Total Litterfall Research Articles

Temporal and structural effects of stands on litter production in Melaleuca quinquenervia dominated wetlands of south Florida

Melaleuca quinquenervia dominates large areas of the Florida Everglades in the southeastern USA where it has transformed sedge-dominated marshes into melaleuca forests. Despite its prevalence, very little is known about the ecology and stand dynamics of this invasive tree. We delineated large-, intermediate-, and small-tree stands in non-flooded, seasonally flooded and permanently flooded areas of Florida in 1997, measured their biological attributes, and then quantified litterfall components for 3–4 year periods. Melaleuca wood components and mature seed-capsules comprised the largest and the smallest portions of aboveground biomass, respectively, while leaves, fine stems, mature fruits, bud scales, floral structures, and residues represented decreasingly smaller fractions of the litter during the succeeding year. Dry weight proportion of leaves in litter was greatest (80.9%) in non-flooded and least (69.1%) in permanently flooded habitats. It was also greatest in small (85.6%) and least in large (64.7%) tree stands. Reproductive structures and mature-fruit fractions in litter were highest in large-tree stands whereas the bud-scale fraction showed no relationship to tree size. Seasonally flooded habitats had the most litterfall, wherein small-, intermediate-, and large-tree stands generated 0.662, 0.882, and 1.128 kg m 2 yr 1 , respectively. Dry weight of stems, leaves, bud–scales, floral structures, and mature fruit fractions in litter increased as the predominant size of the trees in the stand increased. Total annual litter production was highest during 1999–2000. Leaf fall occurred year-round with maximal amount during April, July, and October. Highest amounts of bud scales and floral structures fell during October–January, which corresponded with flushes of vegetative growth and major flowering events. Overall, melaleuca alone accounted for nearly 99% of the total litterfall dry weight in all habitats and months sampled. The amount of non-melaleuca litter was greater in small-tree stands than in intermediate- or large-tree stands. Litterfall data of this nature will be helpful in detecting changes occurring in melaleuca canopies in response to biological control impact and in prescribing site-specific management strategies.

Litterfall in the hardwood forest of a minor alluvial-floodplain

Within mature deciduous forests, annual development of foliar biomass is a major component of aboveground net primary production and nutrient demand. As litterfall, this same foliage becomes a dominant annual transfer of biomass and nutrients to the detritus pathway. We report litterfall transfers of a mature bottomland hardwood forest in a minor alluvial-floodplain within the middle Coastal Plain physiographic province of central Louisiana, USA. Climate is humid subtropical. Floodplain forests of minor alluvial-streams may account for nearly half the remaining acreage of bottomland forests in the Southeastern USA and differ markedly from those of major alluvial-rivers and deep-water swamps. For a 3-year period, litterfall magnitude, components, leaf species, and timing were monitored by monthly collection of materials from litterfall collectors. Variations in litterfall transfers across 10 study-plots and their relationships to forest parameters are evaluated. Mean transfers of total litterfall, leaf fall, reproductive structures, fine wood, and other litterfall were 816, 512, 130, 98, and 76 g m −2 year −1, respectively. Quercus pagoda Raf., Q. nigra L., and Liquidambar styraciflua L. accounted for an average of 49% of annual leaf fall, with 11 tree species and canopy vines accounting for 94% of total annual leaf fall. A total of 38 species and genera contributed to total leaf fall. Variation in total litterfall and leaf fall transfers across the alluvial bottom were related to size of overstory trees and their species composition. Higher and more consistent mass transfers of reproductive structures were observed than previously reported for upland hardwood stands.

Leaf litterfall and decomposition of different above- and belowground parts of birch (Betula ermanii) trees and dwarf bamboo (Sasa kurilensis) shrubs in a young secondary forest in Northern Japan

In many Japanese forests, the forest understory is largely dominated by dwarf bamboo (Sasa) species, which compete with overstory vegetation for soil nutrients. We studied the rate of leaf litterfall, and decomposition and mineralization of carbon (C) and nitrogen (N) from various components (leaf, root, wood, and rhizome) of overstory and understory vegetation in a young Betula ermanii forest from 2002 to 2004. Total litterfall was 377 g m−2 year−1, of which the overstory vegetation contributed about two thirds. A litter decomposition experiment conducted for 770 days indicated that mass loss of different litter components varied significantly, except for Sasa kurilensis wood and rhizome. Relative decomposition rates were significantly greater in the first growth period (June to October) than the dormant period (November to May) in most cases. Rainfall was the most important abiotic variable, explaining 75–80% of the variability in mass loss rates. Concentrations of ethanol soluble substances and N were significantly positively correlated (r=0.77 to 0.97, P<0.05) with mass loss at an early stage (41 days). The ratios of lignin/N and C/N were found to be negatively correlated with mass loss rates at all stages of litter decomposition. C stock loss was similar to that of mass loss, whereas N stock loss was slower, except for S. kurilensis fine root litter. The evergreen understory species S. kurilensis exhibited greater N use efficiency than B. ermanii, suggesting better competitive ability that might favor the production of a high biomass and invasion under tree species like B. ermanii.

Effect of selective logging on forest structure and nutrient cycling in a seasonally dry Brazilian Atlantic forest

AbstractAim The Brazilian Atlantic forest covers c. 10% of its original extent, and some areas are still being logged. Although several ecological studies in Atlantic forest have been published over the past two to three decades, there has been little research on forest dynamics and there is a particular lack of information on the effects of disturbance. The aim of the present study was to assess the impact of selective logging on forest structure, floristic composition soil nutrients, litterfall and litter layer in a seasonally dry Atlantic forest.Location The Mata do Carvão is located in the Guaxindiba Ecological Reserve in São Francisco do ltabapoana district (21°24′ S, 41°04′ W), Rio de Janeiro, Brazil.Methods Four plots (50 × 50 m) were set up in 1995 in each of two stands: unlogged and logged. In each plot, all trees ≥ 10 cm d.b.h. were enumerated, identified and measured. Vouchers were lodged at UENF Herbarium. Five surface soil samples were collected in each plot in the dry season (in October 1995). Litterfall was collected in eight traps (0.50 m2) in each plot over a year from 14 November 1995 to 11 November 1996. The litter layer was sampled in eight quadrats (0.25 m2) in each plot in the dry and wet seasons. Soils were air‐dried, sieved, and chemically analysed. The litter was dried (80 °C), sorted into six fractions, weighed and bulked samples analysed for nutrients.Results Forest stands did not differ in stem density and total basal area, with a total of 1137 individuals sampled in 1996 (564 unlogged and 573 logged), and a total basal area of 15 m2 (unlogged) and 13.0 m2 (logged). However, unlogged stands had more large trees (≥ 30 cm in d.b.h.) and greater mean canopy height. Among the families, Rutaceae and Leguminosae were the most abundant families in both sites, although the Rutaceae had a higher density in unlogged and Leguminosae in the logged stand. The species diversity index was similar between stands. Late‐successional species, such as Metrodorea nigra var. brevifolia and Paratecoma peroba, were less abundant in the logged stand. Selective logging did not affect nutrient concentrations in the soil or in the litter. However, quantities of the nutrients in the total litterfall and in the leaf litterfall and litter layer were higher in unlogged than in logged stands, mainly as a result of fallen M. nigra leaves. Metrodorea nigra was considered a key species in the nutrients dynamics in Carvão forest.Main conclusions Despite the fact that effects on tree diversity and soil nutrients were not clear, selective logging in this Atlantic forest altered canopy structure, increased the relative abundance of some early‐secondary species and decreased the litter input and stock of nutrients. Detailed information on the influence of logging on the distribution and structure of plant populations and in nutrient processes is fundamental for a sustainable logging system to be developed.

Soil Carbon Cycling and Soil CO2Efflux in a Red Pine (Pinus densiflora) Stand

This study was conducted to evaluate forest carbon cycling and soil <TEX>$CO_2$</TEX> efflux rates in a 42-year-old pine (Pinus densiflora) stand located in Hamyang-gun, Korea. Aboveground and soil organic carbon storage, litterfall, litter decomposition, and soil <TEX>$CO_2$</TEX> efflux rates were measured for one year. Estimated aboveground biomass carbon storage and increment in this stand were <TEX>$3,250gC/m^2\;and\;156gC\;m^{-2}yr^{-1}$</TEX>, respectively. Soil organic carbon storage at the depth of 30 cm was <TEX>$10,260gC/m^2$</TEX> Mean organic carbon inputs by needle and total litterfall were <TEX>$176gC\;m^{-2}yr^{-1}\;and\;235gC\;m^{-2}yr^{-1}$</TEX>, respectively. Litter decomposition rates were faster in nne roots less than 2 mm diameter size (<TEX>$<220\;g\;kg^{-1}yr^{-1}$</TEX>) than in needle litter (<TEX>$<120\;g\;kg^{-1}yr^{-1}$</TEX>). Annual mean and total soil respiration rates were <TEX>$0.37g\;CO_2m^{-2}h^{-1}$</TEX> and <TEX>$2,732g\;CO_2m^{-2}yr^{-1}$</TEX> during the study period. A strong positive relationship existed between soil <TEX>$CO_2$</TEX> efflux and soil temperature (r=0.8149), while soil <TEX>$CO_2$</TEX> efflux responded negatively to soil pH (r=-0.3582).

Upland Forest Linkages to Seasonal Wetlands: Litter Flux, Processing, and Food Quality

The flux of materials across ecosystem boundaries has significant effects on recipient systems. Because of edge effects, seasonal wetlands in upland forest are good systems to explore these linkages. The purpose of this study was to examine flux of coarse particulate organic matter as litter fall into seasonal wetlands in Minnesota, and the relationship of this flux to development of mosquitoes (Aedes aegypti). We hypothesized that litter flux into seasonal wetlands was dominated by upland plant litter that was lower quality and slower to breakdown than wetland litter, and that development rate of mosquitoes reared on upland litter was less than those reared on wetland litter. Of total litter fall into the wetlands, 71% originated in upland forest. Carbon to nitrogen ratios differed between upland litter (mostly sugar maple (Acer saccharum) and trembling aspen (Populus tremuloides) leaves) and wetland litter (mostly black ash (Fraxinus nirgra) leaves), averaging 63.9 and 47.7, respectively over two years. Breakdown rate of black ash leaves was faster than upland leaves (k (day−1) = 0.00329 and 0.00156, respectively), based on the average between wetland margins and centers. Development of mosquito larvae fed black ash leaves was faster than larvae fed upland leaves. Our results demonstrate linkages between upland forests and seasonal wetlands through litter fall. The abundance of upland litter in the wetlands may influence litter breakdown and carbon assimilation by invertebrates. Wetlands receiving high amounts of upland versus wetland litter may be lower quality habitats for invertebrates that depend on detrital pools for their development.

Carbon storage, litterfall and soil CO2efflux of a larch(Larix leptolepis)stand

Abstract This study was carried out to evaluate soil carbon cycling of a 36‐year‐old larch (Larix leptolepis) stand in Korea. The aboveground and soil organic carbon storage, litterfall, and soil respiration rates were measured over two‐year periods. The estimated aboveground biomass carbon storage and increment were 4220 gC m-2 and 150 gC m−2 yr-1, respectively. Mean organic carbon inputs by needle and total litterfall were 118 gC m-2 yr-1 and 168 gC m-2 yr-1, respectively. The aboveground carbon increment of the stand was similar to the annual input of carbon from total litterfall. The soil respiration rates correlated exponentially with the soil temperature at a depth of 20 cm (R2 = 0.86). In addition, the exponential regression equation indicated a relatively strong positive relationship between the soil respiration rates and soil temperature, while there was no significant relationship between the soil respiration rates and the soil moisture content. The annual mean and total soil respiration rates were 0.40 g CO2 m-2 h-1 and 3010 g CO2 m-2 yr-1 over the two‐year study period, respectively.

Processes influencing soil carbon storage following afforestation of pasture with Pinus radiata at different stocking densities in New Zealand

Since 1992, afforestation with Pinus radiata D. Don in New Zealand has led to the establishment of over 600 000 ha of new plantation forests, about 85% of which are on fertile pastures used previously for grazing sheep and cattle. While this leads to rapid accumulation of carbon (C) in vegetation, the effects of afforestation on soil C are poorly understood. We examined key soil C cycling processes at the (former) Tikitere agroforestry experimental site near Rotorua, New Zealand. In 1973, replicated stands of P. radiata (100 and 400 stems/ha) were established on pastures, while replicated pasture plots were maintained throughout the first 26-year rotation. In 1996, soil C and microbial biomass C in 0–0.10 m depth soil, in situ soil respiration and net N mineralisation, and soil temperature were lower in the forest than in the pasture, and tended to decline with increasing tree-stocking density. In the 400 stems/ha stands, mineral soil C (0–0.50 m depth) was lower than in the pasture (104 and 126 Mg C/ha, respectively; P &lt; 0.01). Carbon accumulation in the forest floor during the first rotation of these forest stands was 12 Mg C/ha. Using the Rothamsted soil C model (Roth-C), we examined how changes in plant C inputs following afforestation might lead to changes in soil C content to 0.30 m depth. Steady-state pasture inputs of 9.0 Mg C/ha.year were estimated using Roth-C; these C inputs were assumed to decrease linearly during the first 12 years following tree establishment (until canopy closure). Below-ground C inputs in the forest were estimated using steady-state relationships between litterfall and soil respiration; these inputs were assumed to increase linearly between years 1 and 12, after which they remained constant at 1.53 Mg C/ha.year until harvest. Measured changes in soil C (0−0.30 m) during the first rotation, in conjunction with the below-ground inputs, were used to estimate above-ground inputs (as a proportion of total litterfall [3.81 Mg C/ha.year]) to the soil. Our results suggest 10% of litterfall C over one rotation actually entered the mineral soil. Using these results and estimates of additional C inputs to the soil from harvest slash and weeds following harvest, we found mineral-soil C stocks would continue to decline during second and third rotations of P. radiata; the magnitude of this decline depended in part on how much slash enters the mineral soil matrix. We confirmed our modelling approach by simulating soil C changes to within 8% over 19 years following afforestation of pasture at another previously studied site, Purukohukohu. Whether afforestation leads to an increase or decrease in mineral-soil C may depend on previous pasture management; in highly productive pastures, high C inputs to the soil may maintain soil C at levels that cannot be sustained when trees are planted onto these grasslands.

Evaluating the impact of biological control against Mimosa pigra in Australia: Comparing litterfall before and after the introduction of biological control agents

The impact of biological control on the woody weed, Mimosa pigra was investigated by comparing litterfall in 2001–2003 with a previous study performed at the same site, in 1984–1986, before biological control agents were released, and correlating litterfall to individual agent damage. Total litterfall was similar in both studies. However, leaf litterfall was 20% higher than prior to the introduction of biological control agents whilst seed rain was 47% lower overall and 67% lower at the stand edge. Abundance of the flower-feeding weevil Coelocephalapion pigrae lagged variation in flower fall and it was estimated to destroy only 10.6% of flowers. No correlation was found between C. pigrae abundance and seed rain. Neurostrota gunniella and Carmenta mimosa abundances were both highest at the stand edge. Seed rain was negatively correlated with both N. gunniella and C. mimosa damage, declining by ca. 60% at the highest N. gunniella and C. mimosa densities, indicating that both species have a significant impact on mimosa fecundity. However, the introduction of biological control agents is not the only potential explanatory factor affecting mimosa to have changed since the mid-1980s. Alternative hypotheses and implications for the design of future evaluation experiments are discussed.

Litterfall Dynamics of an Evergreen Broadleaf Forest and a Pine Forest in the Subtropical Region of China

Abstract Monthly litterfall was monitored over a 10-year period from an evergreen broadleaf forest (EBF) and a pine forest (PF) in subtropical South China. During this period, litter was also collected bimonthly from the forest floor for 2 years. Total annual litterfall in EBF fluctuated around 9 Mg ha−1 with leaves, branches, and miscellanea accounting for 52.5%, 22.2%, and 25.3%, respectively. Total annual litterfall alternated between high and low values in consecutive years. Storms and pest outbreaks were responsible for most of the peaks in both monthly and annual litterfall. Litter from each of 43 species was recorded, but 9 species contributed about 85% of total litterfall. Dominant species shed their leaves in a more regular pattern with peaks mainly from Jan. to Mar. Pine forest (Pinus massoniana) produced much less litterfall than EBF, with a mean of 2.7 Mg ha−1. Here, leaves accounted for 73.2% of total litterfall, branches only 11.4%, and miscellanea 15.4%. Litter on the ground amounted to 5.2 Mg ha−1 in EBF and 2.9 Mg ha−1 in PF. The results show that this climax forest has much higher litterfall and forest floor mass than the pine forest, and litterfall is rather stable with regard to annual variation. FOR. SCI. 51(6):608–615.

Climatic and litter fall effects on collembolan and oribatid mite species and communities in a beech wood based on a 7 years investigation

During a period of 7 years, between 1989 and 1995, Collembola and Oribatida were investigated in a beech forest on an acid Dystric Cambisol soil in northern Germany. Precipitation and temperature at a nearby climate station were recorded, and litter fall in the forest was measured. For 23 collembolan and 27 oribatid mite species, an analysis was performed concerning the influence of the climate parameters or litter fall on yearly assemblages or single species. Climate influence on the community structure was weak. Composition of the assemblages was relatively constant throughout the period of 7 years. A significant effect was determined for mean annual temperature and July precipitation only. More distinct effects were found in single species. In total, nine collembolan and six oribatid mite species were significantly influenced by litter fall, mean annual temperature, mean January temperature, mean July temperature, total precipitation or July precipitation. Reaction time ranged between 1 and 12 months. Four collembolan species reacted with a retarded yearly occurrence on deep spring temperature. Species diversity of Collembola was negatively correlated with total litter fall, while in oribatid mites the diversity showed a positive correlation.

Young Mangrove Stands Produce a Large and High Quality Litter Input to Aquatic Systems

Mangrove swamps are key ecosystems along the Vietnam coast. Although mangrove litter is thought to represent an important input of organic matter and nutrients to the coastal aquatic systems, the factors determining the quality and size of this litter flux have not been studied so far. We monitored leaf, stipule, twig, and reproductive litter monthly in monocultures of Rhizophora apiculata mangrove forests of 7, 11, 17 and 24 years old in the Camau province, Mekong Delta, Vietnam. Litter traps were used to measure litter fall production from June 2001 till May 2002. Total litter fall was in the range of 8.86–14.16 t DW ha−1 year−1. Leaves were the main component, and represented 70% of litter fall production in all stands. Total litter fall was lower in the older stands but the amount of reproductive litter was significantly higher in these stands (17 and 24 years). Biomass of leaf litter was highest between the end of the wet season and the beginning of the dry season. Phosphorus and nitrogen levels in leaf litter were significantly higher in younger than in older stands. Overall, our study indicated that young stands produced the highest input of litter and particularly of nitrogen and phosphorus to the surrounding aquatic system. Consequently, these stands contribute significantly to the fisheries.

Litter flux in Kuala Selangor Nature Park mangrove forest, Malaysia

The amount of litter production, litter standing crop and export of leaf litter were studied in Kuala Selangor Nature Park mangrove forest, Malaysia. The rates of leaf fall, small branches, bracts, flowers, propagules and total litter varied from 1.63-3.07 g/m2/day, 0.08-0.38 g/m2/day, 0.13-0.39 g/m2/day, 0.01-0.23 g/m2/day, 0.03-2.29 g/m2/day and 2.31-4.46 g/m2/day respectively. Comparatively higher rate of total litter fall was observed during the drier months of July 02, July 03 and August 02; and propagules contributed 31.00 to 52.00% of the total litter fall during the dry season. Relatively higher rate of leaf litter production was observed during February 02 followed by March 03 (intermediate seasons). The rate of total litter production and leaf fall showed significant (F, p&lt;0.05) negative correlations with rainfall and relative humidity while positive correlations were observed with temperature. The amount of small litter standing crop at different seasons varies from 63.45 to 104.59 g/m2 and comparatively higher amount of leaf litter and bract was recorded during the intermediate seasons while relatively higher amount of propagules was observed during the dry season. The export of leaf litter varied from 19.46 to 50.00 % of total leaf fall during the wet and dry months respectively.

Above- and below-ground litter production in three tropical montane forests in southern Ecuador

Litter production from above-ground (leaves, twigs, fruits, flowers) and below-ground (roots) plant organs is an important component of the cycling of carbon and nutrients in forests. Tropical montane forests possess comparatively large quantities of fine-root biomass, suggesting that litter production by dying fine roots may represent a major component of total litter production. In a comparative study in three tropical montane forests of southern Ecuador at 1890, 2380 and 3060 m elevation, we measured leaf-fall by litter trapping and fine-root litter production by sequential soil coring and fine-root biomass and necromass analysis for about 1 y with the objectives (1) to quantify annual above- and below-ground litter production, and (2) to investigate elevational differences in litter production. Leaf litter mass decreased to less than a third (862 to 263 g m−2 y−1) with increasing elevation (1890 m to 3060 m), whereas fine-root litter production increased by a factor of about four (506 to 2084 g m−2 y−1). Thus, the ratio of leaf to fine-root litter shifted by an order of magnitude in favour of fine-root litter production between 1890 to 3060 m. Fine-root litter production was not synchronized with leaf litterfall and was seasonal only at 3060 m with mortality peaks in the drier and the wetter periods. We conclude that dying fine roots represent a very important fraction of total litterfall in tropical montane forests that can exceed the quantity of leaf litter. At 3060 m, the largest part of the organic material on top of the soil must originate from dying fine roots but not from fallen leaves.

Structure and Function of Populus deltoides Agroforestry Systems in Eastern India: 1. Dry matter dynamics

Agroforestry systems based on poplar (Populus deltoides) are becoming popular in eastern and northern parts of India. Therefore studies on the structure and function of the systems are important. The investigations included allometric equations for above- and belowground tree components, crop and plantation floor biomass and litter fall estimation at Pusa, Bihar, India. Biomass, floor litter mass, litter fall and net primary productivity (NPP) of plantations increased with an increase in age of trees whereas, crop biomass for any specific crop interplanted with poplar decreased with the age of the plantation. The total plantation biomass increased from 12.08 to 90.59 Mg ha−1 and NPP varied from 5.69 to 27.9 Mg ha−1 year−1. The biomass accumulation ratio ranged from 2.1 to 3.2. Total annual litter fall was in between 1.95 and 10.00 Mg ha−1 year−1, of which 92–94% was contributed by leaf litter. Compartmental models were developed for dry matter distribution in agroforestry systems involving young (3-year-old) and mature (9-year-old) poplar trees interplanted with various crops, the crops being grown in two rotations maize (Zea mays) – wheat (Triticum aestivum) – turmeric (Curcuma domestica) and pigeonpea (Cajanus cajan) – turmeric. This study substantiates the potential of Populus deltoides G3 under agroforestry combinations.

Litter production, seasonal pattern and nutrient return in seven natural forests compared with a plantation in southern China

Summary The amount and pattern of litterfall and its nutrient return were studied in seven natural forests of Schima superba Gardn. and Champ. (SCS), Castanopsis fabri Hance (CAF), Tsoongiodendron odorum Chun (TSO), Cinnamomum chekiangense Nakai (CIC), Altingia gracilipes Hemsl. (ALG), Castanopsis carlesii (Hemsl.) Hayata (CAC) and Pinus massoniana D. Don (PIM), and compared with that of an adjacent 29-year-old plantation of Chinese fi r ( Cunninghamia lanceolata Lamb.) (CUL) in Jianou, Fujian, China. Mean annual total litterfall over 3 years of observations varied from 4.63 Mg ha � � in the CUL to 8.85 Mg ha � � in the PIM; of this litterfall, the leaf contribution ranged from 62 to 73 per cent. Litterfall in the CAF, ALG and CAC showed an unimodal distribution pattern, while for the fi ve other forests, the litterfall pattern was multi-peak. The rank order of the eight forests, according to nutrient return mass with the exception of P, was different from the order when rank was according to total mass of litterfall. The highest annual N, K and Ca returns from total litterfall were noticed in the TSO, the CAF and the CUL, respectively. The amounts of P and Mg potentially returned to the soil were the highest in the PIM. The leaf fraction provided greater potential returns of N, P, K, Ca and Mg to the soil than other litter fractions. The results of this study demonstrate that natural forests have a greater capability for maintaining site productivity than the monoculture coniferous plantation, due to higher amount of above-ground litter coupled with greater nutrient returns; therefore conservation of natural forests is recommended as a practical measure in forest management to realize sustainable development of forestry in mountainous areas of southern China.

What is NPP? Inconsistent accounting of respiratory fluxes in the definition of net primary production

Primary production represents a globally important flux of carbon between the atmosphere and the biosphere. From an ecological perspective, it measures the rate at which solar energy is stored by plants as organic matter, and is therefore a measure of the rate at which solar energy is captured and made available to the rest of the food chain (Odum 1971). From a biogeochemical perspective, primary production provides links between the biosphere and the climate system through the global cycling of C, water and nutrients (Roy et al . 2001). Gross primary production (GPP) is the total amount of C assimilated by plants within a given area over a specified timeframe. (Here GPP refers to the total C fixed by photosynthesis, minus the C lost by photorespiration. We have adopted the convention of specifying productivity in units of C mass per unit ground area per unit time, although we could have alternatively used units of total biomass, or energy: Odum 1971.) Net primary production (NPP) is GPP less the flux of autotrophic respiration of assimilate used for the plant’s own metabolism ( R ), therefore:

Avaliação estacional da deposição de serapilheira em uma floresta ombrófila mista localizada no sul do estado do Paraná.

Com o objetivo de avaliar a deposição estacional de serapilheira em uma Floresta Ombrófila Mista, instalou-se um experimento em setembro/98 na Estação Experimental de São João do Triunfo, no estado do Paraná. A estação possui uma área de 31,7 ha, dividida em trinta parcelas de 1 ha. Em três dessas parcelas foram instalados 27 coletores (nove em cada uma). As coletas foram realizadas a cada 45 dias, atentando-se sempre para o final das estações. O material coletado foi acondicionado em sacos plásticos, os quais foram identificados com o número do coletor e a parcela na qual está localizado. Após uma pré-secagem, o material de cada coletor foi separado nas frações folhas, galhos e miscelânea. Em seguida, estas foram embaladas em sacos de papel e levadas à estufa à temperatura de 65oC, até peso constante, para a determinação do peso seco por fração de serapilheira. Os dados obtidos até o momento demonstram que a primavera foi a estação que apresentou a maior deposição de serapilheira, seguida pelo inverno, verão e outono, com valores médios (kg/ha) de 2.433,31; 2.164,79; 1.799,72 e 1.339,00 respectivamente. A fração folhas constituiu-se no principal componente, respondendo por 57% da serapilheira total, seguida por galhos com 27% e miscelânea com 16%.

Primary production in an impounded baldcypress swamp (Taxodium distichum) at the northern limit of the range

The ability of baldcypress (Taxodium distichum)swamps to maintain themselves near the northern limit of their range depends on their levels of production, which is not only are response to climate but also to local environmental factors(e.g., impoundment). We asked if primary production was reduced under impounded conditions and if species’ responses to impoundment were individualistic or more generalized. To examine long-term production trends in a permanently impounded baldcypress swamp, a 6-year study of leaf litterfall was conducted in Buttonland Swamp, Illinois, which had been impounded for 10 years before the beginning of the study. Buttonland Swamp is at the northern boundary of the baldcypress swamp region along the Cache River, Illinois, in the Mississippi River Alluvial Valley of the United States. When the litter production of impounded sites was compared to those with natural hydrology in the same region, impounded sites had about half of the total litterfall of natural sites. Overall, leaf litterfall rates declined during the study(201 vs. 113 gm−2 yr−1), but the pattern was negatively correlated with water depth, which explained 97% of the variation in the data. Along the transect with the lowest mean minimum water depth(<0.5 cm), leaf litterfall decreased linearly over 6 years from 377 to 154gm−2 yr−1. Total leaf litterfall rates were lower at the other three depths(5, 43, and 49 cm mean minimum water depths)and remained below 200 gm−2 yr−1 throughout the study. Acer saccharinum, Nyssa aquatica, and Salix nigra were most responsible for the decline in total leaf litterfall. Amounts of leaf litterfall of T. distichum and Liquidambar styraciflua also generally decreased, while that of Cephalanthus occidentalis increased overtime. Because species’ responses to environmental factors such as impoundment are individualistic, models should be based on the responses of individual species, rather than on communities. Our study further suggests that the effects of climate change on impounded swamps may differ from those with natural hydrology, since impounded swamps already have reduced production levels. This finding is particularly relevant since the hydrology of the majority of the world’s riverine ecosystems has been altered.

Population dynamics of four marsupials and its relation to resource production in the Atlantic forest in southeastern Brazil

Variations in mammal population sizes can be related to the availability and abundance of their resources. This study reports the population dynamics of four didelphid marsupials (Didelphis aurita, Philander frenatus, Marmosops incanus and Metachirus nudicaudatus) and its relation to litter fall, used as a measure of resource production. A capture-mark-recapture study (CMR) was carried out in a disturbed area of the Atlantic forest in Rio de Janeiro State, Brazil, in three grids in the locality of Garrafão from April 1997 to February 1999, every other month. Litter was collected every month using 15 squared litter traps of 0.25 m2 in the grids (5 in each grid). Leaves, twigs, reproductive structures and total litter fall rates were calculated as tons ha–1month–1. Population densities, survivorship and recruitment rates were estimated. For D. aurita and P. frenata, population densities were correlated positively only with litter production. For M. incanus, population density was correlated positively with survivorship, litter production and negatively with rainfall. M. nudicaudatus population density was correlated only with recruitment and twigs abundance. The availability of fruits and arthropods had a large influence in the proximal causes on the variation of small mammal populations. In forests where there is an adequate rate of decomposition of the litter, we may understand how resources influence population variation, and litter becomes the base of resources for such marsupials in the Atlantic forest.