Seedling competition between native cottonwood and exotic saltcedar: implications for restoration

Abstract

Altered hydrology of southwestern United States rivers has led to a decline in native cottonwood (Populus deltoides). Areas historically dominated by cottonwood have been replaced by invasive saltcedar (Tamarix chinensis). Restoration of historic hydrology through periodic flooding of riparian areas has been a means of restoring native species. However, due to similarity in germination requirements of cottonwoods and saltcedars, flooding may create an unwanted increase in the number of saltcedar seedlings. Therefore, we evaluated competitive aspects of these cooccurring species in an extant riparian habitat in the arid southwestern US. We measured effects of competition between cottonwood and saltcedar seedlings and among cottonwood seedlings during the first growing season following seedling establishment in 360, 0.5 9 0.5-m plots at the Bosque del Apache National Wildlife Refuge, New Mexico. We used five interspecific density treatments and five intraspecific density treatments. Cottonwood seedling biomass and height were twice that of saltcedar seedlings across all density treatments. As density of cottonwood increased, intraspecific competition increased in severity and biomass of cottonwood seedlings decreased. At 4 plants/0.25 m 2 , cottonwood seedlings had the greatest biomass; whereas, survival was highest at 10 plants/ 0.25 m 2 . Our results support greenhouse studies and suggest that if favorable germination conditions are established for cottonwood in floodplains, saltcedar seedlings that cogerminate could be outcompeted by native cottonwood seedlings.

Distribution and Abundance of Saltcedar and Russian Olive in the Western United States

“…Under natural or naturalized flow regimes, cottonwood and willow seedlings often co-occur with and may outcompete those of saltcedar (Stromberg, 1997;Sher et al, 2002;Nagler et al, 2005;Bhattacharjee et al, 2009;Reynolds and Cooper, 2010). In some parts of the western United States, seeds of native species germinate earlier in the year than saltcedar and tend to grow faster during the first year (Shafroth et al, 1998).…”

The influence of floods and precipitation on Tamarix establishment in Grand Canyon, Arizona: consequences for flow regime restoration

“…Seed production throughout the growing season may confer a selective advantage to Tamarix along regulated rivers that no longer undergo spring floods and have midsummer peak flows when hydroelectric energy demands or agricultural needs are greater. Young Tamarix are inferior competitors when compared with native, riparian trees of the southwestern US (Bhattacharjee et al 2009;DeWine and Cooper 2010;Sher and Marshall 2003;Stevens 1989), but the reproductive phenology of Tamarix is well-suited to altered hydrologic regimes that hinder or preclude native shrub establishment ). The dominance of mature Tamarix in the southwestern US is generally highest along hydrologically altered rivers, whereas native Populus dominance is higher along rivers with minimal alteration (Merritt and Poff 2010;Mortenson and Weisberg 2010;Stromberg et al 2007).…”

“…Restoration floods may allow Populus, Salix gooddingii, Acer negundo L., but also non-native Elaeagnus angustifolia L. to establish (DeWine and Cooper 2007;Friedman and Lee 2002). Recent studies demonstrate the inferior competitive abilities of Tamarix seedlings and adults when compared with native riparian trees (Bhattacharjee et al 2009;DeWine and Cooper 2010;Sher and Marshall 2003;Stevens 1989;Stromberg 1997). In reaches where native phreatophyte species are strongly dominant and currently recruiting, floods timed during spring and early summer may benefit native species.…”

Optimum seedling productivity in cottonwoods: A function of neighbor distance

“…Many land managers use simulated flooding to recruit native species and some consider higher densities as more successful than lower densities, without taking into account that initial high densities of cottonwood may lead to trees with lower DBH and hence low stand volume (Bhattacharjee et al, 2008b;Taylor et al, 2006). The results of our study have a tremendous practical value to managers who may not have high nurse tree density and who use seed bearing branches to establish low but effective plant densities.…”