Litterfall and nutrient dynamics in a montane moist evergreen broad-leaved forest in Ailao Mountains,SW China

Montane moist evergreen broad-leaved forest, dominated byLithocarpus and Castanopsis species,is the most extensive stand of subtropical mountain in Yunnan Province, SWChina. Litter production, standing crop of litter on forest floor and nutrientreturn patterns were studied over nine years (1991–1999) in a stand ofprimary evergreen broad-leaved forest in northern crest of the Ailao MountainRange. There were significant yearly variations in litter production, which ismainly related with the masting year of canopy species, and exceptionalphysicalevents (strong winds and snow) in the natural forest. The mean annual smalllitterfall is 7.12 t ha^–1 yr^–1ofwhich leaf litter account for 65% of the total litterfall. The seasonality ofsmall litterfall was bia-modal, with the main one in the late dry season(April–May) and a lesser one in early winter (October–November).Decomposition quotient value was relatively low with 0.58 for total smalllitterfall. Mean large-wood ( 2.5 cm in diameter) ranged from0.21 to 1.41 t ha^–1 yr^–1 with amean of 0.52 t ha^–1 yr^–1.Concentrations of most elements in leaf and twig were slightly greater in wetmonths than dry months, except for C and K. Woody litter had low N and Pconcentrations compared with the leaf and reproductive parts. Nutrient returntothe soil through small litterfall decrease in the orderC>N>Ca>K>Mg>Mn>Al>P>Fe, while nutrient reserve inlitteron the forest floor was in the declining sequenceC>N>Ca>K>Mg>P>Fe>Al>Mn.     

Effect of typhoon disturbance on fine litterfall and related nutrient input in a subtropical forest on Okinawa Island, Japan

Typhoons are frequent on Okinawa Island, southwestern Japan. The effects of typhoon disturbance on the patterns of fine litterfall and related nutrient inputs in a subtropical evergreen broad-leaved forest were studied over 5 years from May 1996 to April 2001. Annual fine litterfall averaged 7558 kg ha⁻¹ (range from 6188 to 9439 kg ha⁻¹) for six sampling plots over 5 years, which differed significantly among years (p<0.001) but not among plots (p=0.122). A seasonal maximum was most evident for leaf litter component. Woody litter fell more irregularly through the year, and peak fall varied with typhoon and windstorm. The mean ratio of annual litterfall mass of sexual organs to leaves was 0.06, much lower than that in other tropical and subtropical rain forests. Nutrient concentrations varied in litterfall components, but were not significantly different among plots. The lowest concentrations of N and P in leaf litter were observed in March, which is also the month with the greatest leaf fall. However, the highest concentrations were recorded in typhoon season. Nitrogen and P concentrations were 34% and 106% greater in the green leaves that fell during typhoons than in senescent leaves. Mean nutrient inputs by litterfall were: N 83, P 3.2, K 25, Ca 71, Mg 19, Al 12, Na 10, Fe 0.86 and Mn 3.9 kg ha⁻¹ yr⁻¹, and differed significantly among years for all elements (p<0.0005) and among plots only for K (p<0.05) and Mn (p<0.0001). Typhoon disturbance strongly affected annual fine litterfall and related nutrient inputs, which contributed an average of 30% of the annual litterfall mass, and from 30% to 39% (for different nutrient elements) of annual total nutrient inputs. The results from this study suggest that typhoon-driven maintenance of rapid cycling of P and N and their high availability in soil appears to be an important mechanism to maintain productivity in the subtropical forest on Okinawa Island.     

Foliar chemical concentrations in red alder stands of various ages

Summary Six stands of red alder (Alnus rubra Bong.) were sampled to assess the relationship between stand age and foliar chemical concentrations. The stands ranged in age from 9 to 45 years, and were located near Olympia, Washington, on sites of similar soil, aspect, and slope. Foliage was collected in July, and concentrations of most essential nutrients and aluminum were determined. Foliar concentrations of these elements varied among the different stands. Highest concentrations of N, P, Ca, S, Fe, and Al were found in trees of the youngest stand. Concentrations of N, P, S, and Fe were negatively correlated with stand age. The strongest correlation was obtained with P (r=–0.96,P<0.01), followed by N (r=–0.85,P=0.03). Results suggest that declining growth and deterioration of red alder stands with age may be related, at least in part, to limiting supplies of essential nutrients, especially P, N, and S.     

Leaf litter decomposition and nutrient dynamics in a subtropical forest after typhoon disturbance

Decomposition of typhoon-generated and normal leaf litter and their release patterns for eight nutrient elements were investigated over 3 yr using the litterbag technique in a subtropical evergreen broad-leaved forest on Okinawa Island, Japan. Two common tree species, Castanopsis sieboldii and Schima wallichii, representative of the vegetation and differing in their foliar traits, were selected. The elements analyzed were N, P, K, Ca, Mg, Na, Al, Fe and Mn. Dry mass loss at the end of study varied in the order: typhoon green leaves > typhoon yellow leaves > normal leaves falling for both species. For the same litter type, Schima decomposed faster than Castanopsis. Dry mass remaining after 2 yr of decomposition was positively correlated with initial C:N and C:P ratios. There was a wide range in patterns of nutrient concentration, from a net accumulation to a rapid loss in decomposition. Leaf litter generated by typhoons decomposed more rapidly than did the normal litter, with rapid losses for N and P. Analysis of initial quality for the different litter types showed that the C:P ratios were extremely high (range 896 – 2467) but the P:N ratios were < 0.05 (range 0.02 – 0.04), indicating a likely P-limitation for this forest. On average 32% less N and 60% less P was retranslocated from the typhoon-generated green leaves than from the normal litter for the two species, Castanopsis and Schima. An estimated 2.13 g m^–2 yr^–1 more N and 0.07 g m^–2 yr^–1 more P was transferred to the soil as result of typhoon disturbances, which were as high as 52% of N and 74% of P inputted from leaf litter annually in a normal year. Typhoon-driven maintenance of rapid P cycling appears to be an important mechanism by which growth of this Okinawan subtropical forest is maintained.     

Biomass and litter dynamics in a Melaleuca forest on a seasonally inundated floodplain in tropical,northern Australia

Litterfall from a Melaleuca forest was investigated as part of chemical cycling studies on the Magela Creek floodplain in tropical, northern Australia. The forest contained two species of tree, Melaleuca cajaputi and Melaleuca viridiflora, with a combined average density of 294 trees ha^–1. The M. viridiflora trees had diameter breast height measurements ranging from 11.8 to 62.0 cm, median class 25.1–30.0cm and a mean value of 29.2±1.0 cm, compared to 13.0 to 66.3 cm, 30.1–35.0cm and 33.5±1.0cm for M. cajaputi trees. A regression model between tree height, diameter breast height and fresh weight was determined and used to calculate average tree weights of 775±1.6kg for M. viridiflora and 1009±1.6kg for M. cajaputi, and a total above-ground fresh weight of 263±0.3t ha^–1. The weight of litter recorded each month on the ground beneath the tree canopy ranged from 582±103 to 2176±376 g m^–2 with a monthly mean value of 1105±51 g m^–2. The coefficient of variation of 52% on this mean indicates the large spatial and temporal variability in litter distribution over the study site. This variability was greatly affected by the pattern of water flow and litter transport during the Wet season. Litterfall from the trees was evaluated using two techniques - nets and trays. The results from these techniques were not significantly different with annual litterfall collected in the nets being 705 ± 25 g m^–2 and in the trays 716±49 g m^–2. The maximum monthly amount of litterfall, 108 ±55g m^–2, occurred during the Dry season months of June–July. Leaf material comprised 70% of the total annual weight of litter, 480±29 g m^–2 in the nets and 495 ± 21 g m^–2 in the trays. The tree density and weight of litter suggest that the Melaleuca forests are highly productive and contribute a large amount of material to the detrital/debris turnover cycle on the floodplain.     

Chemical composition of soil solutions extracted from New Zealand beech forests and West German beech and spruce forests

Concentrations of ions were measured in soil solutions from beech (Nothofagus) forests in remote areas of New Zealand and in solutions from beech (Fagus sylvatica) and Norway spruce (Picea abies) forests in North-East Bavaria, West Germany, to compare the chemistry of soil solutions which are unaffected by acid deposition (New Zealand) with those that are affected (West Germany). In New Zealand, soil solution SO₄ ^2– concentrations ranged between <2 and 58 mol L^–1, and NO₃ ^– concentrations ranged between <1 and 3 mol L^–1. In West Germany, SO₄ ^2– concentrations ranged between 80 and 700 mol L^–1, and NO₃ ^– concentrations at three of six sites ranged between 39 and 3750 mol L^–1, but was not detected at the remaining three sites. At all sites in New Zealand, and at sites where the soil base status was moderately high in West Germany, pH levels increased, and total Al (Al_t) and inorganic monomeric Al (Al_i) levels decreased rapidly with increasing soil depth. In contrast, at sites on soils of low base status in West Germany, pH levels increased only slightly, and Al levels did not decline with increasing soil depth.Under a high-elevation Norway spruce stand showing severe Mg deficiency and dieback symptoms in West Germany, soil solution Mg²⁺ levels ranged between 20 and 60 mol L^–, and were only half those under a healthy stand. Al_t and Al_i levels were substantially higher the healthy stand than under the unhealthy stand, indicating that Al toxicity was not the main cause of spruce decline.     

The influence of a neotropical herbivore (<Emphasis Type="Italic">Lamponius portoricensis</Emphasis>) on nutrient cycling and soil processes

The role of phytophagous insects in ecosystem nutrient cycling remains poorly understood. By altering the flow of litterfall nutrients from the canopy to the forest floor, herbivores may influence key ecosystem processes. We manipulated levels of herbivory in a lower montane tropical rainforest of Puerto Rico using the common herbivore, Lamponius portoricensis (Phasmatidea), on a prevalent understory plant, Piper glabrescens (Piperaceae), and measured the effects on nutrient input to the forest floor and on rates of litter decomposition. Four treatment levels of herbivory generated a full range of leaf area removal, from plants experiencing no herbivory to plants that were completely defoliated (>4,000 cm² leaf area removed during the 76-day study duration). A significant (P<0.05) positive regression was found between all measures of herbivory (total leaf area removed, greenfall production, and frass-related inputs) and the concentration of NO ₃ ⁻ in ion exchange resin bags located in the litter layer. No significant relationship was found between any of the herbivory components and resin bag concentrations of NH ₄ ⁺ or PO ₄ ⁻ . Rates of litter decay were significantly affected by frass-related herbivore inputs. A marginally significant negative relationship was also found between the litter mass remaining at 47 days and total leaf area removed. This study demonstrated a modest, but direct relationship between herbivory and both litter decomposition and NO ₃ ⁻ transfer to the forest floor. These results suggest that insect herbivores can influence forest floor nutrient dynamics and thus merit further consideration in discussions on ecosystem nutrient dynamics.     

Litter production, leaf litter decomposition and nutrient return in Cunninghamia lanceolata plantations in south China: effect of planting conifers with broadleaved species

This study compared litter production, litter decomposition and nutrient return in pure and mixed species plantations. Dry weight and N, P, K, Ca, Mg quantities in the litterfall were measured in one pure Cunninghamia lanceolata plantation (PC) and two mixed-species plantations of C. lanceolata with Alnus cremastogyne (MCA) and Kalopanax septemlobus (MCK) in subtropical China. Covering 6 years of observations, mean annual litter production of MCA (4.97 Mg·ha⁻¹) and MCK (3.97 Mg·ha⁻¹) was significantly higher than that of PC (3.46 Mg·ha⁻¹). Broadleaved trees contributed 42% of the total litter production in MCA and 31% in MCK. Introduction of broadleaved tree species had no significant effect on litterfall pattern. Total litterfall was greatest in the dry season from November to March. Nutrient returns to the forest floor through leaf litter were significantly higher in both MCA and MCK than in PC (P < 0.05). The amounts of N, K, and Mg returned to the forest floor through leaf litter were highest in the MCA, and P and Ca returns were highest in the MCK. Percent contribution of broadleaf litter to total nutrient returns ranged from 41.7% to 86.9% in MCA and from 49.3% to 74.8% in MCK. The decomposition rate of individual leaf litter increased in the order: C. lanceolata < K. septemlobus < A. cremastogyne. Litter mixing had a positive effect on decomposition rate of the more recalcitrant litter and promoted nutrient return. Relative to mass loss of A. cremastogyne decomposing alone, higher mass loss of the mixture of C. lanceolata and A. cremastogyne was observed after 330 days of decomposition. These results indicate that mixed plantations of different tree species have advantages over monospecific plantations with regards to nutrient fluxes and these advantages have relevance to restoration of degraded sites. Responsible Editor: Alfonso Escudero.     

Nutrient return with leaf litter fall in Fagus sylvatica forests across a soil fertility gradient

Leaf litter fall is an important nutrient flux in temperature deciduous forests which supplies a large part of the rapidly mineralisable nutrient fraction to the soil. This study investigates nutrient return with leaf litter fall in 36 old-growth forest stands of Fagus sylvatica across a broad gradient of soil fertility covering 9 mesozoic and kaenozoic parent material types (three limestones, two sandstones, two clay stones, one sand and one loess substrate). Study objectives were to analyse (i) the dependency of leaf litter nutrient concentrations on soil fertility, and (ii) the relationship between soil fertility and nutrient return with leaf litter at the stand level. Beech stands on the nine parent material types produced similar annual leaf litter masses irrespective of soil fertility or acidity. Leaf litter from the nine parent materials showed only minor variation with respect to N and K concentrations (factors of 1.5 and 1.4), moderate variation for Ca, Mg and P concentrations (factors of 2.2 to 2.9), and high variation for Al and Mn concentrations (factors of 6.7 and 10.5). Consequently, annual nutrient return with litter fall (leaf litter mass x litter nutrient concentration) was more similar among the parent materials for N (165–273 mmol m⁻² yr1) ⁻¹ and K (16–30 mm m⁻² yr⁻¹) than for Ca, P, Mg, Mn and Al. A possible explanation is increased N deposition in recent time. According to a correlation analysis, return rates of N, P, K and Mg (but not Ca) were independent of the pool size of the respective nutrient in the soil. N return rate was neither influenced by the soil pools of Nt, plant- available P (Pa) or exchangeable Ca, K and Mg, nor by soil acidity or the exchangeable Al pool. P return, in contrast, showed a negative relation to soil fertility. We hypothesize that nutrient fluxes with leaf litter fall do not necessarily reduce the fitness of tree populations as has been postulated from a tree-centred view. Rather, we suggest that nutrient fluxes with litter fall can increase, instead of decrease, plant fitness by improving nutrient availability in the densely rooted topsoil which reduces the roots’ carbon and nutrient costs of nutrient acquisition.     

Nutrient transfer by leaf litterfall during a sugar maple decline episode at Lake Clair watershed,Québec,Canada

In a declining sugar maple (SM) stand, we tested the hypothesis that an increasing relative abundance of American beech (AB) and yellow birch (YB) would improve litter quality by providing a higher proportion of litterfall richer in base cations and lower in acidity. From 1989 to 2006, SM leaf fall diminished from 59% (1,718 kg ha⁻¹ year⁻¹) to 36% (915 kg ha⁻¹ year⁻¹) of the total leaf fall biomass. Overall, the increase in AB and YB litterfall compensated for the SM decrease, resulting in constant annual leaf litterfall fluxes (2,803 kg ha⁻¹ year⁻¹) over the period studied. However, because the leaf litter for AB and YB had Ca and Mg concentrations 2–3 times higher than did SM, Ca and Mg concentrations and fluxes in leaf litterfall significantly increased between 1989 and 2006. Leaf litterfall of AB and YB also has a higher base/acid ratio than SM. Consequently, changes in forest composition following SM decline led to a clear improvement in litterfall quality in terms of base cations content and fluxes and acid–base properties.     

Mangrove litter dynamics in La Mancha Lagoon,Veracruz, Mexico

In the mangrove surrounding the coastal lagoon of La Mancha, Veracruz, Mexico, we studied litter fall, litter standing crop, and turnover rates in four different mangrove settings, based on the ecological classification of Lugo and Snedaker (1974). We studied those three prominent ecological processes at the basin, fringe and riverine mangrove settings, being the last one a relict riverine stand. The aim was to describe and compare litter dynamics among mangrove types in a lagoon with an ephemeral inlet, as a way of understanding functional heterogeneity within this coastal ecosystem. The daily average values of litter fall were different (P < 0.01) among mangrove site basin I, formed by Avicennia germinans and Rhizophora mangle (2.35 g/m²/day); basin II, formed by Laguncularia racemosa, Avicennia germinans, and Rhizophora mangle (2.93 g/m²/day); fringe with Rhizophora mangle (2.13 g/m²/day); and relic riverine, also with R. mangle (4.70 g/m²/day). The amount of litter standing crop was different among sites (P < 0.001), and also between the dry and rainy season, for each mangrove type (P < 0.001). Turnover ratios were higher in basin I and basin II sites (6.34 and 7.44 times per year) than in relic riverine and fringe mangroves (1.49 and 2.39 times per year). Interstitial salinity and sediment nutrients varied among mangrove types and could influence litter production. Since this lagoon has an ephemeral inlet, continuous inundation throughout 7–8 months per year has an important effect on litter dynamics.     

Chemical soil properties under five age series ofAlnus nepalensis plantations in the Eastern Himalayas

Summary Five age series stands ofAlnus nepalensis D. Don monocultures have been selected from the Pankhasari range of the Kalimpong forest division in the Eastern Himalayas. Chemical soil propeties such as organic carbon, total nitrogen, CN ratio, available phosphorus and exchangeable cations (Ca⁺², K⁺ and Na⁺) were analysed in all these different ages of plantation stands from the surface to 1 m deep profiles to find out the long term effect ofA. nepalensis on the soil quality of these erosion vulnerable slopes.Organic carbon, available phosphorus and total nitrogen content per-hectare increased with increasing plantation stand age. Analysis of variance for nutrients showed significant variation in depth (total nitrogenP<0.001; organic carbon,P<0.001; available phosphorus,P<0.05; exchangeable Ca⁺²,P<0.01; and exchangeable K⁺,P<0.01) and between plantation stands (organic carbon,P<0.05; and available phosphorusP<0.05). High value of total nitrogen content (34.97t ha^–1) was obtained in 46 yr old stand. Soil pH is low. It increased down the depth and in older plantations. These stands with high soil total nitrogen and organic carbon content show increased fertility of the stands. The cover ofA. nepalensis in rocky, landslide and ecosion prone slopes of the Eastern Himalayas, serves to protect and improve soil quality.     

Influence of stand density on soil CO2 efflux for a Pinus densiflora forest in Korea

We investigated the influence of stand density [938 tree ha⁻¹ for high stand density (HD), 600 tree ha⁻¹ for medium stand density (MD), and 375 tree ha⁻¹ for low stand density (LD)] on soil CO₂ efflux (R _S) in a 70-year-old natural Pinus densiflora S. et Z. forest in central Korea. Concurrent with R _S measurements, we measured litterfall, total belowground carbon allocation (TBCA), leaf area index (LAI), soil temperature (ST), soil water content (SWC), and soil nitrogen (N) concentration over a 2-year period. The R _S (t C ha⁻¹ year⁻¹) and leaf litterfall (t C ha⁻¹ year⁻¹) values varied with stand density: 6.21 and 2.03 for HD, 7.45 and 2.37 for MD, and 6.96 and 2.23 for LD, respectively. In addition, R _S was correlated with ST (R ² = 0.77–0.80, P < 0.001) and SWC (R ² = 0.31–0.35, P < 0.001). It appeared that stand density influenced R _S via changes in leaf litterfall, LAI and SWC. Leaf litterfall (R ² = 0.71), TBCA (R ² = 0.64–0.87), and total soil N contents in 2007 (R ² = 0.94) explained a significant amount of the variance in R _S (P < 0.01). The current study showed that stand density is one of the key factors influencing R _S due to the changing biophysical and environmental factors in P. densiflora.     

Biogeochemical consequences of the transformation of native Cerrado into Pinus caribaea plantations in Brazil

Under the same climatic and edaphic conditions, native savanna vegetation in Brazil, the Cerrado, shows a lower stature and canopy cover than planted Pinus caribaea Morelet forests. To assess the differences in biogeochemical element cycling we compared the nutrient economy of Cerrado and Pinus on three replicate plots of each forest type. The mean nutrient storage in the soil organic layer under Pinus (N: 2630; P: 141; K: 103; Ca: 131; Mg: 20 kg ha^–1) was substantially higher than under Cerrado (N: 23; P: 1.2; K: 0.83; Ca: 5.8; Mg: 1.0 kg ha^–1) probably because the Pinus roots explored a larger soil volume. The Pinus trees had a higher nutrient-use efficiency as indicated by higher mean litter mass per unit nutrient in litter (N: 108; P: 2290; K: 729; Ca: 1360; Mg: 5420; S: 1190; Fe: 2960; Mn: 9990, Zn: 145000) than the Cerrado trees (N: 94; P: 1810; K: 619; Ca: 302; Mg: 938, S: 746; Fe: 1800; Mn: 7880; Zn: 63700). Mean annual small litterfall collected in 0.25-m² samplers between May 1997 and April 1999 was 2.1 Mg ha^–1 in Cerrado and 7.8 in Pinus. The litterfall rates of the 1–3 week collection intervals correlated negatively with the soil matric potential indicating that litterfall was partly related to water stress. The fluxes of N (73 kg ha^–1 year^–1), P (3.7), K (11), S (7.0), and Mn (0.83) to the soil with litterfall under Pinus were greater than the litterfall+turnover of the grass/herbs layer under Cerrado (N: 39, P: 2.8, K: 8.6, S: 5.4, Mn: 0.79 kg ha^–1 year^–1), those of Zn (0.06–0.07) were similar, and those of Ca (Pinus: 5.9/Cerrado: 10), Mg (1.5/4.4), and Fe (2.9/4.0) were smaller. Mean residence times of the organic matter and of all elements were longer in the soil organic layer under Pinus (3.7–26 years in the Oi horizon, 8.1–907 years in the whole organic layer) than under Cerrado (0.22–3.6 years in the Oi horizon, the only organic horizon under Cerrado). Our results demonstrate that the main differences in biogeochemical element cycling between the Pinus forest and the Cerrado consisted of a larger nutrient storage in the organic layer, a higher nutrient-use efficiency, and slower nutrient release rates from the organic layer in the Pinus forest than in the Cerrado. Nutrient cycling as assessed by the nutrient fluxes with litterfall was only partly faster in the Pinus forest than in the Cerrado.     

The keystone role of leaf-removing crabs in mangrove forests of North Brazil

Principle factors which influence mangroveleaf litter turnover, in particular therole of leaf-removing crabs, were evaluatedin a riverine mangrove site nearBragança (Pará, North Brazil). Ourspecial interest was focussed on the roleof the leaf-removing crab Ucidescordatus. Leaf litter fluxes between themangrove forest and the adjacent estuarywere investigated by estimating the biomassand fate of leaf litter material and propagules. Vegetation is dominated by Rhizophora mangle, with Avicenniagerminans trees, both up to 25 m high,found intermittently. During 1997, Rhizophora trees produced around 1.40 gDW m^-2 d^-1 of leave fall and0.75 g DW m^-2 d^-1 of propagules.Leaf decomposition rates on the ground wereabout 0.06 g DW m^-2 d^-1,irrespective of species, habitat or siteexposure. This amount accounts for <3%of total leaf fall. Average leaf litterbiomass present on the ground was 0.01 gDW m^-2 d^-1. When the mangroveforest was flooded (on average 10 days permonth) the quantity of leaf litterand propagules washed out with the springtide was 10 and 17 times greater thanduring neap tide. Nevertheless, tidalexport and decomposition together made upless than 39 percent of annual leaf litterfall. The bulk of the remaining amount isapparently removed by Ucides. Eachcrab consumed about 1.30 g DW of leaflitter material and propagules per day.Since the average density of these crabswas 1.38 crabs m^-2, it is proposedthat Ucides is a keystone species inBragantinian mangroves.     

Utilisation of soil organic P by agroforestry and crop species in the field,western Kenya

A field experiment in western Kenya assessed whether the agroforestry species Tithonia diversifolia (Hemsley) A. Gray, Tephrosia vogelii Hook f., Crotalaria grahamiana Wight & Arn. and Sesbania sesban (L) Merill. had access to forms of soil P unavailable to maize, and the consequences of this for sustainable management of biomass transfer. The species were grown in rows at high planting density to ensure the soil under rows was thoroughly permeated by roots. Soil samples taken from beneath rows were compared to controls, which included a bulk soil monolith enclosed by iron sheets within the tithonia plot, continuous maize, and bare fallow plots. Three separate plant biomass samples and soil samples were taken at 6-month intervals, over a period of 18 months. The agroforestry species produced mainly leaf biomass in the first 6 months but stem growth dominated thereafter. Consequently, litterfall was greatest early in the experiment (0–6 months) and declined with continued growth. Soil pH increased by up to 1 unit (from pH 4.85) and available P increased by up to 38% (1 g P g^–1) in agroforestry plots where biomass was conserved on the field. In contrast, in plots where biomass was removed, P availability decreased by up to 15%. Coincident with the declines in litterfall, pH decreased by up to 0.26 pH units, plant available P decreased by between 0.27 and 0.72 g g^–1 and P_o concentration decreased by between 8 and 35 g g^–1 in the agroforestry plots. Declines in P_o were related to phosphatase activity (R²=0.65, P<0.05), which was greater under agroforestry species (0.40–0.50 nmol MUB s^–1 g^–1) than maize (0.28 nmol MUB s^–1 g^–1) or the bare fallow (0.25 nmol MUB s^–1 g^–1). Management of tithonia for biomass transfer, decreased available soil P by 0.70 g g^–1 and P_o by 22.82 g g^–1. In this study, tithonia acquired P_o that was unavailable to maize. However, it is apparent that continuous cutting and removal of biomass would lead to rapid depletion of P stored in organic forms.     

Spatial Variability in Litterfall,Litter Standing Crop and Litter Quality in a Tropical Rain Forest Region

Understanding the spatial variability in plant litter processes is essential for accurate comprehension of biogeochemical cycles and ecosystem function. We assessed spatial patterns in litter processes from local to regional scales, at sites throughout the wet tropical rain forests of northern Australia. We aimed to determine the controls (e.g., climate, soil, plant community composition) on annual litter standing crop, annual litterfall rate and in situ leaf litter decomposability. The level of spatial variance in these components, and leaf litter N, P, Ca, lignin, α‐cellulose and total phenolics, was determined from within the scale of subregion, to site (1 km transects) to local/plot (~30 m²). Overall, standing crop was modeled with litterfall and its chemical composition, in situ decomposability, soil Na, and topography (r² = 0.69, 36 plots). Litterfall was most closely aligned with plant species richness and stem density (negative correlation); leaf decomposability with leaf‐P and lignin, soil Na, and dry season moisture (r² = 0.89, 40 plots). The predominant scale of variability in litterfall rates was local (plot), while litter standing crop and α‐cellulose variability was more evenly distributed across spatial scales. Litter decomposability, N, P and phenolics were more aligned with subregional differences. Leaf litter C, lignin and Ca varied most at the site level, suggesting more local controls. We show that variability in litter quality and decomposability are more easily accounted for spatially than litterfall rates, which vary widely over short distances possibly in response to idiosyncratic patterns of disturbance.     

Heterogeneous dispersal of tree litterfall corresponding with patchy canopy structure in a temperate mixed forest

Spatial dispersal patterns of fine litter were analyzed in relation to forest structure within a temperate mixed stand, in northeastern Japan. The canopy layer was a mosaic of two types of patches, those of shade-tolerant Abies firma (estimated age being 81–146 yrs.) and early successional deciduous broad-leaved trees (about 45 yrs. of age). Litter input to the forest floor was observed for a period of three years using 38 traps set at a height of 1.2 m. The average annual total of fine litter was 6.233 (dw.) metric tons hectare^-1, 85.7% of the total litterfall. Fine litter was mostly leaves from the overstory (about 64%). Litter distribution maps were drawn, using the Davis's grid method, of the total fine litter and its two main elements, namely A. firma (a 36.1% share) and deciduous broad-leaved species (36.7%). The mosaic distribution of heterogeneous patches of litter was seem to corresponded with distribution of the canopy structure.     

Seasonal patterns of nutrient deposition in a Quercus douglasii woodland in central California

The monthly deposition of total nitrogen, phosphorus, potassium, calcium and magnesium via canopy throughfall, and various components of the litterfall was measured for 31 months under mature Quercus douglasii and in the bulk precipitation in the surrounding open grassland. Seasonal patterns of nutrient concentration in leaf litter, throughfall, and precipitation were also measured. Total annual subcanopy deposition exceeded open precipitation deposition by approximately 45–60x for nitrogen, 5–15x for phosphorus, 30–35x for potassium, 25–35x for calcium, and 5–10x for magnesium. Total annual subcanopy deposition was low in comparison to other oak woodland sites reported in the literature. Throughfall and leaf litter were the primary sources of nutrients and thus determined the seasonal peaks of nutrient deposition. The first autumn rains and leaf fall were associated with one peak in nutrient deposition, and throughfall during early spring leaf emergence was associated with a second peak in potassium, magnesium and phosphorus. Non-leaf plant litter (excluding acorns) provided approximately 15–35% of most nutrients, with twigs and bark depositing over 12% of the annual calcium flux in 1987–1988, and flower litter depositing over 8% of the annual nitrogen flux in 1986–1987. Acorns had high concentrations of phosphorus and nitrogen and during the mast season of 1987–1988 they contained a large proportion of the total subcanopy annual flux of these elements. With acorns excluded, total annual nutrient deposition was similar between years, but timing of nutrient deposition differed. Late summer leaf fall associated with drought, variation in precipitation, and variation in deposition of non-leaf parts were associated with seasonal differences in nutrient deposition between years.     

Influence of daylight and incubation interval on water column respiration in tropical fish ponds

Water column respiration (WCR) was measured in dark BOD bottles for 2, 4 and 8 h intervals during 22 h periods in two 1000 m² ponds stocked withOreochromis niloticus at 1 m^–2, and fertilized weekly with chicken litter at 750 kg total solids ha^–1. Mean WCR ranged from a low of 0.39 mg l^–1 for 8 h nocturnal intervals to a high of 0.62 mg l^–1 for 2-h diurnal intervals. WCR was significantly influenced by daylight and time into the diurnal or nocturnal period when it was determined. Mean WCR was significantly greater during the day than during the night (P<0.01). During the day, 2 h incubation intervals resulted in significantly higher WCR than 4 h or 8 h intervals (P<0.01); length of incubation interval did not significantly influence nocturnal WCR (P>0.05). Higher WCR during the day and during short diurnal incubation intervals was attributed to greater availability of photosynthetic respiration substrate. Diurnal, diel, or nocturnal WCR could be best estimated by a single 2, 4 or 8 h incubation interval, respectively, beginning at 0800 h.