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The invasive shrub Scotch broom (Cytisus scoparius (L.) Link) is a pervasive threat to regenerating Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) stands in the Pacific Northwest, USA. Field observations indicate that the susceptibility of areas to Scotch broom invasion and dominance can vary by site. We selected 10 sites throughout the western Pacific Northwest that spanned a gradient of soil textures and other factors to test the site-specific susceptibility of Douglas-fir to overtopping by Scotch broom. We expected to find that the ability of Scotch broom to dominate a site was mediated by site-level factors, particularly those influencing soil water - the most limiting factor to growth in the region. We found Scotch broom and Douglas-fir were inversely affected by site-level factors. In general, Douglas-fir absolute height growth rates were more competitive with those of Scotch broom on fine-textured soils than on more coarsely textured soils. We also found Douglas-fir to have a more dramatic response to increasing down woody material than Scotch broom. Scotch broom height growth approached an asymptote at 3 m. Sites with fast-growing Douglas-fir were able to surpass this height 6-7 years after planting and appear likely to avoid suppression by Scotch broom. USDA National Institute for Food and Agriculture [GRANT11325729] Published version We thank the Washington Department of Natural Resources, Green Diamond Resource Company, Port Blakely Tree Farms, the National Fish and Wildlife Foundation, and Olympic Resource Management for providing the sites needed for this study. We also thank Dave Peter and James Dollins for their help setting up and maintaining this study, as well as, taking field measurements. Janet Prevey and Matthew Russell helped with model construction. Funding for this project was provided by the USDA National Institute for Food and Agriculture (Grants gov. No. GRANT11325729). Public domain – authored by a U.S. government employee

Scotch broom [Cytisus scoparius (L.) Link] is a large nonnative, leguminous shrub that threatens native plant communities by rapidly invading recently disturbed sites, competing vigorously for soil water and nutrients, and imparting soil legacy effects that inhibit native plants. In the Pacific Northwest, logging debris retention after forest harvesting prevents or slows C. scoparius invasions. A series of studies were conducted to determine potential mechanisms by which logging debris modifies the light environment to limit germination and growth of C. scoparius. In laboratory studies, seed germination did not vary significantly (P > 0.05): (1) between presence and absence of light for several temperature regimes, (2) when exposed to red (660-nm wavelength) versus far-red (730-nm wavelength) light, and (3) across a range of red/far-red light (R/FR) ratios. These results indicate that modification of the light environment by logging debris or plant canopies has little or no influence on C. scoparius germination. In a study to simulate effects of variable mass of logging debris, “heavy” debris (2 kg m−2) caused biologically relevant reductions in photosynthetic photon flux density (PPFD) and R/FR relative to conditions under “light” debris (1 kg m−2). Cytisus scoparius germination did not differ significantly between simulated heavy and light debris; however, values of seedling root and shoot biomass under heavy debris were 16% and 71% of those observed under light debris, respectively. These results indicate that heavy debris limits biomass of C. scoparius seedlings, particularly roots, by reducing both PPFD and R/FR, which increases seedling vulnerability to summer drought or other stressors. Retention of heavy logging debris after forest harvesting has potential application on sites likely to be invaded by C. scoparius, as well as those sites with seedbanks containing C. scoparius.

Effects of intensive forest management on soil phosphorus (P) are unclear and may impact long-term site productivity. We assessed changes in P availability over 10 years associated with harvest intensity (bole-only vs. whole-tree harvest) and vegetation control treatments (initial vegetation control (IVC) vs. five years of annual vegetation control (AVC)) using a P fractionation procedure. Fractions were characterized at 0-15, 15-30, and 30-60 cm soil depths in two coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantations with strongly contrasting soil properties near Matlock, WA (young soils formed in glacial outwash) and Molalla, OR (relatively old soils formed in igneous residuum and exhibiting andic properties). Al and Fe concentrations associated with short-range order minerals were greater at Molalla than Matlock and generally decreased with depth at both sites. We observed decreases in most total-P and P-fraction concentrations across the three soil depths at the Molalla site. Effects were less pronounced and generally inconsistent at the Matlock site. Decreases in total P and P fraction concentrations were greatest in the AVC treatments at Matlock, but opposite trends were observed at Molalla where decreases were greatest with IVC. There was no difference between harvest treatments on the change in P fractions in most instances, with the exception of the 30-60 cm depth at Matlock where concentrations of some P fractions were maintained or increased with bole-only harvesting. Ten-year responses indicate harvest intensity has limited effects on long-term productivity associated with soil P because of the large size of the soil P pools and the relatively small changes in soil P that occurred with treatment. Decreases in P concentrations with AVC at Matlock and IVC at Molalla were larger than the other treatments and highlight the important role of vegetation in P dynamics following harvesting at these sites. USDA Forest Service Pacific Northwest Research StationUnited States Department of Agriculture (USDA)United States Forest Service; Virginia Tech; Green Diamond Resource Company; Port Blakely Tree Farms, LLC This is a product of the Sustainable Forestry component of Agenda 2020, a joint effort of the USDA Forest Service Research and Development and the American Forest and Paper Association. Funds were provided by the USDA Forest Service Pacific Northwest Research Station, Virginia Tech, Green Diamond Resource Company, and Port Blakely Tree Farms, LLC. The authors are grateful to Randall Greggs and Mike Warjone for providing critical financial and logistical support that made this study possible. Special thanks to J. Dollins for assisting with field work and sample preparation, and Stephanie Duston for her assistance in the laboratory. Public domain – authored by a U.S. government employee

We tested the effects of phosphorus (P) fertilization and soil water on the growth, physiology, and total nitrogen (N) accumulation in N-fixing Scotch broom in Olympia, WA. We manipulated soil water and P availability via irrigation and fertilization, respectively, in a completely randomized 2 × 2 factorial on potted one-year old Scotch broom seedlings (n = 20) in an N-deficient sand. There was substantial evidence that increased-irrigation and P-fertilization had similar positive effects on N accumulation in Scotch broom approximately equally. High-irrigation rates were more often associated with positive physiological and growth responses in Scotch broom than fertilization, however. Although the irrigation × fertilization interaction was not significant, there were additive effects of high-irrigation and fertilization on biomass and N content as both were 50% greater in the fertilized-and-high-irrigation treatment relative to the respective fertilized and high-irrigation treatments. We noted an accumulation of N and P in the plant tissues. Analyses indicated a pattern of decreasing function and growth with increasing N and P concentrations in Scotch broom biomass, suggesting plant growth and physiology were limited by some other resource. Total plant N content values ranged from 7.0 ± 1.1 g plant−1 in the control and 23.4 g ± 9.0 plant−1 in the fertilized-and-high-irrigation treatment. Extrapolated to typical densities of comparably sized Scotch broom plants on invaded sites in the western Pacific Northwest, these findings suggest that, at least, 12–65 kg N ha−1 would be found in Scotch broom plants in the field.

Scotch broom is an aggressive invasive species of major concern in coast Douglas-fir forests of the Pacific Northwest USA. Control efforts are common, but potential for ecosystem recovery following Scotch broom removal is unclear. We assessed the potential for ecosystem recovery following broom removal at two sites that contrasted strongly in soil quality (i.e., texture and nutrient pool size) in western Washington and Oregon. Comparisons were made among replicated plots where Scotch broom was never present (uninvaded), retained, or removed. Microclimate (photosynthetically active radiation (PAR), soil temperature and moisture), soil properties, and vegetation were monitored during 2013 to 2017. Scotch broom removal increased PAR and soil temperature at both sites but had limited effects on soil moisture. Concentrations of Ca, Mg, K, and P were significantly lower with Scotch broom removal compared to the uninvaded and retained treatments, with the effect being most pronounced at the low-quality site. NMS ordinations indicated that the treatments differed in vegetation composition, with limited evidence for recovery in the removal treatment. Nonnative and native species varied inversely in their abundance responses, where nonnative species abundance was greatest in the removal treatment, intermediate in the retained treatment, and lowest in the uninvaded treatment, indicating occurrence of a secondary invasion following removal. As with the soil response, effects were more pronounced at the low-quality site. Our findings indicate that Scotch broom removal exacerbates negative effects on soil and plant communities, with little evidence of ecosystem recovery over our study period. These findings highlight the importance of controlling Scotch broom invasions immediately after the species establishes, especially at low-quality sites that are more susceptible to Scotch broom invasion and negative legacy effects.

Recovery of ecosystem properties following removal of invasive plants likely varies with characteristics of the plant and the relative soil quality at a given site. These factors may influence the occurrence of soil legacies and secondary invasions, hindering the effectiveness of restoration strategies. We assessed the potential for ecosystem recovery following removal of N-fixing Scotch broom for 4 years at two sites that contrasted strongly in soil quality in western Washington and Oregon, USA. Comparisons were made among plots, where Scotch broom was never present (uninvaded), retained, or removed. Scotch broom removal increased PAR and soil temperature but had limited effects on soil moisture. Concentrations of soil Ca, Mg, K, and P were significantly lower with Scotch broom removal, with the effect being most pronounced at the low-quality site. NMS ordinations indicated that the treatments differed in vegetation composition, with limited recovery following broom removal. Non-native and native species varied inversely in their abundance responses, where non-native species abundance was greatest in the removal treatment, intermediate in the retained treatment, and lowest in the uninvaded treatment, indicating occurrence of a secondary invasion following removal. As with the soil response, effects were more pronounced at the low-quality site. Our findings indicate that Scotch broom removal exacerbates negative effects on soil chemistry and plant communities, with little evidence of recovery over our study period. These findings highlight the importance of controlling Scotch broom invasions immediately after the species establishes, especially on low-quality sites that are more susceptible to Scotch broom invasion.

At two affiliate sites of the North American Long-Term Soil Productivity Study (Matlock, WA and Molalla, OR, USA), soil chemical properties and stand characteristics of planted coast Douglas-fir (Pseudotsuga menziesii var. menziesii) were compared 15 years after forest harvesting and application of three logging-debris configurations (dispersed, piled, or removed) combined with either initial vegetation control (IVC; year 0) or annual vegetation control (AVC; years 0 to 5). At Matlock, soil carbon (C) and nitrogen (N) concentrations each were 17% greater after IVC than after AVC; at Molalla, soil N was 13% greater where debris was removed than where it was dispersed. At Matlock, cover of nonnative Scotch broom (Cytisus scoparius) after IVC was greater where debris was removed (61%) than where it was piled (27%) or dispersed (7%), despite a control treatment in year 4. Conversely, covers of the native shrubs, trailing blackberry (Rubus ursinus) and salal (Gaultheria shallon) were 20% to 30% greater where debris was dispersed than where it was piled or removed. With AVC versus IVC, Douglas-fir stand volume was 34% to 159% greater at Matlock depending on the logging-debris treatment, and it was 30% greater at Molalla independent of debris treatments. However, Douglas-fir survival and growth after AVC did not differ among logging-debris treatments at either site. Survival of Douglas-fir growing 1 m from debris piles. Debris dispersal or piling at Matlock strongly mitigated Scotch broom impacts to forest productivity compared to debris removal. Our findings demonstrate how disturbance characteristics associated with forest harvesting and regeneration practices can influence vegetation recruitment and competitive relationships to place limits on longer-term forest productivity. USDA National Institute for Food and Agriculture [GRANT11325729]; USDA Forest Service, Pacific Northwest Research StationUnited States Department of Agriculture (USDA)United States Forest Service; Port Blakely Tree Farms LLC; Green Diamond Resource Company Financial support for this research was provided by the USDA National Institute for Food and Agriculture (Grants.gov number: GRANT11325729) and the USDA Forest Service, Pacific Northwest Research Station. The authors are especially grateful to Randall Greggs, Green Diamond Resource Company, and Mike Warjone, Port Blakely Tree Farms LLC, for providing critical logistical and financial support that made this study possible. Thanks also to the helpful comments from the Associate Editor, two anonymous reviewers, and Kim Littke, University of Washington. Public domain – authored by a U.S. government employee

Douglas-fir (Pseudotsuga menziesiivar. menziesii (Mirbel) Franco) plantation forests of the coastal Pacific Northwest have been intensively managed to improve the yield of forest products. However, the long-term effects of these management techniques have received limited research attention in this region. Three affiliate Long-Term Soil Productivity study sites were installed in Douglas-fir forests to understand the impacts of organic matter removals and vegetation control on soil productivity over time. Matlock and Fall River are located in Washington, USA and Molalla is located in Oregon. Organic matter removal treatments included traditional bole-only harvest (BO), whole tree removals (WT), and a whole tree plus coarse woody debris removal (WT+) (Fall River only). Five years of annual vegetation control (AVC) was compared with a conventional initial vegetation control (IVC) treatment at all sites. Douglas-fir biomass allocation to foliage, branch, and stem components was modeled using 15- to 20-year-old trees from this study along with 5- to 47-year-old trees from previous studies on these sites. Across all sites, model predictions indicated that the WT treatment had 7.1 to 9.7 Mg ha&minus, 1 less Douglas-fir biomass than the BO treatment. There was 1.5 to 20.5 Mg ha&minus, 1 greater Douglas-fir biomass in the AVC treatment than in the IVC treatment at all sites. Douglas-fir carbon and nitrogen biomass were consistently lower in the WT treatment, but there were no significant changes in overall site nutrient pools. The AVC treatment resulted in greater Douglas-fir nutrient pools yet there was a net loss in site calcium, magnesium, and potassium due to lower forest floor and soil base cation pools. While WT removals did not significantly affect site nutrition, the decrease in Douglas-fir biomass at all sites and increase in invasive Scotch broom (Cytisus scoparius (L.) Link) biomass at Matlock suggests that the standard practice of retaining harvest residuals is beneficial. The use of intensive vegetation control to improve Douglas-fir biomass and nutrition must be balanced with retaining soil base cations.

Scotch broom [Cytisus scoparius (L.) Link] is a globally important nitrogen (N)-fixing invasive plant species that has potential to alter soil water dynamics, soil chemistry, and plant communities. We evaluated the effects of Scotch broom on soil moisture, soil chemistry, soil temperature, photosynthetically active radiation (PAR), and vegetation communities over 4years at a site recently harvested for timber. Treatments of Scotch broom (either present via planting or absent) and background vegetation (either present or absent via herbicide treatments) were applied to 4m(2) plots. Background vegetation was associated with the greatest decrease of soil water content (SWC) among treatments. During the driest year, Scotch broom showed some evidence of increased early-and late-season soil water usage, and, briefly, a high usage relative to background vegetation plots. On a percent cover basis, Scotch broom had a substantially greater negative influence on SWC than did background vegetation. Surprisingly, Scotch broom was not consistently associated with increases in total soil N, but there was evidence of increasing soil water N when Scotch broom was present. Scotch broom-only plots had greater concentrations of soil water magnesium (Mg2+) and calcium (Ca2+) than other treatments. On a percent cover basis, Scotch broom had a uniquely high demand for potassium (K+) relative to the background vegetation. Average soil temperature was slightly greater, and soil surface PAR lower, with Scotch broom present. Scotch broom-absent plots increased in species diversity and richness over time, while Scotch broom-present plots remained unchanged. Scotch broom presence was associated with an increase in cover of nonnative sweet vernalgrass (Anthoxanthum odoratum L.). Scotch broom generated positive feedbacks with resource conditions that favored its dominance and the establishment of nonnative grass. USDA National Institute for Food and Agriculture [GRANT 11325729] Financial support for this research was provided by the USDA National Institute for Food and Agriculture (Grants.gov number: GRANT 11325729). We wish to thank Green Diamond Resource Company for use of their land and logistical support. We would like to thank James Dollins for all of his efforts on this project. Public domain – authored by a U.S. government employee

We examined plant community organization over the first five growing seasons after clearcut harvesting with retention of two levels of logging debris (light and heavy) and application of four vegetation control treatments (non-sprayed control, aminopyralid (A), triclopyr (T), and A + T). Our study site was 44 km northwest of Olympia, WA., USA, and before forest harvesting it was dominated by Pseudotsuga menziesii. We used a randomized split plot experimental design replicated in 6 blocks (each debris-treatment main plot had four herbicide-treatment split plots). We estimated percent canopy cover by species before forest harvesting and in post-harvest seasons 1–3 and 5 on 100 m2 plots centered in each split plot. We analyzed species composition and diversity and report the response of 10 species groups and several major species to the treatments over five seasons. We used ANOVA to examine annual treatment effects on abundance of major species and species groups as well as ordination and graphical methods to examine succession. Abundance of ruderal species, especially exotics and graminoids, was lower but abundance of native woody shrubs and vines was higher in heavy debris than in light debris. The vines developed higher cover in heavy debris where they used debris as a scaffold to gain a competitive advantage over other species. Heavy debris controlled Cytisus scoparius better than the herbicide treatments. Triclopyr reduced woody dicot, vine and native herb covers, while aminopyralid reduced these groups and Cytisus scoparius, but aminopyralid had less effect on total canopy cover. The combination herbicide treatment reduced woody dicots, vines and Cytisus scoparius, and had the biggest impact on total canopy cover. By year 5 there was little difference in total canopy cover among the herbicide treatments; however, for some species, both debris and herbicide treatment effects were still apparent. The ordination indicated that, by the fifth season, the floristic characteristics distinguishing the debris treatments were still distinct, but not for the herbicide treatments. We conclude that heavy debris is a viable treatment alternative to prevent aggressive exotic species from competing with planted conifers and the native plant community on edaphically dry western Washington sites.

Logging debris has the potential to benefit forest regeneration by increasing resource availability, modifying microclimate, and altering plant community structure. To understand potential mechanisms driving these benefits, we initiated research at a forested site on the Olympic Peninsula, WA that contained the invasive, nonnative competitor, Scotch broom (Cytisus scoparius). Immediately after harvesting the stand of mature coast Douglas-fir (Pseudotsuga menziesii var. menziesii) in late 2011, two levels of logging debris retention were created on replicated plots: 18.9 and 9.0 Mg ha−1, with debris depths averaging 32 and 17 cm, respectively. Within each plot, three herbicide treatments (aminopyralid (A), triclopyr ester (T), and A + T) and a non-sprayed control were applied to split plots in August 2012. Douglas-fir seedlings were planted in early 2013, and microclimate and seedling performance were monitored through 2016. During the growing seasons of 2012–2014, soil water content was greater and soil temperature was lower under heavy debris than under light debris. Survival of planted Douglas-fir seedlings declined an average of 45 and 11 percentage points after intense summer droughts in 2015 and 2016, respectively, but it averaged 7–10 percentage points greater in heavy debris than in light debris during this period. Douglas-fir stem diameter growth was consistently greater in heavy debris than in light debris, with the exception of treatment A + T where diameter did not differ between debris treatments. A reciprocal regression model (R2 = 0.55) predicted that total stem volume of Douglas-fir increased from 19 to 84 dm3 ha−1 as Scotch broom cover decreased from 20% to 0% as a result of the logging debris and herbicide treatments. There were limited treatment effects on mineral soil chemical and physical properties, but forest floor mass and nutrient content were increased in the heavy debris treatment. Five years after forest harvesting (2016), logging debris mass in heavy debris differed little from that in light debris at study initiation, indicating a substantial reduction in fuels and the potential for severe wildfire. Results suggest that, on gravelly soils and possibly other droughty forest ecosystems in the Pacific Northwest, heavy debris will benefit planted Douglas-fir by improving growing conditions and by limiting abundance of nonnative competitors, such as Scotch broom.

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.

Changes in land use over the past century have contributed to substantial losses of longleaf pine (Pinus palustris) woodlands in the southeastern USA and replacement with higher density, mixed pine and hardwood stands that suppress understory development and limit application of prescribed fire. To increase understanding of limiting factors and identify potential approaches for restoring longleaf pine woodlands, we studied initial availability of light and soil water and 2-year (2018–2019) plant community responses after controlling overstory hardwoods in five remnant longleaf pine woodlands having no evidence of previous agriculture at the Savannah River Site near Aiken, SC, USA. Seven hardwood control treatments and a non-treated check were compared in a randomized compete block experiment: cutting, cutting + shredding of logging residues, stem injection with imazapyr herbicide, cutting + basal spray with imazapyr herbicide, cutting + basal spray with triclopyr herbicide, cutting + directed foliar spray with a mixture of glyphosate and imazapyr herbicides, and cutting + broadcast foliar spray with the same herbicide mixture. In the year prior to hardwood cutting (2016), understory light availability averaged 23% of full sun. Throughout the year of treatment installation (2017), average soil water content (SWC) was below permanent wilting point (5.5% SWC) where overstory hardwoods were retained; whereas, it was above wilting point (7.5%) where they had been cut. Thus, combined effects of shade and root competition from overstory hardwoods probably limited cover of herbaceous species in the non-treated check. In the 2 years following treatment, hardwood survival averaged > 99%, 62%, 42% and

Intensive management practices are commonly used to increase fiber production from forests, but potential tradeoffs with maintenance of long-term productivity and early successional biodiversity have yet to be quantified. We assessed soil and vegetation responses in replicated manipulations of logging debris (LD; either retained or removed) and competing vegetation control (VC; either initial or sustained annually for 5 years) for 10 years at two Douglas-fir sites that contrasted strongly in availability of soil nutrients and water. We evaluated (1) survival and growth of Douglas-fir to determine short-term effectiveness for fiber production, (2) change in soil C and nutrient pools as an indicator of longer-term effects of treatments on soil quality and ecosystem production, and (3) vegetation composition and cover for treatment effects on early successional biodiversity. Annual VC caused large increases in Douglas-fir growth at both sites, but increased survival only at the lower-productivity site. In most instances and regardless of site or treatment, soil C and nutrient pools increased following harvesting, but the increases were generally larger with lower intensity practices (LD retained and initial VC). Effects of LD were small and inconsistent at the higher productivity site, but LD retained increased Douglas-fir survival and growth and soil nutrient pools at the lower productivity site. Species diversity was reduced at both sites with annual VC because of increased Douglas-fir cover, but the magnitude was greater and the timing was earlier at the higher quality site where plant communities in all treatments had converged by year 10. Annual VC can be used to increase growth of planted Douglas-fir while maintaining soil nutrient pools for sustained ecosystem productivity, but a concurrent decrease in early successional diversity will occur with impacts increasing with site quality. Logging debris retention can have positive benefits to Douglas fir growth and soil nutrient pools, particularly at lower quality sites. Our results demonstrate a need for careful consideration of site quality to ensure that objectives are realized with regards to fiber production and maintenance of soil productivity and biodiversity with intensive forest management. USDA Forest Service Pacific Northwest Research StationUnited States Department of Agriculture (USDA)United States Forest Service; Port Blakely Tree Farms LLC; Virginia Tech; Green Diamond Resource Company; Randall Greggs; Mike Warjone This is a product of the Sustainable Forestry component of Agenda 2020, a joint effort of the USDA Forest Service Research and Development and the American Forest and Paper Association. Funds were provided by the USDA Forest Service Pacific Northwest Research Station, Virginia Tech, Green Diamond Resource Company, and Port Blakely Tree Farms LLC. The authors are especially grateful to Randall Greggs and Mike Warjone for providing critical financial and logistical support that made this study possible. Special thanks to J. Dollins, D. Stephens, B. Korman, D. Livada, and W. Devine for assisting with field and laboratory measurements. Public domain – authored by a U.S. government employee

Scotch broom (Cytisus scoparius (L.) Link) is a highly competitive, nonnative, leguminous shrub species of major concern in coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) forests of the Pacific Northwest that has potential to impact long-term soil productivity. We conducted a bioassay to assess the potential for legacy effects on soils (e.g., soil nutrient effects, soil seedbank, etc.) following Scotch broom removal and the potential for recovery over time. The bioassay was conducted using glacial-outwash soils from an existing Long-Term Soil Productivity study near Matlock, WA, USA, where Scotch broom had been removed or kept out for 0 (broom present), 4, 10, or 14 years. Soils from each broom removal duration were combined with fertilizer treatments to assess mechanisms of response of three native plant species: yarrow (Achillea millefolium L.), Roemer's fescue (Festuca idahoensis Elmer ssp. Roemeri), and coast Douglas-fir. There was evidence for negative soil legacy effects on Douglas-fir growth and biomass, which decreased with time since broom removal. Responses to the fertilizer treatments indicated the effect was not associated with reduced nutrient availability. In contrast, both yarrow and Roemer's fescue had significantly greater biomass in soil from where broom was recently present, which decreased with time since broom removal. Responses to the fertilizer treatments indicated that this positive legacy effect is associated with nutrient availability, likely increased N. Soils from 0 and 4 years since broom removal were estimated as having the potential to produce over 578,500 Scotch broom germinants ha(-1) . Our results demonstrate the potential for both negative and positive soil legacy effects of broom depending on the responding plant species. Combined effects of negative soil legacies and a large and viable seed bank from Scotch broom create growing conditions likely to hinder long-term productivity of Douglas-fir. USDA National Institute for Food and Agriculture [GRANT11325729] Financial support for this research was provided by the USDA National Institute for Food and Agriculture (Grants.gov number: GRANT11325729). We thank Green Diamond Resource Company for use of their land and logistical support. Thanks also to Dave Peter and James Dollins for assistance with the field and greenhouse work. Public domain – authored by a U.S. government employee

As intensive management of forest plantations and interest in harvesting biomass for energy continue to increase, there is a need to investigate the longer-term effects of harvest-related disturbances and intensive treatments on soil and site productivity. This research focused on three Pacific Northwestern Douglas-fir soil productivity studies around 15 years since harvest that spanned a range in soil nutrients: high soil N and low base cations (Fall River), low soil N and base cations (Matlock), and high soil N and base cations (Molalla). The studies, which had similar organic matter and vegetation control treatments, were compared for differences in belowground and aboveground nutrients as well as differences in periodic stand volume growth. Five years of annual vegetation control (AVC) resulted in the greatest losses of belowground N and base cations compared to one year of vegetation control (IVC) at planting, but also resulted in significantly greater stand volume growth at Fall River and Matlock. Whole tree removal (WT) resulted in lower soil NO3− at Fall River but greater soil NO3− at Matlock due to greater colonization by N-fixing Scotch broom. There was also a decrease in soil exchangeable K due to WT and WT plus coarse woody debris removal (WT + ) at Fall River, which had the lowest initial soil exchangeable K. There was either no effect (Matlock and Molalla) (0–15 years) or a decrease (Fall River) (0–5 years) in stand volume growth due to WT removal. At Fall River, WT, WT+, and AVC treatments had no detectable effect on volume growth from 10 to 15 years. Overall, longer-term effects of organic matter removals and vegetation control on soil and site productivity were variable at each site due to pre-treatment soil nutrition and competition from understory vegetation.

Scotch broom is an N-fixing invasive species that has high potential to alter soil properties. We compared soil from areas of Scotch broom invasion with nearby areas that had no evidence of invasion to assess the influence of broom on soil P fractions and other chemical properties. The study was conducted at two contrasting Douglas-fir sites in Oregon (OR) and Washington (WA), USA with broom invasion for 10 years. We used the Hedley sequential fractionation procedure to assess effects of Scotch broom invasion on P pools of varying bioavailability, and also measured total C, N and extractable nutrient cations. Total soil C and N were significantly higher with broom present at the fine-textured OR site, but there was no effect at the coarse-textured WA site. There was no difference in labile-P measures between the presence and absence of Scotch broom at either site, but there were notable reductions (25–30 %) in the intermediately-available P fraction when broom was present. Extractable nutrient cations (notably K) were lower in the presence of broom at both sites, with the effects most pronounced at the fine-textured OR site. Lasting effects of Scotch broom invasion are likely to be associated with variable changes in soil C, N, and decreases in extractable nutrients and available P. These changes, and other documented effects of Scotch broom on soil, are likely to have lasting effects on Douglas-fir growth after Scotch broom removal that will vary depending soil nutrient status at a given site.

We evaluated the two-year effects of variable-retention harvest on chipmunk (Tamias spp.) abundance () and habitat in mature coniferous forests in western Oregon and Washington because wildlife responses to density/pattern of retained trees remain largely unknown. In a randomized complete-block design, six treatments were applied to 13-ha units at three sites (blocks): four retention levels of original basal area (BA) in an aggregated tree pattern (100, 75, 40, and 15%) and two retention levels in a dispersed tree pattern (15 and 40%). Log-yarding method differed at each site (suspension cable, shovel-loader, or helicopter). We used an information-theoretic approach to compare six candidate regression models for their ability to predict treatment responses of chipmunk and associated habitat variables. Chipmunk had a positive linear relationship with retention level that predicted a 50% reduction in abundance as % BA retention decreased from 100 to 15% (R2 = 0.36). Disturbed soil cover was strongl...

Longleaf pine (Pinus palustris) plantations have been established across the southeastern United States as the first step in restoring the declining savanna ecosystem, yet their long-term stability and development to open canopied woodlands may depend on early density and vegetation management treatments. Commercial thinning (CT) was applied in 2012 (year 18) to a long-term study of longleaf pine community restoration at the Savannah River Site near Aiken, SC to increase abundance of herb species. Although precommercial thinning (PCT) and woody vegetation control increased herb species cover during the first five years of the study, measurements from years 17 to 22 indicated a continuing decline in their cover since year 9 despite application of CT in year 18. Herb species richness, however, increased from 21 to 43 species per 100 m2 area during the last six years of the study, likely a result of disturbances associated with CT and an ice storm in year 20. Application of PCT in 1994, when the plantations were 8–11 years old, reduced their susceptibility to stem bending and breakage from the ice storm, which occurred 20 years later in 2014. Measured 5 months before the storm, pine height: dbh ratio (HD) averaged 78 and 90 for trees growing with and without PCT, respectively, and stem breakage (% of trees) from the ice storm increased linearly (r2 = 0.53) with HD. Pine mortality from the combined effects of glaze ice and wind differed with (28%) versus without (45%) PCT, indicating that long-term stability of longleaf pine plantations depends on early density management.

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 1...

Scotch broom is a large, nonnative shrub that has invaded forests and grasslands in 27 U.S. states. Without treatment, Scotch broom's persistent seedbank ensures a continuing source of regeneration after soil disturbance. In growth chamber studies, five rates of three synthetic auxin herbicides, aminocyclopyrachlor (AC), aminopyralid (AP), and clopyralid (CP), were compared for PRE control of Scotch broom. Cumulative 90-d emergence, mortality, and biomass of seedlings did not vary among herbicides, averaging 42% of seeds sown, 75% of emerged seedlings, and 9 mg seedling−1 for treated containers, respectively, versus 46%, 17%, and 26 mg seedling−1 for nontreated containers. Low rates of each herbicide (< 50% of the maximum labeled rate [MLR]) provided 60 to 80% control, whereas 100% MLR provided 69 to 89% control. Although the herbicides differed in cost per unit seedling mortality (AP < CP < AC), each demonstrated strong potential as a viable treatment for PRE control of Scotch broom.

Scotch broom (Cytisus scoparius (L.) Link) is an invasive, N-fixing shrub in recently harvested Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) forests in the Pacific Northwest. The ability of Scotch broom to dominate a site and displace Douglas-fir in this region may be mediated by site quality and site resource supply. Individual seedlings of Scotch broom (n = 46) and Douglas-fir (n = 46) were planted in a controlled nursery setting and monitored over two years to test the effects of irrigation and fertilization treatments on the physiology and growth of these oft-conflicting species. Overall, Scotch broom remained largely unaffected by resource availability relative to Douglas-fir, which was more sensitive to water and nutrient availability. Scotch broom consistently showed greater assimilation and transpiration rates and plant water potentials than Douglas-fir under all treatments - indicating an elevated ability to acquire soil water resources. The conservative ecology of Douglas-fir resulted in greater water-use efficiency than Scotch broom throughout the experiment, however. Similarly, Douglas-fir crown and height growth started later in the growing season and ended earlier than that of Scotch broom, indicating a longer growing season for Scotch broom but also the importance of resource availability early in the growing season for Douglas-fir given its determinate growth. While Douglas-fir growth reflected the additive effects of increased resource availability, it did not surpass the growth of Scotch broom, which maintained steady growth and biomass accrual under all treatment conditions. The height of Douglas-fir growing under optimized conditions was approximately 40 cm less than that of Scotch broom regardless of treatment regime by the end of the two-year study. This demonstrates how critical early intervention is for land managers in order to control this invasive to avoid Scotch broom overtopping Douglas-fir seedlings during stand establishment. Washington State Department of Natural Resources; U.S.D.A. National Institute for Food and Agriculture [GRANT11325729] We would like to thank the Washington State Department of Natural Resources, Webster Forest Nursery for allowing us to use their facilities to conduct this experiment, with special appreciation for the assistance of John Trobaugh, Eric Jefts, and Viviana Olivares. We would also like to thank Dave Peter, James Dollins, and Alyssa Peter for their help setting up and maintaining this study, as well as, taking field measurements. Funding for this project was provided by the U.S.D.A. National Institute for Food and Agriculture (Grants.gov number: GRANT11325729). Public domain – authored by a U.S. government employee

Four rates of aminopyralid (30, 60, 90, and 120 g ae ha−1 [0.4, 0.9, 1.3, and 1.8 oz ae acre−1]) were compared for their ability to reduce abundance of nonnative dicot species and favor native species in an invaded Cascade Mountain meadow near Trout Lake, WA. Treatments were applied in two replicated studies (June 2009 and 2010), and foliar cover and species richness were monitored for two years. First-year control of nonnative dicots from application of 30 g ae ha−1 of aminopyralid (69%) was greater than that of native dicots (29%); whereas, significant control of both species groups occurred at the higher rates. By the second year after treatment, absolute differences in cover between treated and non-treated plots averaged −17% and −21% for native and nonnative dicots, respectively, and +1% and +27% for native and nonnative monocots, respectively. First-year control of Canada thistle and oxeye daisy was greater after treatment in 2009 (88% and 90%, respectively) than after treatment in 2010 (56% and 55%, respectively), probably because lower spring temperatures in 2010 limited vegetation development and plant susceptibility to aminopyralid. Cover of Kentucky bluegrass and sheep fescue averaged 20% and 6% greater, respectively, in treated plots than in non-treated plots. Application of 30 g ae ha−1 of aminopyralid had no detectable effect on second-year richness of native and nonnative species relative to non-treated plots; however, higher rates caused 24% to 43% reductions in richness of each species group. Research results suggest that application of aminopyralid at 30 g ae ha−1 has the potential to reduce abundance of nonnative dicot species in similar meadow communities of the Pacific Northwest with little or no negative impacts to abundance and richness of native species. As a potential strategy to limit the subsequent spread of Kentucky bluegrass, a grass herbicide, such as fluazifop or sethoxydim, could be added to the treatment.

Logging debris remaining after timber harvest can modify the microclimate and growing conditions for forest regeneration. Debris also can influence tree seedlings indirectly through its effects on development of competing vegetation, although the mechanisms are poorly understood. At two sites in Washington and Oregon (USA) that differed in availability of soil water and nutrients, mechanisms were studied by which logging debris and competing vegetation interacted to influence performance of planted Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii ) seedlings. In a split-plot design, two levels of competing vegetation (presence and absence) and three covers of logging debris (0%, 40%, and 80%) were replicated eight times at each site on 2 × 2-m areas centered on individual Douglas-fir seedlings. Vegetation abundance, seedling growth, and resource availability were monitored for 4 years (2005–2008). Soil water depletion was lower and Douglas-fir water potential and foliar nitrogen were higher in the absence of competing vegetation, resulting in increased seedling growth. The highest seedling growth rates and foliar nitrogen contents occurred where absence of vegetation was combined with 80% debris cover. Where competing vegetation was present, 40% debris cover was associated with decreases in herb cover and soil water depletion and increases in seedling growth relative to 0% or 80% debris covers. At the Washington site where soil quality was lower, the combination of presence of vegetation and 80% debris cover was associated with a 2.4 °C average reduction in summer soil temperatures at 15 cm depth, reduced foliar nitrogen content, and the slowest rates of seedling growth. Potential effects of logging debris, such as mulching (i.e., reduced evaporation of soil water) and interception loss (i.e., reduced precipitation inputs), were minor to non-detectable from sensors buried at 20–40 cm soil depth. Results of the research suggest that retention of moderate levels of logging debris (i.e., 40% cover) after forest harvesting in the Pacific Northwest is likely to increase early growth of Douglas-fir by increasing soil water availability through reduced herb abundance. Where intensive vegetation control is practiced, retention of higher debris levels (i.e., 80% cover) may provide further benefits to seedling growth.

Short-term pulses of increased N leaching typically follow the harvest of forest stands, but the magnitude of these pulses after conventional bole-only (BO) and whole-tree (WT) harvests often is difficult to predict. In this study, we measured N leaching until 6 and 8 years post-harvest on two western Washington Douglas-fir ( Pseudotsuga menziesii var. menziesii ) sites: a relatively low-productivity site with a gravelly loamy sand soil formed in glacial outwash and a high-productivity site with a silt loam soil derived primarily from basalt. We tested BO and WT harvest treatments and presence/absence of 5 years of competing vegetation control (VC). Trends in the magnitude and duration of post-harvest N-leaching pulses differed between sites. At the higher-productivity site, estimated N leaching between years 3 and 8 following harvest totaled 250 and 94 kg N ha −1 in BO and WT harvest treatments with VC, respectively. At the lower-productivity site, estimated N leaching totaled 32 and 17 kg N ha −1 between years 3 and 6 following harvest in BO and WT harvest treatments with VC, respectively. In both BO and WT treatments, annual N leaching did not fall below 2 kg N ha −1 (the rate measured in mature forest stands at both sites) until year 8 at the higher-productivity site and until year 6 at the lower-productivity site. Cumulative amounts of N leached among site/treatment combinations were small compared to the soil total-N pool and ranged from 0.5% to 2.5%. The N leaching patterns among treatments at these two sites suggest that differences in soil N content and C:N ratio, post-harvest vegetation regrowth, and harvest residues influenced the amount of N leached. The major source of leached N was most likely the soil (including forest floor) rather than harvest debris, based on site and treatment comparisons. Although the maximum post-harvest pulse of 250 kg N ha −1 was much higher than values reported in most comparable studies, this level of N leaching is unlikely to be reached under operational conditions, where VC is less intensive than in this study.

Despite widespread use of intensive vegetation control (VC) in forest management, the effects of VC on allocation of biomass and nutrients between young trees and competing vegetation are not well understood. On three Pacific Northwest sites differing in productivity, soil parent material, and understory vegetation community, we evaluated year-5 effects of presence/absence of 5 years of VC on allocation of aboveground biomass and nitrogen (N) between planted Douglas-fir (Pseudotsuga menziesii var. menziesii) and competing vegetation. Equations for predicting bole, branch, foliar, and total dry weights based on stem diameter at a height of 15 cm and total tree height did not differ significantly among sites or by presence or absence of VC. This contrasts with previous research, using diameter at breast height rather than at 15 cm, which found that separate equations were warranted for trees with and without competing vegetation. Estimated whole-tree biomass among the six site/VC combinations ranged from 0.8 to 7.5 Mg ha � 1

To develop silvicultural strategies for restoring longleaf pine ( Pinus palustris Mill.) savannas, mortality and growth of overstory pines and midstory hardwoods and abundance and species richness of herbs were studied for 14 years after pine thinning and nonpine woody control. Pine cover in thinned stands was about half of that in nonthinned stands through year 5, but it lagged by only 8% and 3% in years 9 and 14, respectively, because of vigorous crown responses. Despite a cumulative mortality of 64% of hardwood stems from prescribed fires in years 0, 4, and 9, hardwood basal area in thinned stands (2.1 m2·ha–1) was three times that in nonthinned stands (0.7 m2·ha–1) in year 14. Thinning was associated with 13%–22% more cover and six to eight more species of herbs in years 3–8 but only 6% more cover and two more species in year 14 because of accelerated growth of pine cover and hardwood basal area. However, similar increases in cover and richness of herb species in the woody control treatment were retained through year 14 because it had sustained reductions in hardwood and shrub abundance. Silvicultural strategies that substantially delay encroachment by pines, hardwoods, and shrubs will be those most effective at retaining herb species in longleaf pine savannas, including planting pines at wide spacing, periodic thinning and woody control, and frequent burning.

We assessed changes in mineral soil total carbon (C) and nutrient (exchangeable Ca, K, Mg, and total N) pools to 60 cm depth 5 years after manipulating biomass and competing vegetation at two contrasting Douglas-fir plantations (Matlock, WA, and Molalla, OR). Biomass treatments included whole-tree (WT) and bole-only (BO) harvest, and competing vegetation control (VC) treatments were applied as either initial or annual herbicide applications. There were main effects of biomass removal and VC on the absolute change in soil pools of some elements at both sites, but significant effects were more prevalent at the lower soil quality Matlock site than the Molalla site, and were generally confined to the top 15 cm of soil. In all cases, treatment effects were associated with increases in C and nutrients following BO and initial VC treatments combined with little change in soil pools following WT and annual VC treatments. At the Matlock site, total soil pools (0–60 cm) of C, N, and Ca significantly increased in the BO and initial VC treatments, and Mg increased and K decreased regardless of treatment. At the Molalla site, soil C and nutrient pools did not change in response to treatments, but total soil Mg increased in all treatments during the study period. Correlation analyses indicated little influence of soil nutrient pools on early growth at Matlock likely because soil water is more limiting than nutrient availability at that site, but vegetation growth was correlated to nutrient pools at Molalla indicating changes in pools associated with harvesting and treatment could influence crop development in the future. These early results indicate low potential for intensive management practices to reduce mineral soil pools of C and nutrients, but there is uncertainty on the long-term growth response because treatments may have influenced nutrient storage in pools other than mineral soil.

Where belowground resources are relatively abundant, naturally established trees sometimes occur in very close proximity to one another. We conducted a two-year study to assess the aboveground interactions between Douglas-fir (Pseudotsuga menziesii), grand fir (Abies grandis) and noble fir (Abies procera) seedlings planted in closely spaced (stems 10 cm apart) conspecific and heterospecific pairs. Paired seedling growth also was compared to seedlings planted with no neighbor. Stem height growth was not affected by the presence of a neighbor seedling, although diameter growth was slightly reduced. Branch diameter growth and weight were reduced where seedling crowns overlapped; branch morphological data suggested that this was caused by shading rather than mechanical interactions. Light measurements showed the potential for significant shading, particularly by the relatively large, dense crowns of Douglas-fir. Heterospecific pairs including Douglas-fir demonstrated the competitive production principle in that their mean growth was greater than the average of conspecific pairs of both species. Neighbor seedling height significantly affected subject seedling growth; neighbor effects were similar whether the neighbor seedling was growing on the north or south side of the subject seedling. Light reflected from Douglas-fir crowns had a lower red: far-red ratio than that of noble fir, although there was no evidence of a phytochrome-mediated growth response to the neighbor seedling. While heterospecific seedling pairs showed reduced competition, we found no evidence of facilitation for seedlings growing in very close proximity.

Management practices following forest harvesting that modify organic matter (OM) inputs and influence changes in the soil environment have the potential to alter soil C pools, but there is still much uncertainty regarding how these practices influence soil C flux. We examined the influence of varying amounts of logging-debris retention (0, 40, and 80% coverage) and vegetation control (initial or annual applications) on in situ bulk soil respiration, microbial respiration, and total soil C at two Douglas-fir [ (Mirb.) Franco] sites. Annual vegetation control decreased bulk respiration, which was attributed to reduced root respiration and OM inputs when competing vegetation was absent. There was no difference in potential microbial respiration or total soil C pools between vegetation-control treatments, indicating that OM inputs from competing vegetation were rapidly consumed in situ. Logging-debris retention reduced bulk respiration, microbial respiration, and soil temperature, but the significance and magnitude of the difference were variable. A soil temperature function explained between 44 and 76% of the variation in microbial and bulk respiration, but there was no effect of reduced temperature on microbial respiration with 40% coverage. Total soil C at the end of the experiment was higher with 80% coverage at the site with relatively low initial total soil C, but there was also a significant increase in total soil C at both sites when the logging debris was removed. The results suggest that root decomposition following harvesting causes an increase in total soil C, which is dependent on the magnitude of logging-debris retention, its influence on the soil environment, and ultimately the microbial response.

Although considerable research has focused on the influences of logging debris treatments on soil and forest regeneration responses, few studies have identified whether debris effects are mediated by associated changes in competing vegetation abundance. At sites near Matlock, Washington, and Molalla, Oregon, studies were initiated after timber harvest to quantify the effects of three logging debris treatments (dispersed, piled, or removed) on the development of competing vegetation and planted Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii ). Each debris treatment was replicated with initial and annual vegetation control treatments, resulting in high and low vegetation abundances, respectively. This experimental design enabled debris effects on regeneration to be separated into effects mediated by vegetation abundance and those independent of vegetation abundance. Two to three years after treatment, covers of Scotch broom ( Cytisus scoparius (L.) Link) at Matlock and trailing blackberry ( Rubus ursinus Cham. & Schltdl.) at Molalla were over 20% greater where debris was piled than where it was dispersed. Debris effects on vegetation abundance were associated with 30% reductions in the survival of Douglas-fir at Matlock (r2 = 0.62) and the stem diameter at Molalla (r2 = 0.39). Douglas-fir survival and growth did not differ among debris treatments when effects were evaluated independent of vegetation abundance (i.e., with annual vegetation control), suggesting negligible short-term effects of debris manipulation on soil productivity.

Experimental treatments of logging-debris retention (0%, 40%, or 80% surface coverage) and competing vegetation control (initial or annual applications) were installed at two sites in the Pacific Northwest following clearcutting Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii) stands to assess short-term effects on tree N acquisition, soil N supply, and total soil N. Vegetation control treatments began in the first year after harvest, and logging-debris manipulations were installed 2 years after harvest. Annual vegetation control increased foliar N concentration and content in most years at both sites, which was associated with higher available soil N and increased soil water content. Logging-debris retention treatments had no detectable effect on any of the foliar variables or soil available N at either site. There were no treatment effects on total soil N at the site with relatively high soil N, but total soil N increased with logging-debris retention when annual vegetation control was applied at the site with a low initial soil N pool. Competing vegetation control is an effective means to increase tree N acquisition in the initial years after planting while maintaining soil N pools critical to soil quality. The effect of logging-debris retention on tree N acquisition appears to be limited during early years of stand development, but increased soil N with heavy debris retention at certain sites may be beneficial to tree growth in later years.

Scotch broom is a large, leguminous shrub that has invaded 27 U.S. states. The species produces seeds with a hard coat that remain viable in the soil for years. Growth-chamber studies were conducted to determine effects of temperature regime and cold-stratification period on seed germination. Seedling emergence, mortality, and biomass also were studied in response to sulfometuron and metsulfuron herbicides and variation in soil texture and watering regime. Germination was greatest for a dark/light temperature regime of 15/20 C. Initial rates of germination increased as stratification period was varied from 0 to 60 d, but final germination after 90 d did not differ significantly among periods. Applied alone or in combination, sulfometuron and metsulfuron decreased biomass and increased mortality of seedlings. Mortality from simulated soil drought was greater in the presence versus absence of sulfometuron (20 and 6% mortality, respectively) probably because the herbicide reduced root biomass by 58 to 95%. Invasiveness of Scotch broom is facilitated by a prolonged period of germination across a broad temperature range. Increased control of Scotch broom seedlings with sulfometuron is likely if application is timed to expose recently emerged seedlings to developing conditions of soil drought. Nomenclature: Metsulfuron; sulfometuron; Scotch broom, Cytisus scoparius (L.) Link CYSC4.

Research into postharvest management of forests often focuses on balancing the need for increased biomass yield against factors that may directly impact the productivity of the subsequent stand (e.g. nutrient and water availability, soil microclimate, etc.). Postharvest organic matter management, however, also exerts a strong influence over the translocation of carbon (C) into and through the soil profile and may provide a mechanism to increase soil C content. The effects of contrasting postharvest organic matter retention treatments (bole-only removal, BO; whole-tree removal, WT) on soil solution C concentration and quality were quantified at the Fall River and Matlock Long-term Soil Productivity (LTSP) studies in Washington state. Solutions were collected monthly at depths of 20 and 100 cm and analyzed for dissolved organic C (DOC), dissolved organic nitrogen (DON) and DOC:DON ratio. Comparisons of DOC concentrations with depth illustrate divergent trends between the two treatments, with an overall decrease in DOC with depth in the BO treatment and either an increase or no change with depth in the WT treatment. Trends in DON concentrations with depth were less clear, partly due to the very low concentrations observed, although the relationship of DOC:DON with depth shows a decrease in the BO treatment and little to no change in DOC quality in the WT treatment. This illustrates that more recalcitrant organic matter (higher DOC:DON) is being removed from solution as it moves through the soil profile. Only 35–40% of the DOC moving past 20 cm in the BO treatment is present at 100 cm. Conversely, 98–117% of the DOC at 20 cm in the WT treatment is present at 100 cm. Thus, 11 and 30 kg C ha

We examined the effect of logging-debris retention and competing-vegetation control (CVC, initial or annual applications) on dissolved organic carbon (DOC), dissolved organic nitrogen, and nitrate-N leaching to determine the relative potential of these practices to contribute to soil C and N loss at two contrasting sites. Annual CVC resulted in higher soil water nitrate-N concentration and flux, with the magnitude and duration of the effect greatest at the high-N site. Most of the increase in nitrate-N at the low-N site occurred in treatments where logging debris was retained. Dissolved organic nitrogen increased at the high-N site in March of each year following annual CVC, but the contribution of this increase to total N concentration was small (2%–4% of total N flux). There was no effect of logging-debris retention or CVC treatment on soil water DOC concentrations, indicating that DOC inputs from logging debris and competing vegetation were either retained or consumed in the mineral soil. The estimated increase in leaching flux of dissolved C and N associated with the treatments was low relative to total soil pools, making it unlikely that loss of these elements via leaching will negatively affect future soil productivity at these sites.

Growth and mortality of coast Douglas-fir (Pseudotsuga menziesii var. menziesii) were studied for 25 years after planting seedlings at 1–6-m spacings on a site of moderate quality in the western Cascade Mountains of Washington. Responses were compared to those from two other studies representing high and low site qualities. Third-year height did not differ among spacings (P = 0.80), providing no evidence that close spacing stimulated early growth. Piecewise regression identified the onset of competition-induced mortality when stand density index (SDI [Reineke, L.H. 1933. Perfecting a stand density index for even-aged forests. Journal of Agricultural Research 46, 627–638]) exceeded 52% (S.E. = 4.6) of the species’ maximum or when average crown ratio (CR) declined below 52% (S.E. = 0.9). For a range of SDI values, CR averaged 2–7% points greater at the high-quality site than at the moderate-quality site. In a regression analysis of combined data from the moderate- and high-quality sites, relative values of average stem diameter and stand volume (% of maximum values observed per site) 23–25 years after planting increased and decreased with planting spacing, respectively (R2 = 0.97 and 0.91, respectively). Intersection of these relationships at 3-m spacing indicated a point of equivalent relative development of tree size and stand yield. For a range of site qualities, stands planted at 3-m spacing: (1) maintained tree vigor (CR ≥ 50%) and stability (average height:dbh ratio

In 1- to 2-year-old Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantations near Cave Junction and Glendale, Oregon, sprout clumps of tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.) and other hardwoods were removed with herbicides in April 1983 to leave relative covers of 0%, 25%, 50%, or 100% of the nontreated cover, which averaged 15%. In 1996 (Cave Junction) and 1998 (Glendale), precommercial thinning (PCT) of Douglas-fir and cutting of nonconifer woody species were operationally applied across the four densities of tanoak. In 2005, Douglas-fir in 0% relative cover of tanoak averaged 5–8 cm larger at breast height and 3–6 m taller, and had two to four times the net stand volume of those growing in 100% relative cover. From 1999 to 2005, Douglas-fir stand growth accelerated more rapidly in tanoak relative covers of 0% and 25% than in covers of 50% and 100%. Differential development of Douglas-fir and hardwoods in relative covers of 0%, 25%, and 100%, followed by selection of crop trees via PCT, resulted in three distinct stand structures: pure stands of Douglas-fir with a single canopy layer 12–16 m tall, mixed stands with overstory Douglas-fir (12 m) and midstory hardwoods (7 m), and mixed stands with a single canopy layer (8–9 m).

We evaluated effects of belowground competition on morphology of naturally established coast Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) saplings in 60- to 80-year-old thinned Douglas-fir stands in southwestern Washington. We separately quantified belowground competition from overstory and understory sources using trenching and understory removal. In this light-limited environment of 26 ± 16% (std. dev.) full sunlight, 2-year exclusion of tree root competition by trenching increased sapling stem biomass by 18%, total aboveground biomass by 21%, number of interwhorl buds by 68%, total foliar biomass by 33%, and foliar biomass on branch components over 4 years old by 143%. Belowground competition did not influence shoot:root ratio or foliar efficiency (i.e., stem growth per unit foliage biomass). Sapling needle size, specific leaf area, and internodal distance also were not affected by belowground competition; these variables were apparently a function of the low-light environment. The principal source of belowground competition was roots of overstory trees; effects of belowground competition from understory vegetation were minor. Thus, under a partial overstory, morphology of Douglas-fir regeneration was influenced by both belowground and aboveground competition from overstory trees. In this environment, understory vegetation control would not likely influence belowground competition to an extent that would affect sapling morphology.

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western redcedar (Thuja plicata Donn ex D. Don) seedlings were planted in March 2001 within three clearcut-harvested, shelterwood, or thinned stands of mature Douglas-fir near Olympia, Washington. From 2002 to 2005, areas of vegetation control of 0, 4.5, or 9 m2were maintained with herbicides around a total 162 seedlings per species. Photosynthetically active radiation (PAR) was 34%, 62%, and 100% of full sunlight in thinned stands, shelterwoods, and clearcuts, respectively. Effects of overstory level and vegetation control on seedling growth and resource availability generally were additive. Seedling stem volume index in clearcuts averaged four to eight times that observed in thinned stands, and with vegetation control, it averaged two to four times that observed without it. In thinned stands, relative growth rate of seedling stem volume index had a positive linear relationship with PAR (R2 = 0.38). Foliar nitrogen content of Douglas-fir explained 71% of the variation in relative growth rate. Factors explaining the most variation in foliar nitrogen content differed between thinned stands (PAR, R2 = 0.34) and clearcuts or shelterwoods (midday water potential, R2 = 0.63), suggesting that light and root competition, respectively, were the primary growth-limiting factors for these overstory levels.

We characterized small mammal communities in three loblolly pine (Pinus taeda) stands in the Lower Coastal Plain of South Carolina during June 1998–Aug. 2000 to investigate influence of corridor edges on small mammal distribution. We live-trapped small mammals in three regenerating stands following clearcutting. Harvested stands were bisected by 100-m-wide, 20–23-year-old pine corridors. During 47,040 trap nights, we recorded 907 captures of 661 individual small mammals. Species captured included southern short-tailed shrews (Blarina carolinensis), cotton mice (Peromyscus gossypinus), cotton rats (Sigmodon hispidus), eastern harvest mice (Reithrodontomys humulis), marsh rice rats (Oryzomys palustris), and golden mice (Ochrotomys nuttalli). We did not observe an edge effect (i.e., preference or avoidance) in small mammal captures at the corridor edge. Rodent captures were greatest in harvested stands, declined near the edge of mature pine corridors, and were lowest within corridors. Shrew captures were generally greatest in mature pine corridors and least in the interior of harvested stands. Retention of mature pine corridors of only 100 m may maintain some small mammals (i.e., shrews) that would not occur if stands were completely harvested. South. J. Appl. For. 29(3):148–151.

Chinese privet is a nonnative shrub that has invaded mesic forests throughout the southeastern United States during the past century. Foliar sprays of glyphosate and triclopyr were tested in three factorial experiments that included wide ranges of application rate, timing, and formulation to refine methods for controlling Chinese privet. For spring (April) and fall (October and December) applications, percentage control of privet cover averaged 93 to 100% and 49 to 70% for glyphosate and triclopyr treatments, respectively, whereas for summer (June and August) applications, control averaged 67 to 69% and 14 to 26%, respectively (study 1). However, privet control was not influenced by variation in herbicide rates of 1.7, 3.4, 5.0, or 6.7 kg ae/ha compared with each of the five application timings. No differences were found in August comparisons of liquid vs. dry glyphosate products or water-soluble vs. oil-soluble triclopyr products for each of the four rates (study 2). In a comparison of low rates of glyph...

We studied six pine plantations in coastal South Carolina to determine the influence of clearcutting with corridor retention on small mammal abundance, richness, and diversity. Small mammals were live-trapped in recently clearcut stands that retained pine corridors 100 m in width and in adjacent pine plantations, 20‐23-years-old. We compared small mammal communities between harvested stands with corridors and non-harvested pine stands. We captured 1158 small mammals, representing 844 unique individuals and seven different species in 94,080 trap nights. Rodent abundance, richness, and diversity indices were greater in harvested stands with corridors than in non-harvested pine stands. The early successional habitat created by clearcutting was used by many small mammal species, including cotton rats (Sigmodon hispidus) and marsh rice rats (Oryzomys palustris). Species composition of small mammals within the corridor habitats was similar to that in the non-harvested pine stands. The inclusion of corridors in pine plantation management enhances habitat diversity and ecosystem maintenance and contributes to local diversity of the small mammal community. # 2004 Elsevier B.V. All rights reserved.

In southern pine (Pinus spp.) stands, managers have used a variety of treatments to control hardwood encroachment and improve habitat conditions for northern bobwhites (Colinus virginianus). We compared use of the herbicide Arsenal® (BASF Corporation, Research Triangle Park, N.C.) (imazapyr) and traditional mechanical treatments, with and without fire, to control hardwood encroachment on study sites on Tall Timbers Research Station in the Red Hills Region near Tallahassee, Florida. Hardwood stem density decreased on herbicide and herbicide+burn plots but increased on all mechanically treated plots at 1 year after treatment. Herbicide and herbicide+burn treatments resulted in a >3-fold increase in forb coverage 1 year after treatment, whereas forb coverage did not increase in mechanically treated plots. A single application of imazapyr, with or without prescribed fire, can control hardwood encroachment and stimulate herbaceous species growth. Following treatment, vegetative communities likely can ...

Kudzu is an aggressive, nonnative vine that currently dominates an estimated 810,000 ha of mesic forest communities in the eastern United States. To test an integrated method of weed control, abundances of kudzu and other plant species were compared during 4 yr after six herbicide treatments (clopyralid, triclopyr, metsulfuron, picloram + 2,4-D, tebuthiuron, and a nonsprayed check), in which loblolly pines were planted at three densities (0, 1, and 4 seedlings m−2) to induce competition and potentially delay kudzu recovery. This split-plot design was replicated on each of the four kudzu-dominated sites near Aiken, SC. Relative light intensity (RLI) and soil water content (SWC) were measured periodically to identify mechanisms of interference among plant species. Two years after treatment (1999), crown coverage of kudzu averaged < 2% in herbicide plots compared with 93% in the nonsprayed check, and these differences were maintained through 2001, except in clopyralid plots where kudzu cover increased to 15%. In 2001, pine interference was associated with 33, 56, and 67% reductions in biomass of kudzu, blackberry, and herbaceous vegetation, respectively. RLI in kudzu-dominated plots (4 to 15% of full sun) generally was less than half that of herbicide-treated plots. SWC was greatest in tebuthiuron plots, where total vegetation cover averaged 26% compared with 77 to 111% in other plots. None of the treatments eradicated kudzu, but combinations of herbicides and induced pine competition delayed its recovery.

For 3 years following a severe, November 1992 tornado, abundance and growth of tree regeneration in intact forest-floor and windthrow-pit microsites were studied in three mixed pine and hardwood stands in the Georgia Piedmont, USA. The research had two objectives: (1) determine if performance of tree regeneration differed between microsite types and between pre- and post-tornado cohorts on intact forest-floor microsites, and (2) determine if variation in light and soil water availability from the disturbance affected performance of eight species artificially seeded into intact forest-floor microsites. Near each of the 42 sample points (12–20 per site) spaced on 15 m grids, species and height of tree seedlings were recorded within a 1 m radius plot of intact forest floor and the nearest windthrow pit. Intact forest-floor microsites were dominated by two late-successional species, Acer rubrum (3.5 pre-tornado stems per m 2 and 1.8 post-tornado stems per m 2 ) and Ostrya virginiana (2.6 post-tornado stems per m 2 ), while windthrow pits were dominated by an early successional species, Liriodendron tulipifera (1.7 stems per m 2 ). Although seedling survival did not vary significantly among species or microsite types, first-year height of seedlings in intact forest-floor microsites (24 cm) was significantly greater than those in windthrow-pit microsites (19 cm). Second-year height growth of new seedlings of Cornus florida in intact forest-floor microsites (52 cm) significantly exceeded that of many other combinations of species and microsite type. Species artificially-seeded into intact forest-floor microsites in 1994 and 1995 varied considerably in emergence ( windthrow pits), between cohorts (pre-tornado>post-tornado origin), and among species (mid- to late->early-successional species) indicate that advanced regeneration and new seedlings of A. rubrum , O. virginiana , and C. florida will be long-term dominants of the understory because of their high abundance, initial growth responses, and shade tolerance.