Tag: Lauren Hallett

Effects of Rangeland Compost Amendments on Nematode Abundance

Presenter: Maya Treder – General Science

Faculty Mentor(s): Ashley Shaw, Lauren Hallett

Session: (In-Person) Oral Panel—Fuel, Fire, Grass and Compost, Poster Presentation

California rangelands are often over-grazed, nutrient-depleted, and subject to variable rainfall. Compost amendments are gaining popularity as a management tool due to their potential for soil carbon sequestration. Despite positive effects on plant growth, little is known about how soil communities respond to these amendments, especially across variable precipitation conditions. Nematodes are excellent indicators of soil community responses as they span every trophic level and are sensitive to changing environments. Here, we examined how amendment treatments (compost, fertilizer, none) affect nematode communities across variable precipitation conditions (drought, irrigation, wet). We hypothesized: 1) amendments increase nematode abundance, where compost has a greater positive effect than fertilizer; 2) nematodes respond positively to elevated soil moisture and negatively to drought; 3) effects of amendment and precipitation are interactive, where compost mitigates drought’s effects on nematodes. As expected, compost increased nematode abundance relative to other amendment treatments. However, overall, nematodes were most abundant under ambient precipitation, contrary to expectations. This was due to the precipitation-amendment interaction. While compost and fertilizer had similar positive effects on nematodes under ambient and irrigation, under drought, fertilizer had a negative while compost had a positive effect on nematode abundance compared to the no amendment treatment.

Exploring Grasshopper Feeding Preferences Due on C:N Ratios Across Varying Soil Nutrient Treatments

Presenter(s): Sofi Forsman — Environmental Studies, Marine Biology

Faculty Mentor(s): Lauren Hallett, Gabriella Altmire

Session: (In-Person) Poster Presentation

Montane grassland systems are a rare yet highly important ecotype in the Cascade Range. Anthropogenic disturbances are destabilizing the relationship between plant species and insect herbivores. The purpose of this study is to understand some of the factors that affect grasshopper feeding preferences. This study took place at Bunchgrass Meadow, part of the H.J. Andrews Experimental Forest. Three blocks containing 8 blocks each with different soil nutrient treatments were present. Leaf damage measurements were collected for grass species Bromus Carinatus and legume species Lupine Oreganus. Leaf damage via grasshopper chewing was observed from each plot and compared to soil treatments, carbon to nitrogen ratios within plant tissues, and plant species. I found that grasshopper feeding preferences were significantly impacted by all three independent variables. The variables tested explained roughly 70% of the variation in the experiment. The results of this study imply that changes in soil nutrient treatment can influence the trophic levels in montane ecosystems, highlighting the importance of management strategies that mitigate anthropogenic impacts.

Resolving conflict between oak conservation and organic hazelnut production

Presenter(s): Calvin Penkauskas

Faculty Mentor(s): Lauren Hallett & Alejandro Brambila

Poster 61

 Session: Sciences

Filbertworm (Cydia laiferreana) is a polyphagous moth that burrows into acorns of Oregon white oak (Quercus garryana) and hazelnuts (Corylus spp.). Filbertworm source populations in remnant oak habitat can lead to cyclical infestation in neighboring hazelnut stands. This makes these remaining oak stands, which are mostly on private agricultural land, a potential liability to hazelnut production in Oregon – which accounts for over 90 percent of the US production. Oregon white oak habitat is one of the most reduced habitats in Oregon and is of conservational concern. I’m testing a novel way to mitigate hazelnut filbertworm infestation through pig grazing in oak woodland and organic hazelnut understories. Removal of infested nuts interrupts the developmental stage in the filbertworm life cycle. I hypothesize that controlled grazing will reduce filbertworm populations, nut infestation rates, and herbaceous cover. During Spring and Summer of 2018 I conducted baseline filbertworm inventories via pheromone-lured sticky traps in the canopy and ground-based emergence traps in oak woodland and organic hazelnut orchard on My Brothers Farm in Creswell, Oregon. Grazed and ungrazed plots were established in the woodland and orchard. Domestic pigs (Sus domesticus) were rotated through two-acre pastures in late September/early October with four to five days in each. Understory vegetation was sampled along transects in each plot and acorn density/infestation rates were inventoried before and after treatment. Preliminary results display a reduction of infested acorns in the oak woodland and no effect on understory vegetation. Ongoing filbertworm, acorn, and vegetation monitoring will continue through Fall of 2019.

Nitrogen Composition in Native and Invasive Plants in Relation to Ant Mounds in Serpentine Grasslands

Presenter(s): Elizabeth Baach

Faculty Mentor(s): Lauren Hallett & Eliza Hernández

Poster 1

Session: Sciences

The project I will continue to work on addresses the question, ‘is there a significant difference in nitrogen composition of plants on and off ant mounds in a low nutrition environment, serpentine grasslands?’. This research is significant in two ways: First, it furthers previous works that investigate the relationship between subsurface dwelling animals and the nutrient availability for the plants that grow on the mounds they create. While there has been significant research looking at these relationships, there is less on analyzing elemental plant composition as I propose here. Second, my research will be contributing to the academic understanding of ecology by looking at serpentine grasslands in a new way. These serpentine grasslands receive a lot of attention from academic researchers as the soil in the area has low quantities of essential nutrients, phosphorus and nitrogen, and high levels of toxic heavy metals; this specific soil composition only allows specialized plant species to survive. These plants dominated these grasslands, however, recent research has shown that human activity has increased nitrogen deposition, allowing invasives to begin establishing and outcompeting the native flora. The way I will be furthering this well established understanding of these grasslands will be through the examination of nitrogen content of both native and nonnative grasses and forbs that could be gaining nitrogen naturally or through nutrient upwelling caused by ants. Looking at previous research, my experimental design and considering nitrogen deposition, I expect to find that there will be higher nitrogen composition in invasive plants when comparing native to nonnative status plants. I also believe that plants situated on ant mounds will have higher nitrogen composition than those away from the mounds, this because non-native plants have been shown to outcompete native species in high nitrogen conditions and because ants bring up previously unavailable nutrients to plants.

Hogs and Hazelnuts: resolving conflict between oak conservation and organic agriculture

Presenter(s): Calvin Penkauskas—Environmental Science and Biology

Faculty Mentor(s): Alejandro Brambila, Lauren Hallett

Session 2: Oregon Trails

The Oregon hazelnut industry makes up over 99% of domestic production and 4% worldwide . The key economic pest of hazelnuts in the Pacific Northwest is filbertworm and population sinks are located in nearby oak habitat . This is of concern because there is only 5% of oak habitat left in the Willamette Valley, which is mostly on private agricultural land, and oaks are an important keystone species . Here, I present a case study of a novel strategy to reconcile this conflict by using domesticated pigs (hogs) to reduce pest pressure in surrounding native oak habitat . I investigated the use of hogs to glean filbertworm infested acorns from an oak woodland floor, the effects on the mating population, and the subsequent proportion of infested acorns . My results demonstrate that grazing in oak patches can be an effective method to reduce filbertworm pest populations . While hog silvopasture has potential to be an effective biological pest control method, this practice will only be implemented widely if hazelnut farmers are receptive to the benefits it can provide . Furthermore, in addition to supporting diverse and sustainable farm operations, silvopasturing hogs in oak patches can benefit oak conservation goals by converting them from a landowner’s liability into an asset . Since this novel pest management approach seeks to regionally benefit both environmental concerns and farmers, this example provides a model for similar challenges and conflicts where agricultural and wildlands interact in the same landscape .

Population Dynamics in Endemic Serpentine Grassland Plant Communities Amid Anthropogenic Environmental Change

Presenter(s): Michaela Fishback—Environmental Science

Faculty Mentor(s): Eliza Hernández, Lauren Hallett

Session 6: The Earth, Sky & Everything In Between

Rising rates of nitrogen deposition are threatening the stability of the serpentine grassland ecosystem around the California Bay Area by changing the soil to be a more accessible habitat for invasive nonnative species . The recent increase in nitrogen is largely attributed to air pollution from automotive traffic throughout the region . This area hosts 10% of California’s endemic species in only 1% of the state’s land, making it a critical area for ecological conservation efforts . The plant species native to this area have persisted by inhabiting the characteristically low-resource soil of the serpentine grasslands, giving them competitive advantage over invasive species that require higher resource levels . To study the variation in reproductive success of these plants under different environmental constraints typical of polluted serpentine grasslands, I worked on a greenhouse experiment using a nitrogen-water resource gradient in serpentine-amended soil . Plantago erecta, a native, resource-conservative herb, was sown in competition with Bromus hordeaceus, a nonnative, resource-acquisitive grass . My preliminary findings show that Plantago produces the most seeds when there is no competition from Bromus, low availability of water, and high levels of nitrogen . With low Bromus competition, water availability had less impact on Plantago, while increased nitrogen continued to increase Plantago seed production, suggesting that Plantago may not inhabit a low- nitrogen niche, but potentially a low-water niche . However, with high Bromus competition, Plantago seed production was consistently low regardless of nitrogen and water treatments, suggesting that Bromus competition was too great for the availability of resources to support the population of Plantago .

Arbuscular Mycorrhizal Fungi Colonization Decreases Under High Precipitation and Compost Treatment in Semi-Arid Rangelands

Presenter(s): Justin Day—Biology

Faculty Mentor(s): Ashley Shaw, Lauren Hallett

Session 6: The Earth, Sky & Everything In Between

In California, the application of compost has been proposed as a management strategy to increase forage production and soil carbon sequestration in semi-arid rangelands . However, given this ecosystem’s highly variable climate, having a holistic knowledge of the impacts of composting practices is imperative for sustainable management . Arbuscular mycorrhizal fungi (AMF) are known to confer many benefits to their vascular plants symbiotes—namely through nutrient acquisition— and have been proposed to be important to manage in agricultural systems . The body of knowledge surrounding the influence of compost and rainfall variability on AMF, however, is very limited . The purpose of this study is to explore the AMF-plant relationship with the application of fertilizer or compost across a precipitation gradient . Our results show that AMF colonization under compost treatment alone was not affected, but in combination with high precipitation, AMF colonization was significantly depressed when compared to the ambient precipitation . Additionally, AMF colonization negatively correlates with plant root biomass under the same conditions, suggesting that plant hosts reduce C delivery to AMF under low stress and high resource conditions .