Their analysis of wood density seem quite consistent with previous literature, which tends to find that density has a more stable response to temperature. (dotearth.blogs.nytimes.com)
Individual noise is reduced, thereby enabling the analysis of the impact of weather variations on wood density. (link.springer.com)
This is not something I know too much about, and there does tend to be some site to site variation, but generally speaking adding nitrogen increases ring width and reduces wood density. (climateaudit.org)