How do we know twisted krummholz is older?

We can figure out if a twisted krummholz tree is old at the bottom by taking a tree core at the base and counting the rings. This core at the base helps us establish an age structure. Then we can take another tree core at the bottom of any leaders to learn when any new leaders started growing. Knowing when new leaders started growing can give us an idea of when the growth form changed. (We can look at the climate records to see if this change in growth form happened when temperatures became warmer.)