Graduate Thesis Or Dissertation
 

Relationship of Soil Fungal Communities and Burn Severity to Post-Fire Vegetation Response

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pv63g777x

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  • The effects of fire on above-ground forest systems have been extensively studied. However, research on fire effects on belowground processes is lacking. While the soil microbiome is understood to be vital to conifer growth and regeneration, the complexity of soils means that research on the topic has largely been accomplished on plantation forestry sites and unburned forests. Increases in fire activity increase the urgency to better understand fire’s effects on all aspects of ecosystem function, particularly belowground. Recent work has begun to unravel fire effects on root-zone chemistry; however, this has raised new questions about the effects on below-ground microbiota. Understanding the dynamics of soil in post-fire environments could be vital to post-fire management in forested ecosystems. The study site is the B&B fire complex lands west of Sisters Oregon. The area was affected by a linked pair of wildfires that together burned 90,769 acres (367.33 km2) of Oregon forest during the summer of 2003. Differences in the soil fungal communities were identified across the four burn severity gradients and linkages to vegetation regeneration dynamics and burn severity were identified. Soil samples and vegetation data were collected across four burn severity classes using three vertical strata: overstory trees, seedlings/saplings, and shrub/ground cover. Fungal DNA was extracted from soil samples using Qiagen Soil Pro and amplification and sequencing used EMP high throughput extraction protocol. Sequenced data was filtered through DADA2 ITS Pipeline and compared against the UNITE database. Fungal groups were compared through Multi-dimensional scaling and Indicator Species Analysis (ISA). Differences in species communities across burn gradients were analyzed using Multi-response Permutation Procedure (MRPP) with the n/sum(n) weighting and a Euclidean distance. Overstory vegetation was measured using a basal area prism with BAF 20. A two-meter by two-meter subplot was established on the plot center to quantify seedlings and saplings and a 0.5 by 0.5 square meter microplot centered over the plot center to quantify the percent ground cover of grasses and forbs. Differences in seedling density across the burn severity gradient and comparing unburned and burned sites were analyzed using ANOVA in R 4.2.2. Seedling density was evaluated using a generalized linear model with a negative binomial distribution and a log link utilizing the Compound Poisson Generalized Linear Model Package. High severity plots showed poor stocking success (14%) compared with low (62%) moderate (42%), and unburned (52%) plots. This was indicative of the loss of seed trees, particularly in high-severity sites. Additionally, seedling density was significantly lower in the high-severity sites 250/acre) from the unburned sites (2071/acre). However, seedling densities increased in the low and moderate areas suggesting the retention of seed bank couples with increased available light and moisture. Seedling densities were compounded by the differences found in the fungal communities, particularly the mycorrhizal species. MDS analyses showed similarities between all of the sites except the high severity which showed high dissimilarity. High-severity sites were dominated by saprobic or wood-decaying fungi while the unburned sites had a high population of mycorrhizal species (27%). Rhizopogon sp. (mycorrhizal) were particularly important as they were known for their association with seedlings, attaching to the roots of very young trees. This was particularly important since the species was not found in the high-severity sites, suggesting a strong correlation with seedling success. Strategies for management are discussed including the need for planting, especially in high-severity sites, and the addition of Rhizopogon inoculum to increase reforestation success. Future studies are especially suggested to determine this functional role for Rhizopogon sp. and the associated conifers desired by management.
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