Forest Floor Mass Research Articles

Functional identity drives tree species richness-induced increases in litterfall production and forest floor mass in young tree communities.

Forest floor accumulation is a key process that influences ecosystem carbon cycling. Despite evidence suggesting that tree diversity and soil carbon are positively correlated, most soil carbon studies typically omit the response of the forest floor carbon to tree diversity loss. Here, we evaluated how tree species richness affects forest floor mass and how this effect is mediated by litterfall production and forest floor decay rate in a tree diversity experiment in a subtropical forest. We observed that greater tree species richness leads to higher forest floor accumulation at the soil surface through increasing litterfall production - positively linked to functional trait identity (i.e. community-weighted mean functional trait) rather than functional diversity - and unchanged forest floor decay. Interestingly, structural equationmodelling revealed that this lack of overall significant tree species richness effect on forest floor decay rate was due to two indirect and opposite effects cancelling each other out. Indeed, tree species richness increased forest floor decay rate through increasing litterfall production while decreasing forest floor decay rate by increasing litter species richness. Our reports of greater organic matter accumulation in the forest floor in species-rich forests suggest that tree diversity may have long-term and important effect on ecosystem carbon cycling and services.

Ground Vegetation in Pinus sylvestris Forests at Different Successional Stages following Clear Cuttings: A Case Study.

The impact of intensive forestry on various components of ecosystems has become the main subject of public and scientific debate in many regions in recent years. Forest ground vegetation is considered one of the most consistent and biodiversity-rich indicators of a certain stage of successional forest development. Therefore, changes in this forest component can potentially show the risks of forest damage due to clear-cutting and recovery trends. This study was carried out to identify the ground vegetation species diversity, including species composition and cover, also ground vegetation species relations with organic layer (forest floor) and upper mineral soil parameters at the different successional stages of the Pinus sylvestris L. stand development, including 1–2-year-old clear-cuts, and 6–130 years old stands. This study identified that the herb and dwarf shrub species were more light-demanding in the 2-year-old clear-cuts, as well as in the 6-year and 10-year old P. sylvestris stands compared to the middle-aged and mature forest stands. The dominant ground vegetation species, characteristic for the Pinetum vaccinio-myrtillosum forest type, were negatively dependent on the forest floor mass; they also had negative correlations with the concentrations of total P, K, Ca, and Mg in the forest floor and upper mineral soil but had positive correlations with the soil pH values and total N. The developed regression models of the percentage cover of mosses, herbs and dwarf shrubs according to the P. sylvestris stand age highlight the stabilization of the increase in the moss cover about 30 years after clear-cutting, with no clear trend for vascular species. The herbs and dwarf shrub species were highly variable during the stand rotation due to the species-specific characteristics and random factors rather than due to the influence of stand age. In this study, relatively short-term changes in ground vegetation species composition and percentage cover were determined after clear-cutting, but an important aspect is that new ground vegetation species appeared in the open areas, creating the potential for increasing species diversity. The clear-cutting system supports different species and numbers of herbs and mosses at different stages of stand development, which potentially increases the overall vegetation species diversity of the ecosystem.

Understory plant removal counteracts tree thinning effect on soil respiration in a temperate forest.

Elucidating the response mechanism of soil respiration (Rs) to silvicultural practices is pivotal to evaluating the effects of management practices on soil carbon cycling in planted forest ecosystems. However, as common management practices, how thinning, understory plant removal, and their interactions affect Rs and its autotrophic and heterotrophic components (Ra and Rh) remains unclear. Therefore, we investigated Rs, Ra and Rh by the trenching method from 2011 to 2015 in a Pinus tabuliformis plantation in northern China, subjecting to four treatments (intact control plots [CK], thinning [T], understory removal [UR], and thinning with understory removal [TUR]). Mean annual Rs was significantly increased by thinning (by 15.3%), whereas decreased by UR (by 17.4%), compared with CK. These variations in Rs were mainly attributed to changes in Ra. The increments of Ra were caused by the enhanced growth of fine root biomass after thinning. However, UR led to lower Ra compared with CK (p < .05), indicating that understory growth is inadequate to compensate for the decreased respiring root biomass induced by understory removal. Rs was unchanged between TUR and the intact control plot due to the opposite effects of thinning and UR on the Ra. Changes in Rh exhibited no significant differences among the treatments, partly because of the stable microbial biomass carbon (MBC) and forest floor mass (litter and fine woody debris). No interaction effect between thinning and understory removal was detected on Rs, Ra, and Rh. The lowest temperature sensitivity (Q10 ) value of Ra was found in CK. This study highlights the necessity of incorporating understory plant effects on soil CO2 efflux in assessing forest management practices on soil carbon cycling.

Soil Organic Carbon Stocks in Afforested Agricultural Land in Lithuanian Hemiboreal Forest Zone

In the context of the specificity of soil organic carbon (SOC) storage in afforested land, nutrient-poor Arenosols and nutrient-rich Luvisols after afforestation with coniferous and deciduous tree species were studied in comparison to the same soils of croplands and grasslands. This study analysed the changes in SOC stock up to 30 years after afforestation of agricultural land in Lithuania, representing the cool temperate moist climate region of Europe. The SOC stocks were evaluated by applying the paired-site design. The mean mass and SOC stocks of the forest floor in afforested Arenosols increased more than in Luvisols. Almost twice as much forest floor mass was observed in coniferous than in deciduous stands 2–3 decades after afforestation. The mean bulk density of fine (&lt;2 mm) soil in the 0–30 cm mineral topsoil layer of croplands was higher than in afforested sites and grasslands. The clear decreasing trend in mean bulk density due to forest stand age with the lowest values in the 21–30-year-old stands was found in afforested Luvisols. In contrast, the SOC concentrations in the 0–30 cm mineral topsoil layer, especially in Luvisols afforested with coniferous species, showed an increasing trend due to the influence of stand age. The mean SOC values in the 0–30 cm mineral topsoil layer of Arenosols and Luvisols during the 30 years after afforestation did not significantly differ from the adjacent croplands or grasslands. The mean SOC stock slightly increased with the forest stand age in Luvisols; however, the highest mean SOC stock was detected in the grasslands. In the Arenosols, there was higher SOC accumulation in the forest floor with increasing stand age than in the Luvisols, while the proportion of SOC stocks in mineral topsoil layers was similar and more comparable to grasslands. These findings suggest encouragement of afforestation of former agricultural land under the current climate and soil characteristics in the region, but the conversion of perennial grasslands to forest land should be done with caution.

Nutrient Storage and Stoichiometry of the Forest Floor Organic Matter in Japanese Forests

Nutrient storage in the forest floor is regulated through litter decomposition and nutrient cycling. Stoichiometry of nutrients can provide characterization of the forest floor. To quantify nutrient storage in the forest floor and to determine stoichiometry among different forest types, available data on nutrients were meta-analyzed. The data on nutrients—nitrogen, phosphorus, potassium, calcium, and magnesium—were collected from published reports and original data on Japanese forests. The relationship between nutrient storage and forest floor mass was also examined. Japanese cypress and cedar plantations had small N and P storage in the forest floor with high C:N and C:P ratios, whereas subalpine conifers had large N and P storage in the forest floor with low C:N and C:P ratios; cedar plantations showed large Ca-specific storage in the forest floor. The stoichiometry of the forest floor varied between different forest types, namely C:N:P ratios were 942:19:1 for cedar and cypress plantations, 625:19:1 for broad-leaved forests, and 412:13:1 for subalpine conifers and fir plantations. N storage was closely correlated; however, P and other mineral storages were weakly correlated with the forest floor mass. Nutrient storage and stoichiometry can provide a better perspective for the management of forest ecosystem.

Evaluation of organic carbon stocks in mineral and organic soils in Lithuania

AbstractSoil organic carbon (SOC) stocks at national level were estimated to provide more accurate estimates on SOC for the Lithuanian GHG inventory. The SOC stocks in the forest floor, grassland litter, and in mineral or organic topsoil (0–30 cm) of forest land, grasslands, and croplands were estimated. The assessment was based on forest floor and peat topsoil mass, mineral topsoil bulk density, and carbon concentration in 754 permanent observation plots on 9 × 9 km grid of the National Forest Inventory in Lithuania. The SOC stocks were obtained for eight WRB Reference Soil Groups to provide the estimates for land use, land‐use change, and forestry reporting. The SOC stocks in the forest floor, topsoil of mineral, and peat layers were identified for soils under different land uses. The mean SOC concentrations in the 0–10 and 10–30 cm topsoil of most soil groups, especially fertile forest soils (Cambisols, Luvisols +Retisols) were higher for forest land and grasslands, and lower for croplands. The total averaged SOC stock in the forest floor in mineral and organic soils was 6.97 t ha−1, whereas in the litter of grasslands it was 0.54 t ha−1. The averaged SOC stock in topsoil varied from 56 t ha−1 (Arenosols) to 118 t ha−1 (Cambisols) in mineral forest soils and was 150 t ha−1 (Histosols) in organic forest soils. The total averaged SOC stock in mineral topsoil of forest land, grassland, and cropland was 80, 74, and 72 t ha−1, respectively.

Soil biota and fertility along a gradient of forest degradation in a temperate ecosystem

Soil biota populations are good indicators for the evaluation of soil quality, which is in line with the nutrient cycles in forest ecosystems. To the best of the authors’ knowledge, responses of belowground biota to forest removal intensity have received little attention. The present study aimed to study the effect of low, moderate and high intensities of forest degradation, based on the density of standing trees, in lands covered by Carpinus betulus and Parrotia persica tree species in northern Iran on forest floor, soil properties and fauna and flora activities. In the summer season, a total of 15 forest floor and soil samples (30 × 30 × 10 cm) from each site were transferred to the laboratory. To achieve the temporal pattern of soil biota, sampling was also performed in the fall season. The activities of earthworm groups (i.e. epigeic, anecic, and endogeic) were significantly decreased in order of low > moderate > high levels of forest degradation, with higher populations in the fall season (especially epigeic earthworms). Similarly, greater activity of soil Acarina, Collembola, nematode, protozoa (especially in the fall season), bacteria and fungi (especially in the summer season) were found in forests with low intensity of degradation. Principal component analysis (PCA) indicated higher soil biological activities and fertility in the forest areas with low degradation which can be attributed to the higher density of trees, forest floor mass and quality. This research provides evidence of the strong dependence of below-ground communities on aboveground tree density in temperate forests.

Relative importance of tree species richness, tree functional type, and microenvironment for soil macrofauna communities in European forests.

Soil fauna communities are major drivers of many forest ecosystem processes. Tree species diversity and composition shape soil fauna communities, but their relationships are poorly understood, notably whether or not soil fauna diversity depends on tree species diversity. Here, we characterized soil macrofauna communities from forests composed of either one or three tree species, located in four different climate zones and growing on different soil types. Using multivariate analysis and model averaging we investigated the relative importance of tree species richness, tree functional type (deciduous vs. evergreen), litter quality, microhabitat and microclimatic characteristics as drivers of soil macrofauna community composition and structure. We found that macrofauna communities in mixed forest stands were represented by a higher number of broad taxonomic groups that were more diverse and more evenly represented. We also observed a switch from earthworm-dominated to predator-dominated communities with increasing evergreen proportion in forest stands, which we interpreted as a result of a lower litter quality and a higher forest floor mass. Finally, canopy openness was positively related to detritivore abundance and biomass, leading to higher predator species richness and diversity probably through trophic cascade effects. Interestingly, considering different levels of taxonomic resolution in the analyses highlighted different facets of macrofauna response to tree species richness, likely a result of both different ecological niche range and methodological constraints. Overall, our study supports the positive effects of tree species richness on macrofauna diversity and abundance through multiple changes in resource quality and availability, microhabitat, and microclimate modifications.

Impacts of forest harvest removal and fertiliser additions on end of rotation biomass, carbon and nutrient stocks of Pinus radiata

Forest harvesting practices remove tree biomass and the nutrients that they contain. There is uncertainty around the impact of this nutrient removal on the long-term sustainable production of forests over multiple rotations. To explore the impact of harvest management practices on planted forest sustainability, three long-term trials in Pinus radiata D. Don forests were assessed at the end of their second rotation of 26 to 27 years to determine the impact of harvest residue removal and fertiliser additions on sustainable forest productivity. The harvest residue removal treatments were stem only (SO), whole-tree (WT), and whole-tree plus forest floor (FF) removal with and without urea-nitrogen fertiliser additions (cumulative range across three sites 950 – 3200 kg N ha−1) from early rotation out to mid-rotation (last fertiliser application age range across sites 8 – 22 years). The FF removal treatment reduced soil carbon and nitrogen stocks throughout the subsequent rotation, whereas forest floor carbon and nutrient stocks had recovered from the FF removal treatment by the end of the rotation. Forest productivity was reduced at one site with the FF removal treatment, taking 3 years longer for stems to reach 35 cm diameter at breast height than other residue removal treatments. Between WT and SO harvest residue treatments there were very limited impacts on soil carbon and nutrient stocks, no impact on forest floor mass, carbon and nutrient stocks and the sum of the above ground live biomass, carbon and nutrient stocks or tree productivity. Across all harvest removal treatments fertiliser addition increased soil carbon and nitrogen stocks for sites with low initial soil stocks. The increased soil carbon and nitrogen stocks from fertiliser addition were associated with forest productivity gains with the time to reach 35 cm (diameter at breast height) for one site reduced by 3 – 5 years. Fertiliser addition to sites with FF removal was able to mitigate soil carbon and nitrogen stocks only when very large amounts of fertiliser were added (cumulative amounts of 1150 and 3200 kg N ha−1). The end of rotation results from this long-term study demonstrate the importance of harvest residues and forest floor material at low fertility sites for long-term nutrient sustainability in planted forests.

Litter quantity controls soil macro-invertebrate biomass in warm temperate broad-leaved forests of Southwestern Japan

The biomass distribution of soil macro-invertebrates across various biomes worldwide is an indispensable factor to be taken into account in predicting plant litter decomposition rates in a global perspective. In boreal to cool temperate regions, soil macro-invertebrate biomass is lower in coniferous forests than in deciduous broad-leaved forests, with the difference being attributed to tree species effects via litter quality. On the basis of a simplistic analogy with the litter quality-controlled differences in soil macro-invertebrate biomass between coniferous forests and deciduous broad-leaved forests, soil macro-invertebrate biomass is expected to be lower in evergreen broad-leaved forests that produce leaves with a longer lifespan of lower quality than in deciduous broad-leaved forests. In order to test this expectation, soil macro-invertebrate biomass, forest floor mass, an indicator of litter quantity, and litter pH, a possible index of litter quality were assessed in evergreen broad-leaved forests and deciduous broad-leaved forests under similar abiotic conditions in Southwestern Japan. The total biomass of the entire animal community was depended greatly on earthworms and was significantly higher in evergreen broad-leaved forests than in deciduous broad-leaved forests. The forest types were completely separated by a discriminant function combining the biomasses of twelve major taxa with a high stand-based frequency. Earthworms, spiders, and woodlice were the top three of contribution to the discrimination, the biomasses of all of which were significantly higher in evergreen broad-leaved forests than in deciduous broad-leaved forests. Multiple regression analysis and PCA revealed that the biomass differences in the three taxa between the forest types were predominantly influenced by forest floor mass without any indication of important effects of litter pH. Importance of “litter quantity control” over soil macro-invertebrate biomass in warm temperate forests of Southwestern Japan was concluded.

How do soil microbial communities respond to fire in the intermediate term? Investigating direct and indirect effects associated with fire occurrence and burn severity

Fires transform soil microbial communities directly via heat-induced mortality and indirectly by altering plant and soil characteristics. Emerging evidence suggests the magnitude of changes to some plant and soil properties increases with burn severity, but the persistence of changes varies among plant and soil characteristics, ranging from months to years post-fire. Thus, which environmental attributes shape microbial communities at intermediate time points during ecosystem recovery, and how these characteristics vary with severity, remains poorly understood. We identified the network of properties that influence microbial communities three years after fire, along a burn severity gradient in Sierra Nevada mixed-conifer forest. We used phospholipid fatty acid (PLFA) analysis and bacterial 16S-rDNA amplicon sequencing to characterize the microbial community in mineral soil. Using structural equation modelling, we applied a systems approach to identifying the interconnected relationships among severity, vegetation, soil, and microbial communities. Dead tree basal area, soil pH, and extractable phosphorus increased with severity, whereas live tree basal area, forest floor mass, and the proportion of the ≥53 μm soil fraction decreased. Forest floor loss was associated with decreased soil moisture across the severity gradient, decreased live tree basal area was associated with increased shrub coverage, and increased dead tree basal area was associated with increases in total and inorganic soil nitrogen. Soil fungal abundance decreased across the severity gradient, despite a slightly positive response of fungi to lower soil moisture in high severity areas. Bacterial phylogenetic diversity was negatively related to severity and was driven by differences in nutrients and soil texture. The abundance of Bacteroidetes increased and the abundance of Acidobacteria decreased across the severity gradient due to differences in soil pH. Overall, we found that the effects of burn severity on vegetation and soil physicochemical characteristics interact to shape microbial communities at an intermediate time point in ecosystem recovery.

Soil organic carbon accumulation and several physicochemical soil properties under stone pine and maritime pine plantations in coastal dune, Durusu-Istanbul.

The study was conducted in dune restoration sites introduced with maritime pine (MP, Pinus pinaster Aiton) and stone pine (SP, Pinus pinea L.) at different development stages (diameters at breast height (DBH) in which small-diameter forests (SDF) = 0-8cm, medium-diameter forests (MDF) = 8-20cm, large-diameter forests (LDF) = 20-36cm, and upper large-diameter forests (UDF) = > 36cm). There were 15 replicated plots in each stage of both species and 25 dune sites; thus, a total of 145 sample plots were selected. Soil samples were taken from six different depth layers (0-5, 5-15, 15-30, 30-50, 50-70, and 70-100cm). Forest floors were sampled with five replicates in each plot, and they were separated into leaf + fermentation and humus layers to determine unit mass and carbon concentration. Forest floor mass is significantly increased (17-34t/ha in MP and 28-57t/ha in SP) with the development stage. Low organic carbon (0.09-0.36% in MP and 0.13-0.84% in SP) was found in the top soil layer despite a significant accumulation of forest floor. The soil organic carbon density varies between 3 and 34t C/ha. As the stand development stage increases, clay concentrations in every depth layer increased and soil pH and calcium carbonate values tend to decrease. Results indicated that both species have capability to grow on sandy material within poor nutrient and water capacities in a 50-year restoration process. However, the accumulation of forest floor increased and organic matter storage in the topsoil (0-5cm) remained quite low due to the slow decomposition process.

Формування лісової підстилки в деревостанах за участю липи дрібнолистої в умовах свіжої грабової діброви Західного Поділля

Досліджено формування лісової підстилки в 41-100-річних деревостанів за участю липи дрібнолистої. У складі деревостанів частка липи і дуба коливається від поодиноких дерев до 10 одиниць. У них також представлені клен гостролистий і явір, граб звичайний, в'яз голий, ясен звичайний, черешня та інші види. У деревостанах свіжої грабової діброви Західного Поділля запас не розкладеної лісової підстилки наприкінці вегетаційного періоду коливається в межах 0,28-1,34 кг/м2. Встановлено найменший запас підстилки в деревостанах, де частка липи становить 8-10 одиниць. Відносно чистого липового деревостану в мішаних запас лісової підстилки істотно зріс – у 1,61-4,78 раза. У його складі переважає листя деревних видів, маса якого становить 0,19-1,15 кг/м2 або 51,5-86,3 %. Маса пагонів, плодів, кори тощо у складі лісової підстилки коливається в межах 0,08-0,54 кг/м2 (13,7-48,5 %). Зв'язок нагромадження лісової підстилки з часткою липи у складі деревостанів характеризується тісною зворотною кореляційною залежністю (r = –0,68). Коефіцієнт варіації загальної маси лісової підстилки в деревостанах коливається в межах 6,3-32,1 %. Переважає слабкий і середній рівень мінливості. Аналогічною мінливістю характеризується фракція листя у складі лісової підстилки (V = 5,2–33,9 %). Встановлено значне зростання варіювання фракції пагонів, кори, плодів тощо у складі лісової підстилки, що характеризується переважанням сильних значень коефіцієнтів варіації.Ключові слова: дубові деревостани; лісова підстилка; опад; лісівничо-таксаційні показники; липа дрібнолиста.

Формування лісової підстилки в деревостанах за участю модрини європейської в умовах Кременецького горбогір'я

Досліджено формування лісової підстилки в 14–109-річних деревостанах за участю модрини європейської. У складі деревостанів частка модрини змінюється в межах 1–10 одиниць. Встановлено, що під наметом деревостанів за участю модрини європейської запас лісової підстилки в абсолютно сухому стані становить 0,30–1,96 кг/м². У її складі маса листя і хвої змінюється в межах 0,22–1,18 кг/м², або 9,4–84,9 %, а пагонів, шишок, кори тощо – від 0,08 до 1,55 кг/м², або 15,1–90,6 % від загальної її маси. У модрини у віці молодняків розпочинається і продовжується в середньовікових деревостанів до 50–60 років інтенсивне відмирання пагонів та очищення стовбурів дерев від сучків. Воно призвело до збільшення у складі лісової підстилки маси пагонів і кори до 50–90 %. У чистих модринових деревостанах нагромаджується більший запас лісової підстилки, ніж у мішаних. У молодняків запас лісової підстилки в чистому модриновому деревостані перевищує мішані на 2,1–88,6 %. У середньовікових, стиглих і перестиглих деревостанів такі відмінності становлять 4,7–75,4 %. Показано, що лісостани характеризуються різним варіюванням маси лісової підстилки загалом чи її фракцій у межах деревостану. Коефіцієнт варіації маси лісової в деревостанах виявився в основному середнім і рідше слабким (V = 6,1–20,5 %). Поряд з цим значно зростає варіювання фракцій лісової підстилки. Так, варіювання маси хвої і листя змінюється в межах 6,8–33,1 %, а фракції пагонів, шишок, кори тощо – 6,1–42,9 %.

Inconsistent responses of soil respiration and its components to thinning intensity in a Pinus tabuliformis plantation in northern China

Understanding the responses of soil respiration (Rs) to thinning is essential to evaluate the effects of management practices on carbon cycling in plantation forest ecosystems. However, how Rs and its components (autotrophic, Ra and heterotrophic respiration, Rh) vary with thinning intensity and the underlying mechanisms are not well understood. In the present study we monitored Rs, Ra and Rh over five growing seasons using a trenching method in a Pinus tabuliformis plantation subjected to four thinning treatments (no thinning, CK; light thinning, LT; moderate thinning, MT and heavy thinning, HT). On average, LT and MT significantly increased Rs by 13% and 17%, respectively, compared with the CK. These increments of Rs were ascribed to the enhanced Ra in LT and MT plots, because light and moderate thinning promoted root growth and productivity (higher fine root biomass). However, HT did not result in a further increase in Ra, suggesting that increases in the activity of remaining trees and understory plants did not compensate for the reduced photosynthesis and the amount of respiring tree roots by extensive tree-cut. In contrast to Ra, variation in Rh was unrelated to thinning, partly due to the stable forest floor mass (non-living organic materials such as litter and fine woody debris) and microbial biomass carbon content (MBC) between thinned and control plots. The temperature sensitivity (Q10) of Ra and Rh ranged from 1.40 to 3.07 and 2.34–3.42, respectively. The highest Q10 of Ra was observed in MT while that of Rh occurred in LT. Soil moisture was significantly correlated with Rh but a poor predictor for Ra. Our findings demonstrated that Ra and Rh responded to thinning intensity independently of each other. The intensity of management and plant-mediated biological processes are of particular importance in evaluating the impacts of forest management on C sequestration potential in plantation forests.

Mycorrhizal associations differentiate soil respiration in five temperate monocultures in Northeast China

Tree species associated with different mycorrhizal fungi play a crucial role in the carbon (C) cycling of forest ecosystems, while their effects on soil respiration (RS) and the underlying mechanisms remain uncertain. In this study, we used a common garden experiment that included five monocultures (two arbuscular mycorrhizal – (AM) and three ectomycorrhizal-associated (ECM) temperate tree species) to explore the effects of mycorrhizal associations on the RS and the driving factors. Our specific objectives were to (1) compare the RS between the AM and ECM stands, and (2) explore the driving factors of the RS. We found that the RS in the AM stands was significantly greater (34.3%) than that in the ECM stands. The RS was significantly and positively correlated with microbial biomass C (Cmic), fine roots biomass (Broot), or soil water content (W5), but negatively with forest floor mass (Fmass) or soil dissolved organic C content (Cdis). The best-fitted models of RS explained 46.3%, 38.3%, and 45.4% of the variations in the RS for the AM stands, the ECM stands, and the combined dataset, respectively. However, the factors contributing to the RS varied with mycorrhizal groups. The RS of the AM stands was mainly influenced by Cmic, Broot, root C/N ratio, Fmass, and Cdis, whereas the RS of the ECM stands was mainly affected by litter C/N ratio, Cdis, soil dissolved nitrogen content, soil temperature and W5. These findings highlight the significance of shifts in AM or ECM tree abundance due to forest management and global change in forest C cycling.

Tree species effects are amplified by clay content in acidic soils

The tree species composition of many forests in western and central Europe has changed considerably over the last century, as large areas of mixed deciduous forests were replaced by conifer plantations. In this study, we aim to evaluate whether conversion of mixed broadleaved forest to Norway spruce (Picea abies) on the acidic soils of the Gaume forest (southern Belgium) affected soil quality in terms of soil acidity, exchangeable calcium and aluminium, humus type and earthworm communities, and determine whether this effect is mitigated or amplified by an edaphic gradient in clay content. In this ancient deciduous woodland, stands were partly converted from mixed deciduous forest to Norway spruce monocultures 30–60 years ago. A twin-plot setup was established, where we sampled pairs of adjacent deciduous and Norway spruce plots along a gradient in clay content varying between 3 and 34%. This design allowed to evaluate the effects of soil type and conversion independently. In the deciduous plots, forest type ranged from mixed oak-hornbeam forest to oak-beech forest. The first has a higher clay content, higher exchangeable calcium, mull humus type, low forest floor mass and the presence of burrowing earthworms (endogeics), while the latter is characterised by high forest floor mass and presence of only litter-dwelling earthworms (epigeics), respectively. Our results provide evidence that the natural biogeochemical gradient converges to a narrow and acid range after conversion. When comparing Norway spruce plots with adjacent broadleaved stands, topsoil pH, calcium concentrations and total earthworm biomass were significantly lower, endogeic and epi-anecic earthworms were mostly absent, and the exchangeable aluminium was significantly higher. Contrary to the current paradigm, the impact of conversion in these acidic soils is largest for the stands with the highest clay content, where the larger exchange capacity allows greater accumulation of exchangeable aluminium when pH becomes sufficiently low. These findings have important implications for forest management: for systems near a threshold in soil process domain, it is important to realise that the sites with higher CEC and more favourable pH-values are the ones that will have larger trajectories and deteriorate the most upon acidification. Hence restoring such stands into more natural deciduous or mixed forest may become increasingly difficult.

Logging debris and herbicide treatments improve growing conditions for planted Douglas-fir on a droughty forest site invaded by Scotch broom

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

Activity of an introduced earthworm (Lumbricus terrestris) increases under future rates of atmospheric nitrogen deposition in northern temperate forests

When temperate forests of North America are exposed to long-term experimental levels of atmospheric nitrogen (N) deposition that mimic predicted future rates, elevated concentrations of inorganic N suppress microbial decay processes and increase the mass of the forest floor, storing more carbon (C) as soil organic matter. However, when non-native earthworms were serendipitously introduced to forests subjected to long-term experimental atmospheric N deposition, the greater forest floor mass with a higher N concentration had a positive effect on earthworm activity by increasing earthworm abundance and consumption of the forest floor. Here, we present evidence from a long-term experimental N deposition study showing how the abundance of the introduced earthworm, Lumbricus terrestris, increased significantly under elevated rates of atmospheric N deposition (+363%) in one of four study sites and contributed to a decline in the forest floor (−50%). In addition, mineral soil C (+97%) and N (+117%) concentrations increased as earthworms redistributed a greater proportion of organic matter belowground under experimental N deposition. We conclude that earthworm-induced changes to the forest floor can supersede a decline in microbial decay under experimental N deposition that has previously increased both forest floor mass and turnover time, thereby potentially negating increases in soil C storage.

Can spatial patterns be used to investigate aboveground-belowground links in reclaimed forests?

In forests undergoing reclamation, monitoring spatial patterns and relationships may be one way to decide if reclamation goals have been met. As a first attempt, linkages between soil nutrients and the canopy were assessed based on spatial patterns of trees, forest floor biomass, and seasonal nutrient availability in reclaimed forest sites in northern Alberta, Canada using a spatially explicit protocol (0.5 minimum resolution). Three different stand types, including aspen (Populus tremuloides Michx.), jack pine (Pinus banksiana Lamb.), and white spruce (Picea glauca (Moench) Voss) were assessed. Nutrient supply rate patterns were spatially dependent at scales of 3–20m and varied among seasons suggesting that controls shift seasonally between aboveground and belowground processes. Increased canopy cover and forest floor mass led to increased soil nutrient supply rates for all macronutrients in the aspen stand. Only forest floor mass was associated with increased sulfur and calcium in the pine stand, and canopy cover with increased potassium in the spruce stand. Linkages between aboveground and belowground processes appear to be reestablishing, however further investigation is needed to determine missing parameters controlling nutrient supply, to explicitly compare with natural background sites and account variation in reclamation material.