Reseeding native forbs in the Great Basin: A study of the growth patterns of five forbs and interactions with grass neighbors

Federal agencies are reseeding native forbs, shrubs, and grasses into recently disturbed areas in the Great Basin, with one goal of revegetation efforts to limit the colonization and expansion of invasive species. Unfortunately, basic ecological information on many native forb species is lacking, limiting our ability to construct seed mixes to maximize native species diversity and resistance to invasion by exotics.  This study was designed to measure the relative growth rates of five forbs when grown alone or with a neighbor.  Neighbor species were one of two native grasses, Elymus elymoides and Poa secunda or the exotic annual grass, Bromus tectorum.  The forb species were Eriogonum umbellatum, Lomatium grayi, Machaeranthera canescens, Penstemon speciosus, and Sphaeralcea munroana.  Forbs were grown in a greenhouse, and water and nutrients were not limiting.  Significant differences in absolute growth rate occurred over a 12 week period with S. munroana nearly eight times the total biomass of the next largest forb, M. canescens (24.1 ± 5 g and 3.4 ± 1.2 g).  There was no difference in total biomass for any forb when grown alone versus with a native grass.  Bromus tectorum significantly reduced the growth of all five forbs.  The intensity of competition (reduction in biomass when grown with a neighbor compared to growing alone) varied by species, and was not related to the size of the forb.  Knowledge of above- and belowground growth rates and patterns of water and nutrient uptake is important for developing predictive models of community establishment for Great Basin species.