Forest Floor Accumulation 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.

Nitrogen accumulation in forest floors with introduced Pinus pinea and Pinus pinaster in dune site.

Introduced stone pine (Pinus pinea L.) and maritime pine (Pinus pinaster Aiton) stands were sampled 60years after plantation in Istanbul-Durusu (Terkos), Turkey. Sampling was conducted at four different developmental stages (mean diameter of trees at 1.3-m height (DBH) in stands: SDF = < 8cm, MDF = 8-20cm, LDF = 20-36cm, and UDF > 36cm), with 15 replicated sample plots for each species and developmental stage, for a total of 120 sample plots. The forest floor was sampled in 5 replications in each sample plot. The forest floor samples were divided into two layers: L + F (litter + fermentation) and H (humus), and the oven dry mass and nitrogen (N) content were determined. As a result, the masses of the total forest floor and of both layers were significantly different among the development stages with an increasing trend in maritime pine stands despite no significant difference found in the mass of the humus layer in stone pine stands. However, total forest floor accumulation significantly increased with the development stage (28-60 t/ha in stone pine and 17-64 t/ha in maritime pine). In both species, the N concentrations in the forest floor layers differed significantly among the development stages, and the N concentrations tended to increase as the development stage increased in the L + F layer, whereas a fluctuating trend was observed in the H layer. Although the N content of the humus layer of stone pine did not show a significant difference among the development stages, the N content in the total forest floor was determined to be 0.1-0.5 t/ha in maritime pine and 0.2-0.5 t/ha in stone pine. The relationship between the mean stand DBH and the N stock of the total forest floor was determined to have a higher correlation in maritime pine (R2 = 0.8) than stone pine (R2 = 0.4). In conclusion, the nitrogen concentrations and nitrogen contents of the forest floor were remarkably different in stands introduced with different tree species, indicating the accumulation of forest floor nitrogen.

Thinning and Burning Effects on Long-Term Litter Accumulation and Function in Young Ponderosa Pine Forests

Abstract We measured forest-floor accumulation in ponderosa pine forests of central Oregon and asked whether selected ecological functions of the organic layer were altered by thinning and repeated burning. Experimental treatments included three thinning methods applied in 1989 (stem only, whole tree, no thin—control) in factorial combination with prescribed burning (spring 1991 and repeated in 2002; no burn—control). Forest-floor depth and mass were measured every 4–6 years from 1991 to 2015. Without fire, there was little temporal change in depth or mass for thinned (270 trees ha−1) and control (560–615 trees ha−1) treatments, indicating balanced litterfall and decay rates across these stand densities. Each burn consumed 50–70 percent of the forest floor, yet unlike thinning, postfire accumulation rates were fairly rapid, with forest-floor depth matching preburn levels within 15–20 years. Few differences in forest-floor function (litter decay, carbon storage, physical barrier restricting plant emergence, erosion protection) resulted from thinning or burning after 25 years. An exception was the loss of approximately 300 kg N ha−1 because of repeated burning, or approximately 13 percent of the total site N. This study documents long-term forest-floor development and suggests that common silvicultural practices pose few risks to organic layer functions in these forests. Study Implications: Mechanical thinning and prescribed fire are among the most widespread management practices used to restore forests in the western US to healthy, firewise conditions. We evaluated their effects on the long-term development of litter and duff layers, which serve dual roles as essential components of soil health and as fuel for potential wildfire. Our study showed that thinning and burning provided effective fuel reduction and resulted in no adverse effects to soil quality in dry ponderosa pine forests of central Oregon. Repeated burning reduced the site carbon and nitrogen pools approximately 9–13 percent, which is small compared to C located in tree biomass and N in mineral soil. Litter accumulation after burning was rapid, and we recommend burning on at least a 15–20-year cycle to limit its build-up.

Effects of recovery time after fire and fire severity on stand structure and soil of larch forest in the Kanas National Nature Reserve, Northwest China

Forest recovery may be influenced by several factors, of which fire is the most critical. However, the moderate- and long-term effects of fire on forest recovery are less researched in Northwest China. Thus, the effects of different forest recovery time after fire (1917 (served as the control), 1974, 1983 and 1995) and fire severities (low, moderate and high) on larch (Larix sibirica Ledeb.) forest were investigated in the Kanas National Nature Reserve (KNNR), Northwest China in 2017. This paper analyzed post-fire changes in stand density, total basal area (TBA), litter mass, soil organic carbon (SOC) and soil nutrients (total nitrogen, total phosphorus and total potassium) with one-way analyses of variance. Results indicate that litter mass, TBA, SOC and soil nutrients increased with increasing recovery time after fire and decreasing fire severity, while the stand density showed an opposite response. The effects of fire disturbance on SOC and soil nutrients decreased with increasing soil depth. Moreover, we found that more than 43 a is needed to recover the litter mass, TBA, SOC and soil nutrients to the pre-fire level. In conclusion, high-severity fire caused the greatest variations in stand structure and soil of larch forest, and low-severity fire was more advantageous for post-fire forest stand structure and soil recovery in the KNNR. Therefore, low-severity fire can be an efficient management mean through reducing the accumulation of forest floor fuel of post-fire forests in the KNNR, Northwest China.

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.

The Impact of Management Practices on Soil Fertility and Foliar Nutrient Concentrations in a Spruce (Picea abies Link) Forest Ecosystem of Rodopi Mountainous Area, in Northern Greece

After forest harvesting, organic matter accumulation and soil nutrient availability are usually negatively influenced, especially during the first years. The hypothesis that 15 years after selective harvesting (15Y) the increased forest biomass, together with the enhanced nutrient recycling rates, compared to 5-years after harvesting (5Y), could restore nutrient availability and organic C accumulation (both in forest floor and soil) to similar levels to the intact site, was tested. The aim of this study was to investigate the effect of the timing of management practices (intact forest-control, 5Y, 15Y) on organic matter content, nutrient concentrations in needles, forest floor and soil, in a forest ecosystem of Picea abies L., in Rodopi mountainous area, in northern Greece. Significant differences between the intact site and the other two treatments were found in: i) soil N, P, C/N and exchangeable Ca, ii) organic matter and nutrient accumulation (basically in the upper 30 cm), iii) foliar K, Fe and Zn concentrations. In conclusion: i) forest management practices clearly influenced soil fertility and organic matter accumulation, ii) 15 years after selective harvesting nutrient and organic C accumulation in forest floor, as well as K and Fe accumulation in soil were restored to similar levels to the intact sites; thus, our hypothesis was partially correct.

Dynamics of annual falling debris decomposition and forest floor accumulation

The level of forest ecosystems’ productivity and functioning character may be to a great extent explained by its soil cover properties and carbon cycling peculiarity. The fabric and properties of forest ecosystems’ topsoil (designated in Estonia as “humus cover type”, but by Humusica as “humus form”) depends on the dynamics of annual falling debris (AFD) accumulation-decomposition in the forest floor (FF). For characterization of AFD dynamics or its flow throughout the FF into soil or atmosphere, the mean perennial graphical models were used. The comparative analysis of AFD flow and FF formation dynamics was carried out in four forest ecosystems of the temperate zone of the Atlantic-continental region. The studied forest stands were by their layers structure and interrelationships of the system “plant-soil” in stabilized stage. The used data originated from our previous researches on the dynamics of AFD by different fractions and of fractional composition of the FF. The flow of mean aboveground AFD throughout the FF depends on the quantity and dynamics of the AFD, on fractional composition of AFD and on pedo-ecological conditions of decomposition. The lowest decomposition rate was obtained in fresh moder humus cover (by Humusica Hemi- and/or Eumoder) on Glossic Retisols, but the highest, in fresh forest-mull humus cover (by Humusica Eu- and/or Mesomull) formed on Calcaric Cambisols. Due to the low decomposition rate in ecosystems formed on Glossic Retisols, only readily decomposable parts (herbs, leaves) disappear quickly from the newly formed FF. The more resistant parts of AFD accumulate for many years in a half-decomposed state on the surface of mineral soils (or on A-horizon), forming a multi-layered FF. The superficial density of phytogenic origin FF dry mass on Glossic Retisols is in limits of 21.5–24.5Mg ha−1, whereas the mean accumulation coefficient of FF formation varies from 3.35 to 3.44. The mean amount of phytogenic FF on Calcaric Cambisols with mixed spruce forest was 7.6Mg ha−1 and in the oak forest 3.2 Mg ha-1. The accumulation coefficient of FF formation in conditions of fresh forest-mull type humus cover was in the mixed spruce forest 1.50 and in the pure oak forest 0.66. The most important factors of AFD decomposition-mineralization are biological activity and agrochemical status of soil.

Effects of nitrogen addition on litter decomposition and nutrient release in two tropical plantations with N2-fixing vs. non-N2-fixing tree species

Atmospheric nitrogen (N) deposition has elevated rapidly in tropical regions where N2-fixing tree species are widespread. However, the effect of N deposition on litter decomposition in forests with N2-fixing tree species remains unclear. We examined the effect of N addition on litter decomposition and nutrient release in two tropical plantations with Acacia auriculiformis (AA, N2-fixing) and Eucalyptus urophylla (EU, non-N2-fixing) in South China. Three levels of N additions were conducted: control, medium-N (50 kg N ha−1 yr.−1) and high-N (100 kg N ha−1 yr.−1) in each plantation. Initial decomposition rate (k a ) for the control plots was faster in the AA plantation than in the EU plantation, but later in decomposition, larger fraction of slowly decomposing litter (A) remained in the former. N addition increased the slow fraction (A), decreasing soil microbial biomass and reducing acid-unhydrolyzable residue (AUR) degradation in the AA plantation. In the EU plantation, however, N additions significantly increased initial decomposition rate (k a ) and soil N availability. Furthermore, N addition decreased litter carbon and N release (in the AA plantation), while litter phosphorus release also decreased in both plantations. With ongoing N deposition in future, tropical plantations with N2-fixing tree species would potentially increase carbon accumulation and nutrient retention in forest floor by slowing litter decomposition.

Tree species composition affects productivity and carbon dynamics of different site types in boreal forests

AbstractThe objective was to analyse how differences in the initial proportions of tree species and site fertility affect carbon sequestration in living biomass and soil. We used the individual-based simulation model EFIMOD, which is able to simulate spatially explicit competition between trees for light and nutrients. Simulations were carried out for three site types with distinct initial stocks of soil nutrients. For each site, the 100-years undisturbed dynamics of monocultures and mixtures of three tree species (Betula pendulaRoth,Pinus sylvestrisL. andPicea abies(L.) H. Karst.) was predicted. Changes in the proportions of competing tree species were dependent on the fertility of the site: on poor sites, pine was the most competent species, while on rich sites, spruce increased its proportion during stand succession. Net primary production (NPP) and soil respiration were the highest in stands of two coniferous species and in stands with a high initial proportion of pine. Mixed stands were more productive than monocultures; the highest overyielding was observed with mixtures of two coniferous species. Simulated NPP and carbon stocks in all pools increased from poor to rich sites. The highest carbon stocks in standing biomass were observed for mixtures of conifer species and three-species mixtures; the greatest accumulation of forest floor occurred in stands with high proportions of pine.

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.

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.

Slowed decomposition is biotically mediated in an ectomycorrhizal, tropical rain forest

Bacteria and fungi drive the cycling of plant litter in forests, but little is known about their role in tropical rain forest nutrient cycling, despite the high rates of litter decay observed in these ecosystems. However, litter decay rates are not uniform across tropical rain forests. For example, decomposition can differ dramatically over small spatial scales between low-diversity, monodominant rain forests, and species-rich, mixed forests. Because the climatic patterns and soil parent material are identical in co-occurring mixed and monodominant forests, differences in forest floor accumulation, litter production, and decomposition between these forests may be biotically mediated. To test this hypothesis, we conducted field and laboratory studies in a monodominant rain forest in which the ectomycorrhizal tree Dicymbe corymbosa forms >80% of the canopy, and a diverse, mixed forest dominated by arbuscular mycorrhizal trees. After 2 years, decomposition was significantly slower in the monodominant forest (P < 0.001), but litter production was significantly greater in the mixed forest (P < 0.001). In the laboratory, we found microbial community biomass was greater in the mixed forest (P = 0.02), and the composition of fungal communities was distinct between the two rain forest types (P = 0.001). Sequencing of fungal rDNA revealed a significantly lower richness of saprotrophic fungi in the monodominant forest (19 species) relative to the species-rich forest (84 species); moreover, only 4% percent of fungal sequences occurred in both forests. These results show that nutrient cycling patterns in tropical forests can vary dramatically over small spatial scales, and that changes in microbial community structure likely drive the observed differences in decomposition.

Effects of a Prescribed Fire on Understory Vegetation, Carbon Pools, and Soil Nutrients in a Longleaf Pine-Slash Pine Forest in Florida

We quantified fire-driven loss and post-fire recovery of understory and soil carbon (C) and nutrient pools for one to three years following a single prescribed fire in a naturally regenerated longleaf (Pinus palustris Mill.) and slash pine (Pinus elliottii Engelm. var. elliottii) forest located in north central Florida. Fire immediately reduced total aboveground understory C and nitrogen (N) pools, but these pools recovered to pre-fire levels after three years. Our results also showed that the effect of fire on the understory composition and structure was only short-lived. Prescribed fire significantly reduced total C and N pools in the forest floor (F and H horizons), and this effect persisted for at least one year postfire. Available NH4 , PO43-, Ca2 , Mg2, and K concentrations in the forest floor decreased immediately after fire, but increased in the surface mineral soil (O to 5 cm depth); Ca2 , Mg2 , and K remained elevated for the first year after fire. Fire immediately reduced total ecosystem C and N pools by 40% and 27%, respectively, emitting 3860 g C m-2 and 170 g N m-2 to the atmosphere. The pools recovered to 67% and 76% of pre-fire C and N pools, respectively, after one year. Of the pools measured, C and N recovery in forest floor materials was the slowest, and projections of initial recovery rates suggest that it will take more than six years, the previous fire interval, to reach pre-fire levels. This slow recovery may indicate variation in past rates of forest floor accumulation due to management practices as well as effects of the severity of this or previous fires.

Litterfall and nutrient return in five tree species in a common garden experiment

Canopy litterfall is a significant pathway for return of nutrients and carbon (C) to the soil in forest ecosystems. Litterfall was studied in five even-aged stands of Norway spruce, Sitka spruce, Douglas-fir, European beech and common oak at three different locations in Denmark; two sandy sites, Ulborg and Lindet in Jutland, and one loamy site, Frederiksborg on Zealand. Litterfall was collected during three years from 1994 to 1996 in all five species and during six years from 1994 to 1999 in Norway spruce, Sitka spruce and European beech. The average total litterfall was in the range of 3200–3700 kg ha −1 yr −1 and did not differ significantly among tree species. There were no significant differences in total litterfall among sites during the short period, but during the longer period the richer site Frederiksborg had significantly higher total and foliar litterfall amounts compared to the more nutrient-poor sites Lindet and Ulborg. There were close relationships between foliar and total litterfall suggesting that foliar litterfall can be reliably estimated from total litterfall. Beech and oak bud scale litter was significantly related to foliar litterfall. The amount of branch and twig litter was significantly higher in oak than in other tree species. The average foliar litterfall was well related to the annual volume increment. The relationship differed markedly from previously reported relationships based on global litterfall data suggesting that such relationships are better evaluated at the regional level. Nutrient concentrations and fluxes in foliar litterfall were not significantly different among the five tree species. However, there was a significant effect of site on most nutrient concentrations of the three litterfall fractions, and foliar fluxes of P, Ca and Mn were all significantly highest at Frederiksborg and lowest at Ulborg. The similarity in litterfall inputs to the forest floor under these five tree species suggested that previous reports of large variability in forest floor accumulation should primarily be attributed to differences in litter decomposition.

Long-term influence of stream water chemistry in Japanese cedar plantation after clear-cutting using the forest rotation in central Japan

Because both natural and anthropogenic disturbances affect biogeochemical cycles in forest ecosystems, monitoring is needed to separate their influences. Chronosequence is very useful for such studies. In our study area, plantation through forest rotation on a watershed basis resulted in more than 40 adjacent watersheds of between 0 and 87 years of stand age, kind of chronosequence. Here, we examined the biological similarity of the watersheds and the long-term effects of clear-cutting on stream water chemistry. The stream water NO 3 −–stand age relationship was similar between the two observation years; stream water NO 3 − concentrations increased dramatically in the watersheds after clear-cutting and decreased in 7–10-year-old replanted watersheds. The slope of stream water NO 3 − concentrations between the different watersheds covered by same age stand was significant, at 1:1. Additionally, stream water NO 3 − concentrations were more strongly correlated between the different watersheds covered by same aged stand than between the observations at 4 years intervals within a watershed. These findings indicate that stream water NO 3 − concentration is mainly regulated by stand age, i.e., by vegetation regrowth, rather than watershed-specific characteristics. Hence, adjacent watersheds are biologically similar apart from stand age and can be regarded as a chronosequence. While there was a clear relationship between stream water NO 3 − concentration and stand age, there was significant correlation with stream water SO 4 2−, Ca 2+, Mg 2+, Cl − or Na + between two observations in the same watershed. This indicates that watershed-specific characteristics, rather than vegetation regrowth, control stream SO 4 2−, Ca 2+, Mg 2+, Cl −, and Na + concentrations. After 25 years of clear-cutting Ca 2+, Mg 2+ and Na + concentrations significantly increased. It is likely the contribution of forest floor accumulation with stand development. Based on these results, clear-cutting influences stream chemistry, not only NO 3 −, but also the major cation and the influence of clear-cutting continues for several decades at this study site.

Some forest floor and soil properties of umbrella pine (Pinus pinea L.) and black locust (Robinia pseudoacacia L.) plantations on mine lands in Agacli-Istanbul.

This study was conducted on the mine spoils planted with umbrella pine (Pinus pinea L.) and black locust (Robinia pseudoacacia L.). On forest floor samples; unit mass, total nitrogen and organic matter properties were determined. On soil samples; bulk density, fine soil fraction, pH, organic carbon, total nitrogen, sand, silt and clay percentages were determined. Results in black locust and umbrella pine plantations were compared statistically. In conclusion, 17 year after plantations, average forest floor accumulation was 6707.15 kg/ha under black locust, and 13700.00 kg/ha under umbrella pine. Forest floor and soils of black locust have significantly higher total nitrogen than those of umbrella pine. Keywords: Mine spoil, umbrella pine, black locust, forest floor, soil.

Some soil properties on coal mine spoils reclaimed with black locust (Robinia pceudoacacia L.) and umbrella pine (Pinus pinea L.) in Agacli-Istanbul

This study performed on randomly selected seven sample plots in leguminous black locust (Robinia pceudoacacia L.) plantations and five sample plots in umbrella pine (Pinus pinea L.) plantations on coal mine soil/spoils. Soil samples were taken from eight different soil depths (0-1, 1-3, 3-5, 5-10, 10-20, 20-30, 30-40, and 40-50 cm) into the soil profile. On soil samples, bulk density, fine soil fraction (Ø < 2 mm), sand, silt and clay rates, soil acidity (pH), organic carbon (C(org)), and total nitrogen (N(t)) contents were investigated. Also, some forest floor properties (unit mass, organic matter, and total nitrogen) were determined, and results were compared statistically between umbrella pine and black locust. As a result, 17 years after plantations, total forest floor accumulation determined as 6,107 kg ha(-1) under black locust compared to 13,700 kg ha(-1) under umbrella pine. The more rapid transformation of leguminous black locust forest floor creates organic carbon that migrates further into the mineral profile, and rapid accumulation of C and N in the soil profile was registered. Slower transformation processes of forest floor under umbrella pine result in lower soil N ratio and greater quantity of forest floor. Higher soil pH under leguminous black locust was determined significantly than umbrella pine. In conclusion, the composition of symbiotic nitrogen fixation of black locust appears to be a possible factor favoring carbon and nitrogen accumulation and, consequently, soil development. Clearly, both tree species have favorable impacts on initial soil formation. The umbrella pine generates the more forest floor layer; in contrast, black locust forest floor incorporates into the soil more rapidly and significantly increases soil nitrogen in upper soil layers.

SIMULATED ATMOSPHERIC NO3− DEPOSITION INCREASES SOIL ORGANIC MATTER BY SLOWING DECOMPOSITION

Presently, there is uncertainty regarding the degree to which anthropogenic N deposition will foster C storage in the N-limited forests of the Northern Hemisphere, ecosystems which are globally important sinks for anthropogenic CO2. We constructed organic matter and N budgets for replicate northern hardwood stands (n = 4) that have received ambient (0.7-1.2 g N x m(-2) x yr(-1) and experimental NO3- deposition (ambient plus 3 g NO3(-)-N x m(-2) x yr(-1)) for a decade; we also traced the flow of a 15NO3- pulse over a six-year period. Experimental NO3- deposition had no effect on organic matter or N stored in the standing forest overstory, but it did significantly increase the N concentration (+19%) and N content (+24%) of canopy leaves. In contrast, a decade of experimental NO3- deposition significantly increased amounts of organic matter (+12%) and N (+9%) in forest floor and mineral soil, despite no increase in detritus production. A greater forest floor (Oe/a) mass under experimental NO3- deposition resulted from slower decomposition, which is consistent with previously reported declines in lignolytic activity by microbial communities exposed to experimental NO3- deposition. Tracing 15NO3- revealed that N accumulated in soil organic matter by first flowing through soil microorganisms and plants, and that the shedding of 15N-labeled leaf litter enriched soil organic matter over a six-year duration. Our results demonstrate that atmospheric NO3- deposition exerts a direct and negative effect on microbial activity in this forest ecosystem, slowing the decomposition of aboveground litter and leading to the accumulation of forest floor and soil organic matter. To the best of our knowledge, this mechanism is not represented in the majority of simulation models predicting the influence of anthropogenic N deposition on ecosystem C storage in northern forests.

Changes in Austrian pine forest floor properties in relation with altitude in mountainous areas

Altitudinal studies has become of interest to ecologists concentrated on functional alterations aiming to clarify the effects of limiting factors. Nutrient element release from forest floor (FF) decomposition is suppressed by those factors such as low temperature, shortened vegetation period concluding FF accumulation at high elevation fields. To draw out a response to the FF decomposition issue, FF layers as leaf + fermentation (L + F) and humus (H) were collected from 37 representative sample plots along an altitudinal gradient (from 1,400 m to 1,710 m) on Kaz (Balikesir-Turkey) mountain. Mass, pH, organic matter (OM) and total nitrogen (Nt) contents of FF were investigated to explain the relation between decomposition and altitudinal effects. The results revealed that total FF mass and (L + F), (H) sub-fraction masses through elevation show an insignificant relation with the altitude. No significant difference was found between the altitudinal groups in the OM content of L + F. Besides there are significant negative correlations between OM contents (%) of L + F and H layers and altitude with the coefficient values 0.342 (&lt;I&gt;P&lt;/I&gt;&lt; 0.05) and 0.597 (&lt;I&gt;P&lt;/I&gt; &lt; 0.01), respectively. The Nt content of L + F layer also increases through the elevation revealing a medium correlation with altitude (0.368; &lt;I&gt;P&lt;/I&gt; &lt; 0.05). The increasing Nt and decreasing OM contents show better decomposition rates at higher sites regardless of the altitude induced climatic changes. We assume that the forest floor accumulation under tree canopies provides a better decomposition relying on the microclimatic environment mediated by tree canopies, in spite of the altitude.