Effects of Flooding and Nitrogen Availability on Riparian Vegetation in Arid Ecosystems: Mechanisms Driving Nonnative Species Invasions

EPA Grant Number: U916217
Title: Effects of Flooding and Nitrogen Availability on Riparian Vegetation in Arid Ecosystems: Mechanisms Driving Nonnative Species Invasions
Investigators: Follstad-Shah, Jennifer J.
Institution: University of New Mexico
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $75,722
RFA: Minority Academic Institutions (MAI) Fellowships for Graduate Environmental Study (2003) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Natural and Life Sciences , Biology/Life Sciences


The objective of this research project is to determine if soil nitrogen (N) availability (as measured by extraction of inorganic N from field samples, incubations of soil to determine mineralization potentials, and soil C:N:P ratios) and N resource use (as measured by foliar nitrate reductase activity [NRA], foliar C:N:P ratios, and field estimates of plant N uptake using buried bag methodology) differ between mature stands of Populus deltoides var. wislizenii (cottonwoods) or Tamarix chinensis (salt cedar) along the Rio Grande of New Mexico. Flood events occur intermittently at half of the Populus and Tamarix study sites. If increased N availability is a driver of biological invasions within riparian ecosystems, I hypothesize that: (1) field-available N and N mineralization potentials will be higher in stands of Tamarix than Populus, despite flood effects; and (2) Tamarix should exhibit lower C:N ratios, higher N:P ratios, higher rates of foliar NRA than Populus, and greater estimates of N uptake.


Increased N availability has altered the species composition and productivity of many ecosystems by replacing native plant species with N-demanding or N-responsive species. These results, combined with the fact that N availability within river-floodplain systems is rising worldwide, suggest that increased riparian plant species invasion may be facilitated by differences in the relative abilities of native and nonnative species to utilize nutrients. Tamarix is invading many riparian corridors of the southwestern United States that were once dominated by Populus. Many factors that facilitate Tamarix invasion are well known. Whether Tamarix exhibits greater resource use efficiency of limiting nutrients than native species, however, merits further research.

The data generated by this research project will determine if increased nutrient availability facilitates nonnative species invasion in riparian ecosystems, as it has in other forested and grassland ecosystems. If so, suggestions for improving existing recommendations for Tamarix control and riparian zone restoration will be provided.

Supplemental Keywords:

fellowship, riparian, nitrogen, N, Populus deltoides, Tamarix chinensis.

Relevant Websites:

2004 STAR Graduate Fellowship Conference Poster (PDF, 1p., 185KB, about PDF)

Progress and Final Reports:

  • 2003
  • 2004
  • Final