Mangrove silviculture

M. A. HUBERT, Forestry and Forest Products Division, FAO

The following is a modified extract from the FAO Forestry and Forest Products Study, Tropical Silviculture. It gives the highlights of the silviculture of mangrove forests, and deals with the occurrence; physical factors; silvical factors such as composition, succession seed production, establishment, and stand development; silvicultural practice; and some suggestions as to future research.

The mangrove forest is a community controlled primarily by edaphic factors. Such edaphic communities occur in great variety and varying importance throughout the tropics as successional stages in the development of, or in retrogression from, the major climax communities. Although these communities are the result of many soil factors, structure, composition, aeration, the mineral contents of surface and soil water and water movement, including changes in water levels, probably the most important and most widely distributed are caused by an extreme water regime. As a consequence, a number of forest communities have been recognized variously as riverain, riparian, gallery, varzea, periodic swamp, freshwater swamp, peaty swamp, beach, tidal, and mangrove forests.

For most areas, mangrove forests probably have a greater importance from an economic standpoint than the other edaphic communities listed above, forming in all world areas an important source of timber, fuel, posts, poles, tannin and other minor forest products. The effects of commercial exploitation are more marked and, as a result, these coastal forests are better known. Furthermore, though river swamp or other edaphic forests occupy vast areas in the tropical world and in some areas, as in Malaya and Indonesia, surpass mangrove forests in commercial importance, they have been on the whole less intensively exploited and studied, and included for the most part with other rain forest or deciduous forest in silvicultural discussions. The Mora and Wallaba communities of the Guianas are good examples. Mangrove, moreover, warrants detailed consideration not only because of its commercial importance but also in view of its widespread distribution in all three tropical world areas and the far greater amount of useful information now available on a world basis for this sharply differentiated and silviculturally interesting edaphic forest community.

The word "mangrove" covers two different concepts. In the first place, it denotes those species, numbering some 20 to 40, belonging to several unrelated families but possessing similar physiological characteristics and structural adaptations with similar habitat preferences. In the second sense, it means a complex of plant communities found as a belt of varying width along the tropical shores of sheltered creeks, lagoons, deltas and islands below high tide mark. These edaphic communities are the result of the constantly changing conditions brought about by river deposits, formation of sand bars, lagoons, temporary swamps caused by alterations in river channels, lake borders and drainage patterns, tidal movements of salty or brackish water, in estuaries as well as for considerable distances upstream, and even the effects of wave action along seacoasts on the deposition of silt, mud or sand. Although mangrove species may extend beyond the level of the highest tides, Schimper (1903) defined " mangrove " and " tidal forests ", which he regarded as synonymous, to include the whole formation below the hightide mark. The term is used here in this sense.

Occurrence

In coastal areas, chiefly on muddy, sheltered shores subject to periodic submersion, mangrove forests may occur in widths varying from a few hundred yards (100 meters) to as much as 12 or 15 miles (19 to 24 kilometers). These forests may be on coastal islands varying in size from a few acres or hectares to many square miles or kilometers, in lagoons between these islands and the coastline, as well as in strips reaching upstream for many miles inland. Distribution is world-wide and is usually considered as occurring in two zones. The eastern zone comprises the east African coast as well as the coasts of Pakistan, India, Burma, Malaya, Thailand and the islands down to Australia. The western zone includes the coasts of America and the Caribbean and of West Africa. Although in general the distribution of mangroves of the richest and most luxuriant growth and development agrees with that of rain forest, it extends far north and south of the equator, sometimes beyond the tropics, along coasts of which the inland climax vegetation may be anything from mixed deciduous to desert types. The northern limit of mangrove vegetation extends to south Japan, the Gulf of Aquaba in the Red Sea, Florida in North America and the Bermudas, while it reaches its southern limit in northern New Zealand, in Natal in Africa, and in southern Brazil (about 27° 30') in South America.

Data on the extent of the mangrove formation are not available for many countries. A few figures, however, have been reported: for example, for the Sundarbans (Ganges and Brahmaputra deltas in West Bengal, India, and East Bengal, East Pakistan), 4 million acres (1,600,000 hectares); for Malaya, 320,000 to 380,000 acres (129,500 to 155,500 hectares); for Puerto Rico, over 16,000 acres (6,500 hectares); Fiji Islands, 45,000 to 50,000 acres (18,000 to 20,000 hectares); Kenya, 80,000 acres (32,500 hectares); Tanganyika, 210,000 acres (85,000 hectares); Belgian Congo, 50,000 acres (20,000 hectares); Zanzibar, 40,000 to 50,000 acres (15,000 to 20,000 hectares); and for Indonesia, between 125,000 and 250,000 acres (50,000 and 100,000 hectares). Aerial photographs of the coastal regions of the other countries concerned would undoubtedly reveal a very important acreage of potentially rich mangrove swamps.

Physical factors

Under the extreme edaphic conditions indicated, the effect of climate is less marked and no special summary of such factors seems necessary other than to note the wide range under which the mangrove formation occurs. Although climatic effects are not marked, Stehlé (1945-46) notes that the intense rains of winter seasons, as in the Caribbean, may dilute the salinity of the brackish mud which halophilous mangroves prefer, thus affecting their distribution; while winds, blowing unfixed sand from nearby dunes, may help to fill in mangrove swamps and thus influence composition and development. On the other hand, habitat conditions relating to physical location and resulting soil and water conditions have very important and marked effects on composition, succession, and silviculture. Indeed, one of the most striking features of the typical mangrove habitat is that at any one place the level of the ground is not only gradually rising but is also slowly getting further away from the sea, as accretion seaward takes place owing to continuous deposition of silt brought down by rivers especially in high rainfall areas. In consequence, there are changes in the frequency and duration of submersion and the degree of salinity of the water, and in any one region a wide variation in these environmental factors is possible, as one proceeds from the newly deposited mud banks into the gradually rising interior high ground.

These factors are probably of much greater significance than soil qualities as such. For the most part, the soil in most marginal formations contains a high clay fraction, often compact, blue in color, with low organic matter content. In the newer deposits facing the sea, as well as in the river-borne silt on river banks, the soil is more friable; brownish-black in color, it contains some sand and an important percentage of organic materials. The best development of the mangrove type coincides with occurrence of deep, well-aerated soil, rich in organic matter and low in sand. Good development is also found where the soil is a stiff clay, overlaid with a thin horizon of silt and raw humus. In areas subject to regular tidal inundation's, the subsoil is a raw blue clay; in the drier areas, sandy subsoil is usually found. Approximately the same description is given for mangrove areas in most parts of the eastern and western zones.

Silvical factors

The habitat factors described, relating to peculiar and special location, have a marked effect also on silvical features. For the most part, the mangroves are composed of shrubs or trees forming a characteristic dense evergreen and seemingly impenetrable mass of low forest, ranging from three feet (1 meter) to a hundred or more feet (30 meters) in height. The formation is essentially alike in its physiognomy and ecological relationships in both eastern and western zones. Characteristic species have, for example, special physiological features and structural adaptation to withstand periodic flooding salinity of the water and consequent " physiological dryness "; e.g., Rhizophora species have stilt roots, Bruguiera and Heritiera species have knee roots, while those of Sonneratia, Xilocarpus, Avicennia and Armora send up asparagus-like pointed pneumatophores. Typical species are also characterized by a general tendency toward vivipary. Nearly all have large buoyant fruits or seeds, and thick, dark green coriaceous leaves with xerophytic structure. As Richards (1952) notes, mangroves are probably the most remarkable of all examples among plants of strong resemblances in similar though widely separated environments.

FIGURE 1. - Planting up blank areas with Rhizophora mucronata in mangrove forests (Malaya).

Courtesy, Malayan Forest Service

Composition

The composition in both eastern and western zones is essentially similar. All of the genera of the western mangrove are found in the eastern area, though all species are different. The formation reaches its greatest luxuriance and floristic richness in the wet tropics of the eastern zone, notably Malaya and the Sundarbans, though it is relatively poor in species as compared with most tropical floras. Its essential homogeneity is well illustrated by species lists for several of the countries in each zone, as set out below. For the eastern zone, Troup (1921) shows the approximate composition for Pakistan, India and Burma (Table 1).

TABLE 1. - APPROXIMATE COMPOSITION OF MANGROVE FORMATION FOR PAKISTAN, INDIA AND BURMA (TROUP, 1921)

Species	Sind	Indian peninsula		Sundarbans	Chittagong	Burma	Andamans
	Indus delta	West coast	East coast
Rhizophora mucronata	x	x	x	x	x	x	x
R. conjugata	x	x	-	-	x	x	x
Ceriops candolleana (= C. tagal)	x	x	-	x	x	x	-
C. roxburghiana	x	x	-	x	x	x	-
Kandelia rheedii	-	x	x	x	x	x	x
Bruguiera gymnorrhiza	x	x	x	x	x	x	x
B. eriopetala	-	x	-	-	-	-	-
B. caryophylloides (= B. cylindrica)	-	x	-	-	-	x	-
B. parviflora	-	-	-	x	-	x	x
Carapa obovata (= Xylocarpus granatum)	-	x	-	x	x	x	x
C. moluccensis (= X. gangeticus in Sundarbans)	-	-	-	-	x	-	x
Cynometra ramiflora	-	x	x	x	x	x	x
Lumnitzera racemosa (= L. litorea)	-	x	-	x	x	x	x
L. coccinea	-	-	-	-	-	x	x
Sonneratia acida (S. caseolaris)	x	x	x	x	x	x	x
S. apetala	-	x	-	x	x	x	-
S. alba	-	x	-	-	-	x	x
S. griffithii	-	-	-	-	-	x	-
Scyphiphora hydrophyllacea	-	-	x	-	-	-	x
Aegicera majus	x	x	x	x	x	x	x
Achantus ilicifolius	-	x	-	x	x	x	-
Avicennia officinalis	-	x	x	x	x	x	x
Excaecaria agallocha	-	x	x	x	x	x	x
Nipa fruticans	-	-	-	x	x	x	x
Phoenix paludosa	-	-	-	x	x	x	x

In Indonesia, the following species have been reported: Rhizophora mucronata, R. apiculata, Bruguiera gymnorrhiza, B. sexangula, B. parviflora, Ceriops tagal (syn. C. candolleana), Xylocarpus gnaratum, Sonneratia caseolaris. In Malaya, the principal species are: Rhizophora conjugata, R. mucronata, Bruguiera parviflora B. cylindrica (Syn. B. caryphylloides), B. gymnorrhiza, B. hainessi, B. eriopetala and Ceriops tagal.

For the western zone, lists of the composition of forests in Puerto Rico and Nigeria are available. In Puerto Rico, the four principal species are Rhizophora mangle, Laguncularia racemosa, Conocarpus erecta and Avicennia nitida. In Nigeria and the Belgian Congo, the mangrove forests consist of Rhizophora racemosa (about 99 percent), Avicennia nitida, Laguncularia racemosa and Conocarpus erecta (on the drier fringes of the swamps) and Acrostichum aureum.

One other outstanding feature of mangrove forests affecting composition is the zonation of different plant communities in strips more or less parallel to the shore line, with definite segregation of zonation of the dominant species. For example, in Malaya, the stands along the seaface are usually Avicennia intermedia, A. alba or Sonneratia alba with Rhizophora sp. on somewhat higher ground and Bruguiera behind, often continuing up to the extreme tidal limit of the swamps.

Succession

Succession, with some differences in pioneers, is essentially the same in both zones. Thus in Malaya, for example, mudbanks must be free from inundation for about two days a month before colonization takes place (above the reap-tide high-water mark). Avicennia species, of which A. alba is by far the commonest, are pioneers of the clay accretion areas out by the sea face, while Sonneratia alba is the typical pioneer of mud banks within the estuaries. Avicennia on the heavy sea-face clays is succeeded by Bruguiera cylindrica, as the ground level rapidly rises to extreme tidal levels. On the estuarine silts Rhizophora mucronata replaces Sonneratia alba but the soil level is not built up so quickly.

As the soil becomes better aerated and more humus is incorporated in it the maximum development of Rhizophora forest, principally R. conjugata, is found (sometimes called the " climax " of the mangrove succession). Rhizophora forest is distinctly poorer on heavy clay soils or soils subject to river flooding and sand deposition. Optimum inundation conditions are coverage by all normal high tides with dry periods of four to eight days twice each month at neap tides. It is estimated that more than two thirds of all Malayan mangroves consist of Rhizophora forests characterized by numerous small streams. Associated species are usually Bruguiera parviflora and the fern Acrostichum speciosum with locally Xylocarpus granatum and Ceriops tagal.

As the soil level rises and inundation is less common, other species of Bruguiera are able to establish themselves. These Bruguiera species, probably B. gymnorrhiza, B. hainesii and B. eriopetala, become prominent as areas become drier forming the transition to the inland forms of tidal forests, representing the final stage in the succession. Although Rhizophora can grow up to the limits of tidal flooding, regeneration of these species, as well as those of Bruguiera, becomes uncertain. Here Acrostichum aureum grows densely and is undoubtedly a serious factor preventing the establishment of regeneration, and eventually the tidal forest species of Xylocarpus, Heritiera, Intsia and Lumnitzera (Watson, 1928).

This is essentially the progress of the succession in most mangrove areas of both the eastern and western zones, with only slight variations. In Nigeria, for example, Laguncularia shrubs grow on the newly formed banks at the mouths of creeks emptying into the sea. Inland from these are found Avicennia trees 16 feet (5 meters) in height, and then on the slimy soil Rhizophora can become established. Both Avicennia and Rhizophora, for reasons not clearly understood, can occur in stunted forms. On the edges of swamps, there are found such shrubs as species of Hibiscus, Drepanocarpus and Ecastaphyllum; herbs such as Ipomea and Telanthera. On the sand ridges behind Avicennia stands there are Xylocarpus (syn. Carapa), Cathormion, Phoenix reclinata, Raphia and Elaeis. Where fresh water from streams floods the area Mitragyna ciliata occurs; and in the final stages of dwarf Rhizophora the fern Acrostichum is found.

In spite of striking similarities, however, it is not to be assumed that all mangrove forests will pass through the whole sequence of development and that all the types are present. In this connection, the importance of the study of local variations in the succession in relation to the silvicultural treatment and management of mangrove forests, as caused by the interaction of such factors as frequency of submersion, salinity, the nature of substratum, and the erosive or aggressive action of the sea, cannot be too strongly emphasized.

Holdridge (1940) reports the following changes in composition after cutting:

Species	Present-day percentage	Percentage before human
Laguncularia	50	30
Avicennia	25	30
Rhizophora	20	30
Conocarpus	5	10
	100	100

Indeed, final felling often seems to cause crop deterioration by delaying succession in the early stages, hastening it in the latter stages or encouraging inferior species in the climax stage. Efforts to speed up succession by cutting pioneer Avicennia species seem to bring about prolific regeneration and coppicing, due to the removal of shade to which they are highly intolerant. On the other hand, in the drier areas, felling may encourage the invasion of Bruguiera into Rhizophora stands; and in the driest areas Acrostichum aureum seems to grow densely after felling and may prevent re-establishment of mangrove forest. The entire question of succession following opening up of mangrove forests needs further study.

Seed production and establishment

Seed production is annual and abundant to prolific, with seeds viviparous or otherwise, of high germinability and capable of remaining viable for long periods. Rhizophora and Bruguiera are viviparous, germinating before falling, Avicennia semi-viviparous, others not. 'Seeds' are usually water-borne. Natural layering is reported with Laguncularia, and sprouting common with Avicennia and Rhizophoraceae, though only with young seedlings with the latter genera (Stehlé, 1945-46; Noakes, 1954). Some mangrove species coppice well, particularly in their youth.

Germination and rooting are usually rapid and successful with all important species. The common mangrove species, with a few exceptions, are strongly light-demanding and the natural forest canopy over much of its life is dense and even, with only a sparse undergrowth beneath. The closeness of the canopy inhibits the survival of seedlings of desired species. The most important exceptions in the Malayan area are Bruguiera parviflora and B. gymnorrhiza, both of which are considered undesirable, though the latter is a commercial species of importance in the Andamans (Banerji, 1954). However, as the canopy thins with age or treatment, natural regeneration is almost always present in Malayan areas and in the Sundarbans, though reported as less certain over most of the western zone. Though much regeneration often appears to be almost completely destroyed with removal of the over wood, full natural stocking is ordinarily obtained. Abundant natural regeneration is not a problem in most mangrove forests.

FIGURE 2. - Natural regeneration of Rhizophora mangle in open spot of stand. Mangroves of Central American region.

Courtesy, O. Jurgenson

FIGURE 3. - Natural regeneration of Avicennia nitida and Rhizophora mangle. Mangrove stand of Central American region composed chiefly of Avicennia nitida.

Courtesy, O Jurgenson

In some places, as in Puerto Rico, the salt content may be so high in extensive areas known as "salitrals", that the sun produces a brilliant reflection from the salt crystals. This condition discourages the establishment of natural regeneration unless rain, or fresh water from streams, dilutes the salt. Studies in Puerto Rico have shown also that the size of canopy openings, as well as other factors, may determine whether regeneration will be of the desired species. Water levels appear to play an important role in the determination of such establishment but the exact reasons are not clearly understood.

In some locations, when the seeds are able to settle as a result of favorable water conditions, natural regeneration may become successfully established in less than a year. Normal high tides may cover only part of the surface, while the combination of very high tides in September and October, which usually cover large areas, combined with abundant seed fall, may result in excellent regeneration. The movement of the water, however, may not only bring in seeds but may also carry them away before they can take root. Ordinarily, during periods of normal tide, there are many lagoons and shallow pools but these are not always the sites of good establishment. Various reasons have been offered for this: the high temperature of the water due to insolation, or the salt concentration may be high enough to be toxic to the young seedlings. Planting in such areas has been successful with Rhizophora but not with other mangrove species.

A few other factors also tend to retard or prevent proper regeneration. In Malaya, monkeys may cause minor damage by uprooting seedlings, particularly in plantations; and crabs may be so serious as to prevent completely natural regeneration and even planting as a result of their attacks on the seedlings. In large openings, the fern Acrostichum aureum finds conditions excellent for growth and may take over extensive areas. The fronds may grow to heights of 6 to 12 feet (1.8 to 3.7 meters) and the large masses of rhizomes and roots and the dead and fallen fronds may interfere with the settling of germinating seedlings, though this fern may also protect established seedlings from damage from falling branches and the movement of floating logging debris, often detrimental to the initial establishment of waterborne seeds. In the western zone, the encroachment on drier areas of the giant A. aureum may be serious enough to require burning the ferns during the drier months of January to April, followed by two cuttings with machetes several months apart, to prepare the areas for planting or for natural seeding during the high tides in September-October.

The logging debris may be sufficiently voluminous to prevent the establishment of natural regeneration or to do considerable damage to established seedlings, as such debris floats with the tide. Under Malayan conditions, control of such logging slash by burning has proved impossible. The utilization of as much of the logging material as practicable, perhaps for charcoal where economic conditions permit, may provide a partial answer.

Deep inundations for considerable distances up rivers and creeks and the speed of the receding waters often prevent the seedlings from becoming established naturally; and, in fact, such high tides may sweep away established plantations. Human trespass in heavily populated districts is also a serious problem.

Stand development

Once established, the principal mangrove species grow well, forming straight, clear, cylindrical, sometimes multiple boles with few side branches, and compact crowns. In closed forests, Rhizophora produces straight trunks with compact crowns, and may grow to heights of 70 to 120 feet (21 to 37 meters) with girths of 3 to 7 feet (1 to 2 meters). In Malaya, for example, the normal felling size at the age of 20 to 30 years is 60 to 60 feet (16 to 18 meters) in height and 18 to 30 inches (46 to 76 centimeters) in girth. In Puerto Rico, the sizes are somewhat smaller and data in one area showed a count of more than 17,000 stems of Laguncularia per acre (43,600 per hectare), of which 60 percent were less than ½ inch (1.3 centimeters) in diameter and the largest stem was only 3.7 inches (9.4 centimeters).

FIGURE 4. - Young stand of Laguncularia racemosa reproduced from natural regeneration. Mangroves of Central American region. Observe good farm of stems.

Courtesy, O. Jurgenson

With regard to growth and yield management plans in the eastern zone countries, such as in Malaya and in the Sundarbans, present preliminary data on the mean annual increment as a guide to rotations and cutting cycles. The mean annual increment of mixed Rhizophora forest in Malaya, for instance, culminates at 26 years, making allowance for a three-year regeneration period. A yield table which has been tentatively compiled for the best mangrove forest in Malaya, in Perak, shows a culminating mean annual increment of 130 to 140 cubic feet per acre (9 to 10 cubic meters per hectare) with a final yield of about 3,000 cubic feet per acre (210 cubic meters per hectare). The average mangrove forest in Malaya, however, does not yield as much.

In the case of Bruguiera cylindrica, measurements indicate that this slow-growing species may require at least 40 years to reach commercial size. Actual harvesting yields for this species are not available; similar data from other localities are rather fragmentary. Troup (1921) reports one locality in the Arakan (Burma) as having produced 26 tons per acre (63 metric tons per hectare) of wood and 3 tons per acre (8 metric tons per hectare) of bark at maturity. Management plans in the western zone have not been developed to the point where reliable yield figures are available.

Cleanings and weedings are rarely needed, though thinnings may be carried out if there is a market for the stems. Thinnings are usually by the 'stick' method, i.e., to uniform spacings obtained by using sticks of various lengths, depending on the age of the stand. The final thinning is often heavy enough to encourage regeneration. No important diseases or insects are known to affect mangrove forest, though in Nigeria teredo is reported to be serious and in the western zone termites are listed as a serious pest to living trees. Attacks by buprestid beetles and lepidopterous borers have also been reported.

Silvicultural practice

Under these circumstances, it is understandable that a wide variety of natural regeneration methods, including coppice systems, have been employed with mangrove forests. In the Asian area, where experience has been rich and varied, a number of systems ranging from selection, usually to a minimum girth limit, clear-cutting with and without seed trees, and uniform shelter-wood have all been tried at some time or other. Such systems have been designed primarily to reproduce the better species, usually Rhizophora (or Bruguiera) in pure crops. The coppice system has been found satisfactory in some areas, such as in India and the Carribbean, and with some species (Krishnaswamy, 1962; Stehlé, 1946-46), but as previously indicated, not all of the principal mangrove species sprout satisfactorily. Its application is, therefore, limited. For the most part, silvicultural systems have been designed to take advantage of frequent and abundant seeding. Selective cutting to a fixed minimum girth, while not entirely satisfactory, has produced magnificent crops in many areas. Seed tree cuttings, somewhat more flexible, combined with intermediate feelings to induce advance regeneration, have also been used, though the results have not always been favorable; increased stocking of less desirable species and failures requiring planting have been noted.

Currently, the Malayan system may involve intermediate fellings to induce regeneration in younger age classes, with the final cutting a clear-felling (Noakes, 1964). Results are said to be more satisfactory from the standpoint of volume yield, and adequate regeneration is obtained more uniformly on the cut-over area. Planting on the remainder can be done without too much difficulty. There remains, however, the disadvantage that Bruguiera parviflora tends to regenerate more readily and is dominant among the seedlings left standing after the final cutting. Rotations have been tried from 20-26 to 40 years but maximum volume of trees, 16 to 30 inches (38 to 76 centimeters) in girth, is obtained with rotations of 30 years, particularly for the mixed Rhizophora forest.

In India, various systems have been used. The rotation in Madras is reported by Troup (1921) to be much shorter than in Malaya, in some cases as short as five to ten years. In the Andaman Islands, the most satisfactory method is reported to be clear-cutting and planting. No casualties are replaced, as all blanks are filled with seedlings from seeds, derived from nearby belts of mother trees, carried in by tidal waters. This method of artificial plus natural regeneration is reported as uniformly successful (Banerji, 1964). In the Sundarbans, the largest area under management over many decades, the silvicultural system prescribed is selection and improvement fellings and thinnings (Curtis, 1932).

FIGURE 5. - Extraction by wheelbarrow in mangrove forest Malaya.

Courtesy, Malayan Forest Service

Further study needed

It seems clear that in the mangrove association, special attention must be given to the range of occurrence of a species or association, and the recognition of an optimum belt within the range may help to a large degree to simplify the regeneration problems. Silviculture and management must be concerned with inducing regeneration of a given species or type, whether natural or artificial, for various specific inundation classes. Furthermore, the complicated secondary succession following cutting or natural damage from storms, needs to be investigated, in order to provide a basis for silvicultural practice. Likewise, further study on seed production, the conditions needed for germination and systematic trials, including cost analyses, of different methods of harvest cutting and for the successful establishment of natural regeneration would be desirable.

Nevertheless, although natural regeneration methods are common and, on the whole, successful in mangrove forests, these forests furnish an excellent example of the need to adapt silvicultural practices to local conditions. This must be based on an adequate knowledge of pertinent silvical characteristics, event a formation showing broad and conspicuous physiognomic and ecological similarities over a worldwide range.

Selected references

AUBRÉVILLE, A. Essai de classification et de nomenclature des formations forestières africaines. Centre techn. forestier tropical, Nogent-sur-Marne, 57 p. 1966.

BANERJI, J. "The mangrove forests of the Andamans". Paper presented to the Fourth World Forestry Congress, Dehra Dun. 1964. See Food and Agriculture Organization of the United Nations.

BARNARD, R. C. and SETTEN, G. G. K. "Investigation scheme for growth and increment studies in Johore mangrove forest ". Malay Forester 16 (40) 1953.

BOON, D. A. "Maatregelen ter verzekering van de productie mogelijikheden der bosschen in de Buitengewesten ", Tectona 31. English Summary, 829-846. 1939

BROWN, W. H. and FISCHER, A. F. Philippine Mangrove Swamps. Dep. of Agric. and Natural Resources, Bureau of Forestry Bull. 17, Manila. 1918.

BROWNE, F. G. Forest Trees of Sarawak and Brunei. Govt. Printing Office, Kuching, 370 p. 1965.

BURMA FOREST SERVICE "Silviculture and management of mangrove forests of Burma". Paper presented to the Second Session, Asia-Pacific Forestry Commission, Singapore. 1952.

CAMBODIAN FOREST SERVICE. "Silviculture of the forests of Cambodia - mangrove". Paper presented to the Third Session, Asia-Pacific Forestry Commission, Tokyo. 1965.

COLLIER F. S. "Report on visit to Malaya and Singapore." Malay Forester 15 (9). 1952.

CURTIS, S. J. Working Plan for Forests of Sundarbans Division, Bengal, India (Abstract). 1933.

DANHOF, G. N. " Management of tidal forests of Bakan in Riouw-Lingga archipelago." Tectona 36, 59-72. 1946.

DAVIS, J. H. Jr. The Ecology and Geologic Role of Mangroves in Florida. Carnegie Inst. Wash. Publ. Biol. Abstr. 15 (1). 1941.

DURANT C. C. L. "Growth of mangrove species in Malaya." Malay. Forester 10 (3). 1941.

EGLER F. E. "The dispersal and establishment of red mangrove, Rhizophora mangle in Florida." Carib. For. 9 (4). 1948.

ENDERT, F. H. "De proefbaanmetingen in de Planglong-Gebieden van Bengkalis (Sumatra's oostkust) en Riouw." Tectona 25, English summary, 731-785. 1932.

FERNS, G. W. " Tidal forests in southeast Kalimantan." Indonesian J. For. 4 (3-4-5). 1955.

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS. "Mangrove" (by D. S. P. Noakes). Tropical Silviculture II, 309-318, Rome, 1957.

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS "The mangrove forests of the Andamans (by J. Banerji). Tropical Silviculture II, 319-324. Rome, 1957.

FOXWORTHY, F. W. and MATTHEWS, D. M. Mangrove and Nipa Swamps of British North Borneo. Govt. of Br. Borneo Dep. For. Bull. 3. 1917.

HILLIS, W. E. "Production of mangrove extract in delta region of Papua." Emp For. Rev. 35 (4), 420-436. 1956.

HOLDRIDGE L. R. "Some notes on the mangrove swamps of Puerto Rico." Carib. For. 1. 1940.

INDONESIAN FOREST SERVICE. "Problems of silviculture and management of mangrove forests in Indonesia." Paper presented to the Second Session, Asia-Pacific Forestry Commission, Singapore. 1952.

KEAY, E. W. J. "Rhizophora in West Africa." Kew Bulletin I, 121-127. 1953.

KRISHNASWAMY, V. S. "Problems of Silviculture and management of mangrove forests of India." Paper presented to the Second Session, Asia-Pacific Forestry Commission, Singapore. 1952.

KRISHNASWAMY, V. S. "Silviculture - Natural regeneration including artificial supplementation - Tropical." Paper presented to the Sixth British Commonwealth Forestry Conference, Canada, 10 p. 1952.

LANDON, F. H. "Planting in mangrove forests." Malay Forester 2 (131). 1933.

LANDON, F. H. "Mangrove volume tables." Malay Forester 11 (117). 1948

MARSHALL, C. Sustained yield management of the mangrove Salt-water swamp forests of Fiji. Gov. Press, Suva, Fiji, 19 p. 1951.

MAURAND, P. L'Indochine forestière. Inst. rech. agric. et for. de l'Indochine, Hanoi, 150 p. Mangrove, 137-141. 1938.

MOODIE, A. W. Working plan for Delta Forest Division, Maymyo, Burma. Superintendent Gov. Printing, Burma, Rangoon. 1924.

NOAKES, D. S. P. "Mangrove." Paper presented to the Fourth World Forestry Congress, Dehra Dun. 1954. See also Food and Agriculture Organization of the United Nations.

PARKINSON, C. E. "The Indian species of Xylocarpus." Indian For. 60, 136-143. 1934.

RICHARDS, P. W. The Tropical Plain Forest (an Ecological Study). 450 p. Cambridge, 1952.

RIDLEY, N. H. "Notes on Xylocarpus." Kew Bulletin 7, 228-292. 1938.

ROSEVEAR, D. D. "Mangrove swamps." Farm. and For. and Nigerian Forester 8 (1), 23-30. 1947.

ROUANET, P. "Rapport Guinée française." Report presented to the Première Conf. for. interafricaine, Abidjan. English summary, 187-214. 1951.

SAVORY, H. J. "A note on the ecology of rhizophora in Nigeria." Kew Bulletin 1, 127-128. 1953.

SCHIMPER, A. F. W. Plant-geography (upon a Physiological Basis), Oxford, 839 p. 1903.

SEN GUPTA, J. N. "Problems of Silviculture and management of mangrove forests - West Bengal." Paper presented to the Second Session, Asia-Pacific Forestry Commission, Singapore. 1952.

SETTEN, G. G. K. "Growth and yield of Berus (Bruguiera cylindrica)." Malay Forester 16 (74). 1953.

STEHLÉ, H. "Forest types of the Caribbean Islands." Part 1. Carib. For. 6 (suppl.), 273-408; 7 (suppl.), 337-709. 1945.

SYMINGTON, C. F. "Three Malayan species of Bruguiera." Malay Forester 9 (131). 1940.

TROUP, R. S. The Silviculture of Indian Trees. Oxford. Three volumes, 1, 195 p. 1921.

WALKER, F. S. "The management and exploitation of the Klang Mangrove Forests." Malay Forester 6. 1937.

WALKER, F. S. "Regeneration of Klang mangroves." Malay Forester 7 (71). 1938.

WATSON, J. G. Mangrove Forests of the Malaya Peninsula. Malay. For. Rec. 6, 275 p. 1928

WYATT-SMITH, J. "Malayan species of Bruguiera, Sonneratia, Avicennia." Malay Forester, 17 (21): 156-213; 1963, 1954.

CERTIFICATE OF QUALITY

Species:

Common name (in the language of the exporting country): ..........................
Latin name: ..........................

Name and address of the consignor of the sample: ..........................

Consignor's description of the sample: ..........................

Date of arrival of the sample at the seed control station: ..........................

Result of the test *

* Use International Seed Testing Association rules adopted at Dublin, May 1963..........................

Degree of purity: ..........................
Weight of 1,000 seeds: ..........................
Section of whole seeds, percentage of useless seeds: ..........................
Germinating capacity: ..........................
Any other remarks: ..........................

Certificate:

The above particulars are certified correct.

Director
Seed Testing Station

CERTIFICATE OF ORIGIN

Species:

Common name (in the language of the exporting country): ..........................
Latin name: ..........................

Date of collection: ..........................

Location of the seed-producing stand:

Country: ..........................
Area: ..........................
District: ..........................
Locality: ..........................
Site designation: ..........................
Stand number in national register (if possible): ..........................
Latitude: ..........................
Longitude: ..........................
Altitude: .......................... (meters above sea level).
Aspect: ..........................
Inclination: ..........................

Forest species making up the natural forest (Latin names) - if possible - or reference to phytoclimatic zone: ..........................

Geological conditions and types of soil: ..........................

Description of the seed-producing stand:

Species:

Common name (in the language of the exporting country): ..........................
Latin name: ..........................

How originating: ..........................
Present age: ..........................
Present treatment applied: ..........................

Seed-bearers:

Diameter: ..........................
Height: ..........................
Nature of branches size and inclination: ..........................
Shape of boles: ..........................
Age: ..........................
Remarks, average date of flushing, etc: ..........................

Certificate:

The above particulars are certified correct by the competent forestry officer: ..........................

signature: ..........................
seal: ..........................

The above particulars have been submitted to: ..........................

CONSIGNMENT FORM FAO

Form for international exchanges of seed and other botanical material intended for scientific purposes

Name and address of consignee: ..........................
Name and address of sender: ..........................
Gross weight of package: ..........................
Nature of contents: ..........................
Botanical species: ..........................

Common name: ..........................
Latin name: ..........................

Date, place, and nature of disinfection treatment (if any) to which material has been subjected: ..........................

The weight of the package must not exceed 1 kilogram (approximately 35 ounces); the stamp or seal (if possible) of the institution and the signature of the official responsible for shipment must appear on it.

NOTE: This form for facilitating the exchange of forest seeds and plant material for scientific use, has been approved by the Sixth Session of the Conference of FAO with the following recommendations:

" 1. that in order to establish authenticity, Member Governments take steps to adopt the Certificates of Quality and Origin ..........................;

and,

2. that, to expedite the exchange of seeds and plants for scientific purposes, Member Governments secure recognition by appropriate national agencies of the standard Consignment Form.......................... "