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Title: Drought survival and perennial grass success in the face of cheatgrass invasion: germination, emergence, seedling die-off and reproduction

item Harmon, Daniel - Dan
item Clements, Darin - Charlie

Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: 2/7/2013
Publication Date: 7/22/2013
Citation: Harmon, D.N., Clements, D.D. 2013. Drought survival and perennial grass success in the face of cheatgrass invasion: germination, emergence, seedling die-off and reproduction [abstract]. Soil and Water Conservation Society Meeting, Reno, NV July 21-24, 2013. 68:113.

Interpretive Summary:

Technical Abstract: Cheatgrass (Bromus tectorum) dominance and competitiveness is often attributed to early (fall) germination. We hypothesize that cheatgrass germinates earlier compared to three commonly used restoration/rehabilitation perennial grass species [‘Hycrest’ crested wheatgrass( Agropyron desertorum ssp. critatum), squirreltail (Elymus elymoides), and bluebunch wheatgrass (Psuedorogenaria spicata)]. We also hypothesize that germination is not the only limiting factor, but rather seedling desiccation, regardless of germination timing. While these are well observed characteristics in the field, we wanted to observe them using a more controlled environment eliminating the effect of highly variable interactions from other non-observed plants on field sites. We also set out to observe how soil type affects these processes when variation of site temperature and precipitation are controlled. Using field soil (15ft3 box), four species (Cheatgrass, ‘Hycrest’ crested wheatgrass, squirreltail and bluebunch wheatgrass) were seeded into four soil types (12 soil boxes). In total, 120 seed caches (25 seeds/cache) were buried for each species. Every two weeks (Nov-April), germination, emergence and seedling survival were observed with soil temperature and moisture percent being monitored. By adding new seeds every 2 weeks we were able to delay germination for all species to observe the effect on seedling survival. Precipitation events provided the only water. Results of averages for all soil types combined yielded that cheatgrass germinated first at colder temperatures (2012 January average 0.5C: low -15C: high 21C and 2013 November average 4.4C:low -11C: high 18C) compared to perennials (2012 March average 1.9C: low -7.5C:high 21C and 2013 December average 3.7C: low 0C: high 11.5C). Cheatgrass germinated about 4 weeks earlier in 2012 and 2 weeks earlier in 2013 than the perennials. The months when germination occurred differed considerably between years (January 27th year 1 vs. November 25th year 2). Soil moisture seems to be a greater limiting factor than temperature for germination which occurred after the first fall/winter precipitation event (first significant precipitation event: 2012 {growing season} January 2012 vs. 2013{growing season} November 2012). Cheatgrass germination not only occurred earlier but also at higher rates. By March 1st 2012 (7% gravimetric soil moisture) the percent of total seeds germinated was cheatgrass 46%, bluebunch 27%, ‘Hycrest’ 19% and squirreltail 17%. In 2013 January (29% soil moisture) percent germination was cheatgrass 64%, bluebunch 44%, ‘Hycrest’ 36% and squirreltail 7%. Ranking species by percent germination provided the same results both years regardless of the drastic timing differences. Comparing germination timing and seedling survival (June) all species had increased survival by germinating earlier (seedlings/25 seeds [early March vs. late April] cheatgrass 0.53 vs 0.27, crested wheatgrass 0.66 vs 0.16, bluebunch wheatgrass 0.28 vs 0.16, squirreltail 0.55 vs 0.13). Since the number of seedlings per 25 seeds was comparable between species and very low (less than 1 per cache), we looked at the percent of caches that had any seedling survival, which would represent niche utilization. Cheatgrass demonstrated its dominance with this comparison (Niche utilization: cheatgrass 32%, crested wheatgrass 22%, bluebunch wheatgrass 10%, and squirreltail 11%). We find this the most useful comparison for rangeland management since the goal is establishing a specified density of perennial grasses. Seedling vigor which was represented by biomass (grams per plant) drastically differed between cheatgrass, crested wheatgrass and the 2 native species (crested wheatgrass 2.93g, cheatgrass 0.74g, squirreltail 0.18g, and bluebunch 0.15g). Based on the results, our hypotheses that cheatgrass germinates earli