Patterns in foliar nitrogen (N) stable isotope ratios (δ15N) have been shown to reveal trends in terrestrial N cycles, including the identification of ecosystems where N deficiencies limit forest ecosystem productivity. However, there is a gap in our understanding of within-species variation and species-level response to environmental gradients or forest management. Our objective is to examine the relationship between site index, foliar %N, foliar δ15N and spectral reflectance for managed Douglas-fir (Pseudotsuga menziesii) and loblolly pine (Pinus taeda) plantations across their geographic ranges in the Pacific Northwest and the southeastern United States, respectively. Foliage was measured at 28 sites for reflectance using a handheld spectroradiometer, and further analyzed for δ15N and N concentration. Unlike the prior work for grasslands and shrubland species, our results show that foliar δ15N and foliar %N are not well correlated for these tree species. However, multiple linear regression models suggest a strong predictive ability of spectroscopy data to quantify foliar δ15N, with some models explaining more than 65% of the variance in the δ15N. Additionally, moderate to strong explanations of variance were found between site index and foliar δ15N (R2 = 0.49) and reflectance and site index (R2 = 0.84) in the Douglas-fir data set. The development of relationships between foliar spectral reflectance, δ15N and measures of site productivity provides the first step toward mapping canopy δ15N for these managed forests with remote sensing.

Commercial forestry activities featuring heavy machinery and intensive traffic represent one of the most common degradation processes in infertile Tropical soils. This research aimed to evaluate the potential of sewage sludge (SS) as pedotechnomaterial (PTM) for soil recovery in strongly degraded Entisols with a human-induced, highly compacted densic horizon (A(d)). The area was used as a lumber deposit and for related forestry activities for more than ten consecutive years. Soil recovery activities consisted of: i) SS increasing dose applications (2.5, 5.0, 10.0, 15.0, and 20.0 Mg ha(-1)) in the surface mineral horizon, vs a control; and, ii) pioneer (Pn), secondary (Se), and climax (Cx) native species plantation. Pioneer, Sc, and Cx were characterized by an increasing H and D trend as time went by, with Pn (H and D) > Sc > Cx. After three years, the highest SS dose (20 Mg ha(-1)) provided the best performance in most investigated species. Soil treated with the highest SS dose showed increased SOM, total P, CEC, exchangeable Ca, total Fe, Mn, Cu, and Zn contents after 36 months. No soil nutrient deficiency, potentially toxic elements (PTE) soil pollution, or related hazards were observed. The principal factor analysis showed that SS positively effects soil-plant feedbacks and related behavior. Canonical correspondence analysis explained how soil physical-chemical parameters influenced the whole plant ecological succession over time: i) during the early stage of development, Pn and Sc species were mainly affected by soil pH (SS buffering effect); ii) after one year, Ca, Mn, and CEC strongly influenced D development of mainly Sc species, thus further developing the whole soil-plant system; iii) at the end of the experiment, SOM and several soil macro- and micronutrients greatly influenced more demanding Cx species. For the first time, this research demonstrated the SS efficiency as PTM in strongly degraded Tropical soils; a PTM strongly favoring soil and forest restoration.

The increasing production of biosolids in urban areas has been led to a search for alternative disposal avenues of this residue, which is rich in organic matter and nutrients. Agricultural land application of biosolids, motivated by its fertilizing power, is a widespread practice in many countries, but there are safety and regulatory concerns regarding the presence of pathogens in Class B biosolids. In addition, the scarcity of studies under tropical climate conditions raises questions that impede the agricultural use of this residue in some regions. The objective of this study was to evaluate the survival of thermotolerant coliforms over 12 months (52 weeks) after biosolids application on the surface of a Quartzipsamment neosol cultivated with Eucalyptus. Two different biosolids were studied: those generated by a biological treatment system with complete mixing aeration ponds followed by decantation ponds (Treatment A) and biosolids from a biological treatment system with conventional activated biosolids reactors (Treatment B), both delineated in randomized blocks with four replicates. After application on the forest soil, we estimated an average survival time of 54 weeks for thermotolerant coliforms present in Treatment A biosolids and 93 weeks in Treatment B biosolids. Thermotolerant coliforms persist much longer under tropical climate conditions in Brazil than in comparable studies under temperate climate conditions. This reaffirms the need to carry out studies covering the full range of moisture and temperature regimes in which biosolids are applied as fertilizer.

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−1 less Douglas-fir biomass than the BO treatment. There was 1.5 to 20.5 Mg ha−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.

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.

Human history is intricately linked to the soil. As human populations increased agricultural land use intensified. Wood availability was also important and resulted in the management of forested land for fuel, fiber and food. Soil mapping was an essential tool in planning future expansion of agriculture and resulted in an increased understanding in the factors that regulate soil formation. This understanding eventually lead to the formation of forest soil science as a separate area of research. Early forest soil research focused on silviculture, harvesting, soil chemistry and acid rain. As the science progressed areas of research broadened to include specialized forest harvest methods and eventually to ecosystem-related research designed to understand how soils function as an integral part of the forest.

Long-term research studies are critical to understanding soil productivity and the sustainability of forest and woodland ecosystems around the world. They inform management decisions about best harvest techniques, soil property impacts and recovery, anthropogenic stressors (e.g., forest management, acid rain, climate change), and the influence if governmental policies, guidelines, and regulations. Forest ecosystems represent a major source of drinking water in much of the world making the interaction of atmospheric chemistry, vegetation, land use, soil and water one of global importance. This intimate connection among interacting variables also make forests a logical system to study ecosystem processes. In this chapter we discuss the challenges and benefits of establishing and maintaining long-term studies, the utility of these studies for informing decisions about how to manage forest soil to sustain the delivery of ecosystem services and lessons learned for forest research.

Most of our terrestrial carbon (C) storage occurs in soils as organic C derived from living organisms. Therefore, the fate of soil organic C (SOC) in response to changes in climate, land use, and management is of great concern. Here we provide a unified conceptual model for SOC cycling by gathering the available information on SOC sources, dissolved organic C (DOC) dynamics, and soil biogeochemical processes. The evidence suggests that belowground C inputs (from roots and microorganisms) are the dominant source of both SOC and DOC in most ecosystems. Considering our emerging understanding of SOC protection mechanisms and long-term storage, we highlight the present need to sample (often ignored) deeper soil layers. Contrary to long-held biases, deep SOC—which contains most of the global amount and is often hundreds to thousands of years old—is susceptible to decomposition on decadal timescales when the environmental conditions under which it accumulated change. Finally, we discuss the vulnerability of SOC in different soil types and ecosystems globally, as well as identify the need for methodological standardization of SOC quality and quantity analyses. Further study of SOC protection mechanisms and the deep soil biogeochemical environment will provide valuable information about controls on SOC cycling, which in turn may help prioritize C sequestration initiatives and provide key insights into climate-carbon feedbacks.

Agricultural recycling of human Class B biosolids in sugarcane ( spp.) crop is a promising alternative to reduce the costs of biosolids disposal. However, the presence of fecal contamination indicators such as thermotolerant coliforms and pathogenic organisms such as enterovirus and spp. in biosolids impose barriers to effective and widespread use of biosolids as fertilizer. In addition, there is a scarcity of studies that investigate the persistence of these organisms in tropical soils. This study aimed to evaluate the persistence of pathogenic and fecal indicators for 258 d in a tropical clayey soil amended with human Class B biosolids and cultivated with sugarcane. Treatments were immediate incorporation of biosolids into soil after application (T1) or superficial application of biosolids followed by incorporation after 35 d (T2), emulating the typical procedure in sugarcane fields. Thermotolerant coliforms were estimated to persist for 437 d in T1 and 398 d in T2. For enterovirus, mean estimated persistence time in soil was 26 d for T1, but the sampling frequency was insufficient in T2 for persistence analysis. After 35 d, no enterovirus was detected in any sample. Mean estimated persistence time for viable spp. eggs in soil was 22 d in T1 and 41 d in T2.

Stem sinuosity is a deformation that occurs in Douglas-fir and other tree species. Nutritional deficiencies, such as those of copper, zinc, boron, and calcium have been positively associated with increased stem form deformities. The objective of this study was to analyze available soil and total foliar concentrations of sinuous Douglas-fir stands and determine if these data provided insights into the role of nutrients on sinuosity across different sites. Relationships among genetic gain levels across different sites were also assessed to evaluate whether trees selected for growth and form were better at mobilizing and sequestering nutrients in soils or needles. As data collected were multivariate, Mantel test and permutational multivariate analysis of variance (PERMANOVA) were used to study effects of site, genetic gain levels on soil, and foliar nutrients, with ordinations used to visualize trends. The stands were found to be deficient in boron and calcium, and moderately deficient with respect to zinc and nitrogen. Combining foliar data with soil nutrients revealed that there was differential uptake of these nutrients as compared to other more abundant micronutrients. Results of univariate and multivariate analyses showed that site was the most important predictor, which explained variation among soil nutrient concentrations. Genetic gain level was a significant predictor for variation among soil nutrients; however, not significantly for foliar concentrations according to multivariate analyses. Trends in the data indicate that proper genetic selection could reduce sinuosity while also increasing growth. The results of this study support the contention that no one single factor can explain stem sinuosity. It is likely that sinuous growth in trees is caused by a combination of unbalanced nutrient concentrations and metal deficiencies, as were seen in this study, in addition to genetic, environmental, and physiological factors.

Research has shown significant effects of timber harvest residue management on soil organic carbon (SOC), but less impact has been observed on the available P pool. The objectives of this study were: (1) to estimate the effects of different timber harvest intensities and P fertilization on soil labile P and P fate over time; and (2) to identify which soil P fractions supply P to Eucalyptus plantations cultivated in soils with low P availability. P fractions were assessed using Hedley's sequential extraction methodology, which corresponds to differing degrees of soil P lability. Three timber harvest intensities (stemwood only, whole tree and whole tree plus litter) and two levels of P fertilization (0 and 44 kg ha(-1) of P) were used. A total of 70% of total soil P was found in a non-labile form in the whole tree plus litter removal treatment, while in the whole tree treatment only 66% was found in this form. Removal of harvesting and litter residues resulted in a 40% reduction in the labile P fraction when compared to stemwood only harvested treatment even with fertilizer application. Acid phosphatase activity, which is crucial in mobilizing P for plant uptake, was 45% higher in soils that did not receive P fertilizer, but it did not resulted in higher concentration of labile P. Timber harvest intensity and P fertilizer application did not influence the soil total P concentration over 12 years of Eucalyptus cultivation. However, there was an increase in non-labile and inorganic P fractions and a reduction of labile and organic P fractions with increasing timber harvest intensity. The organic, moderately labile P fraction was the main source of P to the trees under low P availability conditions. Acid phosphatase and low molecular weight organic acid excretion seem to be important strategies of Eucalyptus species to improve P uptake.

Enhanced efficiency fertilizers (EEFs) are used to minimize gaseous losses of applied nitrogen (N). Higher N retention resulting in increased uptake by plants is intended to offset the additional cost of these EEFs. Pacific Northwest Douglas-fir forests are N limited and assumed to have high N retention rates. Assuming N retention rates are high can lead to the over application of fertilizers which is both economically inefficient and detrimental to ecosystem health. We tested the hypothesis that EEF-fertilized plots have the highest ecosystem N recovery rates by tracing four urea-based fertilizers for four weeks after application in five commercially managed Douglas-fir forests in Oregon and Washington. Three EEFs, Environmentally Smart Nitrogen (ESN), N-(n-butyl) (NBPT), and Arborite coated urea fertilizer (CUF), were tested along with unformulated urea granules. These three particular EEFs are designed to reduce volatile losses of ammonia (NH3(gas)). Fertilizers were enriched with N-15, which facilitates the tracing of N as it moves between ecosystem pools. Retention rates were calculated for the forest floor and mineral soil to a depth of 20 cm. Retention rates were not significantly improved with the use of EEFs. On average, 30.2% of the applied N was lost from the system after four weeks. The lack of improvement in N retention with EEFs suggests that volatilization may not be a substantial loss pathway at these sites and therefore the application of these higher cost EEFs is not warranted.

Douglas-fir forests of the coastal Pacific Northwest experience yearly summer droughts; however, the variation in shallow soil available water supply throughout the region is not well understood nor is the effect of future climate change. Soil moisture sensors were installed in 60 Douglas-fir plantation forests over 6 years. Stands were grouped by physiographic regions to describe differences in climate and available water supply. Monthly available water supply (MAWS) (0-50 cm) was calculated as the average daily available moisture content. MAWS was modeled using monthly climate variables, and the equation was then used to predict the change in MAWS due to mild, moderate, and severe climate change predictions. Regional monthly air temperature and precipitation were strongly predictive of MAWS. Mild to severe climate change are predicted to decrease yearly available water supply by 8% to 19%, while summer available water supply will decrease from 25% to 72%. The greatest decreases due to climate change will be found in the coastal regions of Washington and Oregon due to greater negative effects of temperature on available water supply. Climate change, especially the most severe predictions, was shown to have a sizeable effect on shallow soil available water supply in coastal Douglas-fir forests.

Forests provide valuable ecosystem and societal services, including the sequestration of carbon (C) from the atmosphere. Management practices can impact both soil C and nitrogen (N) cycling. This study examines soil organic C (SOC) and N responses to thinning and fertilization treatments. Soil was sampled at an intensively managed Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation in north-western Oregon, USA. Management regimes—thinning, fertilization plus thinning, and no (control) treatment—were randomly assigned to nine 0.2-ha plots established in 1989 in a juvenile stand. Prior to harvest, forest floor and soil bulk density and chemical analysis samples were collected by depth to 150 cm. During a single rotation of ~40 years, thinning treatments significantly reduced SOC and N stocks by 25% and 27%, respectively, compared to no treatment. Most of this loss occurred in deeper soil layers (below ~20 cm). Fertilization plus thinning treatments also reduced SOC and N stocks, but not significantly. Across all management regimes, deeper soil layers comprised the majority of SOC and N stocks. This study shows that: (1) accurately quantifying and comparing SOC and N stocks requires sampling deep soil; and (2) forest management can substantially impact both surface and deep SOC and N stocks on decadal timescales.

Changing climate, land use, and management can impact both surface and deep soil organic carbon (SOC) stocks on decadal timescales, highlighting the importance of accurate measurements of SOC stocks and comparisons. This study compared three soil sampling methods for estimating SOC stocks: clod, core, and excavation. The excavation method was used as the standard by which the other methods were compared. Sampling took place at an intensively managed Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantation in northwestern Oregon, USA. Soil samples were collected by depth to 150 cm. Clod and core method soil bulk density measurements were significantly different at all depths, with the core method consistently resulting in lower soil bulk density. The core method significantly underestimated soil bulk density at all depths deeper than 20 cm and underestimated the SOC stock to a depth of 150 cm by 36%. Most of this difference occurred deeper than 20 cm, where the majority of SOC stocks were contained across all soil sampling methods. The underestimation of soil mass by the core method similarly affected the fixed depth, genetic horizon, and mass based approaches to quantify SOC stocks. This study demonstrated that (1) commonly used soil sampling methods for measuring soil properties should not be assumed to be interchangeable; and (2) regional and global SOC stocks may be largely underestimated due to shallow sampling and the frequent use of core methods.

Applying finely ground silicate minerals to soils could mitigate CO2 emissions by enhancing the rate of carbon sequestration via silicate weathering. Using these minerals instead of agricultural lime to increase soil pH would also eliminate the dissolution of lime as a major source of agricultural CO2 emissions. However, dissolution rates of silicate minerals in the soil environment are uncertain and impacts of their application on the decomposition of soil organic matter have yet to be determined. A 3-month soil incubation was performed to investigate the effects of olivine, a highly weatherable silicate mineral, at two application rates (OLIVlow, OLIVhigh) on soil CO2 flux, available Mg and Al, and pH in comparison to control and lime-amended soils. There was no difference in cumulative net CO2 flux between the olivine-amended soils and the control though total flux from the limed soils was 221% higher than the control. Heterotrophic respiration was also greatest in the lime-amended soils. The weathering rate of OLIVlow (26.7%) was higher than of OLIVhigh (7.1%), but both treatments increased soil pH to a level sufficient to overcome aluminum toxicity. Our results suggest that olivine amendments are an effective tool for carbon sequestration and a suitable replacement for lime.

In many countries, the main reason for severely restricting or outright banning the land application of class B biosolids is the lack of risk assessment for adverse human health impacts. Among pathogens that are not often studied are helminth ova, including that of the spp. Almost all of the knowledge about the persistence of spp. ova in soils fertilized with biosolids is based on studies developed in North America, Europe, and Asia. These studies have almost always been conducted under temperate climate conditions, which may cause erroneous interpretations when the conclusions are extrapolated to tropical regions such as those found in Brazil. This team evaluated the persistence of viable spp. ova in a sandy Quartzipsamment tropical soil, previously planted with × hybrid () and fertilized with biosolids, over a 52-wk period. During the reporting period, the average temperature of soil and biosolids fluctuated between 15 and 30°C, and the average moisture of biosolids fluctuated between 60 and 90%. The estimated persistence time of viable spp. ova after land application was estimated at close to 7 wk, indicating that ova may not be viable for as long as it has been shown to be in studies of more temperate areas. The relationship of temperature with persistence of viable spp. ova in a tropical soil was stronger than moisture content, suggesting that temperature substantially contributed to their nonviability over the course of the experiment.

Soil contains more C than the atmosphere and plant biomass combined. Consequently, it is the most important long-term sink for C within terrestrial ecosystems. An understanding of the potential to induce C sequestration in soils through management is crucial in light of increasing anthropogenic CO2 emissions. Nevertheless, soil has historically been under-represented in C cycling research, especially regarding subsurface (>30 cm) layers and processes. Research on the effects of forest management practices on deep soil C has been lacking. To test the effects of biomass removal and vegetation control treatments on deep soil C, soils were sampled to a depth of 3 m at the Fall River Long-term Soil Productivity Site in western Washington State. Treatments were installed 15 yr previously in a complete randomized block design. No difference was found in total soil C among treatments, but there was significantly less (a = 0.10) C stored at the deepest interval measured (250-300 cm) in the plots with vegetation control (8.6 Mg C ha(-1)) than in those without (16.3 Mg C ha(-1)). These results suggest the stability of soil C pools at Fall River and indicate that more intensive management practices may not deplete C pools at this site, but imply that these deep soil pools may be more sensitive to change than shallow pools. Here, 58.2% of the soil C pool is located below 30 cm, which demonstrates that shallow sampling significantly underestimates soil C pools and highlights the importance of understanding processes that control deep soil C.

Fertilizer response of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantations can vary considerably throughout the Pacific Northwest due to differences in soil and site productivity. In this study, we calculated significant two-, four-, and six-year cumulative volume growth response per tree due to urea fertilization on 71 Douglas-fir installations using a paired t-test. To understand the biogeoclimatic factors affecting fertilizer response, climate, location, soil, and productivity predictor variables were used in boosted regression tree (BRT) and linear discriminant (LDA) analyses to produce models that could predict significant regional response to fertilization. The ability to predict significant volume response decreased with time since fertilization (71-37% from 2 to 6 years), yet installations that were predicted to respond in all years of BRT models had similar response to significantly responding installations (> 5000 cm(3)/yr). The most common predictors of volume response in both model types and all measurement periods were high elevation (> 400 m), low moderate site index (< 42 m at 50 years), and cold winter temperatures (< 4.4 C). The Oregon (OR) Klamath Mountain region contained the greatest coverage of predicted volume response. The Middle Cascade Mountains also had large areas predicted to respond, but in this study OR installations responded better than Washington (WA) installations. The Coast Range, Olympic Mountains, Puget Trough, and Northern Cascade Mountains were predicted to have very little response. This study demonstrates the spatial relationships between climate, soil, and productivity variables that indicate fertilization response across the coastal Pacific Northwest.