Allen, Phil S. , Meyer, Susan E. .
Interactions between Shrub Steppe Perennials and Winter Annual Grass Weeds.
Winter annual grass weeds represent a serious threat to shrub steppe commuities in the Intermountain West. To learn how to restore communities to a state that can resist invasion by these weeds, we established a long-term field experiment. A series of 12 replicated communities of increasing complexity, from perennial grass monocultures to shrub communities with structured understorys, was established from transplants. After two growing seasons, Bromus tectorum (cheatgrass), Aegilops cylindrica (jointed goatgrass), and Secale cereale (annual rye) were fall-seeded in subplots in each experimental plot. Weed biomass was measured the following summer, while perennial survival was evaluated a year later. Communities comprised of one or two perennial grass species were the most heavily invaded by the weeds, with over twice the weed biomass production of treatments where these grasses were planted intermixed with perennial dicots or shrubs. Simple perennial grass communities were also the most heavily impacted by the weeds. Perennial grass mortality was almost twice as high on the cereal rye plots as on the unseeded controls, with intermediate values for cheatgrass- and goatgrass-seeded plots. Shrubs and perennial dicots did not follow this pattern. Shrub mortality was low overall, and while perennial dicot mortality was relatively high, it showed no pattern with respect to the weed treatments. Results of this first year of data collection must be interpreted with caution, as the study year included a wet fall, a mild winter, and a wet spring, conditions ideal for the weeds. The following summer was very dry, setting up the conditions for herbaceous perennial mortality after the weeds depleted near-surface soil moisture. The deeper-rooted shrubs were apparently much less impacted by this soil moisture depletion. Under the conditions of our study, more structurally diverse communities were both better able to resist annual weed invasion and to survive in its aftermath.
1 - USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 N 500 E, Provo, Utah, 84606, USA
2 - Brigham Young University, Department of Plant and Animal Sciences, Provo, Utah, 84606, USA
Presentation Type: Paper
Location: Wasatch (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 10:00 AM