An official website of the United States government
In the introduced range, the successful establishment of an invasive species may be influenced by positive plant-plant interactions. Pre-existing vegetation, particularly conspecific mature trees, can shape the availability and attributes of microsites, thus potentially creating favorable conditions for the establishment of conspecific seedlings through facilitation. Pines are widely introduced in the Southern Hemisphere primarily as forestry plantations; these pines can become invasive, causing detrimental effects on local ecosystems and economies. In the high-elevation grasslands of the Sierras de Córdoba, Central Argentina, pines have begun to invade the native grassland as a result of improper (or lack of) management of pine plantations. During early pine invasion in this semi-arid grassland, we aimed to quantify the influence of adult live pines and on congeneric pine seedling recruitment and survival. For this, 48,000 seeds of Pinus elliottii and P. taeda were sown in three consecutive field trials, under different tree status treatments: live pines, dead pines, and no pines (i.e., open grassland). Seed were sown with and without irrigation and seeded microsites were oriented to the north and south of the live and dead trees. We also considered the hillslope aspect where the sites were located. Our results show that pine seedling recruitment was 57 % higher under live pines compared to dead pines and no pines treatment, but only in the trials that were not irrigated. Microsites south of the live pine trees, more shaded from direct sunlight in the Southern hemisphere, presented 36 % more pine seed germination than those to the north. In terms of topography, hillslope aspects with lower solar incidence (wetter hillslopes) also showed higher pine seedling recruitment. Our results suggest that moisture availability is a dominant factor driving further invasion, and that adult pines may be facilitating the invasion process by creating moister microsites for germination and pine seedling establishment. Thus, the early removal of adult pines is important to consider in the management of pine invasions. They do not only serve as a source of propagules, but also positively affect the establishment of their congeneric seedlings.
more »
« less
Regional Variation in Phragmites australis Reproductive Traits and Seedling Performance in North America
Abstract Seedling recruitment is an important mode of establishment utilized by many invasive plants. In widespread invasive plants, regional variation in the rates of seedling recruitment can contribute to differences in invasion intensity across regions. In this study, we examined regional variation in reproductive traits and seedling performance in a cosmopolitan invasive wetland grass,Phragmites australis. We tested whether nitrogen levels and regions with different histories and intensities of invasion would affect reproductive traits and seedling performance. We sampled invasivePhragmitesinflorescences from 34 populations across three regions in North America: The Northeast (old, most intense invasion), the Midwest (recent, intense invasion), and Southeast (recent, sparse invasion). We hypothesized that NortheastPhragmitespopulations would have the highest reproductive output and seedling performance, and that populations experiencing high nitrogen pollution would have higher reproductive output and seedling performance under high nitrogen conditions. We found that populations in the Northeast had the highest inflorescence mass, as expected. We also found that despite sparse distribution ofPhragmitesin the Southeast, populations from the Southeast displayed a high potential for sexual reproduction. However, increasing watershed-level nitrogen (kg/km2) decreased percent seed germination in Southeastern populations, suggesting that Southeastern populations are sensitive to rising nitrogen levels. While elevated nitrogen improved seedling performance through increased belowground growth in SoutheasternPhragmitesseedlings, elevated nitrogen decreased belowground growth in Midwestern seedlings. These results suggest that the southeastern region of North America may be primed to become an emergent invasion front ofPhragmites, warranting more research into the possible management ofPhragmitesspread in the region.
more »
« less
- PAR ID:
- 10570651
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Wetlands
- Volume:
- 45
- Issue:
- 1
- ISSN:
- 0277-5212
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Periodic fire enhances seedling recruitment for many plant species in historically fire-dependent ecosystems. Fire is expected to promote recruitment by generating environmental conditions that promote seedling emergence and survival. However, fire may also increase flowering and seed production. This makes it difficult to distinguish the effects of microsite conditions from seed availability in observational studies of seedling recruitment. Experiments that manipulate seed inputs across a representative range of conditions are needed to elucidate how seed availability versus microsite conditions influence post-fire seedling recruitment and plant demography. We experimentally manipulated time since fire across 36 patches of remnant tallgrass prairie distributed across 6400 ha in western Minnesota (USA). Over two years, we sowed 11,057Echinacea angustifolia(Asteraceae) seeds across 84 randomly placed transects and tracked 974 experimentally sown seedlings to evaluate how time since fire influenced seedling emergence and survival after experimentally controlling for variation in seed inputs. We also quantified six environmental variables and evaluated whether these covariates were associated with seedling emergence and survival. Fire influenced both seedling emergence and seedling survival. Seedlings emerged from approximately 1 percent of all seeds sown prior to experimental burns. Seeds sown one year after experimental burns emerged at 15 times the rate of seeds sown in the fall before burns, but emergence then declined as time since fire increased. Sowing seeds at high densities reduced rates of seedling emergence but increased overall recruitment. Increases in litter depth were associated with reduced emergence. Meanwhile, the probability that seedlings survived to late summer was greatest when they emerged 0-1 years after fire. The probability of seedling survival decreased with litter depth and increased with the local density of conspecific seedlings. Our findings experimentally support widespread predictions that fire enhances seedling recruitment by generating microsite conditions favorable for seedling emergence and survival – especially by increasing the light available to newly emerged seedlings. Nevertheless, recruitment also increased with seed inputs indicating that both seed availability and microsite conditions influence post-fire recruitment. Explicitly discriminating between seed-limitation and microsite-limitation is critical for understanding the demographic processes that influence plant population dynamics in historically fire-dependent ecosystems.more » « less
-
Abstract Background and Aims In dryland ecosystems, conifer species are threatened by more frequent and severe droughts, which can push species beyond their physiological limits. Adequate seedling establishment will be critical for future resilience to global change. We used a common garden glasshouse experiment to determine how seedling functional trait expression and plasticity varied among seed sources in response to a gradient of water availability, focusing on a foundational dryland tree species of the western USA, Pinus monophylla. We hypothesized that the expression of growth-related seedling traits would show patterns consistent with local adaptation, given clinal variation among seed source environments. Methods We collected P. monophylla seeds from 23 sites distributed across rangewide gradients of aridity and seasonal moisture availability. A total of 3320 seedlings were propagated with four watering treatments representing progressively decreasing water availability. Above- and below-ground growth-related traits of first-year seedlings were measured. Trait values and trait plasticity, here representing the degree of variation among watering treatments, were modelled as a function of watering treatment and environmental conditions at the seed source locations (i.e. water availability, precipitation seasonality). Key Results We found that, under all treatments, seedlings from more arid climates had larger above- and below-ground biomass compared to seedlings from sites experiencing lower growing-season water limitation, even after accounting for differences in seed size. Additionally, trait plasticity in response to watering treatments was greatest for seedlings from summer-wet sites that experience periodic monsoonal rain events. Conclusions Our results show that P. monophylla seedlings respond to drought through plasticity in multiple traits, but variation in trait responses suggests that different populations are likely to respond uniquely to changes in local climate. Such trait diversity will probably influence the potential for future seedling recruitment in woodlands that are projected to experience extensive drought-related tree mortality.more » « less
-
ABSTRACT Invasive species with native ranges spanning strong environmental gradients are well suited for examining the roles of selection and population history in rapid adaptation to new habitats, providing insight into potential evolutionary responses to climate change. The Atlantic oyster drill (Urosalpinx cinerea) is a marine snail whose native range spans the strongest coastal latitudinal temperature gradient in the world, with invasive populations established on the US Pacific coast. Here, we leverage this system using genome‐wide SNPs and environmental data to examine invasion history and identify genotype–environment associations indicative of local adaptation across the native range, and then assess evidence for allelic frequency shifts that would signal rapid adaptation within invasive populations. We demonstrate strong genetic structuring among native regions which aligns with life history expectations, identifying southern New England as the source of invasive populations. Then, we identify putatively thermally adaptive loci across the native range but find no evidence of allele frequency shifts in invasive populations that suggest rapid adaptation to new environments. Our results indicate that while these loci may underpin local thermal adaptation in their native range, selection is relaxed in invasive populations, perhaps due to complex polygenic architecture underlying thermal traits and/or standing capacity for phenotypic plasticity. Given the prolific invasion ofUrosalpinx, our study suggests population success in new environments is influenced by factors other than selection on standing genetic variation that underlies local adaptation in the native range and highlights the importance of considering population history and environmental selection pressures when evaluating adaptive capacity.more » « less
-
Abstract Global warming has been shifting climatic envelopes of many tree species to higher latitudes and elevations across the globe; however, unsuitable soil biota may inhibit tree migrations into these areas of suitable climate. Specifically, the role of mycorrhizal fungi in facilitating tree seedling establishment beyond natural species range limits has not been fully explored within forest ecosystems. We used three experiments to isolate and quantify the effects of mycorrhizal colonization and common mycorrhizal networks (CMN) on tree seedling survival and growth across (within and beyond) the elevational ranges of two dominant tree species in northeastern North America, which were associated with either arbuscular mycorrhiza (AMF,Acer saccharum) or ectomycorrhiza (EMF,Fagus grandifolia). In order to quantify the influence of mycorrhiza on seedling establishment independent of soil chemistry and climate, we grew seedlings in soils from within and beyond our study species ranges in a greenhouse experiment (GE) as well as in the field using a soil translocation experiment (STE) and another field experiment manipulating seedling connections to potential CMNs (CMNE). Root length colonized, seedling survival and growth, foliar nutrients, and the presence of potential root pathogens were examined as metrics influencing plant performance across species' ranges. Mycorrhizal inoculum from within species ranges, but not from outside, increased seedling survival and growth in a greenhouse setting; however, only seedling survival, and not growth, was significantly improved in field studies. Sustained potential connectivity to AMF networks increased seedling survival across the entire elevational range ofA. saccharum. Although seedlings disconnected from a potential CMN did not suffer decreased foliar nutrient levels compared with connected seedlings, disconnected AM seedlings, but not EM seedlings, had significantly higher aluminum concentrations and more potential pathogens present. Our results indicate that mycorrhizal fungi may facilitate tree seedling establishment beyond species range boundaries in this forested ecosystem and that the magnitude of this effect is modulated by the dominant mycorrhizal type present (i.e., AM vs. EM). Thus, despite changing climate conditions beyond species ranges, a lack of suitable mutualists can still limit successful seedling establishment and stall adaptive climate‐induced shifts in tree species distributions.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1007/s13157-025-01900-4
