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Seedling recruitment is a critical driver of population dynamics and community assembly, yet we know little about functional traits that define different recruitment strategies. For the first time, we examined whether trait relatedness across germination and seedling stages allows the identification of general recruitment strategies which share core functional attributes and also correspond to recruitment outcomes in applied settings. We measured six seed and eight seedling traits (lab- and field-collected, respectively) for 47 varieties of dryland grasses and used principal component analysis (PCA) and cluster analysis to identify major dimensions of trait variation and to isolate trait-based recruitment groups, respectively. PCA highlighted some links between seed and seedling traits, suggesting that relative growth rate and root elongation rate are simultaneously but independently associated with seed mass and initial root mass (first axis), and with leaf dry matter content, specific leaf area, coleoptile tissue density and germination rate (second axis). Third and fourth axes captured separate tradeoffs between hydrothermal time and base water potential for germination, and between specific root length and root mass ratio, respectively. Cluster analysis separated six recruitment types along dimensions of germination and growth rates, but classifications did not correspond to patterns of germination, emergence or recruitment in the field under either of two watering treatments. Thus, while we have begun to identify major threads of functional variation across seed and seedling stages, our understanding of how this variation influences demographic processes-particularly germination and emergence-remains a key gap in functional ecology.

Restoration of dryland ecosystems is often limited by low seedling establishment and survival. Defoliation caused by insects and small mammals could be an overlooked cause of seedling mortality. In the sagebrush steppe, we examined the effect of seedling defoliation on the survival of perennial grasses commonly used as restoration materials. Under field conditions, seedlings of three perennial bunchgrass species (non-native Agropyron cristatum , and native grasses Poa secunda and Pseudoroegneria spicata) were defoliated at two intensities (30 % and 70 % leaf length removal) and frequencies (one or two clippings) and compared to a non-defoliated control. Following emergence the first year, clippings occurred at the two-leaf stage; a second clipping occurred 1 month later for repeated defoliation treatments. We monitored seedling survival and tillering for 2 years. We expected higher defoliation intensity and frequency to reduce survival for all species, but only a few treatments reduced Po. secunda survival. Conversely, larger-statured Triticeae (wheatgrasses) benefited from some defoliation treatments. In both years, A. cristatum survival increased with repeated defoliation at both intensities. Defoliation did not affect Ps. spicata survival in the first year, but a single defoliation in the second year resulted in increased survival. In both A. cristatum and Ps. spicata , higher-intensity defoliation reduced the boost to survival resulting from defoliation frequency. Seedlings with more tillers had greater survival probabilities, but tiller number was unaffected by defoliation. Further research may elucidate mechanisms seedlings use to compensate for or benefit from defoliation. In the meantime, managers should aim to select defoliation-tolerant species if they anticipate herbivory will be problematic for restoration sites. [ABSTRACT FROM AUTHOR]

Seed‐based restoration is one of the most difficult challenges for dryland restoration. Identifying environmental conditions that drive variation in seed and seedling mortality across similar restoration efforts could increase understanding of when and where restoration outcomes are likely to be favourable and identify new tools and strategies to improve outcomes.We asked how variation in a suite of environmental predictors influenced germination, emergence, seedling establishment and juvenile survival of four commonly sown perennial grass species across 33 seeding experiments distributed over an ~160,000‐km2 area of the Great Basin, a cold desert system in the western United States.Across experiments, we observed wide variation in the rates of four demographic transitions and wide variation in environmental conditions experienced by plants at each stage. For all species, higher precipitation during the first 30 days following seeding was associated with an increase in germination. Conversely, higher soil temperature over this same time period was associated with a significant decrease in germination and emergence, and soil temperature was associated with a substantial portion of the variation in germination and emergence probabilities observed across our seeding experiments.Within the range of precipitation variation observed, we were unable to detect a significant relationship between seedling establishment the first growing season and cumulative precipitation the first year, precipitation during the first spring growing season or annual climatic water deficit (CWD) the first year. Higher CWD the second growing season reduced seedling survival over that time period.Synthesis and applications. Our results show higher soil temperature negatively impacts grass seedling establishment. Restoration efforts should be prioritized when seasonal or subseasonal temperature forecasts indicate likely periods of below average temperatures. These results also indicate that climate warming will make restoration even more difficult, with our model estimates suggesting the 2°C increase in temperature expected in the Great Basin over the coming decades will decrease germination and emergence by about 30%. Lastly, while our field‐based approach provided insight into short‐term drivers of mortality, it did not provide insight into drivers of longer term survival, suggesting a need for further work on predicting long‐term restoration outcomes. [ABSTRACT FROM AUTHOR]

High disturbance frequency, low water availability, and advantageous growth mechanisms of invasive annual compared to native perennial grasses reduce native grass establishment throughout arid rangelands. Modifying seeding dispersal processes, including seeding rate and time, may increase native grass recruitment by influencing safe site occupation. A better understanding of seedling development through life history stages and the ecological processes occurring during these stages may be necessary to comprehend modified dispersal dynamics on plant community assembly. We tested the effects of spring vs. fall annual grass seeding times, adding water, and varying annual and perennial grass propagule pressure on perennial and annual grass recruitment in an eastern Oregon shrub-steppe ecosystem. Across species, survival rates were lowest between germination and emergence stages. However, perennial grass germination rates were highest when perennials were seeded with annual grasses in autumn. Perennial grass recruitment was generally low, especially when annual grass propagule pressure was higher than 150 seeds m −2 . Although, by the second growing season, perennial grasses had the highest density when perennials were seeded with annuals in autumn and water was added. Consequently, modifying native perennial grass dispersal, like priority autumn seeding and increasing propagule pressure, should produce higher perennial grass recruitment across arid lands. [ABSTRACT FROM AUTHOR]

Our ability to restore rangelands is limited, and it is unknown if seedling herbivory on its own, or in interaction with other stressors, is a major contributor to restoration failure. To address this, we conducted two experiments: a No Defoliation (ND) experiment ( n = 48), in which seedlings from three perennial grasses (crested wheatgrass [ Agropyron cristatum {(L.} Gaertn.], bluebunch wheatgrass [ Psuedoroegnaria spicata {Pursh} Á. Love], Sandberg bluegrass [ Poa secunda J Presl]) were subjected to wet and dry water regimes for 4 mo, and a concurrent Defoliation (D) experiment ( n = 95), in which seedlings were factorially assigned to two defoliation treatments—frequency (LOW, HIGH) and intensity (30% vegetation removal, 70% vegetation removal). Indicators of seedling performance were aboveground and belowground biomass (AGB and BGB), root:shoot ratio, tillering, and mortality. The effect size statistic, Hedge’s g, allowed for comparisons between performance measures. Water stress induced reductions in most performance measures: BGB ( g = ND: –1.3; D: –1.6), root:shoot ratio ( g = ND: n.s.; D: –0.2), and tillering ( g = ND: –1.7; D: –1.2), though not significantly for all species. For ABG, water stress interacted with defoliation, reducing performance less at an intensity of 70% ( g = –2.0) as opposed to 30% ( g = –3.0), but not always significantly in the former. Water stress also caused less reduction in AGB when no defoliation occurred (ND: –0.8; g = D: –2.5). Intensity and frequency of defoliation interacted; seedlings were generally resistant to reductions in performance except at high frequency, 70% defoliation. Agropyron cristatum and P. spicata displayed similar sensitivity to treatments, mostly in terms of changes in AGB and BGB, while P. secunda also experienced increased mortality and reduced tillering. If these differences in sensitivity result in differential survival, herbivory could impact species postrestoration population demographics. [ABSTRACT FROM AUTHOR]

Abstract: Invasive annual grasses tend to construct thinner and less dense root and leaf tissue than native perennial grasses. This allows invasive annuals to grow faster and produce more biomass in the arid grasslands of the United States. Based on these differences we tested the hypotheses that: 1) Competitive effects of the native perennial on the invasive annual will increase as plant developmental stage increases and as drought stress increases. 2) Drought stress will reduce the competitive effect of invasive annuals on native perennials proportionately more than drought stress reduces the competitive effect of native perennials on the invasive annual. 3) Facilitation among native perennial grass seedlings will decrease as developmental stage increases. Competitive effects of native squirreltail, on invasive medusahead, increased as the initial developmental stage of squirreltail increased, but not vice versa. Drought stress reduced the competitive effect of medusahead on squirreltail target biomass more than drought stress reduced the competitive effect of squirreltail on medusahead target biomass. While both squirreltail and medusahead displayed intraspecific facilitation, the net effect of their interspecific interaction was negative for both species. Habitat amelioration manifests itself differently depending on species traits, and can create conditions that simultaneously benefit one species while hindering another. [Copyright &y& Elsevier]