Long-term vegetation dynamics of ponderosa pine forests

I examined the vegetation dynamics of ponderosa pine (Pinus ponderosa) forests in northern Arizona. Most field work was conducted on the Hill plots, five grazing exclosures established in 1912 and sampled in 1941 and 2004. Meta-analytic techniques were used to combine the results from individual sites. Overstory vegetation increased in dominance since 1941, but less where subject to continued livestock grazing than where protected from livestock grazing since 1912. A state-and-transition model for overstory vegetation dynamics is proposed, suggesting that historical development of the overstory is the result of interactions between livestock grazing, fire history, climate, and seed production