Response of Soft Chess (Bromus mollis) and Slender Oat (Avena barbata) to Simulated Drought Cycles

Ewing, Anne L.; Menke, John W.

doi:10.2307/3897929

Cited by 12 publications

(2 citation statements)

References 8 publications

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“…It is probably no coincidence that supporting evidence for fine‐scale deterministic models comes from highly productive systems where competition predominates (Wilson 2007). In our system, both recruitment success and dominant plant cover, with its assumed connection to above‐ and below‐ground resource availability (Grime 2001), varied widely from year to year, as is typical of semi‐arid systems (Ewing & Menke 1983; Figueroa & Davy 1991; Briggs & Knapp 1995; Holmgren et al . 2006; Adler & Levine 2007; Houlahan et al .…”

Section: Discussionmentioning

confidence: 99%

Climatic variability alters the outcome of long‐term community assembly

2007

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Summary 1.We used seed additions to test experimentally whether long-term community assembly unfolds consistently (deterministic model) or whether different outcomes are possible depending on variations in climate and the presence of exotic dominants (stochastic model). The experiment was conducted in homogeneous semi-arid grassland on the northern Great Plains of North America. Native grass seed additions in each of 3 years (1994 -96) were combined factorially with repeated selective herbicide applications to reduce the cover of the extant dominant, a Eurasian C 3 grass ( Agropyron cristatum ). We assessed whether composition converged or diverged among treatments between 1996 and 2004. 2. The outcome of long-term community assembly varied by establishment year, in association with significant variations in monthly growing-season precipitation from 68-year averages during the years when seed was added. In 2004, the added native C 4 grass Bouteloua gracilis dominated plots sprayed and seeded in 1994 and 1995, resisting re-invasion and having significantly higher plot diversity. In contrast, plots sown in 1996 -one of the driest years on record -reverted to the exotic C 3 grass. Seeded but unsprayed plots maintained their pre-treatment dominance by exotic grass. Rainfall variability was also associated with the extent of exotic grass cover and bare soil in unsprayed plots, and natural recruitment by native species from nearby prairie. 3. Establishment success varied significantly among the added species. All seeded grasses, other than B. gracilis , were mostly absent by 2004. The failure of these native C 3 species to establish appears consistent with deterministic assembly models where local abiotic conditions filter out unsuitable species. 4. Synthesis . Our results indicate that stochastic and deterministic processes operate simultaneously to influence community assembly, depending on interactions among climate, seed availability, species identity and disturbance during the initial stages of establishment. Multiple assembly trajectories developed, but the assembled communities did not include all the added species. Conversion of degraded grassland back to native-dominated grassland was possible, but only with the removal of the exotic dominant and seed additions during years that were suitably wet for establishment. Once formed, however, the assembled native community resisted re-invasion. This suggests that native grassland restoration will depend on establishment measures as intense as those used during initial cultivation almost a century earlier.

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Section: Discussionmentioning

confidence: 99%

Climatic variability alters the outcome of long‐term community assembly

2007

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“…Both reproduction and senescence have been shown to be potentially subject to multiple influences, including temperature, rainfall amount and timing, CO 2 concentrations, and photoperiod (Slade et al. , Savelle , Ewing and Menke , b, Jackson and Roy , Zavaleta et al. , Cleland et al.…”

Section: Introductionmentioning

confidence: 99%

Modeling annual grassland phenology along the central coast of California

2017

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Abstract. Grassland phenology is an important component of terrestrial biophysical models, with substantial differences in the cycling of energy, carbon, water, and nutrient fluxes between periods of growth and dormancy. Modeling the phenology of moisture-driven annual grasslands in Mediterranean-type ecosystems (MTEs) remains challenging because although soil moisture is often a direct control on greenup, high rainfall variability during MTE wet seasons makes predicting the optimal time for senescence problematic. For this study, we developed a Mediterranean grassland phenology model (MGPM) to model green-up and senescence for coastal California annual grasslands. Mediterranean grassland phenology model was embedded in an ecohydrologic model, Regional Hydro-Ecologic Simulation System, and simulations of ecosystem fluxes were compared to a simpler fixed-date (i.e., photoperiod) phenology model. Results indicated that a soil water potential threshold was an accurate predictor of grassland green-up initiation. Annual cumulative net primary productivity (NPP cum ) was observed to be a good predictor of senescence initiation, with higher levels of NPP cum associated with delayed senescence initiation. We also observed that photoperiod acts as an additional control on senescence initiation, restricting the window of time during which senescence may occur. Long-term peak NPP cum was noted as a potential control on the timing of this photoperiod window. Inclusion of MGPM into biophysical models is expected to improve the representation of annual grasslands and more accurately simulate ecosystem fluxes.

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