SPATIAL AND TEMPORAL CHANGE OF MANGROVE FOREST

OF MTONI KIJICHI, DAR ES SALAAM - TANZANIA

Presenter Mathias Msafiri Igulu

Promotor Prof Dr Nico KoedamCo- promotor Dr Farid Dahdouh-Guebas and

Griet Neukermans

Introduction

Occur worldwide on tropical and sub-tropical coastlines

Ecologically, they act as breeding, spawning, hatching and nursery grounds for marine animals

They provide construction materials, charcoal, firewood and are source for traditional medicines

Mangroves ecosystems ……….

Introduction Mangrove ecosystems are subjected to various

anthropogenic effects like urban expansion agriculture tourism and aquaculture impoundments

In Dar es Salaam City conversion of mangrove forests to residential and industrial land is the main threat

Dar es Salaam city has growth rate of 6.75% per year

Understanding mangrove dynamics may suggest conservation and management directives

Objectives

General objective is to examine and interpret short and long term change in mangrove of Mtoni-Kijichi

• To examine vegetation structure and regeneration classes of the forest

• To examine long term (decadal) change of the forest by using aerial photographs and the satellite image

• To link current forest structure with the changes and propose management strategies

Source

Dar es salaam

Study site

Mtoni kijichi mangrove

Study site

MethodologyTwo methodologies

Field survey (transect line plot method)

Remote sensing (aerial photographs and satellite image)

Study area and field methodology

Sampling (August-September 2005)

Four transects were sampled, the transects are in the framework of Peri-urban mangrove forest as filters and potential phytoremediators of domestic sewage in East Africa (PUMPSEA) project

Transect and line method was chosen as a standard method to obtain quantitative descriptions of species composition and community structure

Total of 32 plots were sampled randomly

Plot size (10 *10 m2)

All trees were identified to species level

Information recorded

1. For adult trees, circumference (G130 cm)& tree height (m)

2. Regeneration classes (diameter < 8cm)

3. Cut stumps, only counted

Aerial photographs and satellite image (IKONOS, 2005) processing

Purchased from Ministry of Land and Survey at Dar es Salaam Year 1969, 1982 and 1992

Photographs scanned at 300 dpi

Imported into ArcGIS Georeferenced with reference to the satellite image 2005

Assemblages were visually delineated

Sonneratia alba

Ceriops tagal

Saltpan area

Rhizophora mucronata

Avicennia marina

Identification key were made prior to delineation of dominant assemblage (Dahdouh-Guebas et al. 2006)

Results and Discussions (1)

15261022N =

Transect

4321

Hei

ght (

m)

16

12

8

4

015261022N =

Transect

4321

G13

0 (c

m)

200

150

100

50

0

Box-plots display of adult mangrove Height (a) and G130cm (b) distributions at four transects in Mtoni-Kijichi.

Statistical test shows a significant difference in height and G130 distributions (p < 0.05, ANOVA),

Differences between transect 1-2 & 3-4 (p < 0.05 Post hoc Tukey HSD test)

Tree physiognomy

(a) (b)

Transect

Species 1 2 3 4

A. marina 0* 0.0010 0.5747 0.0370

B. gymnorrhiza np 0* 0.0392 0.0157

C. tagal 0.1078 0.0034 0.0003 0*

L. racemosa np np 0* np

R. mucronata 0.0036 0.0005 0* 0*

S. alba 0.0001 0.0017 0.0071 0*

X. granatum np 0.0354 0* 0.0001

*np, the species was not observed and 0* value less that 0.000001. Io > 1, the population is clustered, if Io = 1, randomly dispersed & Io < 1, evenly dispersed.

Distribution of species in the forest (Morisita’s index)

Morisita’s Index (Io) values

Io < 1, evenly dispersedIo = 1, randomly dispersed

Results and Discussions (2)

Io > 1, clustered

Distribution and abundance of regeneration classes

0

500

1000

1500

2000

2500

1 2 3 4

Transects

Juve

nile

s(h

a-1

)

RCI

RCII

RCIII

RCIV

Regeneration status

Statistical testp < 0.05DifferencesBetween the two groups

Ratio RCI:RCII:RCIII = 2: 1: 1Kairo et al. (2002) found 86:51:1 (Uyombo) and 62:17:1(Kirepwe) in KenyaChong (1988) obtained ratio of 6:3:1(Costa Rica)

Seedlings: RCI (height, h < 40 cm ) , juveniles: RCII (40 < h < 150 cm),small trees: RCIII (150 < h < 300 cm) and young trees RCIV h > 300cm

Results and Discussions (3)

Estimation of cut stumps per hectare

0

200400

600800

1000

1 2 3 4

Transects

Cu

t st

um

p (

ha

-1)

Cut stumps status

Results and Discussions (4)

Large number of cut stumps observed at transect 2Statistics test shows a significant difference between transect 1 and 2- 4, p < 0.05

Vegetation map produced from 1967 aerial photograph

Results and Discussions (5)

Vegetation map produced from 1982 aerial photograph

Results and Discussions (6)

Vegetation map produced from 2005 panchromatic satellite image

Position of dominant species remained the same

Results and Discussions (7)

Results and Discussions (8)

Estimation of total area coverage

-5.3-1.4-10.6 % Change from previous image (mangroves only)

179.24191.47194.13219.77Total mangrove cover (ha)

207.83202.20194.13266.72Total area inclusive salt pan and cleared areas (ha)

2005199219821967

Year

Conclusion

The mangrove of Mtoni-Kijichi comprises small assemblages of S.

alba, A. marina, C. tagal, B. gymnorrhiza and R. mucronata (remote

sensing). Field survey indicated the presence of L. racemosa, and X.

granatum.

Taller and bigger trees (G130 > 8 cm) were found close to the river

mouth while shorter and stunted trees dominated the southern

part.

A total of 40.5 hectares of mangroves have been lost from 1967 to

2005, which corresponds to 18 % of the mangrove cover present in

1967.

Regeneration class III and IV were more preferred by cuttersLarge number of cut stumps were found at transect 2, with estimated

760 stumps per hectare

Shall we clear all trees and forget that once there was a mangrove forest here?Or shall we wait longer till they grow into bigger size?