The failure of regeneration of oak (Quercus spp.) and other hardwood species has been noted throughout eastern North America as well as on the eastern Edwards Plateau of central Texas. Previous research has suggested that two factors—prolonged periods of fire suppression and high densities of white-tailed deer—may be particularly influential in preventing seedlings of certain species from reaching the adult size class. It is also possible that these two factors interact, and the success of reintroducing fire to promote hardwood regeneration may depend on local deer density. This study, composed of observational and experimental components, first compared browsing frequency on woody plants in burned and unburned plots at six sites in central Texas. We found that although fire history did not affect browsing frequency, browsing frequency varied significantly among sites (likely due to differences in local deer densities) and among species. In our experimental study, we used cages to protect woody plants from deer herbivory in burned and unburned areas and compared growth after one year to plants of similar size and species that were exposed to herbivory. Plants in burned areas were significantly more likely to increase in height than plants in unburned areas. Similarly, plants protected from herbivory were more likely to increase in height after one year than plants that were browsed. There were no significant differences in the amount of growth woody plants in burned and unburned areas or plants that were caged or uncaged put on during one year. This is likely due to the extreme hot and dry weather that occurred across central Texas during the course of this study. These results support previous research showing that deer are currently limiting hardwood growth of multiple species on the eastern Edwards Plateau. Further, although it appears that fire can be used to stimulate hardwood growth (particularly during a non-drought year) successful hardwood regeneration is unlikely at current deer densities. / text

Prescribed fire is a common tool used to restore native diversity, control invasive species, and reduce fuel loads. However, fire alone can be insufficient to restore pre-settlement vegetation; other factors such as differences in native and invasive species pools, deer herbivory, seed availability, and the spatial pattern of the fire can influence vegetation trajectories and restoration outcomes. Central Texas is a mosaic of savanna and mixed woodlands co-dominated by Quercus buckleyi (Texas red oak) and Juniperus ashei (Ashe juniper). In a savanna, I studied the joint effects of initial species composition (native-dominated or invasive-dominated) and disturbance (high-intensity fire, clipping, or control) on the ability of native species to establish, survive, and resist invasion by Bothriochloa ischaemum, an invasive C4 grass (ch. 1). Native savanna patches were resistant to invasion following high-intensity fire; fire can be used to selectively control B. ischaemum. In central Texas savanna and woodlands, under fire suppression and overabundant white-tailed deer, Quercus spp. are failing to regenerate, while J. ashei is increasing in abundance. To better understand vegetation trajectories following J. ashei removal in savanna, I studied the soil seedbank along a chronosequence of J. ashei invasion (ch. 5). In woodland, I studied the joint effects of prescribed fire and deer (ch. 2), clearing of J. ashei followed by high-intensity slash-pile burns (ch. 3), and wildfires (ch. 4) on the abundance and size of J. ashei and of hardwoods. Hardwoods resprouted vigorously after fire; J. ashei individuals of all sizes were killed by fire and slow to re-colonize. These management interventions failed to increase Q. buckleyi seedling abundance. It is likely that deer control is necessary to allow fire to have positive effects on the regeneration of oaks in this region, and wherever deer are over-abundant. However, deer can indirectly benefit hardwoods by reducing competition with palatable forbs (ch. 3). In general, these results show that fire suppression in central Texas oak-dominated woodlands is causing a shift not to more mesic-adapted species, as observed in the eastern US, but to J. ashei, which is at least as xeric-adapted as oak, a process I termed 'juniperization'. / text

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