Dispersal, legacy effects, and deer directly and indirectly affect community trajectories after clearing and burning
The reintroduction of fire to restore encroached savannas and promote hardwood regeneration in woodlands often fails due to exotic species, over-abundant white-tailed deer, and, in central Texas, re-colonization of Juniperus ashei after fire. We examined the effects of mechanical removal of J. ashei, high intensity burns of the cut material, and deer herbivory on (a) grass, forb, and hardwood cover, (b) individual native and exotic species, and (c) plant community composition. In a J. ashei-dominated woodland site, J. ashei was cut in randomly placed 11-m radius plots; control plots were untreated. Cut plants were piled into a ~5m diameter pile in the center of each cleared circle and burned in small high-intensity fires. Deer were excluded from half of the plots. We recorded the number and size of woody plants pre-treatment, and the cover of woody and herbaceous species for 2 years post-treatment. These treatments replicated common management practices in the region, and achieved the management goal of retaining the 70% canopy cover required by the endangered golden-cheeked warbler.
Ordination found that the burning, cutting, and control treatments produced different assemblages of plant species. All plants and seeds in the heavily-burned areas were killed; dispersal determined what grew there after treatment. Croton monanthogynus and weedy wind-dispersed forbs were common in burned areas. Legacy effects were important in cut-only areas: the pre-treatment woodland contained small patches of remnant grasses that quickly increased in cover after cutting. However, we did not observe a significant increase in the dominant invasive grass, Bothriochloa ischaemum. Hardwood growth rates were higher in cut areas than in untreated plots, presumably due to increased light. Unexpectedly, hardwood cover was lower inside the deer exclosure than outside. An exotic forb, Lactuca serriola, dominated the treated fenced plots, suppressing or at least delaying hardwood regeneration. However, protection from white-tailed deer herbivory may be required for successful hardwood regeneration. Trajectories following disturbance in this system are dependent on restoration method. In the short term, clearing and burning of J. ashei woodland produced small patches of diverse, native-dominated savanna vegetation. These treatments also stimulated hardwood regeneration, which will eventually improve habitat quality for the endangered warbler.