Rooting and vegetative propagation in Laguncularia racemosa

Rooting and vegetative propagation in

Laguncularia racemosa

Carola Elstera,1,*, Laura Perdomob

a Institut fuÈr Allgemeine Botanik und Pflanzenphysiologie, Justus-Liebig-UniversitaÈt, Senckenbergstr. 17-21,

D-35390 Giessen, Germanyb Instituto de Investigaciones Marinas y Costeras, INVEMAR, Apartado Aereo 1016, Santa Marta, Colombia

Received 21 July 1998; accepted 23 November 1998

Abstract

Reproduction and dispersal in mangrove species occurs mainly through propagules. Vegetative

propagation is considered to be insignificant by many researchers, however, for restoration projects,

it could be an important advantage. Therefore, we carried out experiments with shoot cuttings of

Laguncularia racemosa and Rhizophora mangle under controlled conditions as well as in the field

to prove the feasibility of vegetative propagation in these mangrove species.

None of 110 planted R. mangle cuttings survived the experiments, but the results with L.

racemosa were promising. We observed that the single most important factor for survival of L.

racemosa cuttings was rooting of the shoots prior to cutting from the parent trees. This is a common

feature in the study area, the CieÂnaga Grande de Santa Marta, Colombia. Seasonal floodings of

lower branches induce secondary root growth and can even lead to natural vegetative propagation.

Other factors that have favorable effects on the survival of the cuttings are a large shoot diameter,

manual defoliation to reduce transpiration, and direct sun irradiation. Additionally, burying a small part

of the roots in a way that allows some roots to freely float in the surface water, improves the survival rate

to 95%. However, the watering with rooting agents shows slightly negative effects. The surviving shoots

grow rapidly and fruit set can be observed within six months after planting in the field.

In restoration attempts with L. racemosa it is, therefore, possible to bypass the very sensitive

seedling phase by planting shoot cuttings. The value of this method is linked to quicker

establishment and reproduction of the cuttings as well as the possibility to plant them in flooded

areas, where establishment of propagules and survival of seedlings of L. racemosa is very difficult

to achieve. # 1999 Elsevier Science B.V. All rights reserved.

Keywords: Laguncularia racemosa; Mangrove; Rooting; Shoot cuttings; Vegetative propagation

Aquatic Botany 63 (1999) 83±93

* Corresponding author. E-mail: [email protected] Present address: Wiesenstr. 7, 57290 Neunkirchen, Germany.

0304-3770/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.

PII: S 0 3 0 4 - 3 7 7 0 ( 9 8 ) 0 0 1 2 2 - 3

1. Introduction

Vegetative propagation in mangroves is considered insignificant for spreading and

colonisation (Rabinowitz, 1978; Tomlinson, 1986). In general, mangrove species are

supposed to have little or no capacity for vegetative regeneration, and no natural capacity

for vegetative dispersal (Tomlinson, 1986). However, reports on vegetative propagation

can be found: some mangrove genera (e.g., Avicennia, Rhizophora, and Sonneratia) have

a limited ability to spread vegetatively, because their lower branches may recline under

their own weight and root distally (Tomlinson, 1986). A vegetative seaward expansion

through clone formation can be observed in Sonneratia alba J. Smith and in an analogous

manner in Rhizophora sp. (Holbrook and Putz, 1982; Crewz and Lewis, 1991).

Propagation through shoot cuttings and air-layering is known for Sonneratia apetala B.

Ham. and Xylocarpus granatum Koen. (Kathiresan and Ravikumar, 1995). Many authors

wrote about air-layering of Rhizophora mangle L., Avicennia germinans (L.) Stearn, and

Laguncularia racemosa (L.) Gaertn. f. (Pulver, 1976; Carlton and Moffler, 1978; Crewz

and Moffler, 1984; GonzaÂlez and Rivas, 1993). Although most of these experiments

showed promising results during the layering phase and all species can take roots, only

layers of L. racemosa, S. apetala and X. granatum were reported to survive

transplantation into the field.

Reproduction and dispersal of mangroves occurs mainly through propagules. As a

result, most mangrove restoration efforts have relied upon planting of propagules and

seedlings, although seedling mortality is often extremely high. In some cases older,

already established plants have been transplanted (Davis, 1940; Pulver, 1976; Elster,

1997; Elster, 1998). Limited work has been carried out on vegetative propagation, but it

could be a very fast and efficient way of regeneration. Therefore, we investigated the

feasibility of propagating mangroves by the planting of shoot cuttings. Two species were

promising due to their characteristic properties:

1. R. mangle, because the tips of the aerial roots develop a normal root system in contact

with water and these roots can then establish themselves in the soil firmly;

2. L. racemosa, because adventitious roots arise on the lower part of the stems (JenõÂk,

1970), shoots start rooting above ground when flooded and partly inundated branches

can develop an extensive root system (Fig. 1(a) and (b)). The occurrence of lower

branches with secondary roots is a common phenomenon in L. racemosa in the study

area due to prolonged inundations. Many lower branches are continuously flooded for

several months during the rainy season (Elster, 1997). Most of the flooded branches

develop roots during this time. In addition to these observations local fishermen report

that L. racemosa branches used as piles for their stilthouses start to grow.

2. Study sites

The present study was undertaken at two highly disturbed sites in the north of the

CieÂnaga Grande de Santa Marta, a brackish lagoon system on the Caribbean coast of

Colombia (Fig. 2). Human induced changes in the hydrological system of the area, which

have obstructed freshwater entering the connecting channels, has led to a severe increase

84 C. Elster, L. Perdomo / Aquatic Botany 63 (1999) 83±93

in salinity during the past 35 years. As a result, ca. 30 000 ha of the original 51 150 ha of

mangrove forest died (GonzaÂlez, 1991). The surviving mangrove stands are composed

mainly of A. germinans, L. racemosa, and R. mangle. At open sites, Batis maritima L. and

Sesuvium portulacastrum L. can cover large areas. Some of the obstructed channels have

been re-opened recently. Further openings are planned to introduce more freshwater and

re-establish the original hydrological system. It is expected that the devastated areas will

Fig. 1. (a) Branches and shoots of Laguncularia racemosa that started to root while flooded during the main

rainy season 1995 (branch has been pulled out of the water for the photo); (b) Shoots with a well-developed root

system at the end of the main rainy season 1995, when the water level starts to fall.

C. Elster, L. Perdomo / Aquatic Botany 63 (1999) 83±93 85

recover and mangroves regenerate, but since the denuded areas are very large and natural

regeneration will be slow an artificial reforestation is recommended (Ensminger, 1996;

Elster, 1997; Elster, 1998).

The climate of the region is arid and most rainfall occurs between August and

November, the main rainy season. The mean precipitation is ca. 700 mm per year and the

mean temperature is 288C (IGAC, 1973). The hydrological system is mainly influenced

by the changes between the rainy and dry seasons and by the freshwater supply of several

rivers, while the influence of the tide is negligible. A more detailed description of the

study area and the vegetation is given by Serrano DõÂaz et al. (1995) and Elster (1997).

The first study site, Barra Vieja (1085902000N; 7482604300E), consists of some small

sandy islands in a shallow lagoon. The mangrove forest died ca. 30 years ago, when a

newly built road separated the area from the main lagoon system. The original

hydrological conditions were re-established in 1989 by re-opening the connection

between the CieÂnaga Grande and the hypersaline lagoon. Consequently, a slow natural

Fig. 2. Map of the study area and transplantation sites.


regeneration process began, however, at present only one-third is covered by mangroves.

Many propagules reach the site, but only a few seedlings survive.

The second study site was located at kilometer 17 (Km 17) of the CanÄo ClarõÂn, a

freshwater channel which connects the Magdalena river with the CieÂnaga Grande

(1085902400N; 7483605100E). Most trees died 20 years ago when sediment from the

Magdalena river obstructed the channel. The CanÄo ClarõÂn was reopened in January 1996,

but during the first six months the incoming freshwater showed little influence on the

vegetation. Only in some areas, where freshwater washed the soil, were new seedlings

able to establish themselves. Vast parts of the muddy and partly flooded area are covered

by dead mangrove trunks. Only the channel is bordered by living mangroves.

3. Materials and methods

3.1. L. racemosa

During the main rainy season 1995 (August to November), young shoots of L.

racemosa were cut and planted under different conditions to observe their rooting and

growth response. The cuttings varied in diameter (0.3±2.4 cm) and length (20±105 cm)

and had at least four to five buds in accordance with Flinta (1960), who recommended at

least three to four buds and a diameter of up to 2.5 cm for cuttings of Populus. The shoots

used were from healthy, mature trees growing throughout the study area and were

transported in plastic bags to reduce transpiration. They were planted only a few hours

after removal from the trees. Half of the shoots planted had roots before cutting, the other

50% of the shoots did not have roots.

3.1.1. Experiments under controlled conditions

In total, 250 cuttings were planted in plastic pots (height: 25 cm, diameter: 40 cm)

filled with riversand and diluted seawater (ca. 30%). The water level was kept constantly

at the soil surface by watering daily with tap water. The different treatments were: placing

in direct sun (100% light intensity), shade (5% to 10% light intensity), manual defoliation

to reduce transpiration, and watering with two different rooting agents (Neudofix, W.

Neudorf GmbH KG, Postfach 1209, 31857 Emmerthal, Germany; Seradix, 4-indol-3-

ylbutyl-acid, Fa. May and Baher, Dagenham, England) at a concentration of 2g/l water.

The results for both agents did not vary. They were, therefore, classified under `rooting

agents'. The exact numbers of shoot cuttings in each treatment are given in Table 1.

Shoots without roots were placed with their thicker end 10 cm deep into the

substratum, rooted shoots were carefully placed with their rooted part into the sand.

Survival and growth response were reported weekly for at least three months. Survivors

were then transplanted into the field at Barra Vieja (Fig. 2).

3.1.2. Field experiments

Fifteen surviving shoot cuttings from the experiments under controlled conditions were

planted at Barra Vieja in January 1996. The substratum was sandy and flooded shallowly.

In September and October 1996, additional field experiments were carried out at a

shallowly flooded place at Km 17 (Fig. 2). Fifty shoot cuttings were planted at full moon


and 25 each at waxing, waning and new moon. All cuttings were planted without roots

and leaves to assess the reports of local fishermen, that piles used by them for their

stilthouses frequently start budding when driven into the mud at full moon. As a

comparison, rooted cuttings with leaves were planted nearby: 25 with all the roots in the

muddy ground and 20 with some of their roots in the soil and some freely floating in the

surface water. As an overview, the numbers of shoot cuttings in each treatment are given

again in Table 2.

The salinity of the surface and soil water in all field experiments was below 30%, the

light intensity 100%. Survival was reported monthly.

3.2. R. mangle

From September to November 1995, similar experiments were carried out with R.

mangle. A total of 110 shoot cuttings were planted: 40 with leaves and aerial roots, 60

with roots but without leaves, and 10 with leaves but without roots (70 of the 110 cuttings

were planted under controlled conditions and the remaining 40 were planted directly in

the field).

4. Results

None of the R. mangle cuttings survived the experiments. However, the results in L.

racemosa were promising; shoot cuttings in one of the experimental conditions had a

95% survival rate after the first six months (see Tables 1 and 2, and Fig. 4). In addition, a

capacity for natural vegetative propagation and localized spread was encountered. Lower

branches that recline, both root extensively in contact with water (Fig. 1(a) and (b)), and

in the moist ground. Several `young plants' were observed to be actually long branches

laying on the ground, rooted in the soil, and developing new vertical shoots. Sometimes,

these branches were already disconnected from the mother plant.

Table 1Treatments and number of shoot cuttings of L. racemosa under controlled conditions

Cuttings a (�) b a* c * c a a * c * c a (�) b a

-/- d -/- d -/- d L/- e L/- e L/R f L/R f -/R g -/R g -/R g

Total number 35 50 10 20 10 20 20 25 40 20

Sprouting n 1 1 0 0 0 4 3 8 11 5

Cuttings % 2.9 2 0 0 0 20 15 32 27.5 25

Surviving n 1 0 0 0 0 1 2 6 8 3

Cuttings % 2.9 0 0 0 0 5 10 24 20 15

a In shade (5±10% of full sunlight).b Watered with rooting agents.c In direct sun.d Without leaves/roots.e With leaves, without roots.f With leaves/roots.g Without leaves, with roots.Sprouting: all cuttings that started to bud, independently of survival time.Surviving: cuttings with growing buds, survival of at least 10 weeks.


4.0.1. Experiments under controlled conditions

Up to 32% of L. racemosa shoot cuttings planted in the greenhouse started budding,

but ca. 40% of the buds dried out after some days and this caused the shoots to die (Fig. 3

and Table 1). Surviving buds, however, grew rapidly and most of the new twigs reached a

length of 10 to 15 cm within two months. Very thin cuttings with a diameter of <0.5 cm

dried out and all of them died. For thicker shoot cuttings, a correlation between diameter

or length of the cuttings with survival was not found.

Shoots that were not defoliated manually lost their leaves within the first two to three

weeks. The leaves started to dry during the first week and turned brown some days later.

This process occurred more rapidly in the sun than in the shade and in shoots without

roots than in rooted ones. Since a lot of water was lost due to the drying leaves,

undefoliated shoots survived to a lesser degree (8% of the rooted cuttings) than defoliated

shoots (22% of the rooted cuttings). However, direct sun irradiance, produced a higher

survival in the cuttings than when grown in the shade, despite the higher rate of

transpiration (Table 1). Fewer cuttings survived when watered with rooting agents (15%

of the rooted cuttings) than in untreated water (22%, Fig. 3).

The most important and only statistically significant (p < 0.0005, Chi2-Test, Fischer's

Exact Test) factor for a successful propagation was the rooting of the shoots prior to

cutting from the mother tree: only one (0.8%) out of a total of 125 shoots planted without

roots started to grow, whereas 20 (16%) of the 125 shoots planted with roots survived.

4.0.2. Field experiments

After transplanting the surviving shoot cuttings to the field in January 1996, 60% of

them died within two months. After this establishing phase, the number of surviving

plants remained nearly constant (Fig. 4). They grew rapidly and started flowering in June

1996. In July of the same year, the first fruit-set was observed.

None of the shoot cuttings planted without roots in September and October 1996 at Km

17 survived more than three months. About 20% grew new buds or small leaves and

twigs, but they dried out one or two months later. Hence, a propagation without prior

rooting was impossible in the field as well as under controlled conditions. There was no

significant difference in the growth response of the shoots planted in different moon

phases.

Table 2Treatments and number of shoot cuttings of L. racemosa in the field

Cuttings Trans-

plants

Roots in

the soil

Partly

floating

Full

moon

Waxing

moon

Waning

moon

New

moon

L/R L/R L/R -/- -/- -/- -/-

Total number 15 25 20 50 25 25 25

Survival after n 5 10 19 0 0 0 0

six months % 33.3 40 95 0 0 0 0

All cuttings were planted in direct sun; transplants: cuttings from experiments under controlled conditionstransplanted to the field; roots in the soil: all roots placed in the soil; partly floating: only some roots placed inthe soil, some roots floating in the surface water; -/-: cuttings planted without leaves/roots; L/R: with leaves/roots.


The experiments with rooted shoots were much more successful. Of the cuttings

planted with all their roots in the muddy soil 40% survived more than six months.

However, the greatest survival rate (p � 0.001, Chi2-Test, Fischer's Exact Test) was

encountered when some of the roots were not buried by the soil. In this group with some

roots floating in the surface water, a survival rate of 95% was observed (Fig. 4).

5. Discussion

Secondary root growth is very abundant in L. racemosa when sufficient water is

available. The rooting of lower branches in moist soils permits a natural vegetative

propagation and local spread of L. racemosa, similarly as reported by Tomlinson (1986)

Fig. 3. Survival and growth of L. racemosa shoot cuttings. Averages of the different treatments under controlled

conditions (given in Table 1): buds: cuttings started to bud (including buds that dried out and died after some

days); growth: survival during the first 10 weeks of the experiment and growth of new shoots; L/R: cuttings

planted with leaves and roots; -/R: with roots, defoliated; L/-: with leaves, without roots; -/-: without leaves/

roots, (*): watered with rooting agents.

Fig. 4. Survival of transplanted L. racemosa shoot cuttings in the field.


for the genera Avicennia, Rhizophora, and Sonneratia, and by Holbrook and Putz (1982)

and Crewz and Lewis (1991) for Rhizophora sp. and Sonneratia alba. It is often difficult

to distinguish between L. racemosa plants that established themselves in this vegetative

way and individuals established as propagules, because secondary root growth above

ground is frequent in both groups (JenõÂk, 1970; personal observation). In rare occasions,

even a limited capacity for vegetative dispersal is found, as rooted branches may be torn

off by storms and carried away by currents.

The abundant root growth of inundated branches provides good shoot cuttings and is

the crucial factor for the success of an artificial reproduction via cuttings in L. racemosa.

The survival of shoots that did not root before cutting is so rare that these shoots are

useless for reforestation measures. About 30% of them start to produce small leaves, but

usually die within a few days to approximately two months. All the new buds and leaves

dry out because the moisture and reproductive capacity of the cut shoots is used up,

before they are able to establish themselves with new roots in the ground and become

self-sufficient. The same happens to larger cuttings and piles used by local fishermen for

their stilthouses. Although many reports about sprouting piles are known, none of the

piles survived for a longer period of time or grew new branches.

The rooted cuttings, on the other hand, respond well to planting: the survival in the

field can be as high as 95% under favourable conditions and the new shoots grow rapidly.

Due to strong winds moving the shoots, cuttings may fail to become established because

the small fibrous roots are destroyed. In the study area, strong trade winds occur during

the dry season from January to March. This may be one reason for 60% of the cuttings

transplanted in January 1996 dying within two months. In windy areas, as the CieÂnaga

Grande, it is, therefore, advisable to secure the shoots with piles or to grow them in a

greenhouse some weeks prior to planting in the field.

To reduce transpiration it is recommended to partly defoliate the shoots. The best

results can be obtained by planting the cuttings with some of their roots placed in the soil

and others floating in the surface water, as they did prior to cutting from the parent tree.

The higher aeration of the surface water may be the reason for greater survival of the

floating roots and, therefore, of the shoot cuttings. The moon phases do not affect the

survival of the shoot cuttings. However, the most appropriate time of reproducing L.

racemosa by shoot cuttings is the main rainy season, when persistent inundations

stimulate the secondary rooting and wash excess salt out of the soils. Flooded or at least

moist soils are essential for the survival of the cuttings (personal observation) and low

salinities are advantageous to mangrove survival and rooting behaviour (Kathiresan and

Thangam, 1990; Kathiresan and Ravikumar, 1995). During the dry season, when most L.

racemosa branches are not inundated, already developed root systems dry and frequently

die. Roots that penetrated partly into the soil usually survive and stabilize branches and

shoots.

Historically, mangrove restoration attempts have relied upon the uncertain success of

planting propagules or transplanting older specimens (e.g. Davis, 1940; Pulver, 1976).

Most reports indicate high seedling loss, even though the plantings are surrounded by a

protective structure, and it takes from two to four years for surviving propagules to

establish themselves (Carlton and Moffler, 1978). In regeneration projects, these

problems can be avoided by using shoot cuttings and air-layers. The value of shoot


cuttings is linked to their quicker establishment and growth, resulting in rapid fruit

production. L. racemosa cuttings of ca. 50±100 cm length can flower and fruit within half

a year after plantation (this study). On the other hand, air-layering of this species takes ca.

4±6 months, until a sufficiently developed root system is established, and in other

mangrove species this can take even longer (Crewz and Moffler, 1984). Hence, the

cutting of already rooted shoots is much more advisable in L. racemosa than air-layering.

However, the propagation of R. mangle by shoot cuttings is not advisable, as they do not

survive.

Shoot cuttings have other advantages as well. They are able to survive at inundated

sites, whereas L. racemosa propagules are strongly impeded by a waterlevel of 5 cm

above the soil surface, and flooded seedlings die within three weeks (Elster, 1997). Shoot

cuttings are very economical in comparison to transplantation of older plants, growing of

seedlings in greenhouses, or air-layering and hormone application.

Removing mangroves from natural stands may damage the remaining stock by

extensive disturbance and inhibit the natural regrowth of the forests. For vegetative

propagation of L. racemosa by shoot cuttings, only the lowest, flooded branches can be

used, and they are best cut from a boat. Therefore, the impact on the parent trees and

surrounding vegetation is very limited. We did not notice any harmful effects of pruning

in the months following the cutting and other studies indicate that mangroves, especially

L. racemosa, recover well from pruning and windbreak (Pulver, 1976; Baldwin et al.,

1995).

For all the above reasons, cuttings of naturally rooted shoots are a promising feature for

the artificial regeneration of L. racemosa, although the type of vegetative propagation

described is limited to those areas where prolonged inundations induce secondary root

growth. In coastal mangroves that are mainly influenced by the tide, air-layering or

hormone application may be necessary. However, large-scale restoration of mangrove

ecosystems by shoot cuttings is impossible even in suitable forests with long-time

floodings such as the CieÂnaga Grande, because naturally occurring rooted branches are

limited. Available branches should, therefore, be used for those areas, where other means

of natural and artificial regeneration are very difficult or even impossible, for example

flooded soils and less stable substrates that impede seedling establishment (Elster, 1997;

Elster et al., in press).

Acknowledgements

We thank the INVEMAR and CORPAMAG/PRO-CIEÂ NAGA (both Santa Marta,

Colombia) for collaboration and access to laboratory and boat facilities as well as C.

CarbonoÂ and J. DoÈring for technical assistance. We further thank E. Ashton for

improvements on the manuscript. The research was supported by the GTZ (TOÈ B,

`̀ Flanking Program for Tropical Ecology'', PN: 90.2136.1), Eschborn/Germany.

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Rooting and vegetative propagation in Laguncularia racemosa

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