Leaf Litterfall Research Articles

Climatic sensitivity of species’ vegetative and reproductive phenology in a Hawaiian montane wet forest

AbstractUnderstanding how tropical tree phenology (i.e., the timing and amount of seed and leaf production) responds to climate is vital for predicting how climate change may alter ecological functioning of tropical forests. We examined the effects of temperature, rainfall, and photosynthetically active radiation (PAR) on seed phenology of four dominant species and community‐level leaf phenology in a montane wet forest on the island of Hawaiʻi using monthly data collected over ~ 6 years. We expected that species phenologies would be better explained by variation in temperature and PAR than rainfall because rainfall at this site is not limiting. The best‐fit model for all four species included temperature, rainfall, and PAR. For three species, including two foundational species of Hawaiian forests (Acacia koa and Metrosideros polymorpha), seed production declined with increasing maximum temperatures and increased with rainfall. Relationships with PAR were the most variable across all four species. Community‐level leaf litterfall decreased with minimum temperatures, increased with rainfall, and showed a peak at PAR of ~ 400 μmol/m2s−1. There was considerable variation in monthly seed and leaf production not explained by climatic factors, and there was some evidence for a mediating effect of daylength. Thus, the impact of future climate change on this forest will depend on how climate change interacts with other factors such as daylength, biotic, and/or evolutionary constraints. Our results nonetheless provide insight into how climate change may affect different species in unique ways with potential consequences for shifts in species distributions and community composition.

Drought resistance increases from the individual to the ecosystem level in highly diverse Neotropical rainforest: a meta-analysis of leaf, tree and ecosystem responses to drought

Abstract. The effects of future warming and drying on tropical forest functioning remain largely unresolved. Here, we conduct a meta-analysis of observed drought responses in Neotropical humid forests, focusing on carbon and water exchange. Measures of leaf-, tree- and ecosystem-scale performance were retrieved from 145 published studies conducted across 232 sites in Neotropical forests. Differentiating between seasonal and episodic drought, we find that (1) during seasonal drought the increase in atmospheric evaporative demand and a decrease in soil matric potential result in a decline in leaf water potential, stomatal conductance, leaf photosynthesis and stem diameter growth while leaf litterfall and leaf flushing increase. (2) During episodic drought, we observe a further decline in stomatal conductance, photosynthesis, stem growth and, in contrast to seasonal drought, a decline also in daily tree transpiration. Responses of ecosystem-scale processes, productivity and evapotranspiration are of a smaller magnitude and often not significant. Furthermore, we find that the magnitude and direction of a drought-induced change in photosynthesis, stomatal conductance and transpiration reported in a study is correlated to study-averaged wood density. Although wood density is often not functionally related to plant hydraulic properties, we find that it is a good proxy for hydraulic behaviour and can be used to predict leaf- and tree-scale responses to drought. We present new insights into the functioning of tropical forest in response to drought and present novel relationships between wood density and tropical-tree responses to drought.

High biomass production with abundant leaf litterfall is critical to ameliorating soil quality and productivity in reclaimed sandy desertification land

Long-term data regarding soil properties and crop growth are powerful resources substantially contributing to our knowledge of soil-forming processes of reclaimed sandy desertification land. Generalized ecological principles derived from long-term observations that help to maintain or improve soil quality and productivity is critical for guiding field management practices while suitable for newly reclaimed sandy desertification land still need to be evaluated. Here, a 14-yr old experiment showed that soil quality index (SQI) had an “increase-decline-recovery” tendency in irrigation and fertilizer addition desertification lands while it remained at constantly low levels in desertification land with only irrigation. Stably decent yield and net incomes were obtained after 3–4 years’ consecutive irrigation and fertilizer addition management. Correlation between crop productivity and SQI followed a saturation characteristic curve with threshold at 0.5, corresponding to soil organic carbon (SOC) ~5.0 g kg−1, below which crop productivity was linearly declined. 60% of observed inter-annual variations in SQI were explained by quantity of leaf litter, which was three times higher than explanatory power of root residue. No substantial changes occurred in soil mechanical components while the soil microbial biomass carbon, water-stable aggregate and heavy carbon pool in SOC were significantly improved by 2–9 folds in reclaimed desertification lands. Results revealed that increased biomass production with abundant residue retention is crucial for ameliorating soil quality, stabilizing high yield and economic gains, supporting the “High Biomass Cropping System” ecological hypothesis. Ecological limitations and opportunities to sustainable utilization of sandy desertification land were discussed.

Relationship between nutrient and soil loss with respect to land configuration and mulches in ginger (Zingiber officinale)

Change in topography and retention of indigenously available biomass as mulch conserves the resources at the site. In high rainfall areas and hilly tract, soil and nutrient loss has paramount importance as these resources directly contribute to the crop yield. Ginger (Zingiber officinale Roscoe) is sensitive to soil and nutrient losses. The present study was conducted during 2011–12 and 2012–13 with three land configurations, viz. broad bed and furrow (BBF), ridge and furrow (R&F) and flatbed (FB) in main plots and four mulches, viz. Imperata cylendrica (IC), pine needle (PN), paddy straw followed by weed biomass (PS) along with no mulch (NM) in sub-plots and replicated thrice in ginger. The adoption of BBF considerably lowered the soil loss by 74.2% resulting in restoration of nitrogen (N), phosphorus (P) and potassium (K) to the tune of 49.7%, 59.3% and 69.1%, respectively, over FB plots. Similarly, placement of PN significantly reduced the soil loss by 92% and saved a considerable amount of N (49.9%), P (49.4%) and K (58.2%) over NM. In the hilly area, leftover crop residues, abundant weed biomass and ample tree leaf litter fall are not utilized commercially; these materials along with alteration in topography can be potentially utilized for the restoration of soil and nutrient for sustainable ginger production.

English

A study was conducted in the Guinea and Sudan Savannah zones in the Upper East Region of Ghana to investigate the effects of Faidherbia albida on some important soil fertility indicators. Soil sampling and analysis, litter trap, and litter bag techniques were employed to determine the soil’s content of major nutrients, the rate of litterfall production and litter decomposition, respectively. Analysis of variance (ANOVA) was performed to determine differences among treatment means, while Tukey’s highest significant difference (HSD) was used to perform post hoc tests among means within the same sample set. Soils under F. albida tree canopies were found to contain significantly higher organic carbon and total nitrogen than those outside the canopies. Peak leaf litter production occurred during the first three months of the onset of the rainy season. Annual leaf litterfall was 340 g m-2 year-1 in the Guinea Savannah zone and 264 g m-2 year-1 in the Sudan Savannah zone. The high leaf litterfall, followed by high decomposition and mineralization at the beginning of the cropping season, the high nutrient content of its leaves, coupled with its nitrogen fixing ability, make F. albida a potential candidate for soil improvement and improved productivity of major crops in smallholder farming systems. About 37 and 59 adult F. albida trees will be required to supply significant amounts of nitrogen in the Guinea and Sudan Savannah zones, respectively. Key words: Litter bag technique, litter decomposition, litter fall, litter trap technique, soil organic carbon, soil

Changes in streamside riparian forest canopy and leaf litter nutrient flux to soils during an emerald ash borer infestation in an agricultural landscape

The invasive forest insect pest, emerald ash borer (EAB), is causing rapid, widespread ash tree mortality across eastern North America. Riparian (streamside) forests in agricultural landscapes often represent residual patches of high quality forest habitat that, owing to their strong land/water ecological linkages, can be critical for maintaining stream water quality and aquatic and terrestrial biodiversity. When riparian forests contain high numbers of ash trees, EAB can pose a risk of disrupting some of those land/water linkages thereby reducing riparian and aquatic habitat quality. We tracked ash tree mortality, streamside forest canopy cover, leaf litter deposition rates, and nutrient flux to soils in 18 riparian forest plots with an average of 24% ash by stem density over a 5 year period from early to late stages of an EAB invasion (2010–2015). Ash tree mortality increased from an average of 10–98% over 5 years in most plots, but when blue ash were dominant, final ash mortality was about 34%. Despite the nearly complete mortality of ash trees in almost all plots by 2015, the average canopy openness measured at 1.5 m above ground only increased to about 9%, which was significantly higher than the 2010 average of 6% open. Final canopy openness was significantly but weakly (r2 = 0.24) associated with the proportion of ash in riparian plots, indicating highly patchy openness resulting from ash mortality. Ash leaf litter deposition to streamside traps declined by 84% and elm declined by 20%, whereas leaf deposition from the other four most common contributors to riparian leaf litter increased by up to 37% over the same period. The large reductions in ash litter deposition were sufficient to reduce macro-nutrient flux to the streamside forest floor and therefore likely to streams. Amounts of N, C, P, K, and Ca delivered to the streamside soils via leaf litter fall were all consistently, some of them significantly, lower by 2014 than in the baseline year of 2010. Although total leaf litter mass returned to near pre-infestation levels by 2014, the altered composition of leaf litter caused a persistent reduction in nutrient flux to riparian soils. We also measured stem density of regenerating ash saplings ( 0.5 m height) at the end of the study period and found them to be abundant with an average of 2084 stems/ha. Our results provide an empirical demonstration of EAB-induced disruptions to ecological linkages and processes in riparian forests, at least over the short term.

Cocoa agroforest multifunctionality and soil fertility explained by shade tree litter traits

Abstract Manipulating plant functional diversity to improve agroecosystem multifunctionality is a central challenge of agricultural systems world‐wide. In cocoa agroforestry systems (cAFS), shade trees are used to supply many services to farmers, yet their impact on soil functioning and cocoa yields is likely to vary substantially among tree species. Here we compared the impact of five shade tree species (Canarium schweinfurthii (Canarium), Dacryodes edulis (Safou), Milicia excelsa (Iroko), Ceiba pentandra (Kapok tree), Albizia adianthifolia (Albizia)) and unshaded conditions on the functioning of poor sandy savanna soils within eight cocoa farms in Central Cameroon. We assessed the effects of plant functional traits, leaf litterfall and fine root biomass on a range of soil functions and on cocoa yield. Shade trees generally improved soil pH, , and Olsen P content, biomass production of bioassays and soil total C and N content, while leaving cocoa yields unchanged. However, these effects varied largely among species. Improvements of soil functions were low under the two fruit trees (Canarium and Dacryodes), medium under the legume tree Albizia and high under the two timber trees (Milicia and Ceiba). Low litter recalcitrance was most strongly associated with increases in soil fertility indicators such as N and P availability, whereas soil C and N content increased with litter Ca restitution. Synthesis and applications. We demonstrate that cocoa agroforest multifunctionality is substantially influenced by the functional traits of shade tree species. Shade tree species with the most dissimilar traits to cocoa (cocoa showing the lowest leaf litter quality) showed the largest improvement of soil functions. Therefore, selection of shade trees based on their functional traits appears as a promising practice to adequately manage soil functioning. In order to fully assess the beneficial role of shade trees in these agroecosystems. Future research will need to extend this approach to other below‐ground traits and other aspects of multifunctionality such as long‐term cocoa health and yield.

Leaf litter inputs reinforce islands of nitrogen fertility in a lowland tropical forest

The role of lowland tropical forest tree communities in shaping soil nutrient cycling has been challenging to elucidate in the face of high species diversity. Previously, we showed that differences in tree species composition and canopy foliar nitrogen (N) concentrations correlated with differences in soil N availability in a mature Costa Rican rainforest. Here, we investigate potential mechanisms explaining this correlation. We used imaging spectroscopy to identify study plots containing 10–20 canopy trees with either high or low mean canopy N relative to the landscape mean. Plots were restricted to an uplifted terrace with relatively uniform parent material and climate. In order to assess whether canopy and soil N could be linked by litterfall inputs, we tracked litter production in the plots and measured rates of litter decay and the carbon and N content of leaf litter and leaf litter leachate. We also compared the abundance of putative N fixing trees and rates of free-living N fixation as well as soil pH, texture, cation exchange capacity, and topographic curvature to assess whether biological N fixation and/or soil properties could account for differences in soil N that were, in turn, imprinted on the canopy. We found no evidence of differences in legume communities, free-living N fixation, or abiotic properties. However, soils beneath high canopy N assemblages received ~ 60% more N via leaf litterfall due to variability in litter N content between plot types. The correlation of N in canopy leaves, leaf litter, and soil suggests that, under similar abiotic conditions, litterfall-mediated feedbacks can help maintain soil N differences among tropical tree assemblages in this diverse tropical forest.

Tree growth rate and soil nutrient status determine the shift in nutrient-use strategy of Chinese fir plantations along a chronosequence

Nutrient resorption is a key nutrient-use strategy exhibited by perennial plants to overcome nutrient limitations and meet their nutritional demands. However, the factors that drive nutrient resorption with stand development remain largely unknown. In this study, we examined how a nutrient source (soil) and sink (trees) affected the resorption efficiency (RE) of nitrogen (N) and phosphorus (P). Fresh leaves, leaf litterfall, and soil samples were collected from a chronosequence of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook., Taxodiaceae) plantations at the ages of 3, 8–11, 16, 20, 25, 29, and 32 years. The N and P concentrations in stems, branches, leaves, coarse roots, and fine roots, stocks of N and P in soils, and the relative growth rate (RGR) of trees were measured. Fresh leaf N and P concentrations and RE decreased with stand age, while the N:P ratio in fresh leaves as well as the N and P concentrations in leaf litterfall increased. The RGR of trees declined with stand age. Soil P stocks increased but soil N stocks slightly decreased with stand age. A variation partitioning analysis revealed that the combined effect of RGR and soil P stocks on the RE of P (PRE) was stronger than the individual effect of each factor, while the RE of N (NRE) was greatly affected by the individual effect of RGR. With increasing age, Chinese fir plantations shifted from N-limiting to P-limiting conditions, and the nutrient-use strategy changed from “conservative consumption” to “resource spending”. These patterns were co-regulated by the tree growth rate and soil nutrient status. Thus, supply-demand relationships reflected the nutrient cycling status and could provide valuable information for sustainable nutrient management practices in tree plantations.

Novel Representation of Leaf Phenology Improves Simulation of Amazonian Evergreen Forest Photosynthesis in a Land Surface Model

AbstractLeaf phenology in the humid tropics largely regulates the seasonality of forest carbon and water exchange. However, it is inadequately represented in most global land surface models due to limited understanding of its controls. Based on intensive field studies at four Amazonian evergreen forests, we propose a novel, quantitative representation of tropical forest leaf phenology, which links multiple environmental variables with the seasonality of new leaf production and old leaf litterfall. The new phenology simulates higher rates of leaf turnover (new leaves replacing old leaves) in dry seasons with more sunlight, which is then implemented in ORCHIDEE, together with recent findings of ontogeny‐associated photosynthetic capacity, and is evaluated against ground‐based measurements of leaf phenology (canopy leaf area index and litterfall), eddy covariance fluxes (photosynthesis and latent heat), and carbon allocations from field observations. Results show the periodical cycles of solar radiation and vapor pressure deficit are the two most important environmental variables that are empirically related to new leaf production and old leaf abscission in tropical evergreen forests. The model with new representation of leaf phenology captures the seasonality of canopy photosynthesis at three out of four sites, as well as the seasonality of litterfall, latent heat, and light use efficiency of photosynthesis at all tested sites, and improves the seasonality of carbon allocations to leaves, roots, and sapwoods. This study advances understanding of the environmental controls on tropical leaf phenology and offers an improved modeling tool for gridded simulations of interannual CO2 and water fluxes in the tropics.

Plant sex influences aquatic–terrestrial interactions

AbstractA growing body of research shows that plant genetic factors can influence ecosystem processes and structure communities, but one aspect that has received little study is sex differentiation in dioecious plants. Since headwater streams are reliant on riparian leaf litterfall, plant sex differences in leaf traits may influence in‐stream processes. Sitka willow (Salix sitchensis) at Mount St. Helens is dioecious and heavily infested with the stem‐boring weevil (Cryptorhynchus lapathi), which causes branch dieback and summer litterfall. We found that female willow shrubs tend to grow closer to the stream bank, are more likely to be infected by the weevil, and have 42% higher litter C:N than male willows. These factors may lead to increased litter inputs and slower litter mass loss for female willows. The combination of colonization location, herbivore attack, altered litter quality, and slower mass loss results in female shrubs providing more sustained carbon and nutrient resources to microbes and invertebrates in the early successional streams at Mount St. Helens. In addition, since dioecy is a relatively common trait in riparian habitats, it is possible that plant sex plays a far more interesting role in structuring linked terrestrial–aquatic communities and ecosystem processes than previously understood.

Organic nitrogen in residential stormwater runoff: Implications for stormwater management in urban watersheds

Stormwater runoff containing organic nitrogen (N) is a source of potentially bioavailable N in water bodies. Characterization and concentrations of dissolved organic N (DON) and particulate organic N (PON) in urban stormwater runoff are rarely reported and considered in stormwater management. Our objectives were to (1) characterize the organic (DON, PON) and inorganic (NO3− and NH4+) N pools in residential stormwater runoff and (2) determine the rainfall driven landscape sources of runoff PON using an isotopic mixing model with 13C and 15N during a wet season (June–September). We instrumented a 13 ha (0.13 km2) residential catchment located in Florida, United States with an ISCO autosampler and collected stormwater runoff samples (n = 52) over 11 individual stormwater runoff events. Mean concentration of total N in runoff during the wet season was 1.61 mg L−1, of which 37% was DON and 25% was PON. A strong seasonal first flush of PON, giving rise to a large PON:TN ratio, was observed as the wet season progressed from June (PON:TN = 0.39;) to September (PON:TN = 0.12), whereas DON did not display any seasonal variability (mean: 0.66 mg L−1). The isotope mixing model estimated that 76% of PON in the runoff originated from oak detritus (leaves: 50%, acorns: 26%) and the remaining 24% from lawn grass clippings. The dominance of organic N fractions in the urban stormwater runoff suggests that landscape controls on PON and DON are needed to reduce N loading in the urban stormwater runoff. The seasonal first flush of PON indicates that monitoring strategies should focus on how nutrient concentrations in runoff may respond to seasonal drivers such as leaf litterfall and that there may be optimal times for N management, such as after a prolonged dry season in which materials accumulate and pose the risk for later mobilization.

Soil Carbon Storage and Its Determinants in Forest Fragments of Differentiated Patch Size

Research Highlights: Soil carbon storage (SOC) decreased due to forest fragmentation through lower proportion of macroaggregate distribution, higher storage of fine roots and litter falls, and lower fine root production rate. Background and Objectives: Globally, forest fragmentation processes lead to enormous losses of SOC in forests. We investigated SOC and its determinants in forest fragments experiencing edge disturbances in south China. Materials and Methods: Soil aggregate characteristics, dynamics of fine roots, and litter fall were studied from forest edges to interiors. Generalized linear mixed models were used to model the contributions of fine root and litter fall dynamics to carbon concentration in aggregates. Results: Large and small macroaggregates had higher proportion of aggregate distribution and contributed more carbon to SOC in all types of plots in the present study. SOC significantly increased from forest edges to interiors due to carbon concentration of these two aggregate types increasing from edges to interiors, while the proportion of different aggregate distributions was similar within each plot. The same trend was found with increasing forest patch size. Fine root biomass storage had the strongest impact on carbon concentration in large macroaggregates and microaggregates, with higher fine root biomass storage associated with lower carbon concentration. In addition, biomass storage and production rates of both fine roots and litter falls decreased from forest interiors to edges. Our results showed that SOC was significantly decreased due to the lower proportion of large and small macroaggregate distribution, and lower fine root production rate in forest fragments. Conclusions: SOC loss due to effects of forest fragmentation and forest edges occurred through decreased concentrations of soil aggregates and fine root production rates. Results from this study will enhance our ability to evaluate soil aggregate, fine root, and leaf litter fall contributions to SOC within forest fragments, and to suggest basic recommendations for the management and conservation of these forest fragments.

Climate change may alter mercury fluxes in northern hardwood forests

Soils are the largest terrestrial pool of mercury (Hg), a neurotoxic pollutant. Pathways of Hg accumulation and loss in forest soils include throughfall, litterfall, soil gas fluxes, and leaching in soil solution, all of which will likely be altered under changing climate. We took advantage of three ongoing climate-change manipulation experiments at the Hubbard Brook Experimental Forest, New Hampshire, USA: a combined growing-season warming and winter freeze-thaw cycle experiment, a throughfall exclusion to mimic drought, and a simulated ice storm experiment to examine the response of the forest Hg cycle to climatic disturbances. Across these three experiments, we compared Hg inputs in throughfall and leaf litterfall and Hg outputs in soil gas fluxes. Soil solution was measured only in the simulated ice storm experiment. We found that northern forest soils retained consistently less Hg by 16–60% in the three climate manipulations compared to the undisturbed controls (~ 7.4 µg Hg m−2 year−1), although soils across all three experiments still served as a net sink for Hg. Growing-season soil warming and combined soil warming and winter freeze-thaw cycles had little effect on litterfall and throughfall flux, but they increased soil Hg0 evasion by 31 and 35%, respectively, relative to the control plots. The drought plots had 5% lower litterfall Hg flux, 50% lower throughfall Hg flux, and 21% lower soil Hg0 evasion than the control plots. The simulated ice storm had 23% higher litterfall Hg flux, 1% higher throughfall Hg flux, 37% higher soil Hg0 evasion, and 151% higher soil Hg leaching than the control plots. These observations suggest that climate changes such as warmer soils in the growing season or more intense ice storms in winter are likely to exacerbate Hg pollution by releasing Hg sequestered in forest soils via evasion and leaching.

Insect outbreaks have transient effects on carbon fluxes and vegetative growth but longer-term impacts on reproductive growth in a mangrove forest

Mangroves are experiencing frequent severe insect outbreaks, and the bud moth larvae (BML; Lasiognatha cellifera) is one of the most common leaf-feeding insects. However, the effects of insect outbreaks on ecosystem carbon fluxes of mangrove ecosystems are not well understood, and more importantly, the relative effects of these disturbances on vegetative and reproductive growth of mangroves remain unclear. We used measurements of plant litterfall, leaf damage percentage, and insect frass production, satellite-derived normalized difference vegetation index (NDVI), and eddy covariance flux measurements to quantify the impacts of a BML outbreak in 2010 on carbon fluxes and both vegetative and reproductive growth of a mangrove forest. The BML outbreak occurred in 2010 damaged nearly 90% of the foliage, increased the annual leaf litterfall, and decreased the flower and propagule production. Net ecosystem productivity decreased following the insect disturbance and recovered within several months. There were no significant differences in annual carbon fluxes among the four years from 2009 to 2013. In contrast, the flower production significantly decreased and there was nearly no propagule production after the insect outbreak. Reproductive growth did not recover even two years after the insect outbreak. Our results showed that the BML outbreak had asymmetric effects on vegetative and reproductive growth of mangrove forests. Our findings can help us better understand the impacts of insect disturbances on mangrove ecosystems and also have implications for informing mangrove conservation and restoration efforts.

Seasonal variations in C and N fractions under tree-based cropping systems in typic ustochrepts

The growing of tree on cultivated land along with agricultural crops is quite common in sub-montane region of northwest India for dual purpose. It enhances the soil fertility and also provides assurance to farmers in case of extreme conditions. A study was conducted to monitor the influence of season on the content of soil organic carbon and nitrogen under four cropping systems. The experiment was carried out in foothills of lower Himalayas. Soil organic carbon (SOC), particulate organic carbon (POC), aggregates associated carbon (AAC), total nitrogen (TN), available nitrogen (AN) and aggregate associated nitrogen (AAN) were determined from 0 to 15 cm and 15–30 cm soil depths under four cropping systems comprising maize–wheat, agro-horticulture, agroforestry 3-year old and 6-year old plantation. The data so obtained was analyzed by using completely randomized design—factorial design at LSD (P < 0.05). The seasonal variations in C and N fractions were significant. The SOC and TN content were higher on an average 7.3 mg g−1 and 0.86 Mg ha−1 in March than those determined in November (4.9 mg g−1 and 0.45 Mg ha−1). This is due to higher leaf litter fall in winter months (December–February). Lower content of C and N fractions were found in autumn season due to highest rainfall received during the monsoon period (May–October) in this region. This caused the aggregate disruption, washing of SOC and nitrogen loss. The C and N fractions also varied significantly with respect to soil depths and cropping systems and were highest under agroforestry system. The agroforestry systems showed greatest seasonal variation than agro-horticulture and mono-cropping system.

Urban Trees Are Sinks for Soot: Elemental Carbon Accumulation by Two Widespread Oak Species.

Urban trees could represent important short- and long-term landscape sinks for elemental carbon (EC). Therefore, we quantified foliar EC accumulation by two widespread oak tree species-Quercus stellata (post oak) and Quercus virginiana (live oak)-as well as leaf litterfall EC flux to soil from April 2017 to March 2018 in the City of Denton, Texas, within the Dallas-Fort Worth metropolitan area. Post oak trees accumulated 1.9-fold more EC (299 ± 45 mg EC m-2 canopy yr-1) compared to live oak trees (160 ± 31 mg EC m-2 canopy yr-1). However, in the fall, these oak species converged in their EC accumulation rates, with ∼70% of annual accumulation occurring during fall and on leaf surfaces. The flux of EC to the ground via leaf litterfall mirrored leaf-fall patterns, with post oaks and live oaks delivering ∼60% of annual leaf litterfall EC in fall and early spring, respectively. We estimate that post oak and live oak trees in this urban ecosystem potentially accumulate 3.5 t EC yr-1, equivalent to ∼32% of annual vehicular EC emissions from the city. Thus, city trees are significant sinks for EC and represent potential avenues for climate and air quality mitigation in urban areas.

Soil heterogeneity in tree mixtures depends on spatial clustering of tree species

Heterogeneity in soil characteristics promotes and maintains coexistence between a diverse set of species. In forests, trees have species-specific impacts on soil abiotic characteristics and mixing of tree species is being promoted as a tool to ensure high levels of diversity and functioning. Yet, limited knowledge is available on the effect of tree species composition and spatial clustering on heterogeneity in soil characteristics. In this paper we derived heterogeneity of key characteristics of the leaf litterfall, the forest floor and the mineral topsoil (C, N and base cation concentration, C:N ratio and mass) in 53 plots of 7 different tree species compositions. We found that heterogeneity increased from the leaf litterfall, through the forest floor down to the mineral topsoil. Mixing tree species did not lead to an increased heterogeneity in the forest floor and topsoil compared to monocultures. However, we did find that mixed plots where conspecific trees stand in groups are more heterogeneous than plots where species are intimately mixed. Our results imply that heterogeneity in soil characteristics does not necessarily increase with tree diversity, but that within mixed stands the spatial organization of tree species should be considered in relation to the scale at which heterogeneity is desired.

Phenology and litterfall production of Bruguiera sexangula (Lour.) Poir. in the Sundarbans mangrove forests, Bangladesh

A large number of mangrove species are growing in the Sundarbans Reserve Forests (SRF), Bangladesh, yet little is known about their phenology. The aim of the present study was to understand the phonological patterns such as leaf emergence, leaf fall, flower buds, flowers, and propagules maturation, in the mangrove Bruguiera sexangula using litterfall data. This study was conducted at Karamjol and Ghagramari areas of SRF, Bangladesh and using litterfall data over two (2) years. Leaf and stipule litterfall occurred throughout the years, with distinct seasonal patterns. New leaf production was significantly correlated with monthly day length. Mean total litterfall was 18.75 Mg ha−1 yr−1, with the largest component being vegetative organs (68.4%). Flowers and propagules litterfall were highest in summer and rainy season, respectively. Kendall’s coefficient of concordance, W, revealed that flower and propagule were significantly concordant during the study years. Flowers and propagules litterfall were significantly influenced by monthly day length and rainfall, respectively. The development of propagule could be affected by the climate during the development and the number of flowers etc. The average development period from flowers to propagules was around 4 months. B. sexangula did not show any correlation between leaf emergence and reproductive organs production.

Dissolved iron elution from mangrove ecosystem associated with polyphenols and a herbivorous snail.

Interest in the systems supplying dissolved forms of iron to the sea from upland forests and wetlands has increased because iron is abundant on land but has low bioavailability in seawater. This can be a limiting factor for the growth of marine phytoplankton. Organic complex iron, a typical form of iron dissolved in seawater, is supplied to the ocean through rivers from forest and wetland soils. As a related study, we focus on mangrove ecosystems located at the boundary between the land and sea and on polyphenols present in leaves as ligands for the formation of iron complexes. When mangrove leaf litterfalls on the wet forest floor, phenolic compounds leach out from the leaves and might solubilize insoluble iron in the sediments (i.e., iron complexation). However, the reaction mechanism is not simple in the field, and it might be made more complex by tidal currents and intervention by crabs and snails, which consume mangrove leaf litter. In the present study, we focused on a detritivorous snail, Terebralia palustris, as a facilitator of iron solubilization associated with phenolic compounds, and examined how the snail contribute to iron solubilization processes. Our results indicated that the amounts of phenolic compounds in mangrove sediments are strongly related to iron solubilization. Furthermore, the average dissolved iron and phenolic contents in sediments from areas inhabited by the snail were significantly higher than those of sediments where the snail was not present. We additionally report that the solubilization of iron was promoted when snail feces were added to mangrove sediments. In conclusion, we propose that iron solubilization in mangrove sediments is promoted by the interaction between i) iron in the sediment, ii) phenolic compounds derived from mangroves, and iii) the consumption of leaves and the deposition of feces by the snail.