Belowground bud production is linked to population establishment in Sorghastrum nutans (Poaceae)

Belowground bud production mediates many responses of tallgrass prairie grasses to temporal environmental variation, and clonal spread contributes to dominance in successional plant communities. However, we know little about the importance of these regenerative traits for vegetation establishment in grassland restoration and about their regional variability. Further, geographic seed or transplant sources affect plant performance. We investigated the effects of seed source on the number of belowground buds per tiller, clonal spread (total rhizome length adjusted for plant biomass), and population establishment in the native C₄ grass Sorghastrum nutans sown into tallgrass prairie restorations using reciprocal common gardens in three sites (in Nebraska, Kansas, and Oklahoma). We characterized buds per tiller and clonal spread at the plant level and related both traits to population establishment at the restoration plot level. Plant-level bud production significantly differed among seed sources and common garden sites, and was positively associated with plot-level establishment (density and canopy cover), but plant-level clonal spread did not differ among seed sources or common garden sites and was not associated with the plot-level establishment. Our results are among the first to link bud production, which varied among source populations, to differences in plant population establishment. These results suggest that we should more often consider differences among sources in traits closely tied to post-seeding population establishment. The use of sources that possess such traits may facilitate successful establishment in restoration settings.     

Spatial grain of adaptation is much finer than ecoregional‐scale common gardens reveal

Adaptive variation among plant populations must be known for effective conservation and restoration of imperiled species and predicting their responses to a changing climate. Common‐garden experiments, in which plants sourced from geographically distant populations are grown together such that genetic differences may be expressed, have provided much insight on adaptive variation. Common‐garden experiments also form the foundation for climate‐based seed‐transfer guidelines. However, the spatial scale at which population differentiation occurs is rarely addressed, leaving a critical information gap for parameterizing seed‐transfer guidelines and assessing species’ climate vulnerability. We asked whether adaptation was evident among populations of a foundational perennial within a single “empirical” seed‐transfer zone (based on previous common‐garden findings evaluating very distant populations) but different “provisional” seed zones (groupings of areas of similar climate and are not parameterized from common‐garden data). Seedlings from three populations originating from similar conditions within an intermediate elevation were planted into gardens nearby at the same elevation, or 250–450 m higher or lower in elevation and 0.4–25 km away. Substantial variation was observed between gardens in survival (ranging 2%–99%), foliar crown volume (7.8–22.6 dm³), and reproductive effort (0%–65%), but not among the three transplanted populations. The between garden variation was inversely related to climatic differences between the gardens and seed‐source populations, specifically the site differences in maximum–minimum annual temperatures. Results suggest that substantial site‐specificity in adaptation can occur at finer scales than is accounted for in empirical seed‐transfer guidance when the guidance is derived from broadscale common‐garden studies. Being within the same empirical seed zone, geographic unit, and even within 10 km distance may not qualify as “local” in the context of seed transfer. Moving forward, designing common‐garden experiments so that they allow for testing the scale of adaptation will help in translating the resulting seed‐transfer guidance to restoration projects.     

Non‐native conditions favor non‐native populations of invasive plant: demographic consequences of seed size variation?

Trait differences between native and non‐native populations may explain the greater abundance and impact of some organisms in their non‐native ranges than in their native ranges. Here, we conducted reciprocal common gardens in southwestern Turkey (home) and central Argentina (away) to explore the hypothesis that the greater success of the invasive ruderal Centaurea solstitialis in Argentina than Turkey is partially explained by differences between home and away populations. Unusual among common gardens, our experimental design included seed additions to explicitly evaluate population level responses, as well as disturbance and no‐disturbance treatments. We documented seed mass in native and non‐native populations, and during the experiment, we periodically measured density, plant size, and herbivory. After six months, we determined the establishment of plants for populations from both origins in both home and away common gardens. Seed mass was two times larger for Argentinean than Turkish populations. Density, plant size and final establishment were also greater for plants from Argentinean than from Turkish populations, but only in the common garden in Argentina. In Turkey, no differences between population origins were detected for these variables. Herbivory was similar for populations from both origins in both common gardens. As expected, disturbance generally increased plant performance in both regions. Our results suggest that increased seed size in non‐native populations may have demographic consequences under non‐native conditions that can contribute to the invasive success of C. solstitialis. This is the first reciprocal common garden that supports the idea that seed size variation contributes to demographic differences for an invasive species between native and non‐native distributions, but our findings further suggest that seed size effects on demography depend on the ecological context in which population processes occur.     

Nonlocal transplantation and outbreeding depression in the subshrub Lotus scoparius (Fabaceae)

The genetic background of transplants used to create or augment wild populations may affect the long-term success of restored populations. If seed sources are from differently adapted populations, then the relative performance of progeny from crosses among populations may decrease with an increase in genetic differences of parents and in the differences of parental environments to the transplant location. We evaluated the potential for such outbreeding depression by hybridizing individuals from six different populations of Lotus scoparius var. scoparius and L. s. var. brevialatus. We used allozyme data to calculate genetic distances between source populations, and compiled climatic data and measured soil traits to estimate environmental distances between source populations. We found significant outbreeding depression following controlled crosses. In the greenhouse, the success of crosses (seeds/flower × seedlings/seed) decreased with increasing genetic distance between populations revealing genetically based outbreeding depression unrelated to local adaptation. After outplanting to one native site (in situ common garden), field cumulative fitness of progeny (survival × fruit production) decreased significantly with mean environmental distance of the parental populations to the transplant site, but not with genetic distance between the crossed populations. This result is consistent with a disruption of local adaptation. At the second, ecologically contrasting common garden, where low survival reduced statistical power, field cumulative fitness (survival × progeny height) did not decrease significantly with either environmental distance or genetic distance. Overall, intervariety crosses were 40 and 50% as fit (seeds/flower × seedlings/seed × survival × fruits at the first garden or × height at the second) as intravariety crosses. These results suggest that the cumulative outbreeding depression was caused by a combination of genetically based ecological differences among populations and other genomic coadaptation. We conclude that mixing genetically differentiated seed sources of Lotus scoparius may significantly lower the fitness of augmented or restored populations. Genetic and environmental similarities of source populations relative to the transplant site should be considered when choosing source materials, a practice recommended by recent seed transfer policies. Geographic separation was not a good surrogate for either of these measures.     

Burning Influences on Wiregrass (Aristida beyrichiana) Restoration Plantings: Natural Seedling Recruitment and Survival

Regeneration and expansion of Aristida beyrichiana and Aristida stricta (wiregrass) populations in remaining fire‐maintained Pinus palustris (longleaf pine) stands of the southeastern United States has become an objective of land managers. Although growing‐season fire is required for successful wiregrass seed production, studies examining naturally occurring wiregrass seedling dynamics are few. This study investigates how seedling survivorship is affected by season of burn, seedling size, time since germination, and proximity to adult plants. Restoration at this research site was begun in 1992 with the planting of containerized longleaf pine and wiregrass seedlings. Study plots were established in November 1997 after a growing‐season prescribed fire (June 1996) that resulted in successful seed production and seedling recruitment. Burn treatment plots included (1) no burn (control), (2) fire in the dormant season of the first year after germination (March 1998), (3) fire in the growing season of the first year after germination (August 1998), and (4) fire in the growing season of the second year after germination (July 1999). Seedling mortality increased with growing season burning and close proximity to planted adults. Natural seedling recruitment continued into the second year after initial seed‐drop in all plots, which verifies that wiregrass seed banking occurs for a minimum of 2 years after seed drop. Where wiregrass management objectives include population expansion, seedling recruits should be allowed 1 to 2 years post‐germination without growing season fire for successful establishment.     

Plant reproductive strategies vary under low and high pollinator densities

Long‐term variation in the population density of honey bees Apis mellifera across landscapes has been shown to correlate with variation in the floral traits of plant populations in these landscapes, suggesting that variations in pollinator population density and foraging rates can drive floral trait evolution of their host plants. However, it remained to be determined whether this variation in plant traits is associated with adaptive variation in plant reproductive strategies under conditions of high and low pollinator densities. Here we conducted a reciprocal transplant experiment to examine how this variation in floral traits, under conditions of either high and low pollinator density, impacted seed production in the Tibetan lotus Saussurea nigrescens. In 2014 and 2015, we recorded the floral traits, pollinator visitation rates, and seed production of S. nigrescens populations grown in both home sites and foreign sites, where sites varied in honey bee population density. Our results demonstrated that the floral traits reflected those of their original population, regardless of their current location. However, seed production varied with both population origin and transplant site. Seed number was positively correlated with flower abundance in the pollinator‐rich sites, but with nectar production in the pollinator‐poor sites. Pollinator visitation rate was also positively correlated with flower number at pollinator‐rich sites, and with nectar volume at pollinator‐poor sites. Overall, the local genotype had higher seed production than nonlocal genotypes in home sites. However, when pollen is hand‐supplemented, plants from pollinator‐rich populations had higher seed production than plants from pollinator‐poor populations, regardless of whether they were transplanted to pollinator‐rich or ‐poor sites. These results suggest that the plant genotypic differences primarily drive variation in pollinator attraction, and this ultimately drives variation in seed: ovule ratio. Thus, our results suggest that flowering plant species use different reproductive strategies to respond to high or low pollinator densities.     

Reciprocal transplants demonstrate strong adaptive differentiation of the model organism Arabidopsis thaliana in its native range

To quantify adaptive differentiation in the model plant Arabidopsis thaliana, we conducted reciprocal transplant experiments for five years between two European populations, one near the northern edge of the native range (Sweden) and one near the southern edge (Italy). We planted seeds (years 1-3) and seedlings (years 4-5), and estimated fitness as the number of fruits produced per seed or seedling planted. In eight of the 10 possible site × year comparisons, the fitness of the local population was significantly higher than that of the nonlocal population (3.1-22.2 times higher at the southern site, and 1.7-3.6 times higher at the northern site); in the remaining two comparisons no significant difference was recorded. At both sites, the local genotype had higher survival than the nonlocal genotype, and at the Italian site, the local genotype also had higher fecundity. Across years, the relative survival of the Italian genotype at the northern site decreased with decreasing winter soil temperature. The results provide evidence of strong adaptive differentiation between natural populations of A. thaliana and indicate that differences in tolerance to freezing contributed to fitness variation at the northern site. In ongoing work, we explore the functional and genetic basis of this adaptive differentiation.     

Local climate and cultivation,but not ploidy,predict functional trait variation in <Emphasis Type="Italic">Bouteloua gracilis</Emphasis> (Poaceae)

Efforts to improve the diversity of seed resources for important restoration species has become a high priority for land managers in many parts of the world. Relationships between functional trait values and the environment from which seed sources are collected can provide important insights into patterns of local adaptation and guidelines for seed transfer. However, little is known about which functional traits exhibit genetic differentiation across populations of restoration species and thus may contribute to local adaptation. Here, we report the results of a common garden experiment aimed at assessing genetic (including ploidy level) and environmental regulation of several functional traits among populations of Bouteloua gracilis, a dominant C4 grass and the most highly utilized restoration species across much of the Colorado Plateau. We found that leaf size and specific leaf area (SLA) varied significantly among populations, and were strongly correlated with the source population environment from which seeds were collected. However, variation in ploidy level had no significant effect on functional traits. Leaves of plants grown from commercial seed releases were significantly larger and had lower SLA than those from natural populations, a result that is concordant with the overall relation between climate and these two functional traits. We suggest that the patterns of functional trait variation shown here may extend to other grass species in the western USA, and may serve as useful proxies for more extensive genecology research. Furthermore, we argue that care should be taken to develop commercial seed lines with functional trait values that match those of natural populations occupying climates similar to target restoration sites.     

Differentiation and adaptation in <Emphasis Type="Italic">Brassica nigra</Emphasis> populations: interactions with related herbivores

Local adaptation and population differentiation of plants are well documented, but studies on interactions with natural enemies are rare. In particular, evidence for plant adaptation to the local biotic environment, such as herbivores remains poor. We used the black mustard Brassica nigra, an annual species of river valley and coastal habitats to (1) analyse population differentiation in plant traits and herbivory in a common garden experiment, (2) examine home versus away differences in a reciprocal transplant experiment and (3) test whether plants are adapted to local herbivores or vice versa under standard greenhouse conditions. In the common garden experiment, we found significant differentiation in plant traits, leaf damage and herbivore number among seven populations of B. nigra from France and Germany (distance 15–1,000 km). Differences were particularly strong among coastal and river valley populations and did not necessarily increase with geographical distance. A herbivore removal treatment did not change population differentiation when compared with the control allowing natural colonisation. The reciprocal transplant experiment at a scale of 15–30 km did not reveal local plant adaptation, whilst one dominant herbivore species (Meligethes aeneus) occurred in significantly higher numbers on local plants. A greenhouse experiment combining three aphid (Brevicoryne brassicae) and plant populations of the same provenance indicated herbivore adaptation to their local plants rather than plant adaptation, but overall contrasts between local and non-local combinations were not significant. The results suggest that herbivores may counteract local plant adaptation to other environmental factors. Our study has important implications for plant translocations in ecological restoration projects.     

Local adaptation in European populations of Arabidopsis lyrata (Brassicaceae)

We studied local adaptation to contrasting environments using an organism that is emerging as a model for evolutionary plant biology-the outcrossing, perennial herb Arabidopsis lyrata subsp. petraea (Brassicaceae). With reciprocal transplant experiments, we found variation in cumulative fitness, indicating adaptive differentiation among populations. Nonlocal populations did not have significantly higher fitness than the local population. Experimental sites were located in Norway (alpine), Sweden (coastal), and Germany (continental). At all sites after one year, the local population had higher cumulative fitness, as quantified by survival combined with rosette area, than at least one of the nonlocal populations. At the Norwegian site, measurements were done for two additional years, and fitness differences persisted. The fitness components that contributed most to differences in cumulative fitness varied among sites. Relatively small rosette area combined with a large number of inflorescences produced by German plants may reflect differentiation in life history. The results of the current study demonstrate adaptive population differentiation in A. lyrata along a climatic gradient in Europe. The studied populations harbor considerable variation in several characters contributing to adaptive population differentiation. The wealth of genetic information available makes A. lyrata a highly attractive system also for examining the functional and genetic basis of local adaptation in plants.     

Local Adaptation and the Effects of Grazing on the Performance of Nassella pulchra: Implications for Seed Sourcing in Restoration

The use of local seed sources for revegetation is accepted practice to reduce the potential that propagules will be poorly adapted to site conditions. However, data are often lacking to determine the distance within which seed sources represent local genotypes. Short‐term reciprocal transplant studies represent a class of tools to detect local adaptation of target species. We conducted a reciprocal transplant of Nassella pulchra between two central California locations to test for adaptation to local environmental conditions over a 3‐year period. Experimental plots at one location were split between grazed and ungrazed sites to evaluate the potential influence of livestock grazing on the detection or magnitude of local adaptation. During each year of the study, evidence of a home‐site advantage depended on the location, traits studied, and population. At the end of the 3‐year study period, however, we detected consistent evidence of a home‐site advantage for seedling biomass among grazed sites at one location and ungrazed plots at the other location. In effect, local adaptation was only apparent in the final year of the study. Short‐term reciprocal transplant studies are an effective tool to guide the selection of seed sources most likely to germinate and to become established at a restoration site, but such studies cannot rule out local adaptation, which may not be immediately detectable.     

Are local plants the best for ecosystem restoration? It depends on how you analyze the data

One of the key questions in ecosystem restoration is the choice of the seed material for restoring plant communities. The most common strategy is to use local seed sources, based on the argument that many plants are locally adapted and thus local seed sources should provide the best restoration success. However, the evidence for local adaptation is inconsistent, and some of these inconsistencies may be due to different experimental approaches that have been used to test for local adaptation. We illustrate how conclusions about local adaptation depend on the experimental design and in particular on the method of data analysis. We used data from a multispecies reciprocal transplant experiment and analyzed them in three different ways: (1) comparing local vs. foreign plants within species and sites, corresponding to tests of the “local is best” paradigm in ecological restoration, (2) comparing sympatric vs. allopatric populations across sites but within species, and (3) comparing sympatric and allopatric populations across multiple species. These approaches reflect different experimental designs: While a local vs. foreign comparison can be done even in small experiments with a single species and site, the other two approaches require a reciprocal transplant experiment with one or multiple species, respectively. The three different analyses led to contrasting results. While the local/foreign approach indicated lack of local adaptation or even maladaptation, the more general sympatric/allopatric approach rather suggested local adaptation, and the most general cross‐species sympatric/allopatric test provided significant evidence for local adaptation. The analyses demonstrate how the design of experiments and methods of data analysis impact conclusions on the presence or absence of local adaptation. While small‐scale, single‐species experiments may be useful for identifying the appropriate seed material for a specific restoration project, general patterns can only be detected in reciprocal transplant experiments with multiple species and sites.     

Sources of variation in growth, form, and survival in dwarf and normal-stature pitch pines (Pinus rigida, Pinaceae) in long-term transplant experiments

Determining the relative contributions of genetic and environmental factors to phenotypic variation is critical for understanding the evolutionary ecology of plant species, but few studies have examined the sources of phenotypic differentiation between nearby populations of woody plants. We conducted reciprocal transplant experiments to examine sources of variation in growth rate, form, survival, and maturation in a globally rare dwarf population of pitch pine (Pinus rigida) and in surrounding populations of normal-stature pitch pines on Long Island, New York. Transplants were monitored over a 6-yr period. The influence of seedling origin on height, growth rate, survival, and form (single-stemmed vs. multi-stemmed growth habit) was much smaller than the effect of transplanting location. Both planting site and seed origin were important factors in determining time to reproduction; seedlings originating from dwarf populations and seedlings planted at the normal-stature site reproduced earliest. These results suggest that many of the differences between dwarf and normal-stature pitch pines may be due more to plastic responses to environmental factors than to genetic differentiation among populations. Therefore, preservation of the dwarf pine habitat is essential for preserving dwarf pine communities; the dwarf pines cannot be preserved ex situ.     

Phenotypic plasticity and local adaptation favor range expansion of a Neotropical palm

One of the most intriguing questions in plant ecology is which evolutionary strategy allows widely distributed species to increase their ecological range and grow in changing environmental conditions. Phenotypic plasticity and local adaptations are major processes governing species range margins, but little is known about their relative contribution for tree species distribution in tropical forest regions. We investigated the relative role of phenotypic plasticity and local adaptation in the ecological distribution of the widespread palm Euterpe edulis in the Brazilian Atlantic Forest. Genetic sampling and experiments were performed in old‐growth remnants of two forest types with higher (Seasonal Semideciduous Forests vs. Submontane Rainforest) and lower biogeographic association and environmental similarities (Submontane Rainforest vs. Restinga Forest). We first assessed the molecular genetic differentiation among populations, focusing on the group of loci potentially under selection in each forest, using single‐nucleotide polymorphism (SNPs) outliers. Further, we looked for potential adaptive divergence among populations in a common garden experiment and in reciprocal transplants for two plant development phases: seedling establishment and sapling growth. Analysis with outlier loci indicated that all individuals from the Semideciduous Forest formed a single group, while another group was formed by overlapping individuals from Submontane Rainforest and Restinga Forest. Molecular differentiation was corroborated by reciprocal transplants, which yielded strong evidence of local adaptations for seedling establishment in the biogeographically divergent Rainforest and Semideciduous Forest, but not for Restinga Forest and Submontane Rainforest. Phenotypic plasticity for palm seedling establishment favors range expansion to biogeographically related or recently colonized forest types, while persistence in the newly colonized ecosystem may be favored by local adaptations if climatic conditions diverge over time, reducing gene flow between populations. SNPs obtained by next‐generation sequencing can help exploring adaptive genetic variation in tropical trees, which impose several challenges to the use of reciprocal transplants.     

Testing the Home‐Site Advantage in Forest Trees on Disturbed and Undisturbed Sites

Restoration of plant populations is often undertaken using seed or plants from local sources because it is assumed they will be best adapted to the prevailing conditions. However, the effect of site disturbance on local adaptation has rarely been examined. We assessed local adaptation in three southwestern Australian forest tree species (Eucalyptus marginata, Corymbia calophylla, and Allocasuarina fraseriana) using reciprocal transplant trials at disturbed and undisturbed sites. Performance of plants within the trials was assessed over 2 years. Planting location accounted for the majority of the variation in most measures of performance, although significant variation of percent emergence among source populations was also detected. In all species, percent emergence and survival of plants sourced from Darling Range populations was significantly higher than that of plants from the Swan Coastal Plain, regions of contrasting edaphic and climatic environment. Survival of E. marginata over the first 18 months and emergence of C. calophylla were both higher in local plants, providing at least weak evidence for local adaptation. Where a local advantage was observed, the relative performance of local and nonlocal seed did not vary among disturbed and undisturbed sites. Evidence for enhanced establishment from local seed in at least one species leads us to recommend that where sufficient high‐quality seed supplies exist locally, these should be used in restoration. We also recommend longer‐term studies to include the possibility of local adaptation becoming evident at later life history stages.     

Reintroduction of Castilleja levisecta: Effects of Ecological Similarity,Source Population Genetics,and Habitat Quality

A suite of ecological and genetic factors are likely to contribute to reintroduction performance. Potential factors include the ecological similarity between seed source and introduction site, population size and genetic diversity of seed sources, and the habitat quality of the introduction site. We conducted common garden experiments with golden paintbrush (Castilleja levisecta), an endangered species from the Pacific Northwest, U.S.A., in order to test hypotheses about reintroduction performance and to provide management recommendations. Ten common gardens, each composed of C. levisecta individuals grown from seed from six of the remaining populations, were planted into field conditions and monitored during two growing seasons. Plant community characteristics were important predictors of observed variation in C. levisecta performance. Exotic species‐cover at common garden sites was associated with a reduction in performance of first‐year C. levisecta transplants, while survival to the second growing season increased with increasing similarity in plant functional groups between source and common garden sites. Although measures of genetic diversity, population size, and geographic distance are often used to make conservation decisions during species recovery, here they were poor predictors of C. levisecta performance and establishment. We recommend choosing material for reintroduction from ecologically similar habitats, rather than those most proximate geographically, and selecting recovery sites with low exotic species abundance.     

Assessing the effect of genetic diversity on the early establishment of the threatened seagrass Posidonia australis using a reciprocal‐transplant experiment

Two common goals for restoration are rapid plant establishment and long‐term plant persistence. The success of transplanted populations may be jeopardized if the donor transplants are not genetically diverse, and/or poorly matched to their new environment. Here, we test the effects of local adaptation and plot‐level genetic diversity on the early establishment phase of a threatened seagrass species, Posidonia australis, by performing a reciprocal transplant experiment across two genetically and geographically distinct populations in southeastern Australia. Posidonia australis is a long‐lived, slow‐growing species that has no seed bank, and the successful transplantation of live shoots and seedlings is the only available restoration method. Our results show a strong effect of local adaptation and genetic diversity on P. australis survivorship and performance over the first 6 months following transplantation. High‐genetic diversity plots displayed higher survival rates and exhibited reduced productivity and increased carbohydrate reserves within the rhizome. This suggests that high‐diversity plots included shoots that were conserving energy stores by actively reducing growth rates during the early stages of transplantation. The lowest diversity plots exhibited high leaf and root productivity and corresponding low carbohydrate reserves. This may be a sign of stress in the low‐diversity transplants, potentially explaining the very low survival rate. We suggest that future restoration efforts source donor transplants from multiple local sources to ensure both local adaptation and sufficient genetic diversity to increase the likelihood of early establishment success.     

PERSISTENCE OF AMBROSIA TRIFIDA POPULATIONS IN OLD FIELDS AND RESPONSES TO SUCCESSIONAL CHANGES

A population of Ambrosia trifida L. (Asteraceae) in an annually ploughed field and an adjacent 15-year old population in an old field were compared to determine how plant responses, genotypic composition, and genetic variability change in populations over successional time. The two populations were originally part of a large contiguous population in an annually ploughed field. When individuals from the two populations were grown from seed in a common garden, they showed several significant differences in characteristics indicating different genotypic compositions in the two populations. Individuals from the old field population showed earlier emergence, lower leaf mortality, and greater numbers of leaves, biomass, seed production, and reproductive allocation relative to plants from the annually ploughed field. When sown in the field in a reciprocal transplant experiment, individuals from the two populations also differed in patterns of emergence, survivorship, yield, and fecundity. When grown together in a pairwise competition experiment, individuals from the old field population showed competitive superiority with respect to growth and seed production. This genetic differentiation between populations of different successional ages may be explained by natural selection imposed by the changing environment over successional time. However, the history and characteristics of these populations are such that founder effects may also be important in explaining the differences between them. A comparison of levels of variability in 14 different characters of individuals of the two populations showed no evidence that genetic variability in A. trifida populations declined over successional time.     

Native Consumers and Seed Limitation Constrain the Restoration of a Native Perennial Grass in Exotic Habitats

Native consumers and seed limitation may be particularly important in the restoration of native plants where they have been displaced by exotic plants. We used experimental exclosures and seed additions to examine the role of native mammalian consumers and seeding density (500 or 1,000 seeds/m²) in affecting the establishment of a native perennial grass, Purple needlegrass ( Nassella pulchra ), in the grasslands of California. To focus solely on consumers and propagule density, experimental areas were tilled and weeded. Consumers were important determinants of restoration success: averaged across propagule density, consumers reduced N. pulchra seedling recruitment by nearly 30%, reduced seedling height by 44%, reduced plant establishment by 52%, and reduced reproductive tiller length by 43%. Small rodents affected seedling establishment, especially where seeding density was high but did not affect seedling height. Plots accessible by squirrels and rabbits exhibited significantly decreased seedling height and plant establishment, whereas there was no additional impact of allowing large consumers (i.e., deer) access. Despite strong, spatially variable effects of consumers, doubling seed density led to nearly doubled N. pulchra establishment on average. Consumer effects were persistent, shaping N. pulchra abundance in the subsequent growing season and remaining evident over 18 months after the experiment was initiated. Our work suggests that, despite strong consumer effects, seed addition may be a viable strategy for restoration of N. pulchra in invaded areas where it has been displaced by exotic plants, especially when combined with restoration strategies that reduce competition with exotic plants.     

Do seed transfer zones for ecological restoration reflect the spatial genetic variation of the common grassland species Lathyrus pratensis?

A common ecological restoration approach is the reestablishment of vegetation using seed mixtures. To preserve the natural genetic pattern of plant species local seed material should be used. Consequently, seed transfer zones (seed production areas and seed provenance regions) have been delineated for ecological restoration in Germany. Although it is assumed that these transfer zones represent genetic variation, there remains a lack of empirical data. In this study, we analyzed whether seed transfer zones reflect the genetic variation of the common grassland species Lathyrus pratensis. We sampled 706 individuals from 37 populations in Bavaria, Germany and analyzed genetic variation using amplified fragment length polymorphisms. In our study, we observed higher levels of genetic variation and fragment rarity in the southern Bavarian populations compared to northern populations. Our analyses revealed a strong genetic differentiation between southern and northern Bavarian populations delineated along the Danube River. However, seed production areas and seed provenance regions reflected genetic variation of L. pratensis only to a limited degree. Our study illustrates that the level of genetic variation within populations strongly depends on population history. Furthermore, the geomorphological and climatic attributes, which have been used to delineate seed provenance regions, do not reduce gene flow among populations. Seed collections for gene banks and seed production should comprise seeds from populations in southern and northern Bavaria representing the strong genetic variation between both regions, but prioritize southern populations due to higher levels of variation.