Thesis (Ph.D.) - University of Queensland, 2003. / Includes bibliography.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 127-136). Also available on the World Wide Web.

This thesis examines factors limiting understory herb presence and flowering in young second-growth Douglas-fir (Pseudotsuga menziesii) forests on the west side of the Cascade Mountains, Oregon, USA. I studied the belowground effects of canopy trees on understory herbs and shrubs in old-growth forests using trenched plots from which tree roots were excluded. Effects of tree density and stand age were tested by comparing the understory community composition of old-growth stands and pre-commercially thinned and unthinned young second-growth stands. I also examined the effect of conifer basal area on understory herb presence and flowering within one young second-growth watershed. In young stands, I focused on three groups of understory herb species: disturbance-responsive (release), forest generalist and old-growth associated. The effects of root trenching on vegetation and soil moisture were tested in closed-canopy and gap locations in two old-growth Douglas-fir (Pseudotsuga menziesii) forests. Ten years after installation, trenched plots averaged 92% total understory cover while untrenched plots averaged 47% cover. Trenched plots under closed canopies were moister than control plots throughout the growing season; the trenching effect on soil moisture became apparent in the generally wetter gaps only at the end of the growing season. Vegetation responses to trenching were concomitantly larger under closed canopies than in gaps. Stands that had been pre-commercially thinned 20 years earlier exhibited understory composition more similar to old growth than did unthinned stands. Thinned stands exhibited higher frequencies, abundances and density of flowering of old-growth associated herbs than did unthinned stands, but lower than did old-growth stands. Forest generalist and release species showed mixed responses to thinning. I used both general linear models and classification and regression tree models to explore the association of herb species presence and flowering with conifer basal area and abiotic variables. Both modeling approaches yielded similar biological insights. Flowering was more sensitive than presence to current stand basal area. Flowering of old-growth associated and release species was negatively correlated with conifer basal area. Linear models allowed clearer hypothesis tests, while tree-based models had greater explanatory power and provided information about interactions between variables. / Graduation date: 2004

Since the late 1880's western juniper has expanded in range and increased in density in sagebrush-bunchgrass, riparian, and forested plant communities of the Pacific Northwest. Succession to western juniper woodland has been shown to reduce the productivity and diversity of the understory component, result in concentration of soil nutrients beneath juniper canopies, and reduces soil moisture storage. This study assessed understory plant succession, soil nitrogen (N) cycling, litter decomposition, and soil moisture availability following cutting of a western juniper woodland on Steens Mountain, Oregon. Cutting of western juniper reduced below-ground competition for water and N, increasing soil moisture storage and N availability for understory species. Leaf water potentials were less negative, and N concentration and biomass in understory plants were greater in the cut treatment. Understory species responded to improved growth conditions with increased cover, biomass, density, and diversity. In 1993, total understory biomass and canopy cover were 870% and 300% greater, respectively, in the cut treatment than the uncut woodland. Understory succession was dominated by plants present on the site prior to cutting. Results indicated initial that bunchgrass densities of 2 plants/m2 were sufficient for perennial grasses to dominate following juniper cutting. Juniper cutting is an effective method for restoring the understory component in sagebrush rangelands that are currently dominated by western juniper woodland. Nitrogen availability was greatest in cut-interspace locations the first year following treatment and in cut-duff locations in the second year. Nitrification was lowest in cut-slash and woodland-duff locations, areas receiving fresh litter inputs and experiencing lower temperatures than interspace (cut and woodland treatments) and cut-duff locations. Decomposition of juniper litter was two times faster in the cut treatment, however the release of litter N occurred earlier in the woodland. Large inputs of N poor litter from cut juniper slash were hypothesized to have increased microbial demand for N, resulting in immobilization of litter N. Immobilization of litter N may be important in conserving N on sites following cutting. / Graduation date: 1997

Graduation date: 1995

Thesis (M.S.)--Mississippi State University. Department of Forestry. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 244-262). Also available on the World Wide Web.

Orientador: Ricardo Ribeiro Rodrigues / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-22T23:57:55Z (GMT). No. of bitstreams: 1 Zanelli_CarolinaBrandao_M.pdf: 11021724 bytes, checksum: 074f594a75e3131636ec29a9f0cdbc07 (MD5) Previous issue date: 2013 / Resumo: A regeneração consiste no processo de reconstrução e reorganização da composição e estrutura de uma comunidade vegetal, e vem sendo bem estudada em florestas ombrofilas e estacionais sob a ótica da dinâmica de clareiras e da sucessão ecológica. No entanto, a regeneração de espécies lenhosas no cerrado ainda e pouco compreendida, e são poucos os estudos que avaliam conjuntamente o dossel e o sub-bosque em áreas de cerrado. O objetivo deste trabalho foi avaliar a floristica e a fitossociologia da comunidade lenhosa do dossel e do sub-bosque de um cerradão em Assis, SP. O trabalho foi realizado na Estação Ecológica de Assis, em uma parcela permanente de 10,4 ha, parte do "Projeto Parcelas Permanentes" do Programa BIOTA/FAPESP. Essa parcela permanente e subdividida em 256 subparcelas contiguas de 20 m x 20 m, das quais 100 foram sorteadas para amostragem. Para avaliar o dossel, foram considerados os dados já coletados no Projeto Parcelas Permanentes, referentes aos indivíduos lenhosos com perímetro na altura do peito (PAP) ? 15 cm, para as 100 subparcelas sorteadas. Para analisar o sub-bosque, foi delimitado um setor de avaliação de 2 m x 2 m em cada subparcela sorteada, onde foram medidos e identificados todos os indivíduos de espécies lenhosas com altura > 20 cm e PAP < 15 cm. Todas as espécies do dossel e do sub-bosque foram classificadas de acordo com o habitat, com base em estudos regionais de fitossociologia, em categorias não excludentes: floresta (F), quando ha registro da espécie em formações florestais não pertencentes ao cerrado sensu lato; cerradão (C), quando ha registro da espécie em cerradão; e cerrado sensu lato (c), quando ha registro da espécie nas demais fisionomias de cerrado sensu lato. Alem disso, foram calculados os parâmetros fitossociologicos usuais para todas as espécies no dossel e no sub-bosque. Tanto o dossel quanto o sub-bosque do cerradão em Assis foram compostos por espécies intermediarias entre diferentes habitats, a maior parte (46% das espécies no dossel e 36% no sub-bosque) constituída de espécies de cerrado/cerradão, incluindo espécies de ampla distribuição no domínio (como Bowdichia virgilioides, Machaerium acutifolium, Plathymenia reticulata, Pouteria ramiflora, Qualea grandiflora, Roupala montana e Xylopia aromática) e comuns em cerrados da província Meridional (como Eriotheca gracilipes, Eugenia pluriflora, Gochnatia polymorpha, Machaerium brasiliense, Myrcia venulosa e Ocotea corymbosa). Regenerantes das espécies do dossel constituíram a maior parte do sub-bosque do cerradão, tanto em numero de espécies (81% do total, n=60) quanto em valor de importância (221 do total de 300). O cerradão apresentou um conjunto de espécies de sub-bosque composto por arvores de pequeno porte e arbustos heliofitos que também ocorrem nas fisionomias mais abertas de cerrado, incluindo: Lacistema hasslerianum, Miconia albicans, Miconia langsdorffii, Miconia stenostachya, Palicourea marcgravii, Piptocarpha rotundifolia, Psychotria hoffmannseggiana e Psychotria vellosiana. Esse resultado e consistente com as características estruturais do dossel do cerradão, que possibilitam maior entrada de luz ao sub-bosque; e contrasta com o relatado para outras fisionomias florestais, onde as espécies de sub-bosque são tipicamente tolerantes a sombra / Abstract: Regeneration consists on the process of reconstruction and reorganization of the structure and composition of a plant community, and has been intensively studied in ombrophilous and seasonal forests according to the paradigm of gap dynamics and ecological succession. However, regeneration of woody plant species in the cerrado is still poorly understood, and few studies evaluate both the overstory and the understory in cerrado areas. The aim of this study was to investigate the floristics and phytosociology of the woody community of the overstory and understory in a cerradao fragment at Assis, Sao Paulo State, southeastern Brazil. Field work was conducted at Assis Ecological Station, in a 10,4 ha permanent plot, part of the Permanent Plots Project from the BIOTA/FAPESP Program. This plot is divided in 256 contiguous subplots of 20 m x 20 m, of which 100 subplots were randomly selected and analyzed. To study the overstory, we used data collected at the Permanent Plots Project, regarding all woody individuals with perimeter at breast height (PBH) ? 15 cm, for these 100 subplots. To study of the understory, we delimited a sector of 2 m x 2 m within each selected subplot, in which all woody individuals with height > 20 cm and PBH < 15 cm were measured and identified. All overstory and understory species were categorized according to their habitat, based in regional phytosociological studies, into non excluding groups: forest (F), when there is record of the species in forest formations that do not belong to cerrado sensu lato; cerradao (C), when there is record of the species in cerradao; and cerrado sensu lato (c), when there is record of the species in the remaining cerrado sensu lato physiognomies. We also calculated the usual phytosociological parameters for all overstory and understory species. Both the overstory and the understory in the study site were composed of species of intermediate distribution between habitats, the majority (46% of overstory species and 36% of understory species) occurring in cerrado/cerradão, including widely distributed Cerrado species (such as Bowdichia virgilioides, Machaerium acutifolium, Plathymenia reticulata, Pouteria ramiflora, Qualea grandiflora, Roupala montana e Xylopia aromatica) and common southern Cerrado species (such as Eriotheca gracilipes, Eugenia pluriflora, Gochnatia polymorpha, Machaerium brasiliense, Myrcia venulosa e Ocotea corymbosa). Regenerating individuals belonging to overstory species accounted for most of the cerradão understory, both in number of species (81%, n=60) and importance value (221 of the total of 300). At the cerradão, we observed a group of understory species composed of heliophyte and small sized trees and shrubs that also occur in the open cerrado physiognomies, such as: Lacistema hasslerianum, Miconia albicans, Miconia langsdorffii, Miconia stenostachya, Palicourea marcgravii, Piptocarpha rotundifolia, Psychotria hoffmannseggiana e Psychotria vellosiana. This result is consistent with the structural characteristics of the cerradão overstory, which enable light penetration to the understory; and differs from data reported in other forest formations, where understory species are typically shade tolerant / Mestrado / Biologia Vegetal / Mestre em Biologia Vegetal

Invasive species degrade ecosystems by altering natural processes and decreasing the abundance and diversity of native flora. Communities with major fluctuations in resource supply allow invasive species to exploit limiting resources making the community prone to invasion. In the Pacific Northwest, urban forests characterized with limited light and seasonally limited soil moisture are being dominated by nonnative English ivy (Hedera spp). Three observational studies were conducted in the Southern end of Forest Park within the Balch Creek Subwatershed in Portland, Oregon in order to understand 1) how English ivy changes over three growing seasons, 2) how the native understory composition responds to English ivy, 3) if the dominance of English ivy reduces soil moisture to neighboring plants, 4) how English ivy and two co-occurring native herbs (Hydrophyllum tenuipes and Vancouveria hexandra) physiologically respond to seasonal changes in soil moisture. Percent cover of the understory community was collected in both 2010 and 2013 growing seasons in 54 plots in order to understand the change in cover over time. Community response and the relationship with soil moisture was analyzed using percent cover of the understory community and associated environmental variables including soil moisture collected in 128 plots during the 2013 field season. Finally, 15 plots with co-occurring Hedera spp, H. tenuipes and V. hexandra were sampled for stomatal conductance, leaf water potential, and associated environmental variables. Results show ivy cover increases on average 14% between 2010 and 2013 while native understory cover increased on average < 1%. Once ivy forms dense cover over 44% there is a reduction of native richness, diversity and herb cover while also an increase in available soil moisture and deciduous canopy cover. There were disparate impacts to different functional groups and between species. As functional group, the herbaceous community was the most impacted by ivy invasion. The shrubs and fern community had a variable response to ivy invasion. Many of the fern and shrub species least impacted by ivy also had associations with high soil moisture and deciduous canopy cover. Finally, data suggests that ivy does not take advantage of seasonally limiting soil moisture to invade the understory community. This study indicates that English ivy is both efficient at water use and may have the ability to obtain water from distant locations throughout the forest. Once established, ivy has the ability to alter the community composition. Ivy removal and habitat restoration are essential in order to maintain and enhance biodiversity in Forest Park.

Land use practices and exposure to low impact disturbances associated with an urban environment can alter forest structure and function. Past and ongoing research in Forest Park, a large urban forest in Portland, Oregon, suggests that mature mixed Douglas-fir (Psuedotsuga meziesii)-hardwood stands in the more urban end of the park lack a shade-tolerant conifer understory composed of the late successional conifer tree species, such western hemlock (Tsuga heterophylla) and western red-cedar (Thuja plicata). 5-year plot remeasurement data that characterizes productivity and mortality patterns did not show a strong relationship to urban proximity. Plot productivity was generally consistent with values taken from studies of other similarly aged (~100 years old) Douglas-fir /Western Hemlock stands. Mortality was highest in rural plots, and was driven by large windthrow events to canopy trees. Soil organic matter, soil pH, and depth of organic horizon indicated a legacy of soil impact in urban areas most impacted by past intensive logging. The urban mature plot had higher mean soil pH at site (5.87, se: ±0.06) compared to a rural mature, and old growth reference sites located within the park. Although surface organic and A layer soil horizon depth was thinnest at the urban mature site, soil organic matter was not found to be significantly different across sites. Light detection and ranging (LiDAR) data showed that old-growth plots and plots in the middle section of the park had the highest degree of canopy structure as measured by Rumple and standard deviation of point elevation. Measures of stand height showed OG plots and urban plots to have the tallest trees. Rural plots showed a high degree of variability in all LiDAR metrics, showing a wider range of stand height and complexity than urban and middle plots. These results suggest that past land-use and urban proximity affect plot level productivity, soil quality, and above-ground canopy structure in Forest Park. These results clarify how the lack of late-successional tree species might be most linked to differing histories of intensive logging activity within the park. Reduced old-growth legacy features (remnant seed trees, coarse woody debris) in plots with a clear history of aggressive clear-cuts has led to a reduction in regeneration of western hemlock and western red-cedar in the understory.