Subalpine tree seed availability and germination at Niwot Ridge, 2015 - ongoing.

These data were collected to assess how seed availability and site limitations affect conifer germination across species distributions. Our study focused on areas above alpine treeline where subalpine tree species must migrate to track movement of suitable climate, but we also included sites in the core and at the lower ecotone of subalpine forests. We monitored seed availability and germination of new seedlings for four subalpine tree species from 2015-present at Niwot Ridge, Colorado, USA. Seed availability was collected in 66-95 seed traps in 14-17 sites (6-12 traps per site; see data for count per site), depending on year. In the lab, seeds were counted by species. In the field, new germinants were counted by species 3-5 weeks after snow disappearance (i.e., peak germination) and again in late September from 2015 to 2018 only. Only one census of new germinants was conducted from 2019 to 2023. New germinants from prior years were censused in subsequent summers.