Fluxes,stocks and availability of nitrogen in evergreen broadleaf and fir forests: similarities and differences

In this study,nitrogen fluxes or flows in litterfall,nitrogen stocks and available nitrogen in soils of two plots representing evergreen broadleaf and Bulgarian fir forests were assessed.Both plots are in good quality sites and for this reason,the litterfall quantities and nitrogen fluxes were relatively high.The woody litterfall flux of nitrogen was significantly higher in the fir forest than in the evergreen broadleaf one.The total nitrogen stock was higher in the soil under the fir forest.However,the percentage of the available nitrogen(ammonium+nitrates) was significantly higher in the upper 20 cm soil layer of the evergreen broadleaf forest in spite of the higher average C/N ratios in the foliar litterfall of the broadleaf forest and insignificant difference of the C/N ratios in all soil layers of the two ecosystems.The microclimatic conditions(higher soil temperatures in the evergreen broadleaf forest) is probable possible cause for this difference.The available nitrogen in the soils and its retranslocation from senescing leaves cover the nitrogen requirements of trees.It is hypothesized that trees may also take up nitrogen from deeper soil layers.     

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.     

Stocks and dynamics of soil organic carbon and coarse woody debris in three managed and unmanaged temperate forests

The effect of forest conservation on the organic carbon (C) stock of temperate forest soils is hardly investigated. Coarse woody debris (CWD) represents an important C reservoir in unmanaged forests and potential source of C input to soils. Here, we compared aboveground CWD and soil C stocks at the stand level of three unmanaged and three adjacent managed forests in different geological and climatic regions of Bavaria, Germany. CWD accumulated over 40–100 years and yielded C stocks of 11 Mg C ha^?1 in the unmanaged spruce forest and 23 and 30 Mg C ha^?1 in the two unmanaged beech–oak forests. C stocks of the organic layer were smaller in the beech–oak forests (8 and 19 Mg C ha^?1) and greater in the spruce forest (36 Mg C ha^?1) than the C stock of CWD. Elevated aboveground CWD stocks did not coincide with greater C stocks in the organic layers and the mineral soils of the unmanaged forests. However, radiocarbon signatures of the O _e and O _a horizons differed among unmanaged and managed beech–oak forests. We attributed these differences to partly faster turnover of organic C, stimulated by greater CWD input in the unmanaged forest. Alternatively, the slower turnover of organic C in the managed forests resulted from lower litter quality following thinning or different tree species composition. Radiocarbon signatures of water-extractable dissolved organic carbon (DOC) from the top mineral soils point to CWD as potent DOC source. Our results suggest that 40–100 years of forest protection is too short to generate significant changes in C stocks and radiocarbon signatures of forest soils at the stand level.     

The interaction between organic layer and forest growth and forest development on former heathland

Heathland soils are characterized by high acidity and poor nutrient contents. Nutrient availability could then be an important factor in forest growth and development on these soils. The hypothesis to be verified was 1. The enduring change in vegetation composition and production is of great influence especially on the development of the organic layer and on the nutrient distribution between this compartment and the mineral soil, and 2. As a result, forest nutrition and water supply will change during forest growth with consequences for forest development itself. In NW Germany heathland forest development are dominated by heathlands as the initial stage of the succession, naturally established pioneering pine dominated woodlands, and oak and beech dominated forests as the terminal stages. In a comparative study, within these stages of forest succession the nutrient and water supply in the organic layer were investigated with regards to the nutrient and water supply in the mineral soil and to the morphology of the organic layer itself. The successional development was associated with an increased productivity and a marked enrichment of organic material and nutrients in the organic layer, whereas the nutrient storage in the mineral soil was unchanged. The nutrient storage in the organic layer in the forested sites amounted to up to 80% of the plant-available nutrients within the organic layer–mineral soil system. The water supply increased too due to higher water storage and increasing root penetration within the organic layer. However, the increase in water supply was less marked than the nutrient enrichment. Especially the beech-dominated broad-leaved forests depend on higher nutrient and water supply of the organic layer. They have better growth conditions in the late stages of succession, due to an intense humus accumulation by the pioneering birch–pine woodlands. Consequently, the development of the organic layer facilitates the change of coniferous woodlands to forests and woodlands dominated by broad-leaved trees. Using pine as first planted tree is recommended to support this development.     

Does tree species composition control soil organic carbon pools in Mediterranean mountain forests?

We compared soil organic carbon (SOC) stocks and stability under two widely distributed tree species in the Mediterranean region: Scots pine (Pinus sylvestris L.) and Pyrenean oak (Quercus pyrenaica Willd.) at their ecotone. We hypothesised that soils under Scots pine store more SOC and that tree species composition controls the amount and biochemical composition of organic matter inputs, but does not influence physico-chemical stabilization of SOC. At three locations in Central Spain, we assessed SOC stocks in the forest floor and down to 50 cm in the mineral in pure and mixed stands of Pyrenean oak and Scots pine, as well as litterfall inputs over approximately 3 years at two sites. The relative SOC stability in the topsoil (0-10 cm) was determined through size-fractionation (53 μm) into mineral-associated and particulate organic matter and through KMnO₄-reactive C and soil C:N ratio.Scots pine soils stored 95-140 Mg ha⁻¹ of C (forest floor plus 50 cm mineral soil), roughly the double than Pyrenean oak soils (40-80 Mg ha⁻¹ of C), with stocks closely correlated to litterfall rates. Differences were most pronounced in the forest floor and uppermost 10 cm of the mineral soil, but remained evident in the deeper layers. Biochemical indicators of soil organic matter suggested that biochemical recalcitrance of soil organic matter was higher under pine than under oak, contributing as well to a greater SOC storage under pine. Differences in SOC stocks between tree species were mainly due to the particulate organic matter (not associated to mineral particles). Forest conversion from Pyrenean oak to Scots pine may contribute to enhance soil C sequestration, but only in form of mineral-unprotected soil organic matter.     

Carbon and nitrogen in forest floor and mineral soil under six common European tree species

The knowledge of tree species effects on soil C and N pools is scarce, particularly for European deciduous tree species. We studied forest floor and mineral soil carbon and nitrogen under six common European tree species in a common garden design replicated at six sites in Denmark. Three decades after planting the six tree species had different profiles in terms of litterfall, forest floor and mineral soil C and N attributes. Three groups were identified: (1) ash, maple and lime, (2) beech and oak, and (3) spruce. There were significant differences in forest floor and soil C and N contents and C/N ratios, also among the five deciduous tree species. The influence of tree species was most pronounced in the forest floor, where C and N contents increased in the order ash = lime = maple < oak = beech ? spruce. Tree species influenced mineral soil only in some of the sampled soil layers within 30 cm depth. Species with low forest floor C and N content had more C and N in the mineral soil. This opposite trend probably offset the differences in forest floor C and N with no significant difference between tree species in C and N contents of the whole soil profile. The effect of tree species on forest floor C and N content was primarily attributed to large differences in turnover rates as indicated by fractional annual loss of forest floor C and N. The C/N ratio of foliar litterfall was a good indicator of forest floor C and N contents, fractional annual loss of forest floor C and N, and mineral soil N status. Forest floor and litterfall C/N ratios were not related, whereas the C/N ratio of mineral soil (0–30 cm) better indicated N status under deciduous species on rich soil. The results suggest that European deciduous tree species differ in C and N sequestration rates within forest floor and mineral soil, respectively, but there is little evidence of major differences in the combined forest floor and mineral soil after three decades.     

Influence of forest growth on former heathland on nutrient input and its consequences for nutrition and management of heath and forest

The low nutrient supply of heathland soils is often insufficient for the nutrient demand of growing forests and woodlands, and additional atmospheric input of nutrients is beneficial for the tree growth. On old heathland soils tree species influencing nutrient input with regard to higher amounts have competitive benefits on the early stages of succession and/or as first planted trees with consequences for both the successional development and the nutrition and management of heathland and forests. In three stages of heathland forest succession on highly acidified and nutrient poor soil, the influence of the canopies of a Calluna heathland, a pioneering birch-pine woodland, and a terminal oak-beech forest on nutrient input was investigated. Of all investigated species Scots pine has the highest interception of water and nutrients (N, K, Ca, Mg). As a consequence, the nutrient input into the pioneering birch-pine forest is the highest of the three types of ecosystems. This ability to meliorate the nutrient supply by increasing the nutrient input favours pine in the early stages of the succession. The enhanced nutrient input and accumulation within the young successional forest ecosystems involves two different succession and/or management considerations depending upon the further ecosystem development.

• 1.The increasing nutrient availability mitigates the negative influence of the highly acidified nutrient poor soil on the growth of oak and beech and facilitates the conversion of pine dominated woodlands and forests into forests dominated by broadleaved species.
• 2.For regeneration of heathland from naturally established pine woodlands and forests, deforestation have to be combined with techniques of nutrient impoverishment of the soil.

     

Spatially explicit assessment of carbon stocks of a managed forest area in eastern Germany

The Kyoto-protocol permits the accounting of changes in forest carbon stocks due to forestry. Therefore, forest owners are interested in a reproducible quantification of carbon stocks at the level of forest management units and the impact of management to these stocks or their changes. We calculated the carbon stocks in tree biomass and the organic layer including their uncertainties for several forest management units (Tharandt forest, Eastern Germany, 5,500 ha) spatially explicit at the scale of individual stands by using standard forest data sources. Additionally, soil carbon stocks along a catena were quantified. Finally, carbon stocks of spruce and beech dominated stands were compared and effects of thinning intensity and site conditions were assessed. We combined forest inventory and data of site conditions by using the spatial unions of the shapes (i.e., polygons) in the stand map and the site map. Area weighted means of carbon (C) stocks reached 10.0 kg/m2 in tree biomass, 3.0 kg/m2 in the organic layer and 7.3 kg/m2 in mineral soil. Spatially explicit error propagation yielded a precision of the relative error of carbon stocks at the total studied area of 1% for tree biomass, 45% for the organic layer, and 20% for mineral soil. Mature beech dominated stands at the Tharandt forest had higher tree biomass carbon stocks (13.4 kg/m2) and lower organic layer carbon stocks (1.8 kg/m2) compared to stands dominated by spruce (11.6, 3.0 kg/m2). The difference of tree biomass stocks was mainly due to differences in thinning intensity. The additional effect of site conditions on tree carbon stocks was very small. We conclude that the spatially explicit combination of stand scale inventory data with data on site conditions is suited to quantify carbon stocks in tree biomass and organic layer at operational scale.     

Impact of tree species on soil carbon stocks and soil acidity in southern Sweden

Abstract

The impact of tree species on soil carbon stocks and acidity in southern Sweden was studied in a non-replicated plantation with monocultures of 67-year-old ash (Fraxinus excelsior L.), beech (Fagus silvatica L.), elm (Ulmus glabra Huds.), hornbeam (Carpinus betulus L.), Norway spruce (Picea abies L.) and oak (Quercus robur L.). The site was characterized by a cambisol on glacial till. Volume-determined soil samples were taken from the O-horizon and mineral soil layers to 20?cm. Soil organic carbon (SOC), total nitrogen (TN), pH (H₂O), cation-exchange capacity and base saturation at pH 7 and exchangeable calcium, magnesium, potassium and sodium ions were analysed in the soil fraction?<?2 mm. Root biomass (<5 mm in diameter) and its proportion in the forest floor and mineral soil varied between tree species. There was a vertical gradient under all species, with the highest concentrations of SOC, TN and base cations in the O-horizon and the lowest in the 10–20?cm layer. The tree species differed with respect to SOC, TN and soil acidity in the O-horizon and mineral soil. For SOC and TN, the range in the O-horizon was spruce?>?hornbeam?>?oak?>?beech?>?ash?>?elm. The pH in the O-horizon ranged in the order elm?>?ash?>?hornbeam?>?beech?>?oak?>?spruce. In the mineral soil, SOC and TN ranged in the order elm?>?oak?>?ash?=?hornbeam?>?spruce?>?beech, i.e. partly reversed, and pH ranged in the same order as for the O-horizon. It is suggested that spruce is the best option for fertile sites in southern Sweden if the aim is a high carbon sequestration rate, whereas elm, ash and hornbeam are the best solutions if the aim is a low soil acidification rate.     

Nutrient cycles and successional changes following shifting cultivation practice in moist semi-deciduous forests in Nigeria

The nutrient contents of moist semi-deciduous forest, successional regrowth and cultivated soils were studied along with successional changes following clear-cutting and burning. Water-soluble N, P, Ca, Mg and K were measured in the primary forest, successional regrowth, cultivated soils and soils of secondary forests ranging from 1 to 6 years after cessation of cultivation. Clearing and burning of the forest releases stored essential nutrients to soils under cultivation. K and N seem to be lost more rapidly in soils under cultivation than in soils under successional regrowth.It was observed that under shifting cultivation essential nutrients build up temporarily; P and Ca rapidly build up in cultivated soils to values much higher than their original values in the forest soils. Six years after the cessation of cultivation, the soil nutrient level of the successional regrowth was still far from being restored to the level of the primary forest soils.Seedlings and resprouts were equally important in the vegetation recovery of burnt and unburnt clear-cut forest. Seedlings of pioneer woody species established themselves in the burnt and unburnt plots within 4 months. Secondary regrowth in the burnt plot appeared better than in the unburnt plot, although resprouts played a more significant role in the unburnt plot.     

Carbon and nitrogen dynamics in topsoils along forest conversion sequences in the Ore Mountains and the Saxonian lowland, Germany

Carbon and nitrogen stocks and their medium-term and readily decomposable fractions in topsoils were compared in relation to soil microbial biomass and activity along sequences from coniferous to deciduous stands. The study was carried out in the Ore Mountains and the Saxonian lowland, representing two typical natural regions in Saxony, Germany. In accordance with current forest conversion practices, the investigation sites represent different stands: mature conifer stands of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) (type A); Norway Scots spruce and pine with advanced plantings of European beech (Fagus sylvatica L.) or European beech/Common oak (Quercus petreae Liebl.) (type B); and mature deciduous stands of European beech and European beech/Common oak (type C). The investigated forest sites can be grouped into three silvicultural situations according to the development from coniferous stands to advanced plantings and finally mature deciduous forests (chronosequence A–B–C). The organic layer (L, F and H horizons) and uppermost mineral soil (0–10 cm) were analysed for potential C mineralisation, microbial biomass, concentrations of total C and N (TOC and TN) and for medium-term and readily decomposable C and N fractions, obtained by hot- and cold-water extraction respectively. The results showed an increase in organic layer thickness and mass as well as TOC and TN stocks along the forest sequences in the lowland. Yet, underplanted sites with two storeys revealed higher organic layer mass as well as TOC and TN stocks as compared to coniferous and deciduous stands. Stocks of hot- and cold-water-extractable C and N in relation to microbial biomass and its activity revealed a high turnover activity in deeper organic horizons of deciduous forests compared to coniferous stands. The stand-specific differentiation is discussed in relation to microbial biomass, litter quantity and quality and forest structure, but also with respect to the site-specific climatic factors and water budget as well as liming and fly-ash impacts. Results indicate higher dynamics in deciduous stands in the lowland especially during the initial turnover phase. The elevated microbial activity in deeper organic horizons of deciduous litter-influenced sites in spring is discussed as a specific indicator for long-term C sequestration potential as besides C mineralisation organic compounds are humified and thus, can be stored in the organic layer or in deeper soil horizons. Due to liming activities, stand-specific effects on organic matter turnover dynamics have evened out today in the Ore mountain region, but will presumably occur again once base saturation decreases. Here, the stand-specific effect on microbial biomass can currently be seen again as C_mic in the L horizon increased from spruce to beech. Our study sites in the lowland revealed no significant fly-ash impact. Differences between sites were evaluated by calculating the discriminance function. TOC and TN as well as medium-term degradable C and N were defined in this study as indicators for turnover dynamics along forest conversion sites.     

Tree effects on the chemical topsoil features of oak, beech and pine forests

We aimed to study tree effects on the chemical properties of forest soils. We compared soil features of three types of forest ecosystems, each with four stands (replicates): beech forests (Fagus sylvatica), oak forests (dominated by Quercus pyrenaica) and pine plantations (Pinus sylvestris). Five samples from the top 10 cm of soil were taken per stand, from which pH, organic matter content (O.M.), total nitrogen (N) and available calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺) and sodium (Na⁺) were determined. Litter layer depth was measured at each soil sampling point. We also measured tree density and crown diameters at each stand. Our results indicated that soil samples from the four pine plantation stands were more similar while oak and beech stands were characterised by great variability in terms of soil properties and leaf litter depth. Although the identity of the dominant tree species significantly influenced several topsoil chemical properties (increase in pH and available cations in oak forests and higher organic matter and total nitrogen in beech and pine ecosystems), there were other important factors affecting soil features that may be taken under consideration. Differences between soil properties of the three types of forest ecosystems were mainly related to the characteristics of the litter layer and less related to the tree layer structure. Finally, the establishment of pine plantations in naturally deciduous tree areas made the topsoil features more homogeneous.     

Litterfall, litter decomposition and nutrient dynamics in a subtropical natural oak forest and managed plantation in northeastern India

In northeastern India, subtropical forests are over-exploited for timber, fuel wood and common agricultural practice like shifting cultivation, which are responsible for the degradation of natural forest. In degraded areas, large-scale plantations of different species of Quercus have been raised since 1980 for the production of economic Tasar silk. Conversion of natural forest into plantation affects the process of nutrient cycling due to management practices. Thus, it would be of importance to study the litterfall, litter decomposition process and the factors regulating the rate of litter decay in these ecosystems to improve recommendations for their management and conservation. We recorded litterfall by using litter traps and decomposition of leaf litter by nylon net bag technique to understand the amount of organic matter and nutrient return and their release in soils of forest and plantation in Manipur, northeast India. Total litterfall was 419.9 g m⁻² year⁻¹ in plantation and 547.7 g m⁻² year⁻¹ in forest. Litter decomposition rate was faster at plantation site than the forest in the early stage of litter decomposition whereas the reverse was observed at later stages of decomposition. Stepwise regression analysis showed the significant role of relative humidity and mean temperature on mass loss rates in the forest. Relative humidity, maximum temperature, population of fungi and actinomycetes were the best predictor variables for mass loss rates in plantation. Nutrient retranslocation efficiency and the immobilization of N and P in forest litter were higher than plantation. This suggests that Q. serrata growing in natural ecosystem in oligotrophic condition adapted strong nutrient conservation mechanisms to compete with the other plant species for the meager soil nutrients. The same species in plantation loses these adaptive capabilities because of exogenous supply of nutrients and in the absence of intense competition with other plant species. Thus, the optimization of organic and chemical fertilizer input in plantation is recommended for maintaining the soil fertility level to produce quality leaf for silkworm by conserving essential nutrients in the system.     

Acidification and chemical properties of fagus sylvatica l forest soils

Exchangeable Al and acidity of Swedish beech (Fagus sylvatica L.) forest soils are documented and discussed on the basis of known changes in soil chemical properties during recent decades. It is concluded that the pH and base saturation decrease, which has occurred in most forest soils of the region, has been accompanied by increases in the amount of exchangeable and soil solution Al and a greater decrease of the Ca: AI ratio, particularly in the B horizon. An adverse nutritional state now seems to prevail in most beech forest B horizons. Conditions are more favourable in the topsoil due to the formation of Al‐humus complexes which are less available to plant uptake, and in the case of very acid mor layers, a low Al content. However, in A (mull) horizons of intermediate acidity with a rather high clay content and low in humus, conditions approaching those of the B horizon may be found.     

阔叶红松林土壤CO2,N2O排放和CH4吸收的研究

为研究凋落物对CO2,N2O排放和CH4吸收的影响,从2002年9月3日到2003年10月30日,采用静态密闭箱技术对长白山阔叶红松林两种类型土壤生态系统的CO2,N2O和CH4的通量进行测定。两种土壤类型分别为表层有凋落物覆盖和没有凋落物覆盖。研究结果表明,凋落物对CO2,N2O和CH4通量有显著性影响(P<0.05)。有凋落物样地的CO2,N2O和CH4通量的日变化趋势和无凋落物样地中三种气体的日变化趋势相似,且CO2,N2O和CH4的日通量峰值都出现在18:00。有凋落物样地的CO2,N2O和CH4通量的季节变化趋势和无凋落物样地中三种气体的季节变化趋势也相似,但在一年之中,CO2和CH4的峰值出现在六月,N2O的峰值却出现在八月。研究结果还表明有凋落物样地CO2,N2O的日排放通量和年均排放通量明显大于无凋落物样地中两种气体的排放通量,但有凋落物样地的CH4日吸收通量和年均排放通量却小于无凋落物样地的CH4吸收通量。     

Canopy composition as a measure to identify patterns of nutrient input in a mixed European beech and Norway spruce forest in central Europe

The influence of canopy composition on litterfall and throughfall was investigated in a mixed spruce beech forest in central Germany. We hypothesised that different parts of the mixed canopy created distinct patterns of element inputs via litterfall and throughfall. The investigation was carried out in two plots, representing the most contrasting cases of mixed forests: a stand greatly dominated by spruce (SDP) and a stand greatly dominated by beech (BDP). The canopies of the two plots were classified in four categories: pure beech, pure spruce, mixed canopy and gap. Amounts of throughfall water were lower and major element fluxes were higher under spruce than under beech in both plots, indicating that the nutrient inputs under the canopies of individual trees are driven by species-specific properties of the canopies and are quite independent of the degree of admixture. With the exception of K⁺, mixed canopies showed intermediate element inputs via throughfall, compared with pure canopy classes. The K⁺ input was significantly greater under mixed canopies, and these differences were more pronounced in the SDP than in the BDP. Results suggest that individual spruce trees in the BDP induce greater spatial heterogeneity of throughfall input than individual beech trees in the SDP. Nutrient inputs via foliar litterfall were similar among the different canopy classes, but the Mg input was lower under spruce canopy. This effect was balanced by higher Mg input via spruce throughfall. In our study, throughfall was the main source of heterogeneity in nutrient inputs, while foliar litterfall had a homogenising effect.     

Stand restoration burning in oak–pine forests in the southern Appalachians: effects on aboveground biomass and carbon and nitrogen cycling

Understory prescribed burning is being suggested as a viable management tool for restoring degraded oak–pine forest communities in the southern Appalachians yet information is lacking on how this will affect ecosystem processes. Our objectives in this study were to evaluate the watershed scale effects of understory burning on total aboveground biomass, and the carbon and nitrogen pools in coarse woody debris (CWD), forest floor and soils. We also evaluated the effects of burning on three key biogeochemical fluxes; litterfall, soil CO₂ flux and soil net nitrogen mineralization. We found burning significantly reduced understory biomass as well as the carbon and nitrogen pools in CWD, small wood and litter. There was no significant loss of carbon and nitrogen from the fermentation, humus and soil layer probably as the result of low fire intensity. Burning resulted in a total net loss of 55 kg ha⁻¹ nitrogen from the wood and litter layers, which should be easily replaced by future atmospheric deposition. We found a small reduction in soil CO₂ flux immediately following the burn but litterfall and net nitrogen mineralization were not significantly different from controls throughout the growing season following the burn. Overall, the effects of burning on the ecosystem processes we measured were small, suggesting that prescribed burning may be an effective management tool for restoring oak–pine ecosystems in the southern Appalachians.     

Nutrient status of managed and natural forest fragments of Fagus sylvatica in southern Europe

Beech forests located in the southwestern limit of Europe have been affected by severe deforestation and long-term fragmentation. Some of these forests have been subjected to partial cutting, whereas others have been maintained with little or no active management. It has previously been shown that past management has led to substantial changes in tree structure, diversity and plant species. These perturbations, through their influence on the litterfall and forest floor, may affect nutrient cycling and the nutritional status of such fragile ecosystems. Mineral nutrition was investigated in 53 forest fragments by analysis of data corresponding to nutrient concentrations in forest floor, mineral soils and foliage. In comparison with other beech forests in Central Europe subjected to higher levels of air pollution, the stands showed fewer incidences of nutrient deficiencies and lower foliar concentrations of S and heavy metals. Partial cuts carried out in recent decades have reduced the forest floor mass proportional to the intensity of the harvesting. The effect was probably due to the lower litter input and the increased decomposition of litter as a consequence of the environmental changes in forest gaps. The partially cut stands displayed higher foliar levels of K and Mg, which could be attributed to the greater release of these elements as a consequence of the increased decomposition of litter. However, past management has brought about lower foliar concentrations of P and N. Both effects were found to be proportional to basal area and the forest floor mass, which suggests that they are related to the intensity of harvesting. Although the causes are uncertain, this negative effect may be due to a reduction in forest floor thickness, which implies the loss of preferred rooting space for trees.     

Forest soils and carbon sequestration

Soils in equilibrium with a natural forest ecosystem have high carbon (C) density. The ratio of soil:vegetation C density increases with latitude. Land use change, particularly conversion to agricultural ecosystems, depletes the soil C stock. Thus, degraded agricultural soils have lower soil organic carbon (SOC) stock than their potential capacity. Consequently, afforestation of agricultural soils and management of forest plantations can enhance SOC stock through C sequestration. The rate of SOC sequestration, and the magnitude and quality of soil C stock depend on the complex interaction between climate, soils, tree species and management, and chemical composition of the litter as determined by the dominant tree species. Increasing production of forest biomass per se may not necessarily increase the SOC stocks. Fire, natural or managed, is an important perturbation that can affect soil C stock for a long period after the event. The soil C stock can be greatly enhanced by a careful site preparation, adequate soil drainage, growing species with a high NPP, applying N and micronutrients (Fe) as fertilizers or biosolids, and conserving soil and water resources. Climate change may also stimulate forest growth by enhancing availability of mineral N and through the CO₂ fertilization effect, which may partly compensate release of soil C in response to warming. There are significant advances in measurement of soil C stock and fluxes, and scaling of C stock from pedon/plot scale to regional and national scales. Soil C sequestration in boreal and temperate forests may be an important strategy to ameliorate changes in atmospheric chemistry.     

Long-term sustainability of forest ecosystems on sandstone in the Vosges Mountains (France) facing atmospheric deposition and silvicultural change

Since the 1980s, atmospheric deposition acidity has generally decreased in European forest ecosystems. However, at many sites, little or no sign of recovery has been observed yet. Concerns are rising about the sustainability of these ecosystems because of reduced nutrients inputs in atmospheric deposition and the increase in biomass harvesting to supply bio-energy.We used a silver fir plot of the French monitoring network (RENECOFOR, site SP57) typical of the ecosystems on sandstone in the Vosges Mountains, to investigate its functioning and its response facing past and possible future changes. We (1) calculated 12-year-mean “input-output” nutrient budgets, (2) measured the change in soil exchangeable cations and anions, (3) used monitoring data to calibrate a process oriented biogeochemical model, NuCM, that was then used to (4) simulate the consequences of two main scenarios and their combinations: constant or reduced atmospheric deposition, and traditional or whole-tree harvesting.Mean term changes in exchangeable nutrients and input-output budgets showed a loss of exchangeable sulphate and base cations, the level of which depended on the method. This combined efflux induced an acidification of soil solution and an alkalinisation of the soil. The model NuCM was successfully calibrated and scenarios were implemented. A slight recovery was simulated when deposition was maintained constant but combined acid and nutrient atmospheric deposition reduction delayed recovery. Whole-tree harvesting drastically decreased soil fertility compared to traditional silviculture. Hence, biomass harvesting in forests on poor soils may counter recovery in the future.