Mangrove species are uniquely adapted to tropical and subtropical coasts, and although relatively low in number of species, mangrove forests provide at least US $1.6 billion each year in ecosystem services and support coastal livelihoods worldwide. Globally, mangrove areas are declining rapidly as they are cleared for coastal development and aquaculture and logged for timber and fuel production. Little is known about the effects of mangrove area loss on individual mangrove species and local or regional populations. To address this gap, species-specific information on global distribution, population status, life history traits, and major threats were compiled for each of the 70 known species of mangroves. Each species' probability of extinction was assessed under the Categories and Criteria of the IUCN Red List of Threatened Species. Eleven of the 70 mangrove species (16%) are at elevated threat of extinction. Particular areas of geographical concern include the Atlantic and Pacific coasts of Central America, where as many as 40% of mangroves species present are threatened with extinction. Across the globe, mangrove species found primarily in the high intertidal and upstream estuarine zones, which often have specific freshwater requirements and patchy distributions, are the most threatened because they are often the first cleared for development of aquaculture and agriculture. The loss of mangrove species will have devastating economic and environmental consequences for coastal communities, especially in those areas with low mangrove diversity and high mangrove area or species loss. Several species at high risk of extinction may disappear well before the next decade if existing protective measures are not enforced.

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The goods and services that mangrove forests provide to society are widely understood but may be too generally stated to serve as useful guidelines in decision‐making. Understanding the differences between fringe, riverine, and basin forests may help to focus these guidelines and to determine the best use of a particular forest. Fringe mangroves are important primarily for shoreline protection. Riverine forests, which are likely to be the most productive of the three types of forests, are particularly important to animal and plant productivity, perhaps because of high nutrient concentrations associated with sediment trapping. Basin forests serve as nutrient sinks for both natural and anthropogenically enhanced ecosystem processes and are often important sources of wood products. Exploitation of a forest for one particular reason may make it incapable of providing other goods and services.

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Comparative estimates of the leat area lndex (LAI) of a mangrove folest canopy in Peninsular Malaysia were obtained by 3 independent methods (1) from direct measuremc,nt of canopy leaf area above a prescnbed ground area, (L) trom simple measurements of llght flux den5ity above and beneath the cilnopy (3) from ineasulements of dilect beam transmlttance through the canopy Measurements \ \ L I~ also made of the rate of net photosynthesis at dlffcront levels In the canopy LAIs obtained by dlrect measurement rangcd from 2 2 to 7 4 over 4 rephcdte O 25 m' quddlats wlth a mean of 4 9 This hiclh deglee of vanabil~ty was attribut1.d pdrtly to the s~n a l l quadrat size and partly to the spatial h e t e r o q~~~~c~~t y of the canopy In contrast est~iilates of LA1 obtained from log averaged measurements of light transmission over a larger area of forest vaned by less than 5% between replicates, with an average of 5 1 Measurements of dilect beam transmlttance y~e l d e d an average canopy LA1 of 4 4Average rates of net photosynthesis ranged from 4 pmol CO, m -5 ' at the bottom of the cdnopy to about 10 pmol CO2 m s ' at the top of the canopy The LA1 weighted average rate of net photosynt h e m integrated over the entire canopy was 9 pm01 CO, m-' leaf S ' Assuming an etfcctive daylength of 8 h total dally net photosynthetic carbon f~xation was estimated to be 155 kg C ha I d ' giving a n annual net photosynthetic production of 56 t C he ' yr.' This 1s substantially higher than prev~ously reported for mangrove forests K E Y WORDS. Mangrove. C a n o p y . Leaf area index Photosynthesis INTRODUCTIONReliable estimates of mangrove forest primary production are essential for many ecological studies, and for assessing management options for these in~portant coastal ecosystems. The most reliable estimates of pnmary production come from measurement of biomass accumulation over a suitable period of time This usually involves measurement of the increase in DBH (stem diameter at breast height, ca 1.5 m) of all trees in a plot over a period of 1 to 5 yr. DBH measurements are then converted to biomass using allometric relationships (Ong et al. 1984, Putz & Chan 1986, Clough & Scott 1989. Such measurements are laborious and time consuming, and are generally not well suited to broad scale survey and comparative studies. There is thus a need for simple, survey type methods that can provide con~parative data on a broader scale.A relatively simple survey technique for estimating net photosynthetic production by mangrove forests was described by Bunt et al. (1979). Estimates of net photosynthetic production derived from this technique range from 18 to 34 kg C ha-' d-' (equivalent to 6.6 to 11.3 t C ha-' yr-' or 13 to 25 t dry matter ha-' yr-') for a wide range of mangrove forests in Papua New Guinea and northern Australia (Bunt et al. 1979, Boto et al. 1984

1. The architecture and allometry of eight populations of mangrove tree saplings of seven species (1•5-3 m in height) were studied at Sungei Merbok, Kedah, Peninsular Malaysia. Three populations (Bruguiera cylindrica, Bruguiera parviflora and Rhizophora apiculata) were growing in shaded conditions, the other five (Avicennia alba, Rhizophora apicuiata, Rhizophora mucronata, Sonneratia alba and Xylocarpus granatum) were in the open. 2. Comparisons were made between the population specific allometric regressions for dimension pairs of the form In y = b I In x + boo The bifurcation ratio (Rb) for" thebranching system of each sapling was calculated. 3. In the majority of the allometric regressions the populations differed significantly in b o 'but not b l' though some significant slope differences were found, particularly for regressions involving root dry weight. 4. The allometric analysis showed that for saplings of the same height, those growing in the shade had lower shoot dry weight f:lnd lower dry weight and area of leaves than the open-grown ones. The shaded saplings also exhibited a greater accumulation of foliage at the top of the plant. S. Xylocarpus granatum was notable for a low investment in leaves, which was probably explained by recent flushing, and in roots, which may reflect the limited development of pneumatophores in this species. The shaded Bruguiera popUlations showed a relatively high root investment probably because of their abundant pneumatophore development. 6. When compared to published results of allometric analyses for shaded saplings from lowland tropical rain forest and wann temperate rain forest it was found that the shaded mangroves were consistently more similar to the unshaded mangroves than to the rainforest saplings. This may be because the shaded mangroves were growing under higher average irradiances than those from the rain forests. It is argued, however, that mangrove species are inherently more likely to show an architecture better suited to high irradiance conditions than the majority of broad-leaved evergreen rainforest trees.

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