Even though this is about immigration, TFA does note: > Tree rings that are nearly circular indicate that population growth due to immigration was much less si

Even though this is about immigration, TFA does note: > Tree rings that are nearly circular indicate that population growth due to immigration was much less significant than that due to natural-born persons. And I missed that census data is the source. Because at 100% in Firefox, the relevant paragraph ends: > The data was queried from IPUMS-USA and consists of millions of samples of questionnaires from U.S. At 110%, I see that it's actually: > The data was queried from IPUMS-USA and consists of millions of samples of questionnaires from U.S. Censuses. So yeah, I guess that census data didn't include slaves.