[Truncated abstract] Globally, tropical rainforests are noted for their high biodiversity and key roles in carbon storage and influence on climate. Nevertheless, tropical deforestation in many parts of the world continues at an alarming rate. In Papua New Guinea (PNG), tropical rainforest is relatively well maintained, with about 70 % of the land area still covered by primary forest. However, PNG's native forests are coming under increasing pressure, particularly from selective logging for high quality timber. While the forests of PNG, and more broadly the entire New Guinea Island, are recognised as of high conservation and ecological significance, they remain grossly understudied with little knowledge of key ecosystem processes within lowland forests in particular. Such knowledge is urgently required if the impacts of logging and other land-use change are to be assessed and in order to develop sustainable management systems. This thesis investigated the impacts of logging on diversity and nutrient cycling in a lowland tropical rainforest growing on limestone soils in the area of the Mongi-Busiga Forest Management Agreement (FMA, which is a logging concession area), in northeastern PNG. These forests are on relatively young soils and provide a useful contrast to the majority of tropical forests. The research includes a four-year study of the recovery of diversity and structure after logging, and quantified forest structure, tree species diversity, forest biomass and productivity, and nutrient distribution and cycling. This thesis also examines the ecological sustainability of Eucalyptus deglupta plantations in Wasab, PNG as an alternative resource for timber and biomass energy. The thesis concludes with a discussion of long-term forest recovery and sustainable forest management in north-eastern PNG. Two adjacent one-hectare plots were established in lowland tropical rainforest at Mongi-Busiga FMA. One of these plots was subsequently selectively logged, one year after establishment. Before logging, the two one-hectare plots contained a total of 37 families, 70 genera and 110 tree species that were >5 cm in diameter at breast height. Mean basal area was 42.4 m2 ha-1. Two tree species, Madhuca leucodermis (Sapotaceae) and Pometia pinnata (Sapindaceae) accounted for ~60% of the total basal area. Gymnacranthera paniculata (Myristicaceae) was the most common species and accounted for 13% of individuals. ... This study concludes that the Mongi-Busiga forest has many unusual characteristics for a tropical forest, including relatively low diversity of tree species, high accumulation of P in the biomass, and N limitations, compared to other tropical rainforests. However, those extraordinary characteristics may be explained well by the underlying geology of young, marine-derived limestone. Sustainable management of the lowland tropical forests of PNG should consider the consequences of logging on nutrient cycling processes, with the possible significant removal of P from site with repeated logging, as well as the interactions between N and P in these systems. Establishment of Eucalyptus plantations on previously cleared land also has the potential to meet some of the timber and biomass energy requirements of northern PNG in ecologically sustainable manner.

Graduation date: 2006 / Best scan available. Ink on original is smeared.

Previous studies have shown fine sediment was removed from spawning beds when salmon dug nests and subsequent sediment deposition can re-clog the nests, which reduces intergravel flow and threatens egg survival. In the intensively logged Cascapedia watershed it is not known if there is enough sediment deposition to re-clog salmon nests. Furthermore, Cascapedia spawning beds are relatively silt-rich, whereas, the effect of fine sediment has been studied in rivers with sand-rich substrate. I evaluated if sediment-epositing events reduced intergravel flow and if these events inhibited egg survival. / During the summer and fall 2001, sediment deposition into clean gravel occurred at rates proportional to the length and dose of suspended sediment transporting events. Based on the results of an experimental sensor, sediment deposition reduced intergravel water velocities. Habitat conditions within artificial salmon nests, however, remained above critical levels for egg survival. Eggs survived (81%) until mid-April, at which time they were at the pre-hatched life-stage. The data suggests that in Cascapedia rivers, egg survival is likely only inhibited if the spring-freshet erodes or clogs the salmon nests.

Logging and associated skid trails, haul routes, and roads can have significant impacts on the magnitude and timing of sediments in streams in forested watersheds. Loss of vegetation, soil compaction, use of heavy logging equipment, and alteration of natural hydrologic patterns within the watershed can increase landslide rates, create erosion, and generate fine sediments. Selective logging, also called thinning, is a logging practice that leaves some trees within sale units unharvested. The ecological impacts of thinning on stream ecosystems are not fully understood and need further study. My hypothesis was that macroinvertebrate assemblages would be different in streams in non-reference areas that contain recent selective logging compared to streams in reference areas, and in downstream vs. upstream of selective logging units. I also hypothesized that selective logging and high road densities would be associated with increased instream fine sediments. I sampled water quality parameters and macroinvertebrates in three managed and three reference streams in the Clackamas River Basin during the field season of 2013. Turbidity, temperature, dissolved oxygen, conductivity, total dissolved solids (TDS), suspended sediment concentrations (SSC), and flow were sampled at each stream on four occasions during spring through early fall. Macroinvertebrates were sampled once in late summer or early fall. EPA rapid habitat assessments, canopy cover, pebble counts, embeddedness, and slope were also determined. Water quality parameters and macroinvertebrate indices in reference and non-reference sites were compared using t-tests, Welch's tests, or rank based equivalents. Macroinvertebrate assemblage patterns and associated environmental variables were characterized using non-metric multidimensional scaling (NMDS) ordination plots and envfit overlays. Macroinvertebrates had higher abundance and taxa richness in non-reference streams, and indices suggested poorer water quality in non-reference streams. Non-reference streams had a lower percentage of shredders and a higher portion of gatherer-collectors. Associations between land use, fine sediments, and changes in macroinvertebrate metrics and community assemblages were apparent at the reference vs. non-reference scale. It is likely that macroinvertebrates are responding, at least in part, to past logging and high road densities in non-reference streams. Fewer indications were found that recent logging may be affecting water quality and macroinvertebrates. Pearson's correlation coefficients show that the percent of recent logging upstream of study sites was correlated with several measures of fine sediments, suggesting that recent land use may be affecting sediment levels at the subwatershed scale. Stream temperatures increased from upstream to downstream in non-reference sites. Though no continual stream temperature data were collected in this study, the history of continuing temperature standard exceedances in the area suggest that further investigation of how selective logging may be affecting stream temperature and other water quality parameters in the Clackamas Basin is warranted. No other differences in water quality parameters were found from upstream to downstream, possibly because water quality was sufficiently protected, or because signals from land use impacts may be obscured by a several factors, including upstream confounding factors such as roads and past logging, and natural variability.

No description available.

This dissertation integrates a process-based hydrological investigation with an ongoing paired-catchment study to better understand how forest harvest impacts catchment function at multiple scales. We do this by addressing fundamental questions related to the stocks, flows and transit times of water. Isotope tracers are used within a top-down catchment intercomparison framework to investigate the role of geology in controlling streamwater mean transit time and their scaling relationships with the surrounding landscape. We found that streams draining catchments with permeable bedrock geology at the Drift Creek watershed in the Oregon Coast Range had longer mean transit times than catchments with poorly permeable bedrock at the HJ Andrews Experimental Forest in the Oregon Cascades. We also found that differences in permeability contrasts within the subsurface controlled whether mean transit time scaled with indices of catchment topography (for the poorly permeable bedrock) or with catchment area (for the permeable bedrock). We then investigated the process-reasons for the observed differences in mean transit time ranges and scaling behavior using a detailed, bottom-up approach to characterize subsurface water stores and fluxes. We found that the mean transit times in catchments underlain by permeable bedrock were influenced by multiple subsurface storage pools with different groundwater ages, whereas storage in the poorly permeable catchments was limited to the soil profile and that resulted in quick routing of excess water to the stream at the soil bedrock interface, leading to mean transit times that were closely related to flowpath lengths and gradients. Finally, we examined how and where forest trees interacted with subsurface storage during the growing season using a forest manipulation experiment, where we tested the null hypothesis that near-stream trees alone influenced daily fluctuations in streamflow. We felled trees within this zone for two 2.5 ha basins and combined this with isotopic tracing of tree xylem water to test if water sources utilized by trees actively contributed to summer streamflow. We rejected our null hypotheses and found that diel fluctuations in streamflow were not generated exclusively in the near-stream zone. We were unable to link, isotopically, the water sources trees were utilizing to water that was contributing to streamflow. Our results provide new process-insights to how water is stored, extracted, and discharged from our forested catchments in Western Oregon that will help better explain how forest removal influences streamflow across multiple scales and geological conditions. / Graduation date: 2012

Phytophthora lateralis is the causal agent of cedar root rot, a fatal forest pathogen whose principal host is Chamaecyparis lawsoniana (Port-Orford-cedar), a predominantly riparian-restricted endemic tree species of ecological, economical, and cultural importance to coastal Oregon and California. Local scale distribution of P. lateralis is thought to be associated with timber harvest and road-building disturbances. However, knowledge of the landscape-scale factors that contribute to successful invasions of P. lateralis is also important for effective land management of Port-Orford-cedar. P. lateralis is able to infest in wet conditions via stream networks (zoospore) and dry conditions via road networks (resting spore). This study tested the hypothesis that vehicles spread P. lateralis by relating its distribution to traffic intensive, anthropogenic disturbances (i.e. a road network, timber harvest) over a 31-yr period in a 3,910-km² portion of the Rogue River-Siskiyou National Forest in the Siskiyou Mountains of Oregon. Indices of road disturbance (presence/absence, configuration, length, density, road-stream network connectivity) and timber harvest (presence/absence, area, density, frequency) were related to locations of infested cedar populations from a USFS survey dataset using a geographic information system (GIS). About 40% of 934 7th-field catchments were infested with the pathogen. Total road length of the study site was 5,070 km; maximum road density was 8.2 km/km2 and averaged 1.6 km/km² in roaded catchments (n = 766). Timber activities extracted 17,370 ha (2,338 cutting units) of forest across 509 catchments; 345 catchments were cut ≥ twice. Maximum harvest density was 0.92 km²/km² ([mean] = 0.04). Both road networks and timber harvest patchworks were significantly related to cedar root rot heterogeneity. Chi-squared contingency tables showed that infestation rates were 2.2 times higher in catchments with roads compared to roadless catchments and 1.4 times higher in catchments with road-stream intersections compared to those that were unconnected. Infestation was twice as likely in catchments with both harvest and road presence than road presence alone. Single-variable logistic regression showed that a one percent increase in harvest density increased infestation odds 25% and a one-unit (km/km²) increase in road density increased infestation odds 80%. Road and stream network configuration was also important to pathogen distribution: 1) uninfested catchments are most likely to be spatially removed from infested, roaded catchments, 2) only 11% of 287 roaded catchments downstream of infested, roaded catchments were uninfested, and 3) only 12% of 319 catchments downstream of infested catchments were uninfested. Road networks and timber harvest patchworks appear to reduce landscape heterogeneity by providing up-catchment and down-catchment access to host populations by linking pathogenic materials to the stream network. Timber harvest data suggest that while infestation risk to Port-Orford-cedar populations remains high, management policies may have curbed infestation risk in timber-harvested catchments; if this is a result of specific P. lateralis mitigation policies adopted in the late 1980's or broader, region-wide conservation policies (i.e. the Northwest Forest Plan) is yet unclear. / Graduation date: 2012