Effects of nutrient additions on ecosystem carbon cycle in a Puerto Rican tropical wet forest

Wet tropical forests play a critical role in global ecosystem carbon (C) cycle, but C allocation and the response of different C pools to nutrient addition in these forests remain poorly understood. We measured soil organic carbon (SOC), litterfall, root biomass, microbial biomass and soil physical and chemical properties in a wet tropical forest from May 1996 to July 1997 following a 7‐year continuous fertilization. We found that although there was no significant difference in total SOC in the top 0–10 cm of the soils between the fertilization plots (5.42±0.18 kg m^?2) and the control plots (5.27±0.22 kg m^?2), the proportion of the heavy‐fraction organic C in the total SOC was significantly higher in the fertilized plots (59%) than in the control plots (46%) (P<0.05). The annual decomposition rate of fertilized leaf litter was 13% higher than that of the control leaf litter. We also found that fertilization significantly increased microbial biomass (fungi+bacteria) with 952±48 mg kg^?1soil in the fertilized plots and 755±37 mg kg^?1soil in the control plots. Our results suggest that fertilization in tropical forests may enhance long‐term C sequestration in the soils of tropical wet forests.     

The use of DNA barcodes to estimate phylogenetic diversity in forest communities of southern China

To elucidate potential ecological and evolutionary processes associated with the assembly of plant communities, there is now widespread use of estimates of phylogenetic diversity that are based on a variety of DNA barcode regions and phylogenetic construction methods. However, relatively few studies consider how estimates of phylogenetic diversity may be influenced by single DNA barcodes incorporated into a sequence matrix (conservative regions vs. hypervariable regions) and the use of a backbone family‐level phylogeny. Here, we use general linear mixed‐effects models to examine the influence of different combinations of core DNA barcodes (rbcL, matK, ITS, and ITS2) and phylogeny construction methods on a series of estimates of community phylogenetic diversity for two subtropical forest plots in Guangdong, southern China. We ask: (a) What are the relative influences of single DNA barcodes on estimates phylogenetic diversity metrics? and (b) What is the effect of using a backbone family‐level phylogeny to estimate topology‐based phylogenetic diversity metrics? The combination of more than one barcode (i.e., rbcL + matK + ITS) and the use of a backbone family‐level phylogeny provided the most parsimonious explanation of variation in estimates of phylogenetic diversity. The use of a backbone family‐level phylogeny showed a stronger effect on phylogenetic diversity metrics that are based on tree topology compared to those that are based on branch lengths. In addition, the variation in the estimates of phylogenetic diversity that was explained by the top‐rank models ranged from 0.1% to 31% and was dependent on the type of phylogenetic community structure metric. Our study underscores the importance of incorporating a multilocus DNA barcode and the use of a backbone family‐level phylogeny to infer phylogenetic diversity, where the type of DNA barcode employed and the phylogenetic construction method used can serve as a significant source of variation in estimates of phylogenetic community structure.     

Habitat associations of Sterculiaceae trees in a Bornean rain forest plot

Questions: 1. Are trees in a Bornean tropical rain forest associated with a particular habitat? 2. Does the strength of habitat association with the species‐specific optimal habitat increase with tree size? Location : A 52‐ha plot in a mixed dipterocarp forest in a heterogeneous landscape at the Lambir Hills National Park, Sarawak, East Malaysia. Methods : Ten species from the Sterculiaceae were chosen as representative of all species in the plot, on the assumption that competition among closely related species is more stringent than that among more distantly related taxa. Their habitat associations were tested using data from a 52‐ha plot by a torus‐translation test. Results : The torus‐translation test showed that eight out of the ten species examined had significant association with at least one habitat. We could not find negative species‐habitat associations for rare species, probably due to their small sample sizes. Among four species small trees were less strongly associated with habitat than large trees, implying competitive exclusion of trees in suboptimal habitats. The other four species showed the opposite pattern, possibly owing to the smaller sample size of large trees. A habitat had a maximum of three species with which it was significantly positively associated. Conclusions : For a species to survive in population equilibrium in a landscape, habitats in which ‘source’ subpopulations can be sustained without subsidy from adjacent habitats are essential. Competition is most severe among related species whose source subpopulations share the same habitat. On the evidence of source subpopulations identified by positive species‐habitat association, species‐habitat association reduces the number of confamilial competitors. Our results therefore indicate that edaphic niche specialization contributes to coexistence of species of Sterculiaceae in the plot, consistent with the expectations of equilibrium hypotheses.     

Exploring tree-habitat associations in a Chinese subtropical forest plot using a molecular phylogeny generated from DNA barcode loci

Elucidating the ecological mechanisms underlying community assembly in subtropical forests remains a central challenge for ecologists. The assembly of species into communities can be due to interspecific differences in habitat associations, and there is increasing evidence that these associations may have an underlying phylogenetic structure in contemporary terrestrial communities. In other words, by examining the degree to which closely related species prefer similar habitats and the degree to which they co-occur, ecologists are able to infer the mechanisms underlying community assembly. Here we implement this approach in a diverse subtropical tree community in China using a long-term forest dynamics plot and a molecular phylogeny generated from three DNA barcode loci. We find that there is phylogenetic signal in plant-habitat associations (i.e. closely related species tend to prefer similar habitats) and that patterns of co-occurrence within habitats are typically non-random with respect to phylogeny. In particular, we found phylogenetic clustering in valley and low-slope habitats in this forest, indicating a filtering of lineages plays a dominant role in structuring communities in these habitats and we found evidence of phylogenetic overdispersion in high-slope, ridge-top and high-gully habitats, indicating that distantly related species tended to co-occur in these high elevation habitats and that lineage filtering is less important in structuring these communities. Thus we infer that non-neutral niche-based processes acting upon evolutionarily conserved habitat preferences explain the assembly of local scale communities in the forest studied.     

海南尖峰岭热带山地雨林60ha动态监测样地群落结构特征

热带山地雨林是海南岛最占优势的植被类型,以往对热带山地雨林的研究通常基于小尺度,缺乏大尺度上的长期固定样地监测。作者基于海南岛尖峰岭地区60 ha(1,000 m×600 m)植被动态监测大样地,详细描述了该样地所属典型热带山地雨林的群落结构特征,以期为更深入地揭示我国热带雨林地区的物种多样性及其维持机制提供背景资料。尖峰岭大样地20 m×20 m样方水平上海拔和坡度分别在866.3–1,016.7 m和1.7°–49.3°间变化。大样地内共记录到439,676株存活的胸径≥1.0 cm的乔灌木植株,除61个植株未确定种名外,其他分属于62科155属290种。单位面积植株密度为0.7328株/m2(含萌条和分枝),20 m×20 m尺度上单位面积物种数量为32–120种,平均80种。植物属区系成分以热带性质为主,共有136属,占总属数的88.3%;另有鼠李科鼠李属(Rhamnus)为世界分布,木兰科拟单性木兰属(Parakmeria)为中国特有分布。按物种重要值排序,大样地内最具优势(重要值大于2.0)的6个种分别为:大叶蒲葵(Livistona saribus)、白颜树(Gironniera subaequalis)、厚壳桂(Cryptocarya chinensis)、油丹(Alseodaphne hainanensis)、四蕊三角瓣花(Prismatomeris tetrandra)和海南韶子(Nephelium topengii)。优势科为樟科、壳斗科、茜草科和棕榈科,重要值均超过了5.0。取样面积达到7.5 ha或取样数量达到2万株时,计数到的物种数量达到261种,占总物种数量的90.0%。大样地内稀有种和偶见种各占所有物种的20.7%和37.6%。样地内所有个体平均胸径5.22 cm,植株径级分布呈明显的倒"J"形。本文为后续尖峰岭大样地的研究提供了背景资料,尖峰岭大样地的建立也为热带地区生物多样性长期变化监测提供了一个基础平台。     

Spatio-temporal patterns of tree community dynamics in a tropical forest fragment in South-east Brazil

The tree community (dbh > 5 cm) of a fragment of tropical montane semi-deciduous forest in South-east Brazil was repeatedly surveyed over a 19-year period in order to assess spatial and temporal patterns of dynamics. The surveys took place in 1987, 1992, 1996, 2001, and 2006 in a grid of 126 20 × 20 m permanent plots covering almost the entire fragment (5.8 ha). Overall patterns indicated that a self-thinning process has taken place in the fragment since 1992. Community dynamics varied in space and time, with most dynamics highly spatially clustered. With exception of mortality rates, there were no changes in the spatial patterns of community dynamics through time. No relation between edges and dynamics variables was found. Most species with increasing density and basal area were shade-bearers, while most decreasing species were canopy light demanders and pioneers.     

Forest plot as a tool to demonstrate the pharmaceutical potential of plants in a tropical forest of Panama

Based on literature analysis of 308 angiosperm species inventoried from a 50-hectare forest plot on Barro Colorado Island, Panama, 40 species were selected and 80 samples (two samples for every species; leaf + twig and stembark samples) were collected for investigation of their medicinal/pharmaceutical potential. Extracts of these 80 samples were tested in bioassay systems to assess cancer chemoprevention (eight assays), antiplasmodial, cytotoxicity, and anti-HIV activities. Details of bioassay techniques are described. Of the 40 species, 12 (30%) showed activity in one or more of the 11 bioassay systems used. These active species areBombacopsis (= Pachira) quinata, Calophyllum longifolium, Casearia commersoniana, Lozania pittieri, Maclura tinctoria, Mouriri myrtilloides, Olmedia aspera (= Trophis caucana), Pseudobombax septenatum, Spondias radlkoferi, Stylogyne standleyi, Turpinia occidentalis, andVochysia ferruginea. Because literature data on the chemistry ofBombacopsis (= Pachira) quinata, Lozan ia pittieri, Mouriri myrtilloides, Olmedia aspera (= Trophis caucana), Pseudobombax septenatum, andStylogyne standleyi, are lacking, and similar data on the other six species are deficient, further fractionation and isolation work on these active species potentially may yield novel, biologically active structures. This study demonstrates that a plot-based selection of plant species for evaluation of their potential medicinal/ pharmaceutical value has merit in achieving such a goal, and should be used in a program on plant drug discovery.     

DNA barcoding herbaceous and woody plant species at a subalpine forest dynamics plot in Southwest China

Although DNA barcoding has been widely used to identify plant species composition in temperate and tropical ecosystems, relatively few studies have used DNA barcodes to document both herbaceous and woody components of forest plot. A total of 201 species (72 woody species and 129 herbaceous species) representing 135 genera distributed across 64 families of seed plants were collected in a 25 ha CForBio subalpine forest dynamics plot. In total, 491 specimens were screened for three DNA regions of the chloroplast genome (rbcL, matK, and trnH‐psbA) as well as the internal transcribed spacers (ITS) of nuclear ribosomal DNA. We quantified species resolution for each barcode separately or in combination using a ML tree‐based method. Amplification and sequencing success were highest for rbcL, followed by trnH‐psbA, which performed better than ITS and matK. The rbcL + ITS barcode had slightly higher species resolution rates (88.60%) compared with rbcL + matK (86.60%) and rbcL + trnH‐psbA (86.01%). The addition of trnH‐psbA or ITS to the rbcL + matK barcode only marginally increased species resolution rates, although in combination the four barcodes had the highest discriminatory power (90.21%). The situations where DNA barcodes did not discriminate among species were typically associated with higher numbers of co‐occurring con‐generic species. In addition, herbaceous species were much better resolved than woody species. Our study represents one of the first applications of DNA barcodes in a subalpine forest dynamics plot and contributes to our understanding of patterns of genetic divergence among woody and herbaceous plant species.     

Biodiversity inventory of trees in a large-scale permanent plot of tropical evergreen forest at Varagalaiar, Anamalais, Western Ghats, India

A permanent plot of 30 ha (600 × 500 m²) was established for long-term ecological research on biodiversity and forest functioning in a tropical evergreen forest at Varagalaiar, Anamalais, Western Ghats. This paper gives the results of the first census of trees in the 30 ha plot. All trees 30 cm gbh were permanently tagged with sequentially numbered aluminium tags and their girth measured. 148 tree species (in 120 genera and 49 families) were enumerated in a total sample of 13,393 individuals. Species diversity, density and dispersion patterns were determined. The mean species richness, density and basal area per hectare were 65 species, 446 stems and 36.26 m² respectively. The Sorensen similarity index for thirty 1-ha subplots varied from 0.7 to 0.9, indicating the homogeneity in species composition of the stand. The pronounced species hierarchy has resulted in the dominance of four species that occupy four different forest storeys: Drypetes longifolia (lower storey) Reinwardtiodendron anamallayanum (middle storey), Poeciloneuron indicum (upper storey) and Dipterocarpus indicus (emergent). The forest was dominated by Euphorbiaceae in terms of richness (18 species) and abundance of species (3788 stems), and Dipterocarpaceae based on the contribution to basal area (18.4%). Species richness and density decreased with increasing girth-class. Girth class frequency of the stand exhibited an expanding population of trees. Twenty-nine tree species, analysed for spatial dispersion at 1-ha scale, exhibited both clumped and uniform patterns, except Vateria indica which was randomly distributed in one hectare. Repeat census scheduled for subsequent years, will elucidate the behaviour of the individual species and the population dynamics of the tree flora and will be useful for forest conservation and management. It will also help to monitor human activity within this forest.     

秦岭落叶阔叶林25 ha森林动态监测样地物种组成与群落特征

秦岭落叶阔叶林是温带-亚热带过渡区保存较好的植被类型, 群落结构复杂。为了研究该过渡区植被的生物多样性维持机制, 按照CTFS (Center for tropical Forest Science)和中国森林生物多样性监测网络(CForBio)的建设标准, 于2015年在陕西省佛坪国家级自然保护区的落叶阔叶林建立了一块面积25 ha的动态监测样地。本文对样地内胸径(DBH) ≥ 1 cm的所有木本植物进行了调查和统计, 分析了其物种组成、区系特征、径级结构和空间分布格局。结果表明: 样地内DBH ≥ 1 cm的木本植物独立个体有47,739株, 隶属于36科66属119种。温带区系成分的科和属分别占总科数和总属数的41.18%和60.00%, 温带区系特征明显。稀有种有51种, 占总树种的42.86%。落叶树种有106种, 占总树种的89.07%, 在样地内占绝对优势。重要值≥ 1的物种共有20个, 分别占样地总个体数和总胸高断面积的70.35%和57.41%, 重要值最大的物种分别是乔木层的锐齿栎(Quercus aliena var. acutesrrata)、亚乔木层的水榆花楸(Sorbus alnifolia)和灌木层的刺叶栎(Q. spinosa)。样地内所有个体的平均胸径为8.61 cm, 整体径级分布呈倒”J”型, 小径级个体较多, 群落更新良好。除了太白杨(Populus purdomii), 样地内优势种表现出大尺度的聚集分布, 且它们的分布与生境紧密相关, 不同物种表现出不同的生境偏好。     

Stem water storage and diurnal patterns of water use in tropical forest canopy trees

Stem water storage capacity and diurnal patterns of water use were studied in five canopy trees of a seasonal tropical forest in Panama. Sap flow was measured simultaneously at the top and at the base of each tree using constant energy input thermal probes inserted in the sapwood. The daily stem storage capacity was calculated by comparing the diurnal patterns of basal and crown sap flow. The amount of water withdrawn from storage and subsequently replaced daily ranged from 4 kg d^–1 in a 0·20-m-diameter individual of Cecropia longipes to 54 kg d^–1 in a 1·02-m-diameter individual of Anacardium excelsum, representing 9–15% of the total daily water loss, respectively. Ficus insipida, Luehea seemannii and Spondias mombin had intermediate diurnal water storage capacities. Trees with greater storage capacity maintained maximum rates of transpiration for a substantially longer fraction of the day than trees with smaller water storage capacity. All five trees conformed to a common linear relationship between diurnal storage capacity and basal sapwood area, suggesting that this relationship was species-independent and size-specific for trees at the study site. According to this relationship there was an increment of 10 kg of diurnal water storage capacity for every 0·1 m² increase in basal sapwood area. The diurnal withdrawal of water from, and refill of, internal stores was a dynamic process, tightly coupled to fluctuations in environmental conditions. The variations in basal and crown sap flow were more synchronized after 1100 h when internal reserves were mostly depleted. Stem water storage may partially compensate for increases in axial hydraulic resistance with tree size and thus play an important role in regulating the water status of leaves exposed to the large diurnal variations in evaporative demand that occur in the upper canopy of seasonal lowland tropical forests.     

Successional dynamics of the bee community in a tropical dry forest: Insights from taxonomy and functional ecology

Despite the recent rapid growth of tropical dry forest succession ecology, most studies on this topic have focused on plant community attribute recovery, whereas animal community successional dynamics has been largely overlooked, and the few existing studies have used taxonomic approaches. Here, we analyze the successional changes in the bee community in a Mexican tropical dry forest, by integrating taxonomic (species, genus, and family diversity) and functional (sociability, nesting strategy, and body size) information for bees. Over one year, in a successional chronosequence (2–67 years after abandonment) we collected 469 individual bees, representing five families, 36 genera, and 69 species. Linear modeling showed decreases in taxonomic diversity with succession, more strongly so for species. Bee species turnover along succession ranged from moderate to high, decreasing slightly at intermediate stages. An RLQ analysis (ordination method that allows relating environmental variables with functional attributes) revealed clear relations between bee functional traits and the plant community. RLQ axis 1 was positively related to vegetation structural and diversity variables, and to eusociality, while solitary, parasociality, and ground nesting was negatively associated with it. Early successional fallows attract mostly solitary and parasocial bees; older fallows tend to attract eusocial bees with aerial nesting. The continuous taxonomic turnover observed by us and the functional analysis suggest that the disappearance of old fallows from agricultural landscapes would likely result in significant reductions and even local extinctions of particular bee guilds. Considering the low viability of preserving large mature tropical dry forest tracts, the conservation of older successional stands emerges as a crucial component of landscape management.Abstract in Spanish is available with online material.     

Nitrogen and phosphorus resorption in trees of a Mexican tropical dry forest

Resorption efficiency (RE) and proficiency, foliar nutrient concentrations, and relative soil nutrient availability were determined during 3 consecutive years in tree species growing under contrasting topographic positions (i.e., top vs. bottom and north vs. south aspect) in a tropical dry forest in Mexico. The sites differed in soil nutrient levels, soil water content, and potential radiation interception. Leaf mass per area (g m^–2) increased during the growing season in all species. Soil P availability and mean foliar P concentrations were generally higher at the bottom than at the top site during the 3 years of the study. Leaf N concentrations ranged from 45.4 to 31.4 mg g^–1. Leaf P varied from 2.3 to 1.8 mg g^–1. Mean N and P RE varied among species, occasionally between top and bottom sites, and were higher in the dry than in the wet years of study. Senesced-leaf nutrient concentrations (i.e., a measure of resorption proficiency) varied from 13.7 to 31.2 mg g^–1 (N) and 0.4 to 3.3 mg g^–1 (P) among the different species and were generally indicative of incomplete nutrient resorption. Phosphorus concentrations in senesced leaves were higher at the bottom than at the top site and decreased from the wettest to the the driest year. Soil N and P availability were significantly different in the north- and south-facing slopes, but neither nutrient concentrations of mature and senesced leaves nor RE differed between aspects. Our results suggest that water more than soil nutrient availability controls RE in the Chamela dry forest, while resorption proficiency may be interactively controlled by both nutrient and water availability.     

Soil nutrient dynamics in response to irrigation of a Panamanian tropical moist forest

We measured concentrations of soil nutrients (0–15 and 30–35 cm depths) before and after the dry season in control and dry-season irrigated plots of mature tropical moist forest on Barro Colorado Island (BCI) in central Panama to determine how soil moisture affects availability of plant nutrients. Dry-season irrigation (January through April in 1986, 1987, and 1988) enhanced gravimetric soil water contents to wet-season levels (ca. 400 g kg^–1 but did not cause leaching beyond 0.8 m depth in the soil. Irrigation increased concentrations of exchangeable base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), but it had little effect on concentrations of inorganic N (NH₄ ^+C, NO₃ ^– and S (SO₄ ^2–). These BCI soils had particularly low concentrations of extractable P especially at the end of the dry season in April, and concentrations increased in response to irrigation and the onset of the rainy season. We also measured the response of soil processes (nitrification and S mineralization) to irrigation and found that they responded positively to increased soil moisture in laboratory incubations, but irrigation had little effect on rates in the field. Other processes (plant uptake, soil organic matter dynamics) must compensate in the field and keep soil nutrient concentrations at relatively low levels.     

Structure and dynamics of a tropical dry forest in Ghana

Forest under low rainfall (averaging 745 mm yr^-1) on the Shai Hills in S.E. Ghana has redeveloped following cessation of farming in the 1890s. Forest stature is low, with a canopy at about 11 m, principally of three species, Diospyros abyssinica, D. mespiliformis and Millettia thonningii. Drypetes parvifolia and Vepris heterophylla are common understorey trees. Twelve species of woody liane were recorded. Species of thicket vegetation in the area were also present at low density. Most species are evergreen.Tree mortality averaged 2.3% yr^-1 and exceeded recruitment (1.5% yr^-1). Differences between species in mortality and recruitment were pronounced: canopy species showed a small decline in density; understorey species increased markedly and the thicket species declined. Seed production was very variable, but seedling establishment was very poor for all species. Seedling mortality was high (11% yr^-1) especially for small seedlings. These population trends probably represent the latter stages of succession of forest regrowth after farming about 100 years ago.Compared with tropical rain forest, Shai Hills forest has similar relative tree diameter growth (1–3.5% yr^-1), mortality and recruitment rates, and small-litter fall (5.52 t ha^-1 yr^-1).Shai Hills forest differs from rain forest by its short stature, relatively few (evergreen) tree species, poor regeneration from seed, high soil nutrient status and low rainfall. Similar forests have been reported in east Africa and in parts of New Guinea.Abbreviations dbh diameter at breast height (1.3 m) - gbh girth at breast height died May 1984