Lyndon B. Johnson National Grasslands
The Lyndon B. Johnson National Grasslands is a 20,250 acre U.S. Forest Service property in Northeast Wise County, Texas, about 40 miles northwest of Fort Worth. The grasslands is comprised of 64 smaller units spread out across the county. These units represent individual parcels of land that were abandoned during the dust bowl and reclaimed by the government. These parcels together form the LBJ National Grasslands. The grasslands are very diverse, and consist of more than just prairie habitat. Fort Worth Prairie ecosystems as well as West Cross Timbers forests, streams, lakes, and ponds all combine to make the grasslands one of the most diverse pieces of property in Texas.
Flora of the LBJ National Grasslands
Over the last 12 years, BRIT researchers, led by Research Associate Bob O’Kennon, have conducted an ongoing floristic inventory of the LBJ Grasslands. O’Kennon has documented over 1,200 species from the grasslands, including 15 species that were not previously known from North Central Texas and three species not previously known to science. The LBJ Grasslands provides a unique opportunity to understand the natural flora of the area and the effects of land use practices on this particular habitat/ecosystem.
BRIT researchers estimate that there may be as many as 2000 species growing in the LBJ National Grasslands. Less than half of these taxa have been collected and verified. The goal of this flora project is to document the complete list of vascular plants growing in the LBJ National Grasslands. To accomplish this, all plant species encountered within the grasslands are documented and collected as herbarium specimens. These specimens are identified, labeled, glued to high quality paper, and filed into the herbarium. These specimens provide the evidence that a plant was growing in a specific location at a specific time. Many of the specimens collected can be viewed on BRIT’s online digital herbarium. BRIT researchers are in the process of collecting the remaining species.This baseline knowledge of the flora of the LBJ National Grasslands makes the site a prime candidate for the National Ecological Observatory Network (NEON). NEON is an observatory network collecting data on the impacts of climate change, land-use, and invasive species on natural resources and biodiversity. Beginning in 2013 the LBJ Grasslands will provide baseline data for the Southern Plains Division of NEON. BRIT will collaborate with researchers in other fields to document the effects of climate change and land-use change on the flora and fauna of the region.
Flora and Vegetation of Ponds within the LBJ National Grasslands
Within the LBJ Grasslands, there are over 1081 ponds. These ponds were built sometime after 1952, presumably to combat soil erosion during the dust bowl of the 1950s. The ponds change seasonally due to rainfall differences and each pond has a unique group of plants growing within it. There are several factors that influence what plants will grow within a specific ponds. These include water quality, size of the pond, availability of seeds, and frequency of flooding. In addition, as ponds age they progress through a series of successional stages as the pond slowly fills with sediment. Each of these stages is characterized by different plants. Lippert and Jameson defined these stages in 1964:
- Submerged/Floating Stage – open water conditions with pioneering vegetation rooted in the wetland bottom or with vegetation floating on water surface;
- Dried Bed Stage – pond bed after water has receded; often only sparsely vegetated;
- Reed Swamp Stage – shallow water and muddy edges of wetlands dominated by emergent vegetation;
- Sedge Meadow – saturated ground surrounding wetter areas, dominated by sedges;
- Grassland-Composite Stage – upland areas surrounding wetlands with slightly higher levels of moisture than surrounding upland habitat;
- Willow-Cottonwood Stage – trees typically found on outer margins surrounding wetlands. Not an official stage of succession.
The goals of this project are to:
- Identify the plant diversity within ponds in the LBJ National Grasslands.
- Characterize the successional zonation patterns within ponds.
To accomplish this, BRIT researchers visited 312 ponds in the fall of 2012. At each pond all plant species seen were recorded. 25 of these ponds were randomly chosen to collect additional data. In each of these ponds, each ring of vegetation was assessed to determine how much total area each plant covered. Statistical analyses were run on both sets of data to determine what factors influence plant diversity (how many species are found in a pond) and to group rings together into similar vegetation groups.
A total of 143 plants were documented within the ponds. Grasses (Poaceae) were the most common group of plants, followed by Sedges (Cyperaceae) and members of the Sunflower family (Asteraceae). Of the 143 species, only 10 species were found in more than 25% of the ponds sampled. This implies that the ponds vary greatly in the composition of plants that grow within them. On average, each pond contained about 8.5 species and there was a small relationship between number of species and the size of the pond. Eight distinct groups of plant communities were identified. Each of these groups corresponded with the successional groups described previously. These groups represent the fine scale zonation patterns that result from a soil moisture gradient formed as pond water levels drop.