西双版纳热带人工雨林生物量及净第一性生产力的研究

通过标准木法和收获法研究分析了西双版纳热带人工模拟雨林的生物量及净第一性生产力。结果表明,林分总生物量约为390.4t·hm^-2,其中乔木层生物量达362.5t·hm^-2,占总生物量的92.8%,灌木层生物量为19.3t·hm^-2,占4.9%,层间植物9包括附生植物）的生物量为3.6t·hm^-2,草本层生物量为5.0t·hm^-2,分别占1.3%和0.9%。林分净第一性生产力为2227.3g.m^-2.年^-1,其中乔木层的净生产力为1553.5g·m^-2.年^-1,占整个林分净生产力的69.7%,灌木层、草本层及层间植物分别仅占26.9%、2.4%和1.0%,其器官分配比例以茎最高,0达42.0%;其次为叶,占30.2%;枝占13.5%。叶面积指数为7.061。同时建立了林分优势种及乔木层各器官生物量的优化回归模型。     

Radiative forcing of methane fluxes offsets net carbon dioxide uptake for a tropical flooded forest

Wetlands are important sources of methane (CH₄) and sinks of carbon dioxide (CO₂). However, little is known about CH₄ and CO₂ fluxes and dynamics of seasonally flooded tropical forests of South America in relation to local carbon (C) balances and atmospheric exchange. We measured net ecosystem fluxes of CH₄ and CO₂ in the Pantanal over 2014–2017 using tower‐based eddy covariance along with C measurements in soil, biomass and water. Our data indicate that seasonally flooded tropical forests are potentially large sinks for CO₂ but strong sources of CH₄, particularly during inundation when reducing conditions in soils increase CH₄ production and limit CO₂ release. During inundation when soils were anaerobic, the flooded forest emitted 0.11 ± 0.002 g CH₄‐C m^?2 d^?1 and absorbed 1.6 ± 0.2 g CO₂‐C m^?2 d^?1 (mean ± 95% confidence interval for the entire study period). Following the recession of floodwaters, soils rapidly became aerobic and CH₄ emissions decreased significantly (0.002 ± 0.001 g CH₄‐C m^?2 d^?1) but remained a net source, while the net CO₂ flux flipped from being a net sink during anaerobic periods to acting as a source during aerobic periods. CH₄ fluxes were 50 times higher in the wet season; DOC was a minor component in the net ecosystem carbon balance. Daily fluxes of CO₂ and CH₄ were similar in all years for each season, but annual net fluxes varied primarily in relation to flood duration. While the ecosystem was a net C sink on an annual basis (absorbing 218 g C m^?2 (as CH₄‐C + CO₂‐C) in anaerobic phases and emitting 76 g C m^?2in aerobic phases), high CH₄ effluxes during the anaerobic flooded phase and modest CH₄ effluxes during the aerobic phase indicate that seasonally flooded tropical forests can be a net source of radiative forcings on an annual basis, thus acting as an amplifying feedback on global warming.     

Long‐term recovery of the functional community assembly and carbon pools in an African tropical forest succession

On the African continent, the population is expected to expand fourfold in the next century, which will increasingly impact the global carbon cycle and biodiversity conservation. Therefore, it is of vital importance to understand how carbon stocks and community assembly recover after slash‐and‐burn events in tropical second growth forests. We inventoried a chronosequence of 15 1‐ha plots in lowland tropical forest of the central Congo Basin and evaluated changes in aboveground and soil organic carbon stocks and in tree species diversity, functional composition, and community‐weighted functional traits with succession. We aimed to track long‐term recovery trajectories of species and carbon stocks in secondary forests, comparing 5 to 200 + year old secondary forest with reference primary forest. Along the successional gradient, the functional composition followed a trajectory from resource acquisition to resource conservation, except for nitrogen‐related leaf traits. Despite a fast, initial recovery of species diversity and functional composition, there were still important structural and carbon stock differences between old growth secondary and pristine forest, which suggests that a full recovery of secondary forests might take much longer than currently shown. As such, the aboveground carbon stocks of 200 + year old forest were only 57% of those in the pristine reference forest, which suggests a slow recovery of aboveground carbon stocks, although more research is needed to confirm this observation. The results of this study highlight the need for more in‐depth studies on forest recovery in Central Africa, to gain insight into the processes that control biodiversity and carbon stock recovery.     

Above-ground biomass and structure of 260 African tropical forests

We report above-ground biomass (AGB), basal area, stem density and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha⁻¹ (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha⁻¹) similar to those of Bornean forests, and significantly greater than East or West African forests. AGB therefore appears generally higher in palaeo- compared with neotropical forests. However, mean stem density is low (426 ± 11 stems ha⁻¹ greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean forests (cf. approx. 600) and is the signature structural feature of African tropical forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationships with C : N ratio (suggesting a positive soil phosphorus–AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy tropical forests may be particularly sensitive to future precipitation and temperature changes.     

Partitioning net carbon dioxide fluxes into photosynthesis and respiration using neural networks

The eddy covariance (EC) technique is used to measure the net ecosystem exchange (NEE) of CO₂ between ecosystems and the atmosphere, offering a unique opportunity to study ecosystem responses to climate change. NEE is the difference between the total CO₂ release due to all respiration processes (RECO), and the gross carbon uptake by photosynthesis (GPP). These two gross CO₂ fluxes are derived from EC measurements by applying partitioning methods that rely on physiologically based functional relationships with a limited number of environmental drivers. However, the partitioning methods applied in the global FLUXNET network of EC observations do not account for the multiple co‐acting factors that modulate GPP and RECO flux dynamics. To overcome this limitation, we developed a hybrid data‐driven approach based on combined neural networks (NN_C‐part). NN_C‐part incorporates process knowledge by introducing a photosynthetic response based on the light‐use efficiency (LUE) concept, and uses a comprehensive dataset of soil and micrometeorological variables as fluxes drivers. We applied the method to 36 sites from the FLUXNET2015 dataset and found a high consistency in the results with those derived from other standard partitioning methods for both GPP (R² > .94) and RECO (R² > .8). High consistency was also found for (a) the diurnal and seasonal patterns of fluxes and (b) the ecosystem functional responses. NN_C‐part performed more realistic than the traditional methods for predicting additional patterns of gross CO₂ fluxes, such as: (a) the GPP response to VPD, (b) direct effects of air temperature on GPP dynamics, (c) hysteresis in the diel cycle of gross CO₂ fluxes, (d) the sensitivity of LUE to the diffuse to direct radiation ratio, and (e) the post rain respiration pulse after a long dry period. In conclusion, NN_C‐part is a valid data‐driven approach to provide GPP and RECO estimates and complementary to the existing partitioning methods.     

海南尖峰岭热带山地雨林土壤有机碳密度空间分布特征

森林土壤有机碳是陆地碳库的重要组成部分,在碳循环中有着重要的作用。研究热带雨林土壤性质的空间异质性对于深入分析热带雨林植被分布格局与土壤的关系,促进热带雨林的保护等具有重要指导意义。在海南岛尖峰岭热带山地雨林60 hm2大样地内采用野外布点采样、实验室测定和地统计学分析相结合的方法,定量研究了土壤有机碳密度在局域范围内的空间异质性及分布特征。研究结果表明:(1)A(0—10 cm)、B(10—30 cm)、C(30—60 cm)3层土壤有机碳平均密度分别为2.699、2.782、2.434 kg/m2,A、B两层差异性不显著,与C层差异性显著(P0.05);(2)不同层次土壤有机碳密度模型交叉验证结果表明:A层拟合的半方差函数最适模型为指数模型,B、C两层为球状模型;3层土壤有机碳密度的变程分别为:54.2、70.9、97.2 m;块金值与基台值比值分别为:0.512、0.708、0.882,表明A、B两层属中等程度变异,C层具有较大的块金值,属于弱变异,说明在小尺度范围具有更明显的空间异质性,也说明不同层次土壤有机碳密度具有不同程度的空间自相关性;Person相关性分析表明不同层次土壤有机碳密度之间具有不同的相关性:A层与B层及C层之间的相关性要小于B层和C层之间的相关性,说明热带雨林中土壤有机碳密度表层与下层受到不同生态过程的控制。(3)普通克里格插值及绘制的空间分布轮廓图表明:在研究尺度上A、B两层不同深度的土壤有机碳密度的空间分布具有一定的一致性,空间异质性明显,呈斑块状分布;C层空间异质性较弱,具有一定的连续性,呈条带状分布;(4)地形引起的水热分配是影响不同层次土壤有机碳密度空间分布格局的一个重要因素。     

Complexity in water and carbon dioxide fluxes following rain pulses in an African savanna

The idea that many processes in arid and semi-arid ecosystems are dormant until activated by a pulse of rainfall, and then decay from a maximum rate as the soil dries, is widely used as a conceptual and mathematical model, but has rarely been evaluated with data. This paper examines soil water, evapotranspiration (ET), and net ecosystem CO₂ exchange measured for 5 years at an eddy covariance tower sited in an Acacia–Combretum savanna near Skukuza in the Kruger National Park, South Africa. The analysis characterizes ecosystem flux responses to discrete rain events and evaluates the skill of increasingly complex “pulse models”. Rainfall pulses exert strong control over ecosystem-scale water and CO₂ fluxes at this site, but the simplest pulse models do a poor job of characterizing the dynamics of the response. Successful models need to include the time lag between the wetting event and the process peak, which differ for evaporation, photosynthesis and respiration. Adding further complexity, the time lag depends on the prior duration and degree of water stress. ET response is well characterized by a linear function of potential ET and a logistic function of profile-total soil water content, with remaining seasonal variation correlating with vegetation phenological dynamics (leaf area). A 1- to 3-day lag to maximal ET following wetting is a source of hysteresis in the ET response to soil water. Respiration responds to wetting within days, while photosynthesis takes a week or longer to reach its peak if the rainfall was preceded by a long dry spell. Both processes exhibit nonlinear functional responses that vary seasonally. We conclude that a more mechanistic approach than simple pulse modeling is needed to represent daily ecosystem C processes in semiarid savannas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

榕树在西双版纳热带雨林生态系统中的作用

榕树是西双版纳热带雨林中的关键植物类群之一,能够为多种生物提供栖息地和食物,从而维持该地区热带雨林生态系统的物种多样性。一些种类的榕树有绞杀特性,在森林更新演替中能够起到积极的作用;还有些种类的榕树是先锋物种,在植被恢复中起重要作用。但是,近些年对西双版纳的过度开发已经使热带雨林片断化,榕树种群数量大量减少,榕果内的寄生蜂、食榕果动物也受到了不同程度的影响。保护好西双版纳热带雨林中关键植物类群榕树,是保护和恢复热带雨林生态系统的重要措施之一。     

热带季节雨林林冠碳通量不同校正方法的比较分析

利用西双版纳热带季节雨林2003年3月1～9日的CO₂和水汽通量数据,比较了不同校正方法的差异.结果表明,对季节雨林林冠碳通量观测数据进行校正是必要的,但不同校正方法所起的作用有所差异;昼间WPL校正的作用最大,虚温校正的作用最小;t检验证明,经WPL修正后的碳通量值与基准值、无显著差异;聚类分析表明,进行自然风3次旋转校正有利于数值精度的提高.夜间是自然风旋转校正的贡献最大、虚温校正贡献最小;t检验表明,经过WPL修正和平面旋转校正及其组合得到的碳通量值与基准值均有显著差异;而经包含有自然风旋转校正处理后的碳通量值与基准值均无显著差异;聚类分析表明,经过自然风坐标旋转后,再进行WPL修正,有利于数值精度的提高.     

Visitor assemblages at flowers in a tropical rainforest canopy

Abstract Canopy crane‐based studies have been carried out to quantify the sets of arthropods that visit the flowers of a suite of common species of trees, palms and vines within the Cape Tribulation study area. Those Orders that increase significantly in abundance between the budding and flowering stages of inflorescences are identified, and multivariate and univariate comparisons have been made first, among coflowering plant species and second, at different seasons for the same plant species. The analysis has been repeated for both the profile of higher arthropod taxa in the samples and for the relative abundances of families of Coleoptera: one of the Orders most frequently suggested as critical in the pollination biology of Australian rainforests. In all cases significant differences are identified among species confirming that the visitor profile is a plant species‐specific phenomenon. Profiles within plant species at different times also differed. At the ordinal level significant differences in visitor profiles associated with coflowering plants, were observed, variously, in Thysanoptera, Diptera, Lepidoptera, Coleoptera and Hymenoptera. Within the Coleoptera significant differences occurred in relative abundances of Scarabaeidae, Phalacridae, Latridiidae and Curculionidae. Seasonal differences in visitation to Syzygium gustavioides, Normanbya normanbyi and Calamus radicalis, reflected differences in Diptera, Lepidoptera, Homoptera, Thysanoptera, Hymenoptera and Araneida. Within the Coleoptera, the Elateridae and Curculionidae varied significantly between occasions. The various forms of flower/arthropod interaction that may be represented in these results are discussed, as are the implications for pollination.     

Temporal and spatial variation in an Australian tropical rainforest

Abstract This study describes the floristics and structure of a 0.95‐ha lowland tropical rainforest plot at the Australian Canopy Crane Research Facility at Cape Tribulation, Queensland. Five years of post‐cyclonic change in forest floristics and structure following the passage of Tropical Cyclone ‘Rona’ in February 1999 are examined. Local and regional variation in tropical rainforest is examined in comparison with other lowland plots established nearby and mid‐elevation plots located elsewhere in north Queensland at Eungella, Paluma and the Atherton Tablelands. These plots are placed in a broader Australasian context along with lowland rainforest plots at Baitabag and Oomsis, Papua New Guinea. The 2005 survey found 680 stems of 82 species ≥10 cm d.b.h. on the crane plot, an increase of 30.3% in stems and 16.4% of species in the 5 years since the previous survey. The most abundant families were Meliaceae, Euphorbiaceae, Lauraceae, Myrtaceae and Apocynaceae and the most abundant species were Cleistanthus myrianthus, Alstonia scholaris, Myristica insipida, Normanbya normanbyi and Rockinghamia angustifolia. Temporal floristic and structural variation suggests that the crane site remains in an active stage of post‐cyclonic recovery. Local spatial variability in floristics and structure at Cape Tribulation exceeded the variation exhibited by a single plot over a period of 5 years, despite the impact of Cyclone Rona. This finding suggests a high degree of temporal stability within this stand of rainforest despite frequent catastrophic disturbances. The rainforests of Cape Tribulation constitute a relatively unique floristic community when observed in an Australasian context. Variation in rainforest community composition across the region shows the importance of biogeographical connections, the impacts of local topography, environmental conditions and disturbance history.     

西双版纳热带季节雨林的研究

本文以多个样方的资料分析,从群落综合特征上研究了西双版纳热带季节雨林的特点和类型、物种组成、生活型谱、叶级谱等。根据上层标志树种、群落生态外貌特征和生境把西双版纳的热带季节雨林区分为低丘雨林和沟谷雨林二个群系组,各包括若干群系。低丘雨林中面积最大和最有代表性的群系是大药树、龙果林,而沟谷雨林中最有代表性的群系是番龙眼、千果榄仁林。二者相比,低丘雨林的物种多样性要小一些,附生植物相对少一些,小、矮高位芽植物和小叶、落叶树种比例稍高,在生态上向季雨林和热带山地的常绿阔叶林过渡,有更强的地方代表性。沟谷雨林则更接近典型的湿热带雨林。     

Productivity and carbon fluxes of tropical savannas

Aim (1) To estimate the local and global magnitude of carbon fluxes between savanna and the atmosphere, and to suggest the significance of savannas in the global carbon cycle. (2) To suggest the extent to which protection of savannas could contribute to a global carbon sequestration initiative. Location Tropical savanna ecosystems in Africa, Australia, India and South America. Methods A literature search was carried out using the ISI Web of Knowledge, and a compilation of extra data was obtained from other literature, including national reports accessed through the personal collections of the authors. Savanna is here defined as any tropical ecosystem containing grasses, including woodland and grassland types. From these data it was possible to estimate the fluxes of carbon dioxide between the entire savanna biome on a global scale. Results Tropical savannas can be remarkably productive, with a net primary productivity that ranges from 1 to 12 t C ha⁻¹ year⁻¹. The lower values are found in the arid and semi‐arid savannas occurring in extensive regions of Africa, Australia and South America. The global average of the cases reviewed here was 7.2 t C ha⁻¹ year⁻¹. The carbon sequestration rate (net ecosystem productivity) may average 0.14 t C ha⁻¹ year⁻¹ or 0.39 Gt C year⁻¹. If savannas were to be protected from fire and grazing, most of them would accumulate substantial carbon and the sink would be larger. Savannas are under anthropogenic pressure, but this has been much less publicized than deforestation in the rain forest biome. The rate of loss is not well established, but may exceed 1% per year, approximately twice as fast as that of rain forests. Globally, this is likely to constitute a flux to the atmosphere that is at least as large as that arising from deforestation of the rain forest. Main conclusions The current rate of loss impacts appreciably on the global carbon balance. There is considerable scope for using many of the savannas as sites for carbon sequestration, by simply protecting them from burning and grazing, and permitting them to increase in stature and carbon content over periods of several decades.     

Towards improving the assessment of rainforest carbon: Complementary evidence from repeated diameter measurements and dated wood

We explore whether a growth-ring analysis can produce additional information about carbon budgets in tropical forests. Such forests are characterized by a high number of species and by trees that rarely have anatomically distinct annual growth rings, which hampers the application of dendrochronological tools in carbon balance assessments in the tropics. We use forest inventory data and archived annual diameter measurements from the Luki Biosphere Reserve in the southwestern margin of the Congo Basin forest massif. In addition, dated wood data are available from the same location thanks to tag nail traces that allow for the measurement of growth increments over a period of 66 years.We find that precise increment measurements based on dated wood are advisable for small subsets of many less abundant species and for functional species groups characterized by slow growth. The dated wood approach shows that many understory trees with non-periodical rings remain in a steady state for long periods of time. These results suggest a dated wood approach is advisable for studies of growth trajectories of individual trees that might be of importance for carbon assessments in degraded forests.     

Impact of human foraging on tree diversity,composition, and abundance in a tropical rainforest

Tropical forest tree communities are structured by a range of large-scale drivers including elevation, certain high-impact anthropogenic activities (e.g., deforestation), and fires. However, low-impact human activities such as foraging may also be subtly but notably altering the composition of tropical forest tree communities. The study assessed the (i) differences in species diversity, patterns of relative abundance, and pairwise beta diversity between trees with edible and inedible fruits and seeds along an elevation gradient, and (ii) impact of human foraging on the forest tree communities in Oban Division of Cross River National Park, Nigeria. Fifteen permanent 40 by 40 m plots were established along an elevational gradient (120–460 m above mean sea level). All trees of 0.1 m diameter at breast height (dbh) and above were measured, identified, and, with the aid of structured questionnaires, classified into those with edible and inedible fruits/seeds. A total of 35 edible species with density of 128 stems/hectare and basal area of 11.99 m²/hectare, and 109 inedible species with density of 364 stems/hectare and basal area of 22.42 m²/hectare were sampled. However, the evenness of edible and inedible species was similar at pooled and plot levels. For inedible species, there was a positive relationship between pairwise beta diversity and elevation, and this was driven mainly by turnover. In contrast, edible species exhibited a non-significant trend between elevation and beta diversity. Thus, the study showed that human foraging of edible fruits may have subtly influenced patterns of species diversity and community structure in this tropical forest.     

Nutrient enhancement, food quality and community dynamics in a tropical rainforest stream

• 1 A mixed nutrient supplement was added to stream‐side experimental channels in a closed canopy rainforest in tropical Queensland over a 7‐month period, raising nitrogen and phosphorus concentrations well above ambient.
• 2 Nutrient supplements enhanced decomposition of some leaf species, but levels of chlorophyll a and fine particulate organic matter did not differ between treatment and control channels.
• 3 Shredding by Anisocentropus kirramus (Trichoptera) had a significant effect on leaf litter breakdown, but nutrient supplements did not enable A.kirramus to shred more material; however, biochemical analysis of A. kirramus showed that nutrient supplements enhanced the nutritional quality of the litter for this species.
• 4 Treatment channels contained 75% more invertebrates than control channels, but significant differences in abundance (all positive) were detected in only five of the 109 invertebrate species present. There was no change in species richness or evenness between treatment and control channels.
• 5 The limited community response indicates that (a) variables other than nutrients (e.g. light) restricted primary productivity, (b) low nutrient concentrations limit invertebrate production, (c) invertebrate community composition in this closed canopy, forest stream is resistant to nutrient enhancement, and (d) there was no direct relationship between productivity and diversity in this tropical stream.

     

滇东南热带雨林种子植物区系的初步研究

通过对滇东南地区热带雨林植被的初步调查 ,统计滇东南热带雨林种子植物区系有种子植物 119科 ,378属 ,6 73种 (包括变种和亚种 )。种子植物分布区类型组成是主产热带和亚热带的科占 82 .35% ;热带分布属占非世界属数的 93.87% ;典型热带分布种占总种数的 75.93%。热带分布属中以亚洲热带分布属最多 ,占非世界属数的 4 0 .2 7% ;典型热带分布种中以热带亚洲分布及其变型越南 (印度支那 )至云南 (华南 )分布占比例最高 ,分别为 71.4 7%和 16 .34 %。分布区类型分析表明滇东南热带雨林种子植物区系具有热带亚洲区系的特点 ,属于古热带植物区中的马来亚森林植物亚区之中的北部湾区系。进一步分析表明此区系具热带北缘的性质。分布区类型的组成也表明此区系古特有种丰富。     

Effects of land use on surface-atmosphere exchanges of trace gases and energy in Borneo: comparing fluxes over oil palm plantations and a rainforest

This paper reports measurements of land-atmosphere fluxes of sensible and latent heat, momentum, CO(2), volatile organic compounds (VOCs), NO, NO(2), N(2)O and O(3) over a 30 m high rainforest canopy and a 12 m high oil palm plantation in the same region of Sabah in Borneo between April and July 2008. The daytime maximum CO(2) flux to the two canopies differs by approximately a factor of 2, 1200 mg C m(-2) h(-1) for the oil palm and 700 mg C m(-2) h(-1) for the rainforest, with the oil palm plantation showing a substantially greater quantum efficiency. Total VOC emissions are also larger over the oil palm than over the rainforest by a factor of 3. Emissions of isoprene from the oil palm canopy represented 80 per cent of the VOC emissions and exceeded those over the rainforest in similar light and temperature conditions by on average a factor of 5. Substantial emissions of estragole (1-allyl-4-methoxybenzene) from the oil palm plantation were detected and no trace of this VOC was detected in or above the rainforest. Deposition velocities for O(3) to the rainforest were a factor of 2 larger than over oil palm. Emissions of nitrous oxide were larger from the soils of the oil palm plantation than from the soils of the rainforest by approximately 25 per cent. It is clear from the measurements that the large change in the species composition generated by replacing rainforest with oil palm leads to profound changes in the net exchange of most of the trace gases measured, and thus on the chemical composition of the boundary layer over these surfaces.