Litterfall Data Research Articles

Variations in litterfall dynamics, root biomass, and sediment accretion in restored and recolonized mangroves in Leyte, Philippines

Litterfall production and decay, root biomass, and sediment accretion dynamics were investigated from restored ‘planted’ (R5, R8, R15, and R30 stands) and recolonized stands (C5, C12, and C20 stands) to investigate patterns in primary productivity, belowground biomass, and sediment accretion dynamics. Litterfall data was collected using litter traps over 12 months, while decay kinetics was investigated using a litterbag experiment. Root biomass and sediment accretion data were collected using makeshift acrylic corers. Litterfall production increased as stands aged, and tended to stabilize as it matured in restored (R8: 10.05 Mg/ha/yr; R30: 6.1 Mg/ha/yr) and recolonized stands (C5: 18.75 Mg/ha/yr; C20: 9.05 Mg/ha/yr). Leaf litter decay rates (K/d) showed no pattern with stand age, although the recolonized stands (range: 0.059–0.113 K/d) had lower decay rates compared to the restored (range: 0.073–0.123 K/d) and natural stands (range: 0.064–0.123 K/d). Root biomass declined with age in restored stands (R5: 67.16 Mg/ha, R30: 49.67 Mg/ha), but increased in recolonized stands (C5: 5.41 Mg/ha, C20: 19.50 Mg/ha). Very high rates of sediment accretion were found in younger restored (R5: 10.1 cm/yr) and recolonized stands (C5: 8.1 cm/yr) than mature stands (R30: 6.3 cm/yr; C20: 4.3 cm/yr). Our results showed disparities of patterns in mangrove vegetation growth in recolonized stands and huge potential contribution on mangrove productivity when these areas are effectively restored.

HemiPy: A Python module for automated estimation of forest biophysical variables and uncertainties from digital hemispherical photographs

Abstract Digital hemispherical photography (DHP) is widely used to derive forest biophysical variables including leaf, plant, and green area index (LAI, PAI and GAI), the fraction of intercepted photosynthetically active radiation (FIPAR), and the fraction of vegetation cover (FCOVER). However, the majority of software packages for processing DHP data are based on a graphical user interface, making programmatic analysis difficult. Meanwhile, few natively support analysis of RAW image formats, while none incorporate the propagation or provision of uncertainties. To address these limitations, we present HemiPy, an open‐source Python module for deriving forest biophysical variables and uncertainties from DHP images in an automated manner. We assess HemiPy using simulated hemispherical images, in addition to multiannual time‐series and litterfall data from several forested National Ecological Observatory Network (NEON) sites, as well as comparison against the CAN‐EYE software package. Multiannual time‐series of PAI, FIPAR and FCOVER demonstrate HemiPy's outputs realistically represent expected temporal patterns. Comparison against litterfall data reveals reasonable accuracies are achievable, with RMSE values close to the error of ~1 unit typically attributed to optical LAI measurement approaches. HemiPy's PAI, FIPAR and FCOVER outputs demonstrate good agreement with CAN‐EYE. Consistent with previous studies, when compared to simulated hemispherical images, better agreement is observed for PAI derived using gap fraction near the hinge angle of 57.5° only, as opposed to values derived using gap fraction over a wider range of zenith angles. HemiPy should prove a useful tool for processing DHP images, and its open‐source nature means that it can be adopted, extended and further refined by the user community.

Litterfall seasonality and adaptive strategies of tropical and subtropical evergreen forests in China

AbstractTropical and subtropical evergreen broad-leaved forests (EBFs) and needle-leaved forests (ENFs) in China exhibit complex leaf shedding strategies in responses to soil water availability, vapor pressure deficits (VPDs) and sunlight availability. However, the seasonal variations and triggers of litterfall differ significantly in tropical/subtropical forests, and there are still many uncertainties. Herein, we aim to explore the distinct climatic factors of seasonal litterfall in a climate–phenology correlation framework. We collected seasonal litterfall data from 85 sites across tropical/subtropical China and used linear correlation coefficients between sunlight and rainfall to partition synchronous/asynchronous climates. Additional phase analysis and structural equation model analysis were conducted to model the climatic triggers of tropical phenology. Results indicated two types of tropical litterfall phenology under two types of climates. In synchronous climates, where seasonal sunlight and rainfall are positively correlated, the litterfall peak of the unimodal phenology and the first litterfall peak of the bimodal phenology both happen at the end of dry season. The second litterfall peak of the bimodal phenology occurs at the end of rainy season due to water stress. In asynchronous climates, where seasonal sunlight and rainfall are negatively correlated, VPD shows consistent seasonal variations with incoming sunlight. The leaf senescence is accelerated at the end of dry season by higher VPD; while soil water deficit is in anti-phase with sunlight and mainly controls the second litterfall peak of the bimodal phenology in EBF. Our findings provide an important reference for modeling tropical phenology in Earth system models.

Temperature and Precipitation Diversely Control Seasonal and Annual Dynamics of Litterfall in a Temperate Mixed Mature Forest, Revealed by Long‐Term Data Analysis

AbstractLitterfall is a good indicator of overall forest functions in forest ecosystems. Globally, forest litterfall has been extensively investigated, however, there is a lack of long‐term data analysis to show the various litterfall components in relation to environmental factors on the monthly and yearly scales. Here, monthly (May–October) and annual (1981–2018) litterfall including leaves, twigs, bark, reproductive, and miscellaneous fractions were collected in a mixed mature Pinus koraiensis forest on Changbai Mountain in Northeast, China, across 30 years. Based on these long‐term litterfall data, we analyzed the seasonal and annual variations in different litterfall fractions and the internal/external drivers. We observed that both the leaf and total litterfall exhibited a strong, similar seasonal pattern, with the highest levels between September and October, and the annual litterfall had an “S‐shaped” increasing pattern from 1981 to 2018. The other litterfall fractions showed distinct monthly and yearly fluctuations across the 30 years. Mean monthly evapotranspiration and temperature (minimum and maximum) were the best predictors for monthly litterfall. By contrast, the models that best predicted the annual litterfall production included mean annual precipitation and mean monthly precipitation and temperature in May and October. Our study, using a unique dataset of detailed long‐term litterfall dynamics, has potentially major significance for enhancing our understanding of the role of climatic factors controlling forest litterfall amount and seasonality in temperate mixed mature forests. This insight is of paramount importance for modeling and estimating soil carbon sequestration and nutrient cycling of temperate forests under climate change.

Litterfall release, vegetative, and reproductive phenology investigation of Heritiera fomes Buch-Ham in the Sundarbans mangrove forests, Bangladesh: relationship with environmental variables

The study of vegetative and reproductive phenology through litterfall collection of mangrove species is vital for mangrove management and restoration in climate change situation. This study was carried out to investigate vegetative and reproductive phenological pattern of Heritiera fomes using litterfall data in the Sundarbans, Bangladesh for a period of 24 months. Leaf and stipule litterfall released throughout the year with a distinct periodic pattern. Vegetative litterfall (981.9–1211.3 g/sq m/yr) contributed 59.3% of total litterfall (1791.1–1907.3 g/m/yr). The order of vegetative litterfall was leaf > branch > stipule. Peak flowering and mature fruit litterfall were noticed in April (1.52 times of mean monthly flower production) and July (1.56 times of mean monthly production), respectively. Analysis of variance (ANOVA) showed significant difference (p < 0.05) among monthly litterfall productions, whereas t-test showed no significant difference (p > 0.05) of litterfall production between two successive years during study periods. Vegetative and flower litterfall were significantly influenced by maximum wind speed, mean monthly temperature and day length. On the contrary, mature fruits were significantly correlated with rainfall.

Benchmark estimates for aboveground litterfall data derived from ecosystem models

Litter production is a fundamental ecosystem process, which plays an important role in regulating terrestrial carbon and nitrogen cycles. However, there are substantial differences in the litter production simulations among ecosystem models, and a global benchmarking evaluation to measure the performance of these models is still lacking. In this study, we generated a global dataset of aboveground litterfall production (i.e. cLitter), a benchmark as the defined reference to test model performance, by combining systematic measurements taken from a substantial number of surveys (1079 sites) with a machine learning technique (i.e. random forest, RF). Our study demonstrated that the RF model is an effective tool for upscaling local litterfall production observations to the global scale. On average, the model predicted 23.15 Pg C yr−1 of aboveground litterfall production. Our results revealed substantial differences in the aboveground litterfall production simulations among the five investigated ecosystem models. Compared to the reference data at the global scale, most of models could reproduce the spatial patterns of aboveground litterfall production, but the magnitude of simulations differed substantially from the reference data. Overall, ORCHIDEE-MICT performed the best among the five investigated ecosystem models.

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.

A metabolic scaling theory-driven remote sensing approach to map spatiotemporal dynamics of litterfall in a tropical montane cloud forest

Litter production, or litterfall, is a predominant part of the carbon and nutrient cycles of forest ecosystems. As a major and relatively invariable aspect of primary production, litterfall could be a predictor of total plant production. However, the conventional field approach for its estimation is laborious and costly. High temporal resolution optical satellite imagery may strengthen our ability to estimate litterfall over a vast region, but this remote sensing method is limited in some tropical and near-tropical mountainous regions, mainly due to coarse spatial resolution and frequent cloud coverage. The metabolic scaling theory (MST) states that forest productivity (including litterfall) is directly proportional to the mass of the photosynthesis tissue (leaves), and spatially, it may be isometrically scaled using the size of the largest individual in the system. In this study, we investigated the temporal dimension of the MST and hypothesized that the maximum leaf abundance over a year could also be a key determinant of annual litter production. The relationship between the leaf mass during the peak growing season and annual litterfall could facilitate large-scale litterfall mapping in mountainous terrains, since vegetation indices such as the Enhanced Vegetation Index (EVI) or the Normalized Difference Vegetation Index (NDVI), commonly utilized as a surrogate for leaf abundance, can be derived from relatively high spatial resolution satellite imagery. We correlated the summer growing season Landsat Enhanced Thematic Mapper plus (ETM+) EVI and NDVI for 2016 and 2017 and the temporally corresponding annual accumulated field litterfall data acquired from hinoki (Chamaecyparis spp.) dominant tropical montane cloud forests in northeastern Taiwan (23.98 N, 120.97 E). We found that the summer growing season EVI and NDVI may be salient variables to explain the spatial variation of annual litter production ( r2 = 0.39–0.67, p ≤ 0.01). The results have profound implications for applying MST to the regional mapping of ecosystem production across space and time in humid tropical regions, and these implications may facilitate the remote assessment of the terrestrial carbon budget.

Assessing the relative role of climate on litterfall in Mediterranean cork oak forests

Abstract: Litterfall plays a key role in the dynamic of forest ecosystems, ultimately determining forest productivity and carbon and nutrient cycling. Increasing our understanding on the role of structural and environmental factors controlling litterfall amount and seasonality is of paramount importance for modelling and estimating soil carbon sequestration and nutrient cycling under climate change scenarios. However, the effect of climatic conditions on litterfall has been scarcely studied, especially in Mediterranean ecosystems. Here, we used nine years of seasonally collected litterfall data in two contrasting Mediterranean cork oak forests to evaluate the effect of climatic variables on leaf fall and litterfall. First, we isolated the litterfall seasonal trend and the between-sites differences in production by using linear mixed models. Then, we evaluated the effect of climatic variables and whether this effect was site-specific. We found a consistent litterfall seasonal pattern, mainly determined by leaf shedding (70% of litterfall). Leaf fall mainly occurs in spring with a second but much smaller peak in autumn some years. Mean temperature, precipitation and mean wind speed strongly influenced litterfall, but this effect was site-specific. In the forest site located at higher latitude and altitude, leaf fall increased linearly with temperature and showed a positive quadratic response to precipitation. In the water-limited site, leaf fall was reduced as temperature increased and did not respond to precipitation. These results have implications for modelling and predicting soil carbon sequestration, nutrient cycling, and the forest ecosystem productivity. Specifically, carbon and nutrient cycling models can be improved by incorporating idiosyncratic forest sites responses to climatic variability.

Impact of litter quantity on the soil bacteria community during the decomposition of Quercus wutaishanica litter.

The forest ecosystem is the main component of terrestrial ecosystems. The global climate and the functions and processes of soil microbes in the ecosystem are all influenced by litter decomposition. The effects of litter decomposition on the abundance of soil microorganisms remain unknown. Here, we analyzed soil bacterial communities during the litter decomposition process in an incubation experiment under treatment with different litter quantities based on annual litterfall data (normal quantity, 200 g/(m2/yr); double quantity, 400 g/(m2/yr) and control, no litter). The results showed that litter quantity had significant effects on soil carbon fractions, nitrogen fractions, and bacterial community compositions, but significant differences were not found in the soil bacterial diversity. The normal litter quantity enhanced the relative abundance of Actinobacteria and Firmicutes and reduced the relative abundance of Bacteroidetes, Plantctomycets and Nitrospiare. The Beta-, Gamma-, and Deltaproteobacteria were significantly less abundant in the normal quantity litter addition treatment, and were subsequently more abundant in the double quantity litter addition treatment. The bacterial communities transitioned from Proteobacteria-dominant (Beta-, Gamma-, and Delta) to Actinobacteria-dominant during the decomposition of the normal quantity of litter. A cluster analysis showed that the double litter treatment and the control had similar bacterial community compositions. These results suggested that the double quantity litter limited the shift of the soil bacterial community. Our results indicate that litter decomposition alters bacterial dynamics under the accumulation of litter during the vegetation restoration process, which provides important significant guidelines for the management of forest ecosystems.

Measuring leaf area index in rubber plantations − a challenge

In order to estimate water use, water requirements and carbon sequestration of tropical plantation systems such as rubber it is adamant to have accurate information on leaf area development of the plantation as the main determinant of evapotranspiration. Literature commonly suggests a number of different methods on how to obtain leaf area index (LAI) information from tree plantation systems. Methods include destructive measurements of leaf area at peak LAI, indirect methods such as gap fraction methods (i.e. Hemiview and LAI 2000) and radiation interception methods (i.e. SunScan) or litter fall traps. Published values for peak LAI in rubber plantation differ widely and show no clear trend to be explained by management practices or the influence of local climate patterns. This study compares four methods for determining LAI of rubber plantations of different ages in Xishuangbanna, Yunnan, PR China. We have tested indirect measurement techniques such as light absorption and gap fraction measurements and hemispherical image analysis against litter fall data in order to obtain insights into the reliability of these measuring techniques for the use in tropical tree plantation systems. In addition, we have included data from destructive harvesting as a comparison. The results presented here clearly showed that there was no consistent agreement between the different measurements. Site, time of the day and incoming radiation all had a significant effect on the results depending on the devices used. This leaves us with the conclusion that the integration of published data on LAI in rubber into broad ranging assessments is very difficult to accomplish as the accuracy of the measurements seems to be very sensitive to a number of factors. This diminishes the usefulness of literature data in estimating evapotranspiration from rubber plantations and the induced environmental effects, both on local as well as regional levels.

Forest litterfall and its composition: a new data set of observational data from China

AbstractKnowledge of litterfall production and its allocation is important for understanding nutrient cycling and assessing productivity in forest ecosystems; however, available litterfall datasets are rare in China. Consequently, in the present study, data from published studies (1970–2014) on litterfall and its composition in forest ecosystems in China (excluding Hong Kong, Macao, and Taiwan) were collected, critically reviewed, and incorporated in a comprehensive forest litterfall data set for China. The data set included the following litterfall data: leaves, branches, reproductive parts (flowers and fruits), and miscellaneous. Moreover, associated information was also included, i.e., geographical location (latitude, longitude, altitude, aspect, and slope), climate [mean annual temperature (MAT) and mean annual precipitation (MAP)], stand description (forest type, dominant tree species, stand origin, stand age, mean DBH, mean tree height and stand density), and data collection regime (sample frequency and date, trap size, and number). The data set included 904 entries for 168 study sites, that were distributed in various climate zones with latitudes 18.26°–51.50° N, longitudes 82.25°–129.53° E and altitudes 0–4115 m above sea level (a.s.l.), covering broad climatic gradients (−5.4 to 25.4°C in MAT and 370 to 2800 mm in MAP). The data can be used to analyze spatio‐temporal dynamics of China's forest litterfall and its allocation, understand nutrient cycling and assess productivity in forest ecosystems. Finally, the data set is freely available for noncommercial scientific applications.

Comparison of carbon-stock changes, eddy-covariance carbon fluxes and model estimates in coastal Douglas-fir stands in British Columbia

The global network of eddy-covariance (EC) flux-towers has improved the understanding of the terrestrial carbon (C) cycle, however, the network has a relatively limited spatial extent compared to forest inventory data and plots. Developing methods to use inventory-based and EC flux measurements together with modeling approaches is necessary evaluate forest C dynamics across broad spatial extents. Changes in C stock change (ΔC) were computed based on repeated measurements of forest inventory plots and compared with separate measurements of cumulative net ecosystem productivity (ΣNEP) over four years (2003 – 2006) for Douglas-fir (Pseudotsuga menziesii var menziesii) dominated regeneration (HDF00), juvenile (HDF88 and HDF90) and near-rotation (DF49) aged stands (6, 18, 20, 57 years old in 2006, respectively) in coastal British Columbia. ΔC was determined from forest inventory plot data alone, and in a hybrid approach using inventory data along with litter fall data and published decay equations to determine the change in detrital pools. These ΔC-based estimates were then compared with ΣNEP measured at an eddy-covariance flux-tower (EC-flux) and modelled by the Carbon Budget Model - Canadian Forest Sector (CBM-CFS3) using historic forest inventory and forest disturbance data. Footprint analysis was used with remote sensing, soils and topography data to evaluate how well the inventory plots represented the range of stand conditions within the area of the flux-tower footprint and to spatially scale the plot data to the area of the EC-flux and model based estimates. The closest convergence among methods was for the juvenile stands while the largest divergences were for the regenerating clearcut, followed by the near-rotation stand. At the regenerating clearcut, footprint weighting of CBM-CFS3 ΣNEP increased convergence with EC flux ΣNEP, but not for ΔC. While spatial scaling and footprint weighting did not increase convergence for ΔC, they did provide confidence that the sample plots represented site conditions as measured by the EC tower. Methods to use inventory and EC flux measurements together with modeling approaches are necessary to understand forest C dynamics across broad spatial extents. Each approach has advantages and limitations that need to be considered for investigations at varying spatial and temporal scales.

Litter Fall Dynamics of Restored Mangroves (Rhizophora mucronata Lamk. and Sonneratia alba Sm.) in Kenya

AbstractMangrove forests are active carbon sinks and important for nutrient cycling in coastal ecosystems. Restoration of degraded mangrove habitats enhances return of ecosystem goods and services, including carbon sequestration. Our objective was to assess the restoration of primary productivity of reforested mangrove stands in comparison with natural reference stands in Gazi Bay, Kenya. Litter fall data were collected in nine Rhizophora mucronata and Sonneratia alba monospecific stands by use of litter traps over 2 years. Litter was emptied monthly, dried, sorted, and weighed. The reforested and natural stands showed seasonality patterns only in the production of reproductive material. Leaves constituted the highest percentage to total litter fall. Litter productivity rates for the R. mucronata stands were not significantly different and ranged from 6.61–10.15 to 8.36–11.02 t ha−1 yr−1 for the restored and natural stands, respectively. The productivity of 5 years R. mucronata stands reached 5.22 t ha−1 yr−1 and was significantly different from other stands. Litter productivity rates for S. alba stands was 7.77–7.85 for the restored stands and 10.15 t ha−1 yr−1 for the natural stand but differences were not significant. Our results indicate that plantations of at least 11 years have attained litter productivity rates comparable to the natural forests. This suggests that productivity of replanted mangroves is likely to reach complete recovery by this age under the prevailing environmental conditions.

Seasonality of above-ground net primary productivity along an Andean altitudinal transect in Peru

Abstract:Solar irradiance and precipitation are the most likely drivers of the seasonal variation of net primary productivity (NPP) in tropical forests. Since their roles remain poorly understood, we use litter traps, dendrometer bands and census data collected from one hectare permanent plots to quantify the seasonality of above-groundNPPcomponents and weather parameters in 13 sites distributed along a 2800-m altitudinal gradient ranging from lowland Amazonia to the high Andes. We combine canopy leaf area index and litterfall data to describe the seasonality of canopy production. We hypothesize that solar irradiance is the primary driver of canopy phenology in wetter sites, whereas precipitation drives phenology in drier systems. The seasonal rhythm of canopyNPPcomponents is in synchrony with solar irradiance at all altitudes. Leaf litterfall peaks in the late dry season, both in lowland (averaging 0.54 ± 0.08 Mg C ha y−1, n = 5) and montane forests (averaging 0.29 ± 0.04 Mg C ha y−1, n = 8). Peaks in above-ground coarse woodyNPPappears to be triggered by the onset of rainfall in seasonal lowland rain forests (averaging 0.26 ± 0.04 Mg C ha y−1, n = 5, in November), but not in montane cloud forests.

Comparing Throughfall and Litterfall Nutrient Fluxes in a Rubber (Hevea brasiliensis willd. muell-arg) Plantation Agro-ecosystem at Ikenne, South-west Nigeria

This study compares nutrient fluxes (throughfall and litterfall) in a rubber (Hevea brasiliensisWilld. Muell-Arg) plantation agro-ecosystem at Ikenne, SW Nigeria. Throughfallsamples were collected bi-weekly under the rubber canopies (40-, 15-, and 5-year-old) using throughfall funnel collectors with 10 replicates. Litterfall was collected on a monthly basis in the three rubber stands using twenty-four 0.25 m2litter traps (eight replicates in each of the three rubber stands) positioned randomly to estimate total annual litter production (dry biomass)and its main fractions. Throughfall and litterfall samples were analyzed for total nitrogen, sodium, phosphorus, calcium, potassium and magnesium. The annual means of throughfall in the different stands were compared by solution type using one-way analysis of variance (ANOVA), followed by a post-hoc separation of means by the Scheffe-test (p&lt;0.05).The litterfall data were analyzed using one-way analysis of variance based on the representative of 12 months. The results revealed a clear pattern of increased levels of base cations and fluxesof throughfall compared to those occurring in precipitation. Fluxes of Ca2+in throughfallare typically 1.5-2 times greater than those occurring in rainfall. Among the rubber stands, fluxes of K+are also greater in throughfall, consistent with previous studies. The enrichment of elements in throughfallhas been ascribed to the dissolution andwashout of atmospheric materials deposited on the canopy.Comparison of total annual litterfall nutrient budgets show that the 15-year-old rubber stand was cycling more Mg2+, N, Na+, K+, P, and Ca2+in litterfall than the 40-and 5-year-old rubber stands.

Phenological traits of the mangrove Rhizophora stylosa Griff. at the northern limit of its biogeographical distribution

The vegetative and reproductive phenology of the subtropical mangrove species Rhizophora stylosa was investigated at Manko Wetland, Okinawa Island, Japan. We assessed phenology using litterfall data over four years. Leaf and stipule litterfall occurred throughout the year, with distinct seasonal patterns. Kendall’s coefficient of concordance, W, revealed that the monthly changes in leaf and stipule litterfall were strongly and significantly concordant among years. Leaf litterfall was significantly correlated with monthly maximum wind speed and monthly day length, and stipule litterfall was significantly correlated with monthly mean air temperature and relative humidity. Branch litterfall showed no clear monthly pattern and correlated well with monthly maximum wind speed. Mean total litterfall was 11.2 Mg ha−1 year−1, with the largest component being vegetative organs (78.7 %). Flower, fruit, and propagule litterfall were all highest in summer and lowest in winter. The W values revealed that most reproductive organs in litterfall had significant monthly trends. Flower and fruit litterfall were significantly correlated with monthly day length and monthly mean air temperature, respectively. The average development periods from flower buds to flowers, fruits, and mature propagules were approximately 2–3 months, 4–5 months, and 11–12 months, respectively. Except for branches, all vegetative and reproductive components of litterfall had approximately one year cycles.

Multiple observation types reduce uncertainty in Australia's terrestrial carbon and water cycles

Abstract. Information about the carbon cycle potentially constrains the water cycle, and vice versa. This paper explores the utility of multiple observation sets to constrain a land surface model of Australian terrestrial carbon and water cycles, and the resulting mean carbon pools and fluxes, as well as their temporal and spatial variability. Observations include streamflow from 416 gauged catchments, measurements of evapotranspiration (ET) and net ecosystem production (NEP) from 12 eddy-flux sites, litterfall data, and data on carbon pools. By projecting residuals between observations and corresponding predictions onto uncertainty in model predictions at the continental scale, we find that eddy flux measurements provide a significantly tighter constraint on continental net primary production (NPP) than the other data types. Nonetheless, simultaneous constraint by multiple data types is important for mitigating bias from any single type. Four significant results emerging from the multiply-constrained model are that, for the 1990–2011 period: (i) on the Australian continent, a predominantly semi-arid region, over half the water loss through ET (0.64 ± 0.05) occurs through soil evaporation and bypasses plants entirely; (ii) mean Australian NPP is quantified at 2.2 ± 0.4 (1σ) Pg C yr−1; (iii) annually cyclic ("grassy") vegetation and persistent ("woody") vegetation account for 0.67 ± 0.14 and 0.33 ± 0.14, respectively, of NPP across Australia; (iv) the average interannual variability of Australia's NEP (±0.18 Pg C yr−1, 1σ) is larger than Australia's total anthropogenic greenhouse gas emissions in 2011 (0.149 Pg C equivalent yr–1), and is dominated by variability in desert and savanna regions.

小兴安岭白桦次生林叶面积指数的估测

叶面积指数(LAI)是量化冠层结构最常用的参数之一, 准确估测LAI对森林生态系统结构特性的研究具有重要意义。利用半球摄影图像法和LAI-2000法及半球摄影图像法结合凋落物法估测了小兴安岭白桦次生林LAI及其动态变化。 首先对该林型叶凋落末期(11月初)的半球摄影图像进行合理校正(包括木质部分所占比例 <em>α</em>, 冠层水平集聚指数<em>Ω</em>_E), 校正值作为该时期常绿树种的真实LAI(LAI_t), 结合各调查期的凋落物数据, 得到落叶季节(7-11月)的LAI_t, 并以该值为参考值, 对比分析了两种光学仪器法估测值。结果表明: 两种光学仪器法在LAI最大时期低估(分别低估2.83%、6.20%), 其他时期显著高估(平均高估118.13%、89.34%), 但两种光学仪器法与探讨方法估测值存在很好的相关性: LAI_t=-1.1393 + 1.0934·LAI_HP, <em>R</em>²= 0.80; LAI_t=-0.1712 + 0.6259·LAI_LAI-2000, <em>R</em>²= 0.83。研究结果可为将来方便、快捷、准确的估测白桦次生林的LAI提供参考。;Leaf area index (LAI), defined as the total one-sided leaf area per unit ground surface area (m²m^-2), is among the most frequently used parameters for analysis of plant canopy structure. Most ecosystem process models that simulate carbon and water cycles at a stand or regional scale require LAI as an input variable, thus accurate measurement of LAI is essential for conversion of leaf-level processes to the canopy level. The main methods of LAI measurement generally are classifiable into two groups: direct measures, which mainly include destructive sampling and the litterfall method; and indirect measures, which mainly include hemispherical photography and the LAI-2000 plant canopy analyzer. However, using a direct or indirect method alone may not accurately estimate LAI for mixed needle and broadleaf forest or broadleaf forest with a high proportion of evergreen species. Secondary <em>Betula platyphylla</em> is among the most common broadleaf forest types that regenerate naturally after clear cutting of broadleaved-Korean pine forest in the Xiaoxing'an Mountains in north-east China. In the present study, we estimated LAI and its seasonal dynamics in secondary <em>B. platyphylla</em> forest in the Xiaoxing'an Mountains using optical methods (hemispherical photography and the LAI-2000 Plant Canopy Analyzer) and a combinational method (hemispherical photography combined with the litterfall method). In the combinational method, hemispherical photographs obtained in early November were calibrated with consideration of the woody-to-total ratio (<em>α</em>) as well as the clumping index (for clumping beyond the shoots, <em>Ω</em>_E). The calibrated value was regarded as the true LAI (LAI_t) of coniferous species; the LAI_t of the study stand and its seasonal dynamics (from July to November) were obtained by supplementation of the LAI_t of coniferous species by incorporation of litterfall data for each observation. Using this result as a reference value, we compared the results obtained with the two optical methods. The LAI for the litter of <em>B. platyphylla</em> and <em>Larix gmelini</em> accounted for 87.65% of the total litter, and leaves of <em>B. platyphylla</em> began to fall distinctly earlier than those of other species, and the LAI for the litter of <em>B. platyphylla</em> accounted for 98.24% of all species during July and August. Leaf fall for most species excluding <em>B. platyphyll</em>a peaked in mid-September. In contrast to the proposed method, hemispherical photography and LAI-2000 both underestimated LAI by 2.83% and 6.20%, respectively, during the maximum LAI period and overestimated LAI significantly on average by 118.13% and 89.34%, respectively, on other dates. However, hemispherical photography and LAI-2000 yielded LAI values that were significantly correlated with the results obtained with the combinational method; the regression curves were LAI_t= -1.1393 + 1.0934·LAI_HP(<em>R</em>²= 0.80) and LAI_t= -0.1712 + 0.6259·LAI_LAI-2000 (<em>R</em>²= 0.83), respectively. The corrected hemispherical photography data were used to simulate the seasonal dynamics of LAI from May to November, which was indicated to be accurate (<em>R</em>²= 0.87). The LAI estimate obtained with the two optical methods did not differ significantly from July to September, but the estimate with the LAI-2000 method was significantly lower than that obtained with hemispherical photography after October. However, LAI estimated with the two optical methods was significantly correlated (<em>R</em>²= 0.86) for secondary <em>B. platyphylla</em> forest. This study lays a foundation for convenient, rapid and accurate estimation of LAI for secondary <em>B. platyphylla</em> forest in subsequent studies.

Vegetative and reproductive phenology of the mangrove Bruguiera gymnorrhiza (L.) Lam. on Okinawa Island, Japan

Vegetative and reproductive phenology of the subtropical mangrove Bruguieragymnorrhiza was investigated at Manko Wetland, Okinawa Island, Japan. Phenology was assessed using litterfall data over 4 years. Leaf and stipule litterfall occurred throughout the year, with distinct seasonal patterns. Kendall’s coefficient of concordance, W, revealed that the monthly changes in leaf and stipule litterfall were strongly and significantly concordant among years. Leaf litterfall was linked to monthly day length and maximum wind speed, and stipule litterfall was linked to monthly mean air temperature, monthly rainfall, and maximum wind speed. Branch litterfall showed no clear monthly pattern, but tended to vary with monthly maximum wind speed. Mean leaf longevity was 19 months. Mean total litterfall was 10.1 Mg ha−1 year−1, with the largest component being vegetative organs (58 %). Flower and propagule litterfall were highest in autumn and summer, respectively, and lowest in winter. The W values revealed that, of the reproductive organs, only flower litterfall had a significant monthly trend. Flower litterfall was correlated with monthly mean air temperature and relative humidity. The average development periods from flower buds to flowers and from flowers to mature propagules were approximately 1 and 8 months, respectively. It took 9 months to produce mature propagules from flower buds. Except for branches, all vegetative and reproductive components of litterfall had clear annual cycles.