Forest Floor Mass Research Articles

Decadal‐scale changes in forest soil carbon and nitrogen storage are influenced by organic matter removal during timber harvest

AbstractThis study investigates whether different intensities of organic matter removal associated with timber harvest influence decadal‐scale storage of soil organic carbon (SOC) and total nitrogen (TN) in the top 1 m of mineral soil 18 years postharvest in a Pinus taeda L. forest in the Gulf Coastal Plain. We quantified forest harvest‐related changes in SOC, TN, microbial biomass carbon (MBC), and nitrogen (MBN) pools (0–100 cm) in unharvested control stands and in two organic matter removal treatment stands subjected to either (i) merchantable bole/stem‐only harvest or (ii) whole‐tree harvest + forest floor removal. In addition, δ13C of SOC and δ15N of TN were measured in mineral soil to provide insights regarding mechanisms that might explain changes in SOC and TN pool sizes. Soils were sampled seasonally for 1 year. Increasing organic matter removal intensity reduced SOC, TN, MBC, and MBN relative to the unharvested control. Furthermore, soils from whole‐tree harvest + forest floor removal stands had lower δ13C and higher δ15N values, suggesting that increasing organic matter removal may decrease heterotrophic activity as well as increase rates of N loss. Seasonal variabilities in SOC and TN were correlated to changes in forest biological properties such as root biomass and forest floor mass. These results indicate that more intensive harvest methods may lead to decade‐scale decreases in SOC and TN storage in surface and subsurface soils which could influence rates of biogeochemical processes, the availability of soil nutrients, and potential forest productivity.

Riparian Soil Development Linked to Forest Succession Above and Below Dams Along the Elwha River, Washington, USA

Riparian forest soils can be highly dynamic, due to frequent fluvial disturbance, erosion, and sediment deposition, but effects of dams on riparian soils are poorly understood. We examined soils along toposequences within three river segments located upstream, between, and downstream of two dams on the Elwha River to evaluate relationships between riparian soil development and forest age, succession, and channel proximity, explore dam effects on riparian soils, and provide a baseline for the largest dam removal in history. We found that older, later-successional forests and geomorphic surfaces contained soils with finer texture and greater depth to cobble, supporting greater forest floor mass, mineral soil nutrient levels, and cation exchange. Forest stand age was a better predictor than channel proximity for many soil characteristics, though elevation and distance from the channel were often also important, highlighting how complex interactions between fluvial disturbance, sediment deposition, and biotic retention regulate soil development in this ecosystem. Soils between the dams, and to a lesser extent below the lower dam, had finer textures and higher mineral soil carbon, nitrogen, and cation exchange than above the dams. These results suggested that decreased fluvial disturbance below the dams, due to reduced sediment supply and channel stabilization, accelerated soil development. In addition, reduced sediment supply below the dams may have decreased soil phosphorus. Soil δ 15N suggested that salmon exclusion by the dams had no discernable effect on nitrogen inputs to upstream soils. Recent dam removal may alter riparian soils further, with ongoing implications for riparian ecosystems.

Thinning effects on soil and microbial respiration in a coppice-originated Carpinus betulus L. stand in Turkey

Abstract: Effects of thinning on soil respiration and microbial respiration were examined over a 2-year period (2010-2012) in a coppice-originated European hornbeam (Carpinus betulus L.) stand in Istanbul, Turkey. Four plots within the stand were selected; tree density was reduced by 50% of the basal area in two plots (thinning treatment), and the other two plots served as controls. The study focused on the main factors that affect soil respiration (RS) and microbial respiration on the forest floor (RFFM) and in soil (RSM): soil temperature (TS), soil moisture (MS), soil carbon (C), soil nitrogen (N), soil pH, ground cover biomass (GC), forest floor mass (FF), forest floor carbon (FFC) and nitrogen (FFN), and fine root biomass (FRB). Every 2 months, soil respiration was measured using the soda-lime method, and microbial respiration was measured with the incubation method separately for the soil and forest floor. Results were evaluated yearly and over the 2-year research period. During the first year after treatment, RS was significantly higher (11%) in the thinned plots (1.76 g C m-2 d-1) than in the controls (1.59 g C m-2 d-1). However, there were no significant differences in either the second year or the 2-year study period. In the thinned plots during the research period, RS was linearly correlated with GC, Ts and FRB. Thinning treatments did not affect RSM, but interestingly, they did affect RFFM, which was greater in the control plots than in the thinned plots. RSM had a significant and positive correlation with soil N and soil pH, while RFFM was linearly correlated with FFC and C/N ratio of the forest floor in both thinned and control plots during the research period.

Forest floor decomposition, metal exchangeability, and metal bioaccumulation by exotic earthworms: Amynthas agrestis and Lumbricus rubellus.

Earthworms have the potential to reduce the retention of pollutant and plant essential metals in the forest floor (organic horizons) by decomposing organic matter and increasing exchangeability of metals. We conducted a laboratory experiment to investigate the effects of two exotic earthworms, Amynthas agrestis and Lumbricus rubellus, on forest floor decomposition, metal exchangeability, and metal bioaccumulation. Eighty-one pots containing homogenized forest floor material were incubated for 20, 40, or 80days under three treatments: no earthworms, A. agrestis added, or L. rubellus added. For earthworm treatments, A. agrestis and L. rubellus were stocked at densities observed in previous field studies. Pots containing either A. agrestis or L. rubellus had lost more forest floor mass than the control plots after 40 and 80days of incubation. Forest floor pots containing A. agrestis had significantly lower % C (16 ± 1.5%) than control pots (21 ± 1.2%) after 80days. However, L. rubellus consumed more forest floor and C mass than A. agrestis, when evaluated on a per earthworm biomass basis. Exchangeable (0.1M KCl + 0.01M AcOH extractable) and stable (15 M HNO3+ 10 M HCl extractable) concentrations of Al, Ca, Cd, Cu, Mg, Mn, Pb, and Zn in forest floor material were measured. Stable concentrations and % exchangeable metals in forest floor material were similar among treatments. Although exchangeable metal concentrations varied significantly for most metals among treatments (except Mg and Zn), we conclude that earthworms did not increase or decrease the exchangeability of metals. However, earthworms bioaccumulated Cu, Cd, Zn, and Mg and had potentially hazardous tissue concentrations of Al and Pb. This was best illustrated by calculating bioaccumulation factors using exchangeable concentrations rather than total concentrations. Future research is needed to understand the effect of earthworms on metals in other soil types.

Drivers of earthworm incidence and abundance across European forests

Earthworms have a significant influence on the structure, composition and functioning of forest ecosystems, but in spite of their role as ecosystem engineers, little is known on the factors controlling their distribution across European forests. Optimised sampling techniques, as well as more advanced statistical tools and geographical information systems have facilitated studies at the landscape scale. But these, and even larger-scale studies, are scarce due to data limitations, taxonomic inconsistencies and practical issues in linking existing databases. In this continental-scale field-based study we used boosted regression tree modelling to identify and evaluate the relative importance of environmental factors explaining earthworm incidence (presence/absence) and abundance (density and biomass) in European forests. To parameterise our models earthworms were sampled in six forest landscapes along a latitudinal gradient from the boreal north to the Mediterranean south in spring or autumn of 2012, together with several environmental variables. Earthworms were sampled using a combined method of mustard extraction and hand sorting of litter and a soil monolith, after which they were weighed and identified to functional group (epigeic, endogeic and anecic). We found that litter- and soil-related variables best explained earthworm incidence and biomass in European forests, leaving only a minor role to climate-related variables. Among the litter related variables, understory vegetation played an important role in explaining earthworm incidence and abundance. The relative importance of explanatory variables differed between models for incidence, density and biomass and between earthworm functional groups. Our results suggested that threshold values for soil C:N ratio, forest floor pH and understory plant biomass and plant nutrient concentrations have to be attained before earthworms can occur. Beyond these threshold values, variables like soil C:N ratio, tree litter C:P ratio and forest floor mass further explain earthworm biomass. Mechanisms behind these observations are discussed in the light of future earthworm distribution modelling at continental scale.

Changes in forest floor and soil nutrients in a mixed oak forest 33 years after stem only and whole-tree harvest

Vegetation, forest floor, and soils were resampled at a mixed oak site in eastern Tennessee that had been subjected to stem only (SOH), whole-tree harvest (WTH), and no harvest (REF) 33years previously. Although differences between harvest treatments were not statistically significant (P<0.05), average diameter, height, basal area and biomass were 8–18% lower in the WTH than in the SOH treatment 33years after harvest whereas they differed by 2% 15years after harvest. In contrast to results 15years post-harvest, total forest floor mass and nutrient contents were twofold greater in the WTH than in the SOH treatment at 33years post-harvest, due largely to differences in Oa horizon mass. Soil total C concentrations increased significantly (P<0.05) over the first 15years post-harvest in both harvest treatments. Decreases in soil C between 15 and 33years post-harvest were not statistically significant. Soil total N increased significantly in both harvest treatments over the first 15years post-harvest. Consistent decreases in soil total N occurred in the WTH treatment between years 15 and 33 post-harvest that bordered on statistical significance whereas total N was stable over that time period in the SOH treatment. The increases and decreases in soil N content cannot be explained by any known processes of N inputs or outputs. Harvest treatment effects on both Ca2+ and Mg2+ observed at 15years post-harvest are still observable and significant at 33years post-harvest, although decreases between 15 and 33years were found. Treatment effects and changes in soil exchangeable Ca2+ and Mg2+ are consistent with known inputs from decomposing logging residues, inputs from atmospheric deposition, and increments in forest floor and vegetation. No treatment effects were found for soil extractable P, but steady decreases over time were found. No treatment or time effects were found for soil exchangeable K+.

Using spatial ecology to examine above and belowground interactions on a reclaimed aspen stand in northern Alberta

Examining the spatial interactions between above and belowground components of terrestrial ecosystems can give meaningful insight into the ecological processes happening at different scales. Understanding spatial dependence in these processes may help to evaluate reclamation success which is crucial for future management of such areas. The aim of this study was to measure the spatial patterns of soil biogeochemical properties in a young aspen stand reclaimed after oil sands extraction and to evaluate how the patterns were related to nutrient availability. Samples were collected from a 14-year old reclaimed site using a spatially explicit protocol with a minimum resolution of 0.5m. Field-measured variables included forest floor depth and mass, tree cluster (canopy overlap), distance to nearest tree, and resin available nutrients. Soil microbial properties including microbial biomass C and N, basal respiration, and extracellular enzyme activity were measured during an eight-week laboratory incubation experiment. Geo-statistics were applied to examine the spatial patterns and model the space effect. A fine scale (<10m) spatial pattern was found for the majority of stand variables, soil microbial properties, and available macronutrients (N, P, S and base cations). Macronutrients such as N, P and S availability had a fine scale cyclic spatial association with soil microbial properties, with an 8–10m oscillation, which indicated belowground control on these nutrients. Spatial regression models also suggested a stronger microbial influence on the availability of these nutrients when compared to stand characteristics. However, stand characteristics exhibited significant control on base cations and micronutrient availability through the effect of forest floor depth and tree clustering. Although nutrient availability showed strong spatial relationships with belowground processes in the studied reclaimed site, similar relationships with aboveground properties appeared to be weak, and might require further time to develop.

Effects of thinning on soil respiration and microbial respiration of forest floor and soil in an oak (Quercus frainetto) forest

The effects of tree thinning on soil respiration and microbial respiration in a Hungarian oak (Quercus frainetto Ten.) forest were examined over a 2-year period (2010–12). Tree density was reduced to 50% of the basal area. The research focus was on the main factors influencing the soil respiration (RS) and microbial respiration in the forest floor (RFFM) and in the soil (RSM): soil temperature, moisture, carbon (C), nitrogen (N), and pH; groundcover biomass (GC); forest floor mass, carbon and nitrogen; and fine root biomass. RS was measured twice monthly with the soda-lime method, and the incubation method was used to measure RSM and RFFM separately. The results were evaluated annually and over the 2-year research period. Correlation and stepwise regression analyses were used for statistical evaluation. Annual mean RS was significantly higher in thinned plots (1.92 g C m–2 day–1) than in the control plots (1.79 g C m–2 day–1). Over the 2-year research period, RS was higher in the thinned plots, and had linear correlations with GC, soil temperature and fine root biomass. GC was found to be the main factor that determined RS. The control plots had significantly higher RSM in first year, whereas the thinned plots had significantly higher RSM in second year; no significant difference was found over the 2-year research period. RFFM was significantly higher in the control plots than in the thinned plots, by 84% in the second year and by 34% over the 2-year study period. RSM had a linear correlation with soil N content and soil pH, whereas RFFM had linear correlations with C concentration and the C : N ratio of the forest floor in the thinned plots.

Can shrub species with higher litter quality mitigate soil acidification in pine and oak forests on poor sandy soils?

This study, aiming to unravel whether topsoil conditions under tree species with nutrient-poor leaf litter can be altered by admixing a shrub layer, was performed in 12 pine (mainly Pinus sylvestris) and 12 oak (Quercus robur) stands on sandy podzolic soils in north-east Belgium. We examined the effects of presence of a shrub layer on forest floor mass and topsoil chemical properties related to soil acidification. The shrub species included were European rowan (Sorbus aucuparia), alder buckthorn (Rhamnus frangula) and black cherry (Prunus serotina). For each tree species, 60–90years old stands were selected containing shrubs present in varying cover classes: sparse (<20%), intermediate (20–70%) and dense (>70%). The oak stands were characterized by less but ‘nutrient-richer’ litterfall, compared to the pine stands. This was reflected in less humus build-up (FH-horizon) and higher pH, CEC, BS and lower C/N in the topsoil in the oak stands compared to the pine stands. However, despite the fact that the shrubs produced litter with significantly higher base cation and N concentrations than that of the studied tree species, we did not find any significant changes in topsoil conditions in the pine and oak stands under study, even under dense shrub layers (87–91% cover).

The Influence of Fire on the Radiocarbon Signature and Character of Soil Organic Matter in the Siskiyou National Forest, Oregon, USA

AbstractForest fires contribute a significant amount of CO2 to the atmosphere each year, and CO2 emissions from fires are likely to increase under projected conditions of global climate change. In addition to volatilizing aboveground biomass and litter layers, forest fires have a profound effect on belowground carbon (C) pools and the cycling of soil organic matter as a whole. However, the influence of fire on belowground organic matter cycling is not well defined and varies widely with fire severity. We measured soil organic matter (SOM) characteristics across a range of fire severities two years after the 2002 Biscuit Fire in southwest Oregon, USA, to address the following questions: (1) Which C pools are preferentially volatilized or transformed to charcoal under low-severity and high-severity fire? (2) How does fire change the distribution of SOM among density fractions and depths? (3) How does fire affect the general character of SOM including such variables as abundance, C:N ratio, 13C abundance, and 14C abundance? We examined soils from a mixed hardwood-evergreen forest across a range of burn severities: unburned, low severity, mixed severity, and high severity. Results indicated that increasing burn severity led to progressive loss of forest floor mass, but not to progressive loss of C from the mineral soil. Although fire significantly increased the charcoal content of the soils, fire did not significantly change the distribution of soil organic matter between heavy and free or light fractions. Other significant changes in soil organic matter characteristics included a progressive increase in nitrogen (N) with increasing burn severity, possibly due to the encroachment of N-fixing shrubs following the loss of native vegetation. Although qualitative changes in total root abundance following fire were noted, differences among burn severity treatments were not statistically significant. Increased concentrations of rock fragments in burned areas may be suggestive of erosion in these areas, consistent with previous studies documenting varying degrees of soil erosion following fire. In addition, although 13C abundances were similar among severely burned and unburned plots, soils from severely burned plots were significantly depleted in 14C in comparison to soils from unburned plots. This 14C depletion is most likely the combined result of erosion and preferential combustion of organics enriched in 14C relative to the bulk soil, perhaps reflecting a historical pattern of fire occurrence and severity across the landscape.

Carbon and nitrogen accumulation in forest floor and surface soil under different geographic origins of Maritime pine (Pinus pinaster Aiton.) plantations

Aim of study : To determine if plantations consisting of different geographic origins of the Maritime pine (Pinus pinaster Aiton.) could have altered C and N stocks in the forest floor and surface soils.Area of study : Forest floor and mineral soil C and N stocks were measured in four adjacent plantations of different geographic origins of Maritime pine (Gironde, Toulon, Corsica and Spain) and adjacent primary native Sessile oak (Quercus petraea L.) at Burunsuz region in Belgrad Forest where is located in the Istanbul province in the Marmara geographical region between 41°09' -41°12' N latitude and 28°54' - 29°00' E longitude in Turkey.Material and Methods : Plots were compared as common garden experiments without replications. 15 surface soil (0-10 cm) and 15 forest floor samples were taken from each Maritime pine origins and adjacent native Sessile oak forest. C and N contents were determined on LECO Truspec 2000 CN analyzer. The statistical significance of the results was evaluated by one-way Analysis of Variance (ANOVA).Research highlights : Forest floor carbon mass, nitrogen concentration and nitrogen mass of forest floor showed a significant difference among origins. Soil carbon mass and nitrogen mass did not significantly differ among investigated plots.Keywords: carbon sequestration; C/N ratio; decomposition; exotic; tree provenance.

Fine root and litterfall dynamics of three Korean pine (Pinus koraiensis) forests along an altitudinal gradient

Fine root and aboveground litterfall, two large fluxes of nutrients and carbon in the forest ecosystems, are key processes to be considered in efforts of measuring, modeling and predicting soil carbon sequestration. We used sequential coring and litter trap to measure seasonal dynamics of fine root and litterfall in three Korean pine dominated forests along an altitudinal gradient in the Changbai Mountain during the 2012 growing season. Fine root biomass decreased significantly while necromass increased remarkably with altitude. Patterns and amounts of fine root production and mortality varied among forest types. Litterfall decreased significantly with altitude, whereas forest floor mass increased. Carbon inputs through fine root mortality and litterfall decreased significantly with altitude while carbon storage of fine root mass did not differ among forest types and carbon storage of forest floor mass was significantly larger in higher altitudinal forests due to lower turnover rates. This study provided an insight into the variations of fine root and litterfall dynamics among three Korean pine forests which were associated with different vegetation traits and environmental conditions, and also the quantification of carbon fluxes through fine root mortality and litterfall for estimating carbon budget of temperate forest.

Evaluating post-outbreak management effects on future fuel profiles and stand structure in bark beetle-impacted forests of Greater Yellowstone

Large-scale bark beetle (Curculionidae: Scolytinae) outbreaks across western North America have prompted widespread concerns over changes to forest wildfire potentials. Management actions following outbreaks often include the harvest of beetle-killed trees and subsequent fuel treatments to mitigate expected changes to fuel profiles, but few data exist to inform these actions. In both lodgepole pine (Pinus contorta var. latifolia) and Douglas-fir (Pseudotsuga menziesii var. glauca) forests of the Greater Yellowstone Ecosystem, Wyoming, USA, we used the Forest Vegetation Simulator to evaluate how fuel profiles, stand structure, and biomass carbon storage are influenced by various post-outbreak fuel treatments (removal of beetle-killed trees [‘salvage’] followed by either no treatment, prescribed burning, pile-and-burn, or whole-tree-removal). The model was initialized with field data from five unmanaged gray-stage stands in each forest type and projected over 50years of post-treatment time. Across all treatment methods, the strongest projected effects relative to unharvested stands were reductions in coarse woody surface fuels (after 10–20yr), fewer well-decayed standing snags (after 40yr), and reduced biomass carbon storage (throughout all 50years). The reduction in coarse woody surface fuels suggests reduced heat release and resistance to control in future fires. Projected effects on fine fuels, both in the canopy and surface layers, were surprisingly minor or short-lived; natural fall and decay of fine material in unharvested stands led to the convergence of most fuel variables between treated and untreated stands within about a decade, especially in Douglas-fir forests. Most follow-up treatment methods – whether unmerchantable tree parts were left in place, burned, piled, or removed entirely – had similar impacts on most aspects of fuel and stand structure in both lodgepole pine and Douglas-fir forests. However, the prescribed burning treatment was distinct and generally had the strongest effects, owing to greater consumption of forest floor mass and mortality of small trees, which had persistent influences on both the canopy and surface fuel layers. Treatment effectiveness in reducing fuels was mirrored by reductions in biomass carbon storage and recruitment of well-decayed snags, illustrating common tradeoffs involved in fuel treatments. Harvest of beetle-killed trees and subsequent treatments altered the fuel profile and structure of outbreak-impacted stands, but overall effects were similar among treatments, suggesting flexibility in management options in post-outbreak forests.

Chronic nitrogen deposition reduces the abundance of dominant forest understory and groundcover species

Humans have altered the global nitrogen (N) cycle, greatly increasing atmospheric nitrogen deposition in industrialized regions of the world. Groundcover plants can be sensitive indicators of nitrogen deposition impacts. Here, we report results from repeated measurements over a 7year period of groundcover (plants<1.4m tall) and understory (plants with a diameter<5cm at 1.4m in height) vegetation in four mature northern hardwood forests in the north-central United States receiving experimental additions of N (3gm−2year−1 as NaNO3 for 18years). Experimental N deposition reduced the average abundance of sugar maple (Acer saccharum Marsh.) seedlings in the groundcover by>50% (P<0.001). This reduction occurred at all four sites, but was only statistically significant at the two sites where these seedlings were most abundant (site×nitrogen: P<0.001). Our observations of mortality within a large cohort of sugar maple seedlings across three sites provide further evidence of this effect. For these seedlings, experimental N deposition significantly (P<0.05) increased mortality in the weeks following germination, as well as over the longer term, reducing overall survival after 5years by almost 90%. Although groundcover plants accounted for<0.5% of aboveground plant biomass, they contributed up to 10% of ecosystem leaf area and 5% of aboveground litter. At the two sites where sugar maple seedlings were infrequent, understory vegetation was more abundant and dominated by hop-hornbeam (Ostrya virginiana (Miller) K. Koch; 42% of all stems). At these two sites, experimental N deposition significantly reduced the abundance of understory hop-hornbeam by more than 75% (site×nitrogen: P=0.008). The effects of experimental N deposition on the understory and groundcover vegetation occurred without significant decreases in reproductive litter or increases in canopy leaf area. Instead, the negative effects are more likely a by-product of other documented changes caused by the experimental N deposition: increased forest floor mass, decreased mycorrhizal abundance, and increased production of potentially alleopathic phenolic compounds. Because the late-successional species in these forests rely upon groundcover and understory plants for regeneration, the effects of added N on this vegetation have potential implications for future forest composition, particularly given the likely loss of some species in these forests due to exotic pests and pathogens.

Understorey vegetation shifts following the conversion of temperate deciduous forest to spruce plantation

The identity and composition of the overstorey trees can have large impacts on the understorey vegetation in temperate forests. Here, we assess the effects of the conversion of mixed deciduous forests to Norway spruce (Picea abies) plantations on the understorey vegetation composition and diversity. We also investigated whether the effects of this conversion depend on the soil fertility and if they affect the species pool at the landscape scale. The study area contained ancient deciduous woodlands mainly consisting of Quercus spp., Fagus sylvatica and Carpinus betulus in the Gaume, an area with a mild temperate climate in southern Belgium. Spruce plantations were established 30–50years ago in this matrix of deciduous woodlands. Differences in overstorey and understorey vegetation, forest floor and soil characteristics between 40 paired plots in spruce plantations and adjacent deciduous forest were compared along a soil fertility gradient. The forest floor mass was higher and the soil pH was lower in spruce plantations. The composition of the understorey vegetation differed between deciduous forest and spruce plantations: the spruce stands contained more light-demanding and acid-tolerant understorey species than the adjacent deciduous stands. The mean understorey species diversity, i.e., the local species diversity in a plot (α-diversity) as well as the total number of species (γ-diversity), did not differ significantly between the deciduous and spruce stands. Hence, the differing species composition of the spruce plantations contributes to a larger overall species pool and higher across site β-diversity. Although the differences in the environmental variables within a plot pair increased along the fertility gradient, the differences in understorey vegetation diversity between deciduous and spruce stands showed no relationship with the gradient. Only the difference in Ellenberg indicator value for soil reaction (R) within a pair increased with increasing soil fertility. In line with the abiotic changes, the understorey vegetation composition had shifted towards a more acid-tolerant vegetation type 30–50years after conversion to spruce plantations. The increase in light-demanding species was probably due to a more intensive thinning management in the spruce stands.

Forest Floor, Litter Fall and Nutrient Dynamics in Young aged Shisham Forests in Moist Plain area of Kumaon of Uttarakhand

Present paper illustrates the litter and nutrient dynamics of Shisham (Dalbergia sissoo Roxb.) forests at 1-3 years aged growing in Tarai belt of Kumaon of Uttarakhand. The objectives of this study were to determine the litter inputs, nutrients (NPK) and their dynamics. Shisham is commonly occurred in the nutrient poor site because of their leguminous features. This study was carried out in young aged Shisham forests for the estimation of tree density, forest floor, litter fall and nutrients content and returns. The litter trap methods were used for the estimation of forest floor biomass and litter input. However, the nutrients of litters and soil related parameters were calculated as already mentioned various workers. Tree density was 1111 tree/ha in each forest. The average forest floor mass was 2.54 (2yr) –2.84 t ha-1. Of this, herbaceous live accounted for 12-17 %. Among the litter components, partially and more decomposed litter shared maximum. The litter and herbaceous components was found in increasing and decreasing order with age of stand. The forest floor litter was 3.22(3yr)-3.72(1yr) in rainy, 2.78(3yr)-3.10(1yr) in winter and 1.36(2yr)-2.12(3yr). The annual replacement of forest floor litter ranged from 88-97% with a turnover time 1.03-1.14 year. The turnover rate of different nutrients (NPK) was 47-57%. It was decreased with increase in forest age. The total amount of nutrient return to the soil through litter input was 2.20-12.42 for N, 0.21-1.10 for P and 0.65-3.62 kg h-1 yr-1 for K. It was increased with increase of forest age because of higher amount of litter accumulation. The nutrient use efficiency was (NUE) was 66.2-108.1 for N, 745.6-1202.9 for P and 227.0-361.3 for K. The present findings of young age Shisham forest would be beneficial for the further management study of Shisham forest particularly in relation to the litter and nutrients point of view.

Interacting effects of wildfire severity and liming on nutrient cycling in a southern Appalachian wilderness area

Aims Wilderness and other natural areas are threatened by large-scale disturbances (e.g., wildfire), air pollution, climate change, exotic diseases or pests, and a combination of these stress factors (i.e., stress complexes). Linville Gorge Wilderness (LGW) is one example of a high elevation wilderness in the southern Appalachian region that has been subject to stress complexes including chronic acidic deposition and several wildfires, varying in intensity and extent. Soils in LGW are inherently acidic with low base cation concentrations and decades of acidic deposition have contributed to low pH, based saturation, and Ca:Al ratio. We hypothesized that wildfires that occurred in LGW followed by liming burned areas would accelerate the restoration of acidic, nutrient depleted soils. Because soils at LGW had extremely low concentrations of exchangeable Ca 2+ and Mg 2+ dolomitic lime was applied to further boost these cations. We evaluated the effectiveness of dolomitic lime application in restoring exchangeable Ca 2+ and Mg 2+ and subsequently increasing pH and Ca:Al ratio of soils and making Ca and Mg available to recovering vegetation. Methods Five treatment areas were established: severely burned twice (2000 & 2007) with dolomitic lime application (2xSBL); moderately burned twice with lime application (2xMBL); severely burned twice, unlimed (2xSB); moderately burned once (2000), unlimed (1xMB); and a reference area (REF; unburned, unlimed). In 2008 and 2009, we measured overstory, understory, and ground-layer vegetation; forest floor mass and nutrients; and soil and soil solution chemistry within each treatment area. Results All wildfire burned sites experienced substantial overstory mortality. However, understory biomass doubled between sample years on the most recently burned sites due to the rapid regrowth of ericaceous shrubs and prolific sprouting of deciduous trees. Burning followed by lime application (2xSBL and 2xMBL) significantly increased shallow soil solution NO3-N, but we found no soil solution NO3-N response to burning alone (2xSB and 1xMB). Surface soil base saturation and exchangeable Ca 2+ were significantly affected by liming; Ca 2+ concentrations were greater on 2xMBL and 2xSBL than 2xSB, 1xMB and REF.

Leaf Litter Disappearance in Earthworm-Invaded Northern Hardwood Forests: Role of Tree Species and the Chemistry and Diversity of Litter

Earthworm invasion in North American temperate forest reduces forest floor mass, yet the interactions between litter composition, invasive earthworm community composition, and forest floor structure and composition are not well understood. For 2 years, we compared disappearance of leaf litter in field mesocosms in which we manipulated litter composition (monocultures of Quercus rubra, Acer saccharum, and Tilia americana litter, and an equal mixture of all three) and thereby the initial litter chemistry (C, C fractions, N, Ca) in sites with and without the major litter-feeding invasive earthworm species. The disappearance of litter mass followed the same ranking at both the sites: T. americana > equal mixtures > A. saccharum ≥ Q. rubra. However, differences in disappearance rate between the sites depended on litter composition and time. The differences in mass loss among litters of different compositions were greatest at the site invaded by the large litter-feeding earthworm, Lumbricus terrestris, and especially for T. americana and the mixture. Similarly, observed disappearance of the litter mixture was faster than predicted by an additive model at the site with L. terrestris, especially for the higher quality litter component in early summer. Initial litter calcium content was the best predictor (R2 ≥ 0.90) of overall litter mass remaining each year, supporting the idea of the importance of calcium in forest floor dynamics, especially in the presence of calciferous, invasive earthworms.

Restoration of shortleaf pine (Pinus echinata)-hardwood ecosystems severely impacted by the southern pine beetle (Dendroctonus frontalis)

In the Southern Appalachian Mountains of eastern USA, pine-hardwood ecosystems have been severely impacted by the interactions of past land use, fire exclusion, drought, and southern pine beetle (SPB, Dendroctonus frontalis). We examined the effects of restoration treatments: burn only (BURN); cut+burn on dry sites (DC+B); cut+burn on sub-mesic sites (MC+B); and reference sites (REF; no cutting or burning) on shortleaf pine-hardwood forests. We also evaluated the effectiveness of seeding native bluestem grasses. Structural (down wood, live and dead standing trees, shrubs, herbaceous layer) and functional (forest floor mass, C, and N; soil C, N, P, and cations; and soil solution N and P) attributes were measured before and the first and second growing seasons after treatment. We used path analysis to test our conceptual model that restoration treatments will have direct and indirect effects on these ecosystems. Total aboveground mass loss ranged from 24.33Mgha−1 on the BURN to 74.44Mgha−1 on the DC+B treatment; whereas, REF gained 13.68Mgha−1 between pre-burn and post-burn. Only DC+B sites had increased soil NO3–N, NH4–N Ca, Mg, and PO4–P and soil solution NO3–N, NH4–N, O–PO4 for several months.We found a significant increase in the density of oak species (Quercus alba, Q. coccinea, Q. montana, Q. rubra, and Q. velutina) on all burn treatments. However, oaks accounted for a smaller proportion of the total stem density than red maple, other tree species, and shrubs. The high densities of woody species other than oaks, coupled with the fast growth rates of some of these species, suggests that oaks will continue to be at a competitive disadvantage in these pine-hardwood communities through time, without further intervention. Pine regeneration was not improved on any of our burned sites with little to no recruitment of pines into the understory after two years and the pine saplings that were present before the burns were killed by fire on all sites. We found an increase in herbaceous layer cover and richness on all fire treatments. DC+B had higher bluestem grass cover than the other treatments, and it was the only treatment with increased bluestem grass cover between the first (2.96%, SE=0.29) and second (6.88%, SE=0.70) growing seasons. Our path model showed that fire severity explained a large proportion of the variation in overstory response; and fire severity and overstory response partially explained soil NO3–N. These variables, directly and indirectly, explained 64% of the variation in soil solution NO3–N at 30cm soil depth (within the rooting zone for most plants). We found a good-fit path model for herbaceous layer response in the second growing season, where fire severity had direct effects on overstory and herbaceous layer responses and indirect effects on herbaceous layer response mediated through overstory response. Our path model explained 46% and 42% of the variation in herbaceous layer cover and species richness, respectively.

Simulated N deposition negatively impacts sugar maple regeneration in a northern hardwood ecosystem

Summary1. During the next century, atmospheric nitrogen (N) deposition is projected to more than double, potentially leading to a decline in plant diversity as well as a change in plant community composition and structure.2. In a decade‐long field experiment, simulated atmospheric N deposition has slowed litter decay, resulting in an accumulation of forest floor (i.e. Oi &amp; Oe horizons). We reasoned that a greater forest floor mass under simulated N deposition would impose a physical barrier to sugar maple Acer saccharum seedling establishment, thereby reducing seedling populations of an ecologically and economically important tree species.3. To test this idea, we first quantified sugar maple seedling abundance in replicate northern hardwood forest stands receiving ambient atmospheric N (7–12 kg N ha−1 year−1) and experimental atmospheric N deposition, simulating future amounts in eastern North America (ambient plus 30 kg NO3− N ha−1 year−1). Then, we experimentally manipulated forest floor mass under ambient and simulated N deposition treatments. Finally, we transplanted first‐year established seedlings into areas receiving ambient and simulated N deposition and quantified their mortality after 1 year.4. First‐year seedling abundance did not differ under ambient and simulated N deposition; however, there were greater abundances of second‐ and third‐to‐fifth‐year seedlings under ambient N deposition (P &lt; 0·001). In all cases, experimental manipulation to increase forest floor mass, equivalent to that under simulated N deposition, resulted in significantly (P = 0·001) fewer established individuals, regardless of whether the greater forest floor mass occurred under ambient or simulated N deposition. Finally, fewer 1‐year‐old transplanted seedlings survived when grown under simulated N, albeit that result was not statistically significant.5. Synthesis and applications. The slowing of decay and the accumulation of forest floor under anthropogenic N deposition can negatively impact seedling survival and potentially alter stand development and structural diversity. As atmospheric N deposition increases globally, it becomes necessary to understand the mechanisms that lead to population changes for ecologically important tree species. The responses we document should be considered in simulations of future of forest’dynamics, as atmospheric N deposition continues to increase, specifically when sugar maple life‐history traits are included to simulate regeneration, structural diversity and stand development.