Pines versus oaks: effects of fire on the composition of Madrean forests in Arizona
The authors examined historical fire regimes of Madrean pine-oak communities and the effects of fire on current establishment and survivorship. They also compared the response of pine versus oak to fire, i.e. fire resistant species verses sprouting species, and their relative abundance and structure post-fire.
Historically, frequent fires led to abundant seedling recruitment of both pine and oak species, but low survival into maturity. Fire suppression starting in the early 1900’s led to low levels of seedling recruitment, but allowed young trees to mature without disturbance for long periods of time.
Pine and oak have different strategies for dealing with frequent fire. The pine species in this study (Pinus engelmannii and P. leiophylla) are fire resistant while the oak species (Q. hypoleucoides) resprouts after top-kill by fire. These differing responses can lead to differences in abundance post-fire, so that immediately after fire, pines dominate through resistance to fire until oaks, which grow rapidly, catch up in abundance through resilience to fire. The authors suggest that continued fire exclusion may favor oak species over pine due to prolific sprouting in the understory while disrupting pine seedling establishment.