Stewardship of Habitats
Brackenridge Field Lab’s complicated land-use history and urban location have made the management of the site challenging, but have also provided opportunities to test methods of habitat restoration and invasive species control. Over the years, the field lab has been colonized by a wide range of invasive plants and insects, including the notorious imported fire ant, providing both a management challenge and a research opportunity. Our management plans to combat the expansion of these species combine student and faculty observations to inform our goals for restoration.
Tracking Succession in a Patchy Landscape
BFL consists of over a dozen distinct habitat types that are largely related to the land-use history of the site. Each habitat, whether it is a result of quarrying, farming, or flooding, has its own unique community and successional trends. Since the year 2000, undergraduate students have biannually collected survey data from these habitats that provide canopy and sapling tree density and species information on over 3000 trees. These long-term records allow us to predict how the composition of tree communities is shifting due to stresses like drought or disease. Student surveys have also identified which areas have experienced invasion by exotic shrubs and how these shrub populations responded to varying levels of deer herbivory. This data informs our management decisions, suggesting target areas to test restoration techniques and evaluate their effectiveness.
Habitat Restoration Projects
BFL has engaged in habitat restoration for decades, beginning in the 1980s with initiatives to remove invasive Chinaberry trees and reduce juniper encroachment on native grass meadows. Recently, the lab has been combating the increasingly dominant presence of invasive shrubs like ligustrum and nandina in the understory. In the 1990s and 2000s, a resident herd of deer browsed the understory. By the time the deer reached their peak number in 2002, the understory was over-browsed, leaving only sparse shrub cover. However, as the deer population declined, dense thickets of these invasive species became established across the site and their effect on the native shrub community became more obvious. Since 2014, invasive shrubs have been removed from several areas to encourage the growth of native understory plants by removing their exotic competitors. The cleared areas are being monitored to assess the diversity of the community growing from the seed bank and track the recovery of native plant and arthropod communities.
Management of exotic species using Biocontrol
Several of BFL’s community restoration efforts use biocontrols as a management tool, as in the case of the imported fire ant, Solenopsis invicta. Shortly after this invasive species arrived at BFL, ant diversity at the field station plummeted, with S. invicta outcompeting and displacing native species. In the year 2000, a research team at BFL released a species of phorid fly that acts as a parasitoid of S. invicta worker ants with the goal of limiting fire ant dominance. Long-term data collected biannually by undergraduate classes since 2001 has documented the species richness and evenness in BFL’s ant communities. As of October of 2016, this data shows that imported fire ant presence has gradually declined at the field station.
Another invasive species, the giant reed, has become established in large patches along the Colorado river, and has colonized areas across the southern border of the United States. Originally introduced for erosion control, this species outcompetes native riparian plants and can affect the fire and hydrological regimes as it gains dominance in an area. To limit the spread and success of the reed, a gall-forming wasp and a scale insect were released as biocontrol agents in conjunction with the USDA. The success of this biocontrol at the field lab will be assessed over the next several years.