research Highlight: Crown Fires Remove a Fire-Sensitive Canopy Dominant from Oak-Juniper Woodlands
Authors: Charlotte M. Reemts, Carla Picinich & Jinelle H. Sperry
This research highlight summarizes an article recently published in Fire Ecology that examines how oak-juniper woodlands respond to crown fires in Fort Cavazos, and how that affects species like the endangered golden-cheeked warbler.
Central Texas oak-juniper woodlands
The vegetation of central Texas is a mosaic of grasslands, savannas, shrublands, and woodlands. Most of these habitats are dominated by resprouting oaks and other hardwoods, but the woodlands also include the non-resprouting Ashe juniper. The grasslands, savannas/open woodlands, and some shrublands are maintained by fire and, if fire is removed, can be encroached by the native Ashe juniper. However, the closed canopy woodlands need long periods without fire for Ashe juniper to become a co-dominant. The closed canopy woodlands are important as habitat for the endangered golden-cheeked warbler. Other important bird species in the region include the previously endangered black-capped vireo, which uses short shrublands, and many grassland birds.
We monitored woodland recovery after two overlapping crown fires in 1996 and 2009 that burned two habitats: closed-canopy oak-juniper woodlands and juniper-encroached post oak savannas.
Successful hardwood recruitment
Oaks and other resprouting species resprouted quickly after both fires, although woodland structure changed from fewer large trees to many smaller trees. In many other parts of central Texas, high deer populations prevent hardwood seedings from growing into trees. An active hunting program at Fort Cavazos has reduced deer density enough that deer browsing is not limited hardwood recruitment.
Ashe juniper remains absent
Surprisingly, Ashe juniper was essentially eliminated from the fire footprint, even two decades after the first fire. For context, fire managers in the region usually burn every 3-5 years to keep Ashe juniper from encroaching grasslands and savannas. Because the fires were quite large, Ashe juniper seeds needed to spread into the burned area from the edges. That dispersal is apparently progressing slowly. The small seedlings also needed to compete with the large numbers of oak resprouts. The lack of Ashe juniper in the burn woodlands mean that they are no longer suitable habitat for the golden-cheeked warbler, which uses Ashe juniper bark for nest building and forages for insects in the tree canopies.
Crownfires don’t restore overgrown savannas
In the burned savannas (which were only burned in the first fire), juniper was also greatly reduced. However, without continued management, the savannas quickly became even more dense than they had been before fire. As managers of oak woodlands around the United States have found, continued and repeated management is needed to restore and maintain savannas.
Take away messages:
Oak-juniper woodlands that serve as golden-cheeked warbler habitat should be protected from crown fires, because the birds will not able to use burned woodlands for decades.
A single high-intensity fire cannot restore an overgrown savanna, although it could perhaps serve as a starting point for continued and repeated management.
When deer populations are low, oaks and other hardwoods can successfully recruit in both burned and unburned woodlands.
