; seedlings we re most likely to be found where cryptogams dominated. These findings have implications for forest advance under some climate scenarios and succession al hypotheses.