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- Creator:
- Jones, Maureen Gertrude
- Description:
- In most temperate coniferous forests, the vast majority of vascular plant species richness can be found in the understory layer. While the large-scale conversion of forests to plantations has made it increasingly important to understand how understory flora responds to timber harvesting, there is a surprising paucity of data concerning this topic. Ideally, long-term studies using permanent plots would be used to directly assess post-logging patterns of recovery, both for whole floras and for individual species of conservation interest. Unfortunately, these studies are lacking, and alternative approaches are critical. I used a 420 year forest chronosequence to assess the relationship between stand age, overstory cover and vascular plant understory richness and composition in one watershed in the Siskiyou Mountains of Oregon. The chronosequence consisted of six young managed (age 7-44) and nine older unmanaged (age 90-427) stands. All stands were similar in underlying geology, slope, elevation, and aspect. I found a non-linear relationship between stand age and richness, in which richness showed a steady decline as young stands entered canopy closure, then increased as stands gained older forest attributes such as light gaps and structural diversity. I also found that percent open canopy was correlated with total percent understory cover, richness, diversity and changes in species composition. In general, young stands were characterized by high shrub and graminoid cover and old stands were characterized by an abundant herb layer. In my study area, a large proportion of young managed stands are currently entering canopy closure, a stage characterized by low vascular plant species richness and abundance. I use my results to discuss the potential effects of past and future forest management on vascular plant understory species.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
- Creator:
- McGrew, Karen C.
- Description:
- Russian Peak, at an elevation of 8200 feet, is situated in the Salmon Mountains, a north-south trending range centrally located within the Klamath Region of northwestern California. The Salmon Mountains are drained by the Scott River on the east and by the Salmon River on the west; both rivers course northwesterly to discharge into the Klamath River. The Klamath Region is a geologically old and structurally complex series of ranges which grade into the Coast Ranges on the west and into the Cascade Mountains on the northeast. Russian Peak is located in Klamath National Forest, within Siskiyou County, approximately eight miles westsouthwest of the town of Callahan. Access to the area is via Forest Service roads and·unimproved roads off of State Highway 3, which runs northward out of Weaverville. Selection of Russian Peak and its environs as a study area was based on several factors: the lack of bryological collections in the area (Personal communication, Norris, 1973); the presence of relict conifer species as described by Sawyer and Thornburgh (1971); and the presence of a diverse, largely circumboreal moss population on the Marble Mountains, located approximately fifteen miles to the northwest (Spjut, 1971). The objective of the following study was to identify bryophyte species within the area and to determine if the findings would lend further support to the concept of a refugium or "central" area, as described by Whittaker(l961), within the Klamath Region. Collections were made from around five lakes, including their headwaters and drainages, during the summers of 1973 and 1974. A total of 786 specimens were collected, representing 152 species. Collections were made at elevations between 5500 feet and 7200 feet in the following drainages: 1) Sugar Lake and Sugar Creek, August, 1973; 2) South Sugar Lake, August, 1974 (with D.H. Norris); 3) Bingham Lake, September, 1974 (with D.H. Norris); 4) Russian Lake, September, 1973; 5) Waterdog Lake, Lower Russian Lake and South Russian Creek, September, 1973. Bryophytes were collected along paths, in drainages, and from around the lakes. Effort was made to include special habitats, such as springs, marshes, serpentine outcrops, exposed granite walls, rock crevices, and areas adjacent to perennial snow patches. Each collection was identified, checked with specimens from the cryptogamic collection at Humboldt State University, and verified by D. H. Norris. Voucher specimens are on deposit at the Humboldt State University Herbarium (HSC). Collection numbers preceded by the prefix "N" are those of D. H. Norris; all others are those of the author.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
- Creator:
- Archibald, Wiley Hall
- Description:
- Harbor seals have been listed as a species likely to benefit from new Marine Protected Areas (MPAs) in California as part of the Marine Life Protection Act. Whereas seals may experience direct and indirect effects from these MPAs as a whole, the impacts of individual MPAs remains unclear. To support the analysis of the impacts of one new MPA located in South Humboldt Bay (SHB), California, I conducted two studies to measure the site fidelity of individual harbor seals within SHB and to describe the changes in distribution and abundance of hauled-out seals inside and outside the new MPA there. From June 2011 through May 2012, I used radio telemetry to assess site fidelity of 28 individually tagged seals. Most seals had high fidelity (>75%) for SHB haul-outs, indicating that these seals are present enough to potentially benefit from added protection. However, the use of radio telemetry proved difficult and costly for long-term data collection. Therefore, weekly visual surveys were implemented beginning in July 2012 to track the habitat use of all seals hauled-out in SHB. There were significant seasonal differences in seal abundance (ANOVA, F5 = 4.047, p < 0.01) and groupings (ANOVA, F5 = 10.06, p <0.01), particularly between the winter and the spring seasons. In addition to highlighting key seasons for additional management and monitoring, these surveys proved more successful and sustainable than radio telemetry for monitoring year-round impacts of the new MPA on harbor seals.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
4. Reproductive isolation in five hybridizing species of western gooseberries (Ribes: Grossulariaceae)
- Creator:
- Kalt, Jennifer L.
- Description:
- Five species of western gooseberries (Ribes: Grossulariaceae) hybridize to varying degrees in northwestern California and southwestern Oregon. Pollinator surveys and hand-pollination experiments were conducted to identify reproductive barriers between the species pairs. I found little evidence of isolation due to pollinator behavior, since the five species tended to attract the same pollinators. My attempts to assess the level of post-pollination isolation were hindered by high rates of fruit abortion. Nevertheless, it appears that R. roezlii and R. menziesii are fully interfertile, and that unilateral barriers operate when R. lobbii, which has the longest styles of the set, is the maternal parent in crosses with the other species. Since the level of post-pollination isolation is not correlated with the observed frequency of hybridization in the field, ecological and/or geographical differences may play the most important role in isolating the species.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
- Creator:
- DeSiervo, Melissa H.
- Description:
- Disturbances such as wildfire play a major role in the diversity, structure, and composition of plant communities, however, little is known about the differential impacts of fire across landscapes that vary in characteristics such as soil nutrients and site productivity. Theory predicts that productivity can mediate the impacts of fire for reasons related to broad ecological processes and differential selective forces. For instance, ecosystems with lower site productivity are less limited by space and light and consequently experience less pronounced changes in these resources following a disturbance. Moreover, resource availability related to disturbance and productivity can affect the proportion of plants with competitive versus stress-tolerant life history strategies. In this study, we utilized a model system for testing predictions about productivity and disturbance that included a mixed conifer forest across a gradient of edaphically harsh, ultramafic “serpentine” soils and “non-serpentine” soils in the northern Sierra Nevada (California, USA). We predicted that the magnitude of fire effects on plant diversity from a 2008 wildfire would be positively related to productivity (higher on non-serpentine soils) and that these factors would interact as environmental filters driving post-fire species assemblage. In summer 2013 we established 90 vegetation plots in burned areas and 40 plots outside the fire perimeter as a proxy for pre-fire conditions. We found a unimodal relationship between species diversity and fire severity (peaking at low/moderate severity), and mild evidence post-fire changes were more pronounced on non-serpentine soils. In contrast, we found strong evidence that productivity and fire severity interact as drivers of species composition and functional traits with a higher proportion of resprouting shrubs on non-serpentine soils and, contrary to our prediction, more invaders on serpentine soils. We hypothesize that differences in biomass between serpentine and non-serpentine forests were not substantial enough to elicit a differential diversity response, possibly deriving from a weaker serpentine syndrome in this region that has been previously noted. Our study reveals that differences in productivity can mediate the outcome of disturbances in ways that cannot be detected through standard community diversity metrics, and that consideration of life history trait variation is necessary.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
- Creator:
- Ackerman, James D.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
- Creator:
- Vigil, Katie J.
- Description:
- Spotted fever group (SFG) rickettsiae have been shown to cause many human and animal diseases. SRG rickettsial phylotypes G021 and G022 were recently detected in Ixodes pacificus ticks from Napa and California using quantitative real time polymerase chain reaction (qPCR). Prevalence, genotyping, and geographic distribution of SFG Rickettsia species phylotypes in Ixodes pacificus, Dermacentor occidentalis, and mammalian hosts in Califonia have yet to be investigated. A qPCR outer membrane protein A (ompA) gene assay detected and quantified SFG Rickettsia species phylotypes G022 and G021 in I. pacificus (n=265). Of 265 I. pacificus tested, 10 (3.8%) ticks were positive for phylotype G022, while 265 ticks (100%) had phylotype G021. The prevalence of phylotype G022 did not differ between counties (χ2 = 1.42, Pχ2> 0.05) or vegetation habitat types (χ2 = 2.85, Pχ2>0.05). However, the burden of SFG Rickettsia speecies phylotype G021 differed between collection sites (P<0.05) and vegetative type (P<0.05). Habitat vegetation information of the tick collection sites suggested that the density of Rickettsia species phylotype G021 is linked to a predominantly wooded habitat in which its host may reside (P<0.05). Although genomes of I. pacificus and its associated microflora have not been completely assessed, the elevated density and ubiquitous prevalence of SFG Rickettsia species phylotype G021 strongly suggests that it is a bacterial endosymbiont of I. pacificus. The ompA qPCR assay detected Rickettsia species phylotype G021 in coagulated dog blood (n=3/199), I. pacificus (n=18/265) and D. occidentalis (n=3/8) that were collected off shelter dogs. The ompA gene sequencing and alignment between coagulated dog blood, as well as I. pacificus and D. occidentalis ticks collected off dogs revealed 100% nucleotide sequence identity among all samples. OmpA sequencing and alignment between Rickettsia species phylotype G021, all coagulated dog blood, I.pacificus and D.occidentalis samples revealed a 99% sequence identitiy with 100% amino acid sequence identity. Multi-spacer typing (MST) of the intergenic regions revealed four SFG Rickettsia species genotypes (M1, M2, M3, and M4) for mppA-purC locus, two genotypes (R1 and R2) for RpmE-tRNAfMet locus, and two genotypes (D1 and D2) for DksA-XerC locus. MST concatenation with ompA revealed 7 genotypes (T1, T2, T3, T4, T5, T6, and T7), with genotype T7 sharing 100% sequence identity between coagulated dog blood (n=3/199) and D.occidentlis ticks (n=3/8). This suggests that Rickettsia species from D. occidentalis ticks maybe responsible for transmitting a unique Rickettsia species genotype (not found in I.pacificus) to dogs and should be further investigated. MST sequencing of the three intergenic loci concatenated with ompA revealed multiple genotypes, suggesting subspecies diversity amongst Rickettsia species phylotype G021. Future genome sequencing, isolation in cell culture, and mammalian antibody titers are needed to further classify Rickettsia species phylotypes G021 and G022.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
8. Expansion of an introduced species of cordgrass, Spartina densiflora, in Humboldt Bay, California
- Creator:
- Kittelson, Pamela M.
- Description:
- The dominant plant in Humboldt Bay salt marshes is Spartina densiflora, a species of cordgrass apparently introduced from South America. At several salt marshes and restoration sites around Humboldt Bay, distribution of this plant has increased significantly. I investigated the relative contributions of vegetative tiller production and seed germination to the establishment and expansion of S. densiflora. In salt marsh stands, I compared increases in basal area of plants surrounded by potential competitors and those of areas without competing plant species. Plants growing in bare areas without competitors had significantly higher rates of vegetative expansion (p<0.0001). I measured viable seed production, germination rates, seedling survivorship, and growth of adult plants in six salinity treatments. Approximately 1,977 ± 80 viable seeds are produced per plant (0.25 to 0.5 square meters). The number of germinating seeds was inversely related to increases in salinity. Salinity treatments at 19-35 ppt produced significantly lower germination rates than salinities of 0-18 ppt (p<0.0001). Seedling survivorship was 50% at < 4 ppt and 8-14% at > 11 ppt. Lateral expansion of adult, greenhouse grown plants occurred in all salinity treatments, with modest decreases in the highest salinity treatments (p<0.05). My findings indicate that S. densiflora readily expands in bare areas without competitors primarily by vegetative expansion. Lateral tillers are produced by S. densiflora throughout the year, indicating that plants do not become seasonally dormant. Plants in undisturbed salt marshes expand more slowly, limited by potential competitors such as Salicornia virginica and Distichlis spicata. My results suggest that seed germination and survivorship increase during periods of significant freshwater influence. Although S. densiflora produces prolific amounts of seed, colonization of mature salt marshes may be limited by competitors and high salinities. Colonization of protected open areas is more likely, especially if sediment salinities are substantially decreased. Once established, S. densiflora spreads rapidly. Planting of native species such as Salicornia virginica, Distichlis spicata, or Jaumea carnosa may prevent monospecific stands of S. densiflora from developing. Phenological differences and physiological plasticity probably account for the expansion of S. densiflora in disturbed marshes and restoration sites.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
- Creator:
- Camper, Tamara
- Description:
- Numerous studies have analyzed the effect of habitat fragmentation on plant pollinators and herbivores. These studies describe the decrease in pollinator services and seed set in small and isolated patches due to pollinator preference for large, contiguous patches. However, other studies have shown that small and isolated patches may escape herbivory due to dispersal limitations of many insect herbivores. Sidalcea malachroides (Maple-leaved checkerbloom) is a rare plant with a patchy distribution, which requires insect pollen vectors and experiences severe fruit loss to weevil larvae. To test the effect of patch size and isolation distance on pollen reception and pollen limitation, I measured pollen loads on stigmas and the difference in seed set for open and hand pollinated flowers in plants of various combinations of patch size and isolation. To examine the effect of patch reduction and isolation distance on herbivore damage, I scored the total number of damaged seeds per plant. I used multiple regression to analyze these three dependent variables against patch size, isolation distance and other potentially important variables, and separate GLM analysis to examine the effects of abiotic environmental factors. S. malachroides experiences a reduction in pollen reception and an increase in pollen limitation when it occurs in isolated patches. This effect is especially pronounced in small patches. The most striking result was the lack of pollination in small patches isolated by more than 17 meters. Plants in large patches received more pollen grains, but surprisingly, degree of pollen limitation was not related to patch size. Small patches and isolated patches experience reduced damage to weevil larvae; however the effect was weak in comparison to the effect of pollinator services. Since the distribution of S. malachroides is likely limited by seed production and dispersal, and small, isolated patches do not receive adequate pollinator service, care should be taken to consider patch size and isolation distances when analyzing the status of this plant and the effects of land management activities.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology
- Creator:
- Paget-Seekins, Jade
- Description:
- The genus Ribes displays extensive floral diversity. The pollinator shift model suggests that such diversity is an outcome of species shifting to specialize on new pollinators. To test this model, I surveyed the flower visitors of 14 Ribes species at 44 sites in northern California and southern Oregon. Visits to sympatric species in other genera were also counted at each site. For purposes of analysis, visitors were placed into one of ten functionally equivalent groups. Ribes species were chosen to maximize differences in flower size and form; ten floral traits were measured for each species to characterize these differences. Ordination and correlation approaches were used to compare visitor assemblages, both within and between species, as well as to examine the match between differences in flower morphology and visitor assemblages. I found only weak support for the pollinator shift model. Despite the marked differences between Ribes flowers, most of the 14 species were visited primarily by bees. In general, differences in floral morphology were poor predictors of differences in visitor assemblage, but flower depth and width were both correlated with the ordination of species in visitor space. Most Ribes species are not strong pollination specialists. Visitor assemblages varied as much between sites for individual species as they did between different species. Although shifts between pollinators may account for some of the differences between Ribes flowers, it appears that other factors play a greater role in floral diversification.
- Resource Type:
- Masters Thesis
- Campus Tesim:
- Humboldt
- Department:
- Biology