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Litterfall dynamics in Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and birch (Betula) stands in Estonia
Abstract
Canopy litterfall represents an essential aboveground flux in every forest ecosystem, affecting soil carbon and nutrient dynamics as well as soil fertility. However, despite the important role of the canopy litter flux in ecosysteḿs functioning and carbon sequestration, litterfall dynamics is still poorly studied in hemiboreal forests. The main aim of the current study was to estimate average annual litter fluxes in Scots pine, Norway spruce and birch (Betula pendula and Betula pubescens) stands, as well as to compile regional litter models for estimating the annual litter flux. The annual litter flux from a total of 33 pine, 15 spruce and 21 birch stands, with 85, 43 and 53 datapoints, respectively, was included in the study.
Although the annual litter flux depended on site quality index and stand age, no significant relationship was established between stand basal area and litter flux. Average annual canopy litterfall was similar for the studied tree species, being 3.24 ± 0.14 for pine, 3.62 ± 0.16 for spruce and 3.22 ± 0.07 t ha⁻¹ yr⁻¹ for birch across the stands of different ages. For all studied tree species, the relative proportion of needles or leaves in the total annual litter flux declined with stand age, due to the increased share of twigs and other fractions in the litter of older stands. The developed models of the litter flux allow to estimate the annual litter production of the canopy for the studied tree species on the basis of site quality index and stand age.
... The collection of litterfall from different vegetation types revealed that the annual litterfall amount of leaves ranged from 3.35 to 5.50 t/(hm 2 ·year), which was lower than the average annual litterfall amount of 8.53 t/(hm 2 ·year) in Xishuangbanna during the period of 2004-2005 and was similar to that of Dinghushan [5.42 t/(hm 2 ·year)] and Changbai Mountain [5.27 t/(hm 2 ·year)] in 2004-2005, with difference that more study sites were selected and different vegetation types were classified in this study, while the amount of leaf litter of different vegetation types is different because of the forest community type, forest age, latitude, elevation, etc., all affecting the amount of litterfall of the forests [ 24 ]. These influencing factors have not been studied in this paper yet. ...
... It can be seen that the annual litterfall amount showed a decreasing trend with the increase of latitude, indicating that the annual litterfall amount was mainly controlled by the heat factor [ 28 ]. In addition to the influence of temperature, the amount of litter is also related to the type of forest stand and other factors [ 24 ]. ...
Mercury is one of the most toxic heavy metal pollutants, and mercury absorbed by plant leaves accumulates in forests in the form of litterfall. Therefore, in this study, leaf mercury concentrations and mercury fluxes were analyzed in typical sample plots of each vegetation type, which were selected from 7 geographic regions in China. The results showed that the amount of litterfall of each component varied among different vegetation types, with leaves accounting for the largest proportion (51.12% to 80.54%). The annual amount of leaf litter ranged from 3.35 to 5.50 t/(hm²·year). On the seasonal scale, the litterfall amount peaked in the autumn for most vegetation types. On a spatial scale, the litterfall amount displayed a decreasing trend with increasing latitude, with the highest of 8.16 ± 4.61 t/(hm²·year) in the southwestern China, and the lowest was 2.98 ± 0.89 t/(hm²·year) in north China. Moreover, leaf litter mercury concentrations ranged from 2.11 to 236.70 ng/g, with a mean value of 57.92 ± 33.07 ng/g. Leaf mercury concentrations of most tree species increased gradually with the growing period and showed a pattern of higher in the south and lower in the north on the spatial scale. Furthermore, leaf mercury fluxes of the 5 vegetation types ranged from 177.58 to 410.50 mg/(hm²·year), and the accumulation of mercury mainly occurred in autumn. The comprehensive quantification of mercury fluxes in this paper provides data support for the long-term monitoring of litterfall and fundamental information to potentially solve the problem of mercury pollution in China.
... Its ability to adapt to different environmental conditions makes it an ideal model species for studying needle biomass dynamics [17]. Understanding the process of litterfall in Scots pine stands is crucial to identifying this species' role in the global carbon cycle [18]. ...
... The foliar biomass turnover rate (commonly defined as the ratio between measured foliar litterfall and modelled foliar biomass) is crucial for estimating biomass input in soil carbon models and understanding nutrient cycling in forest ecosystems [18,36]. Knowing the turnover rate for different tree species across various geographical regions enhances model accuracy. ...
Understanding needle biomass turnover rates in Scots pine (Pinus sylvestris L.) stands is crucial for modelling forest ecosystem dynamics and nutrient cycling. This study examined needle litterfall and biomass turnover in Scots pine stands of varying ages in temperate forests (western Poland). The research focused on determining how stand age affects needle biomass, litterfall and the associated turnover rates. Data were collected from 20 Scots pine stands aged 26 to 90 years, and needle litterfall was measured and analysed in relation to stand characteristics such as age, density and biomass. The average annual needle litter production of the sampled Scots pine stands was 2008 kg·ha −1 ·year −1 , similar to the values previously reported for this tree species in other temperate forests in Europe. The average needle biomass turnover rate for sampled Scots pine stands was 23.4%. We could not support the hypothesis that this parameter depended on the age of the Scots pine stand. The needle biomass turnover rate showed a positive correlation with crown length and a negative correlation with stand density due to the very weak correlations; however, further research is needed to confirm these relationships. Despite this, the parameter can be used to estimate needle litterfall and can be applicable to conditions corresponding to those of temperate forests in Central and Western Europe. This study also highlights the need for further research on needle biomass turnover in temperate forests to improve the accuracy of carbon and nutrient cycling models. This work contributes to a deeper understanding of the role of needle litterfall in maintaining soil fertility and forest productivity, offering insights into sustainable forest management and conservation strategies.
... A higher C:N ratio and wax coating have been linked to slower decomposition rates and higher tannin content compared to the litter in sycamore plantations [51]. Therefore, the litterfall in the spruce plantations, distinct from the sycamore plantations, introduces plant residues with a higher C:N ratio [52,53]; subsequent microbial-driven decomposition preferentially breaks down hydrophilic compounds, reducing their abundance, while concurrently yielding recalcitrant organic materials with inherent hydrophobic properties [54,55], thereby contributing to the observed increase in hydrophobic components. The observed low hydrophobicity of SOM at the sycamore plantations can potentially be ascribed to the heightened microbial activity involved in plant litter degradation [35]. ...
The stability of soil organic matter (SOM) that governs soil organic carbon (SOC) storage depends on its characteristics and components, but little is known about how tree species in forest ecosystems affect SOM components and characteristics. In this study, we used FTIR spectroscopy to investigate plantations of two ecologically and economically significant tree species-namely, spruce (Picea spp.) and sycamore (Acer pseudoplatanus)-in order to determine how the different litter inputs and root-microbe interactions of these two plantations affect the functional groups, components, and characteristics of their SOM. Soil samples were taken from the topsoil (0-10 cm) and subsoil (10-20 cm). In the 0-10 cm soil depth, the SOM's hydrophilic, hydrophobic, and aromatic components differ between the spruce and sycamore plantations. The hydrophobic components constitute the primary constituents of the SOM of the two forest plantations, in contrast to the expected predominance of the hydrophilic component of the SOM. Also, the high hydro-phobicity (hydrophilic/hydrophobic) in the subsoil of the spruce plantations was attributed to a decrease in hydrophilic components and a subsequent increase in hydrophobic components of the SOM. The sycamore plantations exhibited a higher SOM aromaticity and a greater degree of decomposition than the spruce plantations. The aforementioned distinctions emphasise the contrasting mechanisms involved in transforming and turnover of the two-tree species' soil organic matter (SOM).
... However, due to improved light conditions, the expansion of crowns and thus the recovery of leaf mass are expected to occur in a few years (Juodvalkis et al. 2005). On both sites, the lion's share of the canopy litter flux was made up by leaves, while the proportion of branch litter was negligible, which is in accordance with the earlier results (Uri et al. 2022b). The exception was Site 2 CP, where a larger mass of branch litter indicates intensive self-pruning due to poor light conditions inside the canopy. ...
Pre-commercial thinning (PCT) is a common silvicultural practice for directing the development of the young stand in Nordic and Baltic countries. However, its impact on the stands carbon (C) cycling is still poorly studied. We carried out a comprehensive case study for estimating net ecosystem production (NEP) in unthinned control plot and in moderately and heavily thinned plots (2,500 and 1,500 trees ha⁻¹ remaining, respectively), in the next growing season after PCT in young Betula pendula stands on mineral soil (Site 1) and Betula pubescens stands on drained organic soil (Site 2). Thus, the study demonstrates post-thinning changes in C cycling in stands of two species of the same genus. The control plots of both sites served as C sinks: NEP 1.5 and 3.6 t C ha⁻¹ yr⁻¹ in Site 1 and Site 2, respectively. However, the thinned plots acted as C sinks on Site 1 (1.8 t C ha⁻¹ yr⁻¹) and as C sources on Site 2 (−1.4 and −3.1 t C ha⁻¹ yr⁻¹ in heavily and moderately thinned plot, respectively). The declined net primary production of trees after PCT was compensated for by the production of herbaceous vegetation and stump sprouts. Soil heterotrophic respiration (Rh) was the largest flux in the C budget of both sites and all treatments. Despite the increasing trend of Rh with increasing thinning intensity on Site 2, no statistically significant difference in the annual Rh flux occurred between the treatments in either site.
... In the case of single-story pine monocultures, mainly stand age and canopy closure are important. The amount of litterfall increases rapidly in young stands up to about 40 years old, and from that age slowly approaches a maximum value (Berg et al., 1995;Uri et al., 2022). Thus, in the stands we studied, age differences between individual plots should not have a major impact on the inflow of matter to the forest floor and, indirectly, on the soil fauna. ...
Mass outbreaks of pests defoliating Scots pine monocultures are of constant concern to foresters, and the increase in their frequency under conditions of a warming climate is expected. Repeated mass outbreaks usually involve the same areas, which suggests that predispositions to pest attack are shaped by certain stand characteristics or their habitat conditions. The aim of the study was to examine whether the soil invertebrate communities of pine forests with A. posticalis mass outbreaks differ from those of stands with no mass occurrence of this pest, despite analogous stand-habitat conditions and close proximity. Pine monocultures in two regions of Poland differing in the timing of the pest's mass occurrence were selected for the study. The soils of the studied monocultures, both in outbreak areas and reference tree stands, were characterized by strong acidity and low nutrient status. A lower (soil invertebrate communities) and a higher (Collembola communities) taxonomic resolution were used to assess the differences between the soil fauna of infected and reference stands. We show that soil invertebrate communities of the mass outbreak areas were characterized by impoverishment compared to those of reference forests. However, both invertebrate and Collembola communities, which in outbreak areas consisted of fewer taxa, did not differ significantly in density from reference tree stands. Nonmetric multidimensional scaling (NMDS) ordination of the collembolan communities revealed that not only their composition but also their structure in the mass outbreak areas differed significantly from those of uninfected tree stands. Further research is needed to clarify whether the depletion of soil invertebrates is a result of foliar insect feeding, or is rather a manifestation of weakened stands increasing their predisposition to attacks by pest insects.
This paper presents studies on the structural elements of biogeocenosis living ground cover vegetation for carbon cycle assessment. The ground cover is an extremely important component of forest ecosystems. Plants growing under the canopy of a forest actively participate in the production process: by assimilating carbon dioxide from the atmosphere, they create their biomass and for life remove carbon from circulation. The article carried out an assessment of carbon stocks in the living ground cover of forest ecosystems of oak and pine trees in the forest conditions of Voronezh region. The structure of the ground vegetation in oak (Quercus robur L.) and pine (Pinus silvestris L.) forests is shown to be quite specific. With the underground biomass stock exceeds the above-ground stock on all test sites laid in different plantations and conditions. The amount of carbon deposited by ground vegetation covers is 2.35 t ha⁻¹ for moss in pine plantations and 3.80 t ha⁻¹ for grass. Results show that the largest amount of living ground cover carbon stock in pine plantations is observed in April (32.24 t ha⁻¹), and the smallest in May (13.15 t ha⁻¹). The highest carbon values in oak plantations are found in underground biomass. The highest total carbon stock is in April (25.1 t ha⁻¹) and the lowest in May (10.8 t ha⁻¹).
Shelterwood cutting (SC) has been highlighted as an alternative method to clear-cut (CC)-based even-aged forest management. However, compared to CC, the effect of SC on stand carbon (C) balance is still poorly understood at the ecosystem level. We examined the prompt effect of SC versus CC on ecosystem net primary production (NEP) on a short-term scale, using the C budgeting method combined with eddy covariance (EC) measurements in hemiboreal mature Scots pine stands. The early effect of SC on annual C budget after removing 30–40 % of the growing stock revealed diverse patterns in the studied stands; NEP varied from 0.62 to -1.3 t C ha-1 yr-1 for the C sink and the C source, respectively. However, C loss decreased already in the second post-thinning year and levelled out attaining
-0.41 t C ha-1 yr-1, which is close to balance. Furthermore, C loss declined in the second post-harvesting year at the CC sites as a result of the increased
production of the ground vegetation and the decreased soil heterotrophic respiration (Rh) flux. However, C loss from dry mesotrophic clear-cuts was almost -1.8 t C ha-1 yr-1 for both study sites. Since estimation of the individual C fluxes for C budgeting is associated with variability-induced errors, the estimated values of NEP contain uncertainties of various levels. The estimated annual cumulative Rh flux was significantly higher in the SC versus CC areas and the mean annual Rh values across the study sites were 3.57 ± 0.25 and 2.59 ± 0.09 t C ha-1 yr-1, respectively. Annual estimated NEE after SC was 1.8 ± 0.52 t C ha-1 yr-1, gross primary ecosystem production was 9.28 ±0.97 and total ecosystem respiration was 7.47± 0.28 t C ha-1 yr-1. The discrepancy between the estimated values of NEE and NEP was 1.2 t C ha-1 yr-1. In the short term SC demonstrated some advantage over CC from the perspective of the C cycle, but the difference in NEP values between the SC and CC treatments was not convincingly overwhelming. Hence, SC allows to maintain the forest cover for a longer period and to avoid drastic changes in the landscape; still, after SC, C budget varied between the C sink and the C source.
The ecological and coenotic structure of the living ground cover and the structural and functional features of forest litter for three types of forests were studied: hairy-sedge birch forest, birch-aspen hairy-sedge, soddy-pike birch forest, forming a sequential row as hydromorphism increases within the slope, gradually to the center of the drive-dividing depression. The ecological characteristic of the living ground cover is based on the grouping of ecological-coenotic formations according to A.A. Nitsenko and ecological scales L.G. Ramensky and H. Ellenberg. Increasing hydromorphism is accompanied by an increase in ecological and cenotic diversity. The total trophicity score also increases under conditions of increased hydromorphism – in the soddy pike birch forest – in combination with low Ellenberg acidity index. Conversely, the maximum scores for these indicators, with high variation, belong to the birch-aspen forest, which occupies intermediate positions in the series of increasing hydromorphism. It was established that the studied stands are characterized by destructive and fermentative litters. As hydromorphism increases, the litter deposit increases from 400 to 1400 g/m2 with a simultaneous increase of detritus part in L subhorizon. About 60% of total organic matter deposit concentrated the litter of small-leaved plantations is accounted by easily decomposing fractions. With a regular increasing ash content in the system of subhorizons L–F, the maximum ash content is obtained for detritus fraction of L subhorizon. With a regular increase in the ash content in the system of subhorizons L–F, the maximum ash content is characteristic of the detritus fraction of the subhorizon L. The parameters of the ecological characteristics underlying the method of principal components showed a good grouping of the studied phytocenoses according to the degree of moisture, especially when using the general properties of litter (stocks, thickness, detritus content). The expediency of using the properties of litter to establish the similarities and differences of the studied phytocenoses as characteristics that integrally reflect the characteristics of moisture is revealed. The parameters of the living ground cover in conjunction with a number of structural and functional features of forest litter are adequate indicators of the degree of hydromorphism.
Although changes in tree species composition profoundly affect the structure, function, and processes of mixed forest ecosystems, there is limited knowledge on the effects of these changes on the hydrological functions of the litter layer in Pinus massoniana conifer‐broadleaf mixed forests in subtropical mountains. Here, we investigated three typical P. massoniana forest stands in southwest China: P. massoniana ‐ Liquidambar formosana conifer‐deciduous broadleaf mixed forest (Pm + Lf), P. massoniana ‐ Castanopsis eyrei conifer‐evergreen broadleaf mixed forest (Pm + Ce), and P. massoniana plantation (Pm), and conducted field investigations (litter composition and mass) and indoor immersion experiments to analyse the litter water‐holding capacity (LWHC) of forest stands in their natural state and with artificial ratios combining mixed (needle‐leaf and broad‐leaf) litters. The total litter mass did not significantly differ among the three forest stands ( p > 0.05), but significant differences were observed in the needle‐leaf (0.67–2.92 t hm ⁻² ), broad‐leaf (0.32–1.89 t hm ⁻² ) and bark (0.11–0.34 t hm ⁻² ) masses in the undecomposed layer. The LWHC of different stand types was in the order of Pm + Lf > Pm + Ce > Pm. The maximum water‐holding capacity of different artificial ratios of mixed litters was positively proportional to the broad‐leaf mass and inversely proportional to the needle‐leaf mass, and the P. massoniana ‐ L. formosana mixed litter had a higher maximum water‐holding capacity than the P. massoniana ‐ C. eyrei mixed litter. The LWHC of mixed forests is mainly influenced by stand structure (tree composition) and litter characteristics, and is positively correlated with leaf area, thickness, dry matter content, and surface roughness. This study revealed that the LWHC can be significantly affected by different P. massoniana stands in subtropical mountains. This study will aid the sustainable and ecological management of forest in subtropical mountains, and P. massoniana plantations should be gradually converted into mixed conifer‐broadleaf forests with greater LWHC and buffering capacity.
Litter decomposition is a key process that drives carbon and nutrient cycles in forest soils. The decomposition of five different substrate types was analyzed in hemiboreal coniferous forests, focusing on the mass loss and nutrient (N, P, and K) release of fine roots (FR) and needle litter in relation to the initial substrate and soil chemistry. A litterbag incubation experiment with site-specific FR and needle litter and three standard substrates (green and rooibos tea, α-cellulose) was carried out in four Norway spruce and four Scots pine-dominated stands in Estonia. Substrate type was the primary driver of mass loss and the decay rate of different substrates did not depend on the dominant tree species of the studied stands. Alpha-cellulose lost 98 ± 1% of the mass in 2-years, while the FR mass loss was on average 23 ± 2% after 3-years of decomposition. The FR decomposition rate could be predicted using a corresponding model of green tea, although the rate of FR decomposition is approximately five times lower than the rate of green tea in the first 3-years. The annual decomposition rate of the needle litter is rather constant in hemiboreal coniferous forests in the first 3 years. The initial substrate of fine roots or needle litter and soil chemistry jointly had a significant effect on mass loss in the later stage of decomposition. The critical N concentration for N release was lower for pine FR and needle litter (0.9–1.3% and 0.7–1.1%) compared to spruce (1.2–1.6% and 1.5–1.9%, respectively). The release rate of K depended on the initial K of substrate, while the release of N and P was significantly related to the initial C:N and N:P ratios, respectively. The results show the central role of soil and substrate initial chemistry in the decomposition of fine roots and needle litter across hemiboreal forests, especially at later stage (after 2 years) of decomposition. The slower decomposition and higher retention of N in the fine roots relative to needle litter suggests that fine roots have a substantial role in the carbon and nitrogen accumulation in boreal and hemiboreal forest ecosystems.
The main aim of the current study was to estimate the annual net nitrogen mineralization (NNM) flux in stands of different tree species growing on drained peatlands, as well as to clarify the effect of tree species, soil properties and litter on annual NNM dynamics. Three study sites were set up in May 2014: a downy birch (Betula pubescens Ehrh.) stand and a Norway spruce (Picea abies (L.) Karst.) stand in Oxalis full-drained swamp (ODS) and a Scots pine (Pinus sylvestris L.) stand in Myrtillus full-drained swamp (MDS). The NNM flux was estimated using the in situ method with incubated polyethylene bags. The highest value of NNM was found in stands that were growing on fertile ODS: 127.5 kg N ha-1 yr-1 and 87.7 kg N ha-1 yr-1 , in the downy birch stand and in the Norway spruce stand, respectively. A significantly lower annual NNM flux (11.8 kg N ha-1 yr-1) occurred in the Scots pine stand growing in MDS. Nitrification was highest at fertile ODS sites and ammonification was the highest at the low fertility MDS site. For all study sites, positive correlation was found between soil temperature and NNM intensity. The difference in annual NNM between the downy birch stand and the Norway spruce stand growing on similar drained fertile peatlands was due to litter quality. The annual N input into the soil through leaf litter was the highest at the downy birch site where also the C/N ratio of litter was the lowest. The second highest N input into the soil was found in the spruce stand and the lowest in the pine stand.
AimsUnderstanding the linkage of soil respiration (Rs) with forest development is essential for long-term C cycle models. We estimated the variation and temperature sensitivity (Q10 value) of Rs and its hetero-, (Rh) and autotrophic (Ra) components in relation to abiotic and biotic factors in Norway spruce stands of different ages, and the effect of trenching on microbial and soil characteristics. Methods
Trenching method was used to partition Rs into Rh and Ra. Ingrowth core method was used to estimate fine root production. Soil microbial biomass was measured using manometric respirometers. ResultsRs varied in differently aged stands demonstrating non-linear response to development stage. The variation of Rs was explained by changes in biotic factors rather than by changes in soil microclimate. Rh was more sensitive to Ts than Rs or Ra. After 4 years of trenching soil pH, N, SOM and dehydrogenase activity were significantly changed in trenched plots compared to control plots. Conclusions
Different Q10 values of Rh and Ra in stands of different ages indicate the importance of Rs partitioning. Trenching should be used during a limited number of years because of the possible changes in chemical characteristics of soil and in the activity of soil microbial community.
The temperate forests of North America may play an important role in future carbon (C) sequestration strategies. New multi-year ecosystem-scale C cycling studies are providing a process-level understanding of the factors controlling annual forest C storage. Using a combination of ecological and meteorological methods, we quantified the response of annual C storage to historically widespread disturbances, forest succession, and climate variation in a common forest type of the upper Great Lakes region. At our study site in Michigan, repeated clear-cut harvesting and fire disturbance resulted in a lasting decrease in annual forest C storage. However, climate variation exerts a strong control on C storage as well, and future climate change may substantially reduce annual C storage by these forests. Annual C storage varies through ecological succession by rising to a maximum and then slowly declining in old-growth stands. Effective forest C sequestration requires the management of all C pools, including traditionally managed pools such as bole wood and also harvest residues and soils.
Litterfall is a key parameter in the biogeochemical cycle linking the tree part to the water and soil
part. Both the biomass of the litter and its chemical content (including heavy metals) are needed
to quantify the annual return of elements and organic matter to the soil. Litter decomposition is a
major pathway of nutrient fluxes and determines the organic matter input to forest soils and has a
strong influence on forest productivity and soil nutrient status.
Effects of anthropogenic and natural factors, such as climate change, could influence both
litterfall production and its seasonal progression. Processes like carbon cycling and carbon
sequestration are closely related to stand leaf area index (LAI) and litterfall.
Changes in litterfall are responses to disturbances caused by biotic factors such as insect pests
and/or environmental factors like spring frost, drought, wind, or pollution. Litterfall production is
a quantitative parameter of stand vitality and gives additional information to the visual
assessment of canopy condition already observed in each plot. Direct observation of
abnormalities of the leaves can be performed on the collected litter (leaf size, fungi, and necrosis)
for symptomatology.
Litterfall can also provide temporal and quantitative information about phenological
development of the stand. The quantification of the foliage amount, flowering and fruiting
patterns allows direct measurements of year-to-year variation in phenology as a reaction to short
term weather patterns, long term climate, and tree vitality.
Litterfall area of leaves is also one of the components of direct estimate of LAI, the stand leaf area
per ground area expressed in m2 m-2. LAI describes a fundamental property of the plant canopy in
its interaction with the atmosphere, especially radiation, energy, momentum and gas exchange
(Monteith and Unsworth, 1990). LAI plays a key role in the interception of radiation, canopy
interception (rainfall and deposition), in the carbon assimilation and water evapotranspiration
during the diurnal and seasonal cycles, and in the pathways and rates of biogeochemical cycling
within the canopy-soil system (Bonan, 1995; Van Cleve et al., 1983, Vesterdal et al.,2008 ). Finally,
various soil-vegetation-atmosphere models use LAI (Sellers et al., 1986; and Bonan, 1993). For
evergreen species the annual litter represents the turn-over of needle/leaf area. For deciduous
species, litterfall collection throughout one year and sorting among species is probably the most
accurate way of measuring total LAI, and of calculating the contribution of each species to the
total (e.g. Breda, 2003). This measure can be used as an alternative to mid season instrument
based methods of LAI estimation within the plot (e. Thimonier et al., 2009), or as an annual
addition to a base line obtained by selected destructive harvesting of trees around the plot. LAI
for one species is not simply related to its density or basal area contribution to the stand and
cannot be derived from dendrometrical stand information alone.
The replacement of native forests by tree plantations is increasingly common globally, especially in tropical and subtropical areas. Improving our understanding of the long-term effects of this replacement on soil organic carbon (SOC) remains paramount for effectively managing ecosystems to mitigate anthropogenic carbon emissions. Meta-analyses imply that native forest replacement usually reduces SOC stocks and may switch the forest from a net sink to a net source of atmospheric carbon. Using a long-term chronosequence during which areas of subtropical native forest were replaced by Chinese fir, we show by direct measurement that plantations have significantly accelerated SOC turnover compared with native forest, an effect that has persisted for almost a century. The immediate stimulation of SOC decomposition was caused by warmer soil before the closure of the plantation’s canopy. Long-term reductions in SOC mean residence times were coupled to litter inputs. Faster SOC decomposition was associated with lower soil microbial carbon use efficiency, which was due to smaller litter inputs and reduced nutrient availabilities. Our results indicate a previously unelucidated control on long-term SOC dynamics in native forests and demonstrate a potential constraint on climate mitigation when such forests are replaced by plantations.
This chapter emphasizes the functional roles of microorganisms rather than their taxonomy. The concepts of White-rot, brown-rot, and soft-rot and what they functionally stand for in terms of degradation processes have been presented. These functional concepts have been used as a basis to discuss the degradation of litter tissues. Although the terms originally referred to visually different types of lignin degradation, it now appears that the degradation of not only lignin but also cellulose and hemicellulose is different among the taxonomic groups of microorganisms. The terms relate to the type of rot rather than to the group of organisms—namely, rots giving the wood a white or brown color. The common use of the terms has been adopted and refers to fungi when using the terms white-rot, brown-rot, and soft-rot. As the focuses have been on boreal and temperate systems, with an evident dominance of microorganisms in the decomposition process, special attention have been given to microbial communities and the enzymatic degradation mechanisms for the polymer carbohydrates and lignin. The chapter thus presents basic properties of microorganisms.
Leaf litterfall represents an important nutrient flux in forests, but separating leaves by species and collecting fresh litter annually for nutrient analysis is time-consuming and expensive. To quantify the sources of variation in litterfall nutrient estimates and guide optimal allocation of research effort, we analyzed nutrient concentration (5 years) and mass (6 years) of leaf litter for nine tree species in 13 northern hardwood sites. Coefficients of variation (CVs) in nutrient concentration were higher across sites than over time within sites for most elements; phosphorus was especially variable across sites (56% CV). Thus, to estimate litterfall nutrient fluxes accurately in forests of this type, nutrient analyses should be site-specific as well as species-specific but may not need to be repeated annually (CVs over time averaged 17% for calcium, 21% for magnesium, 28% for potassium, and 32% for phosphorus concentration). Total leaf litterfall mass varied considerably from year to year, ranging from 234 to 370 g·m–2 averaged over 13 sites. We recommend that litter collectors be elevated above the ground to avoid oversampling during extreme wind events. Use of species-specific allometric equations, or even basal area, to estimate the species composition of total litter mass may obviate the need to sort litter by species.
Litter fall data was available for 64 sites in Europe, most of them in Fennoscandia. Included were 48 sites with pine (Pinus spp.), mainly Scots pine (Pinus sylvestris L.), and 16 sites with spruce (Picea spp.), mainly Norway spruce (Picea abies (L.) Karst.). Regressions were calculated for needle and total litter fall against a set of climatic parameters, and the best simple relationships were obtained with annual actual evapotranspiration (AET) and other parameters including temperature, whereas for example, precipitation gave lower r values. For needle litter fall and AET using all data, the R2adj value was 0.635 (n = 64), and for needle litter for pine and spruce separately, the R2adj were 0.576 (n = 48) and 0.775 (n = 16), respectively. AET plus stand age gave highly significant relationships for both coniferous genera combined (R2adj = 0.683), and for pine and spruce separately the corresponding values were 0.655 and 0.843, respectively. Using all available data we found highly significant relationships between needle litter fall and total litter fall. For Fennoscandia, litter fall for Scots pine and Norway spruce were compared. AET versus needle litter fall gave highly significant relationships for Scots pine (R2adj = 0.448, n = 34) and for Norway spruce (R2adj = 0.678, n = 13); the relationships were significantly different from each other.
a b s t r a c t During recent decades, studies of the carbon (C) balance of forest ecosystems have became more actual, mainly in connection with the global increase of CO 2 in the atmosphere. In the present study the stand chronosequence approach was applied to analyse C sequestration dynamics. Study was made of C accu-mulation both in biomass and in the soil in 6–60-year-old silver birch (Betula pendula) stands growing at fertile (Oxalis) sites. As the growth of the studied stands was vigorous, their yield was higher than that presented in several yield tables for earlier periods. The C concentration (C%) in different compartments of the trees varied between 47% and 55%. However, the weighted average of C concentration in the silver birch trees was approximately 50% regardless of stand age. The average C concentration of the herbaceous understorey plants was 43.3 ± 0.5%. The soil C org pool was independent of stand age, and so far there occurred no C accumulation during stand succession, expressed as C org values or stage of forest floor formation. This might indicate fast C org turnover in the soils of the Oxalis site. The total C pool in a mature silver birch stand was 185 t ha À1 of which 50% was accumulated in the aboveground part of the trees. In young birch stands the C pool in aboveground biomass and in the soil accounted for 21–39% and 53–71%, respectively, of the total C pool of a stand. In pre-mature and mature stands the corresponding share accounted for 50–59% of the above-ground C of the trees and 29–38% of the soil C pool. Due to closed canopies, the role of herbaceous under-storey plants as a C sink was modest, constituting 1% or even less of the total C pool of the older stands. The annual C flux 1.6 t ha À1 yr À1 into the soil via litter fall was the largest in the middle-age stand. Our results show that the main C sink in fertile silver birch stands is located in the wooden parts of trees. The C pool in tree biomass increased with stand age, whereas the soil C org pool remained stable. For a more profound understanding of C cycling in silver birch forest, soil respiration fluxes should be measured.
We examined patterns of N and P uptake and release from a wide variety of litter types, including leaves, needles, moss, roots, and wood, for 4 years in three forests (lodgepole pine (Pinuscontorta Loud.), white spruce (Piceaglauca (Moench) Voss)–lodgepole pine, and Engelmann spruce (Piceaengelmannii Parry ex Engelm.)–subalpine fir (Abieslasiocarpa (Hook.) Nutt.)) and a small clearcut, in the Rocky Mountains of Alberta. Decomposition was more rapid and N release began sooner in the clearcut than in the forests, but N release began at the same stage of decomposition at all sites. In most litter types, a period of net immobilization of N was followed by a period of net release; only litter types particularly rich in N had an initial leaching phase. Each litter type initially gained or lost N depending on its original concentration, such that N contents converged after 1 or 2 years. The N content at convergence differed among litter types. Phosphorus was usually released immediately. The rate of P loss also varied according to the initial P concentration, and the P contents of all litter types converged within 1 year. The availability of N and P in the forest floor did not affect the rate of N and P release from a standard substrate placed at all sites. The concentrations of N and P in the litter influenced the rate of uptake of N or P during the first 1–3 years, but was not consistently related to nutrient availability in the forest floors at the four sites.
The aim of this study was to identify the most significant site, stand and climate factors affecting needle (LFneedle) and total (LFtotal) above-ground litterfall production and to develop multiple linear regression (MLR) models that can be used to reliably predict litterfall production in the boreal zone using readily available variables. Unlike most other litterfall production studies, we use climate data for the actual sites and annual litterfall values. A data set including 34 Scots pine stands located throughout Finland was compiled. The data for some stands covered a period of more than 30 years. The age of the stands ranged from 35 to >200 years and all were growing on upland, mineral soil sites. Stand mean annual LFneedle ranged from 22 g m−2 (northern Finland) to 157 g m−2 (southern Finland); corresponding values for LFtotal were 32 and 230 g m−2. Annual LFneedle production accounted between 49 and 75% of stand LFtotal production and explained 88% of the variation in LFtotal over all stands. There was considerable annual variation in litterfall production also within the same stand. The coefficient of variation in LFneedle in each stand ranged from 4 to 58% (mean = 19%) and from 3 to 39% (mean = 22%) for LFtotal. Both LFneedle and LFtotal were highly significantly (p < 0.01) and strongly correlated (Spearman) with latitude, stand basal area, effective temperature sum (ETS) of the current year and even higher with that of the previous year, and the previous years’ July temperature. LFneedle had a weak negative, although significant (p < 0.05) correlation with stand age, but age was not significant for LFtotal. MLR models using latitude and stand basal area (also dominant tree height in the case of LFneedle) as predictive variables accounted for 82% of the variance in both LFneedle and LFtotal. The standard error of the estimate (SEest) was 12.6 g m−2 for LFneedle and 23.3 g m−2 for LFtotal. Latitude effectively described the climate at each stand but ignored the considerable within-stand variation in annual litterfall production. Using the annual values for the climate variables instead of latitude, 70% or more of the variation in both LFneedle and LFtotal in MLR models could be explained. The models are useful tools for predicting annual litterfall in mature Scots pine stands for use in soil organic and carbon models.
Key recent developments in litter decomposition research are reviewed. Long-term inter-site experiments indicate that temperature
and moisture influence early rates of litter decomposition primarily by determining the plants present, suggesting that climate
change effects will be small unless they alter the plant forms present. Thresholds may exist at which single factors control
decay rate. Litter decomposes faster where the litter type naturally occurs. Elevated CO2 concentrations have little effect on litter decomposition rates. Plant tissues are not decay-resistant; it is microbial and
biochemical transformations of materials into novel recalcitrant compounds rather than selective preservation of recalcitrant
compounds that creates stable organic matter. Altering single characteristics of litter will not substantially alter decomposition
rates. Nitrogen addition frequently leads to greater stabilization into humus through a combination of chemical reactions
and enzyme inhibition. To sequester more C in soil, we need to consider not how to slow decomposition, but rather how to divert
more litter into humus through microbial and chemical reactions rather than allowing it to decompose. The optimal strategy
is to have litter transformed into humic substances and then chemically or physically protected in mineral soil. Adding N
through fertilization and N-fixing plants is a feasible means of stimulating humification.
KeywordsLitter decomposition-Humus-Soil organic matter-Forest management-Litter chemistry-Litter quality-Carbon sequestration-Threshold analysis-Plant functional trait analysis-Humification-Nitrogen fertilization-Tree species effects
This paper presents an integrated analysis of organic carbon (C) pools in soils and vegetation, within-ecosystem fluxes and
net ecosystem exchange (NEE) in three 40-year old Norway spruce stands along a north-south climatic gradient in Sweden, measured
2001–2004. A process-orientated ecosystem model (CoupModel), previously parameterised on a regional dataset, was used for
the analysis. Pools of soil organic carbon (SOC) and tree growth rates were highest at the southernmost site (1.6 and 2.0-fold,
respectively). Tree litter production (litterfall and root litter) was also highest in the south, with about half coming from
fine roots (<1mm) at all sites. However, when the litter input from the forest floor vegetation was included, the difference
in total litter input rate between the sites almost disappeared (190–233gCm−2year−1). We propose that a higher N deposition and N availability in the south result in a slower turnover of soil organic matter
than in the north. This effect seems to overshadow the effect of temperature. At the southern site, 19% of the total litter
input to the O horizon was leached to the mineral soil as dissolved organic carbon, while at the two northern sites the corresponding
figure was approx. 9%. The CoupModel accurately described general C cycling behaviour in these ecosystems, reproducing the
differences between north and south. The simulated changes in SOC pools during the measurement period were small, ranging
from −8gCm−2year−1 in the north to +9gCm−2year−1 in the south. In contrast, NEE and tree growth measurements at the northernmost site suggest that the soil lost about 90gCm−2year−1.
Using China’s ground observations, e.g., forest inventory, grassland resource, agricultural statistics, climate, and satellite
data, we estimate terrestrial vegetation carbon sinks for China’s major biomes between 1981 and 2000. The main results are
in the following: (1) Forest area and forest biomass carbon (C) stock increased from 116.5×106 ha and 4.3 Pg C (1 Pg C = 1015 g C) in the early 1980s to 142.8×106 ha and 5.9 Pg C in the early 2000s, respectively. Forest biomass carbon density increased form 36.9 Mg C/ha (1 Mg C = 106 g C) to 41.0 Mg C/ha, with an annual carbon sequestration rate of 0.075 Pg C/a. Grassland, shrub, and crop biomass sequestrate
carbon at annual rates of 0.007 Pg C/a, 0.014–0.024 Pg C/a, and 0.0125–0.0143 Pg C/a, respectively. (2) The total terrestrial
vegetation C sink in China is in a range of 0.096–0.106 Pg C/a between 1981 and 2000, accounting for 14.6%–16.1% of carbon
dioxide (CO2) emitted by China’s industry in the same period. In addition, soil carbon sink is estimated at 0.04–0.07 Pg C/a. Accordingly,
carbon sequestration by China’s terrestrial ecosystems (vegetation and soil) offsets 20.8%–26.8% of its industrial CO2 emission for the study period. (3) Considerable uncertainties exist in the present study, especially in the estimation of
soil carbon sinks, and need further intensive investigation in the future.
There is general agreement that terrestrial systems in the Northern Hemisphere provide a significant sink for atmospheric CO2; however, estimates of the magnitude and distribution of this sink vary greatly. National forest inventories provide strong, measuretment-based constraints on the magnitude of net forest carbon uptake. We brought together forest sector C budgets for Canada, the United States, Europe, Russia, and China that were derived from forest inventory information, allometric relationships, and supplementary data sets and models. Together, these suggest that northern forests and woodlands provided a total sink for 0.6-0.7 Pg of C per year (1 Pg = 10(15) g) during the early 1990s, consisting of 0.21 Pg C/yr in living biomass, 0.08 Pg C/yrin forest products, 0.15 Pg C/yr in dead wood, and 0.13 Pg C/yr in the forest floor and soil organic matter. Estimates of changes in soil C pools have improved but remain the least certain terms of the budgets. Over 80% of the estimated sink occurred in one-third of the forest area, in temperate regions affected by fire suppression, agricultural abandonment, and plantation forestry. Growth in boreal regions was offset by fire and other disturbances that vary considerably from year to year. Comparison with atmospheric inversions suggests significant land C sinks may occur outside the forest sector.
The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory
data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg
C year–1) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year–1 from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year–1 partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year–1. Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year–1, with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the
terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.
Carbon exchange between the terrestrial biosphere and the atmosphere is one of the key processes that need to be assessed in the context of the Kyoto Protocol. Several studies suggest that the terrestrial biosphere is gaining carbon, but these estimates are obtained primarily by indirect methods, and the factors that control terrestrial carbon exchange, its magnitude and primary locations, are under debate. Here we present data of net ecosystem carbon exchange, collected between 1996 and 1998 from 15 European forests, which confirm that many European forest ecosystems act as carbon sinks. The annual carbon balances range from an uptake of 6.6 tonnes of carbon per hectare per year to a release of nearly 1 t C ha(-1) yr(-1), with a large variability between forests. The data show a significant increase of carbon uptake with decreasing latitude, whereas the gross primary production seems to be largely independent of latitude. Our observations indicate that, in general, ecosystem respiration determines net ecosystem carbon exchange. Also, for an accurate assessment of the carbon balance in a particular forest ecosystem, remote sensing of the normalized difference vegetation index or estimates based on forest inventories may not be sufficient.
To evaluate the impact of stand age on the ecosystem's C budget, as well as the post-harvest recovery of the C storages and fluxes, a chronosequence of Scots pine stands from the clear-cut stage up to the age of 110 years was studied. An age-related trend of net primary production (NPP) demonstrated effective C accumulation in the young and middle-aged stands and their levelling out thereafter.
The understorey vegetation contributed 8–46% to total NPP, being lower in the pole and middle-aged stands, but without a clear age related trend. Annual cumulative soil heterotrophic respiration (Rh) demonstrated stable values along the chronosequence, varying between 3.8 and 5.4 t C ha⁻¹ yr⁻¹. The Rh flux of 2.9 t C ha⁻¹ yr⁻¹ at the clear–cut site did not exceed the corresponding value for stands. The NEP along the chronosequence followed the dynamics of the annual biomass production of the trees, peaking at the middle-aged stage and decreasing in the older stands; the NPP of the trees was the main driver directing the dynamics of NEP.
There was no significant correlation between Rh and dynamics of aboveground litter or fine root production, which can partly explain why no relationship was established between annual Rh and stand age.
The total ecosystem C stocks followed the same trend as cumulative tree biomass, peaking in the older stands, however, the soil C stocks varied along the chronosequence irrespective of stand age.
The post-harvest C compensation point was reached at the age of 7-years and C payback occurred at a stand age of 11–12 years. Stands acted as C accumulating ecosystems and average annual C accumulation was around 2.5 t C ha⁻¹ yr⁻¹, except for the youngest stand and the clear-cut area which acted as C sources. In the oldest stand C budget was almost balanced, with a modest annual accumulation of 0.12 t C ha⁻¹ yr⁻¹.
Thinning is the main silvicultural method for improving stand growth and wood quality, however, despite the relevance and extensive use of thinning in forest management, its effect on stand carbon (C) balance is still poorly studied at the ecosystem level. The present case study estimated the two-year post-thinning effect on the C balance of a pole stand and a middle-aged Scots pine stand growing on mesotrophic sandy soils. Moderate thinning from below reduced the stand C storage by 21–24%, however, the amount of C accumulated in woody biomass, which was removed by logging, is expected to recover in both stands in the following four years. The reduced biomass of the trees contributed to the decreased annual net primary production (NPP) of the stand by 9–11%. The absolute value of net ecosystem production decreased by 0.9 and 0.7 t C ha⁻¹ yr⁻¹ in the pole and the middle-aged stand, respectively; still, both thinned plots maintained their C sink status. The production of the herbaceous understorey as well as the production of needles increased in the younger stand after thinning, but this could not compensate for C loss at the stand level. The effect of thinning on the production of mosses and dwarf shrubs was not expressed in either stand, probably due to the too short post-thinning period. Thinning did not significantly affect either total soil respiration or the heterotrophic respiration (Rh). However, it increased the contribution of Rh to total soil respiration, which can be attributed to decreased fine root biomass and root respiration, while the aboveground litterfall was not significantly changed after thinning. Fine root production, which accounted for the main belowground litter input, was significantly lower in both thinned plots. Moderate thinning in the pole and the middle-aged Scots pine stand did not change the ecosystem into a C source and the induced C loss will be compensated during a short post-thinning period.
Although thinning is a widely used silvicultural method, its effect on stand carbon (C) cycling is still poorly studied at the ecosystem level. The present case study estimated the two-year post-thinning effect on the C balance of a pole and a middle-aged silver birch stand. The results demonstrate the multifaceted impact of thinning on the different C fluxes of deciduous forest ecosystems.
The effect of thinning on the C budget of the studied stands was modest: net ecosystem production (NEP) decreased by 1.2 and 1.6 t C ha⁻¹ yr⁻¹ in the pole and the middle- aged stand, respectively; still, both stands remained C sinks. Lower annual production in the thinned stands as a result of the decreased standing biomass of the trees was the main factor for reduced C sequestration capacity. Thinning increased the C accumulation of the herbaceous plants in both stands, however, it did not compensate for the lower C accumulation by the trees. In general, thinning did not affect significantly the soil respiration fluxes; the small post-thinning increase of the annual soil heterotrophic flux, 0.33–0.68 t C ha ⁻¹, was most probably related to elevated soil temperature during the active growing season. The annual aboveground litter flux, i.e. the labile C source of Rh, was not significantly changed by thinning. Fine root production and the belowground C input to the soil remained at the same level in the pole stand and decreased slightly in the middle-aged stand. We conclude that the high production ability and fast C accumulation recovery of silver birch stands growing on fertile soils leads to a balanced C budget already during the short post-thinning period.
Estimation of soil-related carbon (C) fluxes is needed to understand the dynamics of the soil organic carbon pool, to determine changes in the carbon balance and functioning of forest ecosystems, and to support climate change policies.
The objective of the study was to analyse the variation in the most dynamic soil C input (tree and understory above- and belowground litter production) and output (soil respiration) fluxes, in addition to the forest floor, understory and fine root biomass stocks, in eight different Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) sites growing on mineral soils in Estonia. Further, the impact of soil C input and output fluxes on the soil organic carbon (SOC) pool was examined, and the net ecosystem production (NEP) of the stands was estimated.
Fine root production (FRP) of the trees constituted 53% and 28% and needle litter constituted 25% and 28% of the total annual C input to the soil in the Norway spruce and Scots pine stands, respectively. The total FRP of the trees and the understory roots and rhizomes ranged from 211 to 1040 g m−2 yr−1, of which the understory comprised up to 28%. The mean annual soil respiration (Rs) rate was 5.7 ± 0.3 and 6.5 ± 0.3 Mg C ha−1 yr−1 in the pine and spruce stands, respectively, and did not differ significantly between the two groups of stands. The SOC pool of the studied stands depended significantly on both the above- and belowground C input fluxes. Tree-derived litter had the strongest effect on the SOC pool, while the Rh as the main soil C output flux showed no significant impact. The NEP ranged from 4.2 to −1.8 Mg C ha−1 yr−1 and demonstrated a strong negative correlation with stand age. The results affirm the importance of belowground as well as aboveground litter production on carbon accumulation in forest soils.
Litterfall is a major, yet poorly studied, process within forest ecosystems globally. It is important for carbon dynamics, edaphic communities, and maintaining site fertility. Reliable information on the carbon and nutrient input from litterfall, provided by litter traps, is relevant to a wide audience including policy makers and soil scientists. We used litterfall observations of 320 plots from the pan-European forest monitoring network of the "International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests" to quantify litterfall fluxes. Eight litterfall models were evaluated (four using climate information and four using biomass abundance). We scaled up our results to the total European forest area and quantified the contribution of litterfall to the forest carbon cycle using net primary production aggregated by bioregions (north, central, and south) and by forest types (conifers and broadleaves). The 1,604 analyzed annual litterfall observations indicated an average carbon input of 224 g C · m⁻² · year⁻¹ (annual nutrient inputs 4.49 g N, 0.32 g P, and 1.05 g K · m⁻²), representing a substantial percentage of net primary production from 36% in north Europe to 32% in central Europe. The annual turnover of carbon and nutrient in broadleaf canopies was larger than for conifers. The evaluated models provide large-scale litterfall predictions with a bias less than 10%. Each year litterfall in European forests transfers 351 Tg C, 8.2 Tg N, 0.6 Tg P, and 1.9 Tg K to the forest floor. The performance of litterfall models may be improved by including foliage biomass and proxies for forest management.
Estimation of the carbon (C) storages and fluxes in different forest ecosystems is essential for understanding their C sequestration ability. The net ecosystem production (NEP) and the net primary production (NPP) in five downy birch (Betula pubescens) stands, aged between 12 and 78 years, growing on fertile well-drained Histosols, were studied. Drainage of swamp forests is a large-scale manipulation, which causes significant shifts at the ecosystems level, altering C and nutrient cycling a great deal. Young and middle-aged downy birch stands (12–30-year-old) acted as C sink ecosystems, accumulating 1.4–3.0 t C ha⁻¹ yr⁻¹. In the 38-year-old stand NEP was roughly zero; annual C budget was almost in balance. The over-matured downy birch stand (78-year-old) acted as a C source emitting 0.95 t C ha⁻¹ yr⁻¹. Annual woody biomass increment of the stand was the main factor which affected the forest to act as a C accumulating system. Although the highest heterotrophic respiration (Rh) values were measured in the middle-aged stands, mean soil C emission did not differ significantly between the studied stands. Annual total soil respiration (Rs) and Rh ranged from 7.4 to 8.8 t C ha⁻¹ and 4.7 to 6.2 t C ha⁻¹, respectively. Soil temperature appeared to be the dominant driver of the soil CO2 effluxes. Temperature sensitivity (Q10 value) of respiration rates (3.0–5.5), as well as the Rh/Rs (0.6–0.7) varied irrespective of stand age. Both the annual aboveground litter (1.5–1.9 t C ha⁻¹ yr⁻¹) and fine root litter (0.9–1.5 t C ha⁻¹ yr⁻¹) input fluxes were quite similar for the studied stands. However, the annual organic C input into the soil via above- and belowground litter was smaller than the annual Rh efflux, indicating that continuous mineralization of the peat layer reduces the soil organic C pool. The main share of the C stock in the drained swamp downy birch stands was soil C; the storage of C accumulated in the woody biomass of the trees accounted for only 5–20% of the total C storage of the ecosystem.
There is much scientific and political interest in using the transfer of carbon from the atmosphere to the biosphere, or carbon sequestration, to help mitigate the greenhouse effect ( 1 ). Because plants fix carbon dioxide (CO2) by photosynthesis and store carbon in their body (close to half of plant dry matter is carbon), faster carbon uptake by plants through faster growth is widely held to increase carbon sequestration. Yet, this assumption is supported by neither theory nor evidence. Any gain in carbon storage from faster tree growth will be transitory.
Analyses of a time-series of needlefall data showed enhanced needlefall due to unusually warm and dry weather in southeastern Norway during 1986–2000. Needlefall was sampled routinely in ten stands of older Picea abies as part of long-term forest monitoring. Mixed linear models were developed for brown and green needlefall separately. Both the brown and the green needlefall had clear seasonal variations, peaking in October and May, respectively. In addition, the needlefall was correlated with weather conditions. Unusually dry summers were followed by increased brown needlefall in the autumns and winters, and unusually high temperatures were accompanied by increased amounts of green needlefall, in particular in the winter. Using the models, we found that unusually warm and dry weather during these 15 years likely caused an overall surplus of needlefall. Even though the brown needlefall was the dominant fraction of the needlefall, the surplus of green needlefall was of larger magnitude. The results suggest that unusually warm winters and dry summers were the main cause of increased crown defoliation during these years.
Patterns of N, P and Ca cycling through litterfall were evaluated using published information from 62 tropical forests. In general, lowland tropical forests have more N and lower dry mass/N ratios in litterfall than most temperate forests, while N return in montane tropical forests is comparable to that in temperate forests. Calcium return is also high in most tropical forests, but many tropical forests (lowland and montane) have little P return and very high dry mass/P ratios in litterfall compared to most temperate forests. Phosphorus appears to be cycled highly efficiently in such forests. Fine litterfall in the range of tropical forests studied was predicted from climate; the residuals of this regression were positively correlated with P but not N concentrations in litterfall. Amount of fine litterfall (uncorrected for climate) was also significantly correlated with P concentrations in moist and wet lowland tropical forests. Analyses suggest that P but not N availability limits litterfall in a substantial subset of intact tropical forests. Sites on old oxisols and ultisols, especially those in Amazonia, appear to be particularly low in available P.-from Author
Since the publication of the 2nd edition, there have been substantial developments in the field of litter decomposition. This fully revised and updated 3rd edition of Plant Litter reflects and discusses new findings and re-evaluates earlier ones in light of recent research and with regard to current areas of investigation. The availability of several long-term studies allows a more in-depth approach to decomposition patterns and to the later stages of decomposition, as well as to humus formation and accumulation. The latest information focuses on three fields: - the effects of manganese on decomposition and possibly on carbon sequestration, - new findings on decomposition dynamics, and - the new analytical technique using 13C-NMR. © 2014 Springer-Verlag Berlin Heidelberg. All rights are reserved.
[1] Chemical weathering is an integral part of both the rock and carbon cycles and is being affected by changes in land use, particularly as a result of agricultural practices such as tilling, mineral fertilization, or liming to adjust soil pH. These human activities have already altered the terrestrial chemical cycles and land-ocean flux of major elements, although the extent remains difficult to quantify. When deployed on a grand scale, Enhanced Weathering (a form of mineral fertilization), the application of finely ground minerals over the land surface, could be used to remove CO2 from the atmosphere. The release of cations during the dissolution of such silicate minerals would convert dissolved CO2 to bicarbonate, increasing the alkalinity and pH of natural waters. Some products of mineral dissolution would precipitate in soils or be taken up by ecosystems, but a significant portion would be transported to the coastal zone and the open ocean, where the increase in alkalinity would partially counteract “ocean acidification” associated with the current marked increase in atmospheric CO2. Other elements released during this mineral dissolution, like Si, P, or K, could stimulate biological productivity, further helping to remove CO2 from the atmosphere. On land, the terrestrial carbon pool would likely increase in response to Enhanced Weathering in areas where ecosystem growth rates are currently limited by one of the nutrients that would be released during mineral dissolution. In the ocean, the biological carbon pumps (which export organic matter and CaCO3 to the deep ocean) may be altered by the resulting influx of nutrients and alkalinity to the ocean. This review merges current interdisciplinary knowledge about Enhanced Weathering, the processes involved, and the applicability as well as some of the consequences and risks of applying the method.
A 10-year-old stand of loblolly pine (Pinus taeda L.) was thinned to three residual basal area levels: 7.8 m2 ha−1, 12.6 m2 ha−1, and 26.6 m2 ha−1 (unthinned). Monthly temperature, rainfall and needle fall were determined for 5 consecutive years following thinning. The amount of needle fall produced each year was positively related to the amount of basal area on the plot. However, at a given basal area a wide range of needle-fall biomass was observed over the 5 year period. Much of the variation in needle-fall patterns appeared to be correlated with the droughtiness of the growing season. In loblolly pine stands needle fall represents the death of the total needle population formed in the previous year. The amount of needle fall that occurred in a given year varied with the rainfall and temperature conditions that existed in the year the foliage was formed. Average annual needle fall varied by more than 29% from year to year for the unthinned control plots. Maximum monthly needle fall occurred 2 months earlier in dry years than in wet years. These results indicate that accurate predictions of the amount of canopy needle biomass must account for both the effects of the previous year's climate on needle production and the effect of the current year's climate on needle duration. Currently, mechanistic models being used to predict annual net carbon gain, stand productivity or annual evapotranspiration do not adequately consider the interactive effects of climate and stand density on needle biomass dynamics.
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 ON 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 ON 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.
Current annual needle litterfall was analysed in 16 Scots pine stands of different ages, site qualities and latitudes. As a mean, the current needle litterfall was 1605 kg (dw) per ha and year, corresponding to a current annual volume increase of 7.9 m(3). It was shown that the needle litterfall 1) increased with increasing site quality, 2) decreased with increasing stand age, and 3) decreased with increasing latitude. An increase in the number of living age classes of needles in the tree crowns with increasing latitude was observed. This should be considered if total needle biomass in the crowns is to be estimated from litterfall. A method is proposed for calculating current annual needle litterfall in Pinus sylvestris stands of any age, site quality or latitude in Sweden.
Summary 1 Biological carbon sinks develop in mature ecosystems that have high carbon storage when these systems are stimulated to increase productivity, so that carbon gains by photosynthesis run ahead of carbon losses by heterotrophic respiration, and the stocks of carbon therefore increase. This stimulation may occur through elevated CO 2 con- centration, nitrogen deposition or by changes in climate. 2 Sinks also occur during the 'building' phase of high carbon ecosystems, for example following establishment of forests by planting. 3 New methods have been developed to identify biological carbon sinks: ground based measurements using eddy covariance coupled with inventory methods, atmospheric methods which rely on repeated measurement of carbon dioxide concentrations in a global network, and mathematical models which simulate the processes of production, storage and decomposition of organic matter. There is broad agreement among the results from these methods: carbon sinks are currently found in tropical, temperate and boreal forests as well as the ocean. 4 However, on a global scale the effect of the terrestrial sinks (absorbing 2-3 billion tonnes of carbon per year) is largely offset by deforestation in the tropics (losing 1-2 bil- lion tonnes of carbon per year). 5 The Kyoto Protocol provides incentives for the establishment of sinks. Unfortunately, it does not provide an incentive to protect existing mature ecosystems which constitute both stocks of carbon and (currently) carbon sinks. 6 Incentives would be enhanced, if protection and nature conservation were to be part of any international agreement relating to carbon sinks.
Aim The objectives of this study were to determine the relationships between climatic factors and litterfall in coniferous and broadleaf forests in Eurasia and to explore the difference in litterfall between coniferous and broadleaf forests as related to climate at a continental scale.
Location We have used data from across Eurasia.
Methods The relationships between litterfall and climatic factors were examined using linear regression analysis of a compilation of published data from coniferous and broadleaf forests in Eurasia.
Results The relationships between litterfall and climatic factors show that in the temperate, subtropical, and tropical areas, broadleaf forests had higher litterfall than coniferous ones, whilst the opposite was found for boreal forests. Combining all climatic zones, a multiple regression analysis using annual mean temperature (T) and annual precipitation (P) as independent variables gave an adjusted R2 () of 0.272 for total litterfall in coniferous forests (n = 199, P < 0.001), 0.498 for broadleaf litterfall (n = 240, P < 0.001), and 0.535 for combined coniferous and broadleaf litterfall (n = 439, P < 0.001). The linear models for broadleaf stands have significantly higher coefficients for T and P than those for coniferous ones but the intercepts were similar. Thus, litterfall in broadleaf forests increased faster with T and P than that in coniferous forests. Further, a transformation of temperature and precipitation to relative units showed that a relative-unit change in T had a larger impact than P on total litterfall in broadleaf forests. The results indicate that at a continental scale, climatic controls over litterfall differ between coniferous and broadleaf forests.
Conclusions A relative unit change in annual mean temperature has a greater effect on litterfall compared to the same change in annual precipitation across the Eurasian forests. Further, the higher response to T for broadleaf forests indicates a difference in climate control between coniferous and broadleaf forests at a continental scale, and consequently different litterfall responses to climate change.
Models are needed to estimate dynamics of carbon in forest soils, because changes in soil carbon are laborious to measure, and future levels of soil carbon can only be predicted using models.Current process-oriented soil carbon models are not suitable to all forestry-related applications. This is because they require specific input information that is not available for all forests, and their time step is shorter than a year which is typically used in forestry.We developed a dynamic soil carbon model Yasso to be used in forestry applications. Yasso simulates the stock of soil carbon, changes in this stock and the release of carbon from soil on an annual basis. It needs estimates of litter production, information on litter quality and basic data on climate to run.Yasso consists of five decomposition compartments and two woody litter compartments. Its parameter values were determined based on measurements of litter decomposition and soil carbon.The reliability of the output of Yasso was assessed by conducting an uncertainty analysis and comparing model-calculated estimates of soil carbon to measurements taken at different forest sites in southern Finland. According to the uncertainty analysis, the estimates for the amount of soil carbon are uncertain by nature, because they depend mostly on uncertain humus parameters. Still, when linked to a forest simulator to calculate litter production, Yasso gave similar estimates for the amount of soil carbon as were measured. The estimates for changes in soil carbon, on the other hand, are more reliable by nature because they depend on more accurately known parameters.These and other tests conducted so far suggest that Yasso is applicable to forests in a wide range of environments. Further tests will increase confidence in using it for different soils.
The amount and nutrient content of the above-ground litterfall was followed for 9 years in an unfertilized, PKMgB and NPKMgB fertilized Scots pine stand growing on a drained ombrotrophic bog in eastern Finland. The annual litterfall on unfertilized plots was 1995 kg ha−1, of which needles accounted for 74%. The effective temperature sum (threshold value + 5°C) explained 99% of the annual variation in the amount of needle litterfall when the data from one atypical year were excluded from the analysis. Nutrient concentrations were, except for Fe, higher in needle litter than in the other litterfall fractions. Nitrogen, P and K concentrations were low in autumn, and those of Ca and Mn high, possibly owing to variation in the mobility of elements during senescence. The annual litterfall input of N to the soil was 12.4 kg ha−1, and the corresponding values for P and K were 0.08 kg ha−1 and 1.81 kg ha−1, respectively. Fertilization reduced needle litterfall in the first year after treatment, but had no effect thereafter. The amount of other litterfall fractions was not affected by fertilization in any of the 9 years of the study. Nitrogen, P, K and B concentrations increased in the needle litter after both fertilization treatments. The results indicate long-term cycling of fertilizer nutrients on the site.
Litter decomposition is an important process in the global carbon cycle. It accounts for most of the heterotrophic soil respiration and results in formation of more stable soil organic carbon (SOC) which is the largest terrestrial carbon stock. Litter decomposition may induce remarkable feedbacks to climate change because it is a climate-dependent process. To investigate the global patterns of litter decomposition, we developed a description of this process and tested the validity of this description using a large set of foliar litter mass loss measurements (nearly 10 000 data points derived from approximately 70 000 litter bags). We applied the Markov chain Monte Carlo method to estimate uncertainty in the parameter values and results of our model called Yasso07. The model appeared globally applicable. It estimated the effects of litter type (plant species) and climate on mass loss with little systematic error over the first 10 decomposition years, using only initial litter chemistry, air temperature and precipitation as input variables. Illustrative of the global variability in litter mass loss rates, our example calculations showed that a typical conifer litter had 68% of its initial mass still remaining after two decomposition years in tundra while a deciduous litter had only 15% remaining in the tropics. Uncertainty in these estimates, a direct result of the uncertainty of the parameter values of the model, varied according to the distribution of the litter bag data among climate conditions and ranged from 2% in tundra to 4% in the tropics. This reliability was adequate to use the model and distinguish the effects of even small differences in litter quality or climate conditions on litter decomposition as statistically significant. Comment: 19 Pages, to appear in Ecological Modelling
Terrestrial net primary production (NPP) quantifies the amount of atmospheric carbon fixed by plants and accumulated as biomass.
Previous studies have shown that climate constraints were relaxing with increasing temperature and solar radiation, allowing
an upward trend in NPP from 1982 through 1999. The past decade (2000 to 2009) has been the warmest since instrumental measurements
began, which could imply continued increases in NPP; however, our estimates suggest a reduction in the global NPP of 0.55
petagrams of carbon. Large-scale droughts have reduced regional NPP, and a drying trend in the Southern Hemisphere has decreased
NPP in that area, counteracting the increased NPP over the Northern Hemisphere. A continued decline in NPP would not only
weaken the terrestrial carbon sink, but it would also intensify future competition between food demand and proposed biofuel
production.
Forest systems cover more than 4.1 x 109 hectares of the Earth's land area. Globally, forest vegetation and soils contain about 1146 petagrams of carbon, with approximately
37 percent of this carbon in low-latitude forests, 14 percent in mid-latitudes, and 49 percent at high latitudes. Over two-thirds
of the carbon in forest ecosystems is contained in soils and associated peat deposits. In 1990, deforestation in the low latitudes
emitted 1.6 ± 0.4 petagrams of carbon per year, whereas forest area expansion and growth in mid- and high-latitude forest
sequestered 0.7 ± 0.2 petagrams of carbon per year, for a net flux to the atmosphere of 0.9 ± 0.4 petagrams of carbon per
year. Slowing deforestation, combined with an increase in forestation and other management measures to improve forest ecosystem
productivity, could conserve or sequester significant quantities of carbon. Future forest carbon cycling trends attributable
to losses and regrowth associated with global climate and land-use change are uncertain. Model projections and some results
suggest that forests could be carbon sinks or sources in the future.
Amounts of litterfall in some pine forests in the Northern Hemisphere, especially Scots pine
- Berg
Berg, B., Albrektson, A., Berg, M., Cortina, J., Johansson, M.B., Gallardo, A., Madeira, M.,
Kratz, W., Pausas, J., Vallejo, R., McClaugherty, C., 1999. Amounts of litterfall in
some pine forests in the Northern Hemisphere, especially Scots pine. Ann. For. Sci.
56, 625-639. https://doi.org/10.1051/forest:19990801.
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