David H. Peter

Synchronicity and geographic variation in Oregon white oak acorn production in the Pacific Northwest

Abstract We explored geographic patterns and synchrony of Oregon white oak (Quercus garryana) acorn production over 8 years from Vancouver Island, British Columbia to Medford, Oregon. We divided our data into geographic areas: Puget-Willamette Trough, Columbia Gorge-East Cascades (Eastside) xeric, Eastside mesic, Cascade Mountain foothills, Roseburg, and Medford to compare annual acorn production among areas. We observed high within-area synchrony, but synchrony across areas was only apparent in 2004 and 2006 (high production), and 2005 (low production). Correlogram analysis indicated significant acorn crop correlation throughout the Puget-Willamette Trough, but synchrony was higher over greater distances among stands than among trees. Relationships between acorn production and mean monthly temperature or precipitation were examined with correlation analyses for each month between floral initiation and acorn maturation over 8 years of observations. Acorn production in the Puget-Willamette Trough was negatively correlated with spring precipitation, possibly due to an effect on floral processes, and winter temperature, which might relate to bud chilling requirements. In Eastside uplands, June precipitation positively correlated with current acorn production, but negatively correlated with the following years production suggesting a climatically mediated depression by one years production on that in the following year. Eastside production negatively correlated with precipitation in March suggesting precipitation interferes with floral processes at that time. We developed predictive linear regression models for the two analysis areas with largest sample sizes. Oregon white oak masting is similar to that in other white oaks in terms of periodicity and the effects of spring weather, but is also influenced by other weather related factors following floral induction.

Oak Woodland Restoration: Understory Response to Removal of Encroaching Conifers

Oregon white oak (or Garry oak, Quercus garryana) woodlands and savannas of the coastal Pacific Northwest are legacies of an anthropogenic fire regime that ended with European settlement in the mid-1800s. Historically, these oak stands had a sparse overstory and an understory dominated by fire-tolerant grasses and forbs. Post-settlement fire suppression resulted in widespread invasion and subsequent overstory dominance by conifers, causing mortality of shade-intolerant oak trees and shifting understory plant communities to shade-tolerant species. In a study on four southwestern Washington sites, our objective was to determine the effects of overstory conifer removal, primarily Douglas-fir (Pseudotsuga menziesii), on microclimate, native and non-native understory cover, and sapling growth. Overstory conifer removal created a warmer, drier understory microclimate during summer months. Conifer removal had little effect on native understory cover during five years post-treatment; however, cover of non-native plants, primarily grasses and woody understory species, increased significantly during the same period. Height growth of Oregon white oak and Douglas-fir saplings exhibited a delayed, but positive, response to overstory conifer removal, although the treatment response of Douglas-fir was 133% greater than that of oak. Increases in non-native understory cover and the rapid growth of young Douglas-fir indicate the importance of pre- and post-treatment understory management to control undesirable plants and promote native species such as Oregon white oak.

Historical Colonization of South Puget Sound Prairies by Douglas-Fir at Joint Base Lewis-McChord, Washington

Abstract Native Americans used fire to maintain prairies in western Washington, but few prairies remain due to land-use conversion and forest encroachment. We describe the process of forest encroachment on former western Washington prairies. We used 1853–1871 General Land Office Survey data to describe the historical prairie and associated timbered area conditions at six Joint Base Lewis-McChord sites (JBLM). We described modern stands growing in these same areas with stem density, Reineke stand density index (Reineke 1933), and site index. After harvesting selected trees we measured decadal tree-ring increments and analyzed trauma rings on 242 Douglas-fir stumps to reconstruct stand development. We plotted individual tree stem diameter growth curves to illustrate patterns of establishment. Douglas-fir density increased in waves from 1878–1938 associated with low-intensity fires with fire return intervals of 10 to 91 years. Historical tree density, which ranged from < 1 to 49 trees ha-1 has increased to 122 to 207 trees ha-1. Stand development was driven by fires, patterns of establishment, and site potential. Longer fire-free intervals resulted in few larger establishment waves while frequent shorter intervals resulted in multiple smaller cohorts. Woodlands, not prairies, resulted from ten or more year fire frequencies; however, mature forests grew in < 50 years suggesting fire frequencies appropriate for restoration of prairies and woodlands. Modern productive sites produced larger trees that experienced inter-tree competition, suggesting faster forest succession occurred on those sites. Light to moderately thinned Douglas-fir reproduced poorly on our sites. Higher intensity thinning or gap creation may be required for successful regeneration.

Effects of the light environment and stand history on beargrass ( Xerophyllum tenax ) morphology and demography

Abstract Beargrass (Xerophyllum tenax [Pursh] Nutt.) is an herbaceous, evergreen perennial found in higher elevations of the northern Rocky, Sierra Nevada, Klamath, Siskiyou, Cascade and Olympic Mountains and in coastal areas from Washington to northern California. It is used by Native Americans for basketry and is an important floral green, but the conditions needed for reproduction and commercially valuable characteristics are not well known. We studied how the light environment affects size, morphology, color, and reproduction of a lowland, southeastern Olympic Peninsula beargrass population. We examined beargrass crown size distribution in relation to current and past overstory structure and found that beargrass plants had longer, greener leaves, lower crown density, smaller basal diameter, and fewer vegetative offshoots in shaded areas compared to more open areas. Flowering was less and there were fewer seedlings in shaded areas. Beargrass did not reproduce sexually in areas with < 0.3 of full photosynthetically active radiation (equivalent to at least 50% tree cover in our stand). Beargrass abundance matched the locations of anthropogenically maintained woodland openings that have since become forested preventing beargrass reproduction, suggesting that many plants have survived in the shade for more than 60 years. Overstory removal and prescribed burning in a portion of the stand stimulated sexual and asexual reproduction. We concluded that plants in shaded areas, although of somewhat higher commercial quality, are likely to recover more slowly from foliar harvest, and are less likely to be replaced after mortality. Population sustainability requires periodically or permanently open stand conditions.