Grantee Research Project Results

2003 Progress Report: Regional Ecological Resource Assessment of the Rio Grande Riparian Corridor: A Multidisciplinary Approach to Understanding Anthropogenic Effects on Riparian Communities in Semi-arid Environments

EPA Grant Number: R827677
Title: Regional Ecological Resource Assessment of the Rio Grande Riparian Corridor: A Multidisciplinary Approach to Understanding Anthropogenic Effects on Riparian Communities in Semi-arid Environments
Investigators: Raney, Jay , Neuenschwander, Amy , Judd, Frank , Paull, Gene , Crawford, Melba , Lonard, Robert , Tremblay, Thomas , White, William
Current Investigators: Raney, Jay , Crawford, Melba , Neuenschwander, Amy , Paull, Gene , Judd, Frank , Lonard, Robert , Tremblay, Thomas , White, William , Encheva, Tatiana
Institution: The University of Texas at Austin , The University of Texas at Brownsville , The University of Texas - Pan American
Current Institution: The University of Texas at Austin , The University of Texas - Pan American , The University of Texas at Brownsville
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 1999 through August 31, 2002 (Extended to December 31, 2003)
Project Period Covered by this Report: September 1, 2002 through August 31, 2003
Project Amount: $642,496
RFA: Regional Scale Analysis and Assessment (1999) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration

Objective:

Riparian ecosystems of the Southwestern United States are among the most productive ecosystems of North America. The rapid decline of these ecosystems throughout the United States has made riparian conservation a focal issue. This multidisciplinary study of riparian communities along the Lower Rio Grande Valley of Texas and Mexico has several objectives, including: (1) acquiring and analyzing high-resolution, remotely sensed data from multiple sensors; (2) integrating existing and new field data and remotely sensed data into a geographic information system (GIS); (3) ascertaining whether the native vegetation communities are maintaining themselves and identifying the topographic, edaphic, and other ecological factors that perpetuate these communities; (4) interpreting spatial variations in riparian habitats, including comparisons of the north and south banks of the Rio Grande; (5) analyzing temporal changes at specific locations; and (6) developing a foundation for future analysis of riparian floodplain communities by linking local and remotely sensed regional data using GIS.

Progress Summary:

Progress during Year 4 of the project primarily was made in: (1) completing the current land-use mapping, vegetation surveys, and climate analysis; and (2) finalizing the remote data classification, data acquisition, and GIS development and analysis. Work on land-use and climate mapping by The University of Texas at Brownsville (UTB) was completed in 2003. The digital land-use map was transferred to the Bureau of Economic Geology (BEG), where it was entered into the study's GIS. The map also was distributed to the Center for Space Research (CSR) for use as collateral data in classifying riparian vegetation distribution using Landsat Thematic Mapper™ data. In addition, maps on climate (average annual precipitation, September precipitation, average annual temperature, January mean temperature, July mean temperature, heating degree days, and cooling degree days) completed by UTB were entered into the study's GIS for analysis. The climatic maps show systematic variations in precipitation and temperature in the study area, including decreasing average rainfall and increasing average temperatures as one proceeds up the Rio Grande Valley from the Gulf of Mexico. There is evidence that the decreasing annual precipitation up the valley corresponds with a relatively lush mesic plant community in riparian areas near the coast, to a more xeric assemblage farther inland.

Researchers at The University of Texas at Pan American (UT-PanAm) completed and submitted their final report to BEG. Their analysis of riparian vegetation along the lower reach of the Rio Grande is based on samples obtained at seven existing localities between the mouth of the river in Cameron County and Falcon Dam in Starr County, and at four new sites established along the river. They also provided ground truth on vegetation composition at 105 additional sites and subsites for remote sensing analysis. In summary, they found that there were no trees at the mouth of the river, and the vegetation there was similar to that found along the Laguna Madre shore of barrier islands. Mesquite (Prosopis glandulosa) was the dominant tree near the coast, where soil salinity and wind-blown salt spray are greatest, and it was also dominant in the western section of the river near Falcon Dam, where rainfall is least and where the Rio Grande floodplain is narrow. Sugar hackberry (Celtis laevigata) was the dominant tree species at all other sites except at Santa Ana National Wildlife Refuge, where cedar elm (Ulmus crassifolia) and anacua (Ehretia anaqua) were the dominant trees. Granjeno (Celtis pallida) was a dominant shrub throughout the riparian corridor. The dominant trees and shrubs appeared to be replacing themselves. The introduced Guinea grass (Panicum maximum) and buffel grass (Pennisetum ciliare) were dominant species in the ground cover, displacing native species. The researchers noted that present riparian communities may be greatly influenced by human interventions such as construction of dams that have eliminated annual flooding of the Rio Grande. Blair (1950) reported that cedar elm (Ulmus crassifolia) was the dominant tree in the floodplain of the Rio Grande in the Lower Rio Grande Valley of Texas, but our study found that cedar elm was a dominant species only at Santa Ana National Wildlife Refuge (Lonard and Judd, 2002). This species’ distribution and abundance may have been adversely affected by the curtailment of annual flooding of the Rio Grande. It certainly is no longer a widespread dominant species in the riparian zone of the lower reach of the Rio Grande.

Investigators at the Center for Space Research, under the direction of Dr. Melba Crawford, continued analyzing hyperspectral (HYMAP) and multispectral (Landsat TM) data along the Rio Grande Valley to refine our classification of woodlands and riparian vegetation. A new classification showing the distribution of all woodland and riparian vegetation in the Lower Rio Grande Valley was completed using the most recent Landsat imagery, which was acquired between 2000 and 2002. The data set was entered into the BEG GIS for analysis. To make comparisons between the remaining riparian vegetation in Texas and Mexico, we created a 20 km-wide buffer zone along the Rio Grande, with 10 km on the U.S. side and 10 km on the Mexico side (see Figure 1).

Of the total area analyzed (526,936 ha), 49 percent is in the United States, and 51 percent is in Mexico. Of the total woodlands mapped within this area of analysis, 74 percent is in the United States, and 26 percent is in Mexico. Compared with other land cover, however, only small percentages of woodlands remain in the United States (6 percent) and Mexico (2 percent). If we assume that in the past most of the area was vegetated with riparian woodlands and brushlands, as has been suggested by some authors, then almost 95 percent of these wooded areas in the United States and 98 percent in Mexico have been cleared. On the U.S. side, this estimate is in agreement with estimates by Jahrsdoerfer and Leslie (1988) who stated that since the early 1900s, 95 percent of the native brushland has been cleared for agriculture, urban development, and recreation. In riparian areas they estimated that 99 percent of native brush has been destroyed. These percentages are in relatively close agreement with the 91-percent loss of woodlands in Cameron County quantified by Tremblay and White (2002) for the period from the 1930s through the mid-1980s.

We continued to refine our classification of riparian vegetation communities into five classes defined by the presence of evergreen and deciduous species, and combinations of the two. Training sites for hyperspectral and multispectral analyses of Bentsen State Park were determined on the basis of visible analysis and interpretation of high-resolution, digital, color-infrared aerial photographs (digital orthophoto quadrangles) acquired during the winter months and high-resolution hyperspectral data from HyMap. As mentioned in previous reports, this classification into evergreen and deciduous communities is modeled after the U.S. Fish and Wildlife Service (FWS) National Wetlands Inventory Program, in which riparian vegetation inventory and mapping conventions were developed for the Western United States. The FWS classification is hierarchical, with the riparian system having two subsystems, lentic and lotic, subdivided into forested and scrub/shrub classes. These in turn have three subclasses—deciduous, evergreen, and mixed—from which we established five subclasses consisting of the following: (1) evergreen; (2) deciduous; (3) mixed, co-dominant; (4) mixed, evergreen dominant; and (5) mixed, deciduous dominant. Field work is planned in mid-December to ground-truth classified communities and training sites in and around Bentsen State Park.

Figure 1. 20 km Buffer Zone Along the Rio Grande From the Gulf of Mexico to Falcon Dam. Black polygons represent woodland areas.

As mentioned in previous reports, there is a strong correlation between riparian vegetation and soils (soils data from the Natural Resources Conservation Service Soil Survey Geographic database). To further investigate this relationship, we analyzed the distribution of common species of trees and shrubs that were identified at the 100-plus field sites visited by researchers from UT-PanAm. All shrub and tree species identified at the sites were entered into our GIS, and a GIS layer of the common species found at the sites was developed for the analysis of soil relationships. Results indicate that most species were more common on two soils, Laredo Silty Clay Loam and the Rio Grande Silt Loam. There were fewer occurrences on clays such as the Grulla Clay and Harlingen Clay. In addition, we analyzed the relationship between soil salinities and 10 common species of shrubs and trees. This was accomplished by analyzing the number of occurrences of the trees and shrubs on soils with salinities (based on conductivity) ranging from 0 to 4 milli-mhos/cm. This analysis was based on all species found at distinct field check sites and transect locations, as reported by Lonard and Judd (2002). Soil salinity is represented as electrical conductivity in milli-mhos/cm at 25°C. The Natural Resource Conservation Service classifies soils as either nonsaline (0-2) or slightly saline (2-4). Among the results was the finding that Prosopis glandulosa (mesquite) occurred more frequently in slightly saline soils than did other species. This finding is in agreement with that of Lonard and Judd (2002), who found mesquite to be the dominant species near the coast, where the effects of salinity and salt spray are most pronounced.

This relationship between vegetation and soils, when correlated with other parameters such as topography, hydrology, and land use, is useful in analyzing riparian vegetation with respect to historical trends, anthropogenic effects, and optimal sites for re-establishment of riparian tracts.

References:

Blair WF. The biotic provinces of Texas. Texas Journal of Science 1950;2:93-117.

Jahrsdoerfer SE, Leslie Jr. DM. Tamaulipan brushland of the Lower Rio Grande Valley of south Texas: description, human impacts, and management options. U.S. Fish and Wildlife Service Biological Report, Vol. 88, No. 36, 1988, 63 pp.

Tremblay TA, White WA. Historical distribution and loss of woodlands in the Lower Rio Grande Valley. In: Proceedings of the Texas Academy of Science 105th Annual Meeting, Program and Abstracts: Texas Parks and Wildlife, Laredo TX, 2002, p. 57.

Future Activities:

We plan to complete the final report and educational outreach program by February 2004. One final field trip to the Lower Rio Grande Valley will be conducted in mid-December 2003, to complete field analyses of remotely sensed data. Classifying and ground-truthing remotely sensed data, entering data into our GIS, and analyzing and applying models to define riparian relationships with other mapped characteristics then will be completed. Manuscripts in progress will be submitted for publication when they are completed.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Publications Views

Other project views:	All 20 publications	3 publications in selected types	All 2 journal articles

Publications

Type	Citation	Project	Document Sources
Journal Article	Lonard RI, Judd FW. Riparian vegetation of the Lower Rio Grande. Southwestern Naturalist 2002;47(3):420-432.	R827677 (2001) R827677 (2002) R827677 (2003) R827677 (Final)	Abstract: JSTOR First Page Exit
Journal Article	Tremblay TA, White WA, Raney JA. Native woodland loss during the mid 1900s in Cameron County, Texas. Southwestern Naturalist 2005;50(4):479-482.	R827677 (2003) R827677 (Final)	Abstract: BioOne Exit

Supplemental Keywords:

remote sensing, watersheds, land, sediments, ecological effects, ecosystem, habitat, integrated assessment, ecology, scaling, modeling, Gulf Coast, Gulf of Mexico, Mexico, United States, Rio Grande Valley., RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Southwest, Ecology, Hydrology, Ecosystem/Assessment/Indicators, Environmental Chemistry, State, Ecological Effects - Environmental Exposure & Risk, Regional/Scaling, Ecological Risk Assessment, ecological exposure, EMAP, semi-arid environments, Texas, Riparian ecosystem, floodplain communities, ecological assessment, environmental data, anthropogenic, regional scale impacts, Rio Grande Riparian Corridor, agriculture, GIS, landscape patterns, remotely sensed data, land use, scaling methods

Progress and Final Reports:

Original Abstract

2000 Progress Report

2001 Progress Report

2002 Progress Report

Final Report