In our on-going quest to understand how species and communities change in response to warming, we've been tracking migration of a climate threatened conifer. This process has entailed mapping the range edge - precisely - and then monitoring the production of new recruits. If those recruits are outside that range edge, then they are pushing the range forward or infilling - migration.
Climate change in Alaska has been going on some time, since the end of the Little Ice Age, though of course it's accelerating. This provides a nice opportunity to watch adaptation-in-action, sans models, and provides a good empirical check on migration expectations.
Yellow-cedar is a great study case - it is, and has been, culturally important for thousands of years among Indigenous cultures, so it's tracked. It's economically important now. It's ecologically significant, as it dramatically changes the biogeochemistry of the soil. And it's unique among a sea of spruce and hemlock (it's a low diversity forest, so cedar is a highlight). The species should be able to migrate rapidly - the climate is ideal, the plant community is the same as throughout the contiguous range, the topography and edaphic conditions seemingly perfect.
Regeneration is absolutely minimal outside the existing stands. There is some regeneration within the individual stands (ranging from a single tree to a few dozen mature individuals), but not a lot - and regeneration outside is constrained to pretty much the blueberry plant/rusty menziesia plant association (Vacc. and Menz.). It's unclear why - those are productive forests where yellow-cedar isn't expected to actually be competitive, so it's probably less regeneration than it looks like.
The most likely reasons are either 1) herbivory or 2) a lack of disturbance opportunity. We need to test both. The herbivory hypothesis is being informally tested, and currently found lacking, via a few plantations scattered around the area where herbivory is not a factor. Why not eat nice, fertilized plantation trees? A lack of disturbance, on the other hand, explains the pattern - rapid migration historically (these stands got there somehow, and they are separated from the main range by 10-20 km) and then suddenly nothing. That punctuated pattern could be associated with rare, major historical wind disturbance. These stands are not in particularly storm exposed landscapes, however. It could also be snow disturbance, as the stands seem to have originated during colder periods. This could be associated with lower herbivory in the winter too, however - so the work continues!