Michael A. Bollman

Patterns of tree dominance in coniferous riparian forests

This research quantified patterns of riparian tree dominance in western Oregon, USA and then compared the observed patterns with the expected patterns defined from the literature. Research was conducted at 110 riparian sites located on private and public lands. The field sites were selected by probability surveys that were post-stratified by stream order and riparian forest type. An importance value index (IVI), which was the summation of tree relative density, relative frequency, and relative basal area, was used to define tree dominance. The IVI patterns of 19 riparian tree species with respect to ecoregion, geomorphic landform, stream order, and management practice were evaluated. In addition, the riparian trees were assigned to growth habit, life history strategy, and wetland indicator guilds depending on their taxonomy, response to flood disturbance, and wetland ecology, respectively. Douglas-fir, alder, western hemlock, and bigleaf maple were the trees with the highest IVI scores in western Oregon. The general IVI pattern of tree importance on the geomorphic landforms was hardwoods dominating the floodplain, hardwood and coniferous trees co-dominating the terrace, and conifers dominating the transition slope. However, there was considerable variability in the mix of the tree species because of differences in ecoregion, stream order, and management practice. The ecological importance of the dominant species was illustrated by their influence in determining the IVI patterns of the different guilds. For example, Douglas-fir, alder, and western hemlock were one, two, and three in their IVI rankings in western Oregon. The avoider, invader, and resister guilds were also ranked one, two, and three in importance because Douglas-fir, alder, and western hemlock were respectively classified in these groups. Such information is meaningful to developing conservation policy and plans to maintain or restore properly functioning riparian forests for aquatic and terrestrial biota, and to characterize reference condition and biological indicators for long-term ecological monitoring.

EVALUATION OF METRIC PRECISION FOR A RIPARIAN FOREST SURVEY

This article evaluates the performance of a protocol to monitor riparian forests in western Oregon, United States based on thequality of the data obtained from a field survey. Precision isthe criteria used to determine the quality of 19 field and 6 derived metrics. The derived metrics were calculated from thefield data. The survey consisted of 110 riparian sites on publicand private lands that were sampled during the summers of 1996 and 1997. In order to calculate metric precision, some of the field plots were re-measured. Metric precision was defined in terms of the coefficient of variability (CV) and standard deviation and then compared with a pre-defined data quality objective (DQO). A metric was considered precise if the CV met or exceeded the DQO. The geomorphology metrics were not precisewhile the forest stand inventory metrics and forest cover metrics, with some exceptions, were precise. The precision formany of the field and derived metrics compared favorably withthe level of precision for similar metrics reported in the literature. Recommendations are made to improve the precision for some metrics and they include changing the way precision is calculated, re-defining the field protocol, or improving field training.

Chemistry and microbial functional diversity differences in biofuel crop and grassland soils in multiple geographies.

We obtained soil samples from geographically diverse switchgrass (Panicum virgatum L.) and sorghum (Sorghum bicolor L.) crop sites and from nearby reference grasslands and compared their edaphic properties, microbial gene diversity and abundance, and active microbial biomass content. We hypothesized that soils under switchgrass, a perennial, would be more similar to reference grassland soils than sorghum, an annual crop. Sorghum crop soils had significantly higher NO3−-N, NH4+-N, SO42−-S, and Cu levels than grassland soils. In contrast, few significant differences in soil chemistry were observed between switchgrass crop and grassland soils. Active bacterial biomass was significantly lower in sorghum soils than switchgrass soils. Using GeoChip 4.0 functional gene arrays, we observed that microbial gene diversity was significantly lower in sorghum soils than grassland soils. Gene diversity at sorghum locations was negatively correlated with NO3−-N, NH4+-N, and SO42−-S in C and N cycling microbial gene categories. Microbial gene diversity at switchgrass sites varied among geographic locations, but crop and grassland sites tended to be similar. Microbial gene abundance did not differ between sorghum crop and grassland soils, but was generally lower in switchgrass crop soils compared to grassland soils. Our results suggest that switchgrass has fewer adverse impacts on microbial soil ecosystem services than cultivation of an annual biofuel crop such as sorghum. Multi-year, multi-disciplinary regional studies comparing these and additional annual and perennial biofuel crop and grassland soils are recommended to help define sustainable crop production and soil ecosystem service practices.

Wetland and riparian plant communities at risk of invasion by transgenic herbicide-resistant Agrostis spp. in central Oregon

Creeping bentgrass (Agrostis stolonifera) and redtop (A. gigantea) are introduced turfgrasses that are naturalized throughout the northern U.S. Interest in creeping bentgrass has risen following the 2003 escape of a genetically modified (GM), herbicide-resistant cultivar near Madras, Oregon. The objectives of this study were to characterize the floristic attributes of the plant communities associated with naturalized Agrostis populations in the Madras area, and to identify plant communities at risk of invasion by transgenic Agrostis. Vegetation data collected from 62 stratified random vegetation plots with and without A. stolonifera and A. gigantea identified 11 distinct plant communities. Community composition was strongly correlated with an indirect soil moisture index based on the wetland status of individual species. Results indicate that wetland plant communities are at the highest risk of invasion by transgenic A. stolonifera. Also, inter-specific gene flow to A. gigantea could affect additional habitats and plant communities where A. stolonifera is not found. Both A. stolonifera and A. gigantea were invasive in wetland and riparian settings in the Madras study area, and introducing glyphosate (e.g., Roundup®, Rodeo®) herbicide tolerance into these populations would eliminate the primary means of control for these species.

Regional patterns of increasing Swiss needle cast impacts on Douglas-fir growth with warming temperatures

Abstract The fungal pathogen, Phaeocryptopus gaeumannii, causing Swiss needle cast (SNC) occurs wherever Douglas‐fir is found but disease damage is believed to be limited in the U.S. Pacific Northwest (PNW) to the Coast Range of Oregon and Washington (Hansen et al., Plant Disease, 2000, 84, 773; Rosso & Hansen, Phytopathology, 2003, 93, 790; Shaw, et al., Journal of Forestry, 2011, 109, 109). However, knowledge remains limited on the history and spatial distribution of SNC impacts in the PNW. We reconstructed the history of SNC impacts on mature Douglas‐fir trees based on tree‐ring width chronologies from western Oregon. Our findings show that SNC impacts on growth occur wherever Douglas‐fir is found and is not limited to the coastal fog zone. The spatiotemporal patterns of growth impact from SNC disease were synchronous across the region, displayed periodicities of 12–40 years, and strongly correlated with winter and summer temperatures and summer precipitation. The primary climatic factor limiting pathogen dynamics varied spatially by location, topography, and elevation. SNC impacts were least severe in the first half of the 20th century when climatic conditions during the warm phase of the Pacific Decadal Oscillation (1924–1945) were less conducive to pathogen development. At low‐ to mid‐elevations, SNC impacts were most severe in 1984–1986 following several decades of warmer winters and cooler, wetter summers including a high summer precipitation anomaly in 1983. At high elevations on the west slope of the Cascade Range, SNC impacts peaked several years later and were the greatest in the 1990s, a period of warmer winter temperatures. Climate change is predicted to result in warmer winters and will likely continue to increase SNC severity at higher elevations, north along the coast from northern Oregon to British Columbia, and inland where low winter temperatures currently limit growth of the pathogen. Our findings indicate that SNC may become a significant forest health problem in areas of the PNW beyond the coastal fog zone.

Douglas-Fir (Pseudotsuga menziesii (Mirb.) Franco) Transcriptome Profile Changes Induced by Diesel Emissions Generated with CeO2 Nanoparticle Fuel Borne Catalyst

It is important to understand molecular effects on plants exposed to compounds released from use of products containing engineered nanomaterials. Here, we present mRNA sequencing data on transcriptome impacts to Douglas-fir following 2 weeks of sublethal exposure to 30:1 diluted airborne emissions released from combustion of diesel fuel containing engineered CeO2 nanoparticle catalysts (DECe). Our hypothesis was that chamber exposure to DECe would induce distinct transcriptome changes in seedling needles compared with responses to conventional diesel exhaust (DE) or filtered DECe Gas Phase. Significantly increased uptake/binding of Ce in needles of DECe treated seedlings was 2.7X above background levels and was associated with altered gene expression patterns. All 225 Blast2GO gene ontologies (GOs) enriched by up-regulated DECe transcripts were nested within GOs for DE, however, 29 of 31 enriched GOs for down-regulated DECe transcripts were unique. MapMan analysis also identified three pathways enriched with DECe down-regulated transcripts. There was prominent representation of genes with attenuated expression in transferase, transporter, RNA regulation and protein degradation GOs and pathways. CeO2 nanoparticle additive decreased and shifted molecular impact of diesel emissions. Wide-spread use of such products and chronic environmental exposure to DECe may adversely affect plant physiology and development.

Seasonal Soil Moisture Patterns in Contrasting Habitats in the Willamette Valley, Oregon

Abstract Changing seasonal soil moisture regimes caused by global warming may alter plant community composition in sensitive or endangered habitats such as wetlands and oak savannas. To evaluate such changes, an understanding of typical seasonal soil moisture regimes is necessary. The primary objective of this study was to document seasonal soil moisture patterns in herbaceous plant communities across a range of soils typical of Willamette Valley wet prairie, floodplain, and oak savanna habitats. Volumetric soil moisture data were collected periodically from January 2010 through December 2011 at study sites using time domain reflectometry and converted to plant-available soil moisture using moisture release data for each of the soils. In addition, plant communities, soil texture, and soil chemical attributes were evaluated at all sites. Both 2010 and 2011 experienced unusually high spring rainfall, and soils did not begin dry down until about the third week in June. The length of the dry period was similar in both years, but in 2011 it was shifted from mid-July through early September to early August through early October. Well-drained floodplain soils consistently had the lowest soil moisture contents in both years. Wet prairie sites began to dry down shortly after oak savanna sites, and their rates and severity of dry down were similar. These results suggest that the composition of herbaceous plant communities in wet prairie habitats may be influenced more by winter and spring inundation than by summer drought and that the timing of rainfall events during the dry period could influence plant community composition.