Resource professionals engaged in restoration activities aim to collapse undesirable states by shifting resilience mechanisms from those that maintain the degraded state to those that support large amounts of environmental services.  The loss of grassland to woodland is often cited as an example of an undesirable state transition that is difficult to restore.  Even non-resprouting, fire sensitive woody plants, such as ashe juniper (Juniperus ashei) and eastern red cedar (Juniperus virginiana), form ecosystems that are cited as potentially irreversible to the processes (e.g. fire) that maintained the previous state.  We initiated a study at the Texas A&M Agrilife Research Center located near Sonora, TX, USA, to determine if fire can overcome the resilience of a stable, mature juniper woodland.

Results/Conclusions

This study shows the resilience of a juniper dominated phase can be overcome, but such findings are dependent on the conditions present at the time of the fire.  For fires conducted during an extended drought, resulting in high fire intensities, all juniper trees were scorched completely, regardless of tree height or limitations in fine fuel load.  In contrast, the system remained in a juniper dominated phase when fires were conducted in more traditional, easily controlled conditions (i.e. high herbaceous moisture content, low wind speed).  Using this information, we build a framework that depicts the role of fire in maintaining and collapsing states within the grassland-juniper woodland cycle under the present climatic conditions and to forecast how the role of fire will change as a result of future changes in climate.