Nutrient fluxes via litterfall and leaf litter decomposition vary across a gradient of soil nutrient supply in a lowland tropical rain forest

The extent to which plant communities are determined by resource availability is a central theme in ecosystem science, but patterns of small-scale variation in resource availability are poorly known. Studies of carbon (C) and nutrient cycling provide insights into factors limiting tree growth and forest productivity. To investigate rates of tropical forest litter production and decomposition in relation to nutrient availability and topography in the absence of confounding large-scale variation in climate and altitude we quantified nutrient fluxes via litterfall and leaf litter decomposition within three distinct floristic associations of tropical rain forest growing along a soil fertility gradient at the Sepilok Forest Reserve (SFR), Sabah, Malaysia. The quantity and nutrient content of small litter decreased along a gradient of soil nutrient availability from alluvial forest (most fertile) through sandstone forest to heath forest (least fertile). Temporal variation in litterfall was greatest in the sandstone forest, where the amount of litter was correlated negatively with rainfall in the previous month. Mass loss and N and P release were fastest from alluvial forest litter, and slowest from heath forest litter. All litter types decomposed most rapidly in the alluvial forest. Stand-level N and P use efficiencies (ratios of litter dry mass to nutrient content) were greatest for the heath forest followed by the sandstone ridge, sandstone valley and alluvial forests, respectively. We conclude that nutrient supply limits productivity most in the heath forest and least in the alluvial forest. Nutrient supply limited productivity in sandstone forest, especially on ridge and hill top sites where nutrient limitation may be exacerbated by reduced rates of litter decomposition during dry periods. The fluxes of N and P varied significantly between the different floristic communities at SFR and these differences may contribute to small-scale variation in species composition.     

Nutrient stocks in litterfall and litter in cocoa agroforests in Brazil

Aim

To compare the internal balances of nutrients and the rates of nutrient cycling across nine cocoa agroforestry systems consisting of various combination of soil types (Latosols and Cambisols), production systems (cabruca and Erythrina glauca-shade) and fertilization regimes in southern Bahia, Brazil.

Methods

We measured nutrient stocks in litter fall production, in the accumulated litter and fruits. The internal nutrient balance for various simulations was obtained by the following expressions: (1) Balance 1?=?litter – fruit (seeds and husks) and (2) Balance 2?=?(litter?+?husks) – seeds. Annual litter decomposition coefficients (k) and subsequent potential of nutrient release were also investigated. The data were analyzed by principal components analysis and by Pearson correlations.

Results

There was a high degree of dissimilarity among the cocoa agrosystems in relation to the nutrient cycling and the internal nutrient balance. The mean annual litterfall production ranged from 4.6 to 8.5 Mg/ha, and the amount of accumulated litter ranged from 7.7 to 16.8 Mg/ha. The results showed significant differences in quality among litter from cocoa agroforests; the decomposition coefficient of litter and the subsequent nutrient release were regulated by the litter quality. In general, the cocoa-erythrina system presented a higher capacity to recycle nutrients compared to the cocoa-cabruca system, with the cocoa-erythrina system having the largest transfer rate of nutrients through litterfall, high values for the decomposition coefficient of litter and the lowest values for the Mean Residence Time of nutrients. Cocoa tree leaves functioned as a sink of nutrients, while shade tree leaves functioned predominantly as a source. The nutritional reserves of litter?+?cocoa fruit husks, with respect only to the nutrients exported in the seeds, the balance was positive for all nutrients (N, P, K, Ca and Mg) in all agroforests, which emphasizes the potential productive capacity of these agroforests to sustain the estimated production in different harvest cycles.

Conclusions

The internal balance of nutrients reflects an agroforests’s productive capacity, which accumulated litter and cocoa fruit husks may be important nutrient sources that could enable the development of fertilizer recommendation systems aimed at increasing the efficiency of fertilizer use and at maintaining soil fertility in cocoa agroforests. Therefore, further research is needed to develop nutritional balance systems integrating litter?+?fruits stock and other nutrient pathways (e.g., soil quality, biological N fixation, leaching), which were not measured, for making recommendations regarding liming and fertilizers that are suitable for highly complex biological agrosystems, such as cocoa agroforests that have low levels of elements exported during seed production.     

Photosynthesis and successional status of Costa Rican rain forest trees

Seven tree species from three different light environments in the wet lowland forests of Costa Rica were grown under controlled environment conditions to assess light related photosynthetic potentials. Light saturated photosynthesis rates were clearly related to light levels of the field environments. Mean saturated, net photosynthetic rates ranged from 6.8 to 11.3 to 27.7 mol m^–2 sec^–1 for plants from heavy shade, canopy light gaps and man-made clearings respectively. Light saturation of plants from clearings occurred at photosynthetic photon flux densities greater than 1000 mol m^–2 sec^–1 whereas plants from heavy shade environments became light saturated near 500 mol m^–2 sec^–1. Plants that normally occur in intermediate light environments were intermediate in light saturation levels. Mean maximum stomatal conductances ranged from 1.0 to 7.3 mm sec^–1 and followed a pattern similar to photosynthetic rates.     

Regeneration dynamics of alluvial gaps in a warm temperate rain forest in New Zealand

Gaps formed by stream laid gravels in a warm temperate Podocarp-Angiosperm rain forest in New Zealand were quickly invaded by 41 free-standing woody species. Height-age curves for the eight most frequent species were used to construct a 12 yr chronosequence which showed 18 species arrived by 0.9 yr and 33 by 1.9 yr. This rapid invasion was supplied from both gaps and mature forest and fitted the Initial Floristic Model coupled with a Facilitation Mechanism. Over the 12 yr period, stem density and births peaked at 0.9 yr and deaths at 1.9 yr with a natality of 39.5/m², a mortality of 38.5/m² and nearly 99% dying as seedlings. Plant height increased to 5.1 m at 12.1 yr with height increment peaking at 43 cm/yr at 7.3 yr. Maximum potential heights ranged from 4 to 60 m and were positively correlated with longevity which varied from 20 to 1150 yr for 19 known species. A decline in height increment to 0.9 yr showed a below-ground component in intraspecific competition with significant negative correlations between stem density and height indicating a later above-ground component. There was no significant height competition amongst the 11 most frequent species and only one significant negative interspecific association. This suggests high species coexistence for which Equal chance was probably the major mechanism. Given this coexistence, rapid species arrival, early sexual maturity and similar density and height-age patterns, the main dynamic variables may be maximum height, longevity and height increment, all of which are, partly, genetically programmed. Most dynamic affinities are with tropical forest, although height growth and species richness are warm temperate.     

The effect of different anthropogenic disturbances on litterfall of a dominant pioneer rain forest tree in Gabon

Tropical rain forests worldwide are affected by anthropogenic disturbances, and secondary forests that develop afterwards are often dominated by pioneer tree species, but the consequences of different anthropogenic disturbances on nutrient cycling are poorly understood. Because most nutrient cycling in tropical rain forests occurs through litterfall and in the soil organic layer, we measured litterfall of a widespread and dominant pioneer tree, okoume (Aucoumea klaineana, Burseraceae) in Gabon, in one forest previously disturbed by logging and in another by agriculture. Litterfall of okoume trees, measured over 14 months, was 18.2 Mg ha⁻¹ year⁻¹ in the formerly logged forest, which was 72.6% greater than in the forest more recently disturbed by agriculture (10.6 Mg ha⁻¹ year⁻¹). Litter decomposition rates were more rapid in the formerly logged forest, and this may explain why litter thickness was 32% lower in the formerly logged forest, despite the greater litterfall within it. Our results highlight that two widespread anthropogenic disturbances in Gabonese rain forests have significantly different consequences on litterfall of a dominant tree and therefore are likely to have different effects on nutrient cycling and forest ecosystem function.     

Taxonomic and functional ant diversity along a secondary successional gradient in a tropical forest

The taxonomic diversity (TD) of tropical flora and fauna tends to increase during secondary succession. This increase may be accompanied by changes in functional diversity (FD), although the relationship between TD and FD is not well understood. To explore this relationship, we examined the correlations between the TD and FD of ants and forest age in secondary forests at the α‐ and β‐diversity levels using single‐ and multi‐trait‐based approaches. Our objectives were to understand ant diversity patterns and to evaluate the role of secondary forests in the conservation of biodiversity and in the resilience of tropical forests. Ant assemblages were sampled across a chronosequence in the Lacandon region, Mexico. All species were characterized according to 12 functional ecomorphological traits relevant to their feeding behavior. We found that TD and FD were related to forest age at the alpha level, but not at the beta level. α‐functional richness and divergence increased linearly with species richness and diversity, respectively. Also, the relationship between taxonomic and functional turnover was linear and positive. Our results indicated that functional traits were complementary across the chronosequence. The increase in FD was mainly driven by the addition of rare species with relevant traits. The older secondary forests did not recover all of the functions of old growth forest but did show a tendency to recovery. Because older successional stages support more TD and FD, we suggest developing agriculture and forestry management practices that facilitate rapid post‐agricultural succession and thereby better preserve the functionality of tropical forests.     

High litterfall in old-growth and secondary upper montane forest of Costa Rica

Tropical upper montane forests usually comprise trees of small stature with a relatively low aboveground productivity. In contrast to this rule, in the Cordillera de Talamanca (Costa Rica), tall trees (>35 m in height and more than 60 cm in diameter) are characteristic for the upper montane old-growth oak forests which are growing at an altitude of almost 3,000 m close to the alpine timberline. For these exceptional forests, productivity data are not yet available. In this study, we analyzed litterfall and its components (tree leaves, litter of epiphytic vascular and non-vascular plants, mistletoes, twigs and other canopy debris) in three forest stands belonging to different successional stages and related seasonal changes in litterfall to micrometeorological variables. The studied stands were early-successional forest (10–15-year-old), mid-successional forest (40-year-old), and old-growth forest. The stands are dominated by Quercus copeyensis and are located at 2,900-m altitude. Total litterfall was highest in the mid-successional forest (1,720 g m⁻² y⁻¹), and reached 1,288 g m⁻² y⁻¹ in the old-growth forest and 934 g m⁻² y⁻¹ in the early-successional forest. Litter mass was dominated by leaves in all stages (56–84% of total litterfall). In the old-growth forest, however, twigs and small canopy debris particles (33%), epiphytes (6%), and mistletoes (5%) also contributed substantially to litter mass. Leaf litterfall showed a clear seasonal pattern with a negative correlation to monthly precipitation and highest values in the dry season (January–April). However, the strongest correlation existed with minimum air temperature (negative), probably because temperatures already dropped at the end of the rainy season, when precipitation had not yet declined and leaf shedding already increased. In contrast, litterfall of epiphyte mass, and twigs and other debris was mostly dependent on occasional strong winds. We conclude that the upper montane oak forests of the Cordillera de Talamanca are exceptional with respect to the large tree size and the relatively high productivity as indicated by litterfall. Litter mass was especially high in the mid-successional and old-growth forests, where the observed annual totals are among the highest recorded for tropical forests so far.     

南亚热带森林植被恢复演替序列的土壤有机碳氮矿化

采用室内培养的方法,分析了南亚热带鼎湖山森林植被恢复演替序列不同阶段代表性森林—马尾松林、针阔叶混交林和季风常绿阔叶林土壤(0~10cm)CO2、CH4排放/吸收和有机氮矿化的差异.结果表明:3种森林土壤培养52周的CO2-C累积排放量分别为(30.66±3.36)、(58.17±7.25)和(59.31±13.58)mg·kg-1,而其中的65.12%、64.41%和64.12%均在前9周被排放;马尾松林土壤的CO2-C累积排放量一直显著小于针阔叶混交林和季风常绿阔叶林;用相符的二库动力学模型模拟的活性库和惰性库的碳矿化速率均呈递减趋势;土壤培养52周吸收CH4的累积量、培养20周有机氮净矿化量和净硝化量均为马尾松林<针阔叶混交林<季风常绿阔叶林(P<0.05),净矿化的有效氮以硝态氮为主.说明森林植被类型的变化改变了土壤有机碳的分解速率,这是其影响土壤有机碳含量的一种内在方式.     

杨树人工林凋落物养分归还功能研究

对杨树中龄林、成熟林凋落物量、组成特征、季节动态及凋落物中N、P、K、Fe、Ca、Mg含量进行了定位观测和实验测定。结果表明:杨树成熟林的年凋落物量为4.45t·hm^-2·a^-1,是中龄林的1.42倍,两者存在显著差异(p<0.05);叶是凋落物的主要形式,分别占中龄林、成熟林总凋落物量的70.1%和81.5%;凋落物量具有明显的季节动态,表现为"双峰"型;成熟林养分归还量是68.4kg·hm^-2·a^-1,是中龄林48.96kg·hm^-2·a^-1的1.4倍;两林分各养分年归还量的大小顺序为N>Ca>K>Mg>Fe>P;杨树成熟林的N、P、Fe、Mg4种元素的利用率大于中龄林的,而K和Ca元素的利用率却相反。     

Nutrient fluxes in a snow-dominated, semi-arid forest: Spatial and temporal patterns

We tested five hypotheses regarding the potential effects of precipitation change on spatial and temporal patterns of water flux, ion flux, and ion concentration in a semiarid, snowmelt-dominated forest in Little Valley, Nevada. Variations in data collected from 1995 to 1999 were used to examine the potential effects of snowpack amount and duration on ion concentrations and fluxes. Soil solution NO₃ ^–, NH₄ ⁺, and ortho-phosphate concentrations and fluxes were uniformly low, and the variations in concentration bore no relationship to snowmelt water flux inputs of these ions. Weathering and cation exchange largely controlled the concentrations and fluxes of base cations from soils in these systems; however, soil solution base cation concentrations were affected by cation concentrations during snowmelt episodes. Soil solution Cl^– and SO₄ ^2– concentrations closely followed the patterns in snowmelt water, suggesting minimal buffering of either ion by soils. In contrast to other studies, the highest concentration and the majority of ion flux from the snowpack in Little Valley occurred in the later phases of snowmelt. Possible reasons for this include sublimation of the snowpack and dry deposition of organic matter during the later stages of snowmelt. Our comparison of interannual and spatial patterns revealed that variation in ion concentration rather than water flux is the most important driver of variation in ion flux. Thus, it is not safe to assume that changes in total precipitation amount will cause concomitant changes in ion inputs to this system.     

Phyllostomid bat assemblages in different successional stages of tropical rain forest in Chiapas,Mexico

Due to their role in seed dispersal, changes in the community of phyllostomid bats have direct consequences on ecological succession. The objective of this work was to document changes in the structure of bat assemblages among secondary successional stages of tropical rain forest in Chiapas, Mexico. Bats were mist-netted at ground level during 18 months in 10 sites belonging to 3 successional stages: four sites represented early succession (2–8 years of abandonment), four intermediate succession (10–20 years of abandonment), and two late succession (mature old-growth forest).We captured 1,179 phyllostomids comprising 29 species. Phyllostomid species richness was 17 (58% of all species) in the early stage, 18 (62%) in the intermediate stage and 24 (83%) in the late stage. The late successional mature forest possessed nine species that were exclusively found there, whereas early and intermediate successional stages contained only one exclusive species. Sturnira lilium, Artibeus lituratus, Carollia perpicillata, Artibeus jamaicensis and Glossophaga soricina represented 88% of all captured phyllostomid bats. Frugivores made up more than 90% of the species captured in early and intermediate successional stages and 84% in late successional forest. The Bray–Curtis index of dissimilarity showed a replacement of species through successional stages with the largest dissimilarity between early and late stages, followed by intermediate and late, and the lowest dissimilarity between early and intermediate stages. The number of gleaning insectivore species increased during succession. The carnivorous guild was exclusively found in the late stage (three species). We conclude that the late successional mature forest was the main reservoir for the gleaning insectivore and carnivore guilds; however, early and intermediate successional stages possessed a great diversity of species including many frugivores.     

Changes in tree and liana communities along a successional gradient in a tropical dry forest in south-eastern Brazil

We investigated changes in species composition and structure of tree and liana communities along a successional gradient in a seasonally dry tropical forest. There was a progressive increase in tree richness and all tree structural traits from early to late stages, as well as marked changes in tree species composition and dominance. This pattern is probably related to pasture management practices such as ploughing, which remove tree roots and preclude regeneration by resprouting. On the other hand, liana density decreased from intermediate to late stages, showing a negative correlation with tree density. The higher liana abundance in intermediate stage is probably due to a balanced availability of support and light availability, since these variables may show opposite trends during forest growth. Predicted succession models may represent extremes in a continuum of possible successional pathways strongly influenced by land use history, climate, soil type, and by the outcomes of tree–liana interactions.     

Ornithophilous canopy species in the Atlantic rain forest of southeastern Brazil

ABSTRACT.   In tropical ecosystems, birds play a relevant role in plant reproduction. Although hummingbirds are regarded as the most important vertebrate pollinators in the Neotropics, the possible role of perching birds as pollinators has been neglected. From 2003 to 2005, we observed 68 species of plants visited by birds in an Atlantic rainforest in southeastern Brazil, including three canopy species: Spirotheca rivieri (Malvaceae, Bombacoidea), Schwartzia brasiliensis (Marcgraviaceae), and Psittacanthus dichrous (Loranthaceae). Flowers of these three species were visited by 15 different species of perching birds and by hummingbirds. The flowers of these three plants are colorful, ranging from deep red or purple to orange. Spirotheca rivieri blooms during the austral winter and Schwartzia brasiliensis during the summer. The flowers of these two species produce copious amounts of dilute nectar in easily accessible structures and both species appear to depend primarily on perching birds as pollinators, with hummingbirds being secondary or minor pollen vectors. The tubular, narrow flowers of P. dichrous are produced during the austral summer and are visited primarily by hummingbirds. Perching birds also visit the flowers, but destroy them. Our results suggest that previous estimates of the number of perching birds that feed on nectar may be too low and that flowers pollinated by perching birds may be more common in the canopy of Neotropical forests than previously thought.     

Patterns of secondary succession in a mangrove forest of Southern Florida

Summary Successional patterns were studied in mangrove forests which had developed recently in response to salinization of areas formerly supporting freshwater marshes along Biscayne Bay in North Miami, Florida. The population structures of these Induced Forests were compared with an adjacent Historical Forest which consisted of a nearly pure stand ofRhizophora mangle. A mixed forest ofRhizophora andLaguncularia racemosa had developed in intertidal areas, while areas above the mean high water elevation supported a scrub community dominated byLaguncularia. Maximum growth of bothRhizophora andLaguncularia occurred in intertidal areas, while both species were stunted and had sparse, poorly formed canopies in drier environments above the mean high water level. Analysis of population structure suggests that Induced Forests in intertidal areas are undergoing succession to a stand ofRhizophora. Laguncularia is unable to compete effectively withRhizophora in these areas and it is suggested that it eventually will be limited to the drier areas, where competition fromRhizophora will be reduced or absent.formely Kimball     

磨盘山天然次生林凋落物数量及动态

以磨盘山5.76hm2天然次生林群落固定监测样地为平台,均匀布设144个凋落物收集器,于2006年每月末(4—11月)连续收集其凋落物,用以分析群落尺度上的凋落物产量、组成及时空变化。结果表明,天然次生林年凋落量为3039.6 kg/hm2,以凋落叶(2499.2 kg/hm2)所占的比例最大,占年凋落量的82.22%,而凋落枝仅占年凋落量的9.92%,花果皮等所占比例更小,占总量的5%以下。1a内,凋落物收集器内共收集到42种树木的凋落叶,占样地内树种总数(46种)的91.30%,其中花曲柳(Fraxinus rhynchophylla)、核桃楸(Juglans mandshurica)和蒙古栎(Quercus mongolica)3个树种的凋落叶占落叶总量的82.97%,为叶凋落量的主要来源。不同收集器之间凋落量存在较大差异,99个收集器的年凋落量在200—400 g,2个收集器超过600 g;单个收集器全年最多可收集到19种树种的凋落叶,收集到凋落叶种数12种的收集器最多(29个)。凋落量月动态呈单峰型,69.78%的凋落量产生于9—10月份,叶凋落量月动态与凋落总量变化相同。落叶以秋季为主,但树种间叶凋落节律存在差异,其中核桃楸叶的凋落高峰集中在8—9月,花曲柳和春榆(Ulmus japonica)集中在9—10月,色木槭(Acer mono)为10月,蒙古栎叶为10—11月。     

海南岛吊罗山热带山地雨林两个演替阶段的种间联结性

种间联结一直是群落演替理论研究的焦点之一, 关于物种间相互作用与群落演替之间的动态关系仍然存在争议。本文中, 作者通过出现-不出现数据的方差比例、基于2×2列联表的种间联结分析和 ²检验, 对海南岛吊罗山热带山地雨林演替前期和演替后期群落的种间联结性进行了研究, 以揭示种间联结与群落演替的相互作用。结果表明: (1)在演替前期, 群落内所有树种间总体呈正联结, 但不显著; 发展至演替后期达到显著正联结。群落内所有物种间正、负联结种对数占总种对数的比例随演替进程呈现下降趋势, 而无联结种对数的比例则大幅上升; 优势种和伴生种间呈现相同的趋势。这表明群落演替正朝着有利于物种稳定共存的方向发展。(2)演替前期建群种和后期侵入种间正联结与无联结种对数的比例(分别为37.8%与41.5%)远大于负联结的比例(20.7%), 但正联结均不显著; 前期定居树种和后期侵入种通过分割资源而共存, 而且也趋于独立存在。(3)后期侵入种间不存在负联结, 所有正联结(占总对数的33.3%)均达显著水平, 显示它们对生境有相似的适应和相互重叠的生态位。     

Statistical characteristics of forest litterfall in China

正Dear Editor,Litterfall represents a major pathway of carbon and mineral transfer from vegetation to soils,and thus is an important ecological process in carbon and nutrient cycling.Annual litterfall production also influences the amount of fuel accumulated in the forests,which serves as a part of an indicator for     

樟树人工林凋落物养分含量及归还量对氮沉降的响应

氮沉降的持续增加对陆地生态系统的健康发展构成严重威胁,森林是陆地生态系统中重要的组成部分,大量的氮沉降对其结构和功能造成严重影响。凋落物是森林生态系统养分循环的重要组成部分,它对土壤肥力、森林生态系统养分循环等方面具有重要作用。为了探讨亚热带常绿阔叶森林凋落物对氮沉降增加的响应,在湖南省森林植物园以樟树人工林为研究对象进行模拟氮沉降的实验,实验设置4种氮添加水平CK(0g N m~(-2)a~(-1),对照)、LN(5g N m~(-2)a~(-1)),MN(15g N m~(-2)a~(-1)),HN(30g N m~(-2)a~(-1)),研究氮沉降对樟树林年凋落物量、凋落物养分含量以及归还量的影响。结果表明:不同施氮水平下(CK、LN、MN、HN),樟树林凋落物的年凋落量分别为(4.53±0.32)t hm~(-2)a~(-1)、(3.95±0.28)t hm~(-2)a~(-1)、(3.56±0.41)t hm~(-2)a~(-1)、(4.46±0.48)t hm~(-2)a~(-1),施氮抑制了樟树林的凋落量,且低、中氮处理下差异显著(P0.05);施氮处理后凋落物的养分含量大小顺序为:CNCaKMg,凋落物的碳含量没有显著变化,但氮含量都有所增加,因此,施氮降低了樟树凋落物各组分的C/N比;凋落物中元素的年归还量大小顺序表现为:CNCaKMg,施氮处理对凋落物C、K、Ca、Mg归还量有抑制作用,但对凋落物N归还量表现为促进作用。     

Multiple nutrients limit litterfall and decomposition in a tropical forest

To explore the importance of 12 elements in litter production and decomposition, we fertilized 36 1600 m²-plots with combinations of N, P, K, or micronutrients (i.e. B, Ca, Cu, Fe, Mg, Mn, Mo, S, Zn) for 6 years in a lowland Panamanian forest. The 90% of litter falling as leaves and twigs failed to increase with fertilization, but reproductive litter (fruits and flowers) increased by 43% with N. K enhanced cellulose decomposition; one or more micronutrients enhanced leaf-litter decomposition; P enhanced both. Our results suggest tropical forests are a non-Liebig world of multiple nutrient limitations, with at least four elements shaping rates of litterfall and decomposition. Multiple metallomic enzymes and cofactors likely create gradients in the break down of leaf litter. Selection favours individuals that make more propagules, and even in an N-rich forest, N is a non-substitutable resource for reproduction.