Long-Term Soil Productivity Study Research Articles

The Long-Term soil productivity study after three decades

The Long-Term soil productivity study after three decades

Effects of harvesting intensity, vegetation control and fertilization on 5–20 year post-harvest N availability in boreal jack pine and black spruce forest soils in northern Ontario, Canada

The impact of harvesting intensity, vegetation control and fertilization on soil N availability 5–20 years post-harvest was determined at 18 jack pine and black spruce forests in northern Ontario, Canada. The study sites are affiliated with the North American long-term soil productivity (LTSP) study. Boreal forest growth is commonly N limited and young stands approaching crown closure acquire most of their N from the soil. The study sites represented a range of soil types and were harvested with three levels of organic matter removal (stem-only harvest, full-tree harvest and full-tree harvest with organic horizon removal by blading). Three study sites had multiple applications of glyphosate to control competing vegetation and one site included a trial with two applications of N, P, K fertilizer to the full-tree harvest treatment. We used short-term anaerobic laboratory incubations and in-situ closed top tube growing season incubations to determine mineralizable N and net N mineralization, respectively. Profile (organic plus mineral horizons) mineralizable N pools were higher in operational clearcut (stem-only and full-tree harvesting) treatments compared to the uncut reference forest 10–14 years post harvest. Full-tree harvesting with blading significantly reduced profile mineralizable N pools at this time compared to operational harvesting, while the same treatment at one upland site also reduced net N mineralization pools. Profile mineralizable N pools and microbial biomass C and N were lower in full-tree compared to stem-only harvesting treatments, suggesting that increased slash retention with stem-only harvesting was playing a role in enhanced soil N availability at a time when plantations were approaching a period of greater N demand. Fertilization and vegetation control treatments had few effects on N indices, although net N mineralization pools for the stem-only and full-tree harvest that also had the repeated herbicide treatment were consistently, but not significantly, lower than non-herbicided treatments. Soil N indices were useful predictors of dominant height growth for jack pine to a greater degree than for black spruce, and soil N concentrations were as effective at predicting height growth as more resource intensive measurements. Our results point to the importance of continued monitoring of soil and stand conditions at these LTSP sites as treatment effects on soil N cycling and site productivity will likely continue to evolve. At this stage of stand development, full-tree harvesting plus organic horizon removal, followed by operational harvesting has led to lower soil N availability than operational tree-length harvesting, and stands with understory vegetation control are now showing indications of reduced N availability.

Wood stake decomposition twenty years after organic matter removal at the Lake States LTSP sites

Organic matter (OM) is an integral part of site productivity for a forest, and understanding the effects of OM removal on various forms of carbon (C) cycling is important for land managers and for policy makers. In this study, we utilized the Lake States Long-Term Soil Productivity (LTSP) study sites, located along a gradient in soil texture (clay, silt loam and sand) and high to low productivity, to evaluate the impacts of two OM removal treatments on belowground wood decomposition. In 2013, approximately 20 years after the LTSP treatments had been installed, we placed standardized aspen and loblolly pine wood stakes in the mineral soil of plots receiving the bole only harvesting treatment (BO) and the whole tree harvesting with forest floor removal treatment (WT + FF), and in plots in an adjacent unharvested reference area (1350 wood stakes total). Soil was also sampled to characterize the microbial community composition in the various treatments. From 2014 to 2018, wood stakes were removed from each treatment, and mass loss determined. We found significant differences in wood stake decomposition among the three sites, and between the two wood species, but little impact of timber harvesting and surface OM removals on decomposition. Soil microbial composition also reflected site differences in stake decomposition. We conclude that clearcut harvest and surface OM removal had little effect on stake mass loss in the mineral soil 20 years after the treatments were initiated, and the inherent soil factors are now controlling decomposition.

Decomposition of wood stakes in the Pacific Northwest after soil compaction and organic matter removal

Forest operations can affect soil productivity by impacting the amount and distribution of surface organic matter (OM) and changing the properties of surface mineral soil. The North American Long-Term Soil Productivity Study (LTSP) was developed to address such long-term changes after pulse disturbances associated with clearcut harvesting, soil compaction, and OM removal across a wide spectrum of forest sites. From 2000 to 2002 we established a study to assess the impact of four soil disturbance treatments on OM decomposition in the mineral soil on seven LTSP study plots from southern British Columbia, Canada to southern Oregon, USA. The soil treatments were combinations of two levels of compaction and organic matter removal: 1) removal of only merchantable logs [OM0] , 2) removal of all the forest floor and woody material [OM2], 3) no soil compaction after harvest [C0], and 4) “severe” soil compaction after harvest [C2]. Aspen (Populus tremuloides Michx.) and pine (Pinus taeda L.) wood stakes were inserted into the mineral soil of each treatment plot and in an adjacent unharvested control stand to a depth of either 20 or 30 cm (depending on soil depth). At the end of three years the soil compaction and the OM removal treatments had relatively little effect on pine or aspen stake decomposition at the British Columbia study sites. In the United States, soil compaction increased decomposition on the two study sites with coarse-texture mineral soil with surface OM intact. Three key findings were: (1) a strong positive relationship (p = 0.0009) between stake water content and stake mass loss, (2) aspen and pine stake decomposition was greater in the clearcut-LTSP treatments than in the unharvested stands, (3) the rehabilitation of the compacted soil treatment on the British Columbia study sites generally increased wood stake decomposition. However, overall, there were no consistent wood stake decay trends across all sites and LTSP treatments.

Soil compaction and organic matter removal effects on soil properties and tree growth in the Interior Douglas-fir zone of southern British Columbia

Silviculture systems and associated forest harvesting practices that affect the level of soil compaction and organic matter retained on a site will cause changes to soil properties and processes that may affect the growth of planted trees. We present results for soil conditions and tree growth after 15 years for 6 Long-term Soil Productivity Study (LTSP) installations in 2 distinct regions of the Interior Douglas-fir (IDF) biogeoclimatic zone in southern British Columbia (BC). In a 3 × 3 factorial design, three levels of compaction and organic matter removal were replicated in two distinct IDF regions that varied in parent material, but with similar climates. Each treatment was then split and planted with two different species, Douglas-fir and lodgepole pine. In each region, three unique sites (block), all within a radius of 50 km from one other, were installed with the same combination of treatment and species for a total of six replicates, three in each of two regions. Across IDF regions, tree heights on calcareous soils in the Rocky Mountains of south-eastern BC were 36% lower for Douglas-fir and 23% lower for lodgepole pine than on more acidic soils on the Thompson Plateau. There were varying differences across treatments in soil and foliar nutrient concentrations between IDF regions, primarily from regional parent material differences. However, nutrient deficiencies were apparent in both regions and may have limited growth, especially on the more calcareous sites. Increases to soil bulk density (27%) 1 year after compaction did not impact tree survival, height at Year-15, or chemical properties in foliar tissue or soil. Fewer growing season frost events and increased soil water availability during the seedling establishment period was a likely reason for a 25% increase in Douglas-fir survival at Year-15 with the whole tree + forest floor removal (OM3) treatment. However, whole tree + forest floor removal (OM3) also produced a 13–19% reduction in soil N, S, K, and mineralizable N when compared to both stem-only (OM1) and whole tree (OM2) harvesting treatments that kept the forest floor intact. Effects on forest productivity from soil compaction after 15 years appear to be overshadowed by the more prominent effect of organic matter removal treatments during stand establishment and early growth. Future work at these installations focusing on nutrient budget, forest health, and ecosystem carbon stock differences across treatments will provide valuable insight into silviculture and harvesting practices for different species and regions in the dry forests of southern BC.

Effects of forest harvesting and biomass removal on soil carbon and nitrogen: Two complementary meta-analyses

Forest residues and logging slash from pre-commercial forest thinning and regeneration harvests are a potential feedstock for bioenergy production but there has been a concern about the impact of residue removal on forest soil C and N. This study aimed to address such by conducting two meta-analyses using the data available from published literature and an independent dataset compiled from the North American Long-Term Soil Productivity (LTSP) study.For the meta-analysis using literature, we categorized forest harvesting and biomass removal into i) no harvest control, ii) bole-only (BO, partial or clearcut) regular harvests, iii) BO with partial removal of logging slash and/or O horizon (BO+Removal), iv) whole tree harvests (WTH), and v) WTH with slash and O horizon removal (WTH+Removal). Accordingly, we compiled soil C and N data and key statistics (e.g., standard deviation) from 142 scientific articles published since 1979. We compared the results from this meta-analysis with data from 22 installations of the LTSP study where three levels of organic matter removal - BO, WTH, and WTH plus forest floor (+FF, O horizon) removal - as well as an additional vegetation control (+VC) were measured for two decades in either completely randomized or randomized block design.In the literature meta-analysis, BO+Removal (-19.2%), WTH (-15.4%) and WTH+Removal (-24.9%) contained significantly less soil C than no-harvest controls across combined soil depths, while BO had no difference. Within individual mineral soil horizons, only BO+Removal and WTH+Removal treatments contained significantly less carbon than controls. There was a high degree of heterogeneity in treatment response between studies in the literature. The analyses from the LTSP dataset showed no significant difference in combined soil depths for WTH or WTH+VC relative to BO harvest, but there was significantly less soil C in BO+VC (-3.6%), WTH+FF (-8.5%) and WTH+FF+VC (-15.3%). These treatment effects declined over time since harvest, particularly the most intensive treatments. Soil N results largely mirrored soil C in both meta-analyses with smaller estimated effects for most treatments at equivalent depths (except for WTH+Removal and WTH+FF+VC, which remain about the same). There were no significant differences in soil N for combined soil depths between WTH and no-harvest control (in the literature analysis) or BO harvest (for both analyses).Since the most severe losses of soil C and N involved FF removal, WTH that accounts for modest removals (<80%) of harvesting residues may provide a sustainable source of biomass for bioenergy production without additional soil impacts compared to BO harvesting practices.

Legacy effects of non-native Cytisus scoparius in glacial outwash soils: Potential impacts to forest soil productivity in western Washington

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.

Douglas-Fir Biomass Allocation and Net Nutrient Pools 15–20 Years after Organic Matter Removal and Vegetation Control

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.

Logging-debris and vegetation-control treatments influence competitive relationships to limit 15-year productivity of coast Douglas-fir in western Washington and Oregon

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 the edge of debris piles at Matlock averaged 16% greater than that of trees > 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.

Long term effects of intensive biomass harvesting and compaction on the forest soil ecosystem

Forest soil ecosystems can be negatively affected by intensive biomass harvesting due to losses of organic inputs and soil compaction, ultimately leading to reduced forest productivity. In this research, we revisited a site from the North American Long-Term Soil Productivity study located on a sandy Spodosol within the Huron National Forest in Michigan, USA, to measure the effects of aboveground organic matter removal of different intensities (three levels: bole only; whole tree harvest; or whole tree harvest and forest floor removal) and soil compaction (2 levels: no or moderate compaction) nearly 20 years following the initial treatments. The effects of harvesting on the soil microbial community in surface and subsurface soils and on soil nutrient availability in surface soils were evaluated. Additionally, patterns of carbon and nitrogen distribution among soil organic matter pools in surface and subsurface soils were compared using a physical fractionation approach to isolate a free – light fraction of particulate organic matter external to aggregates, an occluded – light fraction, which represents particulate organic matter released from the disruption of soil aggregates, and a heavy or mineral-associated fraction. Whole-tree harvests had significantly different microbial community compositions than bole-only harvests (P = 0.02), a result driven by significantly lower abundance of arbuscular mycorrhizae and greater gram positive bacterial abundance in the whole-tree harvest relative to bole-only harvest conditions. Few differences in soil nutrient availability were apparent 20 years after organic matter manipulations, with the exception of reduced calcium availability where organic matter was removed. Soil compaction resulted in greater microbial biomass (0.19 versus 0.14 μmol g−1 soil), which may have also led to a reduced C:N ratio in the heaviest and oldest soil component and increased P availability as well. Nitrogen concentrations and stocks were greatest at the surface (0–10 cm depth) for the free and light soil fractions in bole-only removal treatments, in contrast to whole-tree harvest treatments where C and N concentrations and C stocks were greater in the subsurface soil (free - light fraction at 20–30 cm depth). The soil microbial community, soil fraction size, and soil C and N stocks differed between surface and subsurface soils, highlighting the soil forming processes at work in this Spodosol, and the importance of sampling multiple depths to address research questions. These results demonstrate the long-term effects of forest management on soil biological, physical, and chemical properties and are useful in evaluating sustainable biomass harvesting practices for comparable forests.

Effects of forest harvest and fertiliser amendment on soil biodiversity and function can persist for decades

Effective management is critical to the establishment and growth of productive and sustainable planted forest ecosystems. Harvesting and nutrient applications can significantly disturb these ecosystems, and long-term studies are critical to evaluating the impacts of these events on the factors that contribute to sustainability. This study used long-term field trial sites to explore the direct and interactive effects of site, management, and other factors on the biogeochemical processes and phylogenetic diversity (bacterial and fungal community composition) within forest soil ecosystems. High throughput sequencing of bacterial (16S rRNA) and fungal (ITS rRNA) phylogenetic marker genes was used to characterise microbial communities in soils from two long-term soil productivity study (LTSP) sites (both >25 years old). The single species (Pinus radiata) trials, at Woodhill and Tarawera forests, allowed for testing of effects of forest management practices, including organic matter removal at harvest and fertiliser addition, on microbial communities. Addition of fertiliser resulted in distinct changes to both bacterial and fungal communities, while organic matter removal at harvest had persistent effects on the composition of fungal species in the soil ecosystem at Woodhill with smaller magnitude effects still seen at Tarawera. In contrast, there was no evidence of long-term effects related to organic matter removal at harvest on the composition of soil bacterial communities, irrespective of site. The two sites had differing soil physicochemical properties and these were also associated with location-based differences in bacterial communities. Overall, bacterial communities were relatively impervious to forest management practices, whereas fungal communities were responsive and the effects on community assemblage were enduring over time. This outcome highlights both the importance of investigating fungal and bacterial communities together in forest ecosystems, and the value of long-term field-based studies. We conclude that while conventional forestry management practices may improve the long-term physicochemical conditions and tree growth, their impacts on soil microbial populations are also enduring.

Effects of timber harvesting on the genetic potential for carbon and nitrogen cycling in five North American forest ecozones

Forest ecosystems are critical to global biogeochemical cycles but under pressure from harvesting and climate change. We investigated the effects of organic matter (OM) removal during forest harvesting on the genetic potential of soil communities for biomass decomposition and nitrogen cycling in five ecozones across North America. We analyzed 107 samples, representing four treatments with varied levels of OM removal, at Long-Term Soil Productivity Study sites. Samples were collected more than ten years after harvesting and replanting and were analyzed via shotgun metagenomics. High-quality short reads totaling 1.2 Tbp were compared to the Carbohydrate Active Enzyme (CAZy) database and a custom database of nitrogen cycle genes. Gene profile variation was mostly explained by ecozone and soil layer. Eleven CAZy and nine nitrogen cycle gene families were associated with particular soil layers across all ecozones. Treatment effects on gene profiles were mainly due to harvesting, and only rarely to the extent of OM removal. Harvesting generally decreased the relative abundance of CAZy genes while increasing that of nitrogen cycle genes, although these effects varied among ecozones. Our results suggest that ecozone-specific nutrient availability modulates the sensitivity of the carbon and nitrogen cycles to harvesting with possible consequences for long-term forest sustainability.

Genet diversity, genetic structure, and trait expression of trembling aspen (Populus tremuloidesMichx.) after clear-cut harvesting and post-harvest soil treatments

Trembling aspen is a fast growing, broadly distributed tree in North America that reproduces by root suckers (clonally) and by seeds (sexually). Since timber harvesting can affect both reproduction pathways by changing the soil properties, we assessed genet diversity, genetic structure, and phenotypic trait expression of trembling aspen populations after clear-cut harvesting in a long-term soil productivity study site in Michigan. A total of 323 stems in replicated plots having heavy soil compaction and surface organic matter (OM) removed, and the untreated controls, were analyzed at microsatellites and for phenotypic traits. Overall, higher spatial aggregation of ramets from the same genet, a greater spatial separation of different genets, and a very good phenotypic separation among genets was observed in the treatment plots. In contrast, for plots with spatially intermixed clones phenotypic separation was much lower. Genetic differentiation was high between individual plots, but soil compaction and OM removal had little effect on genetic differentiation and diversity. One treatment plot was strongly differentiated phenotypically, but not genetically, from all other plots. Consequently, microenvironmental and genetic differences should be considered when forest management effects on trait expressions and productivity are analyzed. Overall, heavy soil compaction and OM removal in fine-textured soil seemed to have restricted the spread of aspen clones.

A metagenomic survey of forest soil microbial communities more than a decade after timber harvesting

The scarcity of long-term data on soil microbial communities in the decades following timber harvesting limits current understanding of the ecological problems associated with maintaining the productivity of managed forests. The high complexity of soil communities and the heterogeneity of forest and soil necessitates a comprehensive approach to understand the role of microbial processes in managed forest ecosystems. Here, we describe a curated collection of well replicated, multi-faceted data from eighteen reforested sites in six different North American ecozones within the Long-term Soil Productivity (LTSP) Study, without detailed analysis of results or discussion. The experiments were designed to contrast microbial community composition and function among forest soils from harvested treatment plots with varying intensities of organic matter removal. The collection includes 724 bacterial (16S) and 658 fungal (ITS2) amplicon libraries, 133 shotgun metagenomic libraries as well as stable isotope probing amplicon libraries capturing the effects of harvesting on hemicellulolytic and cellulolytic populations. This collection serves as a foundation for the LTSP Study and other studies of the ecology of forest soil and forest disturbance.

Long-Term Enrichment of Stress-Tolerant Cellulolytic Soil Populations following Timber Harvesting Evidenced by Multi-Omic Stable Isotope Probing.

Soil management is vital for maintaining the productivity of commercial forests, yet the long-term impact of timber harvesting on soil microbial communities remains largely a matter of conjecture. Decomposition of plant biomass, comprised mainly of lignocellulose, has a broad impact on nutrient cycling, microbial activity and physicochemical characteristics of soil. At “Long-term Soil Productivity Study” sites in California dominated by Ponderosa pine, we tested whether clear-cut timber harvesting, accompanied by varying degrees of organic matter (OM) removal, affected the activity and structure of the cellulose-degrading microbial populations 16 years after harvesting. Using a variety of experimental approaches, including stable isotope probing with 13C-labeled cellulose in soil microcosms, we demonstrated that harvesting led to a decrease in net respiration and cellulolytic activity. The decrease in cellulolytic activity was associated with an increased relative abundance of thermophilic, cellulolytic fungi (Chaetomiaceae), coupled with a decreased relative abundance of cellulolytic bacteria, particularly members of Opitutaceae, Caulobacter, and Streptomycetaceae. In general, harvesting led to an increase in stress-tolerant taxa (i.e., also non-cellulolytic taxa), though our results indicated that OM retention mitigated population shifts via buffering against abiotic changes. Stable-isotope probing improved shotgun metagenome assembly by 20-fold and enabled the recovery of 10 metagenome-assembled genomes of cellulolytic bacteria and fungi. Our study demonstrates the putative cellulolytic activity of a number of uncultured taxa and highlights the mineral soil layer as a reservoir of uncharacterized diversity of cellulose-degraders. It also and contributes to a growing body of research showing persistent changes in microbial community structure in the decades following forest harvesting.

Forest harvesting reduces the soil metagenomic potential for biomass decomposition.

Soil is the key resource that must be managed to ensure sustainable forest productivity. Soil microbial communities mediate numerous essential ecosystem functions, and recent studies show that forest harvesting alters soil community composition. From a long-term soil productivity study site in a temperate coniferous forest in British Columbia, 21 forest soil shotgun metagenomes were generated, totaling 187 Gb. A method to analyze unassembled metagenome reads from the complex community was optimized and validated. The subsequent metagenome analysis revealed that, 12 years after forest harvesting, there were 16% and 8% reductions in relative abundances of biomass decomposition genes in the organic and mineral soil layers, respectively. Organic and mineral soil layers differed markedly in genetic potential for biomass degradation, with the organic layer having greater potential and being more strongly affected by harvesting. Gene families were disproportionately affected, and we identified 41 gene families consistently affected by harvesting, including families involved in lignin, cellulose, hemicellulose and pectin degradation. The results strongly suggest that harvesting profoundly altered below-ground cycling of carbon and other nutrients at this site, with potentially important consequences for forest regeneration. Thus, it is important to determine whether these changes foreshadow long-term changes in forest productivity or resilience and whether these changes are broadly characteristic of harvested forests.

Effects of Nitrogen Deposition on Foliar Litter Decomposition and C, N, Ca, and P Dynamics in a Regenerating Forest

Increases in atmospheric N deposition over the past decades have raised concerns over nitrogen (N) retention and carbon (C) and nutrient cycling in forest ecosystems. Implications for C and nutrient cycling are particularly acute in forests with periodic biomass harvesting. To understand how acid deposition interacts with harvesting removals to affect ecosystem C, N, calcium (Ca) and phosphorus (P) cycling and to assess the ability of dolomitic lime to counteract that effect, we followed decomposition and element dynamics in foliar litter at the Long-Term Soil Productivity (LTSP) study at the Fernow Experimental Forest (FEF) in West Virginia. N deposition in the regenerating hardwood forest LTSP site is enhanced by periodic ammonium sulfate additions (N+S). Other treatments include reference (ref) plot (no additions) and ammonium sulfate plus lime (lime). Fresh litter collected from the forest floor at the LTSP study had oak (48%), yellow poplar (19%), maple (14%), magnolia (12%), cherry (4%), and birch (3%). Fresh litter was collected from treatment plots in November. Air-dried litter was weighed, and placed in nylon litter bags. Litter bags were placed in treatment plots in March after the snow melt. Mass loss, C, N, Ca and P dynamics were followed for 12 months. During the first 7 months of decomposition, N and P were immobilized in litter in all treatments. At 6 months, N immobilization was significantly lower (p=0.006) in the ammonium sulfate treatment (117%) than in the reference (128%) and lime (125%) treatments. At 7 months, N immobilization was significantly lower (p=0.009) in the N+S treatment (104%) than in the reference (113%) and in lime (115%) treatment. After twelve months, there were significant differences among treatments for mass loss, C, Ca, and P dynamics. Remaining mass was highest in lime treatment (43%) and it was significantly higher than the N+S (39%) and reference (37%) treatments. Remaining C was higher in both lime (41%) and N+S (42%) treatments than in reference (36%), and it was significantly different in ammonium sulfate treatment than in reference (p=0.0337). Remaining Ca was significantly higher in ammonium sulfate treatment (42%) than in reference (36%) (p=0.0051). Nitrogen mineralized at 12 months in all treatments, and the remaining P in the N+S treatment (107%) was significantly higher than in the reference (83%) and lime treatment (90%). Increase in N and P contents during decomposition suggest that both N and P are limiting to microbial growth and forests. Decreasing N immobilization and increasing P immobilization during leaf litter decomposition in N addition treatments indicate that atmospheric N deposition may affect nutrient dynamics during litter decomposition and may have an impact on ecosystem scale C cycling and forest productivity. Our results also showed that lime plays a significant role in decreasing litter decay, increasing N immobilization and decreasing P immobilization, which shows the potential of lime to counteract the effects of N deposition. DOI: http://dx.doi.org/10.4038/jepsl.v3i1.7312 Journal of Environmental Professionals Sri Lanka, Vol. 3 No. 1 2014, 30-47

Early Growth Responses of Lodgepole Pine and Douglas-Fir to Soil Compaction, Organic Matter Removal, and Rehabilitation Treatments in Southeastern British Columbia

Abstract Effects of soil compaction, organic matter removal, and rehabilitation on lodgepole pine (Pinus contorta Dougl. ex. Loud.) and Douglas-fir (Pseudotsuga menziesii var. menziesii) were studied after three growing seasons in a long-term soil productivity study established on three calcareous soils in southeastern British Columbia. Effects of soil compaction and organic matter removal on tree growth were site and species specific. Moderate soil compaction increased the diameter and height increment of both species within the stem-only harvest treatment on all three sites, particularly at the coarser textured site (Emily Creek). Compaction tended to reduce tree mortality. Growth of both species was reduced by forest floor removal in the noncompacted soil at Mud Creek and Emily Creek and by whole-tree harvest in the moderately compacted soil at Mud Creek and Kootenay East, possibly due to treatment-induced water limitation. Whole-tree harvest and forest floor removal stimulated lodgepole pine and Douglas-fir growth in the noncompacted soil at Kootenay East. The rehabilitation treatment (established by tilling a heavily compacted soil) reduced lodgepole pine tree mortality on all sites and increased rootcollar diameter and height increment at Mud Creek and Kootenay East. Our findings may provide early growth indication and help assess long-term tree growth trends at these and other long-term soil productivity or related sites.

Negligible effects of severe organic matter removal and soil compaction on loblolly pine growth over 10 years

The long-term soil productivity (LTSP) study was initiated to examine the effect of soil porosity and organic matter (OM) levels on net primary productivity (NPP). The study design calls for three levels of OM removal (bole, whole tree and whole tree plus forest floor) and three levels of compaction (none, moderate and severe) being imposed on harvested sites prior to planting. Additionally, the effect of understory control on NPP was examined as a split-plot treatment. The study has been installed on 62 sites covering a range of climates, soil types and tree species across the United States and Canada. The inclusion of 46 closely related affiliated sites has created the world's largest coordinated research network devoted to investigating the relationship between land management and sustainable forest productivity. In the forefront of the LTSP network are the installations in North Carolina (NC) and Louisiana (LA) which focus on loblolly pine ( Pinus taeda L.) growth. The rapid growth at these sites has resulted in the trees reaching crown closure much earlier than any other LTSP installation. Consequently, these sites may provide the earliest glimpse as to the treatment effects on NPP. Tenth year data from these sites show that large OM removals and severe soil compaction (main treatments) had no significant ( α ≤ 0.1) effect on stand volume but control of the understory (split-plot treatment) resulted in greater stand volume compared to plots with no understory control. Plots ameliorated by a one-time fertilizer addition (NC and LA) and bedding (NC only) resulted in small (+8 and −8% for NC and LA, respectively) to large (+69 and +15% for NC and LA, respectively) changes in mean stand volume compared to the experimental plots. Although there were no main treatment effects on stand volume, extractable soil phosphorus in NC and LA were reduced with increasing OM removal. The reduction of extractable soil phosphorus with increasing OM removal on these already phosphorus deficient sites may affect tree growth in the future but have not yet translated to stand volume differences over 10 years.

Soil physical property changes at the North American Long-Term Soil Productivity study sites: 1 and 5 years after compaction

The impact of forest management operations on soil physical properties is important to understand, since management can significantly change site productivity by altering root growth potential, water infiltration and soil erosion, and water and nutrient availability. We studied soil bulk density and strength changes as indicators of soil compaction before harvesting and 1 and 5 years after harvest and site treatment on 12 of the North American Long-Term Soil Productivity sites. Severe soil compaction treatments approached root-limiting bulk densities for each soil texture, while moderate compaction levels were between severe and preharvest values. Immediately after harvesting, soil bulk density on the severely compacted plots ranged from 1% less than to 58% higher than preharvest levels across all sites. Soil compaction increases were noticeable to a depth of 30 cm. After 5 years, bulk density recovery on coarse-textured soils was evident in the surface (0–10 cm) soil, but recovery was less in the subsoil (10–30 cm depth); fine-textured soils exhibited little recovery. When measured as a percentage, initial bulk density increases were greater on fine-textured soils than on coarser-textured soils and were mainly due to higher initial bulk density values in coarse-textured soils. Development of soil monitoring methods applicable to all soil types may not be appropriate, and more site-specific techniques may be needed for soil monitoring after disturbance.