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A history of species co-occurrence in plant communities is hypothesized to lead to greater niche differentiation, more efficient resource partitioning, and more productive, resistant communities as a result of evolution in response to biotic interactions. A similar question can be asked of co-occurring populations: do individual species or community responses differ when communities are founded with plants sharing a history of population co-occurrence (sympatric) or originating from different locations (allopatric)? Using shrub, grass, and forb species from six locations in the western Great Basin, North America, we compared establishment, productivity, reproduction, phenology, and resistance to invaders for experimental communities with either sympatric or allopatric population associations. Each community type was planted with six taxa in outdoor mesocosms, measured over three growing seasons, and invaded with the annual grass Bromus tectorum in the final season. For most populations, the allopatric or sympatric status of neighbors was not important. However, in some cases, it was beneficial for some species from some locations to be planted with allopatric neighbors, while others benefited from sympatric neighbors, and some of these responses had large effects. For instance, the Elymus population that benefited the most from allopatry grew 50% larger with allopatric neighbors than in single origin mesocosms. This response affected invasion resistance, as B. tectorum biomass was strongly affected by productivity and phenology of Elymus spp., as well as Poa secunda. Our results demonstrate that, while community composition can affect plant performance in semi-arid plant communities, assembling communities from sympatric populations is not sufficient to ensure high productivity and invasion resistance. Instead, we observed an idiosyncratic interaction between sampling effects and evolutionary history, with the potential for seed source of individual populations to have community-level effects., (© 2023 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

Restoration of agricultural fields is challenging, especially in arid and semi-arid ecosystems. We conducted experiments in two fields in the Great Basin, USA, which differed in cultivation history and fertility. We tested the effects of different levels of functional diversity (planting grasses and shrubs together, vs. planting shrubs alone), seed source (cultivars, local or distant wild-collections), and irrigation regime (spring or fall and spring) on restoration outcomes. We sowed either: 1) grasses and shrubs in year one, 2) shrubs only, in year one, 3) grasses in year one with herbicide, shrubs in year two, or 4) shrubs alone in year two, after a year of herbicide. We irrigated for two years and monitored for three years. Shrub emergence was highest in the lower fertility field, where increasing functional diversity by seeding grasses had a neutral or facilitative effect on shrub emergence. In the higher fertility field, increasing functional diversity appeared to have a neutral to competitive effect. After declines in shrub densities after irrigation ceased, these effects did not persist. Grasses initially suppressed or had a neutral effect on weeds relative to an unseeded control, but had neutral or facilitative effects on weeds relative to shrub-only seeding. Initially, commercial grasses were either equivalent to or outperformed wild-collected grasses, but after irrigation ceased, commercial grasses were outperformed by wild-collected grasses in the higher fertility field. Local shrubs initially outperformed distant shrubs, but this effect did not persist. Fall and spring irrigation combined with local shrubs and wild-collected grasses was the most successful strategy in the higher fertility field, while in the lower fertility field, irrigation timing had fewer effects. Superior shrub emergence and higher grass persistence indicated that the use of wild and local seed sources is generally warranted, whereas the effects of functional diversity and irrigation regime were context-dependent. A bet-hedging approach that uses a variety of strategies may maximize the chances of restoration success. [ABSTRACT FROM AUTHOR]

While much research has documented the impact of invaders on native communities and ecosystem services, there has been less work quantifying how invasion affects the genetic composition of native populations. That is, when invaders dominate a community, can they shift selection regimes and impact the evolutionary trajectory of native populations?, The invasion of the annual grass Bromus tectorum in the Intermountain West provides an opportunity to quantify the effects of invasion on natural selection in wild populations. The shift from a perennial-dominated native community to one dominated by a highly competitive annual species alters the timing and intensity of competitive pressure, which has the potential to strongly shift selection regimes for native plants., To quantify traits under selection in contrasting environments, we planted seeds of two native perennial grasses, Elymus multisetus and Poa secunda, into three invaded, invaded but weeded and relatively uninvaded sagebrush systems. We quantified phenotypic traits of seedlings from separate maternal plants, describing differences in phenotypes among individuals. We then asked which traits were associated with survival and plant size in adjacent invaded and uninvaded sagebrush systems, following individual seed performance for 3 years., We found evidence for divergent selection between invaded and uninvaded sagebrush systems, with contrasting phenotypic traits associated with greater survival or plant size in these different growing conditions at all three field sites. For example, at one field site, P. secunda families with higher root tip production were more likely to survive in invaded and weeded environments, but this was not the case in uninvaded environments. Similarly, for E. multisetus, root mass fraction, seed mass and allocation to coarse or fine roots affected survival and plant size, again with contrasting relationships across invaded, weeded or uninvaded environments., Synthesis. Impacts of invasive species extend beyond ecosystem and community composition changes and can affect the evolutionary trajectory of native populations. By quantifying natural selection in invaded landscapes, we identified phenotypic traits that are potentially adaptive in these invaded systems. Importantly, these traits differed from traits associated with success in uninvaded communities. This insight into adaptive, contemporary evolution in native species can guide restoration and conservation efforts. [ABSTRACT FROM AUTHOR]

Competitive interactions with invasive species can cause evolutionary changes in native populations. In the Great Basin, USA, the invasive annual grass Bromus tectorum pre-emptively accesses limiting soil resources through extensive root production. Here, we determined whether evolutionary changes in root traits occurred during re-seeding of Elymus elymoides , a native bunchgrass. We grew plants from seeds collected from survivors in two restoration sites and compared them with plants grown from the original seed, with and without competition from B. tectorum . We quantified competition, root allocation, and morphology over time. Relative to the original seed source, E. elymoides plants that established in restoration sites showed small but significant increases in root biomass fraction, and plants were smaller, both aboveground and belowground, with parallel results seen in both field sites. In contrast, E. elymoides seed sources were not significantly different in competitive response to or in competitive effect on B. tectorum . Thus, results are consistent with natural selection favoring traits that allowed plants to establish in B. tectorum invaded areas but not traits that increased competitive ability. Selecting or breeding restoration plants for smaller size but increased relative root investment could improve establishment under reduced soil resource conditions and hence native plant restoration. [ABSTRACT FROM AUTHOR]

Restoration is an opportunity to study natural selection: One can measure the distribution of traits in source propagules used to found populations, compare this with the distribution of traits in successful recruits, and determine the strength and direction of selection on potentially adaptive traits. We investigated whether natural selection influenced seedling establishment during postfire restoration in the Great Basin, an area where large-scale restoration occurs with a few widely available cultivars planted over a large range of environmental conditions. We collected seeds from established plants of the perennial grass Elymus elymoides ssp. californicus (squirreltail) at two restoration sites and compared the distribution of phenotypic traits of surviving plants with the original pool of restoration seeds. Seeds were planted in common gardens for two generations. Plants grown from seeds that established in the field were a nonrandom subset of the original seeds, with directional selection consistently favoring a correlated suite of traits in both field sites: small plant and seed size, and earlier flowering phenology. These results demonstrate that natural selection can affect restoration establishment in strong and predictable ways and that adaptive traits in these sites were opposite of the current criteria used for selection of restoration material in this system. [ABSTRACT FROM AUTHOR]

Expansion of native pinyon-juniper (Pinus monophylla - Juniperus osteosperma) woodlands can decrease shrub and herbaceous cover in the Intermountain West, U.S., affecting habitat quality and biodiversity. Removing pinyon-juniper woodlands in former sagebrush ecosystems to increase understory cover has a long management history, and short- and long-term monitoring reveal different understory plant community responses. We revisited a 500 mm average precipitation site in the sagebrush steppe of western Nevada, 32 years after three types of tree thinning treatments and seeding had occurred in a mature, closed-canopy woodland. We measured vegetation foliar cover and density within plots arranged in a 3-block randomized design. We found significantly lower cover of P. monophylla in treated plots (average of 2–8%), relative to controls (32%). However, P. monophylla seedlings (<0.5 m tall) were detected throughout all plots (average of 86–160 trees/ha in treated plots, 111 in controls). Cover of perennial graminoids and shrubs was higher in all treatments (600–870% higher grass cover and 470–570% higher shrub cover) than controls. Cover of invasive annual species, primarily Bromus tectorum , was highly variable and not significantly different among plots, but B. tectorum had the highest cover of all species in two of the three woodland removal treatment types. Control plots contained significantly larger perennial canopy gaps compared to all treatments (average of 318 cm vs. 104–133 cm), and had significantly more woody litter cover than clear cut plots (average of 14% vs. 3%). These results suggest tree thinning and removal in tree dominated woodlands can increase shrub and perennial grass cover and reduce litter and canopy gaps, especially in conjunction with seeding, but that tree recolonization over the long-term is inevitable. Perennial forbs did not respond well to treatments (<1% average foliar cover in all plots), and seeding or other treatments may be needed to improve their response. Further, if tree seedlings survive, these plots will likely return to tree dominance without additional treatments. • Long-term data show woodland reduction treatments keep P. monophylla cover low. • Clear-cutting led to increased cover of perennial grasses and shrubs post-treatment. • Seeded grasses were among the highest contributors to foliar cover in treated plots. • Forbs remained absent 32 years after woodland reduction treatments. • P. monophylla seedlings were detected in all plots and may need further treatment. [ABSTRACT FROM AUTHOR]