Seasonal dynamics of prairie sandreed rhizome development

Abstract

Multiple generations of rhizome-connected tillers stabilize soils and produce measurable amounts of herbage on sandy rangeland throughout the world. However, little is known about the dynamics of rhizome development in these clonal plant species. Seasonal relationships between foliar characteristics and rhizomes of prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] were examined on sands range sites at 30-day intervals from May through September 1989 and 1990 at the University of Nebraska, Panhandle Experimental Range near Scottsbluff. Quadrats were excavated each year from two, 5 x 5 Latin Square macroplots in each of 2 grazing histories, long-term rest or current-year deferment. Under dry conditions in 1989, a 65% reduction in the length of new rhizomes during July preceded a 64% reduction in live tillers in August. After which, rhizome length and live tiller density were unchanged and mean tiller weight increased during September. When average precipitation occurred in 1990, a 25% reduction in live tillers and concurrent increases in new rhizome length and mean tiller weight occurred during July. Rhizome bud densities increased throughout the growing season at different but predictable rates (R2 greater than or equal to 0.95) for grazing histories, regardless of precipitation. Length of new rhizomes was highly correlated (R2 = 0.91) with live herbage throughout the growing season. Measurable increases in total rhizome length did not occur until live herbage of prairie sandreed exceeded a threshold of about 50 g m(-2). Maximum increase in length of new rhizomes per unit of live herbage was about 10 cm g(-1) near 100 g m(-2). Given its dependence on vegetative reproduction and relatively high palatability to beef cattle, periodic or repeated years of full growing season deferment may be the only reliable method of obtaining measurable increases in prairie sandreed populations.

Interactions Among Western Ragweed and Other Sandhills Species After Drought

“…The apparent lack of effect of a dry spring on tiller emergence is consistent with a concurrent study at GSL in which rate of prairie sandreed tiller emergence and tiller number were poorly correlated with short-and long-term precipitation totals (Hendrickson et al 2000). Competitive effects of western ragweed that occurred after 10 July may have been linked to epic events of tiller mortality that are common in rhizomatous graminoids during the growing season (Callaghan 1976;de Kroon et al 1992;Reece et al 2002). For example, Reece et al (2002) found that under relatively dry conditions, densities of prairie sandreed tillers declined 25%-64% during July or August.…”

“…However, total organic reserves of the grass species in dormant-season grazed paddocks were similar to nongrazed paddocks, indicating that drought-induced increases in western ragweed were primarily the result of reduced basal area of grasses (Reece et al 2002), rather than vigor.…”

“…Competitive effects of western ragweed that occurred after 10 July may have been linked to epic events of tiller mortality that are common in rhizomatous graminoids during the growing season (Callaghan 1976;de Kroon et al 1992;Reece et al 2002). For example, Reece et al (2002) found that under relatively dry conditions, densities of prairie sandreed tillers declined 25%-64% during July or August. Mortality primarily occurs in small tillers that may be more susceptible to interspecific interference.…”

“…Tiller emergence of rhizomatous C 4 grasses occurs primarily from April to mid-June. From 65% to 85% of prairie sandreed tillers emerge by the end of May (Cullan 1998;Hendrickson et al 2000;Reece et al 2002). If interspecific interference reduced tiller emergence and corresponding endof-season standing crop, yield responses of rhizomatous grasses, expressed as a percentage of paired controls (Table 3), should have declined as initial date of western ragweed removal was delayed.…”

“…Population fluxes of western ragweed often occur between drought and the return of predrought conditions on high-seral sandhills prairie. Western ragweed appears to have the ability to rapidly respond to increased availability of soil water and nutrients resulting from drought and/or grazing-induced reductions in the vigor (Reece et al 1996) or tiller density (Reece et al 2002) of associated species. We hypothesized that western ragweed is a weak competitor with a disproportionately high potential for herbage production early in the growing season compared with associated species.…”