Annual replacement of the tillers of Agropyron desertorum following grazing

Abstract

The annual replacement of tillers of Agropyron desertorum (Fisch. ex Link) Schult., a grazing-tolerant, Eurasian tussock grass, was examined in the field following cattle grazing. Heavy grazing before internode (culm) elongation seldom affected tiller replacement. Heavy grazing during or after internode elongation, which elevates apical meristems, increased overwinter mortality of fall-produced tillers and reduced the number and heights of these replacement tillers. Unexpectedly, tussocks grazed twice within the spring growing season tended to have lower overwinter tiller mortality, greater tiller replacement, and larger replacement tillers than tussocks grazed only once in late spring. These responses of twice-grazed tussocks, however, were still less than those of ungrazed tussocks or tussocks grazed moderately in early spring. The presence of ungrazed tillers on partially grazed tussoks did not increase the replacement of associated grazed tillers relative to tillers on uniformly grazed plants. This result indicates that resource sharing among tillers, if present, is short-lived or ecologically unimportant in this species. Although A. desertorum is considered grazing-tolerant, tiller replacement on heavily grazed tussocks, particularly those grazed during or after internode elongation when apical meristems were removed, was usually inadequate for tussock maintenance. These observations at the tiller (ramet) level of organization in individual tussocks (genet) may explain the often noted reduction in stand (population) longevity with consistent heavy grazing.

Effect of Sheep Grazing on a Leafy Spurge-Infested Idaho Fescue Community

“…Stem or leaf heights have often been used as an indicator of plant vigor (Mueggler 1975, Cook andStubbendieck 1986). For example, 1 year after grazing, stem heights of crested wheatgrass tillers are lower on plants grazed during internode elongation than those grazed before internode elongation (Olson and Richards 1988). In this study, heights of leafy spurge stems and Idaho fescue leaves along grazed transects were lower than along ungrazed transects from 1992 to 1995.…”

Regrowth of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) following defoliation

“…The apical meristem was apparently removed by mowing, necessitating development of new tillers for regrowth. Adequate moisture and optimum temperatures must exist before tiller buds are activated (Morrow and Power 1979;Busso et al 1989); light quantity and quality may also influence axillary bud activation (Olson and Richards 1988a;Murphy and Briske 1992). Conditions for emergence of new tillers were not met until the spring following defoliation.…”

“…In all years, tillers of crested wheatgrass emerged the April following defoliation. In Utah, desert wheatgrass tillers emerge in late summer to autumn, they overwinter and resume growth the following spring (Mueller and Richards 1986;Olson and Richards 1988a). Northern wheatgrass produces tillers continuously through the growing season (Zhang and Romo 1994) whereas smooth bromegrass tillers in autumn and/or spring, depending on time of defoliation (Harrison and Romo 1994).…”

“…Desert wheatgrass tillers can live up to about 14 months (Olson and Richards 1988a), whereas northern wheatgrass tillers can live five years (Zhang and Romo 1994). Despite the short life span of crested wheatgrass tillers, replacement ratios greater than 1.0 indicate that stand density of crested wheatgrass was not impaired by defoliation a single time during the growing season, and in fact the stand was thickening.…”

Season of fire manipulates bud bank dynamics in northern mixed-grass prairie

“…These bud limitations may have consequences for aboveground growth if the timing of disturbance, such as fire and grazing, interferes with critical phenological growth patterns of buds further inhibiting the production or maintenance of belowground buds (Carter et al 2012;Ott and Hartnett 2012). Potential bud limitations or stored reserves regulate aboveground responses to fire and species-specific levels of adaptations to fire (Olson and Richards 1998;Rogers and Hartnett 2001;Dalgleish and Hartnett 2006;Klimešová and Klimeš 2007). Given the role fire has played in shaping grasslands, perennial native grasses that evolved with frequent fire would be expected to be very efficient at maintaining bud reserves and subsequent tiller recruitment.…”