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Mechanisms And Mitigation Of Soil Legacies Of Invasive Grasses
Full text linkThe grass-fire cycle can be accurately re-described as the human-grass-fire cycle, with the majority of invasive grass introductions being deliberate, and the majority of ignitions being anthropogenic in nature. With increased fire risk, and altered fire regimes favoring invasives, inhibiting natives, and depressing the resilience of native ecosystems, the stakes for restoring grass-invaded areas are higher than ever. Invasive grasses often grow in monocultures, outcompeting and suppressing other species, but even when removed, an abundance of research has demonstrated evidence of soil legacies that can hinder restoration efforts. Thus, there is a need to identify specific mechanism of soil legacies associated with invasive grasses that limit or inhibit restoration success, in order to translate that knowledge into mitigation strategies that better target these mechanisms. To begin, I gathered studies examining grasses for allelopathic abilities, to see if phylogenetically conserved allelochemicals, including benzoxazinoids, which are mostly Poaceae specific, points to allelopathy as a key soil legacy mechanism that contributes to disproportionate invasive success in the grass family. By narrowing the frame of the landmark allelopathy analysis by Zhang et al. (2020), I found support for the novel weapons hypothesis in invasive grasses; specifically, the allelopathic impact on native recipients, was more negative when the allelopathic species was a non-native grass, compared to when the allelopathic species was a native grass. Additionally, I found support for the phylogenetic distance hypothesis, supporting other research suggesting that allelochemical impacts depend on the phylogenetic distance of the target plant. I did not find support for the biotic resistance hypothesis, specifically that the allelopathic impact when the allelopathic species was a native grass was more negative on a non-native recipient, than a native recipient. Through this analysis, I showed evidence suggesting that land managers ought to consider testing for allelopathy, or considering allelopathy-informed restoration practices, when trying to restore grass-invaded areas. Next, in a field study at Camp Pālehua (Kapolei, O’ahu, Hawai’i) I compared soil characteristics and the soil microbial community between a Megathyrsus maximus invaded area, and an area that was formerly invaded by Megathyrsus maximus but had been restored by community partner Malama Learning Center 18 months prior to the comparison. The two sites shared a long history of grazing, climate and soil characteristics, and slope. While I could not rule out inherent differences between the sites that existed prior to the restoration, I sought to identify differences in soil characteristics and the soil microbial community that could be attributed, at least in part, to the restoration. While the restoration practice at the Malama Learning Center section was relatively successful, the site continued to require frequent hand-weeding, so I was particularly interested in evidence of a soil legacy in the soil microbial community, specifically any “hold-over” or “hold-out” taxa, that may be contributing to on-going re-emergence of grass species in the native ecosystem. I found a genus of fungi (Glomus) and bacteria (Candidatus Udaeobacter) were abundant at both sites and these genera have been identified in the literature as being associated with pastures, suggesting that, in the restoration site, these genera were hold-overs. This suggests that specific members of the soil microbial community could be contributing to on-going, long-lasting soil legacy effects, such that modifying the soil microbial community could mitigate some of these effects. In the third chapter, I conducted a greenhouse plant-soil feedback study, using a whole soil inoculum design, comparing germination, survival, and above/belowground growth in inoculum added soil to control soil. By using inoculum in less the 5% volume (w/w), I was able to isolate for the impact of the soil microbial community while holding soil characteristics and nutrients constant, to test for a soil microbial community mechanism for a soil legacy of an invasive grass (Megathyrsus maximus). In addition, I implemented a moderate drought treatment at 60% pot capacity to test for the impact of drought on any plant-soil feedback, since drought is expected to impact ecosystems in Hawai’i in the future. The native species used to test for feedback from the invasive grass microbial community was the endemic dry forest shrub Chenopodium oahuense. I found evidence that there was positive con-specific feedback (the grass benefited from its own soil microbial community) and negative hetero-specific feedback (negative impacts of the grass soil microbial community on the native), impacting primarily the belowground growth of both species, suggesting that the soil microbial community mediates belowground competition for space and nutrients. In addition, I found an interaction between the presence of the grass soil microbial community and drought that was associated with delayed germination of Chenopodium oahuense, suggesting that a soil legacy effect may contribute to phenological mismatch for native species as climate change progresses. In the fourth chapter, I conducted an experimental restoration at a separate Megathyrsus maximus invaded section of the Camp Pālehua property in Kapolei, O’ahu, Hawai’i using a soil amendment of activated carbon, alone and in combination with a locally sourced biowaste-based biochar fertilizer, to determine whether these amendments might mitigate the soil legacy mechanisms I had previously investigated. Two native species were used: Plumbago zeylanica and Dodonaea viscosa. I found that soil raking alone prior to planting improved the width of Plumbago zeylanica by 1 cm after 1 year. Raking had two effects that could have benefited plant growth: disruption of soil compaction, and suppression of the no-raking indicator fungi Bionectriaceae. In addition, I found that the height of Dodonaea viscosa increased 4 cm with 0.5 kg/m^2 of activated carbon added. Two potential explanations are the neutralization of any present allelochemicals, and the suppression of specific fungi which were indicators of the treatments lacking activated carbon, including Coniophora, which has been found in other studies examining the soil microbiome of restoration projects on former pastures. The hypothesis that after the initial suppression, the activated carbon treatment would create opportunity for the outplants to recruit new members to the soil microbial community, resulting in indicator species for the activated carbon level, was not supported. Overall, I was able to contribute evidence that allelopathic ability and the soil microbial community contribute to the soil legacies of invasive grasses, and in Megathyrsus maximus in Hawai’i, activated carbon can be used to suppress fungi and/or allelopathy to improve outcomes for some native plants, while raking alone can improve outcomes, potentially by disrupt soil compaction suppressing certain fungi. Activated carbon could be used in small scale-projects to create sustaining native ecosystems that can later be used for soil transplants or to provide soil inoculum in larger areas. Additionally, some of the identified fungi suppressed by activated carbon could be tested in isolation, or in different combinations for their impact on native plants.Ph.D
A Biodiversity Informatics Approach To Preventing Invasions: Using A Whole Non-native Flora To Investigate Introduction Pathways And Methods For Invasion Tracking
Full text linkNegative impacts from biological invasions continue to rise as non-native species spread around the globe. As the costs of controlling these species increases significantly after their establishment and spread, invasion biologists acknowledge that strategies to prevent invasions should be a key focus in addressing invasive species problems. However, numerous species may be introduced each year, making it difficult to prioritize would-be invaders among hundreds of other species. Thus, strategies that identify and regulate pathways for species introductions are needed to complement species-specific approaches. Furthermore, methods to track the rate at which new species establish and their fate after arrival are lacking, despite the need to assess risks from future invaders and evaluate the success of prevention strategies. To address these issues, I gathered data on the date of naturalization for the entire naturalized flora of the Hawaiian Islands alongside data on their origins, native climate type, taxonomy and likely reason for introduction (introduction pathway). By comparing rates of naturalization for each introduction pathway with changes in socioeconomic factors, I reveal that Hawaiʻi has received a diversity of plants from all over the world, and that the rate of ornamental plant naturalizations has risen dramatically since the mid-20th century, reflecting Hawaiʻi’s shift to a tourism-based economy from an agricultural one. I also show that, although many naturalized plants may currently exist in Hawaiʻi at lower elevations with warmer climates, a large proportion are native to climates similar to those found at higher elevations. This pattern is significant because Hawaiʻi’s remnant native-dominated ecosystems exist primarily at higher elevations, indicating that preventing non-natives from establishing in native ecosystems is crucial to conservation of native species. Additionally, the rate of spread between islands has increased since the mid-20th century, highlighting the need to prevent inter-island spread. To explore the pitfalls that arise when measuring rates of naturalization over time, I then focused on a relatively neglected factor that can bias analyses: time lags that accrue when processing data after their collection in the field. Using computer simulations and an analysis of a real-world case study of two independently collected datasets for the Hawaiian Islands, I illustrate how time lags interact with common data retrieval strategies to influence the interpretation of invasion trends. By doing so, I reveal that long lags due to insufficient field surveying can create the illusion of a sudden onset or exponential rise in naturalization rates, whereas lags in identification, reporting and compilation result in the deceptive appearance of an invasion slow down. I also show that harvesting data from already-compiled resources published by experts may introduce a temporal sampling bias because such works are sporadically produced, thereby introducing an additional lag between reporting and data compilation. Lastly, I investigate a strategy for tracking species after their arrival by using Hawaiʻi’s naturalized species checklist as a starting point and applying a well-recognized framework that categorizes the phase of a non-native species’ establishment along the introduction–invasion continuum. After finding that data deficiencies prevent hundreds of species from being categorized within the framework, I show that data from the Hawaiʻi-Pacific Weed Risk Assessment can be reappropriated to predict whether a data-deficient species will progress along the continuum. Ultimately, I reveal that this predictive tool is a promising supplement to on-the-ground monitoring, especially when frequent field surveys are not feasible. Although globalization continues to facilitate numerous invasions, our ability to harness data and solve problems using biodiversity informatics is advancing rapidly. Here, I contribute to this progress by uncovering trends useful to policymakers and managers in invader-rich regions, while also offering guidance on how to improve methods used to measure those trends and track invasions.Ph.D
Abiotic And Biotic Factors Associated With Current And Long-term Native And Non-native Plant Cover Across An Invaded Hawaiian Landscape
Full text linkExtended periods of disturbance and the introduction of non-native species pose major threats to native Hawaiian forests, many of which exist today as remnant patches, harboring native plant species that are on the brink of extinction. When native Hawaiian plant species are faced with competition from biogeographically cosmopolitan non-native species they are often at a disadvantage, especially in easily accessible areas and where high resource availability fuels the growth of invasive species, which can displace existing natives. However, relatively few datasets exist which can give insight into the long-term impacts of anthropogenic disturbance and species introductions on indigenous and endemic Hawaiian plant species across the myriad of abiotic site conditions that exist in the Hawaiian Islands. In addition, the importance of plant functional diversity, phylogenetic diversity, and biogeographical diversity for determining native resilience in invaded oceanic island forests has not been well established. To address this gap in knowledge I established fifty 400 m2 forest plots in the Waiʻanae and Koʻolau mountain ranges on Oʻahu, Hawaiʻi, and assessed current native and non-native plant cover trends in relation to measures of diversity and trait-mediated interactions of the constituent species in each plot. Thirty-two of these plots had also been previously surveyed, which allowed for an assessment of trends in endemic, indigenous, and non-native plant cover over time, and how these trends vary across abiotic gradients from dry to wet forest. The results of this study indicate that native Hawaiian forests may not be successfully regenerating and are being invaded by non-natives. Native and non-native plant cover values were determined by their respective diversity measures, as well as competition for light. invasion success was not related to overall trait dissimilarity, but there are likely additional traits which were not measured in this dissertation that influence competitive outcomes and/or niche filling between natives and non-natives. Non-natives exhibited a variety of successional strategies, reflecting the introduction history of tree species into the Hawaiian Islands for forestry purposes, as well as the intentional or accidental introduction histories of other herbaceous and woody species, and the diverse biogeographical origins from which these species arrived. Long-term trends showed that, as non-native plant richness and abundance has increased over time, native species in aggregate have concomitantly declined. However, this was largely the result of the loss of endemic species richness and cover, which were more susceptible than indigenous species to decline in the face of invasion, even where ungulates were excluded. Endemic species were more dependent on site conditions than indigenous species, which increased in overall cover over time, indicating that generalizations about natives as a single group may be misleading. Some of the indigenous species which increased in cover the most were early successional species, and may thus reflect disturbed or degraded conditions, rather than a trend toward recovery of natural native forests. These results suggest that an upscaling of active management efforts is needed to avoid further decline of native species, particularly endemics, and to stymie the tide of forest invasion by non-native species.Ph.D
Effects of soil disturbance on root colonization by arbuscular Mycorrhizal Fungi and growth of native and invasive plants
Full text linkExperiments were conducted to determine the effects of soil disturbance on arbuscular mycorrhizal fungi root colonization and the growth of invasive and native Hawaiian plants, predicting higher AMP dependency in native species than invaders, with consequent decreased root colonization and plant growth with disturbance. Six species were grouped into 3 pairs (1 native: 1 invasive) and plants were grown in disturbed and undisturbed treatments in the greenhouse and field for 4/6 weeks. Root colonization, root length, stem and seedling height, leaf number, shoot and root biomass, and mycorrhizal dependency (MD) were measured. Root colonization was not affected by disturbance. Disturbance hindered growth of Acacia confusa, Acacia koa, Eidens pilosa, and Eidens sandvicensis. Data from only 1 pair (Acacia sp.) showed native plant MD greater than invader MD. The relationship between soil disturbance, root colonization, and plant growth may be species specific, and no native or invasive species trends were detected.M.S
Impact of Alien Slugs on Native Plant Seedlings in a Diverse Mesic Forest, Oʻahu, Hawaiʻi, and a Study of Slug Plant Food Preferences
No full textIntroduced species have the potential to cause serious ecological disruption, particularly on oceanic islands. When introduced species invade natural areas, endemic species may be threatened, especially when the invasive species represent guilds or functional groups that were previously lacking. Hawai‘i has no native slugs, but over a dozen species are now established. Slugs are important seedling predators in their native habitats, and in introduced habitats they can cause major shifts in the abundance some plant species. In order to better investigate slug impacts on native plants in Hawai‘i, I carried out research which 1. identified differences in the acceptability of five native plant species to five alien slug species 2. assessed the effect of slug herbivory on the growth and survival of three native and two alien plant species, and 3. measured changes in seedling regeneration due to slug herbivory. Results from feeding assays indicated a significant difference in palatability among plant species, but no statistical difference in overall feeding preference among slug species. Urera kaalae (Urticaceae) was found to be significantly more palatable than the other four plant species and, thus, is predicted to be more vulnerable to slug herbivory in the field. I tracked the fate of planted seedlings and natural germinants from the seed bank in both slug-excluded and slug-accessible plots in diverse mesic forest in the Wai‘anae Mountains on the island of O‘ahu. Among seedlings that survived to the end of the experiment, there was no significant difference between slug herbivory treatments in growth index measurements. There was little germination from the seed bank, with no statistical difference in total number of seedlings between treatments. However, two of the three native species, Schidea obovata (Caryophyllaceae) and Cyanea superba (Campanulaceae) had significant reductions in survival of 49% and 53%, respectively, in the slug-exposed treatment. Survival of two invasive species, Clidemia hirta (Meslastomataceae) and Psidium cattleianum (Myrtaceae) was not significantly affected by slugs. This study demonstrates that slugs may pose a serious threat to native plant species by reducing their survival and thereby facilitate the success of certain invasive species.M.S
Changes in growth and survival by three co-occurring grass species in response to mycorrhizae, fire, and drought
Full text linkThe goal of this study was to evaluate the effect of controlled burns, drought and the presence of arbuscular mycorrhizal fungi (AMF) on a dry coastal grassland in Hawai'i Volcanoes National Park. Two introduced African grasses, Hyparrhenia rufa thatching grass, and Melinis repens - Natal redtop, along with one indigenous grass Heteropogon contortus - pili grass composed most of the cover at the study sites. The response of the grasses to fire, AMF infection potential of the soil, and in situ seedling AMF infection were monitored in the field for three years from 1997 to 2000 at Keauhou, Ka'aha, and Kealakomo in Hawai'i Volcanoes National Park. A greenhouse experiment compared the competitive ability of the three grasses with or without AMP inoculation or water stress. The population dynamics of the three grasses were modeled based on their responses to fire, AMF infection, competition and water. At low fire intensities Heteropogon and Hyparrhenia had similar high survival rates while Melinis had a low survival rate. At higher fire intensities all species had low survival rates. The fire decreased the AMF infection potential of the soil at Kaaha, but in situ seedlings AMF infection levels remained high and not statically between the burned and unburned Kaaha sites. In the greenhouse portion of this study Heteropogon biomass increased in response to AMF infection while the other two species did not respond positively to infection. These results suggest that AM fungi increase the growth of the native species, thereby decreasing the impact of competition from two co-occurring alien grasses. When population dynamics were modeled to include the effects of fire, drought and AMF, Melinis and Hyparrhenia produced more biomass in the simulations than the native grass Heteropogon. Drought and AMF decreased the difference in biomass production between the species but did not reverse the competitive ranking of the species.Ph.D
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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