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Paul A. Knapp

Dr. Knapp's academic interests include biogeography, climatology, and dendroecology with a regional focus in the American West. Dr. Knapp's research has focused on examining the influence of atmospheric CO2 enrichment on the growth rates of woody species in arid and semiarid environments, and the paleoclimatology of the interior Pacific Northwest.

There are 36 included publications by Paul A. Knapp :

TitleDateViewsBrief Description
Cheatgrass (Bromus tectorum L) dominance in the Great Basin Desert: History, persistence, and influences to human activities 1996 2016 Cheatgrass (Bromus tectorum L), an exotic annual, is a common, and often dominant, species in both the shadscale and sagebrush-steppe communities of the Great Basin Desert. Approximately 20% of the sagebrush-steppe vegetation zone is dominated by che...
Climatic Regionalization and the Spatio-Temporal Occurrence of Extreme Single-Year Drought Events (1500–1998) in the Interior Pacific Northwest, USA 2002 207 Tree-ring records from western juniper (Juniperus occidentalis var. occidentalis Hook.) growing throughout the interior Pacific Northwest identify extreme climatic pointer years (CPYs) (i.e., severe single-year droughts) from 1500–1998. Widespread an...
Comparative Rates of Western Juniper Afforestation in South-Central Oregon and the Role of Anthropogenic Disturbance 2003 195 We examine changes in canopy cover for adult western juniper from the 1960s to 1994 in central Oregon using repeat aerial photography. We compare changes at four sites with a land-use history of minimal anthropogenic disturbance to changes on adjacen...
Correlation of 700 mb height data with seasonal temperature trends in the Great Basin (western USA): 1947-1987 1992 134 Temperature trends that are part of short-term climatic changes are often explained by a variety of theories, including changes in mean atmospheric pressure patterns. Seasonal 700 mb height data from grid points on the western (40° N, 120° W) and eas...
Detecting potential regional effects of increased atmospheric CO2 on growth rates of western juniper 2001 227 Evidence of an atmospheric CO2 fertilization effect on radial growth rates was uncovered by examining climate—growth relationships for seven western juniper tree-ring chronologies in central Oregon using multiple regression models. Consistent upward ...
Does an August Singularity Exist in the Northern Rockies of the United States? 2008 199 temporal variability. Significant deviations from normal daily maximum temperatures that occur following the passage of a strong midlatitude cyclone in mid- to late August in the northern Rocky Mountains of the United States are recognized in the loc...
Geographical distribution of an 18th-century heart rot outbreak in western juniper (Juniperus occidentalis spp. occidentalis Hook.) 1999 233 Between 1749-1730 a widespread occurrence of fungus-caused heart rot affected western juniper in the interior Pacific Northwest, U.S.A. In this study 12 Juniperus occidentalis spp. occidentalis chronologies collected from various sites throughout the...
HUMAN AGENCY, ENVIRONMENTAL DRIVERS, AND WESTERN JUNIPER ESTABLISHMENT DURING THE LATE HOLOCENE 2004 155 Western juniper (Juniperus occidentalis var. occidentalis) is undergoing rapid rates of expansion, and human activities (domestic livestock grazing, fire suppression) are typically presented as the primary agents of change. To determine the importanc...
Impacts of an Extreme Early-Season Freeze Event in the Interior Pacific Northwest (30 October–3 November 2002) on Western Juniper Woodlands 2005 162 In mid-autumn 2002, an exceptional 5-day cold spell affected much of the interior Pacific Northwest, with minimum temperatures averaging 13°C below long-term means (1953–2002). On 31 October, minimum temperature records occurred at 98 of the 106 reco...
Intermountain West lightning-caused fires: Climatic predictors of area burned 1995 283 An increase in continuous fine fuels promoted by the expansion of aggressive annual exotic grasses in the Intermountain West has altered the region's fire regimes, with both ecologic and economic ramifications. I examine the predictive nature of seas...
JUNIPERUS OCCIDENTALIS (WESTERN JUNIPER) ESTABLISHMENT HISTORY ON TWO MINIMALLY DISTURBED RESEARCH NATURAL AREAS IN CENTRAL OREGON 2000 144 While a trend toward western juniper ( Juniperus occidentalis spp. occidentalis) super-dominance in big sagebrush (Artemisia tridentata) communities of the Pacific Northwest since the late 1800s has been well documented, establishment dates of west...
Lessons in biogeography: Simulating evolution using playing cards 1994 537 This exercise links our day-to-day understanding of probabilities with the concepts of evolution as it relates to biogeographic processes. The complex idea of natural selection is presented in a simple, nonthreatening, and fun way. A variety of scena...
Lewis and Clarks’ Tempest: The ‘perfect storm’ of November 1805, Oregon, USA 2011 217 Three weeks after arriving near the Pacific Northwest (PNW) coast in November 1805, Lewis and Clarks’ Corps of Discovery experienced a two-day windstorm that may have rivaled the strongest historically documented storms of the nineteenth and twentiet...
Long-term soil and vegetation recovery in five semiarid Montana ghost towns 1991 263 Five semiarid Montana ghost towns abandoned for more than 45 years were studied to understand better the nature of soil and vegetation recovery following severe human impacts. Discriminant analysis was used to interpret and classify variation among l...
Occurrence of Sustained Droughts in the Interior Pacific Northwest (A.D. 1733–1980) Inferred from Tree-Ring Data 2004 217 The occurrence of moderate and severe sustained droughts in the interior Pacific Northwest (PNW) from 1733 to 1980 was mapped using 18 western juniper (Juniperus occidentalis var. occidentalis Hook.) tree-ring chronologies. The frequency and duration...
Ocean–Atmosphere Influences on Low-Frequency Warm-Season Drought Variability in the Gulf Coast and Southeastern United States 2011 223 From the 344 state climate divisions in the conterminous United States, nine distinct regions of warm-season drought variability are identified using principal component analysis. The drought metric used is the Palmer hydrological drought index for t...
Pogonomyrmex ewyheei nest site density and size on a minimally impacted site in central Oregon 1996 134 Little is known about the basic characteristics of the western harvester ant (Pogonomyrmex owyheei) in the absence of anthropogenic disturbances. We examined the role of P. owyheei as an agent of disturbance in an area of semiarid vegetation in centr...
Post-drought Growth Response of Western Juniper (Juniperus occidentalis var. occidentalis) in Central Oregon 2001 304 Increased atmospheric CO2 may affect the physiological response of natural trees to drought. We examined radial growth rates developed from five western juniper chronologies to determine if post-drought growth responses have changed. Using prior year...
Radial Growth and Increased Water-Use Efficiency for Ponderosa Pine Trees in Three Regions in the Western United States 2011 143 We examined changes in and relationships between radial growth and intrinsic water-use efficiency (iWUE) of ponderosa pine (Pinus ponderosa) trees, climate, and atmospheric CO2 in the western United States since the mid-nineteenth century. We develop...
Radial growth rate increases in naturally-occurring ponderosa pine trees: a late 20th century CO2 fertilization effect? 2006 300 • The primary objective of this study was to determine if gradually increasing levels of atmospheric CO2, as opposed to ‘step’ increases commonly employed in controlled studies, have a positive impact on radial growth rates of ponderosa pine (Pinus p...
Recent Juniperus occidentalis (Western Juniper) expansion on a protected site in central Oregon 1998 263 The expansion of Juniperus occidentalis (western juniper) has been extensive in the last century, and increases in density and cover have been linked with the indirect effects of domestic livestock grazing (i.e. cessation of periodic fires, increases...
RELATIONSHIPS BETWEEN GEOPOTENTIAL HEIGHTS AND TEMPERATURE IN THE SOUTH-EASTERN US DURlNG WINTERTIME WARMING AND COOLING PERIODS 1996 828 This paper discusses the relationship between geopotential heights and mean winter surface temperature and the characteristics of interannual variability in the south-eastem USA during cooling and warming periods from 1946 to 1992. Data from 83 His...
Seasonal association between mid-tropospheric pressure patterns and precipitation in the western Great Basin 1994 135 Associations between seasonal 700 mb height data and precipitation data in the western Great Basin, USA, are examined from 1947 through 1991 using bivariate regression. Results show that approximately one-third of precipitation variability in the stu...
Secondary plant succession and vegetation recovery in two western Great Basin Desert ghost towns 1992 579 Secondary succession and vegetation recovery patterns are examined in two abandoned mining camps in the western Great Basin Desert. Results from ANOVA and Tukey comparison tests indicate that, after approximately 70 years of recovery, significant dif...
Soil Loosening Processes Following the Abandonment of Two Arid Western Nevada Townsites 1992 147 Soil compaction was measured at four sites within two abandoned mining camps in the western Great Basin Desert, Nevada. Bulk density and macroporosity values were generated from soil samples collected in areas of different land use intensities in c...
Spatial characteristics of regional wildfire frequencies in Intermountain West grass-dominated communities 1997 325 Understanding the environmental factors that influence spatial patterns of rangeland wildfires facilitates both fire and land management decisions. I used discriminant analysis to examine ignition frequency of lightning-initiated fires in grass-domin...
Spatio-temporal patterns of large grassland fires in the Intermountain West, U.S.A 1998 229 The spatial and temporal occurrence of large grassland fires (>2008 ha) in the Intermountain West was examined for the period 1980 through 1995. Results suggest that these fires are largely predictable through space and time. Of the 360 large fires, ...
Topoedaphic and morphologic complexity of foliar damage and mortality within western juniper (Juniperus occidentalis var. occidentalis) woodlands related to an extreme meteorological event 2007 157 Aim: An extreme early season freeze event in October 2002 resulted in significant foliar damage and/or mortality within western juniper woodlands. We identify the geographical patterns of tree damage based on morphological, topographical and edaphic ...
Trends in mid-latitude cyclone frequency and occurrence during fire season in the Northern Rockies: 1900-2004 2007 251 We examined changes in the timing and frequency of major midlatitude cyclones (MLCs) during August through October for eight climate stations in the Northern Rockies from 1900-2004. As MLCs can effectively diminish fire activity through both cooler t...
Use of atmospheric CO2-sensitive trees may influence dendroclimatic reconstructions 2008 143 We examined recent radial growth increases in western juniper trees using an 11-site chronology dating from AD 1000-2006. By various measures, radial growth during the late 20th/early 21st centuries was exceptional, with increases occurring absent of...
Use of GIS in optimizing timber-thinning strategies in the eastern Sierra Nevada 1993 176 This paper demonstrated the use of Geographic Information System (GIS) to develop timber thinning strategies on the Kyburz Planning Area of the Tahoe National Forest in northeastern California. The primary criteria used in an assessment of selective ...
The use of large-scale aerial photography to inventory and monitor arid rangeland vegetation 1990 370 Interpretation of large-scale color infrared and color aerial photography can be a labor- and cost-effective means to make inventory of and monitor rangelands while maintaining accuracy. Ground measurements of total vegetation cover, tree, shrub and ...
Vegetation change and the role of atmospheric CO2 enrichment on a relict site in central Oregon: 1960-1994 1996 349 Atmospheric CO2 enrichment is increasingly implicated as a contributory cause of vegetation change on North American rangelands. To explore the role of the rising CO2 content of the earth's atmosphere as an agent of vegetation change, we revisited (J...
Western juniper expansion on adjacent disturbed and near-relict sites 1999 135 We determined rates of western juniper (Juniperus occidentalis spp. occidentalis Hook.) density and cover change during the period 1951 to 1994 at 3 adjacent sites with nearly identical elevation, slope, aspect, soils, plant communities, and climate,...
Window of Opportunity: The Climatic Conditions of the Lewis and Clark Expedition of 1804–1806 2004 259 ABSTRACTLewis and Clark's entry into to the American West in search of an inland Northwest Passage is considered among the greatest expeditions in American history. The Corps of Discovery were also lucky as their travels west of the 100th meridian oc...
Winter temperature variability during warming and cooling periods in the conterminous United States: 1947-1992 1999 176 Much literature has reported on the concept of increased surface temperature variability during cool periods, although analyses on temperature records have rendered inconsistent results. In addition, temperature variability during transition periods ...