Litterfall Fluxes Research Articles

Dynamics of PAH deposition, cycling and storage in a mixed-deciduous ( Quercus-Fraxinus) woodland ecosystem

Estimates of standing biomass and fluxes of biomass in a mixed-deciduous woodland were derived, and used with results for concentrations of seven polycyclic aromatic hydrocarbons (PAHs) in different compartments of the woodland system to quantitatively assess some of the key fluxes and burdens of PAHs in this complex system. We quantified PAH burdens in air, in leaves of three deciduous tree species, in leaf litter and in soil, and uptake of PAHs by the tree leaves; PAH fluxes in litterfall, and deposition to the litter layer on the woodland floor during winter were calculated from these data. Air burdens exhibited marked seasonal variations for all compounds, with lowest values in summer when combustion-related emissions were low. Leaves did not accumulate large burdens of PAHs while on the trees and consequently, litterfall-associated fluxes of PAHs were small, representing only a fraction of the burdens in the litter layer to which they were deposited. Higher PAH burdens in air in winter, combined with the organic-matter-rich nature of the litter layer, are thought to be responsible for fluxes of PAHs to the litter layer in winter being 20–170 times the peak litterfall fluxes. The soil compartment was calculated to contain 25 years' worth of deposition of benzo[ ghi]perylene, the most recalcitrant PAH in this study. Storage quotients for fluoranthene, pyrene, benzo[ k]fluoranthene and benzo[ a]pyrene burdens in soil represented 7–10 years' worth of deposition, while fluorene and phenanthrene storage in soil approached unity with inputs (1 and 3 years' worth of deposition, respectively). The relative importance of storage and loss processes was therefore closely related to the physico-chemical properties of the PAH, and is discussed in relation to the cycling of carbon in the woodland.

Phosphorus cycling in a Mexican tropical dry forest ecosystem

The study was conducted in five contiguous small watersheds (12–28 ha) gauged for long-term ecosystem research. Five 80 × 30 m plots were used for the study. We quantified inputs from the atmosphere, dissolved and particulate-bound losses, throughfall and litterfall fluxes, standing crop litter and soil available P pools. Mean P input and output for a six-year period was 0.16 and 0.06 kg⋅ha−1⋅yr−1, respectively. Phosphorus concentration increased as rainfall moved through the canopy. Annual P returns in litterfall (3.88 kg/ha) represented more than 90% of the total aboveground nutrient return to the forest floor. Phosphorus concentration in standing litter (0.08%) was lower than that in litterfall (0.11%). Phosphorus content in the litterfall was higher at Chamela than at other tropical dry forests. Mean residence time on the forest floor was 1.2 yr for P and 1.3 yr for organic matter. Together these results suggest that the forest at Chamela may not be limited by P availability and suggest a balance between P immobilization and uptake. Comparison of P losses in stream water with input rates from the atmosphere for the six-year period showed that inputs were higher than outputs. Balances calculated for a wet and a dry year indicated a small P accumulation in both years.

Nitrogen deposition to and cycling in a deciduous forest.

The project described here seeks to answer questions regarding the role increased nitrogen (N) deposition is playing in enhanced carbon (C) sequestration in temperate mid-latitude forests, using detailed measurements from an AmeriFlux tower in southern Indiana (Morgan-Monroe State Forest, or MMSF). The measurements indicate an average atmosphere-surface N flux of approximately 6 mg-N m(-2) day(-1) during the 2000 growing season, with approximately 40% coming from dry deposition of ammonia (NH3), nitric acid (HNO3), and particle-bound N. Wet deposition and throughfall measurements indicate significant canopy uptake of N (particularly NH4+) at the site, leading to a net canopy exchange (NCE) of -6 kg-N ha(-1) for the growing season. These data are used in combination with data on the aboveground C:N ratio, litterfall flux, and soil net N mineralization rates to indicate the level of potential perturbation of C sequestration at this site.

The importance of leaching from litter collected in litterfall traps.

Litterfall (LF) is usually collected by means of open traps. However, this litter will be subject to leaching by the throughfall which passes through the accumulated litter in the traps. The nutrients lost during this leaching are not taken into account in the calculation of LF nutrient fluxes. We report the results from a 2-month (August-September) study carried out in 8 northern coniferous forest stands to assess the possible importance of leaching from litter in LF traps. Compared to throughfall (TF), the litterfall leachate (LFLgross), which includes a throughfall component, had significantly (p < 0.05) higher concentrations and fluxes of Ca, Mg, Na and S. The average net LFL (i.e., LFLnet = LFLgross - TF) fluxes were 21 (Ca), 7 (Mg), 57 (K), 10 (Na), 10 (N), and 19 (S) mg m-2 mo-1. LFLnet accounted for 42%, 37% and 50% of the LFLgross flux, and for 91%, 51% and 49% of the total litterfall flux (i.e., LF + LFLnet) of Na, S and K, respectively. For Ca, Mg and N, the LFLnet flux accounted for 64%, 58% and 29% of the LFLgross flux, and for < 14% of the total litterfall flux. Compared to TF, LF was the dominant return pathway for Ca, Mg and N to the forest floor regardless of whether LFLnet was included or not. However, for K and S, taking LFLnet into account determined whether TF or LF was the dominant pathway. TF remained the dominant pathway for Na even when LFLnet was included.

Nutrient inputs in litterfall and rainwater fluxes in 27-year old red, black and white spruce plantations in Central Ontario, Canada

This study was undertaken to examine some nutrient cycling pathways in plantations of several species within the genus Picea. As no such studies currently exist, species within this genera in eastern North America are often managed inappropriately in a collective fashion, when in fact major differences in nutrient demand and utilization may occur. Nutrient inputs in throughfall, stemflow and litterfall fluxes were investigated in white spruce ( Picea glauca (Moench.) Voss), red spruce ( Picea rubens Sarg.) and black spruce ( Picea mariana (Mill.) BSP) plantations growing on the same site. The study was carried out in 1992 and 1993 in a replicated, 26–27-year old planting in the Swan Lake Forest Research Reserve, Algonquin Provincial Park, Ontario. Annual litterfall fluxes of N, P, K, Ca and Mg were always greatest in white spruce when compared to the other two spruces. For example, the N flux was estimated to be 2.72 g m −2 for white spruce as compared to 1.39 g m −2 and 1.62 g m −2 for red and black spruce, respectively. While this pattern held for N, P and K in the total throughfall and stemflow flux (e.g. for N: 0.28 g m −2 for white as opposed to 0.19 g m −2 (red) and 0.17 g m −2 (black)), there were no differences in the Ca and Mg fluxes. Incident precipitation was enriched in total N, organic N, NH 4 +–N and K beneath white spruce as compared to red or black spruce, but not in Ca, Mg or NO 3 −–N. The canopies of all three species decreased P loadings to the forest floor. Elemental returns of N, P, Ca and Mg in the annual litterfall flux exceeded returns in the combined water fluxes by 4–16 times, depending upon tree species and nutrient. For K, water fluxes for all three species were marginally higher than those in litterfall. The results indicate the need for species-specific information on the interaction of crown structure and tree morphology on nutrient deposition and re-cycling in plantation systems.

Calcium, potassium, and magnesium cycling in a Mexican tropical dry forest ecosystem

We estimated the fluxes, inputs and outputs of Ca, K,and Mg in a Mexican tropical dry forest. The studywas conducted in five contiguous small watersheds(12–28 ha) gauged for long-term ecosystem research. A total of five 80 × 30 m plots were used for thestudy. We quantified inputs from the atmosphere,dissolved and particulate-bound losses, throughfalland litterfall fluxes, and standing crop litter pools. Mean cation inputs for a six-year period were 3.03 kg/ha for Ca, 1.31 kg/ha for K, and 0.80 kg/ha for Mg. Mean outputs in runoff were 5.24, 2.83, and 1.79 kg/ha, respectively. Calcium, K, and Mgconcentrations increased as rainfall moved through thecanopy. Annual Ca return in the litterfall (11.4 g/m2) was much higher than K (2.3 g/m2)and Mg (1.6 g/m2). Litterfall represented 99%of the Ca, 84% of the Mg, and 53% of the K, totalaboveground return to the soil. Calcium concentrationin standing litter (3.87%) was much higher than K(0.38%) and Mg (0.37%). These concentrations werehigher (Ca), lower (K), or similar (Mg) to those inlitterfall. Residence times on the forest floor were0.86, 1.17, and 1.77 yr for K, Mg, and Carespectively. Compared to the residence time fororganic matter at the site (1.31 yr), these resultssuggest slow mineralization for Ca in this ecosystem. Budget estimates were calculated for a wet and a dryyear. Results indicated that nutrients accumulated inthe dry but that nutrients were lost during the wetyear. Comparison of Ca, K, and Mg losses in streamwater with the input rates from the atmosphere for thesix-year period show that inputs are lower thanoutputs in the Chamela tropical dry forestecosystem.

Dynamics of organic matter and nutrient return from litterfall in stands of ten tropical tree plantation species

We studied the rates and patterns of carbon and nutrient fluxes in litterfall in ten tropical tree plantation species grown at the USDA Forest Service Arboretum in the Luquillo Experimental Forest, Puerto Rico. The stands were 26-years old and grew under similar climatic and edaphic conditions. Individual plantation species ranked differently in terms of their capacity to return mass and specific nutrients to the forest floor, and with respect to their efficiency of nutrient use. The species that returned the most mass did not return the most P, N, or cations. Moreover, species differed according to the amount of N and P resorption before leaf fall. These differences reflect the variation in the ecophysiological response of each species to edaphic and climatic conditions. The difference between average and minimum resorption values of the species studied indicate that other environmental factors, such as heavy winds or the physical effects of heavy rains, can force the shedding of non-senesced leaves. This higher quality material, although not very much in quantity, can provide a small pulse of available nutrients to the forest floor community. The same holds true for other high nutrient/low mass fractions of litterfall such as reproductive parts and miscellaneous materials. In areas with no prevalent or strongly seasonal water limitations, temporal variations of leaf litter on the forest floor are the combined result of the rate of fall and decomposition of the falling material, and the diverse responses of species to different environmental cues. Leaf fall was inversely correlated to reduced water availability in three of the species studied. Leaf fall of the other species was correlated either to daylight duration or minimum temperatures. The results highlight the importance of understanding species performance relative to nutrient and mass metabolism before selection for plantation use, or for rehabilitation of degraded lands.

Nutrient status of Amazonian caatinga forests in a seasonally dry area: nutrient fluxes in litter fall and analyses of soils

Amazonian caatinga, a low-stature forest type confined to seasonally waterlogged white-sand soils, occurs at La Esmeralda (Orinoco basin) under a lower rainfall than at San Carlos (RIo Negro basin), where many previous studies have been made. The nutrient status of forest types at La Esmeralda are compared and related to those of forests at San Carlos. At La Esmeralda, stature declines from well-drained palm-rich forest (PRF), via waterlogged tall caatinga (TC), to superficially waterlogged short caatinga (SC). Along this sequence, total fine litter fall decreased (7.6, 6.7, and 5.2 Mg·ha n1 ·year n1 ), N flux decreased (66, 59, and 40 kg·ha n1 ·year n1 ), Ca flux increased (27, 44, and 85 kg·ha n1 ·year n1 ), P flux decreased nonsignificantly, and there was no trend in Mg or K fluxes. Resin-exchangeable P concentrations of 0n10 cm soil samples increased along the sequence (20, 28, and 30 μg·g n1 ). The conclusion that N is in increasingly short supply as a result of waterlogging agrees with results previously obtained at San Carlos. The P flux in leaf litter fall of forests at La Esmeralda (range 1.0n1.3 kg·ha n1 ·year n1 ) is lower than that of tall caatinga at San Carlos (2.0 kg·ha n1 ·year n1 ) or itypicali rain forests (mean 2.6 kg·ha n1 ·year n1 ), suggesting that P is also relatively scarce.

The First Five Years in the Reorganization of Aboveground Biomass and Nutrient Use Following Hurricane Hugo in the Bisley Experimental Watersheds, Luquillo Experimental Forest, Puerto Rico

Five years after Hurricane Hugo reduced the aboveground biomass by 50 percent in two forested watersheds in the Luquillo Experimental Forest of Puerto Rico, regeneration and growth of survivors had increased the aboveground biomass to 86 percent of the pre-hurricane value. Over the 5 yr, the net aboveground productivity averaged 21.6 Mg.ha-1 yr-' and was faster than most plantations and secondary forests in the area. Woodfall and associated nutrient fluxes never attained pre-storm values but by the fifth yr, mean daily total litterfall, and N, P, K, Ca, and Mg fluxes in litterfall were 83, 74, 62, 98, 75, and 81 percent of their pre-disturbance values, respectively. Aboveground nutrient pools of these nutrients ranged from 102 to 161 percent of their pre-disturbance values and were larger after 5 yr because of higher nutrient concentrations in the regeneration compared to the older wood that it replaced. The following sequence of ecosystem reorganization during this first 5 yr period is suggested. An initial period of foliage production and crown development occurred as hurricane survivors re-leafed and herbaceous vegetation and woody regeneration became established. During this period, 75 to 92 percent of the nutrient uptake was retained in the aboveground vegetation and there was a relatively low rate of aboveground carbon accumulation per mole of nutrient cycled. This initial period of canopy development was followed by a peak in aboveground productivity that occurred as early successional species entered the sapling and pole stages. This period was followed by the establishment of the litterfall nutrient cycle and an increase in the net productivity per mole of nutrient cycled. During this 5 yr period, the Bisley forest had some of the lowest withinstand nutrient-use-efficiencies and some of the highest levels of aboveground productivity ever observed in the LEE The study demonstrates that high levels of productivity and rapid rates of aboveground reorganization can be achieved with rapid within-system cycling and inefficient within-stand nutrient use.

Regional-scale linkages of terrestrial and lotic ecosystems in the Amazon basin: a conceptual model for organic matter

Terrigenous organic matter originating at the margins of streams in headwater regions of the Amazon basin accounts for a large part of the organic matter carried by the major tributaries of the basin. The purpose of this paper is to articulate our present understanding of terrestrial to lotic transfers in these headwater regions in the form of a conceptual model. On a regional scale, the headwaters of the Amazon basin may be subdivided into four dominant terrain types: (1) terra firme forests developed on oxisols and ultisols, (2) campina forest developed on spodosols, (3) savanna developed on oxisols, ultisols, and alfisols and (4) montane forest developed on ultisols and inceptisols. Within these terrains terrigenous organic matter is transferred to streams via direct litterfall and blow-in, groundwater baseflow, stormflow, and seepage from fringing wetlands. Based on the limited available data and data from other systems, our current conceptual model is as follows. Direct litterfall contributions from overhanging canopies are similar across the basin and on the order of 0.7 kg/m2/year. Blow-in contributions are probably on the order of 20% of direct litterfall fluxes. Groundwater baseflow contributions of organic matter (OM) are strongly correlated with soil type and fall into two distinct classes, one draining the campina terrain which is characterized by high dissolved organic carbon (DOC) concentrations (> 20 mg/l) and another draining terra firme, savanna, and montane terrains which is characterized by lower DOC concentrations (< 5 mg/l). Groundwater OM contributions are also compositionally distinct, with elevated proportions of hydrophobic organic molecules in groundwater draining campina. Stormflow contributions across the basin are dominated by saturation overland flow originating in riparian areas, and transferred OM consists primarily of litter washed in from the surrounding forest floor and material flushed from fringing wetlands. In montane terrains, however, there may also be a significant erosive input of soil OM. Contributions of OM from fringing wetlands are most prevalent in lowland terrains where broad, flat riparian zones provide ample sites for wetland development. Both stormflow and seepage from fringing wetlands transfer a wide spectrum of OM composition, ranging from freshly fallen leaves to heavily decomposed and refractory dissolved molecular forms.

Effects of base cation fertilization on soil and foliage nutrient concentrations, and litter-fall and throughfall nutrient fluxes in a sugar maple forest

Application of base cation fertilizers is widely used to ameliorate decline symptoms in hardwood forests in southern Quebec, but little is known about the effects of fertilization on nutrient cycling. Control and fertilized plots in a sugar maple (Acersaccharum Marsh.) dominated stand were monitored over a 4-year period to determine the effects of fertilization on exchangeable soil base cations in soil, foliar nutrient concentrations, and fluxes of N, K, Ca, and Mg in litter fall and throughfall. Fertilization had a large, immediate effect on exchangeable K, whereas effects on Ca and Mg were delayed and restricted to the organic forest floor, presumably because of the lower solubility of the limestone-based Ca and Mg components of the fertilizer. Fertilization raised pH in the organic forest floor the second and third years after application but had no effect in the B horizon. Foliar K, Ca, and Mg were elevated in the year of fertilization, but foliar concentrations of Ca and Mg did not differ from, or were lower than, controls in following years. Litter-fall K flux was increased by fertilization, but litter-fall Ca and Mg fluxes and all through-fall base cation fluxes were unaffected. In control plots, nutrient concentrations in soil remained relatively constant throughout the study, but foliar concentrations and, in particular, litter-fall fluxes varied widely from year to year. This natural variation caused control plots to shift from a state of deficiency in N, Ca, and Mg to a nutrient-sufficient state between the first and second years of study. Fertilization effects are superimposed on a naturally variable nutrient cycling system, and controls on this variability must be understood if fertilizer response is to be accurately predicted.

Leaf litterfall concentrations and fluxes of elements in deciduous tree species

The influence of tree species and soil properties on leaf litterfall concentrations and fluxes of elements were studied in three mixed deciduous forest stands. Leaf litterfall fluxes of sixteen elements were measured during autumn defoliation in 100 to 150 yr old individuals of Fagus sylvatica L., Quercus robur L., Carpinus betulus L., Tilia cordata Mill, and Acer platanoides L. Compared to throughfall and precipitation, leaf litterfall dominated the flux of P, Ca, Mn, N and Mg (in decreasing order) to the soil below the tree canopies. For K and especially S and Na, however, the importance of leaf litterfall input to the total fluxes was small. Fluxes and especially concentrations of Ca, Mg, K, P and partly N were positively related to base saturation of the soil, while Mn was negatively related due to a higher mobilization rate and plant uptake of this element on acid soils. Litterfall fluxes for C. betulus were strongly positively influenced by base saturation and fluxes were usually higher than for F. sylvatica and Q. robur at the richest site. Quercus robur had often the lowest fluxes, especially of Ca and Mg. Tilia cordata had the highest leaf litter concentrations in twelve of the sixteen elements, and the highest fluxes particularly of N and K. Acer platanoides had the highest or among the highest concentrations and fluxes of Ca, Zn and Mn. The concentration of Al in C. betulus leaf litterfall, was about five times higher than in all other tree species at all sites.

Nutrient cycling in red spruce forests of the Great Smoky Mountains

Nutrient distributions, concentrations, and fluxes in two red spruce (Picearubens Sarg.) stands in the Great Smoky Mountains are described and used to evaluate various hypotheses for recent decline of this species. These forests, like others in the southern Appalachians, were relatively rich in N and low in base cation status. The combination of high atmospheric N and S deposition, little or no N or S retention, relatively high N mineralization, and extremely acid soils caused soil solutions to be dominated by NO3−, SO42−, Al, and H+. Soil solution Al in these sites (most of which was in monomeric form) occasionally reached levels noted to inhibit base cation uptake and root growth in solution culture studies. These pulses of Al were driven by pulses of NO3− and, to a lesser extent, SO42− in soil solution. However, fine roots were present at depths of up to 60 cm in the mineral soil, indicating that Al concentrations had not become consistently toxic to roots. Solution fluxes (both throughfall and soil leaching) exceeded litter-fall fluxes for all the macronutrients at both sites, a typical situation for K and S, but most unusual for N, P, Ca, and Mg. There are significant implications of these fluxes and of the apparent net uptake of N by foliage in terms of how vegetation uptake and translocation are calculated. Some new formulations are suggested, but measurement errors in systems with such a predominance of hydrologic fluxes make foliar leaching and, therefore, uptake and translocation calculations extremely uncertain. Although there are no outward signs of decline in these forests (other than balsam fir (Abiesbalsamea (L.) Mill.) mortality due to the balsam woolly adelgid (Adelgespiceae (Ratz.))), the high rates of NO3− leaching rates and the borderline soil solution Al values suggest that these systems are under stress. Whether these factors actually lead to a dieback or growth decline remains to be seen.

Studies on the dynamic properties of terrestrial ecosystems based on a simulation model II. Tropical rainforest dynamics and stability as influenced by stem mortality

Further analysis of tropical rainforest dynamics and stability in relation to stem mortality has been conducted using a microcomputer model developed in a previous study (Oikawa, 1985). By simulation experiments covering a period of 100 years, the effects of changing stem mortality (δc) upon a tropical rainforest were investigated. Increasing stem mortality ranging from a standard value (3%yr−1) to a 4-fold value (12%yr−1) brings about decreases in stem biomass and thus total living biomass, and a contrasting increase of stem litterfall flux at the steady state of the forest ecosystem. At the same time, the decreased stem biomass at the steady state is predicted to result in increases of gross production (Pg) and net production (Pn), and an improvement in production efficiency of the model rainforest expressed as the Pn/Pg ratio. similar simulation experiments predict that the improved production efficiency in the forest with a 4-fold stem mortality is able to enhance tolerance to less productive environments such as a prolonged dry season or a reduced incident light flux density. On the other hand, the standard stem mortality (δc=3%yr−1), which was estimated as a probable value for the Pasoh forest, West Malaysia, is considered to approximate the lower threshold necessary for attaining forest stability. Based on the results obtained, the significance of δc for the dynamics and stability of a tropical rainforest ecosystem is discussed in relation to the competition and tolerance of trees. In addition, the effectiveness of the simulation approach adopted here is emphasized.

Nutrient dynamics within amazonian forest ecosystems

A comparative analysis on the rate of fine litterfall and its associated nutrient fluxes was carried out in a mixed forest on Tierra Firme, a tall Amazon Caatinga and a Bana on podsolized sands near San Carlos de Rio Negro. There was seasonality in leaf fall and total litterfall in mixed forest and tall Amazon Caatinga forest but no definite trend in the Bana. Litterfall curves were significantly correlated among sites indicating common regulating factors in the three forests. Leaf litter from mixed forest on Tierra Firme was richer in N with extremely low Ca and Mg concentrations; tall Amazon Caatinga litter had higher P and Mg concentration, while Bana litter was low in N but K concentration was twice as high as in the other two forests. Annual fine litterfall in Tierra Firme mixed forest was nearly 4 times higher than in Bana, But N flux was 10 times higher, while Ca and Mg fluxes were similar. Tall Amazon Caatinga had Ca and Mg fluxes in litterfall 2-3 times higher than the other two forests. Within-stand efficiency of nitrogen, calcium and magnesium use, as measured by biomass/nutrient ratios, differentiates Tierra Firme from Caatinga and Bana forest: Tierra Firme has the lowest N, but the highest Ca and Mg use efficiencies. Higher P use efficiency was measured in Bana followed by Tierra Firme and Caatinga; while Tierra Firme and Caatinga showed similar higher K use efficiencies than Bana. N/P ratios indicates that Tierra Firme forest is limited by P availability, while low N availability predominates in Caatinga. Bana appears limited by both N and P. These differences probably relate to variations in degree of sclerophylly and leaf duration which determine leaf nutrient concentrations in the ecosystems studied.

Sampling variability in nutrient cycling studies in some forested ecosystems of Westland, New Zealand

Abstract Field collectors were used to collect monthly samples of litterfall, rainfall, and throughfall for a two-year period, and soil drainage beneath the soil organic horizon and at the base of the rooting zone for 12 months, in two indigenous and four pine forest plots in Westland. CoeffiCients of variation (CVs) for estimates of components of litterfall, rainfall, through fall, and soil drainage below the organic soil and rooting zone and their associated nutrient fluxes 10 kg/ha/yr are given. Litterfall variability was greatest on plots where canopy closure was incomplete or where wood-fall was a significant component of litterfall. CVs for nutrient fluxes in litterfall was generally similar to, or lower than those for dry weight of litterfall. Incident rainfall was very uniform (CV 2–3%). Variability increased markedly (CV 16–31%) as a result of rainfall passing through the forest canopy. Nutrient fluxes in bulk precipitation and throughfall were considerably more variable than a!l10unts of precipitation and throughfall respectively. For Soil drainage, samples collected by tension-free (tray) lysimeters gave results approximately 2–5 times more variable than those for tension lysimeters. For the latter variability was generally similar to that for throughfall nutrient fluxes. Choice of the number of field collectors to be used should be based on the degree of inherent variability, which depends on the ecosystem. In practice, it will also depend on the availability of resources. Generally, 3–5 rain gauges, 20–25 throughfall gauges and littertraps, and 10–20 lysimeters are considered to be a suitable compromise for some indigenous and pine forests in Westland, New Zealand. Some form of stratified random sampling is desirable for collection of throughfall and litterfall in forests with open canopies. Wood-fall, other than for small twigs, was inadequately sampled by 12 littertraps. It is suggested that for the major components of wood-fall larger areas of the forest floor be regularly sampled.

Nutrient fluxes in litterfall and decomposition in four forests along a gradient of soil fertility in southern Ohio

To determine how soil nutrient availability influences nutrient cycling, fluxes of nutrients through litterfall and decomposition were determined for four forest stands similar in all respects except soil nutrient availability and microclimate, within Neotoma Valley, a small watershed in southern Ohio, U.S.A. Litterfall varied from 10 to 60% among sites while nutrient concentrations and masses in new leaf litter varied as a function of extractable soil nutrient levels. Mass loss from litterbags was significantly higher in more fertile sites. Stepwise regression indicated that initial litter nitrogen and phosphorus concentrations were strongly correlated with relative decomposition rate while lignin concentration and microclimate variables were only correlated weakly. Thus, both litterfall nutrient transfers and decomposition rates were under the control of soil nutrient levels. Nitrogen was immobilized in litter at all sites during the 1st year of decay; litter from more fertile sites mineralized nitrogen during the 2nd year, while that from less fertile sites continued to immobilize nitrogen. Phosphorus and calcium mineralization rates were strongly correlated with the availability of these elements in the soil. Magnesium and potassium were leached rapidly from litter; amounts mineralized were correlated with amounts in litterfall. Interrelations among soil fertility, litterfall, and nutrient mineralization, as well as litter redistribution, are discussed as processes important in the development and maintenance of the soil fertility gradient in this watershed.

Estructura y funcionalismo de un encinar montano en el Montseny. IV: producción de hojarasca

Litterfall and its concomitant mass and nutrient (Na, K, Ca and Mg) fluxes to the forest floor are studied in a montane-Mediterranean evergreen-oak (Quercos ilex L.) wood at La Castanya (Montseny, Barcelona). Litterfall is colected biweekly in 16 (only 8 during the first 6 months) conical, 0.25 m litterfall traps randomly distributed over a 0.22 ha experimental plot. Results from the first year of study (May 1978 - May 1979) are reported in this paper. Litterfall a mounted to 4.5 t ha-1 yr-1, not including in this figure the branches longer than 40 cm or thicker than 5mm. Leaves represented 3.08 t ha-1 yr-1 (68.11% of litterfall), twigs 1.05 t ha-1 yr-1 (23.22%), and fruits and inflorescences 0.14 t ha-1 yr-l (3.21%). Leaf fall exhibited a distinct seasonal maximum in late spring-early summer, but total litterfall peaked later when an autumn hailstorm and a November windstorm struck the forest. Nutrient contents of freshly-fallen evergreen-oak litter were within the range of published values for this species. Nutrient fluxes in litterfall were (kg ha-1 yr-1): Na 0.76, K 18.28, Ca 41.64 and Mg 5.43. Throughfall data from Roda et al. (1980) allowed to compute the following nutrient fluxes in litterfall plus throughfall (kg ha-1 yr-1): Na 9.1, K 38.0, Ca 64.7 and Mg 9.3.