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Some conservation biology and environmental issues in the eastern Edwards Plateau region:
Development and its consequences
Welcome to the front lines of conservation! many endangered species, rapid population growth, an extensive urban/rural interface, a private land state, a challenging political environment....
The federally listed threatened and endangered species in this region include
- black-capped vireo (Vireo atricapillus. habitat: shrub savanna and shrubland (see above). threats: development (habitat loss); cowbird (lays eggs in nest; associated with cattle and with lawns, suburbs); fire ant (eats nestlings)
- golden-cheeked warbler (Dendroica chrysoparia). habitat: mixed woodlands (see above). threats: development (habitat loss); blue jay (a non-native predator of nestlings found in suburbanized areas)
- various karst invertebrates, for example, the Tooth Cave pseudoscorpion (Microcreagris texana)and the Kretschmarr Cave mold beetle (Texamaurops redelli). habitat: caves, subterranean fractures in limestone. threats: pesticide runoff from lawns; silt from soil erosion; other pollutants from developed areas; fire ants; filling in of caves by buildings, parking lots, and trash
- various salamanders, including the Barton Springs salamander (Eurycea sosorum), Texas blind salamander (Eurycea rathbuni)and San Marcos salamander (Eurycea nana). habitat: various springs and water-filled fractures in the aquifer. threats: pollutants in the aquifer, including silt, road runoff, and pesticides; reduction in flows due to pumping and drought.
- San Marcos gambusia (Gambusia georgei). habitat: springs in the San Marcos river. threats: reduction in flow; pollution.
- Texas wild rice (Zizania texana). habitat: San Marcos River. threats: recreational use of the river; pollution; invasive non-native species; changes in river flow.
Two of the unlisted but endangered plants species in the Austin area are
- canyon mock-orange (Philadelphus ernestii). habitat: edge of limestone cliffs, often with elbowbush (Foresteria), shrubby boneset (Eupatorium havanense), silktassel (Garrya ovata), etc. threats: development (habitat loss); probably also deer browsing.
- bracted twistflower (Streptanthus bracteatus). habitat: uncertain. threats: development (habitat loss); deer herbivory
Non-native species that reduce native biodiversity include
- Solenopsis invicta (fire ants)
- domestic cats, presumably
- Bothriochloa ischaemum (King Ranch bluestem)
- cattle, goats, and ‘exotic ungulates’, when overstocked
In addition, there are a number of non-native plant species that may become problems and should therefore probably not be planted as landscaping any more. All of these have already become problems in other regions.
- nandina (Nandina domestica)
- Chinese tallow (Triadica sebifera)
- chinaberry (Melia azedarach)
- Chinese privet (Ligustrum sinense)
- Japanese honeysuckle (Lonicera japonica)
- fountain grass (Pennisetum spp.)
Since the reservoirs are a novel habitat, it is difficult to say that non-native invasive species are reducing biodiversity, but there are at least two non-native aquatic plants that are causing problems in these ‘lakes’, Eurasian watermilfoil (Myriophyllum spicatum) and hydrilla (Hydrilla verticillata).
Development and its consequences
Perhaps the largest single source of environmental issues on the eastern Edwards Plateau is the rapid growth of San Antonio, San Marcos, Austin, Round Rock, and the suburbanizing areas around them. Further west, many formerly rural areas have become retirement communities or vacation resorts. Outside the urban areas large ranches are being replaced by ‘ranchettes’ of one to twenty acres, similar to what is happening in many Western states. Texas, however, is a private land state, so almost all of the land is available for development.
Habitat is lost as former ranchland is converted to suburbs. The presence of lawns is thought to increases cowbird and bluejay populations. Potentially invasive plants are planted for landscaping, lawns, and gardens.
Development brings with it increases in runoff rates, reduced recharge rates, increased water pollution, and increased pumping from the aquifer, all of which affect aquatic species (see above). As impermeable cover increases, creeks alternate between going dry and flooding, which erodes their banks and alters the environment of aquatic and riparian species.
Fire and hunting becomes less available as management tools as housing density increases.
The increasing population causes more use of recreational areas, which tends to degrade the quality of the habitat for conservation.
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