Soil respiration, carbon and nitrogen leaching, and nitrogen availability in response to harvest intensity and competing vegetation control in Douglas-fir (Pseudotsuga menziesii) forests of the Pacific Northwest

Management practices following forest harvest can affect long-term soil productivity through alteration of soil carbon (C) and nitrogen (N) pools, but processes contributing to change are poorly understood. I assessed effects of three levels of logging-debris retention in combination with initial or annual applications of competing vegetation control (CVC) following forest harvesting on soil C flux, N leaching, foliar N of planted Douglas-fir, and changes in soil N and C pools for two years at two sites with contrasting soil properties. Soil C flux was lower when heavy amounts of logging debris were retained, due largely to lower bulk soil and microbial respiration as there was no difference in dissolved organic C (DOC) flux among logging-debris treatments. Increased soil C when heavy amounts of logging debris were retained at the site with lower initial soil C reflected the lower C flux, but soil C was increased at both sites when logging debris was removed, likely due to greater decomposition of belowground organic matter (OM). There was no difference in DOC leaching or soil C between CVC treatments at either site, despite lower OM inputs to mineral soil with annual CVC. Higher bulk soil respiration in the initial CVC treatment indicated that OM inputs from competing vegetation were rapidly consumed, and contributed little to mineral soil C. The most pronounced effects on N leaching and foliar N were associated with annual CVC, which increased Douglas-fir foliar N at both sites, and total N leaching below the rooting zone at the high-N site. However, estimated mass of leached N was small relative to the site soil N pool, and it is unlikely that the loss will negatively affect soil productivity. Logging-debris retention had little influence on Douglas-fir foliar status or N leaching, but soil N was higher at the end of the experiment when heavy amounts of logging debris were retained at the low-N site. There appears to be small potential for logging-debris removal and annual CVC to reduce soil productivity at these sites after harvesting, but logging-debris retention may improve soil productivity, particularly at sites with low initial pools of C and N

Limited Effects of Precipitation Manipulation on Soil Respiration and Inorganic N Concentrations Across Soil Drainage Classes in Northern Minnesota Aspen Forests

It is critical to gain insight into the responses of forest soils to the changing climate. We simulated future climate conditions with growing season throughfall reduction (by 50%) and winter snow removal using a paired-plot design across a soil drainage class gradient at three upland, Populus-dominated forests in northern Minnesota, USA. In situ bulk soil respiration and concentrations of extractable soil N were measured during the summers of 2020–2021. Soil respiration and N concentrations were not affected by throughfall reduction and snow removal, which was largely attributed to the limited treatment effects on soil moisture content and soil temperature. Drainage class was only a significant factor during the spring thaw period in 2021. During this period, the poorly drained plots had lower respiration rates compared to the well-drained plots, which was associated with the drainage class effects on soil temperature. The results of the companion laboratory incubation with varying levels of soil moisture also indicated no effect of the treatment on soil respiration, but effects of drainage class and moisture content on respiration were observed. Our results indicate that the combined effects of reduced summer and winter precipitation on soil respiration and N dynamics may be limited across the range of conditions that occurred in our study

Soil texture and other site-level factors differentially affect growth of Scotch broom (Cytisus scoparius) and Douglas-fir (Pseudotsuga menziesii) seedlings in the western Pacific Northwest

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 ten 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 six to seven years after planting and appear likely to avoid suppression by Scotch broom.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Effects of Biochar on Drought Tolerance of <i>Pinus banksiana</i> Seedlings

Drought is a major stressor of tree seedlings regarding both natural and artificial regeneration, especially in excessively drained, sandy outwash soils. While climate change is expected to cause an increase in the total annual precipitation in the Upper Midwest, USA, the timing of the precipitation is predicted to result in longer periods of drought during the growing season. Biochar, a material created through the pyrolysis of organic matter, such as wood waste, has been proposed as a soil amendment that may increase the water holding capacity of a soil. Biochar has mostly been studied in agricultural settings, and less is known about the impact of biochar on forest soils and tree seedlings. We used a greenhouse experiment to test the ability of biochar to improve the drought tolerance of jack pine (Pinus banksiana) seedlings via increased soil water holding capacity. The seedlings were planted in sandy soil treated with three levels of biochar (none, 3% by weight, and 6% by weight) in two experiments, one manipulating the timing of drought onset and the other controlling the amount of water that seedlings received. Our results showed no significant effects of biochar on seedling survival, growth, or physiology under drought conditions. While this outcome did not support the hypothesis that biochar would increase seedling performance, the biochar amendments did not negatively affect seedlings, indicating that biochar may be added to soil for carbon storage without having negative short-term impacts on tree seedlings

Harvest impacts to stand development and soil properties across soil textures: 25-year response of the aspen Lake States LTSP installations

In addition to long-standing concerns about sustaining forest productivity, maintaining forest ecosystems under changing conditions and emerging threats has become increasingly important when planning forest management. With the aim of understanding effects of management on both productivity and recovery, we quantified the 25-year impact of varying degrees of organic matter (OM) removal and soil compaction on above-ground biomass, soil carbon and nutrients, soil bulk density, and stand development in aspen-dominated forests in the upper Lake States region of the US. Treatment impacts were assessed at three different sites with comparable overstory composition, but with varying soil texture, site quality, and climate. Across all sites, soil C and N generally decreased with increasing OM removal, and bulk density increased with increasing compaction; 25-year observations indicate recovery of bulk density at the surface (0–10 cm) but not at deeper portions of the soil profile. At the most productive site (loamy soils) with favorable initial soil porosity, severe compaction decreased mean aboveground biomass (-46%), particularly of trees (-73%). Biomass at 25 years did not differ among organic matter removal treatments (e.g. stem-only harvest), but a greater increase in soil C occurred with stem-only harvest relative to whole-tree harvest plus forest floor removal. In contrast, at a less productive site with sandy soils poorly buffered to nutrient and C removals, whole-tree harvest reduced biomass by 25% (tree biomass declined 35%) relative to stem-only harvest while compaction treatments did not differ in effects on biomass production, soil C or soil N. On clay soils, compaction treatments did not significantly impact biomass production, but whole-tree harvest plus forest floor removal reduced tree biomass by 47% relative to whole-tree harvest alone. Assessment of mean relative density indicates canopy closure has not yet occurred at the least productive site (clay soils) or the more severely disturbed stands at the intermediate site (sandy soils), suggesting the possibility for treatment impacts not yet discernible to become more pronounced as stands develop and nutrient uptake continues in the future. Our results align with concepts of soil quality and texture-specific limitations to growth, underlying a need to understand key soil limitations when considering forest management impacts to aboveground structure and productivity.This article is published as Curzon, Miranda T., Robert A. Slesak, Brian J. Palik, and Julia K. Schwager. "Harvest impacts to stand development and soil properties across soil textures: 25-year response of the aspen Lake States LTSP installations." Forest Ecology and Management 504 (2022): 119809. Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted

Harvest Impacts to Stand Development and Soil Properties Across Soil Textures: 25-Year Response of the Aspen Lake States LTSP Installations

In addition to long-standing concerns about sustaining forest productivity, maintaining forest ecosystems under changing conditions and emerging threats has become increasingly important when planning forest management. With the aim of understanding effects of management on both productivity and recovery, we quantified the 25-year impact of varying degrees of organic matter (OM) removal and soil compaction on above-ground biomass, soil carbon and nutrients, soil bulk density, and stand development in aspen-dominated forests in the upper Lake States region of the US. Treatment impacts were assessed at three different sites with comparable overstory composition, but with varying soil texture, site quality, and climate. Across all sites, soil C and N generally decreased with increasing OM removal, and bulk density increased with increasing compaction; 25-year observations indicate recovery of bulk density at the surface (0–10 cm) but not at deeper portions of the soil profile. At the most productive site (loamy soils) with favorable initial soil porosity, severe compaction decreased mean aboveground biomass (-46%), particularly of trees (-73%). Biomass at 25 years did not differ among organic matter removal treatments (e.g. stem-only harvest), but a greater increase in soil C occurred with stem-only harvest relative to whole-tree harvest plus forest floor removal. In contrast, at a less productive site with sandy soils poorly buffered to nutrient and C removals, whole-tree harvest reduced biomass by 25% (tree biomass declined 35%) relative to stem-only harvest while compaction treatments did not differ in effects on biomass production, soil C or soil N. On clay soils, compaction treatments did not significantly impact biomass production, but whole-tree harvest plus forest floor removal reduced tree biomass by 47% relative to whole-tree harvest alone. Assessment of mean relative density indicates canopy closure has not yet occurred at the least productive site (clay soils) or the more severely disturbed stands at the intermediate site (sandy soils), suggesting the possibility for treatment impacts not yet discernible to become more pronounced as stands develop and nutrient uptake continues in the future. Our results align with concepts of soil quality and texture-specific limitations to growth, underlying a need to understand key soil limitations when considering forest management impacts to aboveground structure and productivity

Ash Presence and Abundance Derived from Composite Landsat and Sentinel-2 Time Series and Lidar Surface Models in Minnesota, USA

Ash trees (Fraxinus spp.) are a prominent species in Minnesota forests, with an estimated 1.1 billion trees in the state, totaling approximately 8% of all trees. Ash trees are threatened by the invasive emerald ash borer (Agrilus planipennis Fairmaire), which typically results in close to 100% tree mortality within one to five years of infestation. A detailed, wall-to-wall map of ash presence is highly desirable for forest management and monitoring applications. We used Google Earth Engine to compile Landsat time series analysis, which provided unique information on phenologic patterns across the landscape to identify ash species. Topographic position information derived from lidar was added to improve spatial maps of ash abundance. These input data were combined to produce a classification map and identify the abundance of ash forests that exist in the state of Minnesota. Overall, 12,524 km2 of forestland was predicted to have greater than 10% probability of ash species present. The overall accuracy of the composite ash presence/absence map was 64% for all ash species and 72% for black ash, and classification accuracy increased with the length of the time series. Average height derived from lidar was the best model predictor for ash basal area (R2 = 0.40), which, on average, was estimated as 16.1 m2 ha&minus;1. Information produced from this map will be useful for natural resource managers and planners in developing forest management strategies which account for the spatial distribution of ash on the landscape. The approach used in this analysis is easily transferable and broadly scalable to other regions threatened with forest health problems such as invasive insects

Evaluating Adaptive Management Options for Black Ash Forests in the Face of Emerald Ash Borer Invasion

The arrival and spread of emerald ash borer (EAB) across the western Great Lakes region has shifted considerable focus towards developing silvicultural strategies that minimize the impacts of this invasive insect on the structure and functioning of black ash (Fraxinus nigra) wetlands. Early experience with clearcutting in these forests highlighted the risks of losing ash to EAB from these ecosystems, with stands often retrogressing to marsh-like conditions with limited tree cover. Given these experiences and an urgency for increasing resilience to EAB, research efforts began in north-central Minnesota in 2009 followed by additional studies and trials in Michigan and Wisconsin to evaluate the potential for using regeneration harvests in conjunction with planting of replacement species to sustain forested wetland habitats after EAB infestations. Along with these more formal experiments, a number of field trials and demonstrations have been employed by managers across the region to determine effective ways for reducing the vulnerability of black ash forest types to EAB. This paper reviews the results from these recent experiences with managing black ash for resilience to EAB and describes the insights gained on the ecological functioning of these forests and the unique, foundational role played by black ash

The Effects of Combined Throughfall Reduction and Snow Removal on Soil Physical Properties Across a Drainage Gradient in Aspen Forests of Northern Minnesota, USA

Climate change is projected to alter precipitation patterns across northern latitudes, with decreased snow accumulation and summer rainfall predicted. These changes may alter soil physical properties such as soil strength, which would have implications for the feasibility of forest management activities. Reductions in summer and winter precipitation were simulated using a paired-plot design with throughfall reduction and snow removal as treatments across four soil drainage classes (well, moderately well, somewhat poor, and poorly drained) at each of three locations in northern Minnesota, USA. Snow removal caused large reductions in soil temperature and significantly deeper penetration of frost that varied by drainage class, where frost depth decreased with decreasing (wetter) drainage. There was a positive relationship between air freezing index and frost depth, where the rate of frost development was much higher in the snow removal treatment compared to the control (r2 of treatment = 0.8, slope = 0.093, p \u3c 0.001; r2 of control = 0.18, slope = 0.012, p \u3c 0.001). Throughfall reduction had limited effects on soil water content (SWC) and inconsistent effects on soil strength; relationships between SWC and strength were positive, negative, or non-existent. Based on these findings, changes in soil physical properties with altered precipitation are likely to manifest primarily in winter. Drainage class and air freezing index may be used to predict when sufficient soil frost is present for forest management activities to occur without detrimental effects to soil functions