Department of Commercial Crops Fruits & Forestry

Mangroves species found in Zanzibar

There about ten mangroves species found in Zanzibar

Rhizophora mucronata . Mkoko magondi
Bruguiera gymnorrhiza . Msisi/Mfinzi
Ceriops tagal . Mkandaa / Mkoko mwekundu
Xylocarpus granatum . Mkomafi/Mkaumwa/ Mkuo
Xylocarpus molucensis . Mkaumwa wa kijani (tunda lake)
Heritiera littoralis . Msikundazi
Avicennia marina . Mchu
Lumnitzera racemosa . Kilalamba
Sonneratia alba . Mlilana
Pemphis acidula . Kilalamba dume

Ceriops tagal is the most exploited species in all the mangrove management Units of Chwaka. It constitutes 65%, 59% 55% and 45% of all cut trees at Mapopwe , Ukongoroni, Charawe and Michamvi respectively. It nevertheless has good regeneration especially at Ukongoroni where it accounts for 60% of all seedlings and forms the most dense partches.

The other places are Michamvi(52%), Mapopwe (50%) and Charawe (32%). In terms dominance, which is a measure of wood volume, this species is very important at Ukongoroni where it accounts for 58% compared to 49% 17% and 13% at Charawe , Michamvi ,and Mapopwe respectively. This is contributed by the fact that about 79% , 74%, and 54% of the trees of this species at Mapopwe, Michamvi and Charawe respectively are within the dbh of 2-4 cm. While at Ukongoroni, this class contains only 31%.

In view of the heavy exploitation of this species in all the sites and that most trees appear to be young (2-4 cm dbh), a species specific control on its exploitation could be contemplated as a possible management intervention.

Rhizophora mucronata is moderately exploited in all the management units. It accounts for 28%, 27%, 17% and 16% of all cut trees at Ukongororni, Mapopwe ,Charawe and Michamvi respectively. It however has good to poor regeneration of 33%, 17%, 11%, and 1.7% at Mapopwe , Ukongoroni, Charawe and Michamvi respectively. This species forms the most dense stands at Mapopwe (31%) compared to Michamvi (18%), Ukongoroni(15%)and Charawe(8%). In terms of wood volume this species is very important at Mapopwe where it commands a relative dominance of 68%, compared to 21%, 18%, and 4% at Michamvi, Ukongoroni and Charawe respectively. This is a reflection of both density and stem thickness in the different sites.

Given the low rate of regeneration of the species, the need for controlled exploitation can not be overemphasized.

Brugiera gymnorhiza is exploited moderately at Michamvi where it contributes to about 21% of all cut trees. It is also in this area that the species the most dense stands. In the other areas where it is also not very dense, it is not exploited at all, 0% at Ukongoroni and Charawe, and 5% at Mapopwe.

In terms of wood volume as determined by relative dominance, This species is most important at Michamvi, where it commands 34% of the total wood. It is least important at Charawe(4%) as is the case with Rhizophora mucronata.

Xylocarpus granatum is moderately exploited at Charawe where it contributes 27% of all cut trees, compared to 0% at both Ukongoroni and michamvi and 1.7 % at Mapopwe. The species has poor regeneration though, 12%, 11%, 0.16% and 0% at Charawe,Ukongoroni, Michamvi and Mapopwe respectively. The species is both relatively dense(24%) and dominant(39%) at Charawe and is decidedly not important in the other three sites.

In general this species is not very abundant and given the poor regeneration and that most of its individuals are young (45-66% in the 2-4cm dbh range) a stricter control on its exploitation probably lead to an increase in its abundance.

This species can be described as present but rather rare. It is only present at Michamvi where it attains a relative density and dominance of 9% and 18% respectively. It is not being exploited probably due to its rare occurrence.

Sonneratia alba is also comparatively rare, only featuring at Michamvi at a relative density of 4%, and relative dominance of 7%.There is some exploitation of this species at Michamvi to the level of about 12%, and as is the case with A. marina this species is almost not regenerating at all in any of the management Units.

Other species ie Xylocarpus molucensis, Heritiera littoralis, Pemphis acidula and Lumnitzera racemosa are present in insignificant populations. Any level of exploitation of these pushes them towards extinction. Management intervention would probably improve the chances of increasing their populations.

It is of interest to note the presence of a bird nesting ground at Shakani, a tiny island within the Ukongoroni mangrove management Unit. There is a wide variety of birds nesting here. Informers told the survey team that already there is a small scale tourist operation where by villagers from Michamvi take tourists by boat to this bird sanctuary for a token fee., something which is not happily received by the villagers of Ukongoroni and Charawe who also claim ownership of the tiny Shakani island. They feel that they are being robbed of some revenue and are advocating for sharing such revenue.

It was also observed in the Charawe and Ukongoroni area that fishermen use poison (Utupa) in the fishponds. In these ponds there was an obvious absence of juvenile fish unlike in the ponds at Mapowe, where there was no incidence of poison fishing. This is a serious issue that needs to be addressed to by management.

In addition to this, there were also observed a number of bee hives in the Ukongoroni mangrove area. It might interest management to try to encourage bee keeping as an alternative livelihood activity which may help reduce the pressure on the mangroves.