Why has woody plant density been increasing in dryland ecosystems? In a new paper in @pnas.org we show that increasing tree density in pinyon-juniper woodlands could largely be a result of long-term population growth, rather than recent anthropogenic effects. www.pnas.org/doi/10.1073/...

We use age structure data from PJ populations across the western US. All of these populations are dominated by young trees. But using simple population models, we show that observed increases in tree establishment are highly predictable using pre-1800 tree establishment rates.

Our results have broader implications for how we interpret forest and woodland histories. Stand age data are the net result of multiple processes: establishment rates, survival rates, and total population size. Interpreting stand histories from these datasets requires accounting for these processes.