COS 69-6
Understanding factors that impact restoration success in a thornscrub ecosystem

Wednesday, August 13, 2014: 9:50 AM
314, Sacramento Convention Center
Krysten N. Dick, Biological Sciences, University of Texas at Brownsville, Brownsville, TX
Heather D. Alexander, Biological Sciences, University of Texas at Brownsville, Brownsville, TX
Jonathan D. Moczygemba, Laguna Atascosa National Wildlife Refuge, United States Fish and Wildlife Service, Los Fresnos, TX

Plants experience multiple abiotic and biotic stressors that limit their growth and survival, and understanding the relative impacts of these factors is important to restoration success in fragmented ecosystems. In this study, we examined three factors that may influence the growth and survival of Tamaulipan thornscrub seedlings at Laguna Atascosa National Wildlife Refuge in southern Texas. Each factor (herbivory, competition with invasive grasses, and growth in a semi-arid environment) was paired with a restoration treatment that will help seedlings overcome these conditions (herbivore exclosures, grass-specific herbicide, and seedling tubes). To determine the impact of these stressors, we treated ~1,200 seedlings with 16 different combinations of restoration treatments in January 2013. An additional aspect of this study includes seedling tube removal at 0, 6, 12, and 24 months to understand the temporal influence of this treatment on plant growth. To quantify seedling growth and impact of stressors, basal diameter, seedling height, browse intensity, and invasive grass cover were measured on each seedling every 4-mo over a 1-yr period (January 2013-January 2014). This study will continue until fall of 2014. 


After one year, seedlings in tubes grew 1.25-4.80x faster and were 36.8-71.6% taller than seedlings without tubes, regardless of combination with fence or herbicide treatments. While the addition of herbivore exclosures and herbicide treatments also increased seedling height, the effects were substantially less pronounced than for seedling tubes. Seedlings treated with tubes for 6-mo grew only 0.32-2.02x faster and 9.2-33.8% taller than seedlings without tubes, regardless of fence or herbicide treatment combinations. Our results suggest that a 6-mo treatment of seedling tubes is not enough time and exposes the seedling to elements that affect their growth. The largest mean seedling height and fastest growth rate is produced by combining herbicide, herbivore exclosures, and seedling tubes. We found that seedling basal diameter growth within tubes is greater than outside of tubes, but the combination of herbicide and herbivore exclosures creates an equivalent response in basal diameter growth. This trend suggests that the alleviation of stressors (invasive grasses and herbivores) allows seedlings to allocate more growth belowground. The combination of all treatments (herbivore exclosures, herbicide, and seedling tubes) appears to be the most successul technique for seedling restoration based on both height and basal diameter growth.