Seed and seedling traits have strong impacts on establishment of a perennial bunchgrass in invaded semi‐arid systems

Fast grassland recovery from viable propagules after reintroducing traditional mowing management on a steep slope

Semi-natural grasslands on steep slopes often show high plant species diversity. These grasslands were traditionally maintained through mowing and/or grazing. The traditional management practices help to maintain species diversity, whereas land abandonment reduces diversity by increasing competition from dominant species and reducing seedling recruitment. The reintroduction of management can reverse species diversity declines, but suitable grassland restoration programs are scarce in Japan. To study the effect of short-term abandonment on seedling ecology, we monitored the vegetation of a Susogari grassland that had been abandoned for 3 years; the grassland occupies a steep slope (ca. 50°) on a hillside above paddy fields, and was traditionally mown. We monitored the vegetation before abandonment, in the 3rd year of abandonment, and in the 1st and 2nd years after restoration of mowing management. Emergence and survival of seedlings was monitored for 18 months after reintroduction of management. We monitored 1,183 seedlings of grassland species and non-target annuals in ten 1-m2 plots. After mowing was reintroduced, most grassland species reappeared or increased in the first and second years. Few seedlings of perennial plants and no seedlings of annuals flowered. An exotic species, Solidago altissima, had a lower survival rate (10%) than grassland species (>30%), and all but two grassland species survived over the 18-month period. Although vegetation composition was not fully recovered, our findings suggest that a steep slope acts as a strong filter that inhibits the establishment of non-target species while enhancing persistence of target grassland species.

Reforestation of high elevation pines: Direct seeding success depends on seed source and sowing environment

Forest persistence in regions impacted by increasing water and temperature stress will depend upon species' ability to either rapidly adjust to novel conditions or migrate to track ecological niches. Predicted, rapid climate change is likely to outpace the adaptive and migratory capacity of long-lived isolated tree species, and reforestation may be critical to species' persistence. Facilitating persistence both within and beyond a species' range requires identification of seed lots best adapted to the current and future conditions predicted with rapid climate change. We evaluate variation in emergent seedling performance that leads to differential survival among species and populations for three high elevation five-needle pines. We paired a fully reciprocal field common garden experiment with a greenhouse common garden study to (1) quantify variation in seedling emergence and functional traits, (2) ask how functional traits affect performance under different establishment conditions, and (3) evaluate whether trait and performance variation demonstrates local adaptation and plasticity. Among study species-limber, Great Basin bristlecone, and whitebark pines-we found divergence in emergence and functional traits, though soil moisture was the strongest driver of seedling emergence and abundance across all species. Generalist limber pine had a clear emergence advantage as well as traits associated with drought adaptation, while edaphic specialist bristlecone pine was characterized by low emergence yet high early survival once established. Despite evidence for edaphic specialization, soil characteristics alone did not explain bristlecone success. Across species, trait-environment relationships provided some evidence for local adaptation in drought-adapted traits, but we found no evidence of local adaptation in emergence or survival at this early life stage. For managers looking to promote persistence, sourcing seed from drier environments is likely to impart greater drought resistance into reforestation efforts through strategies such as greater root investment, increasing the probability of early seedling survival. This research demonstrates, through a rigorous reciprocal transplant experimental design, that it may be possible to select climate- and soil-appropriate seed sources for reforestation. However, planting success will ultimately rely on a suitable establishment environment, requiring careful consideration of interannual climate variability for management interventions in these climate and disturbance-impacted tree species.

Local adaptation of seed and seedling traits along a natural aridity gradient may both predict and constrain adaptive responses to climate change

PREMISE

Variation in seed and seedling traits underlies how plants interact with their environment during establishment, a crucial life history stage. We quantified genetic-based variation in seed and seedling traits in populations of the annual plant Plantago patagonica across a natural aridity gradient, leveraging natural intraspecific variation to predict how populations might evolve in response to increasing aridity associated with climate change in the Southwestern U.S.

METHODS

We quantified seed size, seed size variation, germination timing, and specific leaf area in a greenhouse common garden, and related these traits to the climates of source populations. We then conducted a terminal drought experiment to determine which traits were most predictive of survival under early-season drought.

RESULTS

All traits showed evidence of clinal variation-seed size decreased, germination timing accelerated, and specific leaf area increased with increasing aridity. Populations with more variable historical precipitation regimes showed greater variation in seed size, suggestive of past selection shaping a diversified bet-hedging strategy mediated by seed size. Seedling height, achieved via larger seeds or earlier germination, was a significant predictor of survival under drought.

CONCLUSIONS

We documented substantial interspecific trait variation as well as clinal variation in several important seed and seedling traits, yet these slopes were often opposite to predictions for how individual traits might confer drought tolerance. This work shows that plant populations may adapt to increasing aridity via correlated trait responses associated with alternative life history strategies, but that trade-offs might constrain adaptive responses in individual traits.

Phenotypes and environment predict seedling survival for seven co‐occurring Great Basin plant taxa growing with invasive grass

Trait–environment correlations can arise from local adaptation and can identify genetically and environmentally appropriate seeds for restoration projects. However, anthropogenic changes can disrupt the relationships between traits and fitness. Finding the best seed sources for restoration may rely on describing plant traits adaptive in disturbed and invaded environments, recognizing that while traits may differ among species and functional groups, there may be similarities in the strategies that increase seedling establishment. Focusing on three grass genera, two shrub species, and two forb genera, we collected seeds of all taxa from 16 common sites in the sagebrush steppe of the western United States. We measured seed and seedling characteristics, including seed size, emergence timing, and root and shoot traits, and compiled a suite of environmental variables for each collection site. We described trait–environment associations and asked how traits or environment of origin were associated with seedling survival in invaded gardens. Sampling seven taxa from the same sites allowed us to ask how trait–environment–performance associations differ among taxa and whether natural selection favors similar traits across multiple taxa and functional groups. All taxa showed trait–environment associations consistent with local adaptation, and both environment of origin and phenotypes predicted survival in competitive restoration settings, with some commonalities among taxa. Notably, rapid emergence and larger seeds increased survival for multiple taxa. Environmental factors at collection sites, including lower slopes (especially for grasses), greater mean annual temperatures (especially for shrubs and forbs), and greater precipitation seasonality were frequently associated with increased survival. We noted one collection site with high seedling survival across all seven taxa, suggesting that conditions within some sites may result in selection for traits that increase establishment for multiple species. Thus, choosing native plant sources with the most adaptive traits, along with matching climates, will likely improve the restoration of invaded communities.

Living with exotic annual grasses in the sagebrush ecosystem

Exotic annual grasses dominate millions of hectares and increase fire frequency in the sagebrush ecosystem of North America. This devastating invasion is so costly and challenging to revegetate with perennial vegetation that restoration efforts need to be prioritized and strategically implemented. Management needs to break the annual grass-fire cycle and prevent invasion of new areas, while research is needed to improve restoration success. Under current land management and climate regimes, extensive areas will remain annual grasslands, because of their expansiveness and the low probability of transition to perennial dominance. We propose referring to these communities as Intermountain West Annual Grasslands, recognizing that they are a stable state and require different management goals and objectives than perennial-dominated systems. We need to learn to live with annual grasslands, reducing their costs and increasing benefits derived from them, at the same time maintaining landscape-level plant diversity that could allow transition to perennial dominance under future scenarios. To accomplish this task, we propose a framework and research to improve our ability to live with exotic annual grasses in the sagebrush biome.

Evaluating the fitness effects of seed size and maternal tree size on Polylepis tomentella (Rosaceae) seed germination and seedling performance

In vascular plants, larger seeds are generally associated with higher germination potential, healthier seedlings and overall higher rates of survivorship. How this relationship holds or what other physiological tradeoffs evolved in plants adapted to high-altitude environments, such as the tropical and subtropical highland Polylepis tree, remain unclear. In this study, we evaluated the relationship between seed mass and seedling performance by testing the reserve effect, the metabolic effect, and the seedling-size effect hypotheses in Polylepis tomentella Weddell (Rosaceae). Since the relationship between fitness and seed size can often depend on maternal plant size, we additionally investigated the association between germination success, seedling performance (survival, relative growth rate (RGR) and height), and size of bearing-seed trees under controlled greenhouse conditions. Our results showed that heavier seeds are more likely to germinate, but we did not find evidence that could support the reserve effect, metabolic effect or seedling-size effect. As seedlings from larger and medium seeds exhibited comparatively similar RGR, survival percentages and final size, maternal plant size was positively associated with improved seed quality and seedling performance. These results demonstrate that seed mass and maternal size during early seedling establishment are critical for Polylepis persistence, demography and conservation.