Researchers tested how neighboring resident plants in alpine meadows of Colorado influenced the ability of Engelmann spruce and limber pine to establish above their ranges, in the alpine meadows. They applied heat and water to certain plots and examined how a neighboring alpine plant – Rocky Mountain snowlover – affected tree establishment, and, for comparison, how snowlover was affected by neighboring plant removal. Engelmann spruce seedlings showed lower survival and expansion potential than limber pines. Engelmann spruce required moist conditions to expand its range that were facilitated by neighboring snowlover providing shade or buffering surface temperatures. Removing Rocky Mountain snowlover did not affect limber pine establishment. Contrary to expectations, Rocky Mountain snowlover survival was reduced without neighbors near its low elevation range limit. Overall results imply likely range expansion by limber pine with consequences for alpine plant diversity and ecosystem function. 

Jabis, M.D., Germino, M.J., Kueppers, L.M., 2020, Colonisation of the alpine tundra by trees - Alpine neighbors assist late-seral but not early-seral conifer seedlings: Plant Ecology & Diversity, https://doi.org/10.1080/17550874.2020.1762134