Compensatory Photosynthesis, Water-Use Efficiency, and Biomass Allocation of Defoliated Exotic and Native Bunchgrass Seedlings

Compensatory increases in net photosynthetic assimilation rates (Anet) following herbivory are well documented in adult rangeland grasses but have not been quantified in bunchgrass seedlings, which may be more sensitive to tissue loss than established plants. To address this, we twice removed 30% and 70% leaf area of seedlings of crested wheatgrass (Agropyron cristatum [L.] Gaertn., var. Hycrest II) and the native bluebunch wheatgrass (Psuedoroegnaria spicata [Pursh] Á. Love, var Anatone) and compared Anet and aboveground and belowground growth of these to unclipped control plants. Compensatory Anet occurred only after the second clipping, roughly 1 month after the first, and was similar in magnitude and duration between species and treatments, ca. 26% higher than control plant Anet for 2 weeks following clipping. Despite similar compensatory Anet between species, increases in Anet were more proportional with increased stomatal conductance to water vapor (gs) in crested wheatgrass. This resulted in higher intrinsic water use efficiency (WUEi = Anet/gs) integrated across the postclipping recovery period compared with WUEi of bluebunch seedlings, which declined with clipping. Differences in WUEi were attributable to differences in root-to-shoot ratios and root tissue quality (specific root mass; g dry mass · m-2 root area), which were lower in crested wheatgrass. We concluded that compensatory photosynthesis is an important component of seedling herbivory tolerance, and that observed differences in post-herbivory WUEi could help improve management strategies by informing seedling selection criteria to help develop methods aimed at minimizing impacts of herbivory during the seedling stage. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Temporal Variability in Microclimatic Conditions for Grass Germination and Emergence in the Sagebrush Steppe

Sagebrush steppe ecosystems in the western United States are characterized by harsh environmental conditions with high annual and seasonal variability in both precipitation and temperature. Environmental variability contributes to widespread failure in establishing stands of desired species on degraded and invaded landscapes. To characterize seasonal microclimatic patterns and planting date effects on restoration outcomes, we evaluated long-term simulations of seed germination response of cheatgrass (Bromus tectorum L.), bottlebrush squirreltail (Elymus elymoides [Raf] Swezey), and Idaho fescue (Festuca idahoensis Elmer) to annual patterns of soil temperature and moisture. Extremely high annual variability in both the conditions favorable for germination and patterns of post-germination drought and thermal stress make it difficult to justify general inferences about seedbed treatment and planting date effects from individual, short-term field studies. We discuss the interpretation of individual-year and seasonal plant establishment factors and offer a mechanistic model for interpreting planting date and year effects on initial seedling establishment. Historical ranking and mechanistic descriptions of individual-year seedbed conditions may allow for expanded inferences through meta-analysis of limited-term field experiments. © 2015 Published by Elsevier Inc. on behalf of The Society for Range Management.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Impact of Cultivation Legacies on Rehabilitation Seedings and Native Species Re-Establishment in Great Basin Shrublands

Little is known about how cultivation legacies affect the outcome of rehabilitation seedings in the Great Basin, even though both frequently co-occur on the same lands. Similarly, there is little known about how these legacies affect native species re-establishment into these seedings. We examined these legacy effects by comparing areas historically cultivated and seeded to adjacent areas that were seeded but never cultivated, for density of seeded crested wheatgrass (Agropyron cristatum [L.] Gaertn.) and native perennial grasses, vegetation cover, and ground cover. At half of the sites, historically cultivated areas had lower crested wheatgrass density (P<0.05), and only one site had a higher density of crested wheatgrass (P<0.05). Likewise, the native shrub Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young) had lower cover (P<0.05) in historically cultivated areas at half the sites. Sandberg bluegrass (Poa secunda J. Presl.) density was consistently lower in historically cultivated areas relative to those seeded-only. At sites where black greasewood (Sarcobatus vermiculatus [Hook.] Torr.) and bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey) were encountered, there was either no difference or a higher density and cover within historically cultivated areas (P<0.05). Likewise, cover of exotic forbs, especially halogeton (Halogeton glomeratus [M. Bieb.] C. A. Mey.), was either not different or higher in historically cultivated areas (P<0.05). Bare ground was greater in historically cultivated areas at three sites (P<0.05). These results suggest that cultivation legacies can affect seeding success and re-establishment of native vegetation, and therefore should not be overlooked when selecting research sites or planning land treatments that include seeding and or management to achieve greater native species diversity.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information