Non-woody Litter Research Articles

Woody Litter Increases Headwater Stream Metal Export Ratio in an Alpine Forest

Headwater streams have low productivity and are closely linked to forest ecosystems, which input a large amount of plant litter into streams. Most current studies have focused on the decomposition process of plant litter in streams, and the effects of non-woody and woody litter on metal transfer, accumulation, and storage in streams are poorly understood. Here, we addressed how non-woody and woody litter affect metals in headwater streams in an alpine forest on the Eastern Tibetan Plateau. This area is the source of many rivers and plays an important regulatory role in the regional climate and water conservation. Through comparisons of five metal concentrations, exports and storage in headwater streams with different input conditions of plant litter, our results showed that the input of woody litter could significantly increase flow discharge and increase the metal export ratio in the water. Similarly, the input of non-woody litter could reduce the metal concentration in the water and facilitate the stable storage of metals in the sediment in the headwater streams. Therefore, allochthonous non-woody and woody litter can affect the concentration of metals in water and sediment, and the transfer and accumulation of metals from upstream to downstream in headwater streams. This study provides basic data and new findings for understanding the effects of allochthonous plant litter on the accumulation and storage of metals in headwater forest streams and may provide new ideas for assessing and managing water quality in headwater streams in alpine forests.

Methyl bromide and methyl chloride fluxes from temperate forest litter

Methyl halide fluxes were measured from fine (nonwoody) litter samples at a temperate deciduous forest site in Scotland on 16 occasions over more than a year and at a coniferous forest site. The resulting mean (±1 sd) CH 3 Br and CH 3 Cl fluxes were 4.1 ± 3.7 ng kg −1 h −1 and 0.98 ± 0.62 μg kg −1 h −1 , respectively, for dry mass leaf litter and 5.7 ± 6.3 ng kg −1 h −1 and 0.47 ± 0.14 μg kg −1 h −1 for dry mass needle litter. Temporal variations of net fluxes from leaf litter were significantly greater than spatial variations suggesting seasonality in the fluxes. The mean CH 3 Cl/CH 3 Br mass ratio of fluxes was ∼200 (to 1 sig. fig.), an order of magnitude larger than the ratio of their estimated global turnovers. Temperate forest litter may be a moderate net source of CH 3 Cl globally but a negligible source of CH 3 Br. These statements refer to the nonwoody litter component only. ► Methyl halide fluxes were measured from forest non-woody litter samples in Scotland. ► At a single site, temporal variations in fluxes were significantly greater than spatial variations. ► Findings indicate temperate forest litter may be moderate source for CH 3 Cl globally but negligible for CH 3 Br.

Wood decomposition model for boreal forests

Abstract The decomposition of woody litter is a biochemical process, controlled by physical, chemical and biological environmental conditions. To develop a practicable model of this complex process, it is necessary to identify the major controlling factors and quantify their effects. We used four data sets (total N = 2102) on mass loss of decomposing woody litter in Northern Europe to extend an earlier decomposition model of non-woody litter and make it suitable for describing also decomposition of woody litter. We compared alternative ways to model the effects of size and chemical composition of woody litter on decomposition using the Bayesian model selection theory. The best model fitted to the diverse data sets (woody litter of four tree species, diameter 0.5–60 cm, time series up to 70 years) with little systematic error. Based on this result, we concluded that the extended model is suitable for describing decomposition of woody litter of the common tree species in the boreal forests studied. According to the model developed, frequently observed sigmoidal patterns in mass loss of woody litter are related to high concentrations of slowly decomposing lignin compounds and these patterns become stronger with an increasing size of decomposing woody litter.

Changes in net ecosystem productivity with forest age following clearcutting of a coastal Douglas-fir forest: testing a mathematical model with eddy covariance measurements along a forest chronosequence

We hypothesized that changes in net ecosystem productivity (NEP) during aging of coastal Douglas-fir (Pseudotsuga menziesii Mirb. Franco) stands could be explained by (1) changing nutrient uptake caused by different time scales for decomposition of fine, non-woody and coarse woody litter left after harvesting, (2) declines in canopy water status with lengthening of the water uptake pathway during bole and branch growth, and (3) increases in the ratio of autotrophic respiration (R (a)) to gross primary productivity (GPP) with phytomass accumulation. These hypotheses were implemented and tested in the mathematical model ecosys against eddy covariance (EC) measurements of forest CO(2) and energy exchange in a post-clearcut Douglas-fir chronosequence. Hypothesis 1 explained how (a) an initial rise in GPP observed during the first 3 years after clearcutting could be caused by nutrient mineralization from rapid decomposition of fine, non-woody litter with lower C:N ratios (assart effect), (b) a slower rise in GPP during the next 20 years could be caused by immobilization during later decomposition of coarse woody litter, and (c) a rapid rise in GPP between 20 and 40 years after clearcutting could be caused by nutrient mineralization with further decomposition of coarse woody litter and of its decomposition products. During periods (a) and (b), heterotrophic respiration (R (h)) from decomposition of fine and coarse litter greatly exceeded net primary productivity (NPP = GPP - R (a)) so that Douglas-fir stands were large sources of CO(2). During period (c), NPP exceeded R (h) so that these stands became large sinks for CO(2). Hypothesis 2 explained how declines in NPP during later growth in period (c) could be caused by lower hydraulic conductances in taller trees that would force lower canopy water potentials and hence greater sensitivity of stomatal conductances and CO(2) uptake to vapor pressure deficits. Enhanced sensitivity to vapor pressure deficits was also apparent in the EC measurements over the post-clearcut chronosequence. Hypothesis 3 did not contribute to the explanation of forest age effects on NEP.

Lignin and enhanced litter turnover in tree plantations of lowland Costa Rica

We quantified the effect of overstory species composition on forest floor dynamics in lowland Costa Rica. Aboveground litter production and forest floor mass were measured over 1 year in 16-year-old single-species plantations established in a randomized complete block design with four blocks. The tree species investigated (=experimental treatments) were Hyeronima alchorneoides, Pentaclethra macroloba, Pinus patula subsp. tecunumanii, Virola koschnyi, Vochysia ferruginea, and Vochysia guatemalensis. Organic matter fluxes in litterfall, which averaged 10.1 Mg ha −1 year −1, were similar to those reported from comparable Neotropical plantations, whereas nitrogen fluxes in litterfall (up to 210 kgN ha −1 year −1) were high. Litter production was significantly greater beneath Hyeronima and V. ferruginea than beneath Virola, primarily due to high rates of non-woody litter production by Hyeronima, large amounts of twig litter production by V. ferruginea, and low production of both fractions by Virola. V. ferruginea had significantly more branch litter on the ground than did any other species, whereas Hyeronima had the largest accumulations of non-woody (mostly leaf) litter. Accumulations of woody litter correlated closely with rates of branchfall: branches ≤1 cm in diameter persisted on the forest floor for 0.9 year on average, independent of species. Rates of decay of non-woody litter, in contrast, varied significantly among species, with fastest rates (2.8 year −1) observed beneath Pentaclethra and the slowest decay rates (1.5 year −1) in plots of V. guatemalensis. Contrary to expectations, litter decay rates increased with increasing lignin contents, paralleling results of a concomitant study that found a significant negative correlation between litter lignin and surface-soil organic matter content. Our results demonstrate that different overstory-tree species generate significantly different forest floors, in terms of mass, composition and dynamics. These differences affect soil restoration, tree regeneration and other ecological processes important to selecting species for tropical plantation establishment and reforestation efforts.

Do rates of litter decomposition tell us anything we really need to know?

Results of several long-term studies of non-woody litter decomposition in forests indicate that we need to rethink why and how we measure rates of litter decomposition. Effects on litter decomposition rates were postulated to explain some of the nutritional effects of factors such as tree species, forest harvesting and fertilization. However, the accumulated experimental evidence indicates that litter decomposition rates do not mediate these responses. Many studies have reported litter mass loss becoming extremely slow at values considerably below 100%, indicating that early decay rates may not accurately foreshadow the entire decay process. Exclusion of soil faunal activities from current measurements of decomposition rates seriously reduces the likelihood that we are properly modeling decomposition. Finally, the use of regression and correlation analyses to determine which climate or initial litter quality factors control decay rate has led to many unwarranted and potentially misleading conclusions. These concerns are illustrated with examples from a suite of litter decomposition studies in British Columbia, Canada. Insights into nutrient cycling and carbon storage in ecosystems are more likely to arise from measuring the mass and nutrient content of annual litter input and determining the maximum decomposition limit and nutrient content at that stage, than by measuring early rates of decay. Improved predictions of relative decay rates of plant litters are likely to arise from a holistic approach based on plant life attributes rather than correlations based on individual initial litter chemistry parameters. Finally, a better understanding of the fate of faecal material of soil fauna is necessary before we can accurately predict and model litter decomposition.

Sources and Transformations of Organic Matter in Surface Soils and Sediments from a Tidal Estuary (North Inlet, South Carolina, USA)

Surface soil and sediment samples collected along a forest-brackish marsh-salt marsh transect in a southeastern U.S. estuary were separated into three different fractions (sand, macro-organic matter, and humus) based on size and density. Elemental, stable carbon isotope, and lignin analyses of these samples reveal important contrasts in the quantity, composition, and sources of organic matter, between forest and marsh sites. Elevated nitrogen contents in humus samples suggest nitrogen incorporation during humification is most extensive in forest soils relative to the marsh sites. The lignin compositions of the macro-organic and humus samples reflect the predominant type of vegetation at each site. Lignin phenol ratios indicate that woody and nonwoody litter from, gymnosperm and angiosperms trees (pines and oaks) is the major source of vascular plant-derived organic matter in the forest site and that angiosperm, grasses (Juncus andSpartina) are the major sources of lignin at the marsh sites. The phenol distributions also reveal that oxidative degradation of lignin is most extensive in the forest and brackish marsh zones whereas little lignin decay occurs in the salt marsh samples. In forest soils, most organic matter originates from highly altered forest vegetation while at the brackish marsh site organic matter is a mixture of degradedJuncus materials and microbial/algal remains. Organic matter in the salt marsh appears to be composed of a more complex mixture of sources, including degradedSpartina detritus as well as algal and microbial inputs. Microbial methane oxidation appears to be an important process and a source of13C depleted organic carbon in subsurface sediments at this site.

Litter decomposition as a potential natural source of methyl bromide

We assessed the potential significance of global litter decay as a new source of atmospheric methyl bromide. We combined information on the global distribution and quantity of litter decay, litter bromine content, and the halogen‐methylating ability of wood‐rotting fungi to produce a spatially explicit estimate of CH3Br emission from litter decay. The uncertainties are large and the potential methyl bromide source varies greatly in response to assumptions made, including those regarding the efficiency of bromine utilization and release. Our best estimate of the potential flux from woody litter, 0.5–5.2 kT yr−1, is unable to account for the entire “missing source.” Additional possible fluxes from regions of inadequate data and from nonwoody litter may raise this total. This proposed decomposition source is of potential interest to budget calculations and should be experimentally characterized and quantified.

Decomposition and carbon cycling of dead trees in tropical forests of the central Amazon.

Decomposition rate constants were measured for boles of 155 large dead trees (>10 cm diameter) in central Amazon forests. Mortality data from 21 ha of permanent inventory plots, monitored for 10-15 years, were used to select dead trees for sampling. Measured rate constants varied by over 1.5 orders of magnitude (0.015-0.67 year-1), averaging 0.19 year-1 with predicted error of 0.026 year. Wood density and bole diameter were significantly and inversely correlated with rate constants. A tree of average biomass was predicted to decompose at 0.17 year-1. Based on mortality data, an average of 7.0 trees ha-1 year-1 died producing 3.6 Mg ha-1 year-1 of coarse litter (>10 cm diameter). Mean coarse litter standing-stocks were predicted to be 21 Mg ha-1, with a mean residence time of 5.9 years, and a maximum mean carbon flux to the atmosphere of 1.8 Mg C ha-1 year-1. Total litter is estimated to be partitioned into 16% fine wood, 30% coarse wood, and 54% non-woody litter (e.g., leaves, fruits, flowers). Decomposition rate constants for coarse litter were compiled from 20 globally distributed studies. Rates were highly correlated with mean annual temperature, giving a respiration quotient (Q 10) of 2.4 (10°C-1).

CO emissions from degrading plant matter (II).

From relationships between integrated daily CO emissions and received solar radiation obtained for different standing dead grasses in field experiments in a savanna region in South Africa, and making use of ecosystem and solar irradiation databases, we derive estimates on global CO production and seasonality from photochemical decay of dry grasses and litter. The photochemical CO source strength from standing dead plant material and litter in various grassland ecosystems and deciduous forests ranges from 20 to 65 Tg CO per year (1 Tg = 1012 g). Accounting for potentially CO emitting ecosystems not included in the data set, we estimate that 60 ± 30 Tg of CO are annually emitted by photochemical degradation of decaying plant matter, mostly in the tropics. We further estimate thermal CO production from the global topsoil non-woody litter pool on the basis of global climate data and measured Arrhenius parameters to add another 40 Tg CO per year, much depending on the chosen parameters, and probably uncertain by a factor of 2. The total global source of CO by these mechanisms may thus be in the range 100 +70-50 Tg CO per year. Although the estimated CO source strength is a relatively small contribution to the global CO budget (2–8%), CO emissions may significantly compensate for CO deposition on soils in the tropics during certain times of the year. Currently, modelling studies mostly impose a constant CO deposition velocity from the atmosphere to the soil surface, based generally on measurements on bare soil. Future modelling efforts may need to include geographical and photochemical factors which play a role in CO exchange in tropical ecosystems.

Litter decomposition under snow cover in a balsam fir forest

In a subalpine balsam fir forest in Quebec, Canada, mass losses, respiration rates, and nitrogen and sulphur dynamics were measured on fir needles, birch leaves, lichens (mixed species), and small twigs decomposing under deep (> 1.5 m) winter snow for 6 months. Mass losses ranged from <6% (twigs) to 70% (lichens) and relative decomposition rates of needles and leaves were reversed from those expected at higher temperatures. Isolation of fir needles from direct contact with the snow did not affect decay rate, nor was decay accelerated by spring snowmelt. In situ respiration rates increased from about 1 mg CO2/(g∙day)) in February to 3–5 mg CO2/(g∙day)) in May, mostly because of rising temperatures. Summer respiration rates were much higher (> 6 mg CO2/(g∙day)). Nitrogen and suphur concentrations increased in all nonwoody litter over winter, but only birch leaves and some fir needles appeared to assimilate nutrients from the environment. Melting snow could easily have provided all of the nitrogen and sulphur taken up by decomposing litter. Decomposing lichens released 40 and 60%, respectively, of their initial nitrogen and sulphur contents. A literature review indicates mass losses from leaf litter decomposing under deep snow vary according to the proportion of labile material in the litter and usually constitute 40–60% of total first-year mass losses. Key words: decomposition, winter, balsam fir, snow.

Studies of Mineral Cycling in a Montane Rain Forest in New Guinea: II. The Production and Disappearance of Litter

(1) Litter production and the quantity of litter remaining on the ground were monitored for a 12-month period in undisturbed Lower Montane Rain forest at an altitude of c. 2400-2500 m in the Eastern Highlands of New Guinea. Four sites, each 20 x 10 m, were studied in contrasting situations; one site (on a ridge) was a natural gap caused by the fall of a large tree, and the other three sites (on a broad ridge, on a steep slope and in a valley bottom) were of well-developed, mature or late-building phase trees. (2) At each site litter fall was measured in sixteen traps 1 x 1 m. The average litter production for the four sites was 755 ? 27 (s.e.m.) g m-2 yr1 (non-woody material 635 ? 20 g m-2 yr1), and no significant differences were found between the sites. (3) It is estimated that about 1000 of the leaf dry weight is grazed by phytophagous insects, and a further 100% is withdrawn by the trees before the leaves are shed. Density measurements made on healthy twigs, and on twigs in the litter fall, suggest that considerable decomposition occurs before the twigs fall as litter. (4) Estimates of the annual rate parameter for litter disappearance, based on the relationship between the standing crop of litter on the ground and the annual litter production, range between 1-04 for the Ridge Site and 1-55 for the Valley Site. (5) The decomposition of leaf litter of six tree species (Dacrycarpus cinctus, Elaeocarpus ptilanthus, Litsea sp. 65, Macaranga albescens, Planchonella firma and Schizomeria sp. 203) and a widespread bamboo (Nastus productus) was studied over 325 days at the Ridge and Valley Sites by enclosing the litter in plastic mesh. There were no significant differences between the two sites. (6) Only 1500 of the original dry weight of leaves of Elaeocarpusptilanthus remained after 325 days. Leaves of other tree species disappeared more slowly (57-74% of the dry weight remained). Of the bamboo leaves 56%/ remained. (7) The average rate of disappearance for the seven species, equivalent to 47-48% in the first year, is much less than the rate calculated from the standing crop of litter and the annual litter production (100148%0 for non-woody litter); this and other evidence suggests that the time-course of disappearance is linear rather than exponential.

Annual Tree‐Litter Production by Successional Forest Stands, Juneau, Alaska

Litter production in four stands (pioneer Alnus—Salix to old—growth Tsunga heterophylla/Picea sitchensis) for 3 years averaged 2,850 kg/ha. Production varied among stands and years, but no real differences were apparent. Nonwoody litter was about 64% of total litter and, although less variable, there were no consistent differences for stands nor years.

Fluctuations in Litter-Fall in a Mixed Deciduous Woodland over a Three-Year Period 1966-68

from 499 g/m2 to 525 g/m2 in the three years. Non-woody litter varied from 363 g/m2 to 393 g/m2 and showed low variability both between collection sites and between years whilst woody litter varied from 106 g/m2 to 162 g/m2 and showed high variability. Seasonal pattern in litter-fall was very marked, up to 81 % of the annual total falling in the period September to November. The difference in leaf-fall periodicity between hazel and the overstorey was clearly demonstrated during each of the three years considered.