Leaf Litterfall Research Articles

Leaf litter effects on seed and seedling predation of the palm Astrocaryum murumuru and the legume tree Dipteryx micrantha in Amazonian forest

ABSTRACTThe amount of leaf litter fall produced by different tree species in tropical forests varies in space and time. Falling litter may cover seeds and thereby enhance their survival by making their detection by seed predators more difficult. Tests were made to determine whether Astrocaryum murumuru and Dipteryx micrantha seeds survive better in microsites covered by leaf litter. Seed numbers and litter cover on the forest floor were experimentally manipulated. How natural variation in leaf litter cover and thickness affects seed and seedling survival of these two plant species was also examined. Seed survivorship was significantly higher for both plant species in microsites with leaf litter than in those with bare soil. Results from an experiment in which the litter was not disturbed showed that Astrocaryum seed survival was positively correlated with litter thickness (defined as the number of overlying dead leaves). Astrocaryum seedling survival was also significantly affected by leaf litter; more seedlings survived in shallow litter. Leaf litter had no effect on Dipteryx seedling survival. The results of the study suggest that early recruitment of both Astrocaryum and Dipteryx is influenced by the spatial distribution and amount of forest leaf litter.

PHOSPHORUS DYNAMICS IN A LOWLAND AFRICAN RAINFOREST: THE INFLUENCE OF ECTOMYCORRHIZAL TREES

PHOSPHORUS DYNAMICS IN A LOWLAND AFRICAN RAINFOREST: THE INFLUENCE OF ECTOMYCORRHIZAL TREES

Litter dynamics in riverine mangrove forests in the Guayas River estuary, Ecuador.

The hypothesis that rates of litter turnover in mangroves are controlled by local geophysical processes such as tides has been studied at sites with mostly small tides (<1 m) and minor crab consumption of leaf litter. Our study describes litter dynamics of three riverine mangrove sites (M1, M2, M3), inhabited by the mangrove crab Ucides occidentalis, located in a macrotidal (>3 m) river-dominated tropical estuary in Ecuador (2.5°S latitude). There were statistical effects of site and depth on soil salinities, but all mean salinities were <17 g kg-1. Daily rates of leaf litter fall were higher in the rainy compared to the dry season, although no seasonal effects were observed for other components of litter fall. Annual total litter fall rates were significantly different among sites at 10.64, 6.47, and 7.87 Mg ha-1 year-1 for M1, M2, and M3, respectively. There were significant site (M3 > M2 > M1) and season (rainy > dry) effects on leaf degradation, and both effects were related to differences in the initial nitrogen content of senescent leaves. Mean leaf litter standing crop among the sites ranged from 1.53 to 9.18 g m-2, but amounts were strongly seasonal with peak values during September in both years of our study (no significant year effect) at all three sites. Leaf turnover rates based on leaf fall estimates and litter standing crop were 10- to 20-fold higher than estimated from rates of leaf degradation, indicating the significant effect of leaf transport by tides and crabs. Field experiments demonstrated that the mangrove crab can remove daily additions of leaf material within 1 h at all three sites, except during August-October, when the crab is inactive on the forest floor. Even though there is seasonally elevated leaf accumulation on the forest floor during this time, leaf turnover rates are much higher than expected based on leaf degradation, demonstrating the importance of tidal export. This is the first description of how crabs influence litter dynamics in the New World tropics, and results are similar to higher rates of crab transport of leaf litter in the Old World tropics. Even in riverine mangroves with high geophysical energies, patterns of litter dynamics can be influenced by ecological processes such as crab transport.

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.

ABOVEGROUND PRODUCTION IN SOUTHEASTERN FLOODPLAIN FORESTS: A TEST OF THE SUBSIDY–STRESS HYPOTHESIS

It has been hypothesized that periodically flooded forests have higher rates of aboveground net primary production than upland forests and near-continuously flooded forests, but a competing hypothesis holds that the benefits of periodic inputs of nutrients and water may be diminished by stresses associated with anaerobic soils or drought. To test these hypotheses, we measured groundwater table depths and aboveground productivity in floodplain forests of South Carolina and Louisiana. We established paired plots on locally dry, intermediate, and wet topographic positions across three hydrologic transects in each state. These plots encompassed upland hardwood, bottomland hardwood, and cypress swamp forests. Measurements of leaf litterfall, wood production, and groundwater table depth were made in 1987 and 1988. We then used mean growing-season water depth (MWD) to group the plots into three classes: wet (>0 cm), intermediate (0 to −60 cm), and dry (<−60 cm). Aboveground net primary production (NPP) on wet plots (2-yr mean ± 1 sd = 675 ± 271 g·m−2·yr−1) was significantly lower than on intermediate and dry plots (P ≤ 0.02). There was no significant difference between intermediate and dry plots (107 ± 189 and 1038 ± 91) g·m−2·yr−1, respectively). In addition, aboveground NPP on intermediate plots was not significantly different from 22 temperate upland forests in the literature. Combining our data with data from the literature, we found that aboveground NPP on wet plots was negatively related to MWD with a slope of −5 g·m−2·yr−1·cm−1. On sites with evidence of hydrologic disturbance (>25% dead stems) the slope of this line was 5 times greater (−24 g·m−2·yr−1·cm−1). We conclude that the subsidy–stress hypothesis does not adequately describe patterns of NPP across Southeastern U.S. floodplain forests. Conditions of periodic flooding and flowing water do not often lead to high rates of productivity compared with upland forests. However, extensive flooding is nearly always a significant stress on forest productivity, particularly when the flooding regime has been recently perturbed through levee construction or impoundment. Our data support a more complex interaction between subsidy and stress factors.

Site fertility and leaf nutrients of sympatric evergreen and deciduous species of Quercus in central coastal California

Leaf and soil nutrient levels interact with and may each influence the other. We hypothesize that to the extent soil fertility influences the nutritional state of trees, soil fertility should correlate with summer leaf nutrient levels, whereas to the extent that trees influence soil nutrient levels, the quality of leaf litterfall should correlate with soil fertility. We examined these correlations for five sympatric oak species (genus Quercus) in central coastal California. Soil fertility, including both nitrogen and especially phosphorus, correlated significantly with summer leaf nutrient levels. In contrast, phosphorus, but not nitrogen, in the leaf litterfall correlated positively with soil nutrients. These results suggest that soil nitrogen and phosphorus influence tree nutrient levels and that leaf phosphorus, but not leaf nitrogen, influence soil fertility under the trees. Feedback between the soil and the tree for phosphorus, but not nitrogen, is apparently significant and caused by species-specific differences in leaf quality and not by litterfall quality differences within a species. We also compared functional differences between the evergreen and deciduous oak species at our study site. There were no differences in soil nitrogen and only small differences for soil phosphorus between the phenological types. Differences in leaf nutrient concentration were much more pronounced, with the evergreen species having substantially lower levels of both nitrogen and phosphorus. Evergreen species conserved more phosphorus, but not more nitrogen, than the deciduous species, but there was no consistent relationship between retranslocation and either soil nitrogen or phosphorus. These results do not support the hypothesis that evergreenness is an adaptation to low soil fertility in this system.

Leaf litterfall, leaf area index, and radiation transmittance in cypress wetlands and slash pine plantations in north-central Florida

The seasonal dynamics of leaf litterfall and leaf area index (LAI, all-sided basis), light penetration and the vertical distribution of surface area index, and the feasibility of estimating LAI from radiation transmittance were studied from April 1993 to March 1994 in the canopies of three cypress (Taxodium ascendens) wetlands and their surrounding slash pine (Pinus elliottii) uplands in Florida flatwoods. Annual leaf litterfall ranged from 324 to 359 g m−2 in the wetlands, which was very close to the average for 11 sites throughout Florida of 340±26 g m−2. The seasonal pattern of the normalized LAI obtained for the dominant tree species in the ecosystems could be used to construct the seasonal dynamics of LAI at the ecosystem scale. The vertical distribution of surface area index in the wetlands was significantly different from that in the surrounding pine uplands. The maximum LAI of cypress wetlands in this area was about 8 m2 m−2, which was higher than the maximum of slash pine plantations of 6 m2 m−2. Cypress leaves were strongly erectophile in space. Results showed that the LAI-2000 canopy analyzer could generally be used to estimate forest LAI, whether the forest canopy was closed or not, if an overall clumping index of 2.00 was applied. However, as LAI decreased, the relative error contained in the radiation-based LAI estimates increased. This indicated that foliage clumping at the stand scale was more important than that at the tree or branch scale.

Substrate limitations for heterotrophs: Implications for models that estimate the seasonal cycle of atmospheric CO2

We examine the sensitivity of the seasonal cycle of heterotrophic respiration to model estimates of litterfall seasonality, herbivory, plant allocation, tissue chemistry, and land use. As a part of this analysis, we compare heterotrophic respiration models based solely on temperature and soil moisture controls (zero‐order models) with models that depend on available substrate as well (first‐order models). As indicators of regional and global CO2 exchange, we use maps of monthly global net ecosystem production, growing season net flux (GSNF), and simulated atmospheric CO2 concentrations from an atmospheric tracer transport model. In one first‐order model, CASA, variations on the representation of the seasonal flow of organic matter from plants to heterotrophs can increase global GSNF as much as 60% (5.7 Pg C yr−1) above estimates obtained from a zero‐order model. Under a new first‐order scheme that includes separate seasonal dynamics for leaf litterfall, fine root mortality, coarse woody debris, and herbivory, we observe an increase in GSNF of 8% (0.7 Pg C yr−1) over that predicted by the zero‐order model. The increase in seasonality of CO2 exchange in first‐order models reflects the dynamics of labile litter fractions; specifically, the rapid decomposition of a pulse of labile leaf and fine root litter that enters the heterotrophic community primarily from the middle to the end of the growing season shifts respiration outside the growing season. From the perspective of a first‐order model, we then explore the consequences of land use change and winter temperature anomalies on the amplitude of the seasonal cycle of atmospheric CO2. Agricultural practices that accelerate decomposition may drive a long‐term increase in the amplitude, independent of human impacts on plant production. Consideration of first‐order litter decomposition dynamics may also help explain year‐to‐year variation in the amplitude.

A spatially explicit model of leaf litter fall in hemlock–hardwood forests

A spatially explicit model of leaf litter fall was developed for hemlock–hardwood forests using litter-trap data from mapped forest plots and from isolated trees. The model assumes that litter declines exponentially with distance, as shown by the litter traps from isolated trees, and that a variable allometric equation describes the relationship of DBH to foliage biomass. Model parameters were estimated by a maximum likelihood method using field data from one mapped plot and then tested on a second plot. Predicted leaf fall of sugar maple (Acersaccharum Marsh.), yellow birch (Betulaalleghaniensis Britton), basswood (Tiliaamericana L.), and eastern hemlock (Tsugacanadensis (L.) Carrière) was consistent with the leaf fall measured in 20 traps (r = 0.86, 0.77, 0.95, 0.92, respectively). Data from 100 paired litter traps show the similarity of litter fall at sites 2.7 m apart; trap contents in two successive autumns were also comparable. The model results show that hemlock has the narrowest leaf-fall shadow, while basswood has the broadest. The average radius within which 90% of the leaf litter fall to a trap originates is 17.1 m. A litter fall model can be used to predict nutrient inputs to the forest floor based on a stem map, and strengthens links between population and ecosystem ecology.

Leaf litter decomposition and mulch performance from mixed and monospecific plantations of native tree species in Costa Rica

An experiment with native trees was established in 1991 on degraded pasture in the Atlantic lowlands of Costa Rica to examine the influence of mixed and monospecific plantation designs on tree growth and nutrient cycling. As part of this study, leaf litter decomposition rates and mulch performance were compared among four native tree species, Callophylum brasiliense Cambess, Jacaranda copaia (Aubl.) D. Don, Vochysia guatemalensis J.D. Smith, and Strypnodendron microstachyum Poepp. et Endl. Leaf litter of V. guatemalensis, J. copaia and the mixed plantation decomposed the fastest, with less than 16% of the initial weight remaining at 12 months. C. brasiliense had the slowest decomposition rate with 23% of the leaf litter remaining at 12 months. V. guatemalensis had the greatest amount of annual leaf litter fall and accumulation. J. copaia showed high levels of annual litter fall but fluctuating forest-floor litter accumulation, and the mixture showed intermediate patterns of annual leaf litter fall and accumulation. All mulch treatments improved maize seedling performance in comparison with unmulched controls. S. microstachyum mulch was found to have the most beneficial effect on initial maize seedling height growth and N uptake. Recommendations are drawn from the results to suggest potential uses of these species in forestry and agroforestry systems.

Temporal patterns of soil nutrients in a Panamanian moist forest revealed by ion-exchange resin and experimental irrigation

The effect of seasonal water availability on soil nutrients and soil N transformations was investigated by irrigating two large plots of mature tropical forest on Barro Colorado Island (BCI), Panama, during the dry season for five consecutive years. Methods included (i) nutrient accumulation by ion-exchange resins placed on the surface of the mineral soil for contiguous 21-day periods, (ii) monthly mineral soil (0–10 cm) extractions and incubations for inorganic N and P concentrations, and (iii) leaching loss of nutrients from leaf litter samples. Rates of nutrient accumulation by the resins showed a great deal of variation between sampling dates and among years in control plots; albeit, seasonal patterns were slight, except for the highest Ca values near the end of the wet season and inorganic P (Pi) and SO4 values that peaked during the dry season. Irrigation had remarkably little effect on nutrient accumulation rates by resins, except for an increase in Mg and Na values, but did affect the timing in the temporal variation in K, Na, Ni and Pi values. In contrast, inorganic N (Ni) and Pi pools and N transformation rates in the mineral soil hardly varied among sampling dates and did not show any response to irrigation. We hypothesize that the timing of leaf litterfall and nutrient leaching from forest floor litter can set up temporal patterns in the levels of soil nutrient at the surface of the mineral soil, but the temporal patterns essentially disappear with depth in the mineral soil.

Fine litter input to terrestrial humus forms in Colombian Amazonia.

A comparative litter fall study was made in five rain forest stands along a gradient of humus form development and soils in the Amazon lowlands of eastern Colombia. The total fine litter fall was highest in a plot on a well drained soil of the flood plain of the Caquetá River (1.07 kg · m-2 · y-1), lower in three plots on well drained upland soils (0.86, 0.69, and 0.68 kg · m-2 · y-1), and lowest in a plot on a poorly drained, upland podzolised soil (0.62 kg · m-2 · y-1). In the four upland plots, leaf litter fall patterns were highly associated, which points at climatic regulation. Litter resource quality, as represented by nutrient concentrations and area/weight ratio of the leaf litter fall, was comparatively high in the flood plain plot. In the upland plots, concentrations and fluxes of Ca, Mg, K, and P were as low as in oligotrophic central Amazonian upland forests. This questions generalisations that the western peripheral region of the Amazon basin should be less oligotrophic than central Amazonia. The upland plot on the podzolised soil showed the lowest concentrations and fluxes of N. Mean residence times of organic matter and nutrients in the L horizons hardly differed between the five plots, suggesting that edaphic properties and litter resource quality are of little importance in the first step of decomposition. Mean residence time of organic matter in all ectorganic horizons combined (estimated on the basis of litter input and necromass on the forest floor, and uncorrected for dead fine root input) varied from 1.0 y in the flood plain forest, 1.1-3.3 y in the well drained upland forests, and 10.2 y in the forest on the podzolised soil.

Biomass and litterfall of Ceriops tagal and Rhizophora mucronata in the mangrove forest of Gazi Bay, Kenya

Biomass and (leaf) litter production of stands of Rhizophora mucronata and Ceriops tagal were assessed in an East African mangrove forest. Inundation frequency of the R. mucronata stand was twice a day (on average 575 min day-1), whereas the C. tagal stand was inundated only during spring tides (on average 116 min day-1). The highest above-ground biomass (24.9 � 4.0 kg dry weight m&lt;.-2) was present in the R. mucronata stand, in which leaf litter production was 2.51 � 1.15 g DW mw2 day-1. Above-ground biomass and leaf litterfall in the C. tagal stand were 4.01 � 0.34 kg DW m-2 and 1.05 � 0.49 g DW m-2 day-1, respectively. There was a distinct seasonal pattern in litterfall in both stands, with lower litterfall values in the wet season. Chloride concentrations were relatively high in senescent leaves, compared with those in green leaves. The decreased litterfall during the wet periods may be related to a reduced accumulation of chloride in the leaves. The difference in inundation frequency between the R. mucronata and C. tagal stands is expected to cause a more substantial tidal export of fallen leaves from the R. mucronata stand. As nitrogen resorption before defoliation was similar for C. tagal (50.9%) and R. mucronata (50.1%), tidal flushing may cause larger nitrogen losses from the R. mucronata stand.

Spatial and temporal variation in litter fall of Avicennia marina (Forssk.) Vierh. in the Brisbane River, Queensland, Australia

Leaf, woody and reproductive litter fall in a sub-tropical stand of Avicennia marina (Forssk.) Vierh. was measured monthly, along four transects (two in mature forest, two in regrowth) at three tidal inundation levels, for 2 years to investigate the spatial patterns of litter fall in relation to position on the shore and vegetation maturity. Litter fall in 1992/1993 was 831.3 g dry weight (DW) m −2 year −1 and in 1993/1994, 921.7 g DW m −2 year −1. Over the 2 year period, leaf litter fall accounted for 47% of total litter fall, reproductive litter 30% and woody litter 23%. Leaf fall was seasonal with a maximum in the wet summer season; wood fall was aseasonal but positively correlated with periods of high wind. Reproduction was biennial with fruit fall in the dry winter season. Litter fall was consistently higher at the mid tidal level and decreased up- and down-shore from this point. Rates of litter fall were independent of the maturity of the stand and tree density but organic cycling was much slower in the mature forest. Larger trees produced more fruit, but fruit production per unit of tree biomass was greater in smaller trees.

Litter dynamics of recently harvested and mature bamboo savannas in a dry tropical region in India

ABSTRACTAnalysis of litterfall, nutrient return and floor mass dynamics was made in mature and recently harvested bamboo savanna sites in a dry tropical region in India. The total annual litterfall was 590 and 267 g m–2 in mature and harvested sites, respectively. Of the total litterfall, 58–77% by weight was contributed by leaf litter. Although litterfall occurred throughout the year, as much as 72–83% of the leaf litterfall was recorded during winter (December–February). Seasonal distribution of total litterfall was: rainy 12–22% of annual, winter 64–65% and summer 13–22%. Nutrient concentrations in bamboo leaf litter were low compared with the other species growing in the same region. Annual nutrient return through litterfall amounted to: 28–49 kg N ha–1, 1.32.9 kg P ha–1, 33–85 kg Ca ha–1, 12–32 kg K ha–1 and 1.4–2.8 kg Na ha–1. While maximum accumulations of fresh litter on the ground occurred in summer, the partly decayed and particulate litter categories peaked in the rainy season. Decaying litter categories showed 1.5–3 times greater nutrient concentrations than the concentrations in fresh leaf litter. Marked immobilization of N and P occurred in decomposing leaf and particulate litter. The mean annual nutrient content of the floor was (kg ha–1): N 29–40, P 1.0–1.9, Ca 13.8–23.9, K 14.6–15.3 and Na 0.85–0.99. The annual turnover in litter layer was: 63–81% for dry mass and 64–90% for different nutrients.

Phosphorus limitation of forest leaf area and net primary production on a highly weathered soil

We tested the hypothesis that P was the nutrient limiting net primary production of a nativeMetrosideros polymorpha forest on a highly weathered montane tropical soil in Hawaii. A factorial experiment used all combinations of three fertilizer treatments: nitrogen (N), phosphorus (P) and a mix of other essential nutrients (OE), consisting primarily of mineral derived cations and excluding N and P. P addition, but not N or OE, increased leaf area index within 12 months, foliar P concentration measured at 18 months, and stem diameter increment within 18 months. Stem growth at 18 months was even greater when trees fertilized with P also received the OE treatment. N and P additions increased leaf litterfall and N and P in combination further increased litterfall. The sequence of responses suggests that increased available P promoted an increase in photosynthetic area which led to increased wood production. P was the essential element most limiting to primary production on old volcanic soil in contrast to the N limitation found on young volcanic soils.

The biogeochemical cycling of Hg in forests: Alternative methods for quantifying total deposition and soil emission

A biogeochemical cycling approach to the Hg cycle is explored using existing data from the literature in order to begin to identify important processes that might be studied in detail and extrapolated to a regional scale. If it is assumed that all foliar Hg is taken up from the atmosphere, then estimates of total Hg deposition are rather easily made from measurements of leaf litterfall and throughfall. This assumption needs absolute verification before such an extrapolation can be made, however, because litterfall is a major Hg flux to the forest floor. Hg0 evolution from soils can be an important process and needs to be measured in more ecosystems. The diffusion model for soil gaseous efflux may be useful in this regard and deserves testing. There is a critical need for a systematic analysis of Hg cycles using common protocols so as to minimize artifacts associated with sampling methodology (i.e., soil Hg efflux). This should be done in several soil and forest types, given the high degree to which Hg transformations in and emissions from soils are dependent upon soil organic matter content, redox potential, and temperature.

Litterfall and Nutrient Cycling in Four Rain Forests in the Sringeri Area of the Indian Western Ghats

Small litterfall was collected at monthly intervals for 3 years from traps in two evergreen lowland rain forests, a lower montane (shola) forest, and a moist deciduous forest in the Western Ghats of Karnataka, India. The range of the mean annual total small litterfall (in t ha' yr1) was 1 1.6-13.9 and that for leaf litterfall was 8.4-10.6 t ha' yrI. The lowest values were for the moist deciduous forest and the highest for the lower montane forest. In all cases there was a seasonality of the litterfall with high weights during the dry season. The chemical composition of the litterfall showed generally high concentrations, which did not differ greatly between plots, and which reflected the similarly high soil nutrient status in all the plots. The moist deciduous forest had the highest leaf litterfall concentrations of phosphorus, potassium and calcium and the least of nitrogen. The small litterfall mass is much higher than that reported earlier for forests in nearby areas of the Ghats by Rai & Proctor (1986b) and the differences from the present study are not easy to explain.

Topographic Variation of Soil Nitrogen Dynamics at Walker Branch Watershed, Tennessee

Abstract Understanding the spatial and temporal variability of soil nitrogen (N) transformations is central to quantifying the N dynamics and productivity of ecosystems. The objectives of this work were to examine spatial and temporal variation of soil N dynamics and to identify factors correlated with topographic variation in soil N dynamics in a forest watershed. Net N mineralization and net nitrification potential were measured by aerobic laboratory incubations of surface (0-7 cm) mineral soils. Principal components analysis was used to describe sampling sites across the watershed based on 13 site characterization variables. A topographic index used in hydrologic modeling, In (α/tan β), was calculated for each site as the natural logarithm of the ratio of the upslope drainage area per unit contour length (α) to the local slope angle (tan β). Soils from valley floors had greater total N concentrations, lower carbon-to-nitrogen (C:N) ratios, greater potential net nitrification, and greater microbial activity (as indicated by short-term urease assays) than soils from ridges. Mean net nitrification potential was 0.59 μg N g-1 d-1 in surface soils from valley floors and was &amp;lt; 0.01 on ridges and slopes. The first principal component was related to the N and C properties of soils, leaf litter, and leaf fall at a site. The second principal component was related to forest stand composition. The topographic index was significantly correlated with important variables related to soil N dynamics. Once calibration data are derived, this index may be useful as a first approximation to total soil N concentrations and soil C:N ratios in forest watersheds because In (α/tan β) can be calculated from geographic information systems that contain topographic data. For. Sci. 40(3):497-512.

Litterfall and seasonal patterns of nutrient accumulation in Dactyladenia barteria (Hook f ex. Oliv.) Engl. bush fallow at Ozala, Nigeria

Litterfall and seasonal pattern of nutrient accretions of Dactyladenia barteria, a bush fallow species, were studied at Ozala, Nigeria for 52 weeks (26 May 1985 to 24 May 1986). Total litterfall was continuous throughout the year, with a peak from December to May, corresponding to the dry and early rainy season. The dry season (November–March) had 65.5% of the total leaf litterfall. The mean total litterfall of the leaf, flower/fruit and twig litter component was 977.2±6.7 g m −2. Litterfall correlated positively with maximum air temperature but negatively with rainfall. Except for K, there were no significant seasonal variations in the mean concentrations of N, P, Na, Ca, Mg, organic C and C:N ratios in the D. barteria leaf litter. The contributions of each litter part to the total nutrient input at Ozala in order of magnitude were as follows: leaf, flower/fruit, twig litter. The study stresses the great potentials of this species for alley cropping/farming.