Predicting the retreat and migration of tidal forests along the northern Gulf of Mexico under sea-level rise

Tidal freshwater forests in coastal regions of the southeastern United States are undergoing dieback and retreat from increasing tidal inundation and saltwater intrusion attributed to climate variability and sea-level rise. In many areas, tidal saltwater forests (mangroves) contrastingly are expanding landward in subtropical coastal reaches succeeding freshwater marsh and forest zones. Hydrological characteristics of these low-relief coastal forests in intertidal settings are dictated by the influence of tidal and freshwater forcing. In this paper, we describe the application of the Sea Level Over Proportional Elevation (SLOPE) model to predict coastal forest retreat and migration from projected sea-level rise based on a proxy relationship of saltmarsh/mangrove area and tidal range. The SLOPE model assumes that the sum area of saltmarsh/mangrove habitat along any given coastal reach is determined by the slope of the landform and vertical tide forcing. Model results indicated that saltmarsh and mangrove migration from sea-level rise will vary by county and watershed but greater in western Gulf States than in the eastern Gulf States where millions of hectares of coastal forest will be displaced over the next century with a near meter rise in relative sea level alone. Substantial losses of coastal forests will also occur in the eastern Gulf but mangrove forests in subtropical zones of Florida are expected to replace retreating freshwater forest and affect regional biodiversity. Accelerated global eustacy from climate change will compound the degree of predicted retreat and migration of coastal forests with expected implications for ecosystem management of State and Federal lands in the absence of adaptive coastal management.     

Vertical accretion and shallow subsidence in a mangrove forest of southwestern Florida,U.S.A.

Simultaneous measurements of vertical accretion from artificial soilmarker horizons and soil elevation change from sedimentation-erosion table(SET) plots were used to evaluate the processes related to soil building infringe, basin, and overwash mangrove forests located in a low-energy lagoonwhich receives minor inputs of terrigenous sediments. Vertical accretionmeasures reflect the contribution of surficial sedimentation (sedimentdeposition and surface root growth). Measures of elevation change reflectnot only the contributions of vertical accretion but also those ofsubsurface processes such as compaction, decomposition and shrink-swell. Thetwo measures were used to calculate amounts of shallow subsidence (accretionminus elevation change) in each mangrove forest. The three forest typesrepresent different accretionary environments. The basin forest was locatedbehind a natural berm. Hydroperiod here was controlled primarily by rainfallrather than tidal exchange, although the basin flooded during extreme tidalevents. Soil accretion here occurred primarily by autochthonous organicmatter inputs, and elevation was controlled by accretion and shrink-swell ofthe substrate apparently related to cycles of flooding-drying and/or rootgrowth-decomposition. This hydrologically-restricted forest did notexperience an accretion or elevation deficit relative to sea-level rise. Thetidally dominated fringe and overwash island forests accreted throughmineral sediment inputs bound in place by plant roots. Filamentous turfalgae played an important role in stabilizing loose muds in the fringeforest where erosion was prevalent. Elevation in these high-energyenvironments was controlled not only by accretion but also by erosion and/orshallow subsidence. The rate of shallow subsidence was consistently3–4 mm y^–1 in the fringe and overwash island forests butwas negligible in the basin forest. Hence, the vertical development ofmangrove soils was influenced by both surface and subsurface processes andthe processes controlling soil elevation differed among forest types.The mangrove ecosystem at Rookery Bay has remained stable as sea levelhas risen during the past 70 years. Yet, lead-210 accretion data suggest asubstantial accretion deficit has occurred in the past century (accretionwas 10–20 cm < sea-level rise from 1930 to 1990) in the fringe andisland forests at Rookery Bay. In contrast, our measures of elevation changemostly equalled the estimates of sea-level rise and our short term estimatesof vertial accretion exceeded the estimates by the amount of shallowsubsidence. These data suggest that (1) vertical accretion in this system isdriven by local sea-level rise and shallow subsidence, and (2) the mangroveforests are mostly keeping pace with sea-level rise. Thus, the vulnerabilityof this mangrove ecosystem to sea-level rise is best described in terms ofan elevation deficit (elevation change minus sea-level rise) based on annualmeasures rather than an accretion deficit (accretion minus sea-level rise)based on decadal measures.     

Use of waste materials as nursery growing media for <Emphasis Type="Italic">Pinus halepensis</Emphasis> production

Peat moss is gradually being replaced by other materials as a growing medium in forest nurseries due to economic and ecological constraints. In this study, six different mixtures were tested, mixing peat moss (P) and pine bark (B) with digested sewage sludge (S) activated sewage sludge (A) and paper mill sludge (M), as growing media for Pinus halepensis seedlings; three different waste doses were applied. Seed germination percentage, seedling growth and foliar nutrient content after 1 year in a greenhouse and percentage survival after transplanting were recorded. The influence of base substrate (P or B) on germination percentage changed in different ways according the type of waste. The order of the different applied mixtures by suitability (germination rate and seedling growth) from best to worst was as follows: activated sludge with peat, activated sludge with pine bark, sewage sludge with peat, sewage sludge with pine bark, paper mill sludge with pine bark and finally paper mill sludge with peat.     

Fine root respiration in the mangrove Rhizophora mangle over variation in forest stature and nutrient availability

Root respiration uses a significant proportion of photosynthetically fixed carbon (C) and is a globally important source of C liberated from soils. Mangroves, which are an important and productive forest resource in many tropical and subtropical countries, sustain a high ratio of root to shoot biomass which may indicate that root respiration is a particularly important component in mangrove forest carbon budgets. Mangroves are often exposed to nutrient pollution from coastal waters. Here we assessed the magnitude of fine root respiration in mangrove forests in Belize and investigated how root respiration is influenced by nutrient additions. Respiration rates of excised fine roots of the mangrove, Rhizophora mangle L., were low (4.01 +/- 0.16 nmol CO(2) g(-1) s(-1)) compared to those measured in temperate tree species at similar temperatures. In an experiment where trees where fertilized with nitrogen (N) or phosphorus (P) in low productivity dwarf forests (1-2 m height) and more productive, taller (4- 7 m height) seaward fringing forests, respiration of fine roots did not vary consistently with fertilization treatments or with forest stature. Fine roots of taller fringe trees had higher concentrations of both N and P compared to dwarf trees. Fertilization with P enhanced fine root P concentrations in both dwarf and fringe trees, but reduced root N concentrations compared to controls. Fertilization with N had no effect on root N or P concentrations. Unlike photosynthetic C gain and growth, which is strongly limited by P availability in dwarf forests at this site, fine root respiration (expressed on a mass basis) was variable, but showed no significant enhancements with nutrient additions. Variation in fine root production and standing biomass are, therefore, likely to be more important factors determining C efflux from mangrove sediments than variations in fine root respiration per unit mass.     

珠江口红树林湿地保护规划的基本思路

珠江口是珠江出海口流经区域的简称,包括香港、澳门特别行政区和广州市、深圳市、珠海市、东莞市、中山市等。历史上该地区曾分布着大片的天然红树林,但是由于社会经济的快速发展,红树林资源遭到不同程度的破坏。文章将珠江口沿岸红树林湿地作为一个整体区域进行考虑,提出实施保护工程的基本思路,通过红树林保护工程、红树林恢复工程等措施,全面恢复湿地功能,改善区域河口生态环境,保护生物多样性,增强红树林防御台风、海啸、赤潮等自然灾害的能力。     

Sediment mixing and accumulation in a mangrove ecosystem: evidence from 210Pb, 234Th and 7Be

210Pb, 234Th and 7Be activities were measured to establish sediment accumulation rates, estimate sediment mixing rates, and determine the depth of the sediment mixed layer in the Sepetiba Bay mangrove ecosystem near Rio de Janeiro City, Brazil. Three sediment cores were collected from Enseada das Garças, a typical exposed tidal flat region with a sequence of sedimentary features. The seaward edge of this sequence is a mud flat with the landward portion covered with Spartina alterniflora followed by mangrove vegetation. An additional core was collected on an overwash island near Barra de Guaratiba, which is cover with mangroves without a mud flat or Spartina alterniflora sequence. Sediment accumulation rates were determined to range up to 1.8cm/yr with the Spartina alterniflora having the maximum rate. Mixing rates were estimated for the Spartina alternifloracore at 40cm2/yr based on 210Pb and 7Be from the upper mixed region of the core. The 234Th activity in this core suggested that either mixing or the input of 234Th were not in steady state. The sediment mixed region depth ranged from 4cm to greater than 30cm. At the Enseada das Garças site the mixing depth decreased in the landward direction (i.e. mud flats > 30cm, Spartina alterniflora 11cm, mangroves 4cm). Along with this decrease in sediment mixing depth was a shift from physical to biological mixing. The Barra de Guaratiba core had a sediment mixed layer of 13cm as a result of physical and intense biological activity.     

Mangrove community recovery potential after catastrophic disturbances in Bangladesh

The objective of this study was to compare the variation in the soil seed banks and the aboveground vegetation in relation to three habitats, i.e., swamp forests, grassland and sand dunes within the Sundarbans mangrove forests of Bangladesh. We collected vegetation data (species and their percentage cover) by using quadrat sampling: 10 m × 10 m for swamp forests and 5 m × 5 m for grassland and sand dunes. We estimated the density of viable seeds of species in the seed bank by counting germinants from soil cores in a germination chamber. Species richness and composition of both aboveground vegetation and the soil seed banks differed significantly among habitats. We identified a total of 23 species from the soil seed bank. Of these, two were true mangrove species and the remaining were non-mangrove species, including halophytic grasses, herbs and mangrove associate species. Our results confirm that mangrove species do not possess a persistent soil seed bank. The presence of high-density non-mangrove and associated mangrove species in the soil seed bank implies that after frequent catastrophic disturbances which limit incoming propagules from adjacent forest stand, large canopy gaps can easily become invaded by non-mangrove and mangrove associate species. This would result in the formation of a cover of non-mangrove species and cryptic ecological degradation in mangrove habitats. We suggest that forest managers should actively consider gap plantations with mangrove species in the large canopy gaps created after catastrophic disturbances to counteract the invasion of non-mangrove species and cryptic ecological degradation.     

珠江口红树林湿地保护与修复的基本思路

珠江口是珠江出海口流经区域的简称,包括香港、澳门特别行政区和广州市、深圳市、珠海市、东莞市、中山市等。历史上该地区曾分布着大片的天然红树林,但是由于社会经济的快速发展,红树林资源遭到不同程度的破坏。文章将珠江口沿岸红树林湿地作为一个整体区域进行考虑,提出实施保护工程的基本思路,通过红树林保护工程、红树林恢复工程等措施,全面恢复湿地功能,改善区域河口生态环境,保护生物多样性,增强红树林防御台风、海啸、赤潮等自然灾害的能力。     

Production of <Emphasis Type="Italic">Pinus halepensis</Emphasis> seedlings inoculated with the edible fungus <Emphasis Type="Italic">Lactarius deliciosus</Emphasis> under nursery conditions

Inoculation with edible fungi bestows an added value on mycorrhized plants since production of mushrooms as a secondary crop can be an economically-valuable resource in forestry management. In order to establish a protocol for controlled mycorrhization of Pinus halepensis with the edible fungus Lactarius deliciosus, several factors such as fertilisation (35, 60 or 120 mg total N and 13.5, 27 or 54 mg total P), potting substrate (sphagnum peat or sphagnum peat/vermiculite) and fungal inoculum (mycelial slurry produced in a bioreactor, alginate beads or peat/vermiculite) were assessed. The most effective inoculum was mycelial slurry at a dose of 10 ml/plant. The two potting substrates assessed were compatible with mycorrhiza formation. The greatest number of mycorrhized seedlings was obtained with a moderate level of N (35 mg/plant) or P fertilisation (27 mg/plant). Inoculation did not produce a consistent growth effect on P. halepensis, but seedlings met the quality requirements, making them suitable for planting out.     

中国广东红树林资源现状与保护对策

According to the survey of Guangdong mangrove resource in 2001 and author‘s field investigations in the past 5 years, the total mature mangrove land area of Guangdong Province was estimated at 9084 hm2, accounting for 41.4% of total mangrove land area of China. These mangrove forests totally consisted of 50 species belonging to 28 families, distributed at more than 100 locations along the coastlines of Guangdong and most of them present a high dense and dwarf appearance. The Ass. Avicennia marina is the most dominant mangrove association. The investigation results showed that the mangrove forests with coverage rates above 0.7 accounted for 68.0% of the total mangrove land area of the province and 77.8% of mangrove forests was less than 2 m in tree height. Since 1950, 54.6% of mangrove forests have disappeared due to paddy rice reclaim,aquaculture and city constructions. Derivational conservation efforts are still weakly empowered and should be strengthened intensively. The author suggested that mangrove laws and regulations should be enforced, mangrove scientific research should be strengthened; and mangrove conservation awareness of local community should be raised on conservation of mangroves.     

Effects of previous forest types and site conditions on species composition and abundance of naturally regenerated trees in young <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> plantations in northern Japan

Naturally regenerated trees in young Cryptomeria japonica plantations were investigated in 141 quadrats of 10 × 50 m within a watershed of 1,000 ha, and factors affecting their composition and abundance were examined. The species composition of naturally regenerated trees was classified into four types. Dominant species were Swida controversa, Magnolia hypoleuca and Pterocarya rhoifolia in Type A1, Betula maximowicziana, M. hypoleuca, Quercus crispula and Castanea crenata in Type A2, Q. serrata and C. crenata in Type B1, and Pinus densiflora in Type B2. The results of path analysis showed significant influences of previous forest type and geology among the factors that correlated with the species composition of naturally regenerated trees; previous forest type in particular showed a higher absolute path coefficient value. Species composition types of naturally regenerated trees corresponded to the previous forest types: Types (A1 and A2) corresponded to the natural forests composed of Thujopsis dolabrata var. hondai, Fagus crenata, Aesculus turbinata, etc., Type B1 corresponded to the secondary Q. crispula and Q. serrata forest, and Type B2 corresponded to the secondary P. densiflora forest, respectively. The abundance of naturally regenerated trees was strongly affected by geology; i.e., plantations on soft-sedimentary dacitic tuff contained great amounts of colonizing P. densiflora trees.     

Severe hail damage to mangroves at Port Curtis, Australia

A hailstorm in October 1994 was found to have moderately or severely impacted on 5.3% of the mangrove forests in Port Curtis. All mangrove species showed evidence of hail damage, including the three most common species (Rhizophora stylosa, Ceriops tagal and Avicennia marina). Physical effects of hail damage included stripping of leaves from plants, holes punched through leaves, bruising to bark, divots removed from bark, branch and plant death. Speciesspecific differences in vulnerability to the effects of hail were observed with C.tagal experiencing relatively higher mortality rates than the other two common mangrove species. A delayed pattern of mortality was observed in two species _ C.tagal and A.marina. Alterations to mangrove community structure included: (1) reductions in stem density, stem diameter and basal area, (2) reductions in canopy cover (based on a photographic index of foliage projective cover) and (3) changes in relative abundance of species in mangrove zones. Recovery was observed in some stands but others had not recovered to prehail levels of canopy cover two years after the hailstorm. Recovery had occurred by regeneration of fresh leaves but no recruitment of young plants had been observed during the study. The forests in the impact area were dominated by either Ceriops tagal or Rhizophora stylosa with Avicennia marinaas a subdominant in places. C.tagal dominated forests within the impact area were relatively more severely affected (41.8% in the severe category) than R.stylosa dominated communities (only 17.4% in the severe category). This indicated that C.tagal dominated forests were more vulnerable to the effects of hail damage than R.stylosa dominated forests. In addition, hailimpacted C.tagal dominated forests represented a relatively high percentage of the area of C.tagal dominated forests in Port Curtis (44.3%). This percentage was much higher than hailimpacted R.stylosa dominated forests in Port Curtis (2.7%). These two factors – relatively severe impact on C.tagal communities and a relatively higher percentage affected within the Port Curtis area – illustrate that hailstorms, as a form of natural disturbance, are an important influence on the forest ecology of mangrove ecosystems in this region.     

Inorganic sediment budget in the mangrove-fringed Fly River Delta,Papua New Guinea

Six oceanographic moorings were maintained for 8 weeks across the mouth of the mangrove-fringed Fly River estuary from April to June 1995 in the southeast trade wind season. A further 4 moorings were deployed for 8 weeks along the estuary channel in 1992, also in the southeast trade wind season. These data were used to estimate net exchange of suspended sediment between the estuary and the Gulf of Papua. A net inflow of fine sediment into the estuary from the coastal ocean was found to be considerable, about 40 tonnes s^-1 or about 10 times the riverine inflow rate, resulting in a calculated, spatially averaged vertical accretion rate of 2 mm year^-1. Mangroves may account for trapping 6% of the riverine sediment inflow or about 1/4 of the riverine clay inflow. If this sediment was distributed only over the observed accumulation zones near islands the local accumulation rates in these zones would reach 4 cm year^-1. Estimates of soft sediment mass accumulation rates (1–10 kg m^-2 year^-1) in the channel from Pb-210 and C-14 measurements from cores of deltaic mangrove mud cannot account for this accumulation rate on a 100–1000 year time scale. The fate of the remaining sediment is unknown, it may be exported from the estuary in the monsoon season.     

Age-related variations in delta(13)C of ecosystem respiration across a coniferous forest chronosequence in the Pacific Northwest

We tested the hypothesis that forest age influences the carbon isotope ratio (delta13C) of carbon reservoirs and CO2 at local and regional levels. Carbon isotope ratios of ecosystem respiration (delta13C(R)), soil respiration (delta13C(R-soil)), bulk needle tissue (delta13C(P)) and soil organic carbon (delta(13)C(SOC)) were measured in > 450-, 40- and 20-year-old temperate, mixed coniferous forests in southern Washington, USA. Values of delta13C(R), delta13C(R-soil), delta13C(P) and delta13C(SOC) showed consistent enrichment with increasing stand age. Between the youngest and oldest forests there was an approximately 1 per thousand enrichment in delta13C(P) (at similar canopy levels), delta13C(SOC) (throughout the soil column), delta13C(R-soil) (during the wet season) and delta13C(R) (during the dry season). Mean values of delta13C(R) were -25.9, -26.5 and -27.0 per thousand for the 450-, 40- and 20-year-old forests, respectively. Both delta13C(R-soil) and the difference between delta13C(R) and delta13C(R-soil) were more 13C enriched in older forests than in young forest: delta13C(R) - delta13C(R-soil) = 2.3, 1.1 and 0.5 per thousand for the 450-, 40- and 20-year-old forests, respectively. Values of delta(13)C(P) were proportionally more depleted relative to delta13C(R): delta13C(R) - delta13C(P) = 0.5, 2.2 and 2.5 per thousand for the 450-, 40- and 20-year-old forests, respectively. Values of delta13C(P) were most 13C-enriched at the top of the canopy and in the oldest forest regardless of season (overall values were -26.9, -28.7 and -29.4 per thousand for the 450-, 40- and 20-year-old forests, respectively). Values of delta13C(SOC) from shallow soil depths were similar to delta13C(P) values of upper- and mid-canopy needles. All delta13C data are consistent with the hypothesis that a decrease in stomatal conductance associated with decreased hydraulic conductance leads to increased CO2 diffusional limitations in older coniferous trees. The strong associations between delta13C(P) in needles with delta13C(R) and delta13C(R-soil) at the forest level suggest that 13C observations scale between leaf and ecosystem levels.     

Rainfall interception in a moso bamboo (Phyllostachys pubescens) forest

In recent years, moso bamboo (Phyllostachys pubescens) forest areas in Japan have rapidly expanded, and bamboo is now invading nearby natural or plantation forests. To date, only one study has examined the rainfall interception of a moso bamboo forest. In that study, it was reported that the interception ratio (interception/rainfall) of the bamboo forest did not exceed the interception ratios of other natural and plantation forests (n = 4) in Japan. To expand the current state of knowledge about rainfall interception of bamboo forests, we measured throughfall and stemflow at another bamboo forest site. Annual rainfall (Rf), throughfall (Tf), and stemflow (Sf) during the measurement period were 2,105, 1,556, and 322 mm, respectively. Annual rainfall interception at the plot (I) was 228 mm. Tf/Rf, Sf/Rf, and I/Rf were 73.9, 15.3, 10.8%, respectively. I/Rf was less than 20% throughout the year except in October, the month with lowest rainfall. We also summarized rainfall interception data from 19 other natural and plantation forests. The I/Rf value of our site did not exceed the I/Rf values of these natural and plantation forests (n = 19). Our data will be useful for assessing changes in water resources that result from replacement of natural or plantation forests by bamboo forests.     

Restoration of the mangrove vegetation in the Mahanadi delta,Orissa, India

In India, mangroves occupy 6740 km² of which the Mahanadi delta andBhitarkanika mangrove forests of Orissa cover 191.44 km², most of whichhas been severely overexploited. World wide concern to conserve mangrovesnecessitated propagation of mangroves to re-establish them on barren andswampy land along tidal creeks around Paradeep port of Orissa. Avicenniaofficinalis, Aegiceras corniculatum, Bruguiera parviflora, B. sexangula,Ceriops decandra, Excoecaria agallocha, Heritiera fomes, Kandelia candel,Rhizophora mucronata, Sonneratia apetala were vegetatively propagated andplanted over 10 ha of degraded salt-marshy wetlands of Mahanadi delta inpure and mixed stands depending on the intensity and the frequency of tidalinundation at the experimental site. Survival was significantly higher(80%) in S. apetala followed by A. officinalis, R. mucronata, K.candel and H. fomes (70–75%). S. apetala recorded the maximumgrowth in height (3.0 m after 2 years) whereas C. decandra showed theminimum growth (0.5 m). Growth performance was better with plants in mixedstands than the plantation with single species. This gives us hope topropagate and re-establish mangroves for conservation in scientificallymanaged plantations in a physiologically arid environment.     

Water availability and branch length determine delta(13)C in foliage of Pinus pinaster

The stable carbon isotope composition (delta(13)C) of foliage integrates signals resulting from environmental and hydraulic constraints on water movement and photosynthesis. We used branch length as a simple predictor of hydraulic constraints to water fluxes and determined the response of delta(13)C to varying water availability. Foliage up to 6 years old was taken from Pinus pinaster Ait. trees growing at four sites differing in precipitation (P; 414-984 mm year(-1)) and potential evaporation (ET; 1091-1750 mm year(-1)). Branch length was the principal determinant of temporal trends in delta(13)C. The strong relationship between delta(13)C and branch length was a function of hydraulic conductance, which was negatively correlated with branch length (r(2) = 0.84). Variation in P and ET among sites was reflected in delta(13)C, which was negatively correlated with P/ET (r(2) = 0.66). However, this analysis was confounded by differences in branch length. If the effects of branch length on delta(13)C were first removed, then the 'residual' delta(13)C was more closely related to P/ET (r(2) = 0.99), highlighting the importance of accounting for variation in hydraulic constraints to water flux between sites and years. For plant species that exhibit considerable phenotypic plasticity in response to changes in environment (e.g., variation in leaf area, branch length and number, or stem form), the environmental effects on delta(13)C in foliage can only be reliably assessed if deconvoluted from hydraulic constraints.     

深圳湾福田保护区红树林生态系统服务功能价值评估

对深圳湾福田保护区红树林的生态服务功能价值进行了研究,结果表明:深圳湾福田保护区现有生态系统服务功能年总价值4 894.4万元,深圳湾红树林湿地生态系统单位面积生态功能价值约10.74万元/hm2a,其中红树林价值2 702.4万元,河道价值282万元,淤泥滩涂价值674万元,海域价值1 840万元,基建填土区观光旅游价值260万元,林地价值76万元。深圳湾福田保护区红树林生态系统服务功能价值中,生产生态系统产品等9个分项的总和为2 928万元。对环境氮与磷的去除价值、重金属吸附价值、二氧化碳固定和氧气释放价值等在内的生态系统净化功能价值共占14.2%。深圳湾的所有红树林类型中,秋茄+桐花树+白骨壤生态系统类型单价最大值为12.3万/hm2a。深圳市梧桐山森林生态系统服务功能价值为1.076 4～1.148 4万元/hm2a,显著低于本研究红树林生态系统服务功能价值,约占单位面积红树林生态系统的生态价值10%。香港米埔红树林生态系统的生态服务功能价值(13.7万港元/hm2a)高于深圳湾红树林生态系统,约高出21%。改造后的深圳湾生态系统服务功能价值预期可达7 243.48万元。     

Sedimentation in Mangrove Forests

The tidal currents in mangrove forests are impeded by the friction caused by the high vegetation density. The tidal currents are also complex comprising eddies, jets and stagnation zones. The sediment particles carried in suspension into the forest during tidal inundation are cohesive, mainly clay and fine silt, and form large flocs. These flocs remain in suspension as a result of the turbulence created by the flow around the vegetation. The intensity of sedimentation is largest for trees forming a complex matrix of roots such as Rhizophora sp. and smallest for single trees such as Ceriops sp. The flocs settle in the forest around slack high tide. At ebb tides the water currents are too small to re-entrain this sediment. Hence the inundation of coastal mangrove forests at tidal frequency works as a pump preferentially transporting fine, cohesive sediment from coastal waters to the mangroves. Mangroves are thus not just opportunistic trees colonising mud banks but actively contribute to the creation of mud banks.     

两广地区主要森林类型的年土壤呼吸及空间分布研究

研究根据广东和广西(两广)地区森林类型分布图、主要森林类型的年土壤呼吸数据库以及中国日值格点气温、降水数据,建立线性模型预测两广地区主要森林类型的年土壤呼吸速率和年土壤呼吸通量。结果表明,两广地区主要森林类型年土壤呼吸速率为常绿阔叶林864.18 gC/m~2/yr>其他森林811.03 gC/m~2/yr>针叶林791.43 gC/m~2/yr>灌木林780.18 gC/m~2/yr>落叶阔叶林758.80 gC/m~2/yr>竹林731.49 gC/m~2/yr>针阔混交林684.91 gC/m~2/yr。两广地区森林年土壤呼吸通量为204.41 TgC/yr,其中常绿阔叶林最大,为77.41 TgC/yr,针叶林次之,为56.81 TgC/yr,具体为常绿阔叶林>针叶林>灌木林>落叶阔叶林>针阔混交林>竹林>其他森林,顺序与各种森林类型面积大小一致。各森林类型的土壤呼吸通量主要与森林面积有关,森林面积越大土壤呼吸通量越大。