Warren D. Devine

Mycorrhizas on nursery and field seedlings of Quercus garryana

Oak woodland regeneration and restoration requires that seedlings develop mycorrhizas, yet the need for this mutualistic association is often overlooked. In this study, we asked whether Quercus garryana seedlings in nursery beds acquire mycorrhizas without artificial inoculation or access to a mycorrhizal network of other ectomycorrhizal hosts. We also assessed the relationship between mycorrhizal infection and seedling growth in a nursery. Further, we compared the mycorrhizal assemblage of oak nursery seedlings to that of conifer seedlings in the nursery and to that of oak seedlings in nearby oak woodlands. Seedlings were excavated and the roots washed and examined microscopically. Mycorrhizas were identified by DNA sequences of the internal transcribed spacer region and by morphotype. On oak nursery seedlings, predominant mycorrhizas were species of Laccaria and Tuber with single occurrences of Entoloma and Peziza. In adjacent beds, seedlings of Pseudotsuga menziesii were mycorrhizal with Hysterangium and a different species of Laccaria; seedlings of Pinus monticola were mycorrhizal with Geneabea, Tarzetta, and Thelephora. Height of Q. garryana seedlings correlated with root biomass and mycorrhizal abundance. Total mycorrhizal abundance and abundance of Laccaria mycorrhizas significantly predicted seedling height in the nursery. Native oak seedlings from nearby Q. garryana woodlands were mycorrhizal with 13 fungal symbionts, none of which occurred on the nursery seedlings. These results demonstrate the value of mycorrhizas to the growth of oak seedlings. Although seedlings in nursery beds developed mycorrhizas without intentional inoculation, their mycorrhizas differed from and were less species rich than those on native seedlings.

Western redcedar response to precommercial thinning and fertilization through 25 years posttreatment.

There is little information available on the long-term effects of managing western redcedar (Thuja plicata Donn ex D. Don). In a 15- to 20-year-old naturally regenerated second-growth redcedar stand on a poor site on the Olympic Peninsula of Washington, we tested crop tree (largest 250 treesha -1 ) response to precommercial thinning and fertilization in a replicated study. Fertilization treatments were N or N+P applied at study installation and year 13; precommercial thin- ning occurred at installation. Precommercial thinning without fertilization produced a sustained increase in periodic indi- vidual-tree basal area (BA) growth rate from years 3 through 25 posttreatment. However, through year 12, higher BA growth rates resulted from fertilization. During years 13 through 25, when intraspecific competition increased, the highest BA growth rate resulted from the combination of fertilization and precommercial thinning. Compared with the unthinned- unfertilized control, fertilization without thinning increased year-25 crop-tree height by 34% and BA by 137%; thinning without fertilization increased height by 11% and BA by 91%. Height to live-crown base was decreased by thinning but increased by fertilization, while thinning significantly increased stem taper on the lower bole. Treatment responses and fo-

Release of Oregon White Oak from Overtopping Douglas-fir: Effects on Soil Water and Microclimate

Many former Oregon white oak (Quercus garryana) woodland and savanna stands in the coastal Pacific Northwest have been invaded by Douglas-fir (Pseudotsuga menziesii) during the past century as a result of fire suppression. Douglas-fir overtop and suppress the shade-intolerant oak, causing its eventual mortality. Removal of Douglas-fir is necessary for restoration of these oak ecosystems, but such action will influence belowground and near-ground conditions, affecting residual trees and understory communities. In a three-year study on a glacial outwash soil near Olympia, Washington, we compared soil and microclimate conditions near overtopped and released oak trees to determine how soil water content (SWC), throughfall, soil and air temperature, and vapor pressure deficit (VPD) are affected when oak is released from overtopping Douglas-fir. In each year, volumetric SWC near all trees declined from ~0.25 m3 m−3 to ~0.10 m3 m−3 during the growing season, but this decline was delayed approximately one month in the released condition. Additionally, minimum SWC during late summer was 0.02 to 0.03 m3 m−3 greater near released trees than near overtopped trees. The understory in the released condition consumed more soil water than that in the overtopped condition, but only in the first year after release. During light rain events from May through July, throughfall was 170% greater in the released condition than in the overtopped condition. Release from Douglas-fir increased soil temperature, maximum air temperature, and maximum VPD. Release of oak trees from overtopping Douglas-fir reduced early- to mid-summer competition for soil water, which will likely benefit the formerly suppressed oak trees.

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.

Estimating tree biomass, carbon, and nitrogen in two vegetation control treatments in an 11-year-old Douglas-fir plantation on a highly productive site

We sampled trees grown with and without competing vegetation control in an 11-year-old Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) plantation on a highly productive site in southwestern Washington to create diameter based allometric equations for estimating individual-tree bole, branch, foliar, and total aboveground biomass. We used these equations to estimate per-hectare aboveground biomass, nitrogen (N), and carbon (C) content, and compared these results to (1) estimates based on biomass equations published in other studies, and (2) estimates made using the mean-tree method rather than allometric equations. Component and total-tree biomass equations were not influenced by the presence of vegetation control, although per-hectare biomass, C, and N estimates were greater where vegetation control was applied. Our biomass estimates differed from estimates using previously published biomass equations by as much as 23 percent. When using the mean-tree biomass estimation approach, we found that incorporating a previously published biomass equation improved accuracy of the mean-tree diameter calculation.

Acorn storage alternatives tested on Oregon white oak

We assessed various combinations of storage factors: bag type, temperature, duration, and antifungal pre-storage treatments for white oak acorn storage, using Oregon white oak (Quercus garryana Douglas ex Hook. [Fagaceae]) acorns from 7 seed sources. Acorn viability remained high (84%), even after 2 y of refrigerated storage, but the majority of these acorns germinated between 6 and 12 mo after entering storage. Germination during storage differed significantly by seed source. The likelihood of successful storage of Oregon white oak acorns was increased by placing washed, healthy-appearing acorns in storage at a near-freezing temperature (1.6 °C [35 °F]) soon after collection. Sealed conventional freezer bags or specialized gas-permeable plastic bags were equally effective in maintaining viability. For 6-mo storage under the best treatment combination, 77% of acorns remained viable but ungerminated in storage, compared to 89% viability prior to storage.

Planting native oak in the Pacific Northwest.

The extent of oak woodland and savanna habitat in the Pacific Northwest has been dramatically reduced since settlement in the mid-1800s. This report presents a practical guide for landowners and managers who are interested in reestablishing native oak by planting seedlings. Keys to successful establishment are (1) planting quality seedlings, (2) controlling competing vegetation to increase soil water availability, and (3) protecting seedings from animal damage. A variety of effective cultural treatments, including mulch and tree shelters, are described in detail. Although early growth rates of planted oak seedlings are quite variable, even within the same site, this variation decreases over time after the seedlings become established.